UNIVERSIDADE ESTADUAL PAULISTA
“JÚLIO DE MESQUITA FILHO”
Instituto de Ciência e Tecnologia
Campus de São José dos Campos
ORIGINAL ARTICLE DOI: https://doi.org/10.4322/bds.2024.e4368
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Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
Evaluation of flexural strength and degree of conversion of temporary
crown materials at different aging periods in artificial saliva
Avaliação da resistência à flexão e do grau de conversão de materiais para coroas provisórias em diferentes períodos de
envelhecimento em saliva artificial
Huda Abbas ABDULLAH1 , Zahraa Abdulaali AL-IBRAHEEMI2 , Manhal Abdul-Rahman MAJEED3 , Suhad AL-NASRAWI2
1 - Tikrit University, College of Dentistry, Department of Conservative Dentistry. Tikrit, Iraq.
2 - University of Kufa, Faculty of Dentistry, Department of Conservative Dentistry. Najaf, Iraq.
3 - University of Baghdad, Collage of Dentistry, Aesthetic and Restorative Dentistry Department. Baghdad, Iraq.
How to cite: Abdullah HA, Al-Ibraheemi ZA, Majeed MA, Al-Nasrawi S. Evaluation of exural strength and degree of conversion of
temporary crown materials at different aging periods in articial saliva. Braz Dent Sci. 2024;27(4):e4368. https://doi.org/10.4322/
bds.2024.e4368
ABSTRACT
Objective: Evaluate the effects of different storage periods on exural strength (FS) and degree of conversion (DC)
of Bis-Acryl composite and Urethane dimethacrylate provisional restorative materials. Material and Methods: A
total of 60 specimens were prepared from four temporary crown materials commercially available and assigned
to four tested groups (n = 15 for each group): Prevision Temp, B&E CROWN, Primma Art, and Charm Temp
groups. The specimens were stored in articial saliva, and the FS was tested after 24 h, 7 d, and 14 d. A standard
three-point bending test was conducted using a universal testing machine. Additionally, the DC was determined
using a Fourier transform infrared spectroscopy (FTIR) device. The data were analyzed statistically using two-
way ANOVA, Tukey`s HSD post-hoc test, and the Bonferroni test, all at a 5% signicance level. For each group,
a paired samples test was applied to compare the DC of the immediate and 24 h samples. Results: The highest
FS value was found for the Prevision Temp material, while the Charm Temp material showed the lowest FS, with
no statistically signicant difference between the mean values of the groups at 24 h; while there were signicant
differences at 7d and 14 d of storage. However, within each group, the aging had no signicant impact on the
FS, except for an increase in the FS of the B&E CROWN group after 14 d. Prevision Temp also had the highest
mean DC value. At each time interval, signicant differences were recorded. Moreover, within each group of
material, aging signicantly increased the DC, except for the Primma Art. Conclusion: Bis-acryl composite resin
materials exhibited higher exural strength compared to traditional methyl methacrylate resin during the 14
d investigation period. Aging in articial saliva did not signicantly affect the mechanical performance of the
tested materials. Materials with higher DC values showed greater exural strength; where the Prevision Temp
showed higher FS and DC values than the other tested materials.
KEYWORDS
Aging; Articial saliva; Degree of conversion; Flexural strength; Temporary crown material.
RESUMO
Objetivo: Avaliar os efeitos de diferentes períodos de armazenamento na resistência à exão (RF) e no grau
de conversão (GC) de materiais provisórios à base de compósito de Bis-Acril e de Dimetacrilato de uretano.
Material e Métodos: Um total de 60 corpos de prova foram preparados a partir de quatro materiais para coroas
provisórias comercialmente disponíveis, divididos em quatro grupos testados (n = 15 por grupo): Prevision
Temp, B&E CROWN, Primma Art e Charm Temp. Os corpos de prova foram armazenados em saliva articial, e
a RF foi avaliada após 24 horas, 7 dias e 14 dias. Um teste padrão de exão em três pontos foi realizado usando
uma máquina universal de ensaios. Adicionalmente, o GC foi determinado utilizando um espectrofotômetro de
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Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
INTRODUCTION
Permanent fillings represent one of the
most rapidly advancing elds in dentistry. The
use of permanent prosthetics is considered the
most beneficial and convenient solution for
patients [1]. However, prosthetic rehabilitation
with permanent restorations involves multiple
clinical and laboratory procedures at various
stages. During these intervals, which can range
from a few days to up to 20 days, patients need
to maintain normal family and social activities.
