Aim: To evaluate the effect of combined thermocycling and artificial saliva pH on flexural strength, surface microhardness, as well as clasp retention and deformation of two different thermoplastic polymers.
Materials and methods: Three groups were created, heat-cured polymethyl methacrylate, acetal, and poly-ether-ether ketone (PEEK) resins. Specimens were wrapped in plastic bags containing artificial saliva with three pH values (acidic 5.8, neutral 7.2, and alkaline 8.3). Two Aker clasps materials (acetal and PEEK), for premolar and molar, were stored in neutral salivary pH. Specimens were subjected to 2,000 thermocycles (5–55°C). Surface microhardness, flexural strength, and clasp retention and deformation were evaluated before and after aging. Data were analyzed by ANOVA, Tukey\'s test, Student\'s t-test, and paired t-tests (p < 0.05).
Results: Thermal cycling at acidic and alkaline pH significantly decreased flexural strength and surface microhardness of acetal. It had no significant effect on PEEK properties. Poly-ether-ether ketone showed statistically significant higher mechanical properties in all groups. Acetal clasps exhibited a statistically significant deformation and a corresponding decrease in retention after thermocycling at neutral pH.
Conclusion: Mechanical properties of acetal, as well as its clasp retention and deformation, significantly decreased after combining thermal and pH aging and thermal cycling in neutral pH, respectively. Meanwhile, PEEK clasps were not significantly affected.
Clinical significance: Different intraoral variables may significantly affect mechanical performance, retention, and deformation of TMs used for denture base and clasp construction. Some of these TMs may behave better than the other types with recommended improvement of the design like increasing clasp cross-section area.
Ernst CP, Canbek K, Euler T, et al. In vivo validation of the historical in vitro thermocycling temperature range for dental materials testing. Clin Oral Investig 2004;8(3):130–138. DOI: 10.1007/s00784-004-0267-2.
Minich DM, Bland JS. Acid-alkaline balance: role in chronic disease and detoxification. Altern Ther Health Med 2007;13(4):62–65.
Cavalcanti AN, Mitsui FHO, Ambrosano GMB, et al. Influence of adhesive systems and flowable composite lining on bond strength of class II restorations submitted to thermal and mechanical stresses. J Biomed Mater Res - Part B Appl Biomater 2007;80(1):52–58. DOI: 10.1002/jbm.b.30567.
Archadian N, Kawano F, Ohguri T, et al. Flexural strength of rebased denture polymers. J Oral Rehabil 2000;27(8):690–696. DOI: 10.1046/j.1365-2842.2000.00552.x.
Mazzitelli C, Monticelli F, Toledano M, et al. Effect of thermal cycling on the bond strength of self-adhesive cements to fiber posts. Clin Oral Investig 2012;16(3):909–915. DOI: 10.1007/s00784-011-0576-1.
Morresi AL, D’Amario M, Capogreco M, et al. Thermal cycling for restorative materials: does a standardized protocol exist in laboratory testing? A literature review. J Mech Behav Biomed Mater 2014;29:295–308. DOI: 10.1016/j.jmbbm.2013.09.013.
Hristov I, Yankov S. Thermoplastic materials in the dental practice: a review. Int J Sci Res 2017;6:1074–1076.
Nandal S, Ghalaut P, Shekhawat H, et al. New era in denture base resins: a review. Dent J Adv Stud 2013;01(03):136–143. DOI: 10.1055/s-0038-1671969.
Arda T, Arikan A. An in vitro comparison of retentive force and deformation of acetal resin and cobalt-chromium clasps. J Prosthet Dent 2005;94(3):267–274. DOI: 10.1016/j.prosdent.2005.06.009.
De Torres EM, de Siqueira Damasceno II, do Amaral BA, et al. Effect of acetyl resin retentive arms on the retentive force of circumferential clasps: an in vitro study. J Prosthodont Res 2012;56(3):216–221. DOI: 10.1016/j.jpor.2011.09.003.
Muhsin SA, Wood DJ, Johnson A, et al. Effects of novel polyetheretherketone (PEEK) clasp design on retentive force at different tooth undercuts. JODR 2018;5:13–24.
Tannous F, Steiner M, Shahin R, et al. Retentive forces and fatigue resistance of thermoplastic resin clasps. Dent Mater 2012;28(3):273–278. DOI: 10.1016/j.dental.2011.10.016.
Schwitalla AD, Spintig T, Kallage I, et al. Flexural behavior of PEEK materials for dental application. Dent Mater 2015;31(11):1377–1384. DOI: 10.1016/j.dental.2015.08.151.
Najeeb S, Zafar MS, Khurshid Z, et al. Applications of polyetheretherketone (PEEK) in oral implantology and prosthodontics. J Prosthodont Res 2016;60(1):12–19. DOI: 10.1016/j.jpor.2015.10.001.
Polychronakis N, Lagouvardos EP, Polyzois G, et al. Color changes of polyetheretherketone (PEEK) and polyoxymethelene (POM) denture resins on single and combined staining/cleansing action by CIELab and CIEDE2000 formulas. J Prosthodont Res 2019(2):6–13. DOI: 10.1016/j.jpor.2019.06.005.
Parlani S, Agarwal B, Malaiya A, et al. Evaluation of flexural modulus of flexible denture base material kept in water, denture cleanser, artificial saliva, and open air for different time intervals: an in vitro study. Int J Prosthodont Restor Dent 2018;8:54–58.
