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.e4005
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Braz Dent Sci 2024 Jan/Mar;27 (1): e4005
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.
Assessment the retentive force and XRD analysis on the recycling
esthetic thermoplastic acetal clasps
Avaliação da força de retenção e análise de DRX dos grampos de resina estética termoplástica acetal reciclada
Rasha Mohammed ZWWYER1 , Nidhal Sahib MANSOOR1
1 - Middle Technical University, College of Health and Medical Techniques, Prosthodontic Dental Techniques Department. Baghdad, Iraq.
How to cite: Zwwyer RM, Mansoor NS. Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal
clasps. Braz Dent Sci. 2024;27(1):e4005. https://doi.org/10.4322/bds.2024.e4005
ABSTRACT
Objective: To reduce environmental biohazards, technicians should be educated with safe biological waste disposal
procedures and dental material recycling. The present study assesses the retentive force, deformation test and XRD
analysis of re-injection acetal resin clasps. Material and Methods: specimens were prepared for clasp retention test
injection according to the manufacture’s instruction for acetal resin. The rst group represent control group with (100%
New) and other ve groups as experimental groups (group II (25% old +75% new), group III (50% old + 50%) new,
and group IV (75% old + 25% new) with different percentages between new acetal materials and old acetal materials,
while two last groups with several times (group V (100% old) and group VI (re-injection two times)) only used old
acetal materials. The X-ray diffraction (XRD) device used to give structural information for the materials to be tested.
The study data were analyzed via One-way ANOVA (LSD) at a signicant P-value of (p≤0.05) and a condence level of
95%. Results: After comparing the results, a signicant improvement in the retentive force of acetal clasp specimens after
re-injection two times there was found high mean value in group re-injection two times and lower mean value recorded
in control group. In XRD patterns of there was no diffraction peak refers to crystal structure of acetal resin. Conclusion:
the present study ndings concluded that the recycling of acetal resin enhanced the retentive force of acetal clasp and
not affected on the crystal structures of material.
KEYWORDS
Acetal clasp; Esthetic clasp; Recycling; Retentive force; XRD.
RESUMO
Objetivo: Para reduzir os riscos biológicos ambientais, os técnicos devem ser educados com procedimentos seguros
de eliminação de resíduos biológicos e reciclagem de material dentário. O presente estudo avalia a força de retenção,
teste de deformação e análise de DRX de grampos de resina acetal reinjetada. Material e Métodos: as amostras foram
preparadas para o teste de retenção dos grampos e a injeção realizada de acordo com as instruções do fabricante
para resina de acetal. O primeiro grupo representa o grupo controle com (100% novo) e os outros cinco grupos como
grupos experimentais (grupo II (25% antigo + 75% novo), grupo III (50% antigo + 50% novo) e grupo IV (75%
antigo + 25% novo) com porcentagens diferentes entre materiais de acetal novos e antigos, enquanto os dois últimos
grupos (grupo V (100% antigo) e grupo VI (reinjeção duas vezes)) utilizaram apenas materiais de acetal antigos. O
dispositivo de difração de raios X (DRX) foi utilizado para fornecer informações estruturais dos materiais a testados.
Os dados do estudo foram analisados por ANOVA um fator (LSD) com um valor P signicativo de (p≤0,05) e um nível
de conança de 95%. Resultados: Após a comparação dos resultados, foi encontrada uma melhora signicativa na
força de retenção das amostras de grampo de acetal após duas reinjeções, além disso, foi registrado um maior valor
médio no grupo reinjeção duas vezes e menor valor médio no grupo controle. Nos padrões de DRX não houve pico de
difração referente à estrutura cristalina da resina acetal. Conclusão: os resultados do presente estudo concluíram que a
reciclagem da resina de acetal aumentou a força retentiva do grampo e não afetou as estruturas cristalinas do material.
PALAVRAS-CHAVE
Grampo de acetal; Grampo estético; Reciclagem; Força de retenção; DRX.
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Braz Dent Sci 2024 Jan/Mar;27 (1): e4005
Zwwyer RM et al.
Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal clasps
Zwwyer RM et al. Assessment the retentive force and XRD analysis on the
recycling esthetic thermoplastic acetal clasps
INTRODUCTION
The difficulty in the current world is in
reducing, reusing, and recycling various resources.
Reusing is a phrase used to refer to reusing the
materials that can be reused and minimizing
material waste, whilst reducing is used to refer
to reducing the amount of the earth’s resources
and utilization should only be when necessary.
Since recycling is the second source of oxygen
for modern life, attempt to recycle all resource
you can to maintain a cleaner, greener world [1].
In order to fulll both patient aesthetic needs
and the requirement for denture retention, a
material known as exible thermoplastic resin
was introduced into dentistry [2]. When it comes
to replacing missing teeth with the nest possible
aesthetics, removable partial dentures (RPDs)
are seen to be the best and most practical option.
The display of the clasp assemblies was one of
the main issues with RPDs. One of the numerous
more modern methods used to address this issue
involves etching the retainer’s arm and covering it
with a tooth-colored resin nish. The mechanical
qualities of these aesthetic retainers also play
a signicant part in their success and intraoral
use, despite the fact that their outward look is of
fundamental importance [3].
Early in the 1990s, acetal resin, along
with tooth-colored clasps, was employed to
create a complete partial denture framework
in dentistry. Formaldehyde is polymerized
to create acetal resins. A chain of alternating
methyl groups connected by an oxygen molecule
makes up the homopolymer poly(oxyethylene)
(POM) [4]. The lack of aesthetic appeal of
cobalt chromium (CoCr) clasps drives the hunt
for thermoplastic resin clasps to solve this issue.
In light of this, Polyoxymethylene (POM) has
been employed in the creation of RPD retaining
and supporting components [5]. The exibility
of the thermoplastic acetal clasp would enable
the retainer to be positioned in deeper occlusal
rests on the abutment teeth [6]. The surface of
the tooth is not scratched by acetal resin clasps,
which maintain retention. Acetal resin clasps
are attractive and are offered in 16 distinct
hues. Using a stereomicroscope for a qualitative
investigation, it was discovered that the use
of cast Co-Cr and acetal resin clasps caused
enamel to develop linear scratches and grooves.
The enamel only received minor scratches
when an acetal resin clasp was used. Optical
prolometry produced statistically signicant
ndings with the Co-Cr clasp. Acetal resin clasps
had negligible impact. The retentive force of the
cast Co-Cr clasp dropped from 12.4 N to 8.1 N.
The acetal resin clasp’s retentive force decreased
from 5.2 N to 4.03 N at the conclusion of the
trial [7]. The molecular and atomic structure of
a crystal can be determined using a technique
called X-ray diffraction analysis (XRD), in which
the crystalline atoms cause an X-ray beam
to diffract in a number of distinct directions.
The density of the electrons inside the crystal can
be visualized in three dimensions by estimating
the intensities and angles of these diffracted
beams. The average atom locations in the crystal
can be calculated from this electron density [8].
The goal of this study was to assess the
retentive force and XRD of re-injection acetal
resin as esthetic clasp in different percentages
or several times.
The null hypothesis stated that the tested
characteristics will not be changed by recycling
acetal resin as an aesthetic clasp in different
percentages or several times.
MATERIAL AND METHODS
Sixty clasp specimens for retentive force test
were divided to six groups as Group I: Control
group (Group I) with 100% New acetal material,
Group II:25% New acetal material + 75% Old
acetal material, Group III: 50% New acetal
material + 50% Old acetal material, Group IV:
75% New acetal material + 25% Old acetal
material, Group V: 100% Old acetal material and
Group VI: re-injection for two-time acetal material.
Preparation the percentages for clasp reten-
tion test groups
Each flask contains three specimens to
ensure the exact percentages for each group and
each ask, the weight of the empty capsule is 3 g,
according to the pilot study. In this study, it was
found that every 12 g of acetal is sufcient to
inject a ask containing three samples of acetal.
The old material is preparation by acetal sprue
is collected and cutting by cutter and re-injection
with new acetal resin.
Preparation the study tooth model
A study tooth model was constructed
to represent an ideal RPD situation with a
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Braz Dent Sci 2024 Jan/Mar;27 (1): e4005
Zwwyer RM et al.
Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal clasps
Zwwyer RM et al. Assessment the retentive force and XRD analysis on the
recycling esthetic thermoplastic acetal clasps
standardized undercut. The occlusal rest
measurements of a case study model of a zirconia
rst upper molar in size 34 were the same as those
utilized for the Co-Cr clasp. This was a spoon-
shaped design with a 1 mm thickness, 3 mm
width, and a right angle to the minor connector
on the proximal surface, as shown in Figure 1.
Block acrylic resin and clasp design prepara-
tion
In rectangular acrylic blocks, tooth was
inserted vertically up to the level of the cement-
enamel connection. They were created using a
wax pattern and the test machine’s specications
(30 mm 14 mm 25 mm). Molding processes for the
heat-cured PMMA (vertex, Germany) were the same
as those used in traditional dentistry laboratories
for the compression method of water-bath curing.
A 3-D scanner (Swing 3-D dental scanner) (Medit
extraoral scanner, Corea) as shown in Figure 2.
Software designer program was used to scan the
research model. The system depth scale was used to
digitally measure the undercut amount as shown in
Figure 3. The study tooth model was exported into
stereolithography (Stl) le form after surveying so
that it could be retrieved and used to construct the
acetal clasps [9] .Undercut of 0.25 mm depth was
determine with software designer program [10].
According to the most typical traditional design
pattern, the clasp was created. Software was used
to organize the clasps’ design into the disc space.
The machine then used wax blank discs to grind
these digital patterns into 3D wax clasps. Number of
software processing program were used to complete
this step [11].
Clasp injection
Hard dental die stone molding compound
(Type IV, Zhermack, Italian) was prepared
following the manufacturer’s instructions (W/P:
20 ml / 100 g) and used to mold the wax designs.
The wax clasp was individually invested utilizing a
cylindrical mass of investment material to prevent
any undercuts that would inuence the nal clasp
design during the asking technique. The wax was
removed with a wax extraction equipment after
asking and embedding the wax patterns. After
that, a hot water and detergent solution was used
to clean the mold cavity. A layer of acceptable
separating material (Vertex, Germany) for thermo-
pressing purposes was then put to the surface
of the mold after it had dried for 30 seconds.
The mold was then left to dry about 12 hours [11].
The acetal resin (Evidsun, Russian) sample
was made according to the manufacturer’s
instructions. Acetal resin that had been heated
and softened was injected into the mold, and it
was cured at 220°C for 20 minutes at an injection
pressure of 7-8 bar. The samples were deasked,
polished with thermal resin nishing burs after
drying, and then polished to a high shine with
a swans down mop as shown in Figure 4 [12] .
Figure 1 - Preparing the study tooth model design using exocad
software.
Figure 2 - Scan the studied model by dental scanner after complete
the process.
Figure 3 - Digital surveying and measuring the undercut area by
using software program.
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Zwwyer RM et al.
Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal clasps
Zwwyer RM et al. Assessment the retentive force and XRD analysis on the
recycling esthetic thermoplastic acetal clasps
Clasps retentive force testing
Specimens were xed to a universal testing
device (BOTO, China). Utilizing the cylindrical
pin connected (Figure 5), three withdrawal forces
were applied to each clasp. The retentive force of
this clasp was calculated as the average of the three
measurements. Retentive forces were measured
in Newton (N) and the specimens were examined
at room temperature with a crosshead speed of
0.5 mm/minute. Using a particular attachment
in the device, the clasps were xed to the upper
portion of the testing machine, and the acrylic
block was xed to the lower portion. Both of these
approaches provided a straight path while cycling
and may have reduced or eliminated any torquing
possibilities, which may have favorably inuenced
the results of the experiment. Torquing too much
could harm the results of clasps [9].
For clasp deformation, Before and after
applying force, the software micrometer was used
to measure the distance between the tips of the
clasps’ reciprocal and retentive arms using digital
reference points as illustrated in Figure 6 [9].
X-ray diffraction analysis
The X-ray diffraction (XRD) device (PANalytical,
AERIS) used to give structural information for the
materials to be tested. It was done on six specimens.
One specimen from each six groups.
