Wear Potential of Dental Ceramics and its Relationship with Microhardness and Coefficient of Friction

Wear characteristics of esthetic resin matrix and zirconia reinforced lithium disilicate CAD/CAM materials: two-body wear and surface topography analysis

BACKGROUND

This in vitro study assessed the wear behavior of different CAD-CAM blocks and the abrasion of the enamel antagonist against these materials.

METHODS

64 disk-shaped specimens were prepared from 8 different CAD/CAM blocks as follow: one lithium disilicate glass ceramics block "IPS Emax CAD" as control group, two zirconia reinforced lithium silicate "Vita Suprinity & Celtra DUO," one interpenetrating network ceramic block "Vita Enamic," Three resin-based block composites "Lava Ultimate, Cerasmart & Brilliant-crios" as well as one hybrid nanoceramic "Shofu block HC". All specimens were mounted against canine and tested for two body wear analysis using a chewing simulating loading machine (100,000 cycles, 50 N, 5/55 °C). The amount of wear loss was measured for each specimen using a digital precise scale. Wear area before and after the chewing simulation were evaluated using an optical profilometer. Data analysed using one-way ANOVA test followed by Tukey's post hoc.

RESULTS

The results showed a significantly higher wear loss in resin matrix ceramics in comparison to glass ceramics. However, for tooth wear glass ceramics had significantly higher value than hybrid ceramics.

CONCLUSIONS

Resin based CAD/CAM Blocks gives a superior result when evaluating the wear behavior and its effect on the opposing tooth surface.

The Wear Behavior of Glass-Ceramic CAD/CAM Blocks against Bovine Enamel

The wear of enamel and crown restorative materials often occur by occlusion. The purpose of this study was to evaluate the wear volume between glass-ceramics used for CAD/CAM blocks (lithium disilicate: Initial LiSi block (LIS), IPS e.max CAD (IPS), zirconia-reinforced lithium silicate glass-ceramics: Celtra DUO (DUO), VITA Suprinity (VITS) and feldspar-based glass-ceramics: Vitablocs Mark II (MAK)) and bovine tooth enamel using a two-body wear test, the hardness, three-point bending strength, micro-structure and the element components of glass-ceramics. The data were analyzed using a one-way analysis of variance and Tukey's multiple comparison test (α = 0.05). IPS and DUO with relatively large size crystal gain had significantly larger abrader wear volumes. Zirconia-reinforced lithium silicate glass-ceramics (DUO, VITS) caused significantly greater wear volume in antagonist enamel. MAK with scale-shape crystals grains produced distinct scratches after wear tests, both in the material itself and in the enamel. A strong correlation between the mechanical properties (hardness, three-point bending strength) and wear volume could not be confirmed. The type of glass-ceramic, size, and shape of the crystal grains affected the wear behavior of the glass-ceramics for CAD/CAM blocks. Therefore, dentists should consider that wear behavior varies with crystal structure, size, and shape in glass-ceramics for CAD/CAM blocks.

Enamel wear against monolithic zirconia restorations: A meta-analysis and systematic review of in vitro studies

OBJECTIVE

An assessment was performed to identify and evaluate dental enamel wear caused by monolithic zirconia restoration. Literature searches were conducted in PubMed, Science Direct, Cochrane Evidence, and the Cochrane Library up to May 2020.

MATERIAL AND METHODS

Studies were selected for systematic review according to the inclusion (articles conducted on the wear of enamel samples opposing monolithic zirconia) and exclusion (case reports, non-English articles, and monolithic zirconia samples facing other materials rather than human enamel) criteria. Of those, articles on polished and glazed monolithic zirconia subjected to a 50 N vertical load with a range of 240,000-250,000 cycles, equivalent to 1 year of in vivo mastication, were included in the meta-analysis.

RESULTS

In total, 3968 articles were pooled. Twenty-five articles met the inclusion criteria for the systematic review. Three studies were included in the meta-analysis. The results showed that the enamel wear against monolithic zirconia was within the statistically accepted level. Moreover, the polished monolithic zirconia surface caused less enamel wear than the glazed surface.

