Effect of surface finishing and polishing procedures on color properties and translucency of monolithic zirconia restorations at varying thickness

Surface roughness and optical characteristics evaluations after chairside adjustment of different zirconia types

STATEMENT OF PROBLEM

Limited evidence is available for the effect of chairside adjustment using rotary cutting instruments on the surface roughness and optical properties of different zirconia types.

PURPOSE

To evaluate the effect of simulated adjustments on surface roughness and optical properties of different zirconia types.

MATERIALS AND METHODS

Three Partially Stabilized Zirconia (PSZ) types based on mole percent yttria (Y) concentration from the same manufacturer (Katana; Kuraray) were used: 3Y-PSZ, 4Y-PSZ, and 5Y-PSZ. Thirty disk-shaped specimens (Ø14 × 1.2 mm) from different zirconia types (N = 90) were prepared. Specimens were either left without adjustment (NA), adjusted with Dialite ZR finishing and polishing system (Brasseler) (APol), or adjusted with course diamond instruments only (ADia). The specimens were distributed into 9 groups (n = 10): Group 3Y-PSZ/NA, Group 3Y-PSZ/APol, Group 3Y-PSZ/ADia, Group 4Y-PSZ/NA, Group 4Y-PSZ/APol, Group 4Y-PSZ/ADia, Group 5Y-PSZ/NA, Group 5Y-PSZ/APol, and Group 5Y-PSZ/ADia. The surface roughness of specimen was analyzed using an Atomic Force Microscope (AFM) (Bruker's Dimension Icon, Bruker) and Root Means Square (RMS) were recorded (nm). Surface Gloss (SG), Translucency Parameter (TP), and Contrast Ratio (CR) values of all groups were recorded using an integrating sphere spectrophotometer. Statistical analysis was performed using analysis of variance (ANOVA) and Tukey's multiple comparison tests for pairwise comparisons at p < 0.05 and 95% confidence interval.

RESULTS

APol had no effect on the surface roughness (p = 0.88) while ADia had a significant negative effect (p < 0.05) despite the type of zirconia. Out of the three testes optical properties, only SG was negatively affected by ADia for all types of zirconia (p < 0.05). The two adjustment types did not affect the TP of all the tested zirconia (p = 0.91). The CR was not affected by the tested adjustments for all zirconia types (p = 0.726).

CONCLUSION

Proper zirconia adjustment following a sequence of burs and polishers can maintain acceptable roughness and optical properties. Adjustment of zirconia with rough diamond can lead to deleterious effects and should be avoided.

CLINICAL SIGNIFICANCE

Chairside adjustment of zirconia could lead to rougher surface and unpredictable changes of surface gloss. Therefore, zirconia adjustment should be minimized to the greatest extent possible and a proper protocol should be followed if had to be done.

Optical properties of recycled zirconia for dental applications

STATEMENT OF PROBLEM

While waste zirconia can be recycled, whether the optical properties of recycled zirconia match those of commercially available zirconia is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the optical properties of recycled zirconia by assessing its color, translucency, and opalescence across different thicknesses and shades.

MATERIAL AND METHODS

Sixty specimens were prepared from 3 mol% yttria-stabilized tetragonal zirconia polycrystal blocks (Lava Plus; 3M ESPE) (group C); 60 other specimens were prepared from waste blocks of the same zirconia (group R). The specimens were further categorized into 4 subgroups (n=15) based on their thicknesses (1.0 mm or 1.5 mm) and shades (A1 or A3). Specimen color was measured with a spectrophotometer (Easyshade Advance 4.0; Vita ZahnFabrik). The parameters of color difference (ΔE00), translucency (TP), contrast ratio (CR), and opalescence (OP) were calculated. Grain size analysis was performed using scanning electron microscopy. Data were analyzed with analysis of variance (ANOVA) (α=.05).

RESULTS

Significant differences in translucency and opalescence were observed between groups C and R in all specimens (P<.001). Group R exhibited a range of TP (4.89 to 11.27), CR (0.74 to 0.91), and OP (3.36 to 8.65) values. The ΔE00 values between groups C and R ranged from 13.99 to 21.31. Both thickness and shade significantly affected the ΔE00 values (P<.001). The grain size in group C was not significantly different from that in group R (F=0.364, df=1, P=.555). The TP and OP values of group R decreased with increasing thickness (P<.001).

CONCLUSIONS

Recycled zirconia was less translucent and opalescent than commercially available zirconia. The color difference between commercially available and recycled zirconia exceeded the acceptable threshold, even when using the same staining procedure. Recycled zirconia exhibited reduced translucency and opalescence with increasing thickness.

Translucency of chairside monolithic zirconias using different sintering ovens: An in vitro investigation

OBJECTIVE

To evaluate the translucency of several monolithic zirconias (MZ) processed in various sintering ovens designed for single-visit, chairside use.

