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Subramanian EMG, Vignesh Ravindran, Ganesh Jeevanandan. Comparison of Amount of Tooth Reduction in Primary rst Molar for Stainless Steel, Zirconia and Fibre-glass Crowns – In-
Vitro Study. Int J Dentistry Oral Sci. 2021;8(7):3427-3430.
3427
OPEN ACCESS https://scidoc.org/IJDOS.php
Comparison of Amount of Tooth Reduction in Primary rst Molar for Stainless Steel, Zirconia and
Fibre-glass Crowns – In-Vitro Study
Research Article
Subramanian EMG1*, Vignesh Ravindran2, Ganesh Jeevanandan3
1 Professor and Head, Department of Pediatricand Preventive Dentistry, Saveetha Dental College and Hospitals, Saveetha University, Saveetha Institute
of Medical and Technical Sciences, Velappanchavadi, Chennai – 77, Tamil Nadu, India.
2 Senior Lecturer, Department of Pediatric and Preventive Dentistry, Saveetha Dental College and Hospitals, Saveetha University, Saveetha Institute of
Medical and Technical Sciences, Velappanchavadi, Chennai – 77, Tamil Nadu, India.
3 Reader, Department of Pediatric and Preventive Dentistry, Saveetha Dental College and Hospitals, Saveetha University, Saveetha Institute of Medical
and Technical Sciences, Velappanchavadi, Chennai – 77, Tamil Nadu, India.
International Journal of Dentistry and Oral Science (IJDOS)
ISSN: 2377-8075
*Corresponding Author:
Subramanian EMG. B.D.S., M.D.S.,
Professor, Department of Pediatricand Preventive Dentistry, Saveetha Dental College and Hospitals, Saveetha University, Saveetha Institute of Medical and Technical Sciences,
Velappanchavadi, Chennai – 77, Tamil Nadu, India.
Tel: +91 9884125380
E-mail: Subramanian@saveetha.com
Received: April 20, 2021
Accepted: July 09, 2021
Published: July 19, 2021
Citation: Subramanian EMG, Vignesh Ravindran, Ganesh Jeevanandan. Comparison of Amount of Tooth Reduction in Primary rst Molar for Stainless Steel, Zirconia and Fibre-
glass Crowns – In-Vitro Study. Int J Dentistry Oral Sci. 2021;8(7):3427-3430.
Copyright: Subramanian EMG©2021. This is an open-access article distributed under the ter ms of the Creative Commons Attribution License, which permits unrestricted use,
distribution and reproduction in any medium, provided the original author and source are credited.
Introduction
Early childhood caries is dened as the presence of carious lesion
in one or more teeth in children less than 71 months of age and
the labial surface of the upper anterior teeth is one of the most
Early Childhood Caries is a multifactorial disorder which contin-
ues to be a global health problem for decades in children which
needs to be intercepted to prevent early loss of primary dentition
which could lead to space loss. Stainless steel crowns (SSCs) has
been the benchmark in providing a semi-permanent restoration
for teeth in primary dentition affected by caries, decalcication
in the cervical region, developmental defects like hypoplasia, and
also as a full coronal restoration in case of teeth treated by pulpot-
omy or pulpectomy.[1] Their advantages with strength, retention
and minimal tooth preparation could not overcome the obvious
disadvantage of hampering esthetics. Modications in the SSCs
like open-faced SSCshave been tried which make the work tedi-
ous, time consuming and also technique sensitive.[2] Pre-veneered
SSCs have also been used which increased parents’ satisfaction un-
til the fracture of resin leading to facing loss.[3] Zirconia crowns
made its debut in 1991 which had a paradigm shift in providing
full coronal restorations in primary anterior teeth.These crowns
allow the practitioners to provide patients with superior, highly
polished, esthetic results. Many brands have then evolved in the
manufacture of Zirconia crowns.[4] But all the manufacturers
state that there is a comparatively higher tooth reduction while us-
ing Zirconia crowns. This was proved by the study done by Clark
et al., which concluded thatCheng Crowns required more tooth
reduction than stainless steel crowns for primary teeth among the
different brands used in their study (EZ Pedo, Kinder Krowns,
NuSmile ZR).[5] Fibre glass crowns were recently introduced in
2018 by Figaro Crowns™, Inc., USA. It is composed of bre
glass and also contains titanium oxide and ferrous oxide which
Abstract
Purpose: To evaluate the amount of crown reduction required for stainless steel crown, zirconia crown and bre glass crown in
primary rst molar.
