Bond strength of 4META-MMA-TBB resin to a CAD/CAM composite resin block and analysis of acetone-insoluble cured resin residues at adhesive interfaces

Abstract

This study investigated the adhesion of 4META-MMA-TBB resin to CAD/CAM composite resin blocks. CAD/CAM composite resin blocks were subjected to alumina blasting, ceramic primer treatment, or both, and then bonded with 4META-MMA-TBB resin. The tensile bond strength of 4META-MMA-TBB resin to blocks without surface treatment was approximately 20 MPa, but with surface treatment, it significantly improved to approximately 40 MPa. Cohesive failure was observed in some blocks with surface treatment with both alumina blasting and ceramic primer. As a result of Soxhlet extraction of the adhesive interface with acetone solvent and FT-IR spectrum analysis, it was found that PMMA remained on the block surface when surface treatment with both alumina blasting and ceramic primer were performed. These results demonstrated that the bond strength of 4META-MMA-TBB resin is significantly improved when both alumina blasting and ceramic primer are applied as surface pretreatment to the CAD/CAM composite resin block.

Full text

INTRODUCTION
Due to concerns regarding metal allergies1) and aesthetic
demands2), the use of computer-aided design/computer-
aided manufacturing (CAD/CAM) composite resin blocks
in prosthetic treatment is increasing2). CAD/CAM
composite resin blocks have superior elasticity, high
load-bearing capacity, and excellent milling properties,
compared to ceramic materials, making CAD/CAM
composite resin a useful alternative to metal3,4). On
the other hand, it has been reported that CAD/CAM
composite resin crowns often causes detachment5).
Composite resin cements are commonly used for
attaching CAD/CAM composite resin crowns6). However,
Shinagawa et al. reported that 4META-MMA-TBB
resin showed signicantly higher early bond strength
to CAD/CAM composite resin blocks than composite
resin cement7). Furthermore, Hata et al. reported
that the bond strength of 4META-MMA-TBB resin to
sandblasted PEEK was signicantly higher than that
of composite resin cements8). 4META-MMA-TBB resin
is said to be fundamentally different from CAD/CAM
composite resin blocks in terms of two mechanisms:
interfacial polymerization initiation9) and subsequent
polymerization10). To date, the mechanism by which
4META-MMA-TBB resin attaches to CAD/CAM
composite resin remains unclear. Therefore, in this
study, we investigated the bond strength of 4META-
MMA-TBB resin to a CAD/CAM composite resin.
We also examined the residual 4META-MMA-TBB
resin components insoluble in acetone at the adhesive
interface using Soxhlet extraction and Fourier-transform
infrared spectroscopy (FT-IR).
MATERIALS AND METHODS
Materials
The materials used in this study are listed in Table
1. Katana Avencia Blocks (Kuraray Noritake Dental,
Tokyo, Japan) were used as CAD/CAM composite resin
blocks, Super Bond C&B (Sun Medical, Moriyama,
Japan) was used as 4META-MMA-TBB resin, and
Ceramic Primer (Super Bond PZ Primer, Sun Medical)
was used as the surface treatment agent.
Methods
1. Experiment 1: Bond strength measurement
1) Preparation of adherends
CAD/CAM composite resin blocks were sliced to 3
mm thickness using a low-speed cutter and used as
adherends. The surfaces of adherends were nished
into regular at surfaces with 2000-grit silicon carbide
papers to exclude the inuence of mechanical retention,
focusing only on the efcacy of surface treatment. The
adherend surfaces were divided into four groups based
on pre-treatment options: (1) no pre-treatment (CT), (2)
blasting with 50 μm alumina at 0.2 MPa followed by
10 min of ultrasonic cleaning in distilled water and air
drying (AB), (3) treatment with PZ primer (PZ), and (4)
treatment with PZ primer after the same treatment as
AB (AB+PZ).
2) Bonding procedure
Two adherend surfaces were bonded with 4META-
MMA-TBB resin. From polishing the adherend to
surface treatment and subsequent bonding, the process
was carried out in a single step with few intervals.
Twenty four hours after bonding, the adherend was cut
into 1×1×6 mm slices using a low-speed cutter to create
Bond strength of 4META-MMA-TBB resin to a CAD/CAM composite resin block
and analysis of acetone-insoluble cured resin residues at adhesive interfaces
Sadaaki MURAHARA, Asami UENODAN, Hiroaki YANAGIDA and Hiroyuki MINAMI
Department of Fixed Prosthodontics, Kagoshima University, Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima
890-8544, Japan
Corresponding author, Sadaaki MURAHARA; E-mail: murasada@dent.kagoshima-u.ac.jp
This study investigated the adhesion of 4META-MMA-TBB resin to CAD/CAM composite resin blocks. CAD/CAM composite resin
blocks were subjected to alumina blasting, ceramic primer treatment, or both, and then bonded with 4META-MMA-TBB resin. The
tensile bond strength of 4META-MMA-TBB resin to blocks without surface treatment was approximately 20 MPa, but with surface
treatment, it signicantly improved to approximately 40 MPa. Cohesive failure was observed in some blocks with surface treatment
with both alumina blasting and ceramic primer. As a result of Soxhlet extraction of the adhesive interface with acetone solvent and
FT-IR spectrum analysis, it was found that PMMA remained on the block surface when surface treatment with both alumina blasting
and ceramic primer were performed. These results demonstrated that the bond strength of 4META-MMA-TBB resin is signicantly
improved when both alumina blasting and ceramic primer are applied as surface pretreatment to the CAD/CAM composite resin
block.
Keywords: 4META-MMA-TBB resin, CAD/CAM composite resin block, Soxhlet extraction, Fourier-transform infrared spectroscopy
Received Apr 15, 2024: Accepted Aug 30, 2024
doi:10.4012/dmj.2024-107 JOI JST.JSTAGE/dmj/2024-107
This is an open access article under the CC BY license
https://creativecommons.org/licenses/by/4.0/
Dental Materials Journal 2024; : –

