ArticlePDF AvailableLiterature Review

Abstract

Purpose: The strength of 3D-printed resins is affected by different factors, but review articles clarifying these factors are limited. This review lists the factors affecting the strength of 3D-printed resins and the possible correlations between them to answer the study question: what are the factors affecting the flexural strength of 3D-printed resins? Methods: A database search (PubMed, Google Scholar, and Scopus) was performed, limited to English-language publications between 2010 and February 1, 2022. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used for study selection. The modified Consolidated Standards of Reporting Trials (CONSORT) checklist was used to determine the risk of bias of the included studies in this review. The data analysis was descriptive due to the presence of many variables in the included studies. Results: Out of 123 studies, 26 were reviewed for full-text analysis, and 19 met the inclusion criteria and were thus included in this systematic review. The included studies were divided according to the investigated resin: 5 studies tested provisional restorations, 7 tested denture base resins, 2 tested occlusal devices, 3 tested orthodontic appliances, 1 tested denture teeth, and 1 tested surgical guide resins. These studies investigated the flexural strength of 3D-printed resins, with different factors such as reinforcement with fillers or nanofillers; printing orientation, angulation, and directions; post-polymerization time and temperature; third-party printing (switching between printers and materials); printing layer thickness; and post-printing rinsing time. Most factors significantly affected the flexural strength of 3D-printed resin. Conclusions: The strength of 3D-printed resins could be improved with one or more of the following factors: filler or nanofiller addition; printing orientation, angulation, or directions; printing layer thickness; and post-polymerization time and temperature. However, further studies combining these factors are recommended. This article is protected by copyright. All rights reserved.
Received: 7 October 2022 Accepted: 4 January 2023
DOI: 10.1111/jopr.13640
REVIEW
Factors affecting flexural strength of 3D-printed resins: A
systematic review
Mohammed M. Gad BDS,MSc Shaimaa M. Fouda BDS,MSc,PhD
Department of Substitutive Dental Sciences,
College of Dentistry, Imam Abdulrahman Bin
Faisal University, Dammam, Saudi Arabia
Correspondence
Mohammed M. Gad, Department of Substitutive
Dental Sciences, College of Dentistry, Imam
Abdulrahman Bin Faisal University, P.O. Box
1982, Dammam 31441, Saudi Arabia.
Email: mmjad@iau.edu.sa
Abstract
Purpose: The strength of 3D-printed resins is affected by different factors, but review
articles clarifying these factors are limited. This review lists the factors affecting the
strength of 3D-printed resins and the possible correlations between them to answer the
study question: What are the factors affecting the flexural strength of 3D-printed resins?
Methods: A database search (PubMed, Google Scholar, and Scopus) was performed,
limited to English-language publications between 2010 and February 1, 2022. The
Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)
guidelines were used for study selection. The modified Consolidated Standards of
Reporting Trials (CONSORT) checklist was used to determine the risk of bias of the
included studies in this review. The data analysis was descriptive due to the presence of
many variables in the included studies.
Results: Out of 123 studies, 26 were reviewed for full-text analysis, and 19 met
the inclusion criteria and were thus included in this systematic review. The included
studies were divided according to the investigated resin: 5 studies tested provisional
restorations, seven tested denture base resins, 2 tested occlusal devices, 3 tested
orthodontic appliances, 1 tested denture teeth, and 1 tested surgical guide resins. These
studies investigated the flexural strength of 3D-printed resins, with different factors,
such as reinforcement with fillers or nanofillers; printing orientation, angulation, and
directions; post-polymerization time and temperature; third-party printing (switching
between printers and materials); printing layer thickness; and post-printing rinsing
time. Most factors significantly affected the flexural strength of 3D-printed resin.
Conclusions: The strength of 3D-printed resins could be improved with one or more
of the following factors: filler or nanofiller addition; printing orientation, angulation,
or directions; printing layer thickness; and post-polymerization time and temperature.
However, further studies combining these factors are recommended.
KEYWORDS
3D printing, additive manufacturing, flexural strength, prosthodontics, provisional restorations
3D printers are now easy to use, consistent, inexpensive, and
smaller and lighter than before.1They can produce com-
plex or multiple structures at the same time.2,3 Commonly
used 3D printers in the dental field are based on stereolithog-
raphy (SLA) or digital light processing (DLP) technology.
In both methods, the object is built in layers from a pho-
topolymer. In SLA, a laser light track is used to polymerize
the resin, whereas, in DLP, a digital projector screen flashes
light through the entire layer to build the 3D structures.3,4
The photopolymer resin consists of 75% oligomers, 25%
monomers, and photopolymerization initiators, which, when
exposed to ultraviolet light, cleave primary radicals that
react with the oligomers and monomers and lead to
polymerization.5
3D-printing technology can fabricate several objects simul-
taneously, with less wasted material. It can also produce
complex shapes with many undercuts.5,6 Therefore, 3D
printing technology is used to fabricate numerous dental
appliances, including dentures, maxillofacial prostheses, den-
tal implants, orthodontic appliances, metal bridges, clasps
of removable partial dentures,1surgical guides, diagnostic
models, and occlusal splints.3
J. Prosthodont. 2023;1–15. © 2023 by the American College of Prosthodontists. 1wileyonlinelibrary.com/journal/jopr
2GAD AND FOUDA
TABLE 1 Systematic search strategy
Focus questions
What are the factors influencing flexural
strength of 3D-printed resins?
PICOS
P: Participant 3D-printed resins
I: Interventions Factors affecting strength
C: Comparison 3D-printed provisional, denture base, stents, and
orthodontic appliances resins
O: Outcomes Effect of factors on flexural strength
Dental appliances are affected by several stresses in the
oral cavity, such as chewing forces and parafunctional habits.
Flexure strength is one of the important properties of a dental
material that indicates its mechanical behavior. Accordingly,
investigating the flexure strength of 3D-printed resins is
essential. The printing nature and photopolymerization of
3D-printed resin are the main causes for lowering its strength
in comparison to milled and conventional resins.7
Understanding the influence of printing parameters on the
printed object properties is essential to improve the quality of
printed dental appliances. Several studies have investigated
the factors affecting the flexural strength of 3D-printed resins
and methods to improve it to implement this technology for
clinical applications with proper performance. However, the
published papers that have summarized and systematically
analyzed these factors are limited and might have not dis-
cussed all the influential factors. Therefore, a comprehensive
evaluation of the available data may be beneficial to iden-
tify the factors influencing the flexural strength of 3D-printed
dental appliances. The present systematic review was per-
formed to map these factors and overview all the parameters
that affect the strength of 3D-printed resin.
METHODS
This review was performed to answer the focus question:
What are the factors affecting the flexural strength of 3D-
printed resin? The PICO question included 3D-printed resins
as the participants and factors affecting flexural strength as
the intervention, comparing 3D-printed resins used for the
fabrication of different dental prostheses to determine the
outcome of different factors on flexural strength (Table 1).
The Preferred Reporting Items for Systematic Reviews and
Meta-Analysis (PRISMA) guidelines (Fig 1) were followed
to select the included studies.8
Only peer-reviewed publications were included in this
review, according to the inclusion and exclusion criteria. The
inclusion criteria were original full-length articles of in vitro
studies evaluating the effect of different factors on the flex-
ural strength of 3D-printed resins used for fabricating dental
appliances, published in English. The preparation and test-
ing of specimens according to American Dental Association
(ADA) or International Standards Organization (ISO) stan-
dards was an additional criterion. The sample size, proper
statistical analysis, and results must be stated clearly using
international system units. Review articles, short communi-
cations, abstracts, articles published in languages other than
English, and articles that did not investigate the flexural
strength or factors affecting the strength of 3D-printed resin
were excluded. In addition, studies that included specimens
in the form of a dental appliance (i.e., denture, surgical stent,
and bridge) were excluded because they were not fabricated
according to ADA or ISO specifications for testing strength.
After registration of the review in PROSPERO
(CRD42022296091), two investigators (MMG and SMF)
performed an online search through the PubMed/MEDLINE,
Embase, Google Scholar, Scopus, and Web of Science
databases for publications between 2010 and February 1,
2022. The search was performed using the terms strength/3D
printing, 3D printing/denture base, 3D printing/provisional,
3D printing/occlusal devices, 3D printing/splints, 3D print-
ing/orthodontic appliances, 3D printing/orientations, 3D
printing/post-curing time, 3D printing/direction, and 3D
printing/angulation. The combined term search was per-
formed with MeSH terms and the Boolean system. A further
hand search was performed to ensure that no studies meeting
the inclusion criteria were missed and to check the most
relevant articles.
The included studies were screened for data collection by
two investigators (MMG and SMF) and tabulated according
to the inclusion criteria and the required data to be extracted
(Table 2). Any missing data or confusion about findings was
discussed between the investigators to finalize and unify the
data collection scheme of included and excluded studies.
For the risk of bias assessment, the quality of the studies
included in this review was evaluated following the modi-
fied Consolidated Standards of Reporting Trials (CONSORT)
checklist. Articles with only two “yes” responses to the CON-
SORT checklist were considered at high risk of bias, articles
with three “yes” responses were considered at medium risk of
bias, and articles with four “yes” responses were considered
at low risk of bias (Table 3).9,10
Due to the included studies’ variation in investigated fac-
tors affecting the strength of 3D-printed resin (additives,
printing layer thickness, printing orientations, post-curing
time, post-curing temperature, and rinsing time) and the dif-
ferent printing technologies used (SLA and DLP), descriptive
data analysis was employed because quantitative statistical
meta-analysis was not applicable in this review.