Methods: Thirty primary posteriortypodont teeth were divided into three groups and assigned to: Stainless steel crown (3M
ESPE SSC), Fibreglass crown (FigarocrownsTM) and Zirconia crown (NuSmile ZR). Teeth were prepared, and assigned crowns
were checked for t. Teeth were weighed prior to and after preparation. Weight changes served as a surrogate measure of tooth
reduction.
Results: Analysis of variance showed a signicant difference in tooth reduction among the three types. On applying Tukey’s hon-
est signicant difference test, it revealed a signicant high mean difference between SSC &NuSmile ZR followed by NuSmile ZR
& Figaro and Figaro& SSC. It implied the highest tooth reduction with NuSmile ZR and least with SSC.
Conclusions: Zirconia crowns required more tooth reduction than stainless steel crowns. Fibreglass crowns can provide an alter-
native due to lesser preparation and acceptable esthetics.
Subramanian EMG, Vignesh Ravindran, Ganesh Jeevanandan. Comparison of Amount of Tooth Reduction in Primary rst Molar for Stainless Steel, Zirconia and Fibre-glass Crowns – In-
Vitro Study. Int J Dentistry Oral Sci. 2021;8(7):3427-3430.
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OPEN ACCESS https://scidoc.org/IJDOS.php
synergistically add unsurpassed strength and enhanced cosmetic
value. Although the manufacturer suggests that these crowns re-
quire lesser tooth reduction as compared to Zirconia crowns [6],
this study was aimed to evaluate the amount of crown reduction
required for stainless steel crown, zirconia crown and bre glass
crown in primary rst molar.
Methods
Thirty primary mandibular left rst molar typodont teeth (Kil-
gore International, Inc., Coldwater, Mich., USA) were obtained
and divided into three groups: (1) 3M ESPE SSCs (3M ESPE
GA, St. Paul, Minn., USA); (2) Figaro crowns (Figaro Crowns,
Inc.; USA);and (3) NuSmile ZR (NSZ; Orthodontic Technolo-
gies, Houston, Texas, USA); Each group contained 10 samples.
The description about the crowns used in the study are given
in table 1. Each typodont tooth was weighed three consecu-
tive times to the ten thousandths of a gram using a calibrated
WensarTM precision electronic balance (Wensar Weighing Scales
Limited, Chennai, Tamilnadu, India). All measured weights were
recorded using an Excel spreadsheet (Microsoft, Inc., Redmond,
Wash., USA), and the arithmetic mean was calculated for each
sample tooth. The size of the crowns used for each group was
determined by measuring the mesio-distal width of the typodont
tooth to be prepared to receive the restoration. The images of the
crowns used in the current study is shown in gure 1. Manufac-
turer’s recommendations for both tooth preparation and bur use
were reviewed for each brand of crown. NuSmile ZR suggested
various burs such as tapered diamonds or diamond footballs but
did not require specic burs.6Figaro Crowns Inc. suggested use
of medium wheel or doughnut diamond bur for occlusal reduc-
tion and ame diamond for proximal reduction.[7] Teeth were
prepared as per manufacturer instructions by a single operator
to properly receive the crown. The typodont preparations for the
different crowns used are shown in gure 2. The operator and
a senior faculty member calibrated themselves with three trial
preparations in which they mutually agreed upon the amount of
reduction necessary to achieve the required t. These teeth were
not included in the study. During the course of the study, the
faculty member randomly selected three prepared teeth from each
group to verify the proper t. If the operator, based on faculty
evaluation, did not achieve a proper t, the sample in question
was reduced to a greater extent until both operator and faculty
member were in agreement. When this occurred, two additional
samples from that group were randomly selected for evaluation
for proper t, resulting in 50 percent of the samples within that
group being evaluated by the faculty member. Post-weights for
each tooth were then obtained in triplicate and recorded in the
same manner as pre-weights. Each tooth’s change in weight was
calculated and used in statistical analysis as a surrogate measure
of the degree of aggressiveness of tooth preparation required for
the proper t of each crown. The data were normally distributed,
as tested by Shapiro-Wilk tests, so differences were assessed with
one-way analysis of variance using the conventional alpha of 0.05
to identify any statistically signicant difference. The source of
signicance was assessed using Tukey’s HSD as the post hoc test.
