Effect of Filler Content on Chipping Resistance of Denture Teeth

Objectives:  Recent trends to place implant-supported overdentures allow patients to exert increased bite force, which presents a greater mechanical challenge to denture teeth. This study developed a test for comparing the chipping resistance of denture teeth. Methods:  Specimens were fabricated using central incisors (mold B73) from three Ivoclar Vivadent denture tooth product lines SR Phonares NHC (NHC), SR Phonares II (II), and SR Ortholingual DCL (DCL). Denture teeth were set in G10 fiber-reinforced acrylic holders (Atlas Fibre Company) using the corresponding denture base materials. NHC specimens were subjected to cyclic, slow monotonic, and impact loading, applying force at a variety of angles, locations, and contact types to identify a test method that produced the same failure mode as clinical specimens, which had been previously retrieved, de-identified, and disinfected by the manufacturer. The failure mode was chipping originating subsurface and propagating to the buccal surface near the incisal edge. Then, 12 specimens per group were tested using the selected protocol of monotonic loading (10N/s) applied at 30-degree angle to the lingual surface within 1mm of the incisal edge using a tooth-shaped stainless steel indenter in 37°C DI water. All specimens were fractographically examined. Microstructural analysis was performed using stereological techniques at the failure origin of four specimens per group. Results:  The failure loads were normally distributed (Shapiro-Wilk p=0.60) and had equal variances (p=0.94). One-way ANOVA followed by Tukey’s HSD found that Groups II and DCL had significantly higher failure load than Group NHC (p=0.008). Means (95% CI) were 596N(484N, 707N), 581N(478N, 684N), and 378N(285N, 472N), respectively. For Groups NHC and II, filler volume fractions were 0.505(0.456, 0.554) and 0.630(0.584, 0.676). Mean free paths were 5.09µm(4.97µm, 5.20µm) and 5.29µm(4.84µm, 5.75µm). The microstructure of Group DCL was too fine to successfully perform stereology. Conclusion: Chipping resistance increased with increasing filler volume fraction.