RESULTS
Selected studies and risk of bias
After screening studies and applying the inclusion and exclu-
sion criteria, out of 123, only 19 articles were included in
this review (Fig 1). Table 3summarizes the methodologi-
cal quality of the included studies according to the modified
CONSORT checklist.9Although different factors and param-
eters were investigated in the included studies, all the studies
STRENGTH OF 3D-PRINTED RESINS 3
TABLE 2 Included studies investigated factors affecting flexural strength (FS) of 3D-printed resins
References Printed
Resin/type/
printer/brand name
Layer thickness/
PCT/Temp. Factors Control
Sample
size
Specimens
dimensions
ADA/ISO: testing
parameters Aging Results and outcomes
11 Occlusal splint
SLA
Epoxy-based resin
(Somos Watershed
XC 11122; DSM)
(SLA350; 3D
Systems)
0.15 µm
PCT 15 min oven
(PCA Device;
DSM)
Temp. (NS)
Horizontally,
vertically, and
at a 45angle
Autopolymerized
acrylic resin
n=10 2 ×2×25 mm3
ISO (NS)
Speed of 10 mm/min
A total of 10
specimens/group
water stored (14
days)
Wet vs. dry storage
Printing directions and
water storage affected
the flexural properties
of SLA-manufactured
occlusal device. The
optimal printing
direction to resist
fracture for an occlusal
device is vertical object
and technology
12 Denture base
DLP
NextDent Denture,
photocuring 3D
printing system
(Envision Tech,
Gladbeck,
Germany)
(NS) Incorporating
CNCs-AgNPs
Unmodified n=664×10 ×3.3 mm3,
0270.1-2011/ISO
20795-1:2008
dentistry-base
polymers-Part 1:
denture base
polymers speed
5 mm/min
No aging CNCs-Ag increased the
FS of PMMA at 0.05
and 0.1 wt.%, whereas
at higher concentration,
the FS was similar to
pure resin and started
to decrease at 0.25%
13 Surgical guide
SLA
Form 2, Formlabs
Dental SG resin
(Formlabs Inc.,
Somerville, MA,
USA)
SLA 3D-printer
(Form 2, Formlabs
Somerville, USA)
50 µm
PCT =15 min
Temp. (NS)
0,45
, and 90
orientations
Three curing
ovens—90
orientation
GS (n=119) 5 ×5×30 mm3
ISO 4049
Speed
0.75 ±0.25 mm/
min
No aging The highest FS and
modulus were found
with 90specimens.
The use of different
curing units did not
affect the flexural
properties of printed
objects
14 Removable
CAD–CAM
prostheses
SLA
NextDent Base;
Vertex Dental
3D printer (Form 2;
Formlabs)
100 µm
PCT
Man. instructions
(Cure Den;
DENTIS)
Printing
orientations (0,
45, and 90)
0n=10 80 ×10 ×4mm
3
International
Standards
Organization (ISO)
178 (NS)
No aging The FS was significantly
affected by the printing
orientation with the
highest values recorded
at 0, followed by 45
and 90, respectively
(Continues)
4GAD AND FOUDA
TABLE 2 (Continued)
References Printed
Resin/type/
printer/brand name
Layer thickness/
PCT/Temp. Factors Control
Sample
size
Specimens
dimensions
ADA/ISO: testing
parameters Aging Results and outcomes
15 Provisional
restoration
Two 3 D
printers,
MiiCraft
Ultra 125
DLP and
Phrozen
Sonic mono
LCD
NextDent C&B MFH
AA Temp. (AA) and
C&B MFH (C&B)
100 µm
PCT
Form Cure Temp.
60C at (0, 15, 30,
45, 60, 90, 120, and
180 min)
Phrozen cure at room
temperature (0, 1,
5, 10, 15, and
30 min)
3D-printing resins
designed for
DLP 3D
printers can be
used
successfully in
a mono-LCD
3D printer
Switching of
printers and
resins and, post
curing units and
time
(NS) n=62×2×25 mm3
ISO10477 (NS)
No aging Interim resins designed
for DLP 3D printers
can be successfully
used in mono-LCD 3D
printers if the printed
specimens are
post-polymerized in a
more powerful
post-polymerization
unit or in a less
powerful
post-polymerization
unit for a longer time
16 Provisional
restoration
SLA
Nextdent C&B
(Nextdent,
Soesterberg, the
Netherlands),
Nextdent C&B
MFH (Nextdent,
Soesterberg, the
Netherlands),
ZMD-1000B
temporary
(DENTIS, Daegu,
Korea), and
DIOnavi C&B
(DIO Incorporated,
Busan, Korea)
100 µmand
photocuring was
performed for 20 s
per layer
60C
Orientation 0for the
build platform
Post-curing times
of 15, 30, 60,
90, and 120 min
GS n=20 2 ×2×25 mm3
DIN EN ISO 4049
(dental
polymer-based
materials) (NS)
No aging The post curing time
(60–90 min) increased
the strength of the 3D
printed resin. At least
60 min of post-curing
time is required to
improve the overall
clinical performance of
the 3D printed
provisional restoration
17 Biomedical
appliance
(Ortho.)
DLP
NextDent Ortho Rigid
3D printer
(NextDent 5100)
Manu. Inst.
post-processed
according to the
manufacturer’s
instructions using a
UV oven
(NextDent
LC-3DPrint Box,
3D Systems,
NextDent B.V.)
Aminated
nanodiamonds
0.1 wt.%
Unmodified n=18
n=6
3.3 ×10 ×64 mm3
ISO 20795-2
International
Standard
Crosshead speed of
5 mm/min
Stored dry at
23 ±2Cfor
24 ±2h
Thermocycling (5000
cycles)
Addition of 0.1% A-ND
significantly improved
the mechanical
properties of
3D-printed biomedical
appliances
(Continues)
STRENGTH OF 3D-PRINTED RESINS 5
TABLE 2 (Continued)
References Printed
Resin/type/
printer/brand name
Layer thickness/
PCT/Temp. Factors Control
Sample
size
Specimens
dimensions
ADA/ISO: testing
parameters Aging Results and outcomes
18 Splint and
surgical
guides
DLP
(ASIGA MAX,
SCHEU-DENTAL
GmbH, Iserlohn,
Germany)
A methacrylate-based
acrylic resin
light-curing resin
(bisphenol-A-
ethoxylate
diacrylate
[Bis-EMA]), used
for the manufacture
of 3D-printed
resins
Variables
Temp. 60C
Post-curing
method,
printing layer
thickness, and
water storage
GS n=96 (3.2 ×10.0
×65.0 mm3)
(NS)
(NS)
For each subgroup,
half of the
specimens was
stored in distilled
water at 37Cfor
30 days, whereas
the other half was
dry stored under
ambient laboratory
conditions
(23 ±1C) before
testing
The mechanical
properties of 3D
printed occlusal splints
are affected by the
post-curing method,
water storage, and
printing layer
thickness. The
combination of heat
and light within the
post-curing unit can
enhance the
mechanical properties
and degree of
conversion of 3D
printed occlusal splints
The FS increased with
decreasing printing
layer thickness
19 Provisional
restorations
DLP
Nextdent C&B
3Delta Temp.
Freeprint Temp.
Freeprint and
Nextdent C&B
50 µm 3Delta
100 µmPCT
Freeprint Temp. and
3Delta Temp. were
post-cured for
2×2000 flashes
under a nitrogen
atmosphere
Next Dent 30 min
Temp. (NS)
Printing direction
and aging
(thermocycling)
(NS) T=360
n=20
2×2×25 mm3
ISO 4049 (NS)
Aging procedures
were 1-day storage
in distilled water at
37Cand
additionally
followed by
thermocycling for
10,000 cycles, with
a dwell time of 30 s
and a transfer time
of 5 s
The printing direction has
a significant influence
on the mechanical
properties of the
specimens. An
alignment of the layers
perpendicular to the
direction of the load is
preferred. However, the
material itself had the
greatest influence on
FS followed by aging
and printing direction
20 Provisional
restorations
SLA
Detax Freeprint
Tem p. an d
Nextdent MFH
50-µmPCTMan.
Inst. post-curing
unit under nitrogen
gas. Temp. (NS)
Printing angle and
load direction
0,45
,90
(NS) n=10 25 ×2×2mm
ADA-ANSI
specification no. 27
tested according to
ASTM
D790-Standard
speed of 2 mm/min
No aging The FS was higher at 0,
therefore, it depends on
to the degree of
orientation
(Continues)
6GAD AND FOUDA
TABLE 2 (Continued)
References Printed
Resin/type/
printer/brand name
Layer thickness/
PCT/Temp. Factors Control
Sample
size
Specimens
dimensions
ADA/ISO: testing
parameters Aging Results and outcomes
21 Ortho resin
DLP
NextDent Ortho Rigid
3D printer (NextDent
5100, 3D Systems,
NextDent B.V.)
(NS)
PCT =10 min
(NS)
Zwitterion-
incorporated
3D-printable
PMMA
Unmodified n=10 64.0 ×10.0
×3.3 mm3
International Standard
ISO 20795-2
dentistry–based
polymers—Part 2:
Orthodontic base
polymers
Before testing stored
at 37C in distilled
water for 48 h
Thermocycling was
conducted between
5 and 55C with a
dwell time of 45 s
for 850 cycles,
corresponding to 1
month
FS decreased with the
addition of Zwitterion.
However, their values
exceeded the minimum
requirements (50 MPa
for strength and
1500 MPa for
modulus) set by ISO
20795-2
22 Provisional
restoration
DLP
NextDent
Printer (Kulzer 3D
Printer System,
Australia)
50 µm thickness
PCT =20 min
Temp. (NS)
High-performance
light curing unit at
200 W for 20 min
(HiLite Power 3D;
Kulzer)
Reinforced with
modified ZrO2
nanoparticles
(0–5 wt.%)
Unmodified n=15 25 ×2×2mm
3
International
Standards
Organization (ISO)
10477, (NS)
Stored in artificial
saliva for 3 months
at 37C. The
artificial saliva
solutions were
replenished every
fortnight to ensure
consistency and
freshness
throughout the
storage time
periods
The addition of ZrO2
nanoparticles (3%, 4%,
and 5%) significantly
improved the FS
compared to
unmodified printed
resin
However, after storage in
artificial saliva (3
months), the reduction
of strength was more
pronounced after
incorporating higher
filler content compared
to groups having lower
filler content
23 Denture base
resin (NS)
(third-party
3D-printer)
NextDent Base
(Vertex-Dental
B.V.) (Form 2,
Formlabs)
100 mm per layer
10 min PCT
Temp. ???
Printing
orientation
Horiz. vs.
vertical and
type of
3D-printer
(third-party
3D-printer)
(NS) n=565×10 ×3mm
3
ISO (NS)
Speed of 1 mm/min
Stored in water at
37 C for 24 h
The resins printed with
manufacturer-
recommended 3D
printer have higher
strength than the resins
printed with a
third-party 3D-printer
and those printed with
a vertical orientation
24 ORTHO
Hard splint
SLA
Form 3B, Formlabs,
Somerville, MA,
USA
100 µm layer height
3D printer
PCT 20 min
Temp. 80 C without
inert gas
Support structures
(5 mm in height)
Effect of post
rinsing time.