Therefore, modern prosthodontics relies on
temporary crowns and bridges to provide patients
with functional solutions while awaiting the nal
restorations [2-5].
Provisional restorations play a crucial role in
xed prosthodontics treatment, bridging the gap
between tooth preparation and the placement of
permanent prosthetics, such as veneers, inlays,
onlays, crowns, bridges, and implants [1,3].
The strength of a prosthesis refers to the
stress required to induce fracture or a certain
degree of plastic deformation. One way to assess
a prosthesis’s ability to endure functional loads
is by measuring the material’s exural strength
(FS), also referred to as transverse strength. This
indicates the material’s resistance to a static load
and combines aspects of compressive and tensile
strength tests, including proportional and elastic
properties limits [4,6].
The mechanical and physical properties
of dental acrylic and resin-based materials
(including dimethacrylate and composites) are
influenced by the degree of polymerization.
High levels of residual monomer can negatively
impact properties, leading to reduced hardness,
strength, wear resistance, and color stability.
Furthermore, the oral mucosa and adjacent
tissues, including the pulp, may get irritated by
the residual monomer [7].
However, it was necessary to examine the
mechanical properties of provisional materials
immediately after mixing and curing, respectively,
because they are tted and luted directly after
fabrication. Another key factor for ensuring long-
term durability is the conversion of most monomers
into polymers during the material’s polymerization
process, which results in an adequate degree
of conversion (DC). A low DC leads to poorer
mechanical properties and quicker degradation of
dental restorations. Consequently, the DC of the
double bonds within the resin matrix is considered
crucial for both the mechanical performance and
the longevity of the restoration [8,9].
The goal of the study was to evaluate
the strength of materials used for provisional
prosthetic fillings. The research sought to
compare the physical and mechanical properties
of four commercially available restorative
materials. The null-hypothesis tested was two-
fold: rst; that there is no signicant difference
in the FS between the tested materials at different
aging periods, and second that there would be
no difference in DC among the provisional crown
and bridge materials at different aging periods.
infravermelho com transformada de Fourier (FTIR). Os dados foram analisados estatisticamente utilizando ANOVA
de dois fatores, teste post hoc de Tukey HSD e o teste de Bonferroni, todos com nível de signicância de 5%. Para
cada grupo, foi aplicado um teste pareado para comparar o GC entre as amostras imediatas e as de 24 horas.
Resultados: O maior valor de RF foi encontrado para o material Prevision Temp, enquanto o material Charm
Temp apresentou a menor RF, sem diferença estatisticamente signicativa entre as médias dos grupos após 24
horas. Contudo, diferenças signicativas foram observadas nos períodos de 7 e 14 dias de armazenamento. No
entanto, dentro de cada grupo, o envelhecimento não teve impacto signicativo na RF, exceto por um aumento
na RF do grupo B&E CROWN após 14 dias. O Prevision Temp também apresentou o maior valor médio de GC.
Em cada intervalo de tempo, foram registradas diferenças signicativas. Além disso, dentro de cada grupo de
materiais, o envelhecimento aumentou signicativamente o GC, exceto para o Primma Art. Conclusão: Os
materiais de resina composta à base de Bis-Acril exibiram maior resistência à exão em comparação com as
resinas tradicionais de metacrilato de metila durante o período de investigação de 14 dias. O envelhecimento
em saliva articial não afetou signicativamente o desempenho mecânico dos materiais testados. Materiais com
maiores valores de GC apresentaram maior resistência à exão, sendo o Prevision Temp o material com maiores
valores de RF e GC em comparação aos demais testados.
PALAVRAS-CHAVE
Envelhecimento; Saliva articial; Grau de conversão; Resistência à exão; Material para coroas provisórias.