CONCLUSION

This review indicates that monolithic zirconia restorations cause acceptable antagonist enamel wear. Moreover, the meta-analysis results agreed that the final restoration's surface texture plays an essential role in the wear process.

CLINICAL SIGNIFICANCE

Monolithic zirconia restorations have been widely used in dental practice because they eliminate the chipping problems resulting from using veneered restorations. With recent technology development, monolithic zirconia has obtained more esthetic features and a more natural look. However, due to the high strength and surface roughness of monolithic zirconia, wear on the antagonist's teeth was detected. The results showed that this wear amount was statistically acceptable and lower than other ceramics such as feldspathic porcelain and enamel. Furthermore, surface treatment methods must be applied to minimize tooth wear, as polished or glazed surfaces interfere with enamel loss.

Friction and wear behavior of chairside CAD-CAM materials against different types of antagonists: An in vitro study

STATEMENT OF PROBLEM

Studies on the friction and wear behavior of recently introduced chairside computer-aided design and computer-aided manufacture (CAD-CAM) restorative materials are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the wear behavior of chairside CAD-CAM materials against different types of antagonists (human tooth enamel, composite resin, and feldspathic porcelain).

MATERIAL AND METHODS

Specimens (14×14×2 mm) of different CAD-CAM materials (Brilliant Crios, Lava Ultimate, Vita Enamic, Vita Suprinity) were obtained by using a low-speed precision cutter (n=10). Wear tests were performed with a 20-N load, 2.5-mm/s sliding speed, 1-mm sliding distance, and 1500 cycles via a tribometer according to ASTM-G133. The coefficient of friction (CoF) of the material pairs was measured and recorded by using a special software program. Surface roughness (Ra), maximum wear depth, and mean maximum wear depth were measured with a profilometer, and values were analyzed by using 2-way ANOVA and the Bonferroni correction. Vickers hardness of CAD-CAM specimens was determined with a microhardness tester. Microhardness values were analyzed by using 1-way ANOVA and Tukey post hoc tests. Worn surfaces were observed by scanning electron microscopy and a 3D noncontact profilometer to determine the wear pattern and primary wear mechanisms.

RESULTS

Significant differences were found in the interactions between CAD-CAM materials and different types of antagonists (P<.001) for maximum wear depth, mean maximum wear depth, CoF, and Ra values.

CONCLUSIONS

Vita Suprinity exhibited superior wear resistance and Ra against all antagonists compared with other CAD-CAM materials. However, Vita Suprinity increased the destructive effects on antagonists. The safety of CAD-CAM materials is best determined when the wear behavior of materials and their effect on the antagonist are evaluated together.

Wear resistance and abrasiveness of CAD-CAM monolithic materials

STATEMENT OF PROBLEM

Computer-aided design and computer-aided manufacturing (CAD-CAM) restorations are in contact with the antagonist tooth, either a natural tooth or a restoration. Therefore, clinicians should be aware of the wear resistance of CAD-CAM materials and the wear behavior of the antagonist.

PURPOSE

The purpose of this in vitro study was to evaluate the wear resistance and abrasiveness of CAD-CAM materials.

MATERIAL AND METHODS

In a 2-body wear test, the materials IPS e.max CAD (Ivoclar Vivadent AG), Vita Suprinity (Vita Zahnfabrik), Lava Ultimate (3M ESPE), Vita Enamic (Vita Zahnfabrik), and Lava Plus (3M ESPE) acted as abraders and, together with bovine enamel, also as antagonists. Each antagonist wheel ran against each abrader wheel for 200000 cycles, with a spring force of 15 N, and at a rotational speed of 1 Hz in distilled water. The wear rate was determined with a surface profilometer. The surfaces were observed with scanning electron microscopy, and their hardness, coefficient of friction, and roughness were evaluated.