Pre-treatment weights of the posterior teeth weighed an average
of 0.738 grams (±0.001 standard deviation [SD]), with all 30 spec-
imens ranging between 0.736 to 0.739 grams.
Results
Using One-way ANOVA, there was no signicant difference in
the pre mean weight of tooth substance in all three brands. How-
ever, there is a highly statistical signicant difference (p = 0.000)
in the post mean weight of tooth substance in all three crowns
used (Table 2). On pair wise comparison using Tukey’s HSD post
Hoc test, there is a signicant high mean difference between SSC
& NuSmile ZR followed by NuSmile ZR& Figaro and Figaro &
SSC. This implies that the mean tooth substance removed is high
for NuSmile ZR compared to SSC and Figaro (Table 3). The per-
centage reduction in weight is more for NuSmile ZR followed by
Figaro and SSC. SSC has less tooth removal compared to Figaro
and NuSmile ZR. (Table 4).
Table 1. Comparison of Features of the different crowns used in the current study.
Crowns Sizes Manufacturer rec-
ommended bur use
Manufacturer reduction re-
quirements Key features
3M ESPE
[SSC] 7-Feb Recommendations are
provided
Occlusal surface: 1.0-1.5 mm
Proximal: 1mm
Remove any cervical shoulders
Bevel line angles
Final seat: Active
Crimping increases retention
NuSmile
ZR
[Zirconia]
0-6 Recommendations are
provided
Incisal edge: 1.5-2.0 mm
occlusal: 1.0-1.5 mm
Circumferential axial reduction:
0.5-1.25 mm (or 20-30%)
SubgingivaL: feather margin
circumferentially 1-2 mm
Round all line and point angles
Final seat: passive
NuSmile ZR try in crowns
avoids contamination of the
crown actually cemented
NuSmile ZR adjustment
burs available
Light and extra
light shades
Figaro
[Fi-
bre-glass]
XS, Sm,
M, L, XL
Recommendations are
provided
Incisal/occlusal edge: 1.0-2.0 mm
Circumferential axial reduction:
1.0-1.5 mm
SubgingivaL: feather margin
circumferentially 1-1.5 mm
Round all line and point angles
Final seat: slightly active / passive
Pre-beveled margins – no
crimping [Flex Fit]
Polishing burs recommended
for high point reduction on
the crown
Subramanian EMG, Vignesh Ravindran, Ganesh Jeevanandan. Comparison of Amount of Tooth Reduction in Primary rst Molar for Stainless Steel, Zirconia and Fibre-glass Crowns – In-
Vitro Study. Int J Dentistry Oral Sci. 2021;8(7):3427-3430.
3429
OPEN ACCESS https://scidoc.org/IJDOS.php
Discussion
SSCs have been used for decades in pediatric dentistry but have
gone through various modications and makes it time consum-
ing for the operator and the patient. Zirconia crowns are estheti-
cally pleasing alternative to SSCs and are widely used due to par-
ent satisfaction. The exural strength of zirconia oxide materials
has been reported to be between 900 - 1100 MPa which is ve
times greater than standard glass ceramics.[8] Another important
property is their fracture toughness making them perdurable and
a highly strong restoration.[9, 10] Currently many brands of Zir-
conia crowns are available that allows practitioners to provide pa-
tients with superior, highly polished, esthetic results.[11, 12] The
recently introduced bre-glass crowns (FigaroTMInc.) are made
of multiple ber mesh sheets of berglass, aramid, carbon or
quartz bers embedded with an outer cosmetic composite resin.
The titanium oxide and ferric oxide helps to increase strength and
adds esthetics. The tooth preparation as suggested by the manu-
facturer is that it is minimal as similar for SSCs. There is enhanced
adaptation by the Flex t technology used which reduces crimp-
ing step and also allows the operator to make any occlusal reduc-
tion on the crown if necessary.
In the current study, a highly statistical signicant difference was
noted in the post mean weight of tooth substance among all three
crowns used. The typodont tooth weights before the preparation
had a standard deviation of 0.001 gms, i.e. the typical typodont
tooth differed less than a thousandths of a gram from others in
the sample. Therefore they were considered homogeneous in size
and weight, as received from the manufacturer. This uniform-
ity of the typodont teeth helped achieve statistically signicant
differences and completely attribute the results to the different
crowns used in the study.
