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Evaluation of the mechanical properties of different materials for manufacturing occlusal splints

Abstract

This study aimed to compare the mechanical properties of various occlusal plate materials by analyzing surface roughness, Knoop microhardness, flexural strength, and modulus of elasticity. Fifty samples were prepared and classified as SC (self-curing acrylic resin), WB (heat-cured acrylic resin), ME (acrylic resin polymerized by microwave energy), P (resin print), and M (polymethylmethacrylate polymer block for computer-aided design/computer-aided manufacturing). The data were analyzed using a one-way analysis of variance and Tukey’s honestly significant difference test. Surface roughness was the same in all groups. The surface hardness of group M was statistically superior. The samples from groups P and M had higher flexural strength than other samples. The modulus of elasticity of group SC was statistically lower than that of other groups. The mechanical properties of the materials used to make the occlusal plates differed, and group M achieved the best results in all analyses. Therefore, clinicians must consider the material used to manufacture long-lasting and efficient occlusal splints.

Bruxism; Occlusal Splints; Mechanical Tests

Introduction

Bruxism is a group of disorders involving the temporomandibular joints (TMJs), masticatory muscles, which are primarily responsible for TMJ movement, and related structures characterized by the squeezing or grinding of teeth due to jaw immobilization or projection.11. Theroux J, Stomski N, Cope V, Mortimer-Jones S, Maurice L. A cross-sectional study of the association between anxiety and temporomandibular disorder in Australian chiropractic students. J Chiropr Educ. 2019 Oct;33(2):111-7. https://doi.org/10.7899/JCE-18-3
https://doi.org/10.7899/JCE-18-3...

2. Jivnani HM, Tripathi S, Shanker R, Singh BP, Agrawal KK, Singhal R. A study to determine the prevalence of temporomandibular disorders in a young adult population and its association with psychological and functional occlusal parameters. J Prosthodont. 2019 Jan;28(1):e445-9. https://doi.org/10.1111/jopr.12704
https://doi.org/10.1111/jopr.12704...
-33. Lobbezoo F, Ahlberg J, Glaros AG, Kato T, Koyano K, Lavigne GJ, et al. Bruxism defined and graded: an international consensus. J Oral Rehabil. 2013 Jan;40(1):2-4. https://doi.org/10.1111/joor.12011
https://doi.org/10.1111/joor.12011...
This event can occur while sleeping, as rhythmic (creaking) or non-rhythmic (squeezing) dental contact or while awake as repetitive or sustained dental contact and static or dynamic jaw contraction.33. Lobbezoo F, Ahlberg J, Glaros AG, Kato T, Koyano K, Lavigne GJ, et al. Bruxism defined and graded: an international consensus. J Oral Rehabil. 2013 Jan;40(1):2-4. https://doi.org/10.1111/joor.12011
https://doi.org/10.1111/joor.12011...
,44. Lobbezoo F, Ahlberg J, Raphael KG, Wetselaar P, Glaros AG, Kato T, et al. International consensus on the assessment of bruxism: report of a work in progress. J Oral Rehabil. 2018 Nov;45(11):837-44. https://doi.org/10.1111/joor.12663
https://doi.org/10.1111/joor.12663...
Occlusal splints are typically used to treat temporomandibular disorders symptoms and to prevent the harmful effects of bruxism in the stomatognathic system, particularly sleep bruxism, such as muscle and dental pain and dental elements fractures.55. Al-Moraissi EA, Farea R, Qasem KA, Al-Wadeai MS, Al-Sabahi ME, Al-Iryani GM. Effectiveness of occlusal splint therapy in the management of temporomandibular disorders: network meta-analysis of randomized controlled trials. Int J Oral Maxillofac Implants. 2020 Aug;49(8):1042-56. https://doi.org/10.1016/j.ijom.2020.01.004
https://doi.org/10.1016/j.ijom.2020.01.0...
,66. Venugopalan S, Murthykumar K. The effect of occlusal splint therapy on masticatory muscle activity-a systematic review. Int J Dent Oral Sci. 2021;:2325-30. https://doi.org/10.19070/2377-8075-21000459
https://doi.org/10.19070/2377-8075-21000...