Rinsed with
isopropanol for
5min,12min,
20 min, 30 min,
1 h, and 12 h
Conventional
material used
for fabricating
orthodontic
appliance
n=12 30 ×5×5mm
3
ISO 20795-2:2013
Speed (NS)
No aging Increasing the
post-rinsing time
resulted in decreasing
the FS of 3D-printed
orthodontic appliances
(Continues)
STRENGTH OF 3D-PRINTED RESINS 7
TABLE 2 (Continued)
References Printed
Resin/type/
printer/brand name
Layer thickness/
PCT/Temp. Factors Control
Sample
size
Specimens
dimensions
ADA/ISO: testing
parameters Aging Results and outcomes
25 Denture base
material
DLP
IMPRIMO LC
Denture;
Scheu-Dental
GmbH, Iserlohn,
Germany
(NS) Post-curing
methods
(NS) 64
n=16
10.0 ×65.0
×3.3 mm3
ISO (NS)
Speed of 5 mm/min
Wet storage for 30
days vs. dry-stored
(23 ±1C) for 24 h
FS of 3D-printed denture
base resin could be
improved by increasing
the post curing
temperature
26 Denture teeth
SLA
Denture teeth resin
A2, Formlabs
Form 3, Formlabs
50 µm
Orientation 120for
the build platform
Post-curing
temperatures
(40, 60, and 80
C) for different
periods (15, 30,
60, 90, and
120 min)
GS (n=15) 25 ×2×2mm
3
ISO 10477 Standard
(NS)
No aging Increasing the post-curing
temperature
significantly improved
the FS of 3D printed
resin
27 Denture base
material
DLP
3D printer (Kulzer 3D
Printer System,
Australia)
100 µm thickness Post-curing for 0,
5, 10, or 20 min
HP (n=10). 65 ×10 ×3.3 mm3
(ISO) 20795-1 for
denture base
polymers
Speed 5 mm/min
Artificial saliva at
37Cfor48h
(immediate groups)
and 6 months as
aged group
FS of 3D-printed denture
base material
significantly improved
with the increase in
post-curing time up to
20 min
28 Denture base
material
SLA
NextDent Base
(Vertex-Dental B.V.)
50 µm thickness SiO2
nanoparticles
Unmodified n=10 64 ×10 ×3.3
±0.2 mm3
ISO 20795-1: 2013
(NS)
Distilled water for
48 h at 37C
followed by TC 1000
cycles
Addition of SiO2NP to
3D-printed denture
base resin improved the
FS. However, thermal
cycling adversely
affected the tested
property
29 Denture base
(NS)
Denture base material
was used (V-Print
dentbase, VOCO
GmbH, Cuxhaven,
Germany)
V-Print Denture &
Solflex 650,
Way2Production,
Vienna, Austria
Printed in horizontal
position
Layer thickness not
mentioned
Post-curing
methods (diff.
devices)
Autopolymerized
acrylic resin
n=20 A disk measuring
1.5 mm in
thickness with
12 mm in diameter
Biaxial strength was
tested according to
DINENISO
6872:2008 at room
temperature (23C)
(NS)
No aging FS was significantly
affected by the
post-curing methods,
which might be
attributed to the
different wavelengths
of post-curing devices.
Therefore, an
appropriate post-curing
method is required to
optimize the FS of
3D-printed denture
materials
Note: NS, not stated (in case of printing parameter, printed according to manufacture instructions). However, for specimen testing, mean was missed in the article.
Abbreviations: ADA, American Dental Association; CNCs-Ag, cellulose nanocrystals-silver nanoparticles; DLP, digital light processing; GS, green state (without post-curing); LCD, liquid crystal display; PCT, post-curing temperature; SiO2NP,
silicon dioxide nanoparticles; SLA, stereolithography.
8GAD AND FOUDA
Identification (2010-2022) on
PubMed/MEDLINE, Web of Science, Scopus
Duplicated/ irrelevant titles
excluded [n=74]
Studies included for abstract
review [n=49]
Studies excluded: Did not answer
the research question [n=23]
Total number of studies [n=123]
Articles assessed for eligibility
[n=26]
Articles excluded: Did not meet the
inclusion criteria [n=7]
3-units bridge [2]
Complete denture [1]
Flexural strength was not tested [2]
Factors affecting flexural strength
were not tested [2]
Articles included; factors affecting
flexural strength of 3D printed resin
[n=19]
Provisional restorations [n=5]
Denture base resins [n=7]
Denture teeth [n=1]
Occlusal devices [2]
Orthodontic appliances [n=3]
Surgical guide [n=1]
Identification
Screening
Eligibility
Included
FIGURE 1 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram of the study selection process
described the tested factors adequately and clearly. They also
included adequate reports on the abstract, background and
objectives, intervention, and outcomes. None of the included
studies described the methods of randomization, allocation,
implementation, or access to full trial protocols.11–29 Only
one study28 reported how the sample size was determined.
Data analysis
The 19 studies included in this review11–29 investigated
different types of 3D-printing resins. Five tested the 3D-
printing resin used for the fabrication of interim fixed
prostheses,15,16,19,20,22 seven for denture bases,12,14,23,25,27–29
one for denture teeth,26 two for occlusal devices,11,18
three for orthodontic appliances,17,21,24 and one for surgical
guides13 (Figure 1).
Factors influencing flexural strength
The factors that could affect the flexural strength of 3D-
printed resin can be classified into preprinting, printing, and
post-printing factors. Preprinting factors involve the addition
of reinforcing agents to the 3D-printed resin. Printing fac-
tors include printing parameters, such as printing orientation,
layer thickness, use of a third party, and the location of printed
objects on the printing platform. Post-printing factors include
the post-curing parameters (time, temperature, and curing
unit), post-rinsing time, finishing and polishing methods, and
STRENGTH OF 3D-PRINTED RESINS 9
TABLE 3 Risk of bias of the selected studies
References12a2b34567891011121314
Risk
of bias
11 YesYesYesYesYesNoNoNoNoNoYesYesYesNoNoLow
12 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
13 YesYesYesYesYesNoNoNoNoNoYesYesYesNoNoLow
14 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
15 YesYesYesYesYesNoNoNoNoNoYesYesYesNoNoLow
16 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
17 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
18 YesYesYesYesYesNoNoNoNoNoYesYesYesNoNoLow
19 YesYesYesYesYesNoNoNoNoNoYesYesYesNoNoLow
20 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
21 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
22 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
23 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
24 YesYesYesYesYesNoNoNoNoNoYesYesYesNoNoLow
25 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
26 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
27 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
28 Yes Yes Yes Yes Yes Yes No No No No Yes Yes Yes Yes No low
29 YesYesYesYesYesNoNoNoNoNoYesYesYesYesNoLow
Note: The information regarding the following parameters was assessed as reported (Y) or not reported (N): (1) structured summary of trial design, methods, results, and conclusions;
(2a) scientific background and explanation of rationale; (2b) specific objectives and/or hypotheses; (3) the intervention for each group, including how and when it was administered,
with sufficient detail to enable replication; (4) completely defined, prespecified primary and secondary measures of outcome, including how and when they were assessed; (5) how
sample size was determined; (6) method used to generate the random allocation sequence; (7) mechanism used to implement the random allocation sequence; (8) who generated
the random allocation sequence; (9) if done, who was blinded after assignment to intervention; (10) statistical methods used to compare groups; (11) results for each group, and the
estimated size of the effect and its precision (e.g., 95% confidence interval); (12) trial limitations, addressing sources of potential bias, imprecision, and, if relevant, multiplicity of
analyses; (13) sources of funding and other support; (14) where the full trial protocol can be accessed, if available.
storage. Five studies investigated the effect of additives on the
flexural strength of 3D-printed resin.12,17,21,22,28 Six studies
investigated the effect of printing orientations,11,13,14,19,20,23
one tested the effect of printing layer thickness,18 and six
investigated the influence of post-curing time, temperature,
rinsing time, and different curing units.16,18,25,26,27,29 Only
two studies investigated the effect of using 3D-printed resins
with different printers or post-curing units other than those
recommended by the manufacturer15,23 (Table 2).
Preprinting factors (reinforcement)
The additives incorporated into 3D-printed denture base
resin were silver nanoparticle–loaded cellulose nanocrys-
tals (CNCs–AgNPs),12 zwitterions,21 and silicon dioxide
nanoparticles (SiO2NP).28 Zirconium dioxide nanoparticles
(ZrO2NP)22 were added to 3D-printed interim-fixed prosthe-
ses and animated nanodiamonds (NDs) to 3D-printed resin
for orthodontic appliances.17 As shown in Table S1, four
additives—CNCs–AgNPs, ZrO2NP, NDs, and SiO2NP—
increased the flexural strength of 3D-printed resins.12,17,22,28
Conversely, zwitterion as an additive showed a decrease
in flexural strength.21 For CNCs–AgNPs, the flexural
strength increased only at low concentrations and showed
a decline compared to pure resin at a high concentration
(0.25 wt.%).
Printing factors
Both printing orientation (Table S2) and printing layer thick-
ness (Table S3) affected the flexural strength of 3D-printed
resin. Regarding printing orientations, different results were
reported, possibly resulting from the different types of 3D-
printed resins included in this review. Three studies14,20,23
found that 0orientation was associated with the highest flex-
ural strength compared to 45and 90. For 45, one study11
showed higher flexural strength than both 0and 90, and one
study showed higher flexural strength than 90orientation.14
In contrast, two studies demonstrated higher flexural strength
for specimens printed at 90orientation (vertically) than
0.11,13 One study19 demonstrated that the effect of printing
orientation was dependent on the material. Another reported
an insignificant difference between the flexural strength of
an object and its position on the build platform.13 The layer
thickness implemented in printing dental appliances varies
from 25 to 150 µm. This review included only one study that
10 GAD AND FOUDA
tested the effect of layer thickness on flexural strength and
found increased strength with decreased layer thickness.18
The specimens in most studies were printed using one of
the three printing technologies of SLA,11,13,14,16,17,20,24,26,28
DLP,12,13,18,19,21,22,25,27 or liquid crystal display (LCD).15
Two studies did not state the printing technology used.23,29
Among the included studies, none compared the effect of
the printing technology on the flexural strength of 3D-printed
resins.
Two studies tested the effect of a third party (switching
resins, printers, and curing units) on flexural strength. One
study23 found that the printer type affected the strength of
3D-printed resin (Table S4). The other suggested that switch-
ing the printers with resin type did not affect the strength if the
post-polymerization time and temperature were increased or
a powerful post-polymerization unit was used.15 Chen et al15
demonstrated that the use of a third party should be accom-
panied by adequate post-polymerization methods of using
powerful post-curing units or increasing the post-curing time
or temperature to obtain adequate flexural strength of the
printed resin.