A signicant high mean difference was noted when compared
between SSC and Zirconia crowns i.e. higher removal of tooth
structure in the latter. This shows that the former needs lesser
tooth reduction (7% reduction in weight) and therefore a less like-
ly exposure of pulp then the latter which had a close to 3 times
greater tooth reduction than SSC (20.7% reduction in weight).
Hence the chances of pulpal exposure with the use of zirconia
crowns is more likely. This was similar to the study done by Clark
et al., which concluded zirconia restorations required slightly less
than twice as much tooth structure removalwhen compared to the
SSCs (upto 185 percent).[5]
A signicant mean difference was also noted when compared be-
tween SSC and Fibre-glass crowns but was approximately half the
mean difference lesser when compared to Zirconia crowns. Al-
though a signicant mean difference was noted when compared
between bre-glass and zirconia crowns, the mean difference in
reduction of tooth substance was comparatively higher than the
mean difference between bre-glass and SSCs. This shows that
the bre-glass crowns had a tooth reduction as closer to the SSCs
which can provide an operator’s ease, faster crown preparation
and lesser chances for pulpal exposure.
Apart from the longevity of crowns, the operators’ ease in han-
dling the crown and esthetical concerns of the parent needs to
Table 2. Comparison of Mean of tooth substance removed (grams) for the three crowns.
Crowns NPre Mean ± SD F Value p Value Post Mean ± SD F Value p Value
SSC 10 0.7387 ± 0.0003
1.997 0.155
0.6838 ± 0.0004
4079.452 0.000*NuSmile ZR 10 0.7378 ± 0.0012 0.5849 ± 0.0039
Figaro 10 0.7386 ± 0.0012 0.6441 ± 0.0015
*Sig at 0.05 level, One-way ANOVA
Table 3. Pairwise Comparison of mean tooth substance removed in all three crowns.
Crowns Mean difference p Value 95% Condence Interval
SSC vs. NuSmile ZR 0.099 0.000* 0.0961 - 0.1015
NuSmile ZR vs. Figaro 0.059 0.000* 0.0564 - 0.0618
Figaro vs. SSC 0.040 0.000* 0.0369 - 0.0424
*Sig at 0.05 level, PostHoc test - Tukey’s HSD
Table 4. Typodont tooth weights before and after tooth preparation for the three different crowns tested.
Crowns Pretreatment tooth
weight (grams)
Post-treatment tooth
weight (grams)
Mean ± SD weight of tooth
substance removed
% reduction
in weight
SSC 0.739 0.684 0.0549 ± 0.0005 7.4
NuSmile ZR 0.738 0.585 0.1529 ± 0.0030 20.7
Figaro 0.739 0.644 0.0945 ± 0.0019 12.8
Each value represents the arithmetic mean of the averaged three repeated weights for each of the 10 specimens.
Subramanian EMG, Vignesh Ravindran, Ganesh Jeevanandan. Comparison of Amount of Tooth Reduction in Primary rst Molar for Stainless Steel, Zirconia and Fibre-glass Crowns – In-
Vitro Study. Int J Dentistry Oral Sci. 2021;8(7):3427-3430.
3430
OPEN ACCESS https://scidoc.org/IJDOS.php
be taken into account. Though zirconia crowns can full the es-
thetical point of view, it lacks the operators ease as it has a high-
er tooth reductions and requires a passive t. SSCs can provide
an operators’ ease but doesn’t meet the esthetical requirements.
While bre-glass crowns may provide an alternative by bridging
the gap between the two.
The major limitation of this study was that it is in-vitro in nature.
While zirconia crown preparations are signicantly more aggres-
sive than SSC preparations, determining the clinical repercussions
of aggressive tooth reduction, such as mechanical exposure of
the pulp, is beyond the scope of this study. A randomised clinical
trial would be necessary in the future to determine the longevity
and esthetical satisfaction among the parents using the new bre-
glass crowns to justify its clinical performance.
Conclusion
The following conclusions could be made within the limitations
of the current study:
1. Stainless steel crowns had the least tooth reduction among the
crowns used
2. Fibre-glass crowns (FigarocrownsTM Inc.) can provide an aes-
thetic alternative along with minimal reduction of tooth structure.
3. Zirconia crowns required signicantly more tooth reduction
than stainless steel crowns in the posterior primary dentition.
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