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Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
MATERIAL & METHODS
Four commercially available chemically
polymerized provisional crowns and xed dental
prosthesis resins were utilized in the present
study. Details of the materials used are provided
in Table I. Based on a pilot study, the sample
size was calculated at an 80% power and 95%
confidence level with 10 MPa as a minimum
expected difference between the means of the
comparison groups and 9.5 standard deviation.
The results indicated that each group should
be composed of 14.17 specimens. Thus, 15
specimens were considered for each group and
a total of 60 samples were chosen..
Sample preparation
Sixty bar-shaped specimens (25×2×2 mm),
with 15 specimens for each provisional material,
were prepared using a specially designed custom-
made split Teon mold (Figure 1a), according to
ISO 4049 [10].
A layer of petroleum jelly was applied to
the Teon mold to facilitate the easy removal
of the specimen after complete polymerization.
Prior to sample preparation, a small quantity of
the material was placed on a mixing pad without
the auto-mixing tip to ensure both orifices
were open. Each provisional material was then
dispensed using the manufacturer’s mixing tip
and syringed directly into the mold, slightly
overlling it while it was positioned on a glass
plate. To standardize the procedure, the time
from the start of mixing to the end of dispensing
into the mold was kept consistent at 1 min for
all materials. After placing the material, a second
glass plate was set on top of each unset material.
The material was left to set in the mold for 15
min to ensure complete polymerization. Once
fully set, the mold was carefully opened, and the
specimens were carefully examined to eliminate
samples containing visible defects such as cracks
or bubbles. The excess was removed by gently
abrading with 600-grit silicon carbide paper [11].
The specimens were checked by a vernier caliper
for accurate dimensions (Figure 1b).
The specimens were allowed to dry at room
temperature for 30 min. Subsequently, specimens
of each material were randomly divided into four
groups of 15 specimens each and assigned to
three different storage periods.
Preparation of the articial saliva and aging
process
To prepare a neutral solution (pH 7.0) of
articial saliva, the following composition was
used: 100 mL Na2HPO4 (2.4 mM), 100 mL of
KH2PO4 (2.5 mM), 100 mL of NaCl (1.0 mM),
100 mL of KHCO3 (1.50 mM), 100 mL of CaCl2
(1.5 mM), 100 mL of MgCl2 (0.15 mM), and 6 mL
of citric acid (0.002 mM) [12].
Table I - Resin materials used in the present study for prosthetic filling
Materials Manufacturers Composition Shade Polymerization
Prevision Temp Kulzer GmbH Germany Multifunctional methacrylic ester. Bis-Acryl composite A2 Self-cure
B&E CROWN B&E South Korea Bis-Acryl composite A2 Self-cure
Primma art FGM – Brazil Bis-Acryl composite A2 Self-cure
Charm temp Dent kist -Korea Barium Glass, Urethane dimethacrylate (UDMA) A2 Self-cure
Figure 1 - (a) The mold used in fabricating specimens and (b) Prepared specimens of provisional restorative materials.
(a) (b)
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Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
Specimens from each material were stored
for 24 h, 7 d, and 14 d at 37˚C in articial saliva
in labeled plastic jars. During the storage periods,
the solutions were not changed. Figure 2 shows
specimens from each material stored in articial
saliva in labeled plastic jars.
Flexural strength test
After each storage period, the specimens
were taken out of the saliva bath. Residual
articial saliva was wiped off the surface with
tissue paper, and the specimens were allowed to
air-dry for 5 min.
The specimens were tested for FS using a
universal testing machine with a three-point
bending test (see Figure 3). The specimens were
placed on supports spaced 20 mm apart, and
the crosshead speed of the machine was set to
1 mm/min [13]. Each specimen was subjected to
incremental loading until it exed and fractured.
The load required to break the specimen was
recorded in kN and then converted to N. The F
was calculated using the following Equation 1.
2
3 / 2 FS FL bd=
(1)
Here, F represents the force or load needed to
break the samples; L is the distance between the
supports which is 20 mm; b is the width of the
specimen which is 2 mm and d is the thickness of
the specimen, also 2 mm. The resulting value for FS
is expressed in MPa where 1 MPa equals 1 N/m2.