In the literature, the mechanism of action of occlusal splints needs to be better established.77. Reichardt G, Miyakawa Y, Otsuka T, Sato S. The mandibular response to occlusal relief using a flat guidance splint. Int J Stomatol Occlusion Med. 2013;6(4):134-9. https://doi.org/10.1007/s12548-013-0093-8
https://doi.org/10.1007/s12548-013-0093-...
Some studies attribute therapeutic success to occlusal modification, which reduces bruxism effects.88. Alencar Junior F, Becker A. Evaluation of different occlusal splints and counselling in the management of myofascial pain dysfunction. J Oral Rehabil. 2009 Feb;36(2):79-85. https://doi.org/10.1111/j.1365-2842.2008.01913.x
https://doi.org/10.1111/j.1365-2842.2008...
Others refer to shifting the condyle position to achieve a more stable and higher load distribution in the TMJ.99. Ekberg EC, Sabet ME, Petersson A, Nilner M. Occlusal appliance therapy in a short-term perspective in patients with temporomandibular disorders correlated to condyle position. Int J Prosthodont. 1998;11(3):263-8. However, there are no concerns due to the lack of uniformity among studies.77. Reichardt G, Miyakawa Y, Otsuka T, Sato S. The mandibular response to occlusal relief using a flat guidance splint. Int J Stomatol Occlusion Med. 2013;6(4):134-9. https://doi.org/10.1007/s12548-013-0093-8
https://doi.org/10.1007/s12548-013-0093-...

For this therapy, occlusal splints can be made with conventional acrylic resins (self-curing, heat-curing, or microwave-polymerized acrylic resins), polymethylmethacrylate (PMMA) polymers made with a computer-aided design/computer-aided manufacturing (CAD/CAM) system, or materials made with 3D printers.1010. Benli M, Eker Gümüş B, Kahraman Y, Gökçen-Rohlig B, Evlioğlu G, Huck O, et al. Surface roughness and wear behavior of occlusal splint materials made of contemporary and high-performance polymers. Odontology. 2020 Apr;108(2):240-50. https://doi.org/10.1007/s10266-019-00463-1
https://doi.org/10.1007/s10266-019-00463...
During parafunctional habits, the materials are constantly subjected to high occlusal effort, which can reach 785 N.1111. Nishigawa K, Bando E, Nakano M. Quantitative study of bite force during sleep associated bruxism. J Oral Rehabil. 2001 May;28(5):485-91. https://doi.org/10.1046/j.1365-2842.2001.00692.x
https://doi.org/10.1046/j.1365-2842.2001...
They must have adequate occlusal stability to withstand applied loads and the oral environment without changing their mechanical properties.66. Venugopalan S, Murthykumar K. The effect of occlusal splint therapy on masticatory muscle activity-a systematic review. Int J Dent Oral Sci. 2021;:2325-30. https://doi.org/10.19070/2377-8075-21000459
https://doi.org/10.19070/2377-8075-21000...
,1212. Gholampour S, Gholampour H, Khanmohammadi H. Finite element analysis of occlusal splint therapy in patients with bruxism. BMC Oral Health. 2019 Sep;19(1):205. https://doi.org/10.1186/s12903-019-0897-z
https://doi.org/10.1186/s12903-019-0897-...

With the advancement of digital technologies, new materials for the fabrication of occlusal splints are becoming available, and their mechanical properties may differ from those of conventional acrylic resins. Because of improved materials and fabrication methods, studies have reported that these new occlusal splint fabrication methods, such as printed resin and milled blocks in CAD/CAM, are efficient. However, to improve and favor long-term success for clinicians, it is critical to evaluate the efficacy of these new materials.1010. Benli M, Eker Gümüş B, Kahraman Y, Gökçen-Rohlig B, Evlioğlu G, Huck O, et al. Surface roughness and wear behavior of occlusal splint materials made of contemporary and high-performance polymers. Odontology. 2020 Apr;108(2):240-50. https://doi.org/10.1007/s10266-019-00463-1
https://doi.org/10.1007/s10266-019-00463...

This study aimed to compare the mechanical properties of various materials used to manufacture occlusal splints by analyzing the surface roughness, Knoop microhardness, flexural strength, and modulus of elasticity. The null hypothesis predicted that there would be no difference in the mechanical properties of the different materials tested.