Post-printing factors
The effect of post-printing factors on the flexural strength
of 3D-printed resin was tested in eight studies: four on
post-curing units (Table S5)13.18,25,29 and four on curing con-
ditions (Table S6).16,24,26,27 The post-curing device and its
specifications, such as light intensity and wavelength range,
impact the flexural strength (Table S6). An increase in post-
curing time and temperature was associated with increased
flexural strength, as reported by two studies testing the influ-
ence of post-curing time16,27 and one study testing the effect
of post-curing temperature.26 One study tested the effect of
post-rinsing time on flexural strength and reported deterio-
ration with increased rinsing time.24 The influence of curing
units on the strength of 3D-printed resin was evaluated in four
studies.13,18,25,29 Unkovskiy et al13 stated that the curing units
included in their study were unlikely to change the flexural
strength of the 3D-printed resin used for the fabrication of
surgical guides. Perea-Lowery et al18,25 reported an enhance-
ment of the mechanical properties and degree of conversion
of 3D-printed occlusal splints and denture base resin with the
combination of heat and light within the post-curing unit. Li
et al29 tested the effect of post-curing devices on the flexu-
ral strength of denture base resin and reported a significant
correlation.
Four studies17,19,21,28 tested the effect of thermal cycling
on 3D-printed resin and reported the deterioration of the
flexural strength after exposure to thermal stress. Five
studies11,18,22,25,27 tested the specimens after storage in saliva
or water and found an associated decline in flexural strength.
Some studies tested the effect of artificial aging with
other factors on the flexural strength of 3D-printed resin.
Aati et al22 and Gad et al28 found that the addition of
ZrO2NP and SiO2NP, respectively, improved the flexural
strength of 3D-printed resin but that aging through stor-
age in saliva or thermocycling reduced it (Table S1). Keßler
et al19 found that the printing orientation and aging influ-
enced the flexural strength of 3D-printed resin, but the effect
of aging was higher than printing orientation (which was
material-dependent; Table S2).
The combined effect of multiple factors on flexural
strength was also tested but in limited studies. The effect of
printed layer thickness with the post-polymerization method
and water storage was investigated in one study.18 Decreas-
ing the layer thickness and the use of a post-curing unit
that combines light and heat resulted in increased flexural
strength, whereas water storage reduced the flexural strength
of printed occlusal splint resin (Table S3). Bayarsaikhan
et al26 found that increasing the post-curing temperature
and time significantly increased the flexural strength of
3D-printed denture teeth (Table S6). Chen et al15 tested
the effect of post-curing methods with the use of a third
party for the fabrication of 3D-printed provisional restora-
tions. They concluded that switching the printers with
3D-printed resin should be accompanied by a suitable post-
polymerization method to obtain adequate flexural strength15
(Table S4).
DISCUSSION
To answer the study question, the parameters that could affect
the strength of 3D-printed resins were classified into three
categories: preprinting, printing, and post-printing factors.
The preprinting factors included printing material, print-
ers, and printing resin modifications. The printing factors
included printing orientation, direction, layer thickness, light
intensity (laser power and speed), and penetration depth. The
post-printing factors included post-curing time, temperature,
rinsing, polishing, and storage. As the printed resin passes
through these steps during fabrication, one or a combina-
tion of these factors may influence the strength of the printed
object. This review confirmed that these factors affected the
flexural strength of 3D-printed resin and must be considered
before printing.
Preprinting factors (reinforcement)
Dental appliances are subjected to several stresses intraorally
and must have adequate mechanical and physical proper-
ties to withstand these. Previous studies have reported lower
strength of 3D-printed resin compared to milled and heat-
polymerized resin.7,30 The deteriorating effect of thermal
changes on the mechanical properties of 3D-printed resin
was significantly higher than that on heat-polymerized resin.7
Therefore, several studies suggested the reinforcement of 3D-
printed resin by the addition of fillers.12,17,22,28 Many types
of fillers have enhanced the properties of 3D-printed resin
when added to it in proper concentrations and using methods
to improve its bonding to the resin matrix.12,22,28
STRENGTH OF 3D-PRINTED RESINS 11
Although the addition of nanofillers improved the strength
of 3D-printed resin, the type, size, and concentration of the
nanofiller are important factors that could affect the strength
of the resin.17,22,28 The addition of fillers or nanofillers at
high concentrations might have adverse effects on flexural
strength due to clustering of the particles.28 Therefore, it is
important to determine the proper concentration of the added
filler that results in bonding with the resin matrix before form-
ing clusters.22,28 The addition of SiO2NP to 3D-printed resin
was tested in two concentrations; higher flexural strength was
found with 0.25% than 0.5%.28 CNCs–AgNPs enhanced the
flexural strength at low concentrations, but at high concentra-
tions, the flexural strength was markedly reduced.12 ZrO2NP
was tested in concentrations between 1% and 5%, and the
highest flexural strength was reported with 5%.22 In contrast,
zwitterion reduced the flexural strength when added to 3D-
printed resin. The color of the final nanocomposites is another
important factor that should be considered when selecting a
filler and its concentration. Previous studies have reported
noticeable whitish and grayish colors with the addition of
ZrO2NP and ND, respectively, to heat-cured resin.30
Printing factors
Printing orientations and directions
3D-printed objects are anisotropic because they are manu-
factured in layers. Therefore, the properties of the printed
object depend on the building orientation, and the direction
of the exerted force could have different impacts on it. An
association between the printing orientation and the mechan-
ical properties of 3D-printed objects has been reported in
the literature.2,19,20 Accordingly, the decision to follow the
manufacturer’s recommendations or modify the printing ori-
entation to improve the strength is critical.5,19 The effect
of the printing orientation is also related to the relation
between the direction of the applied load and the printing
layer direction.20 This might be applied for bar-shaped spec-
imens, but in reality, the built objects such as denture bases,
provisional restorations, splints, surgical guides, or remov-
able appliances are not printed in one plane but rather in
multiplanes and curvatures according to the restoration con-
figurations. Therefore, the printing orientation that results in
high strength must be considered for the plane subjected to
more stress during functions (i.e., the horizontal part of the
palate and the connection of the provisional bridge).
The number of layers needed to fabricate a 3D-printed
object depends on the printing orientation. The number
of layers is increased in a perpendicular compared to a
horizontal orientation. Adhesion within the same layer is
stronger than between different layers.7Additionally, shrink-
age between the layers occurs and depends on the build
direction and layer orientation.2,14,20 Moreover, the printing
orientation associated with the least support area is preferred
because less time is needed for finishing and polishing.31
Most of the studies found that the printing orientation
significantly influenced the flexural strength of 3D-printed
resins. However, variation was found between studies regard-
ing the effect of different printing orientations on flexural
strength. Higher flexural strength was reported at horizon-
tal orientation19 compared to vertical.13 When the specimens
were built vertically, the load direction became parallel to
the printing direction, resulting in poor strength31 due to the
weak adhesion between successive layers. However, other
factors affect the strength of adhesion between successive
layers, including the composite resin type, the adhesion
surface dimension, and the polymerization rate. These con-
sequently affect the flexural strength of vertically printed
products.13,14,20,31 A study reported that 3D-printed restora-
tion at 30,45
, and 60showed higher flexural strength
compared to that manufactured at 0and 90, with the highest
flexural strength value at 30.32
Printing layer thickness
The flexural strength of a 3D-printed object is increased with
the reduced thickness of the printed layers.18 The flexural
strength of the specimens printed with a 50-µm layer thick-
ness was higher than those printed with a 100-µm thickness.
The reason for that could be the better polymerization of thin
layers due to the preservation of light intensity as it pene-
trates the resin bulk from the surface inward, unlike the thick
layers.18 Therefore, if printing is done with thick layers, it
is preferably accompanied by increased post-polymerization
time, temperature, or using a curing unit with high light inten-
sity to increase the strength of the printed resin. However,
the effect of water sorption is an important factor that should
be considered when determining the preferred printing layer
thickness. Water sorption could result in water penetrating the
layers and moving them apart from each other, which could
have a higher effect on specimens with multiple layers.7
Accordingly, it is important to investigate the effect of long-
duration water storage on the strength of printed resin with
thin layers.
The printing orientation along with the printing layer thick-
ness could affect the strength of the printed object due to the
effect of the printing axes (X,Y, and Z).14 The resolution of
the vertical printing axis Zis often higher than that of the
horizontal axis XYdue to lower light refraction toward the
vertical axis than toward the horizontal axes.13,14 The print-
ing layer thickness of 25 or 50 µm is smaller than the X- and
Y-axis resolution, so a vertical print might be stronger with
thin layers. With thick printing layers (100 µm) and better
resolution in the X- and Y-axes than the Z-axis, a horizontal
print might be stronger. The variations might be attributed to
the differences in the printing orientations and printing layer
thickness that ranged between 25 and 100 µm. To confirm
these explanations, further investigation combining the effect
of layer thickness and the printing orientation on the strength
of the printed object is required.
12 GAD AND FOUDA
Printing position on the build platform
The light source, intensity, penetration depth, and distribu-
tion affect the strength of 3D-printed objects.27 The position
of specimens on the printing platform could affect their prop-
erties even if they are printed at the same time.21 The flexural
properties of the specimens in the same row were more incon-
sistent than that of the specimens in the same column, which
might have resulted from the differences in the time of laser
exposure.29 The moving tank that contains the liquid resin
might also be responsible for the slight discrepancies along
the columns. When the tank moves from one side to another
during printing each layer along the rows, it might cause a
peel force to the initial layer, causing its slight shift sideward
along the rows.13 The objects printed on the marginal row
of the build platform might have a different flexural strength
than those in the middle.13 Similarly, Tahayeri et al. stated
that the intensity of the laser output affects the mechanical
properties of 3D-printed resin.3
Post-printing factors
Post-curing devices and conditions
The effect of the post-curing unit on the flexural strength of
3D-printed resin was tested in four studies13,18,25,29 (Table
S5). Three studies reported that the curing unit could sig-
nificantly affect the flexural strength. One study mentioned
no effect13 of the curing unit on the flexural strength, but it
used the same curing time and wavelength range with the
different curing units, which might be the reason for the find-
ings. Moreover, the possible variation between studies might
result from the differences between the curing units, such as
light type and source, as well as the curing conditions (envi-
ronment, in nitrogen gas atmosphere and pressure) and the
different wavelength ranges. The presence of a nitrogen gas
atmosphere enables the post-curing process to be carried out
under inert conditions to overcome the detrimental effect of
the oxygen inhibition layer.18 Another element is the temper-
ature of the curing oven, which directly affects the strength
when combined with these factors.