Table 1 Materials used in this study
Material Product Component Manufacturer
CAD/CAM
composite block
KATANAAVENCIA
Block
Light anhydrous silicic acid, oxidized
aluminium, urethane dimethacrylate, colorant
Kuraray Noritake
Dental,
Tainai, Japan
Resin Cement Super Bond C&B
Monomer: methyl methacrylate,
4-methacryloxyethyl trimellitate anhydride
Catalyst: tri-n-butyl borane,
Polymer: polymethyl methacrylate
Sun Medical,
Moriyama, Japan
Ceramics Primer Super Bond PZ
Primer
Liquid A: methyl methacrylate, phosphate ester
monomer, etc.
Liquid B: methyl methacrylate, silane compound
Sun Medical
Fig. 1 1) A schematic diagram of the Soxhlet extraction
method (https://commons.wikimedia.org/wiki/File:
Soxhlet_extractor.svg. Public domain).
2) An image of the Soxhlet extractor.
1) 2)
microtensile test specimens. Thirty specimens were
prepared for each group.
3) Thermal cycling
Fifteen specimens from each group were subjected to
10,000 cycles of thermal cycling of 5°C and 55°C. The
remaining specimens immediately underwent adhesion
testing without thermal cycling.
4) Tensile adhesion test
Tensile load at a crosshead speed of 1.0 mm/min was
applied using a universal tabletop precision tester
(AUTOGRAPH EZ-S, Shimadzu, Kyoto, Japan).
Maximum load (N) at fracture was recorded. The
measured data was analyzed using a statistical software
EZR version1.65 (Saitama Medical Center, Jichi Medical
University, Saitama, Japan). We performed two-way
analysis of variance (ANOVA) with the surface treatment
methods and the thermal-cycling as independent factors
(α=0.05). Multiple comparisons were carried out using
the Bonferroni-Dunn test to identify the signicant
differences among the groups (α=0.05).
5) Fracture types
After tensile adhesion testing, fracture surfaces were
observed using a stereomicroscope (ZEISS SteREO
Discovery.V12). The fracture surfaces of the specimens
were classied into three types: (1) adhesive failure (AF)
at the interface between the cement and the block, (2)
cohesive failure (CF) within the block, and (3) mixed
failure (MF).
2. Experiment 2: Analysis of the acetone-insoluble resin
and block adherend surface
1) Preparation of specimens
CAD/CAM composite resin blocks were sliced to a
thickness of 1 mm using a low-speed cutter and used as
adherends. One side of the adherends was polished under
water irrigation with waterproof emery paper #2000
to create the adherend surface. The adherends were
divided into four groups based on pre-treatment of the
adherend surface as follows: (1) no pre-treatment (CT),
(2) blasting with 50 μm alumina at 0.2 MPa followed by
10 min of ultrasonic cleaning of the surface in distilled
water and air drying (AB), (3) treatment with PZ primer
(PZ), and (4) treatment with PZ primer after the same
treatment as AB (AB+PZ). Masking tape (Mending tape,
Kokuyo, Tokyo, Japan) was used to create a bonding
area of φ5 mm. 4META-MMA-TBB resin was applied
to the adherend surface using the brush-on technique
to a thickness of approximately 50 μm. The surface was
covered with a polyester sheet and allowed to stand at
room temperature for 30 min followed by incubation at
37°C with 100% humidity in a constant temperature
chamber for 24 h. The polyester sheet was removed to
expose the MMA-based adhesive material. The block
was then placed at the bottom of a cylindrical lter
paper (THIMBLE FILTER No.84, ADVANTEC, Tokyo,
Japan), and soluble components were extracted using a
2
Dent Mater J 2024; : –

