Simulated clinical adjustment and intra-oral polishing of two translucent, monolithic zirconia dental ceramics: An in vitro investigation of surface roughness. (October 2020)

• Record Type: Journal Article
• Authors: Jum'ah, Ahmad A.; Brunton, Paul A.; Li, Kai Chun; Waddell, J Neil
• Is Part Of: Journal of dentistry. Volume 101(2020:Oct.)
• Publication Date: 2020-10
• Subjects: Zirconia -- Tetragonal phase -- Cubic phase -- Surface roughness -- Polishing -- Translucent -- Dental ceramics; Dentistry -- Periodicals; Dentistry -- Periodicals; Dentisterie -- Périodiques; Electronic journals; 617.6005
• DOI: 10.1016/j.jdent.2020.103447
• Languages: English
• ISSNs: 0300-5712

Abstract

Abstract: Objective: To assess the surface roughness and residual flaws in two translucent zirconia substrates following simulated clinical adjustment and intra-oral finishing/polishing. Materials and methods: Specimens were prepared from two translucent (5Y-ZP/8Y-ZP) and one conventional (3Y-TZP) zirconia substrates (n = 84 p/g). Arithmetic mean roughness parameter (Ra ) was determined for all experimental groups at four stages (n = 21 p/g): (1) as-sintered, (2) surface grinding using a zirconia cutting diamond bur, (3) polishing using 1-step, 2-step or 4-step intra-oral polishing kits, and (4) laboratory polishing/glazing. Scanning electron microscopy (SEM) was used to evaluate residual surface flaws. Data were statistically analysed using a two-way ANOVA test, multiple and pairwise comparisons were performed using a Bonferroni post hoc test. Results: Ra was significantly higher for as-sintered and ground 5Y-ZP/8Y-ZP compared to 3Y-TZP ( p ≤ 0.001). Material type and polishing protocol had statistically significant effect on Ra (p < 0.001). The 4-step polishing resulted in the lowest Ra in 3Y-TZP/5Y-ZP ( p ≤ 0.001). No significant differences were observed between different polishing protocols in 8Y-ZP ( p≥ 0.655). Glazing significantly reduced Ra in all materials compared to other polishing protocols ( p ≤ 0.001) except for the 4-step protocol in 3Y-TZP ( p = 0.195). SEM revealed pronounced surface flaws in ground 5Y-ZP/8Y-ZP. Grinding of 3Y-TZP induced ductile material removal and thereby, minimal cohesive material loss. The 4-step polishing protocol resulted in the fewest and shallowest surface flaws in all groups. Glazing of 3Y-TZP resulted in the most homogenous surface contrary to 5Y-ZP/8Y-ZP. Conclusions: The finest surface finish was achieved using the 4-step polishing protocol in all studied materials. This protocol might be inadequate however for polishing of ground 5Y-ZP/8Y-ZP as a result of the pronounced surface damage induced by the grinding process. The glazing of 5Y-ZP/8Y-ZP might not be as predictable as for 3Y-TZP. Clinical significance: The higher susceptibility to surface damage, as a result of increasing dopant concentration, may render polishing of ground, translucent zirconia more complicated compared to the conventional 3Y-TZP counterparts.