The changes in the mechanical properties and color of
3D-printed resin with the curing time are mainly due to
the photoinitiator.34,35 An appropriate combination of the
photoinitiator and co-initiator, as well as the correct expo-
sure time to the light source, can improve the mechanical
strength of the printed resin.26 Various types of photoini-
tiators are used, including diphenyl (2,4,6-trimethylbenzoyl)
phosphine oxide, bis phenyl (2,4,6-trimethylbenzoyl) phos-
phine oxide, camphorquinone, and 2-(dimethylamino) ethyl
methacrylate.16 Post-polymerization is highly dependent on
the type of the curing chamber, the frequency and inten-
sity of the UV light, the exposure time, and the composition
of the photosensitive resin, which can potentially affect the
mechanical strength and biocompatibility of the 3D-printed
resin.16,26 The photoinitiator type has a major role in the
post-curing outcome associated with the curing method. The
appropriate wavelength can efficiently react with a photoini-
tiator, increasing the degree of conversion and improving the
mechanical properties of the printed resin.29 The strength
variations between the curing devices might be attributed
to the different wavelength absorption ranges, from narrow
to wide, and the absorption peak (Table S5) of each curing
device.27 Therefore, the curing methods combined with the
photoinitiator type should be considered an important factor
affecting the strength of printed resins and required focus in
future research. Hence, the appropriate post-curing method
should be investigated for the respective photosensitive
resin.
Post-curing time
The green state of printed resins has low mechanical
strength.13,16,26 Therefore, an additional curing process has
been recommended to increase the degree of conversion
and decrease the residual monomer.27 Adequate post-
curing time results in consistent polymerization through the
3D-printed object, which improves the mechanical properties
and reduces anisotropy.16,36 3D-printed resin should be post-
cured in a UV light box or at higher temperatures according
to the manufacturer recommendations (15–30 min). How-
ever, 1–2 h of post-polymerization time was recommended
to increase the 3D-printed resin flexural strength.3,16 In com-
parison to the factors that affect the flexural strength of
printed resin, the post-curing time could be a reasonable
factor that improves the properties of the printed object
regardless of its configurations.13,16 Therefore, future studies
should focus more on post-curing time alone and in combina-
tion with other factors applicable to prosthesis configuration
fabrications.
Post-curing temperature
The post-curing temperature could have a significant effect on
the polymerization process.15 The higher temperature makes
the polymerization process faster and increases the diffu-
sion of free monomers and their crosslink throughout the
specimen.26,37 Therefore, it could improve the anisotropy of
3D-printed objects by providing more homogeneous curing
and thus better mechanical properties.26,38
Post-printing rinse
The post-processing strategy could have a significant effect
on the properties of the printed resin. Some variations in
manufacturers’ recommendations might be present in this
strategy. Removal of the remaining monomer from the printed
objects could be done using an ultrasonically activated
ethanol bath or centrifugal force.2Increasing the post-rinsing
time inversely affected the flexural strength of printed objects.
STRENGTH OF 3D-PRINTED RESINS 13
The reason for this could be the time dependency of the
swelling effect. The post-rinsing time when increased allows
the solvent molecules to infiltrate into the resin matrix, result-
ing in polymer network relaxation and thus a decrease in
flexural strength.24
Switching printers with different resins and
post-curing units (third-party)
Manufacturers set the guideline for the fabrication of printed
objects and recommend using the same printing system of
the resin brand to achieve the best results. They also validate
the printers for all used materials with the matching printing
parameters. Open software gives flexibility for a third-party
concept (alternative printers with different printing resins).
However, following recommendations regarding using the
respective printing system (printer, printed resin, and post-
curing unit as specified by the manufacturer) results in printed
objects with more accuracy and strength.23 Furthermore, we
hypothesized that changes would occur in the material prop-
erties if a different printer were used than that recommended
by the manufacturer due to differences in the polymerization
method.19 Nevertheless, a study reported that the resin used
for DLP could be printed with LCD technology with similar
properties.15 On the same track of switching the printers and
resins, the curing units were used alternatively in some stud-
ies. The Scheu oven (post-curing unit) contains a nitrogen
gas atmosphere that allows post-curing in inert conditions,
preventing oxygen inhibition and its deteriorating effect and
resulting in better strength of the printed object.18 Moreover,
the use of a powerful curing unit could improve the flexu-
ral strength of printed resin at a similar post-polymerization
time.15
Finishing, polishing, and water storage
No reported standardized protocols exist for finishing and
polishing of 3D-printed resins, except for the removal of
supporting structures and then polishing as conventional
methods. This was also not tested with different printing
factors as a variable. Another factor that could affect the prop-
erties of printed objects is their storage in water after printing
until insertion or cementation. Artificial aging showed dete-
rioration of the flexural strength of 3D-printed objects.2,12
Storage in water reduced the flexural strength of printed spec-
imens due to its plasticizing effect on the polymer network.28
The effect of storage in water or saliva on the flexural
strength was tested for 3D-printed resin used for the fabrica-
tion of occlusal splints, provisional restorations, and denture
bases.11,18,22,25,27 The tested time for storage ranged from
14 days to 6 months. All the included studies reported a
reduction of flexural strength following storage in water or
saliva. However, the reduction of flexural strength was still
within the accepted limits of the corresponding material.
Even with the highest tested time (6 months), the flexural
strength was above the ISO requirement for denture base
materials (65 MPa).27 However, further studies investigating
the effect of water sorption on the strength of 3D-printed resin
for longer times are required.
ISO recommendations and 3D-printed resin
strength
The reported flexural strength of most materials after curing
was within the range of ISO recommendations regarding the
type of printed resin, with the different tested factors includ-
ing artificial aging. The flexural strength of denture base resin
ranged between 65 and 171 MPa, which is in accordance with
the ISO standard for the flexural strength of denture base
materials (65 MPa, ISO 20795-1:2013),39 even after stor-
age in artificial saliva.27 Similarly, for interim prostheses, the
flexural strength was over 50 MPa, the minimal requirement
for the flexural strength of interim resins specified in the ISO
10477 standard.15,40 The lowest flexural strength reported
for orthodontic resin was 92 MPa, exceeding the minimum
requirements of materials used for orthodontic appliances
(50 MPa) set by ISO 20795-2.21
This review included different types of resins from dif-
ferent manufacturers, used for the fabrication of provisional
prostheses, denture bases, splints, surgical guides, occlusal
devices, orthodontic appliances, and denture teeth (Table 2).
However, the manufacturers did not provide full information
about the composition of these materials, the monomer type,
or their chemical formulae. Accordingly, we recommend fur-
ther investigations of the materials and the effect of their
compositions based on the literature, and that the manufac-
turers give more information about their products to allow
conducting these future studies.
3D-printed resin has insufficient physical properties and
mechanical strength. Therefore, an enhancement of its
mechanical properties could be achieved by reinforcement of
the printed resin. Additives could be a promising method to
improve the strength of printed resin and must be considered
but with proper guidelines. They should not affect the resin
color, fluidity, or light penetration depth, and they should
assure the normal distributions within the resin fluids. Resolv-
ing anisotropy and increasing the polymerization rate could
be accomplished through the selection of an appropriate post-
curing process, including the post-curing unit, temperature,
and time. Increasing the post-curing time and temperature
could be used to increase the flexural strength of printed
resin.16,26 The printing layer thickness is also considered to
affect the degree of polymerization.18 Most manufacturers
of 3D-printed resins recommend the use of the correspond-
ing printing system, including the 3D printer and post-curing
machine, to obtain the best results of the printed object. How-
ever, various 3D printers and post-curing equipment are now
available in the market, making it difficult for all clinicians
to access the several types of equipment that are suitable
for various resins.16 However, based on this review, using
the specified printers, resins, and curing unit following the
14 GAD AND FOUDA
manufacturer recommendations is better than the availability
concept.
CONCLUSIONS
Factors affecting the flexural strength of 3D-printed resin can
be categorized into preprinting, printing, and post-printing
factors. The strength of 3D-printed resins was affected by
all the tested factors when used separately or in combi-
nation. Preprinting factors included filler and nanoparticle
addition, with most of the tested additives improving the
strength of 3D-printed resins. Printing factors affected the
flexural strength, and the effect of printing orientation on
flexural strength showed variation between studies. Reducing
the printing layer thickness increased the flexural strength.
Increasing the post-polymerization time and temperature
increased the flexural strength, whereas increasing the post-
rinsing time reduced it. The third-party concept is one factor
with a role in the strength of 3D-printed resin, but following
manufacturer guidelines is recommended.
CONFLICTS OF INTEREST
The authors have no conflicts of interest in the current study.
ORCID
Mohammed M. Gad BDS,MSc https://orcid.org/0000-
0003-3193-2356
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SUPPORTING INFORMATION
Additional supporting information can be found online in the
Supporting Information section at the end of this article.
How to cite this article: Gad MM, Fouda SM.
Factors affecting flexural strength of 3D-printed
resins: A systematic review. J Prosthodont.
2023;1–15. https://doi.org/10.1111/jopr.13640
... Ribeiro, et al. [32] emphasized that CAD/CAM PMMA resins consistently exhibit superior mechanical properties, such as higher flexural strength and lower porosity, compared to 3D-printed resins, due to their homogeneous structure and lack of layer-by-layer fabrication . Similarly, Gad, et al. [33] highlighted that while 3D printing offers unmatched precision and customization capabilities, subtractive techniques remain advantageous for producing materials with higher resistance to mechanical stress, particularly for long-term provisional restorations . The versatility and cost-effectiveness of 3D printing, however, make it an attractive option for cases requiring rapid fabrication or unique geometries. ...
... Rectangular samples provide a more standardized and reproducible testing format, whereas fixed dental prostheses introduce more complex geometries that may better mimic clinical conditions but also create more variability in mechanical performance. The complexity of the prosthesis design, such as connector thickness and the distribution of material stress points, could lead to differing results in flexural strength tests [33]. ...
... Another factor that influences the heterogeneity across studies is testing protocol, including the load and speed applied during flexural strength testing, which varies across studies [33]. Differences in loading rates or maximum forces can significantly impact the outcome, as faster loading rates may induce earlier failure, while higher load capacities can push materials beyond their expected functional limits [35]. ...