Fig. 2 Tensile bond strength (MPa) of the different
groups.
Same lowercase letters indicate no signicant
difference among surface treatment groups without
thermal cycling. Same uppercase letters indicate
no signicant difference among surface treatment
groups with 10,000 thermal cycles. * indicates
no signicant difference within the same surface
treatment group before and after thermal cycling.
Table 2 Fracture modes after the bonding test (number of specimens)
AF CF MF
CT 15 0 0
CT (Thermo.) 15 0 0
AB 15 0 0
AB (Thermo.) 15 0 0
PZ 15 0 0
PZ (Thermo.) 15 0 0
AB+PZ 7 5 3
AB+PZ (Thermo.) 5 4 6
CT: no pre-treatment, AB: blasting with 50 μm alumina, PZ: treatment with PZ primer, AB+PZ: treatment with PZ primer
after the same treatment as AB
glass Soxhlet extractor with acetone solvent (FUJIFILM
Wako Pure Chemical, Osaka, Japan) to remove acetone-
soluble components of the MMA-based adhesive in the
block. A schematic diagram of the Soxhlet extraction
method used is shown in Fig. 1-1), and a photograph is
shown in Fig. 1-2). The glass Soxhlet extractor consisted
of a ask (a) containing the solvent at the bottom, a
glass container equipped with lter paper containing
the solid specimen in the middle, and a glass condenser
tube (c) at the top. This is the simplest and most basic
apparatus for chemical analysis11). When the ask (a) is
heated, the solvent evaporates, the condensed solvent in
the top condenser tube (c) drips down through the reux
side tube (b) into the adherend-containing ltration unit
(d), where a small amount of soluble target component
is dissolved, and then, returned to the ask (a). Since
the target component (mainly PMMA in this case) has
a higher boiling point than the solvent, repeating this
reux cycle gradually concentrates the PMMA in the
ask, leaving behind insoluble components from the
chemical bonding in the solid sample.
After extraction, the surface of the adherend was
dried to remove acetone solvent, and the presence of
residual hardened 4META-MMA-TBB resin on the block
surface was visually observed using an optical microscope
(SMZ-10, Nikon, Tokyo, Japan) at ×10 magnication. The
adherend surface was further analyzed by ATR method
using FT-IR (Spectrum 100, Perkin Elmer, Shelton, CT,
USA) to conrm whether PMMA, the main component of
residual MMA-based adhesive material, was present on
the block surface.
RESULTS
Experiment 1
1. Tensile bond strength
The results are shown in Fig. 2. Compared to the control
group (CT), groups AB, PZ, and AB+PZ all exhibited
signicantly higher bond strength. No signicant
differences were observed among groups AB, PZ, and
AB+PZ. There were also no signicant differences
observed in any group before and after thermal cycling.
2. Fracture modes
The fracture modes are shown in Table 2. In the
AB+PZ group, cohesive and mixed fractures of CAD/
CAM composite blocks were observed. In other groups,
interfacial fractures were observed.
Experiment 2
1. Visual observation
Optical images are shown in Fig. 3. In the AB+PZ group,
where both alumina blasting and PZ primer treatment
were performed, remnants of hardened material were
observed in the central region. No remnants were
observed in other groups.
3
Dent Mater J 2024; : –

