Wear behavior and abrasiveness of monolithic CAD/CAM ceramics after simulated mastication

Abstract

Objectives: To evaluate the wear resistance and abrasiveness of monolithic CAD/CAM ceramics.

Materials and methods: Rectangular-shaped specimens (12 mm × 6.5 mm × 1.5 mm) were sectioned from the following CAD/CAM blocks (n = 10); partially crystallized lithium disilicate (PLD), experimental fully crystallized lithium disilicate (FLD), zirconia-reinforced lithium silicate (ZLS), super-translucent monolithic zirconia (SMZ), and ultra-translucent monolithic zirconia (UMZ). Silicon carbide papers were used to mechanically flatten and polish the surfaces. PLD specimens were subjected to a combined crystallization/glazing firing cycle. Ceramic specimens were mounted to the wear device and tested for 200,000 cycles against human premolars at 20 N force and 2 mm sliding distance. Artificial saliva was used as a lubricant. The teeth were scanned using micro-CT before and after the wear test and the generated models were overlapped to determine the volumetric tooth loss. Before and after the test, specimens' weights and surface roughness (R_a) values were measured, and the differences were calculated. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were utilized for microstructural and chemical analysis. Statistical analysis was performed using one-way ANOVA or an equivalent test for non-parametric results. Significance level was set at P ≤ 0.05.

Results: The type of ceramic material affected the ceramic and antagonist wear rates (P < 0.001). PLD and ZLS had the highest ceramic and antagonist wear, whereas UMZ and SMZ demonstrated the lowest wear values. The FLD group showed comparable antagonist wear and significantly less ceramic wear than PLD and ZLS.

Conclusions: Monolithic zirconia demonstrated the best wear resistance and least abrasiveness to the antagonist. The experimental lithium disilicate was more wear-resistant than other glass-ceramic groups.

Clinical relevance: Monolithic zirconia is wear-resistant and gentle on the antagonist. In contrast, glass-ceramics are more abrasive to enamel.

Keywords: CAD/CAM; Dental ceramics; Micro-CT; Surface roughness; Volumetric enamel loss; Wear.

Fig. 1

a Overlapping of the 3D models. b Boolean subtraction of the worn area. The black arrow represents the worn area

Fig. 2

Boxplots illustrate the volumetric enamel loss after 200,000 wear cycles. PLD; partially crystallized lithium disilicate, FLD; fully crystallized lithium disilicate, ZLS; zirconia-reinforced lithium disilicate, SMZ; super-translucent monolithic zirconia, UMZ; ultra-translucent monolithic zirconia. P-value: Dunn’s post hoc test, significance p < 0.05. The letters show the significant difference among groups. Groups that do not share a letter are significantly different

Fig. 3

Ceramic wear after 200,000 wear cycles. PLD; partially crystallized lithium disilicate, FLD; fully crystallized lithium disilicate, ZLS; zirconia-reinforced lithium disilicate, SMZ; super-translucent monolithic zirconia, UMZ; ultra-translucent monolithic zirconia. P-value: Tukey’s post hoc test, significance p < 0.05. The letters show the significant difference among groups. Groups that do not share a letter are significantly different

Fig. 4

Scanning electron micrograph images at magnifications 15 × , 500 × , and 1000 × showing the worn surfaces of the ceramic specimens after 200,000 wear cycles against the buccal cusps of natural premolars. PLD; partially crystallized lithium disilicate, FLD; fully crystallized lithium disilicate, ZLS; zirconia-reinforced lithium disilicate, SMZ; super-translucent monolithic zirconia, UMZ; ultra-translucent monolithic zirconia. b and c show severe debris retained on the worn surface of PLD (black arrows). Crack lines are present on surfaces of PLD and ZLS (white arrows)

Fig. 5

Scanning electron micrograph images of etched glass–ceramic specimens taken with spot size 3 at magnifications 1200 × (a, c, e), and 5000 × (b, d, f) showing the crystalline morphology for the worn surfaces. PLD; partially crystallized lithium disilicate, FLD; fully crystallized lithium disilicate, ZLS; zirconia-reinforced lithium disilicate. Detached areas (continuous white arrows) and debris (dotted white arrows) are seen on the worn surface of PLD. A transverse crack is obvious on the worn surface of FLD (black arrow)