Article
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Objectives The aim of this systematic review and network meta-analysis was to compare the flexural strength of provisional fixed dental prostheses (PFDPs) fabricated using different 3D printing technologies, including digital light processing (DLP), stereolithography (SLA), liquid crystal display (LCD), selective laser sintering (SLS), Digital Light Synthesis (DLS), and fused deposition modeling (FDM). Materials and methods A comprehensive literature search was conducted in databases including PubMed, Web of Science, Scopus, and Open Grey up to September 2024. Studies evaluating the flexural strength of PFDPs fabricated by 3D printing systems were included. A network meta-analysis was performed, using standardized mean differences (SMDs) and 95% confidence intervals (CIs) to assess the effects of each system on flexural strength. Results A total of 11 in vitro studies were included, with 9 studies contributing to the network meta-analysis. SLS (77.70%) and SLA (63.82%) systems ranked the highest in terms of flexural strength, while DLP ranked the lowest (23.40%). Significant differences were observed between SLS and multiple other systems, including DLP (-14.58, CI: -22.67 to -6.48), LCD (-14.65, CI: -25.54 to -3.59), FDM (-12.87, CI: -23.30 to -2.52), SLA (-11.41, CI: -18.74 to -4.01), and DLS (-10.89, CI: -21.23 to -0.67). Direct comparisons were limited, with DLP vs. SLA having the most data. Other comparisons were predominantly indirect. Conclusions SLS and SLA systems exhibited superior flexural strength compared to other systems. However, the limited number of direct comparisons and reliance on indirect evidence suggest that further research is necessary to confirm these findings.
... Three-dimensional printing has become the latest technology to be utilized in dentistry, specifically the 3D printing of resin materials [1]. The use of dental 3D-printed resin includes provisionals, crowns, dentures, implants, orthodontic appliances, surgical guides, and diagnostic models [2]. Three-dimensional printing can also be utilized for bioactive scaffolds in periodontal tissue regeneration and bone regeneration [3,4]. ...
... The 3D-printed scaffold imitates the extracellular matrix, favoring the growth of cells [4,5]. The field of dentistry uses two main technologies for 3D printing: stereolithography (SLA) and digital light processing (DLP) [2]. SLA and DLP methods utilize photopolymer resin (75% oligomers, 25% monomers, photopolymer initiator) to create dental 3D-printed resin materials in a layer-by-layer process [2]. ...
... The field of dentistry uses two main technologies for 3D printing: stereolithography (SLA) and digital light processing (DLP) [2]. SLA and DLP methods utilize photopolymer resin (75% oligomers, 25% monomers, photopolymer initiator) to create dental 3D-printed resin materials in a layer-by-layer process [2]. When the photopolymer initiators are exposed to UV light in the 3D printing process, they create primary radicals that react with the oligomers and monomers [2]. ...
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Objective: The aim of this study was to evaluate the cure efficiency and biocompatibility of a novel iron-based coordination complex used as a photoinitiator in comparison to conventional ethyl (2,4,6-trimethylbenzoyl) phenylphosphinate (TPO-L) and camphorquinone (CQ) as photoinitiators in dental 3D-printed resins. Materials and Methods: Experimental dental resin formulations were prepared by blending 1:1 ratio of Bis-GMA and TEGDMA, to which 0.2 wt% of either the iron-based coordination complex or CQ were added, along with 0.2 wt% EDAB and 0.4 wt% IOD, and the TPO-L. The degree of conversion (DC) was measured using Fourier transform infrared spectroscopy (FTIR). Biocompatibility was assessed by evaluating the viability of L929 fibroblast-like cells using the MTT assay 24 h post-exposure. Statistical analyses included a two-way ANOVA followed by Tukey’s test for post hoc comparisons, with significance at p < 0.05. Results: The degree of conversion for the iron-based coordination complex (84.54% ± 1.69%) was significantly higher than that for the TPO-L (78.77% ± 1.25%) and CQ-based resins (73.21% ± 0.47%) (p < 0.001). The iron-based coordination complex and TPO-L resins exhibited significantly higher conversion than CQ-based resins (p < 0.001). Regarding biocompatibility, the cell viability test revealed that the iron-based coordination complex demonstrated the highest cell viability at 86.5% ± 10.24%, followed by TPO-L with 80.03% ± 11.07%. CQ showed the lowest cell viability of 51.29% ± 8.44% (p < 0.05). Tukey’s test confirmed significant differences between CQ and other photointiators (p < 0.05), while no significant difference was found between TPO-L and the iron-based coordination complex. Conclusions: This study introduces a novel iron-based coordination complex photoinitiator that demonstrates enhanced cure efficiency and comparable biocompatibility to TPO-L, while significantly reducing the cytotoxicity associated with CQ. Its longer absorption wavelength supports deeper layer curing, making it a promising alternative for dental 3D printing, particularly in bioactive scaffold applications requiring minimized cytotoxicity.
... Both Saini et al. [14] and Gad et al. [32] explored the complex factors influencing the flexural strength of 3D-printed resins in dentistry, emphasizing the importance of polymerization and fabrication parameters. Saini et al. [14] highlighted significant variability in flexural strength among different 3D printing technologies and resin materials, identifying substantial differences in performance between types like SLA-3D, DLP, and conventional PMMA, with a notable mean difference in flexural strength and high heterogeneity (I2 = 99%). ...
... Saini et al. [14] highlighted significant variability in flexural strength among different 3D printing technologies and resin materials, identifying substantial differences in performance between types like SLA-3D, DLP, and conventional PMMA, with a notable mean difference in flexural strength and high heterogeneity (I2 = 99%). Similarly, Gad and Fouda [32] identified critical variables such as filler addition, printing orientation, and post-polymerization treatments that significantly affect strength. Both studies underscore the nuanced impact of manufacturing techniques and material choices on the mechanical properties of 3D-printed dental prosthetics, suggesting a need for further research to optimize these factors for enhanced clinical outcomes. ...
Article
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Background and Objectives: The use of stereolithographic (SLA) 3D printing technology in dentistry has expanded, particularly for the fabrication of provisional dental restorations. Understanding the mechanical properties and quality of SLA 3D-printed materials is essential to ensure clinical success and patient safety. This systematic review aims to critically evaluate and summarize the available evidence on the mechanical properties and quality of SLA 3D-printed materials. Methods: A comprehensive literature search was conducted in PubMed, Scopus, Embase, Cochrane, and Web of Science up to October 2024. Studies comparing the mechanical properties of SLA 3D-printed provisional restoration materials with those of milled, conventional, or other additive manufacturing methods were included. Nine studies met the inclusion criteria. Data on flexural strength, hardness, fracture resistance, surface roughness, marginal adaptation, accuracy, cement film thickness, shear bond strength, and biofilm formation were extracted and analyzed. Results: The findings from the included studies indicate that SLA 3D-printed materials exhibit varied mechanical properties. Some studies reported that SLA 3D-printed resins had significantly lower flexural strength and hardness compared to milled PMMA and bis-acrylic resins. Other studies found that SLA 3D-printed resins showed clinically acceptable marginal adaptation, surface roughness, and fracture strength comparable to those fabricated by subtractive manufacturing and conventional methods. In terms of accuracy, build orientation influenced the dimensional accuracy of SLA-printed restorations. Studies assessing cement film thickness found that SLA-printed provisional restorations had higher cement film thickness compared to other materials. Regarding repairability and fatigue resistance, limitations were observed in some SLA resins. Conclusions: The mechanical properties and quality of SLA 3D-printed materials for provisional dental restorations vary among studies. While SLA technology holds promise for efficient fabrication of provisional restorations, inconsistencies in material properties suggest a need for further research to optimize materials and printing parameters. Standardization of protocols is necessary to ensure reliable clinical performance of SLA 3D-printed provisional restorations.
... Post-printing factors encompass post-curing conditions (time, temperature, and curing device), post-rinsing duration, finishing and polishing techniques, and storage practices [65]. Additives are used to increase the strength of 3D-printed denture base resin, including zirconia nanoparticles, titanium dioxide nanoparticles, zinc oxide nanoparticles, silver nanoparticle-loaded cellulose nanocrystals at low concentrations, silicon dioxide nanoparticles, essential oil microcapsules, and nanocarbon [71][72][73][74]. Furthermore, zirconia nanoparticles were incorporated into 3D-printed interim fixed prostheses, while animated nanodiamonds were added to 3D-printed resin for orthodontic appliances [71,75,76]. ...
... Additives are used to increase the strength of 3D-printed denture base resin, including zirconia nanoparticles, titanium dioxide nanoparticles, zinc oxide nanoparticles, silver nanoparticle-loaded cellulose nanocrystals at low concentrations, silicon dioxide nanoparticles, essential oil microcapsules, and nanocarbon [71][72][73][74]. Furthermore, zirconia nanoparticles were incorporated into 3D-printed interim fixed prostheses, while animated nanodiamonds were added to 3D-printed resin for orthodontic appliances [71,75,76]. Besides mechanical properties, the surface and optical properties of the 3D-printed resins were chosen to be improved. ...
Article
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Additive manufacturing (3D printing) has transformed dentistry by providing solutions with high precision and accuracy achieved through digital workflows, which facilitate the creation of intricate and personalized structures. Additionally, 3D printing promotes cost efficiency by reducing material waste and errors while enabling on-demand production, minimizing the need for extensive inventories. Recent advancements in 3D-printed resin materials have enhanced their clinical applications by improving mechanical strength, biocompatibility, esthetics, and durability. These innovations have facilitated the fabrication of complex and patient-specific structures, such as dental prostheses, surgical guides, and orthodontic appliances, while significantly reducing production time and material waste. Ongoing research and innovation are expected to strengthen resin properties, including strength, translucency, and durability, broadening their clinical applications. The ongoing evolution of 3D printing technology is poised to play a critical role in driving per-sonalized treatments, streamlining clinical workflows, and shaping the future of dental care. This narrative review comprehensively examines the production techniques and clinical applications of 3D-printed photopolymer resins across various dental specialties, including prosthodontics, orthodontics, pediatric dentistry, maxillofacial surgery, periodontology, endodontics, and conservative dentistry. Additionally, the review provides insight into the transformative impact of these technologies on patient care, highlights existing challenges, and suggests future directions for advancing resin properties and their integration into routine dental practice.
... The mechanical behavior of a material indicates its underlying physical and chemical characteristics [21]. The 3D printing orientation significantly affects the mechanical performance of additively manufactured dentures, thereby influencing the force distribution across dentures [22]. A recent systematic review focused specifically on the effect of print orientation on denture base accuracy without Diagram illustrating the definitions of trueness, precision, and accuracy. ...