RESULTS

Lava Plus and IPS e.max CAD exhibited the highest potential for wear of Lava Ultimate. These 2 materials, together with Vita Suprinity, provided the highest wear of enamel and Vita Enamic. Vita Suprinity and IPS e.max CAD had higher wear than Lava Plus, and the inverse was also true. Vita Enamic and Lava Ultimate were among the materials that caused the lowest wear of enamel and all other evaluated materials. Scanning electron microscopy images revealed that except for Lava Ultimate, all other materials damaged enamel, in which Vita Suprinity and IPS e.max CAD were more aggressive when sliding against the materials. Lava Plus had the greatest hardness, followed by Vita Suprinity and IPS e.max CAD, Vita Enamic, and then Lava Ultimate. The coefficient of friction varied from 0.42 to 0.53. The Vita Enamic and Lava Ultimate showed the highest surface roughness.

CONCLUSIONS

The nanofilled composite resin and polymer-infiltrated ceramic were more antagonist-friendly (whether enamel or CAD-CAM material) than glass-ceramics and zirconia. Care should be taken when selecting the material that will contact mainly with glass-ceramics. Hardness should also be considered when selecting a material.

The ball-on-disk cyclic wear of CAD/CAM machinable dental composite and ceramic materials

The purpose of this study was to investigate the wear volume and the principal strain of machinable dental composite and ceramics in simulated mastication. A ball-on-disk wear test was performed for 3,000 cycles in water, using nine ball/disk combinations of three commercial CAD/CAM materials: feldspathic, lithium disilicate glass ceramics, and a highly loaded composite material (n = 7 for each combination). The wear volume was optically measured using a digital scanner and analyzed for statistical differences based on the materials (α = 0.05). We used non-linear finite element analysis to calculate the principal strain. The wear volume of the ball was significantly larger than that of the disk when hardness and fracture toughness of the former was lower than that of the latter and vice versa (P < 0.05). The lithium disilicate glass ceramic constantly showed lower wear volume than the opposing antagonist. Except for the same material pairs of feldspathic and composite, the ball or disk specimen that showed a larger wear in the occluding pair coincided with the one with higher maximum strain. It was not possible to predict the magnitude of wear, whereas the result suggested a strong association between the maximum strain and wear volume of the ceramic surface.

Changes to Glazed Dental Ceramic Shade, Roughness, and Microhardness after Bleaching and Simulated Brushing

PURPOSE

To evaluate shade stability, surface roughness, microhardness, and compressive strength of a glazed feldspathic ceramic subjected to bleaching and simulated brushing.

MATERIALS AND METHODS

Eighty-eight glazed feldspathic ceramic specimens were made from microparticulate leucite and divided into eight groups (n = 10). The whitening products used were: Opalescence Trèswhite Supreme (Ultradent), Opalescence®\ PF 15% (Ultradent), and Oral-B 3D White Whitestrips. All substances for whitening were used for 4 hours/day for a period of 14 days; the control group was not bleached. Next, half of the specimens were individually brushed. Microhardness and surface roughness data were subjected to three-way ANOVA and Tukey test. The diametrical tensile strength data were subjected to two-way ANOVA. The shade change data were analyzed using Kruskal-Wallis, Mann-Whitney, and the Student-Newman-Keuls test. The significance level was set at 5%.

RESULTS

Glazed feldspathic ceramic surface microhardness was significantly affected by bleaching agents (p = 0.007). Initially, glazed ceramic microhardness was significantly higher than that observed after contact with the bleaching agents, whether or not brushing was performed. The specimens submitted to bleaching in preloaded trays presented lower surface roughness values after brushing (p = 0.037). The surface roughness was significantly lower in the brushed specimens (p = 0.044). The diametrical tensile strength was not significantly affected by the application of bleaching agents (p = 0.563) or by brushing (p = 0.477). When the specimens were brushed, however, shade change was significantly influenced by the bleaching agent used (p = 0.041).

CONCLUSIONS

Bleaching agents associated with brushing cycles can alter surface properties and shade stability of glazed feldspathic ceramics, though such findings may not reflect the performance of unglazed feldspathic ceramics.