Methodology

According to ISO 20795-1, 50 samples were made with 64 × 10 × 3.3 mm (± 0.2 mm) dimensions, based on the material and method used to produce the occlusal plates (Table 1). The sample was drawn from a previous study.1313. Aguirre BC, Chen JH, Kontogiorgos ED, Murchison DF, Nagy WW. Flexural strength of denture base acrylic resins processed by conventional and CAD-CAM methods [Internet]. J Prosthet Dent. 2020 Apr;123(4):641-6. https://doi.org/10.1016/j.prosdent.2019.03.010
https://doi.org/10.1016/j.prosdent.2019....

Table 1
Description of the materials used to make the study samples.

Preparation of samples

Four 64 × 10 × 3.3 mm matrices (Smart Dent Bio Bite Splint; Smart Dent, Sao Carlos, Brazil) were printed on a 3D dental printer (Miicraft Ultra Series; Smart Dent, Sao Carlos, Brazil) as models for the inclusion of the muffles using special type IV plaster (Elite Dental Stone; Zhemarck, Badia Polesine, Italy) and laboratory condensation silicone (Reflex Lab; Yller Biomaterials, Pelotas, Brazil) for manufacturing the samples in the following groups: self-curing acrylic resin (SC), heat-cured acrylic resin (WB), and acrylic resin polymerized by microwave energy (ME). After the plaster crystallized, the muffles were opened, the matrices were removed, and the mold was obtained, which was filled with resins from SC, WB, and ME that were manipulated according to the manufacturers’ recommendations.

In the SC group, the monomer and polymer were manipulated, inserted into the muffle molds, and polymerized for 20 min in a pressure cooker with 20 pounds of compressed air as recommended by the manufacturer. In the WB group, the manipulated resin was polymerized in a hot water bath at 70°C for 30 min and, subsequently, at 100°C for 1 hour and 30 min. In the ME group, the resin was manipulated and polymerized using microwave energy in a 900 W oven for 20 min at 20% power and then for 5 min at 60% power.

Group resin print (P) was manufactured in a virtual project using specific software (Exocad Dental CAD; Align Technology, San Jose, USA) and printed with resin (Smart Dent Bio Bite Splint; Smart Dent, Sao Carlos, Brazil) at an angle of 90° and 50 μm layer thickness on a dental 3D printer (Miicraft Ultra Series; Smart Dent, São Carlos, Brazil) and underwent post-processing with isopropyl alcohol for 5 min and exposure to UV light for 10 s. Group M samples were prepared from an experimental PMMA resin block (acrylic resin manipulated and polymerized at a temperature of 120°C and a pressure of 80 pounds of nitrogen) and milled using a milling machine (VHS S1) from the same virtual project used for group P.

All samples were finished and polished with sandpaper grains of 150, 220, 400, 600, 800, and 1000 (Microcut; Buehler, Lake Bluff, Illinois). After polishing, all samples were stored for 24 h in distilled water at 37 °C. Mechanical analyses were carried out.

Knoop microhardness

Knoop microhardness values were determined by applying a 25-g load to a microhardness device (HMV-2T; Shimadzu Corp., Kyoto, Japan) for 10 s. For each sample, three measurements were recorded for each sample.1414. Andreotti AM, Goiato MC, Moreno A, Nobrega AS, Pesqueira AA, Santos DM. Influence of nanoparticles on color stability, microhardness, and flexural strength of acrylic resins specific for ocular prosthesis. Int J Nanomedicine. 2014 Dec;9(1):5779-87. https://doi.org/10.2147/IJN.S71533
https://doi.org/10.2147/IJN.S71533...

Surface roughness (Ra)

A roughness meter was used to calculate the Ra (portable roughness meter SJ-411; Mitutoyo, Suzano, Brazil). Each sample was placed in the center of the apparatus, and the profilometer’s measuring tip was focused on its surface. A reading was taken at random in the center of the specimen. Two parallel readings to the right and left of the center were taken, and the average was calculated after these three readings. Ra values (the arithmetic mean of Ra) were measured with a 300 µm sweep lasting 12 s.1515. Moda MD, Godas AG, Fernandes JC, Suzuki TY, Guedes AP, Briso AL, et al. Comparison of different polishing methods on the surface roughness of microhybrid, microfill, and nanofill composite resins. J Investig Clin Dent. 2018 Feb;9(1): https://doi.org/10.1111/jicd.12287
https://doi.org/10.1111/jicd.12287...
The initial values were in angström (Å) and were converted to the nanometric scale (nm).