Fourier Transform Infra -Red Spectroscopy
(FTIR)
The DC was measured using a Spectrum™
100 FTIR device (Bruker, Germany) equipped
with a universal diamond ATR unit (spectral
range: 4000–500 cm−1; spectral resolution:
<0.5 cm−1). For the analysis, 10 specimens from
each temporary material were prepared using the
same sample preparation technique previously
outlined. For each material, ve specimens were
tested immediately after mixing and five after
24 h. To determine the DC, the FTIR spectra of the
mixed materials were collected immediately after
mixing (4 scans per specimen) and also after 24 h.
In the present study, the DC (%) was
calculated by comparing the proportion of
residual carbon double bonds in the sample at 24
h to the amount present immediately after mixing
using the internal standard method. The quantity
of remaining carbon double bonds was assessed
from the absorbance spectrum, specifically
between the aliphatic double bond peak at
1637 cm-1 and the aromatic double bond peak at
1608 cm-1, before and after polymerization using
the baseline method. The absorbance peak at
1637 cm-1 is attributed to aromatic double bonds.
Figure 3 - Specimens in the universal testing machine (a) unloaded and (b) loaded conditions.
Figure 2 - Specimens stored in artificial saliva.
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Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
The degree of conversion for each material
was determined using the following Formula 2
(1637 /1608) peaks height after polymerization
DC% 1 100%
(1637 /1608) peaks heights before polymerization
=−×
(2)
Statistical analysis
Flexural strength data were assessed using
a two-way ANOVA test (
P
<0.05) to detect
signicant differences between materials and
aging conditions. This was followed by a Tukey´s
HSD multiple comparison test (p<0.05) to
pinpoint the specific factors affecting the FS
values. Statistical analysis for the DC data of the
groups of tested materials was performed using
one way analysis of variance (ANOVA) and the
Bonferroni test at a significance level of 5%.
Paired samples test was applied to compare the
DC of the immediate and 24 h periods in each
group of the tested materials.
RESULTS
Flexural strength
The mean, standard deviation, and
P
values
of the FS among groups and different storage
times are presented in Table II. The highest FS
value was found for the Prevision Temp material,
while the Charm Temp material showed the
lowest FS value.
Two-way ANOVA of the FS results showed
no statistically signicant difference between the
mean values (
p
> 0.05) of the groups at 24 h,
while there were signicant differences at 7 and
14 d of storage times within each group. Aging
had no signicant impact on the FS, except for an
increase in FS in the B&E CROWN group after 14 d.
Degree of conversion (DC) analysis
FTIR analysis Immediately
The DC was determined by analyzing the
FTIR results from each sample and calculating
the percentage for each sample group. Signicant
differences in DC values for the temporary
materials were found in the present study (p
< 0.05). The mean values and their standard
deviations (SD) along with the
P
values are
presented in Table III and illustrated in Figure 4.
Prevision Temp had the highest mean DC
value, with significant differences among the
tested material groups at each time interval.
(p < 0.05). In relation to aging within each
material, increases in DC values were recorded,
which were signicant, except for the Primma
Table II - Descriptive statistics, two-way ANOVA test, and Tukey´s HSD test for comparison of significance of FS among the different groups
at different storage times
Groups 24 h 7 d 14 d F
p
value
Mean (±SD) Mean (±SD) Mean (±SD)
Prevision Temp. 94.20 (8.93)Aa 102.80 (3.12)Aa 98.80 (5.45)Aa 1.011 .393
B&E CROWNs 85.00 (6.32)Aa 85.40 (6.63)Ba 98.00 (7.48)Bb 4.690 .031
Primma Art 91.20 (4.47)A94.40 (4.83)AB 91.00 (5.05)AB .958 .411
Charm Temp. 78.80 (9.49)A79.40 (7.14)B79.80 (7.30)B.015 .985
F 2.852 14.164 9.828
p
value .070 .000* .001*
Uppercase letters demonstrate column differences, while lowercase letters demonstrate raw differences (
p
> 0.05).
Table III - Descriptive statistics, one-way ANOVA test, Bonferroni test, and paired t test for comparison of significance of DC values among
the different groups at different storage times.