Nogueira SS, Ogle RE, Davis EL. Comparison of accuracy between compression- and injection-molded complete dentures. J Prosthet Dent 1999;82(3):291–300. DOI: 10.1016/s0022-3913(99)70083-1.
Assunção WG, Gomes ÉA, Barão VA, et al. Effect of storage in artificial saliva and thermal cycling on Knoop hardness of resin denture teeth. J Prosthodont Res 2010;54(3):123–127. DOI: 10.1016/j.jpor.2009.12.001.
Medeiros IS, Gomes MN, Loguercio AD, et al. Diametral tensile strength and Vickers hardness of a composite after storage in different solutions. J Oral Sci 2007;49(1):61–66. DOI: 10.2334/josnusd.49.61.
Momoi Y, Hirosaki K, Kohno A, et al. Flexural properties of resin-modified “hybrid” glass-ionomers in comparison with conventional acid-base glass-ionomers. Dent Mater J 1995;14(2):109–19. DOI: 10.4012/dmj.14.109.
Budtz-Jorgensen E. Materials and methods for cleaning dentures. J Proth Dent 1979;42:619–623.
Stewardson DA, Shortall AC, Marquis PM. The effect of clinically relevant thermocycling on the flexural properties of endodontic post materials. J Dent 2010;38(5):437–442. DOI: 10.1016/j.jdent.2010.02.003.
Gale MS, Darvell BW. Thermal cycling procedures for laboratory testing of dental restorations. J Dent 1999;27(2):89–99. DOI: 10.1016/s0300-5712(98)00037-2.
Stavridakis MM, Kakaboura AI, Ardu S, et al. Marginal and internal adaptation of bulk-filled class I and cuspal coverage direct resin composite restorations. Oper Dent 2007;32(5):515–523. DOI: 10.2341/06-157.
Wimmer T, Huffmann AM, Eichberger M, et al. Two-body wear rate of PEEK, CAD/CAM resin composite and PMMA: effect of specimen geometries, antagonist materials and test set-up configuration. Dent Mater 2016;32(6):e127–e136. DOI: 10.1016/j.dental.2016.03.005.
Zok FW, Miserez A. Property maps for abrasion resistance of materials. Acta Mater 2007;55(18):6365–6371. DOI: 10.1016/j.actamat.2007.07.042.
Fitton JS, Davies EH, Howlett JA, et al. The physical properties of a polyacetal denture resin. Clin Mater 1994;17(3):125–129. DOI: 10.1016/0267-6605(94)90135-x.
Arikan A, Ozkan YK, Arda T, et al. An in vitro investigation of water sorption and solubility of two acetal denture base materials. Eur J Prosthodont Restor Dent 2005;13(3):119–122.
Lekha K, Savitha N, Roseline M, et al. Acetal resin as an esthetic clasp material. J Interdiscip Dent 2012;2:11.
Ardelean L, Bortun CM, Podariu AC, et al. Manufacture of different types of thermoplastic. Thermoplast - Compos Mater 2012; 25–48.
Rusu LC, Ardelean L. CAD/CAM technology concerning biocompatibilty in zirconia all-ceramic restoration. Rev Chim (Bucharest) 2012;63:513–515.
Liu B, Thayumanavan S. Substituent effects on the pH sensitivity of acetals and ketals and their correlation with encapsulation stability in polymeric nanogels. J Am Chem Soc 2017;139(6):2306–2317. DOI: 10.1021/jacs.6b11181.
Bagheri R, Tyas MJ, Burrow MF. Subsurface degradation of resin-based composites. Dent Mater 2007;23(8):944–951. DOI: 10.1016/j.dental.2006.06.035.
Katsikis N, Zahradnik F, Helmschrott A, et al. Thermal stability of poly(methyl methacrylate)/silica nano- and microcomposites as investigated by dynamic-mechanical experiments. Polym Degrad Stab 2007;92(11):1966–1976. DOI: 10.1016/j.polymdegradstab.2007.08.009.
Jaekel DJ, MacDonald DW, Kurtz SM. Characterization of PEEK biomaterials using the small punch test. J Mech Behav Biomed Mater 2011;4(7):1275–1282. DOI: 10.1016/j.jmbbm.2011.04.014.
Kurtz SM, Devine JN. PEEK biomaterials in trauma, orthopedic, and spinal implants. Biomaterials 2007;28(32):4845–4869. DOI: 10.1016/j.biomaterials.2007.07.013.
Gao S, Gao S, Xu B, et al. Effects of different pH-values on the nanomechanical surface properties of PEEK and CFR-PEEK compared to dental resin-based materials. Materials (Basel) 2015;8(8):4751–4767.
Ray BC. Temperature effect during humid ageing on interfaces of glass and carbon fibers reinforced epoxy composites. J Colloid Interface Sci 2006;298(1):111–117. DOI: 10.1016/j.jcis.2005.12.023.
Sethi S, Ray BC. Environmental effects on fibre reinforced polymeric composites: evolving reasons and remarks on interfacial strength and stability. Adv Colloid Interface Sci 2015;217:43–67. DOI: 10.1016/j.cis.2014.12.005.
Wu JC, Latta Jr GH, Wicks RA, et al. In vitro deformation of acetyl resin and metal alloy removable partial denture direct retainers. J Prosthet Dent 2003;90(6):586–590. DOI: 10.1016/j.prosdent.2003.09.020.
N’Diaye M, Pascaretti-Grizon F, Massin P, et al. Water absorption of poly(methyl methacrylate) measured by vertical interference microscopy. Langmuir 2012;28(31):11609–11614. DOI: 10.1021/la302260a.