... The orientation of the printed object significantly influences factors such as the angle of the light source, depth of light penetration, and direction of layer deposition, all of which affect the overall accuracy of the printed object [25,28,31,32,45]. Furthermore, variables such as light penetration, laser intensity, and the direction of layer curing play critical roles in determining the final accuracy and reproducibility of printed products [22,45]. Notably, the refractive characteristics vary by axis, exhibiting greater refraction on the X-and Y-axes than on the Z-axis. ...
Article
Full-text available
Purpose: This systematic review evaluated the effect of different printing orientations on the physical-mechanical properties and accuracy of resin denture bases and related specimens. Study selection: Utilizing PRISMA 2020 guidelines, a comprehensive search of PubMed, Web of Science, Cochrane, and Scopus databases was conducted until June 2024. Included studies examined the accuracy, volumetric changes, and mechanical or physical properties of 3D-printed denture bases in various orientations. Studies without relevant data were excluded. Bias risk was assessed using a modified CONSORT checklist. Results: This review included 24 studies on 3D-printed denture base resins, mainly based on stereolithography and digital light processing. Horizontal orientation (0°) generally enhanced flexural strength, while tilted and vertical orientations (90°) reduced it. Microhardness results varied due to differences in materials, layer thicknesses, and post-curing. Surface roughness was highest at 45°. Vertical orientation uses less material but is less time-efficient. Microbial adhesion, influenced by surface roughness, varied with printing orientation without a clear consensus on the optimal direction. Conclusions: Printing orientation significantly impacts the physical and mechanical properties and accuracy of 3D-printed resin dentures. A horizontal orientation (0°) improved flexural strength, while accuracy and adaptability were better at 45° and 90°. Surface roughness, translucency, and chemical stability are also affected by orientation, post-curing, and material choice. Although a 90° orientation reduces material use, it increases printing time. Standardized study designs are recommended for drawing definitive conclusions in future research.
... 9 Two previous systematic reviews have addressed the print orientation impact. AlGhamdi and Gad 10 focused on denture base accuracy, and Gad et al 11 analyzed the flexural strength of 3D printed resins, with a limited number of studies related to resin devices: 2 occlusal devices, 3 orthodontic appliances, and 1 surgical guide resin. Recently, print orientation has been recognized as one of the most significant factors affecting the properties of printed parts, [12][13][14][15][16][17] and a substantial body of literature has emerged that focuses on the effects of print orientation on resin devices. ...
... Moreover, the short cross-section of the interlayer path of vertically printed specimens may facilitate and accelerate fracture. 11,54 Vertical orientation is preferred for high production, as the printing templates will fit two to three times more parts than with horizontally printed parts. 43,55 The effect of orientation on the flexural properties of occlusal devices has been reported to be limited, with comparable mechanical outcomes with the slight superiority of the vertically printed specimens. ...
Article
Statement of problem: Different factors affect 3-dimensionally (3D) printed resin products. However, evidence on the effect of the print orientation on resin dental devices is lacking. Purpose: The purpose of this systematic review and meta-analysis was to assess the impact of print orientation on the properties and accuracy of 3D printed implant surgical guides, occlusal devices, clear orthodontic retainers, and aligners. Material and methods: The electronic databases PubMed (MEDLINE), Cochrane, and Scopus were comprehensively searched in July 2024. A modified Consolidated Standards of Reporting Trials (CONSORT) statement was used to judge the included studies, and the data were analyzed by the RevMan 5.4 software program of the Cochrane collaboration by applying an inverse variance analysis (α=.05). Results: Twenty-six records were included. Complete arch, solid surgical guides with horizontal printing orientation exhibited the highest accuracy (P≤.01). Short-span surgical guides printed vertically showed relatively high accuracy (P≤.05). Hollow or mesh devices might not be affected by orientations. Occlusal device accuracy favored horizontal orientation, but correlated with the technology and materials, while the accuracy of orthodontic aligners revealed controversial findings, assuming the limited impact of orientation on orthodontic aligners. The cytotoxicity of occlusal devices was a material-related biological characteristic and unaffected by orientation. Although flexural strength favors horizontal orientation, conflicting results were observed for physical and other mechanical properties due to several variables. Conclusions: Horizontal orientation is recommended for printing complete arch surgical guides, while the accuracy of short surgical guides might favor vertical orientation. The physical mechanical properties depend on the printing orientation, technology, material, and printed parts, but horizontal orientation might produce parts with the best mechanical performance.
... The correlation between layer thickness and the strength of printed resin was observed by Perea-Lower et al. [41], where post-polymerized specimens with reduced layer thickness exhibited significantly higher flexural modulus and hardness values. Groups printed with 100 μm layers demonstrated the poorest performance in flexural strength, and scanning electron microscopy (SEM) images revealed larger voids, which can act as potential failure points within the specimen and lead to fracture [30,42], thereby decreasing mechanical performance [43]. ...
Article
Evaluate the impact of printing parameters on flexural strength (σ), flexural modulus (E), precision, and surface topography characteristics of a resin used to produce provisional restorations. 450 bars for provisional restorations were printed using the SLA printing (25 × 2x2mm ISO-4049), and randomly divided into 30 groups (n = 15) according to the following factors: “printing layer thickness” (25 μm;50 μm;100 μm), “Build angle” (0°,30°,45°,60°,90°) and “thermocycling-TC” (with or without). Following printing, the samples underwent cleaning with isopropyl alcohol. Photopolymerization was performed for 15 min with an UV lamp. Subsequently, each bar was assessed using a digital caliper at 11 specific points in three dimensions for comparison with the STL file area for precision analysis. Half of the samples underwent thermocycling. All samples were submitted to the σ test. Data for σ (MPa), and (GPa) and precision (mm) were analyzed using 3 and 2-way ANOVA, respectively, and Tukey’s post hoc test (5%). Micro-CT, 3D profilometry, and SEM were also performed and analyzed descriptively. The 90°/25μmTC (63.0 ± 4.5) showed the highest σ, being only statistically similar to the 45°/25μmTC (57.7 ± 3.1). For precision 0°/25 μm (–2.56 ± 0.04) expressed the greatest variation to the other experimental groups with a sample shrinkage of 25.6% compared to the STL file. The profilometry revealed that the 30º/25 μm group showed prominent peaks and valleys, presenting elevated roughness values with an average of Sa (28.25 μm). Moreover, it was observed that the groups with a 60° angle presented the lowest porosity values. A print layer thickness of 25 μm combined with a build angle of 90º and 45º resulted in higher σ and greater precision.
... High trueness indicates that the printed object closely aligns with its intended dimensions, while high precision signifies that the 3D printer consistently produces objects with the same dimensions across multiple prints. Although there has been research on the accuracy of 3D printed objects, studies specifically focusing on the accuracy of 3D printed dental working models remain limited [13][14][15]. The present systematic review, thus, is conducted to comparatively evaluate the accuracy of 3D printed full-arch dental models manufactured using different printing techniques with digital reference models. ...
Article
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The present systematic review and meta-analysis aimed to evaluate and compare the accuracy of different 3D printing techniques used for fabricating full-arch dental models against digital reference models. The review included studies that assessed the accuracy of stereolithography (SLA), digital light processing (DLP), PolyJet, and fused filament fabrication (FFF) technologies. A total of seven studies were analyzed, providing insights into the trueness and precision of 3D-printed models. The findings reveal that while all examined 3D printing technologies produced models with clinically acceptable accuracy, DLP and PolyJet techniques consistently demonstrated superior precision and trueness compared to SLA and FFF. The results indicate that DLP and PolyJet technologies are particularly suitable for applications requiring high dimensional fidelity, such as in Prosthodontics. However, the studies also highlighted some limitations, including small sample sizes and variations in study design, which may impact the generalizability of the results. Future research should focus on large-scale clinical trials and explore the impact of post-processing on model accuracy. This review underscores the importance of selecting appropriate 3D printing technologies based on clinical requirements to ensure optimal outcomes in dental prosthetics.
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This review explores the rapid advancements in additive manufacturing, particularly 3D printing, within dentistry, focusing on bioprinting. It highlights the technology's efficiency, cost-effectiveness, and environmental sustainability while comprehensively analyzing its historical development, classification, and applications. The study compares additive manufacturing with conventional subtractive methods like CNC milling and evaluates the materials used. A thorough literature search across PubMed, Scopus, Web of Science, Cochrane, and Google Scholar was conducted, focusing on recent developments in 3D printing and CAD/CAM technologies in dentistry. The review identifies key applications, including surgical guides and root analog implants in implant dentistry, as well as the production of dental models, denture bases, and metal frameworks. Though prosthodontics is in the early stages of adopting 3D printing, advancements in materials and technologies are paving the way for its broader application. This review provides valuable insights for researchers and developers, emphasizing the potential of additive manufacturing to become a dominant chairside production method. Keywords: Computer-aided design/computer-aided manufacturing (CAD/CAM); Additive manufacturing; CNC milling; Subtractive manufacturing; Medical scaffolds; Bioink; Tissue regeneration.
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Objective This study investigated the effect of post curing light exposure time on the physico-mechanical properties and cytotoxicity of a 3D-printed PMMA-based denture material in comparison to a conventional heat-cured alternative as a control. Methods 3D-printed specimens were fabricated followed by post-curing for 0, 5, 10 or 20 min at 200 W and light wavelength range of 390–540 nm. Heat-cured specimens were fabricated using a standard protocol. Specimens were placed in artificial saliva at 37 ℃ for 48 h (immediate groups) and 6 months (aged group), then evaluated flexural strength/modulus, fracture toughness, microhardness, and degree of conversion. Water sorption and solubility was assessed after 28 days. Flexural strength, flexural modulus, and fracture toughness were tested through three-point bending tests, while the surface hardness was tested using Vickers’s test. Fractured specimens were viewed by scanning electron microscope (SEM). Cytotoxicity in term of cell viability was evaluated using human oral fibroblasts. Results Flexural strength/modulus, fracture toughness and surface hardness significantly improved with the increase in light curing time up to 20 min. The same pattern of improvement was found with degree of conversion, water sorption, solubility, and cell viability. There was no significant difference (p < 0.01) between heat-cured material and 3D specimens post-cured for 20 min in term of flexural strength/modulus, surface hardness, and degree of conversion at the two-storage time points. Significance Generally, the physico-mechanical properties of the 3D-printed denture base material improve as post curing time increases up to 20 min which exhibited comparable performance as the conventional heat-cured control.