Groups Immediate 24 h Paired t test
p
value
Mean (SD) Mean (SD)
Prevision Temp. 46.610 (4.430)Aa 52.108 (2.661)Ab 3.863 0.018
B&E CROWNs 33.976 (1.581)Ba 40.570 (2.795)Bb 3.647 0.022
Primma Art 42.250 (2.828)Aa 46.342 (2.682)Ca 1.878 0.134
Charm Temp. 34.120 (2.709)Ba 40.062(2.848)BDb 4.870 0.008
F 20.875 21.218
p
value 0.000 0.000
Uppercase letters demonstrate column differences, while lowercase letters demonstrate raw differences (
p
> 0.05).
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Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
Art. At the immediate time of testing, signicant
differences between each pair of materials were
observed, except between the Prevision Temp
and Primma Art groups, and the B&E CROWN
and Charm Temp groups.
FTIR analysis after 24 hours
The DC (DC%) mean values obtained from
different temporary materials after 24h showed
that the Prevision Temp group had the highest
mean DC value, and significant differences
between each pair of materials were observed,
except between the B&E CROWN and Charm
Temp groups.
The majorityof the groups demonstrated no
statistically signicant differences between the
immediate and 24 h (
P
< 0.005) time periods,
and the DC values after 24 h showed higher
mean values than the immediate measurement.
However, Prima Art showed no significant
difference between the two time intervals.
DISCUSSION
Provisional fixed dental prosthesis are
fundamental elements of fixed prosthodontic
treatment success. However, it must meet
biological, esthetic, and mechanical criteria.
These criteria involve the ability to withstand
functional loads, resist removal forces, maintain
proper alignment of the abutments, protect the
pulpal tissues, prevent bacterial contamination
and preserve the periodontal tissues [14,15].
Flexural strength refers to a material’s ability
to resist bending without fracturing, which is
essential for dental restorations to endure the
forces encountered during chewing [16]. It is a
key property for provisional restorative materials
used in long-term provisionalization since it plays
a crucial role in the success of xed prosthodontic
treatments. Additionally, the DC of the material
can reflect both its mechanical properties
and the durability of the restoration [8]. It
can be anticipated that interactions between
saliva, food particles, and beverages in the oral
environment might damage and degrade dental
restorations [15]. Therefore, the present study
was carried out to investigate the effects of
different storage periods on the FS and DC of four
bis-acryl resin provisional restorative materials.
According to the result of the present study, there
are signicant differences in the FS and DC values
among the tested materials with signicant effect
for the aging periods since the FS enhanced with
time. Therefore, the null-hypothesis was rejected.
Within each group of materials, aging had a
non signicant effect on the FS, however, the FS
increased in the B&E CROWN group after 14 d.
Firstly, this may be attributed to the continuous
exposure to moisture which could induce further
cross-linking, improving the internal structure.
Secondly, the storage in articial saliva allows
stress relaxation, reducing internal tensions,
leading to higher FS over time [17]. Bis-acryl
composites with specic groups demonstrated
better FS compared to those containing urethane
dimethacrylate (Charm Temp). However, the
incorporation of multifunctional methacrylic
ester into the bis-acryl composite improved its
FS, similar to the performance observed with
the Prevision Temp group. All provisional resin
materials evaluated in the present study exhibited
FS exceeding the ISO 4049 limit of 50 MPa,
Figure 4 - Mean and standard deviation for DC (%) of the tested temporary prosthetic filling materials.
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Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
measured 24 h after mixing [18]. The FS of all
bis-acryl resins notably improved after 24 h of
storage and continued to maintain these elevated
levels after 7 days of storage. It is important to
highlight that, in comparison with other studies,
there is limited information in the literature
regarding the tested materials. Direct comparison
among various studies cannot be done since this
property is material specic and was continuously
developed to improve the material properties.
Based on their chemical composition, pro-
visional materials can be categorized into two
primary groups. The rst group consists of acrylic
resin-based materials, which includes polymeth-
ylmethacrylate (PMMA) and polyethylene or
butyl methacrylate (PEMA). The second group
encompasses composite resins such as urethane
dimethacrylate (UDMA) and bisphenol A-glycidyl
dimethacrylate (Bis-GMA) [19,20]. In relation
to the effect of storage time, the current results
agree with the studies by Balkenhol et al. [21]
They observed that all bis-acryl resin materials
which are auto-polymerized exhibited low FS
10 min after mixing. However, this strength
increased after 1 to 72 h of storage in water at
37°C and also after thermo-cycling. This early low
strength could be attributed to insufcient cross-
linking between oligomers during the initial set-
ting phase. As cross-linking progresses over time,
the materials exhibit greater fracture resistance.