Strength and flexural modulus

Each sample was flexed on the universal testing machine (EMIC model DL 3000; EMIC, Sao Jose dos Pinhais, Brazil) for the three-point flexural strength and modulus of elasticity test at a constant speed of 5 mm/min until a fracture occurred.1616. Goiato MC, Santos DM, Moreno A, Iyda MG, Rezende MC, Haddad MF. Effect of disinfection and storage on the flexural strength of ocular prosthetic acrylic resins. Gerodontology. 2012 Jun;29(2):e838-44. https://doi.org/10.1111/j.1741-2358.2011.00570.x
https://doi.org/10.1111/j.1741-2358.2011...
Flexural strength and modulus of elasticity were measured in MPa.

Data analysis

One-way analysis of variance (ANOVA) was used to determine statistically significant differences between groups for surface roughness, Knoop microhardness, flexural strength, and modulus of elasticity. Tukey’s honestly significant difference test was used to compare variables with statistical significance. All statistical analyses were done using statistical software (SPSS Statistics 17.0; SPSS Inc., Chicago, USA). A p-value < 0.05 was considered statistically significant.

Results

Table 2 shows that the one-way ANOVA test showed a statistically significant difference in Knoop hardness, flexural strength, and flexural modulus. Table 3 shows all groups’ mean values and standard deviations based on the test and the Tukey test results. When compared to other groups, group M and group P have the highest and lowest microhardness values, respectively. Regardless of the polymerization method, there was no significant difference between conventional acrylic resins. Groups P and M had higher mean values in the flexural strength tests; no significant differences were found between groups P and M. However, there was a significant difference in flexural strength between groups SC, WB, and ME. The SC group had lower modulus of elasticity values than the other groups. The milled resin showed superior mechanical properties in all tests.

Table 2
One-way ANOVA results of surface roughness, microhardness, flexural strength, and modulus of elasticity tests.

Table 3
The mean values (standard deviation) and Tukey test results for the tests showed a statistically significant difference in the one-way ANOVA.

Discussion

The study’s null hypothesis was partially accepted because the Ra test showed no statistically significant differences among the groups tested. However, the mechanical properties of the evaluated materials varied in the other tests.

Occlusal plate uniformity contributes to the patient’s oral health and longevity.1717. Rahal JS, Mesquita MF, Henriques GE, Nóbilo MA. Surface roughness of acrylic resins submitted to mechanical and chemical polishing. J Oral Rehabil. 2004 Nov;31(11):1075-9. https://doi.org/10.1111/j.1365-2842.2004.01344.x
https://doi.org/10.1111/j.1365-2842.2004...
A previous study reported that a Ra value of <0.2 µm does not affect the number of microorganisms or their pathogenicity.1818. Quirynen M, Marechal M, Busscher HJ, Weerkamp AH, Darius PL, Steenberghe D. The influence of surface free energy and surface roughness on early plaque formation. An in vivo study in man. J Clin Periodontol. 1990 Mar;17(3):138-44. https://doi.org/10.1111/j.1600-051X.1990.tb01077.x
https://doi.org/10.1111/j.1600-051X.1990...
The Ra test revealed no statistically significant differences between groups in this study. The variation ranged from 0.07 µm for group ME to 0.15 µm for group M. Another comparative study reported differences between heat-cured acrylic resin and microwave-cured acrylic resin groups; when compared to self-curing acrylic resin, the latter had higher Ra values than the others.1919. Berger JC, Driscoll CF, Romberg E, Luo Q, Thompson G. Surface roughness of denture base acrylic resins after processing and after polishing. J Prosthodont. 2006;15(3):180-6. https://doi.org/10.1111/j.1532-849X.2006.00098.x
https://doi.org/10.1111/j.1532-849X.2006...
Because of the amount of residual monomer in self-curing resin, it facilitates the formation of pores and impairs the mechanical properties of this group.2020. Bates JF, Stafford GD, Huggett R, Handley RW. Current status of pour type denture base resins. J Dent. 1977 Sep;5(3):177-89. https://doi.org/10.1016/0300-5712(77)90001-X
https://doi.org/10.1016/0300-5712(77)900...