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Objectives: This study evaluated the biocompatibility, mechanical properties, and surface roughness of CAD-CAM milled and rapidly-prototyped/3D-printed resins. Methods: Six groups of resin specimens were prepared, milled-base (MB), milled-tooth shade (MT), printed-tooth shade (PT), printed-base with manufacturer-recommended 3D-printer (PB1), printed-base with third-party 3D-Printer (PB2), printed-base in a vertical orientation (PB2V). Human epithelial (A-431) and gingival (HGF-1) cells were cultured and tested for biocompatibility using Resazurin assays. Three-point bending and nanoindentation tests measured the mechanical properties of the resin groups. Surface roughness was evaluated using a high-resolution laser profilometer. ANOVA and post-hoc tests were used for statistical analyses (𝜶=0.05). Results: MB revealed a higher ultimate strength (p=0.008), elastic modulus (p=0.002), and toughness (p=0.014) than PB1. MT had significantly higher elastic modulus than PT (p<0.001). Rapidly-prototyped resin samples with a manufacturer-recommended 3D-printer (PB1) demonstrated higher ultimate strength (p=0.008), elastic modulus (p<0.001), hardness (p<0.001) and a reduced surface roughness (p<0.05) when compared with rapidly-prototyped groups using a third-party 3D-printer (PB2). Rapidly-prototyped samples manufactured with a vertical printing orientation (PB2V) revealed a significantly lower elastic modulus than samples groups manufactured using horizontal printing orientation (PB2) (p=0.011). There were no significant differences in biocompatibility between any of the investigated groups. Conclusions: Within the limits of this present study, CAD-CAM milled and rapidly-prototyped complete denture resins performed similar in terms of biocompatibility and surface roughness. However, the milled denture resins were superior to the rapidly-prototyped denture resins with regards to their mechanical properties. Printing orientation and type of 3D-printers can affect the resin strength and surface roughness. Clinical significance: Appropriate CAD-CAM manufacturing technique should be considered whilst manufacturing removable complete dentures (CDs) as the mechanical properties and surface roughness may vary. When fabricating CDs with the rapid-prototyping technique, it seems favorable to employ the correct printing orientation and a 3D-printer that is recommended by the resin manufacturer.
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Objective: To characterize and investigate efficacy of loading functionalized ZrO2 nanoparticles in 3-dimensional (3D) printed acrylate ester-based resin subjected to accelerated aging in artificial saliva. As well as to evaluate the effect of ZrO2 nanoparticle volume fraction addition on mechanical and physical properties of printed composite. Methods: Functionalized ZrO2 nanoparticles were characterized using TEM and Raman spectroscopy. 3D printed dental resin was reinforced, with ZrO2 nanoparticles, in the concentration range (0-5wt.%). The resulted nanocomposites, in term of structure and physical/mechanical properties were evaluated using different mechanical testing, microscopic and spectroscopic techniques. Results: ZrO2 based nanocomposite was successful and formed composites were more ductile. Degree of conversion was significant at the highest level with blank resin and 1wt.%. Sorption revealed reduction associated with volume fraction significant to neat resin, however solubility indicated neat and 4wt.% had the lowest significant dissolution. Vickers represented critical positive correlation with filler content, while nanohardness and elasticity behaved symmetrically and had the maximum strength at 3wt.% addition. In addition, 3wt.% showed the highest fracture toughness and modulus. Improvement of flexural strength was significantly linked to filler concentration. Overall properties dramatically were enhanced after 3 months aging in artificial saliva, especially degree of conversion, microhardness, nanoindentation/elasticity, and flexural modulus. However, significant reduction was observed with flexural modulus and fracture toughness. Significance: The outcomes suggest that the newly developed 3D printed nanocomposites modified with ZrO2 nanoparticle have the superior potential and efficacy as long-term provisional dental restoration materials.
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Purpose To evaluate the flexural strength (FS), impact strength (IS), surface roughness (Ra) and hardness of 3D-printed resin incorporating silicon dioxide nanoparticles (SNPs). Materials and Methods A total of 320 acrylic specimens were fabricated with different dimensions according to test specifications and divided into a control group of heat denture base resin, and 3 test groups (80/test (n = 10), of unmodified, 0.25wt% and 0.5wt% SNPs modified 3D-printed resin. 10,000 thermal cycles were performed to half of the fabricated specimens. FS, IS (Charpy impact), Ra, and hardness were evaluated and the collected data was analyzed with ANOVA followed by Tukey's post hoc test (α = 0.05). Results Incorporating SNPs into 3D-printed resin significantly increased the FS, IS (at 0.5%) and hardness compared to unmodified 3D-printed resin (P˂0.001). However, the FS of pure 3D-printed and 3D/SNP-0.50% resin and IS of all 3D-printed resin groups were significantly lower than the control group (P˂0.0001). Hardness of 3D/SNP-0.25% and 3D/SNP-0.50% was significantly higher than control and unmodified 3D-printed resin (P<0.0001), with insignificant differences between them. The Ra of all 3D-printed resin groups were significantly higher than control group (P<0.001), while insignificant difference was found between 3D-printed groups. Thermal cycling significantly reduced FS and hardness for all tested groups, while for IS the reduction was significant only in the control and 3D/SNP-0.50% groups. Thermal cycling significantly increased Ra of the control group and unmodified 3D-printed resin (P<0.001). Conclusion The addition of SNPs to 3D-printed denture base resin improved its mechanical properties while Ra was not significantly altered. Thermal cycling adversely affected tested properties except IS of unmodified 3D-printed resin and 3D/SNP-0.25%, and Ra of modified 3D-printed resin.
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Objective: This study investigated the influence of postpolymerization of a three-dimensional (3D) printed denture base polymer. The effect of post-curing methods on surface characteristics, flexural strength, and cytotoxicity was evaluated. Methods: A total of 172 specimens were additively manufactured using one denture base material (V-Print dentbase, VOCO) and further post-cured by different light-curing devices, including Otoflash G171 (OF), Labolight DUO (LL), PCU LED (PCU), and LC-3DPrintbox (PB), respectively. Polymethyl methacrylate resin (PalaExpress Ultra) was used as a reference (REF). Afterward, surface topography was observed using scanning electron microscopy, and surface roughness was measured (n = 6). Furthermore, flexural strength was tested (n = 20). Cytotoxicity was evaluated by the extract and direct contact tests. The data were analyzed using the Kolmogorov-Smirnov test and one-way ANOVA followed by Tukey's multiple comparisons and Kruskal-Wallis tests (p < 0.05). Results: The different post-curing methods applied did not significantly influence surface topography and roughness (Ra). Meanwhile, specimens post-cured by PCU (162.3 ± 44.16 MPa) and PB (171.2 ± 34.41 MPa) showed significantly higher flexural strength than those post-cured by OF (131.3 ± 32.87 MPa) and REF (131.2 ± 19.19 MPa), respectively. Additionally, various post-curing methods effectively decreased the cytotoxic effects of 3D-printed denture base polymer. Conclusions: Different post-curing methods did not significantly alter the Ra values of the 3D-printed denture base material. However, flexural strength was significantly affected by the postpolymerization methods, which might be attributed to the different wavelengths of post-curing devices. In addition, various postpolymerization methods reduced the cytotoxic effects of the 3D-printed denture base polymer. Clinical significance: Flexural strength of additively manufactured denture bases depends on the postpolymerization strategy. Therefore, an appropriate post-curing method is required to optimize the flexural strength of 3D-printed denture materials.
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Purpose : This in vitro study evaluated the flexural strength, impact strength, hardness, and surface roughness of 3D-printed denture base resin subjected to thermal cycling treatment. Methods : According to ISO 20795-1:2013 standards, 120 acrylic resin specimens (40/flexural strength test, 40/impact strength, and 40/surface roughness and hardness test, n = 10) were fabricated and distributed into two groups: heat-polymerized; (Major.Base.20) as control and 3D-printed (NextDent) as experimental group. Half of the specimens of each group were subjected to 10,000 thermal cycles of 5–55°C simulating 1 year of clinical use. Flexural strength (MPa), impact strength (KJ/m²), hardness (VHN), and surface roughness (μm) were measured using universal testing machine, Charpy's impact tester, Vickers hardness tester, and profilometer, respectively. Data were analyzed by ANOVA and Tukey honestly significant difference (HSD) test (α = 0.05). Results : The values of flexural strength (MPa) were 86.63 ±1.0 and 69.15 ±0.88; impact strength (KJ/m²) - 6.32 ±0.50 and 2.44 ±0.31; hardness (VHN) - 41.63 ±2.03 and 34.62 ±2.1; and surface roughness (μm) - 0.18 ±0.01and 0.12 ±0.02 for heat-polymerized and 3D-printed denture base materials, respectively. Significant differences in all tested properties were recorded between heat-polymerized and 3D-printed denture base materials (P<0.001). Thermal cycling significantly lowered the flexural strength (63.93 ±1.54 MPa), impact strength (2.40 ±0.35 KJ/m²), and hardness (30.17 ±1.38 VHN) of 3D-printed resin in comparison to thermal cycled heat-polymerized resin, but surface roughness showed non-significant difference (P = 0.262). Conclusion : 3D-printed resin had inferior flexural strength, impact strength, and hardness values than heat-polymerized resin, but showed superior surface roughness. Temperature changes (thermal cycling) significantly reduced the hardness and flexural strength and increased surface roughness, but did not affect the impact strength. This article is protected by copyright. All rights reserved
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The aim of this study was to assess the translucency of denture base acrylic resin reinforced with zirconium dioxide (ZrO2NPs), silicon dioxide (SiO2NPs), and diamond (DNPs) nanoparticles. A total of 130 heat-polymerized acrylic discs (15×2.5 mm) were fabricated conventionally and divided into control and experimental groups according to nanoparticle type and concentration (0.5, 1, 1.5, and 2.5 wt%). Unmodified acrylic resin specimens served as control. All specimens were thermocycled (5,000 cycles). Translucency was measured using a spectrophotometer. ANOVA and post-hoc Turkeys’ test were used for data analysis at α=0.05. The translucency of modified PMMA was significantly lower than control (p<0.05) except 0.5% ZrO2NPs and SiO2NPs (p>0.05) which exhibited the highest translucency values among modified groups. As the NPs concentration increased, the translucency decreased and the lowest value was seen with 2.5% DNPs (1.18±0.10). The addition of ZrO2NPs, SiO2NPs, and DNPs into denture base resin decreased the translucency.