Additionally, stress buildup within the polymer
network during polymerization may make the
materials more prone to fracture during the initial
setting phase [22].
The mean FS of the Prevision Temp
group specimens, which contains polymethyl
methacrylate (PMMA), is substantially higher
than the average exural strength of the Charm
Temp specimens, which contains urethane
dimethacrylate (UDMA) after 7 and 14 d. The
reason for the difference in FS can be partially
attributed to differences in chemical composition.
The polymerization process is vital in determining
the FS of various materials since it involves
the chemical reaction where monomers, the
basic units of polymers, link to form a more
complex structure. Partial polymerization
can lead to structural weaknesses, decreased
bond strength between polymer chains, and
decreased mechanical characteristics. When used
in various provisional materials, the monomers
exhibit differences in characteristics such as the
exothermic heat generated during polymerization
and resistance to shrinkage. However, during
polymerization, resin shrinkage tends to occur
towards the center of the mass, which can cause
variations in FS. The lightly polymerized urethane
dimethacrylate (UDMA) resin showed the lowest
FS, highlighting a considerable strength disparity
between materials. For the UDMA specimens,
excess material was removed during the initial
polymerization phase and then placed back into
the mold for complete curing. This process might
have caused specimen distortion and alterations
in FS [23,24].
The current result is in agreement with
Poonacha et al. [23] since they compared the FS
for three provisional materials, and they found
that the FS of methacrylate resin decreased
significantly, whereas bis-acrylic composite
resins exhibited a notable increase in FS after
being stored in articial saliva for 24 h. Further
support was gained from Mehrpour
et al
. [25],
when they compared the FS of five interim
restorative materials. They stated that Bis-acryl
resins were statistically superior to traditional
methacrylate and light-cured resins. Therefore,
they recommended that application of bis-acryl
resins should be deliberated in patients with
heavy occlusion and in cases that need long-term
use of interim restorations.
The current results of the DC support and
justied the FS results since greater FS values
combined with greater DC values . Several
techniques have been described for assessing the
DC in resins; one of them being Fourier transform
infrared spectroscopy. The use of FTIR in the
present study offers several benets, including
specicity, sensitivity, high reliability and cost-
effectiveness [21,26,27].
In the present study, the tested materials
showed decreased DC values ranging between
33.9% to 46.6% when measured immediately,
and 40% to 52% after 24 h.
This was in agreement with previous studies
since they stated that the DC of acrylic resin
based temporary crowns and FPD materials
were lower than those of restorative composite
resins [21,26,27]. This is because provisional
crown materials have a greater proportion
of di-methacrylate monomers compared to
restorative composite resins. As the amount of
di-methacrylates in these composites increases,
the DC generally decreases [27].
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Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
FTIR analysis conrmed that the DC after
24 h showed higher mean values than the
immediate measurement with no significant
differences. This result is in agreement with
Altarazi et al. [28] who found that no signicant
difference (P > 0.05) in DC was observed when
the post-curing time was extended from 20 to
50 minutes. Balkenhol
et al.
found a positive
relationship between the duration of storage
and mechanical properties [21]. Koumjian and
Nimmo observed similar ndings and additionally
found that dry storage yielded higher transverse
strength values for all materials compared to wet
storage. Moreover, several earlier studies have
demonstrated signicant improvements in the
mechanical properties of specic bis-acryl and
PMMA interim resin materials when comparing
storage times of 1 h to 24 h [14,29].
Prevision Temp and Primma Art both have
a relatively higher DC than the B&E CROWN
and Charm Temp. This result may be attributed
to the correlation between the DC and rate of
polymerization. Consequently, a quicker setting
time typically results in a lower DC. After
polymerization, any remaining unpolymerized
monomer can impact the mechanical and physical
properties, as well as biocompatibility, potentially
decreasing dimensional stability and strength.
Therefore, the higher DC mean of the Prevision
Temp and Primma Art can improve the FS [27].