RESULTS
Retentive force test
The mean of retentive force value and
standard deviation for each group are listed
in Table I. The smallest retention force values
(17.3329±1.632948 N) were found in control group
while, the largest values (20.9997±2.419075 N)
were in the re-injection two times group. Statistically
there is signicant difference between the groups
are reveal by applying the (ANOVA) test.
The LSD test between groups of retentive force
test showed signicant difference between control
group and all experimental groups except the group
IV that show non-signicant (p> 0.05), and highly
signicant difference between control group and
group re-injection two time (p<0.001) (Table II).
Clasp deformation test
A single group’s means for two variables
are compared using the Paired-Samples T Test
technique. After applying the force, Table III
demonstrated a statistically signicant (p value
0.05) increase in the separation (mm) between
the retentive and reciprocal arms.
X-Ray Diffraction (XRD) analysis
XRD showed the peaks of the specimens
of all groups. In XRD patterns of there was no
Figure 4 - Acetal clasp specimen after polishing and finishing on
the study tooth mold.
Figure 5 -Testing procedure of acetal clasp specimen after mounted
on a universal testing machine.
Figure 6 - Aker clasp deformation determined by utilizing a
software micrometer to measure the distance between the points
of the reciprocating and retentive arms.
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Zwwyer RM et al.
Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal clasps
Zwwyer RM et al. Assessment the retentive force and XRD analysis on the
recycling esthetic thermoplastic acetal clasps
Table I - Mean values, standard deviation, standard error, and 95% confidence interval of mean parameters concerning mean values of the
retentive force (N) test for the studied group’s readings and the two extreme values (min. and max.)
Mean Std.
Deviation Std. Error
95% Confidence
Interval for Mean
Minimum Maximum ANOVA test
p-value
Lower
Bound
Upper
Bound
Group I
(Control) 17.33 1.63 .51 16.16 18.50 15.33 19.33
P=0.001 Sig.
P<0.05
Group II
(25% Old + 75% New) 19.06 1.91 .61 17.69 20.44 16.00 22.00
Group III
(50% Old + 50% New) 19.07 1.41 .45 18.06 20.08 16.67 21.33
Group IV
(75% Old + 25% New) 18.59 1.76 .56 17.34 19.86 16.67 22.00
Group V
(100% Old) 20.27 2.04 .65 18.81 21.72 17.33 23.33
Group VI
(Re-injection two time) 20.99 2.42 .77 19.27 22.73 18.00 24.67
Table II - The LSD test between groups of retentive force test mean difference(I-J), standard error and p-value reading of all study groups
(I) Groups (J) Groups Mean
Difference (I-J) Std. Error P-value
Group I (Control)
Group II (25% Old + 75% New) -1.73* .85 .045
Group III (50% Old + 50% New) -1.73* .85 .045
Group IV (75% Old + 25% New) -1.27 .85 .140
Group V (100% Old) -2.93* .85 .001
Group VI (Re-injection) -3.67* .85 .00
Group II (25% Old + 75% New)
Group III (50% Old + 50% New) .00 .85 1.00
Group IV (75% Old + 25% New) .47 .85 .58
Group V (100% Old) -1.20 .85 .16
Group VI (Re-injection) -1.93* .85 .026
Group III (50% Old + 50% New)
Group IV (75% Old + 25% New) .467 .85 .58
Group V (100% Old) -1.20 .85 .16
Group VI (Re-injection) -1.93* .85 .026
Group IV (75% Old + 25% New0 Group V (100% Old) -1.67 .85 .05
Group VI (Re-injection) -2.40* .85 .006
Group V (100% Old) Group VI (Re-injection) -.733 .84 .39
*The mean difference is significant at the 0.05 level.
Table III - Paired sample T test to compare between groups for clasp deformation test
Groups
Applied Force
T test (P value)
Before After
Group I (Control) 8.017 8.490 2.839 (0.0422S)
Group II (25% Old + 75% New) 8.871 9.518 3.992 (0.0023HS)
Group III (50% Old + 50% New) 8.784 9.324 2.729 (0.0428 S)
Group IV (75% Old + 25% New) 8.193 9.002 3.319 (0.0013HS)
Group V (100% Old) 8.872 9.376 2.404 (0.0342 S)
Group VI (Re-injection two time) 8.683 9.146 3.239 (0.0392 S)
S: Significant difference (p value < 0.05), HS: High significant difference (p value < 0.01).