Fig. 3 The surface appearance of all the groups.
1) The surface appearance of the CT group. 2)
The surface appearance of the AB group. 3) The
surface appearance of the PZ group. 4) The surface
appearance of the AB+PZ group.
1)
2)
3)
4)
Fig. 4 The FT-IR spectrum of CAD/CAM composite resin
block surface (below) and the PMMA spectrum
(above).
Fig. 5 The FT-IR spectra of all the groups.
1) The FT-IR spectrum of the CT group. 2) The FT-IR spectrum of the AB group. 3) The FT-IR spectrum of the PZ
group. 4) The FT-IR spectrum of the AB+PZ group.
1)
2)
3)
4)
2. FT-IR
Spectra of PMMA polymer and CAD/CAM composite
resin blocks are shown in Fig. 4. The presence of PMMA
4
Dent Mater J 2024; : –

is indicated by strong absorption peaks around 3,000
cm−1 and 1,200 cm−1 (red arrows). Since the 3,000 cm−1
peak is signicantly affected by impurities, particular
attention should be paid to the 1,200 cm−1 peak12). FT-
IR spectra of block surfaces after Soxhlet extraction for
each group are shown in Fig. 5, along with PMMA
spectra for comparison. In the central area of the bonding
interface, PMMA-derived spectra were observed in the
AB+PZ group but not in other groups.
DISCUSSION
The bond strength of 4META-MMA-TBB resin to CAD/
CAM composite resin blocks exceeded 20 MPa even in
the CT group. Bond strength increased signicantly
following pre-treatment using alumina blasting or
ceramics primer. Although no signicant differences
were found among the AB, PZ, and AB+PZ groups,
cohesive and mixed fractures of CAD/CAM composite
blocks were only observed in the AB+PZ group. This
result suggests that, in the AB+PZ group, 4META-MMA-
TBB resin closely attaches to the CAD/CAM composite
resin block surface whereby the two are almost fully
integrated. To conrm this, we extracted acetone-soluble
4META-MMA-TBB resin at the adhesive interface using
the Soxhlet extraction method and performed FT-IR
analysis on residual PMMA. The results showed that
there was PMMA derived from 4META-MMA-TBB resin
that could not be removed by acetone extraction in the
AB+PZ group. Previous studies have reported on the
effectiveness of micro-mechanical retention by alumina
blasting13-18). The ceramics primer used in this study
contains silane coupling agents and phosphate ester
monomers. Meanwhile, the CAD/CAM composite resin
blocks used in this study are formulated with silica and
alumina as llers. The effectiveness of silane coupling
agents for silica18,19) and the effectiveness of phosphate
ester monomers for alumina20,21) have been reported. The
results of this study showed the same trends as those
reports, with the adhesive strength of 4META-MMA-
TBB resin to CAD/CAM composite resin blocks being
signicantly improved by performing either alumina
blasting or ceramic primer treatment. However, we
observed no obvious residual PMMA after Soxhlet
extraction using acetone as a solvent in groups where
only alumina blasting or ceramic primer was applied.
Therefore, it has been conrmed that both chemical
bonding to the ller and mechanical bonding is necessary
to achieve strong adhesion between the 4META-MMA-
TBB resin and CAD/CAM composite resin blocks used in
this study. However, within the scope of this study, the
mechanism by which the adhesive layer is formed has
not been claried. Asakura et al. investigated the effects
of sandblasting, silane coupling treatment, and MMA-
containing primer treatment on the bond strength of 11
types of CAD/CAM composite resin blocks and reported
that bond strength varied signicantly depending on
the block22). To further elucidate the issue, similar
investigations should be conducted on other commercial
blocks and standardized specimens made only from
matrix resin. 4META-MMA-TBB resin is a PMMA resin
that contains 4-META as an adhesive monomer and
TBB as a polymerization initiator. To further elucidate
the issue, similar investigations should be conducted
on PMMA resins using polymerization initiators other
than TBB. Additionally, the inuence of the adhesive
monomer 4-META should also be further investigated.
CONCLUSION
The study demonstrated that pre-treatment with
alumina blasting and ceramics primer signicantly
improved the bond strength between 4META-MMA-
TBB resin and the CAD/CAM composite resin blocks
used in this study, and that an acetone-insoluble PMMA
layer is formed at the adhesive interface.
CONFLICT OF INTEREST
The authors do not have any nancial interest in the
companies whose materials are included in this article.
REFERENCES
1) Wataha JC. Biocompatibility of dental casting alloys: A
review. J Prosthet Dent 2000; 83: 223-234.
2) Tsitrou EA, Northeast SE, van Noort R. Evaluation of the
marginal t of three margin designs of resin composite crowns
using CAD/CAM. J Dent 2007; 35: 68-73.
3) Rohr N, Coldea A, Zitzmann NU, Fischer J. Loading capacity
of zirconia implantsupported hybrid ceramic crowns. Dent
Mater 2015; 31: 279-288.
4) Awada A, Nathanson D. Mechanical properties of resin-
ceramic CAD/CAM restorativematerials. J Prosthet Dent
2015; 114: 587-593.
5) Komine F, Honda J, Kusaba K, Kubochi K, Takata H. Clinical
outcomes of single crown restorations fabricated with resin-
based CAD/CAM materials. J Oral Science 2020; 62: 353-
355.
6) Calheiros-Lobo MJ, Vieira T, Carbas R, da Silva LFM, Pinho
T. Effectiveness of self-adhesive resin luting cement in
CAD-CAM blocks —A systematic review and meta-analysis.
Materials (Basel) 2023; 16: 2996.
7) Shinagawa J, Inoue G, Nikaido T, Ikeda M, Burrow MF,
Tagami J. Early bond strengths of 4-META/MMA-TBB resin
cements to CAD/CAM resincomposite. Dent Mater J 2019; 38:
28-32.
8) Hata K, Komagata Y, Nagamatsu Y, Masaki C, Hosokawa
R, Ikeda H. Bond strength of sandblasted PEEK with dental
methyl methacrylate-based cement or composite-based resin
cement. Polymers 2023; 15: 1830.
9) Imai Y, Kadoma Y, Kojima K, Akimoto T, Ikakura K, Ohta T.
Importance of polymerization initiator systems andinterfacial
initiation of polymerization in adhesive bonding ofresin to
dentin. J Dent Res 1991; 70: 1088-1091.
10) Taira Y, Imai Y. Review of methyl methacrylate (MMA)/
tributylborane (TBB)-initiated resin adhesive to dentin. Dent
Mater J 2014; 33: 291-304.
11) Luque de Castro MD, Priego-Capote F. Soxhlet extraction:
Past and present panacea. J Chromatogr A 2010; 1217: 2383-
2389.
12) Popescua A, Vasileb C, Brebub M, Popescua GL, Moldovan M,
Prejmerean C, et al. The characterization of recycled PMMA.
J Alloys Compd 2009; 483: 432-436.
13) Öztas N, Alaçam A, Bardakcy Y. The Effect of air abrasionwith
two new bonding agentson composite repair. Operative Dent
5
Dent Mater J 2024; : –