The study found that variations in the
mechanical properties of provisional materials
are linked to the type of monomer system
employed [4], and the chemical composition
of the materials [30]. A contemporary category
of materials used for provisional crowns and
FPD are di-methacrylate based composites,
developed to address the issues associated with
mono-methacrylates. During polymerization,
these di-methacrylate monomers form cross-links
which restrict the movement of the monomers
due to the early solidification of the polymer
network. Additionally, methacrylate groups on
polymer chains that have not reacted cannot
move through the matrix because they are already
bonded to the polymer [27,31].
One of the limitations of the current study is
that it was an
in vitro
study, which differs from
what occurs in the clinical conditions inside the
oral cavity where additional considerations for
temperature, moisture, and pH are required.
Moreover, the present study only evaluated
the FS and DC, which justied the mechanical
behavior. Therefore, additional studies could be
conducted on other properties such as fatigue
strength, tensile strength, repairability, color
stability along with solubility, biocompatibility
and permeability. All that could be conducted in
the future as
in vitro and in vivo
studies.
From a clinical perspective, all tested
interim crown materials demonstrated FS values
exceeding the ISO 10477 minimum standard
of 50 MPa, making them suitable for interim
restorations [32]. The FS of the materials
remained unaffected after aging, which is a
positive feature for interim crowns to withstand
stress and occlusal load [33]. Bis-acryl composite
resin provisional materials are preferred over
methacrylate resins due to their superior
mechanical properties. For cases requiring high
mechanical strength after fabrication, bis-acryl
composite resins, particularly the Prevision Temp,
are recommended as the best option.
A lower DC is associated with a lower
polymerization rate and a greater amount of
unpolymerized monomer which can negatively
impact the material’s mechanical properties as
well as its biocompatibility. This can lead to
reduced dimensional stability, strength, wear
resistance, and softening of the resin [34].
Furthermore, unpolymerized monomers can leach
into the oral environment, potentially causing
cytotoxic effects on the pulp and oral mucosa,
inhibiting protein synthesis in oral epithelial
cells [35]. Therefore, a higher DC improves the
biocompatibility of the polymer-based provisional
crowns and xed partial dentures.
CONCLUSION
Within the study’s limitations, it can be
concluded that all bis-acryl composite resin
materials exhibited higher FS compared to
traditional methyl methacrylate resin over the 14
d investigation period, with the Prevision Temp
outperforming the B&E CROWN and Primma
Art. Aging in articial saliva did not signicantly
affect the mechanical performance of the tested
materials. Additionally, materials with higher DC
values showed greater FS. Clinically, bis-acryl
composite resin materials are recommended
when high mechanical strength is crucial.
9
Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
Acknowledgements
We are extremely grateful to Dr. Julkar
from Haider for his valuable contributions in
preparation of the present work.
Author’s Contributions
HAA: Conceived, designed the analysis,
and writing draft. ZAAI: Collected the data.
MAM: Performed the data analysis. SAN: Formal
analysis, Validation, Supervision, Reviewing and
Editing.
Conict of Interest
We declare no conicts of interest related
to the present article. The views expressed are
entirely those of the authors and have not been
affected by any nancial or personal relationships.
Funding
The authors declare that no nancial support
was received.
Regulatory Statement
The present article did not include the
use of hazardous materials, living organisms,
or any procedures that could potentially harm
the environment. There was no requirement
to adhere to specific regulations related to
occupational health and safety or environmental
protection. All appropriate steps were taken to
ensure adherence to ethical research standards
and laboratory safety protocols.
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Braz Dent Sci 2024 Oct/Dec;27 (4): e4368
Evaluation of flexural strength and degree of conversion
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artificial saliva
Abdullah HA et al.
Evaluation of flexural strength and degree of conversion of temporary crown materials at different aging periods in artificial saliva
Abdullah HA et al. Evaluation of flexural strength and degree of conversion
of temporary crown materials at different aging periods in
artificial saliva
Date submitted: 2024 May 08
Accept submission: 2024 Nov 12
Suhad Al-Nasrawi
(Corresponding address)
University of Kufa, Faculty of Dentistry, Department of Conservative Dentistry,
Najaf, Iraq
Email: suhad.alnasrawi@uokufa.edu.iq
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