The mean Ra value of 0.1 µm found in this study for milled PMMA samples was similar to that found in another study, which found a value of 0.192 µm for the same variable.1010. Benli M, Eker Gümüş B, Kahraman Y, Gökçen-Rohlig B, Evlioğlu G, Huck O, et al. Surface roughness and wear behavior of occlusal splint materials made of contemporary and high-performance polymers. Odontology. 2020 Apr;108(2):240-50. https://doi.org/10.1007/s10266-019-00463-1
https://doi.org/10.1007/s10266-019-00463...
Because there is no standardization in polishing, the roughness variable is quite inconsistent in the literature, resulting in divergent mean values.1616. Goiato MC, Santos DM, Moreno A, Iyda MG, Rezende MC, Haddad MF. Effect of disinfection and storage on the flexural strength of ocular prosthetic acrylic resins. Gerodontology. 2012 Jun;29(2):e838-44. https://doi.org/10.1111/j.1741-2358.2011.00570.x
https://doi.org/10.1111/j.1741-2358.2011...
The results of this study showed that Ra is standardized using the polishing technique, regardless of the material used to manufacture the occlusal plates.

The Knoop hardness test analyzes the microhardness of various materials using a tool with a diamond tip.2121. Gong J, Wang J, Guan Z. A comparison between Knoop and Vickers hardness of silicon nitride ceramics. Mater Lett. 2002;56(6):941-4. https://doi.org/10.1016/S0167-577X(02)00641-9
https://doi.org/10.1016/S0167-577X(02)00...
These data describe the material’s resistance to forces, which is critical for occlusal splints that receive a high force load in function.2222. Prpic V, Slacanin I, Schauperl Z, Catic A, Dulcic N, Cimic S. A study of the flexural strength and surface hardness of different materials and technologies for occlusal device fabrication. J Prosthet Dent. 2019 Jun;121(6):955-9. https://doi.org/10.1016/j.prosdent.2018.09.022
https://doi.org/10.1016/j.prosdent.2018....
In this study, group M had a higher microhardness than the other groups. In previous studies, milled PMMA samples yielded similar and favorable results. 2323. Al-Dwairi ZN, Tahboub KY, Baba NZ, Goodacre CJ, Özcan M. A Comparison of the Surface Properties of CAD/CAM and Conventional Polymethylmethacrylate (PMMA). J Prosthodont. 2019 Apr;28(4):452-7. https://doi.org/10.1111/jopr.13033
https://doi.org/10.1111/jopr.13033...
These blocks are industrially polymerized at high temperatures and pressures, resulting in improved chemical, mechanical, and aesthetic properties.2424. Kelvin Khng KY, Ettinger RL, Armstrong SR, Lindquist T, Gratton DG, Qian F. In vitro evaluation of the marginal integrity of CAD/CAM interim crowns. J Prosthet Dent. 2016 May;115(5):617-23. https://doi.org/10.1016/j.prosdent.2015.10.002
https://doi.org/10.1016/j.prosdent.2015....
There was no significant difference compared to conventional acrylic resins, which contradicts the previous study.2525. Fraunhofer JA, Suchatlampong C. The surface characteristics of denture base polymers. J Dent. 1975 May;3(3):105-9. https://doi.org/10.1016/0300-5712(75)90060-3
https://doi.org/10.1016/0300-5712(75)900...
The heat-curing resin group had a higher hardness. Polished samples can explain this distinction in water, which reduces the hardness of these heat-curing resins due to the water sorption phenomenon.2525. Fraunhofer JA, Suchatlampong C. The surface characteristics of denture base polymers. J Dent. 1975 May;3(3):105-9. https://doi.org/10.1016/0300-5712(75)90060-3
https://doi.org/10.1016/0300-5712(75)900...
,2626. Braun KO, Mello JA, Rached RN, Del Bel Cury AA. Surface texture and some properties of acrylic resins submitted to chemical polishing. J Oral Rehabil. 2003 Jan;30(1):91-8. https://doi.org/10.1046/j.1365-2842.2003.00997.x
https://doi.org/10.1046/j.1365-2842.2003...