2003; 28: 149-154.
14) Arao N, Yoshida K, Sawase T. Effects of air abrasion with
alumina or glass beadson surface characteristics of CAD/CAM
compositematerials and the bond strength of resin cements. J
Appl Oral Sci 2015; 23: 629-636.
15) Cho SD, Rajitrangson P, Matis BA, Platt JA. Effect of
Er,Cr:YSGG laser, air abrasion, and silane application on
repaired shear bond strength of composites. Oper Dent 2013;
38: 58-66.
16) Reymus M, Roos M, Eichberger M, Edelhoff D, Hickel R,
Stawarczyk B. Bonding to new CAD/CAM resin composites:
Inuence of air abrasion and conditioning agents as
pretreatment strategy. Clin Oral Investig 2019; 23: 529-538.
17) Moura DMD, Dal Piva AMO, Januário ABDN, Verissímo AH,
Bottino MA, Özcan M, et al. Repair bond strength of a CAD/
CAM nanoceramic resinand direct composite resin: Effect of
aging and surfaceconditioning methods. J Adhes Dent 2020;
22: 275-283.
18) Nejat A, LeeJ, Shah S, Lin C, Kulkarni P, Chavali R, et al.
Retention of CAD-CAM resin composite crowns following
different bonding protocols. Am J Dent 2018; 31: 97-102.
19) Matinlinna JP, Lung CYK, Tsoi JKH. Silane adhesion
mechanism in dental applications and surface treatments: A
review. Dent Mater 2018; 34: 13-28.
20) Borges GA, de Goes MF, Platt JA, Moore K, de Menezes FH,
Vedovato E. Extrusion shear strength between an alumina-
based ceramic and three different cements. J Prosthet Dent
2007; 98: 20-215.
21) Baldissara P, Valandro LF, Monaco C, Ferrari M, Bottino MA,
Scotti R. Fatigue resistance of the bond of a glass-inltrated
alumina ceramic to human dentin. J Adhes Dent 2006; 8: 97-
104.
22) Asakura M, Aim K, Hayashi T, Matsubara M, Mieki A, Ban
S, et al. Bonding characteristics of silane coupling agent and
MMA-containing primer to various composite CAD/CAM
blocks. Polymers 2023; 15: 3396.
6Dent Mater J 2024; : –