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Zwwyer RM et al.
Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal clasps
Zwwyer RM et al. Assessment the retentive force and XRD analysis on the
recycling esthetic thermoplastic acetal clasps
diffraction peak refers to crystal structure of
acetal resin as show in Figure 7.
DISCUSSION
Any dental material’s initial mechanical
characteristics can be used to predict the main
cause of clinical failure and make a choice for a
particular application. To enhance the mechanical
qualities, new materials for load-bearing areas
have recently been proposed. There is not any
previous work on the subject because both the
material employed in this study and the concept
of research for re-injection of the substance are
new. As a result, we lacked citations for previous
research. Compared to new acetal resin claps, the
Aker clasp design, manufactured from re-injected
acetal resin material, showed a significantly
stronger retention force, according to the data
collected during this study. This investigation’s goal
was to contrast the retentive forces of six different
acetal clasp groups. According to Davenport, the
clasp’s exibility is inuenced by its thickness,
section, length and material, and a more exible
clasp offers less retention [10]. In the present
study the retention force of re-injection two times
clasp shows the higher retentive force that’s due
to more the acetal material is exposed to heat and
injection for several times, the exibility decreases.
Clinically adequate retention for thermoplastic
clasps may be achieved at dimensions that are
different from Co-Cr clasp; a clasp with increase
in thickness may be necessary in order to engage
a deep undercut area [13]. Since thermoplastic
material is less stiff than metals and alloys, this
might be required. It also lessens the chance of
traumatic overloading [14, 15].
The distance between two clasp tips
(deformation) increased signicantly in acetal
clasps between the control and experimental
groups. This is according to previous studies [9, 16],
They found that acetal clasps with greater exibility
deformed more than those with greater stiffness.
Co-Cr clasps upon aging and wear. Consequently,
the clasps’ retentive forces gradually diminish as
they undergo plastic deformation, and breaking
could happen while using them [11].
Figure 7 - XRD patterns of all study groups represent the Pos. [°2θ] with horizontal axis and intensity with vertical axis with three peaks of
Crystallite Size only [Å].
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Zwwyer RM et al.
Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal clasps
Zwwyer RM et al. Assessment the retentive force and XRD analysis on the
recycling esthetic thermoplastic acetal clasps
CONCLUSION
This study’s limitations show that the new
acetal clasps with a 0.25mm undercut had the
lowest initially retentive force and the maximum
initial retentive force were observed in the two-
time re-injection acetal clasps. On the other hand,
the re-injection of acetal material and reuse had
no effect on the crystalline structure whereas
the acetal clasps showed a modest increase in
the distance between the tips of the clasps after
re-injection.
Author’s Contributions
RMZ: Methodology, Writing – Original Draft
Preparation. NSM: Supervision.
Conict of Interest
We have no conicts of interest to disclose
regarding this article. The opinions expressed
are solely those of the authors and have not
been influenced by any financial or personal
relationships.
Funding
The authors received no nancial support
for the research, authorship, and/or publication
of this article.
Regulatory Statement
This article did not involve the use of
any hazardous materials, living organisms,
or any procedures that could harm the
environment. There was no need to comply
with any specic regulatory laws or regulations
regarding occupational health and safety or
the environment. All necessary measures were
taken to ensure compliance with ethical research
practices and laboratory safety.
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Braz Dent Sci 2024 Jan/Mar;27 (1): e4005
Zwwyer RM et al.
Assessment the retentive force and XRD analysis on the recycling esthetic thermoplastic acetal clasps
Zwwyer RM et al. Assessment the retentive force and XRD analysis on the
recycling esthetic thermoplastic acetal clasps
Rasha Mohammed Zwwyer
(Corresponding address)
Middle Technical University, College of Health and Medical Techniques,
Prosthodontic Dental Techniques Department, Baghdad, Iraq.
Email: rshamhmdzwyrklh@gmail.com
Date submitted: 2023 Aug 19
Accept submission: 2024 Jan 24