Meanwhile, because the additional polymerization that this material underwent compensated for the water sorption phenomenon, the hardness of self-curing resins increased during this mechanical polishing process.2626. Braun KO, Mello JA, Rached RN, Del Bel Cury AA. Surface texture and some properties of acrylic resins submitted to chemical polishing. J Oral Rehabil. 2003 Jan;30(1):91-8. https://doi.org/10.1046/j.1365-2842.2003.00997.x
https://doi.org/10.1046/j.1365-2842.2003...
,2727. McCracken WL. An evaluation of activated methyl methacrylate denture base materials. J Prosthet Dent. 1951;2(1):68-83. https://doi.org/10.1016/0022-3913(52)90014-0
https://doi.org/10.1016/0022-3913(52)900...
A previous study reported that printed resins had lower hardness values than milled and conventional acrylic resins 2828. Wesemann C, Spies BC, Sterzenbach G, Beuer F, Kohal R, Wemken G, et al. Polymers for conventional, subtractive, and additive manufacturing of occlusal devices differ in hardness and flexural properties but not in wear resistance. Dent Mater. 2021 Mar;37(3):432-42. https://doi.org/10.1016/j.dental.2020.11.020
https://doi.org/10.1016/j.dental.2020.11...
. These findings could be explained by water storage, which reduces the hardness of printed materials2929. Reymus M, Stawarczyk B. In vitro study on the influence of postpolymerization and aging on the Martens parameters of 3D-printed occlusal devices. J Prosthet Dent. 2021 May;125(5):817-23. https://doi.org/10.1016/j.prosdent.2019.12.026
https://doi.org/10.1016/j.prosdent.2019....
with high water uptake capacity after manufacturing.3030. Berli C, Thieringer FM, Sharma N, Müller JA, Dedem P, Fischer J, et al. Comparing the mechanical properties of pressed, milled, and 3D-printed resins for occlusal devices. J Prosthet Dent. 2020 Dec;124(6):780-6. https://doi.org/10.1016/j.prosdent.2019.10.024
https://doi.org/10.1016/j.prosdent.2019....

The fracture resistance of a sample is referred to as its flexural strength.3131. Ajaj-Alkordy NM, Alsaadi MH. Elastic modulus and flexural strength comparisons of high-impact and traditional denture base acrylic resins. Saudi Dent J. 2014 Jan;26(1):15-8. https://doi.org/10.1016/j.sdentj.2013.12.005
https://doi.org/10.1016/j.sdentj.2013.12...
In this study, the results were statistically similar between group P and group M and higher than those of the other groups. Milled PMMA samples had higher flexural strength than printed samples3232. Fark T, Hummel C, Hähner A, Nin T, Hummel T. Characteristics of taste disorders. Eur Arch Otorhinolaryngol. 2013 May;270(6):1855-60. https://doi.org/10.1007/s00405-012-2310-2
https://doi.org/10.1007/s00405-012-2310-...
, but this difference was not statistically significant in this study. Although there was no statistical difference, the PMMA block fabrication method reduced the formation of pores and errors compared to the printed samples group.3030. Berli C, Thieringer FM, Sharma N, Müller JA, Dedem P, Fischer J, et al. Comparing the mechanical properties of pressed, milled, and 3D-printed resins for occlusal devices. J Prosthet Dent. 2020 Dec;124(6):780-6. https://doi.org/10.1016/j.prosdent.2019.10.024
https://doi.org/10.1016/j.prosdent.2019....
A previous study reported that the acrylic resins polymerized by microwave (group ME) performed better than other acrylic resins.3333. Barbosa DB, de Souza RF, Pero AC, Marra J, Compagnoni MA. Flexural strength of acrylic resins polymerized by different cycles. J Appl Oral Sci. 2007 Oct;15(5):424-8. https://doi.org/10.1590/S1678-77572007000500010
https://doi.org/10.1590/S1678-7757200700...
Although there was no statistical difference between the microwave-polymerized acrylic resins and other conventional acrylic resins, the microwave-polymerized acrylic resins had higher flexural strength values.3333. Barbosa DB, de Souza RF, Pero AC, Marra J, Compagnoni MA. Flexural strength of acrylic resins polymerized by different cycles. J Appl Oral Sci. 2007 Oct;15(5):424-8. https://doi.org/10.1590/S1678-77572007000500010
https://doi.org/10.1590/S1678-7757200700...
Similar results may have occurred between groups SC and WB because pressure is used in the curing process in group SC, which can improve the fracture resistance of this resin due to less pore formation and overestimate its properties compared to other studies.3434. Donovan TE, Hurst RG, Campagni WV. Physical properties of acrylic resin polymerized by four different techniques. J Prosthet Dent. 1985 Oct;54(4):522-4. https://doi.org/10.1016/0022-3913(85)90425-1
https://doi.org/10.1016/0022-3913(85)904...

A high modulus of elasticity allows the material to better resist the forces applied to it, which is essential for manufacturing occlusal plates subject to forces >785 N.1111. Nishigawa K, Bando E, Nakano M. Quantitative study of bite force during sleep associated bruxism. J Oral Rehabil. 2001 May;28(5):485-91. https://doi.org/10.1046/j.1365-2842.2001.00692.x
https://doi.org/10.1046/j.1365-2842.2001...
The modulus of elasticity was similar between groups WB, ME, P, and M and was statistically higher than that of group SC. According to this study. The mechanical properties of self-curing resin samples are worse in most analyses (hardness, flexural strength, and elastic modulus) because this material contains more residual monomer, which affects their mechanical properties.2020. Bates JF, Stafford GD, Huggett R, Handley RW. Current status of pour type denture base resins. J Dent. 1977 Sep;5(3):177-89. https://doi.org/10.1016/0300-5712(77)90001-X
https://doi.org/10.1016/0300-5712(77)900...

The polymerization method of samples made with self-curing acrylic resin was one of the study’s limitations. The manufacturer recommends that polymerization be performed in a pressure cooker with 20 pounds of compressed air for 20 min. Most studies only performed polymerization on the bench; hence, compared to other studies, this work may have overestimated the mechanical properties of the self-curing acrylic resin.3333. Barbosa DB, de Souza RF, Pero AC, Marra J, Compagnoni MA. Flexural strength of acrylic resins polymerized by different cycles. J Appl Oral Sci. 2007 Oct;15(5):424-8. https://doi.org/10.1590/S1678-77572007000500010
https://doi.org/10.1590/S1678-7757200700...
Another limitation can be found in the sample polishing sequences. Metal polishing sandpaper granulations of 150, 220, 400, 600, 800, and 1000 were used to finish the samples in this study. However, other studies recommend mechanical polishing in a vise with pumice paste, lime powder, a soft brush, and a felt cone. 1818. Quirynen M, Marechal M, Busscher HJ, Weerkamp AH, Darius PL, Steenberghe D. The influence of surface free energy and surface roughness on early plaque formation. An in vivo study in man. J Clin Periodontol. 1990 Mar;17(3):138-44. https://doi.org/10.1111/j.1600-051X.1990.tb01077.x
https://doi.org/10.1111/j.1600-051X.1990...
Another limitation is that important methodologies were not carried out, such as degree of conversion, scanning electron microscopy analyses, color stability, and others. Finally, few studies have compared the mechanical properties of acrylic resins based on the polymerization method. Therefore, additional studies are required to provide strong evidence for the findings of this study.

Conclusion

According to the results of this study, there was a difference in the mechanical properties of the materials used to manufacture occlusal splints, with milled resin outperforming the others in analysis.

Acknowledgments

The Federal District Research Support Foundation supported this study. The authors thank the Trion 3D Planning Center for providing the printed samples and Fabio Mesquita dos Santos for the milled samples.

References

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Publication Dates

  • Publication in this collection
    28 Apr 2023
  • Date of issue
    2023

History

  • Received
    21 Sept 2021
  • Accepted
    21 Nov 2021
  • Reviewed
    6 Dec 2022
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