METHODS

Discs (n = 40) from zirconia blocks were fabricated for each MZ at manufacturer-recommended minimal thicknesses, as provided in each material's instructions for use: IPS e.max ZirCAD LT (ZLT); CEREC Zirconia+ (CZ+); 3M Chairside (3M); KATANA Zirconia (KT). Groups (n = 10) were sintered following manufacturer instructions for each oven: CEREC SpeedFire, Ivoclar CS4, Ivoclar CS6, and Ivoclar S2 (laboratory furnace control). Specimens were highly polished on one side and glazed on the other. Each side was measured with a spectrophotometer against white and black backgrounds to determine translucency parameter (TP) and contrast ratio (CR) values. Results for TP and CR for each material and oven combination were compared with a linear mixed model. Oven precision was evaluated using the Kruskall-Wallis test.

RESULTS

Glazed specimens were more translucent than polished ones (p < 0.001). ZLT and CZ+ were more translucent than 3M and KT regardless of the sintering oven (p < 0.01). Several oven/material combinations reached or exceeded the S2 oven TP: CS4 with CZ+ and 3M; CS6 with ZLT and KT (p < 0.01). SpeedFire was significantly less precise (p < 0.05) and produced lower TP values for ZLT, CZ+, and KT (p < 0.01). Results for TP and CR were highly correlated.

CONCLUSIONS

MZ surface finish, material thickness, and oven used all had a significant effect on translucency. Some chairside-oriented solutions produced results with translucency equal to conventionally processed zirconia.

CLINICAL SIGNIFICANCE

The translucency of a ceramic restoration is an important factor in determining its esthetics. Clinicians desiring the most esthetic outcomes with monolithic zirconia should be aware of the significant effects that surface finishing, material thickness, and the sintering oven used can have on restoration translucency.

Optical effect of rapid sintering protocols on different types of zirconia

STATEMENT OF PROBLEM

Rapid sintering protocols are available for the fabrication of zirconia restorations, but whether rapid sintering influences color or translucency is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of different rapid sintering protocols on the color and translucency of cubic and tetragonal zirconias.

MATERIAL AND METHODS

Sixty disk-shaped specimens of 1-mm-thick cubic (DD CubeX2) and tetragonal (DD Bio ZX2) zirconia were investigated. Specimens of each type of zirconia were divided into three groups: conventional, speed, and superspeed sintering protocols. The conventional group of each zirconia type served as the control for calculating color differences. Translucency for each group was assessed by the translucency parameter and contrast ratio. Two-way analysis of variance was used for statistical analysis of the data (α=.05).

RESULTS

The translucency of cubic and tetragonal zirconia decreased after speed and superspeed sintering (P<.001). Superspeed sintering resulted in a greater color change than speed sintering (P<.001).

CONCLUSIONS

Rapid sintering protocols produced a significant effect on the color and translucency of cubic and tetragonal zirconias.

Effect of translucency of CAD-CAM ceramic restorative materials and scanning aid conditions on the accuracy of intraoral scans

Background/purpose

Subsurface scattering from translucent material would affect the digital scans. This study aimed to evaluate the effect of translucency of ceramic restorative materials and scanning aid conditions on the accuracy of intraoral scans.

Materials and methods

Identical anatomic contour crowns with ten ceramic restorative materials were fabricated: five zirconia, three lithium disilicate glass-ceramic, and two leucite reinforced glass-ceramic. The models with ceramic crowns were digitized with an intraoral scanner (IOS) and analyzed for accuracy (n = 10) with and without a scanning aid. Scan time efficiency was recorded. Square-shaped specimens with 1.0-mm thickness were fabricated with the same materials, and translucency parameter (TP) values were measured. One-way ANOVA, Welch ANOVA, and a post-hoc pairwise comparison or independent t-test were used for trueness and time analysis, and the F-test was used to examine the precision (α = 0.05). Pearson correlation test was conducted.

Results

Significant differences were revealed for trueness with no scanning aid condition and for TP values (P < 0.05). In contrast, no statistically significant differences were observed for trueness with a scanning aid. A strong correlation (r = 0.854, P < 0.01) between TP value and trueness with no scanning aid was revealed. By applying a scanning aid, trueness was improved and scan time efficiency significantly increased (P < 0.05).

Conclusion

The translucency of ceramic restorative materials negatively affects the accuracy of IOS scan without a scanning aid; however, the scan accuracy and time efficiency of IOS scanning for ceramic restorations can be improved by applying scanning aid, and prostheses with high quality without unnecessary labor can be produced.

Intraoral occlusal adjustment time and volume required for CAD/CAM crowns fabricated with different virtual mounting methods (A randomized crossover trial)

OBJECTIVE

To measure the required clinical time and volume of occlusal adjustment when the maxillary cast is positioned in a virtual articulator using one of three methods: digitization of a facebow-mounted mechanical articulator (group A), virtual Bonwill triangle (group B) or a 3D face scan (group F).

MATERIALS AND METHODS

In this randomized, triple-blind, crossover trial; 11 participants were enrolled. Every participant had one molar indicated for a single crown restoration. Three crowns were designed and milled for every participant molar totaling 33 crowns. Each of the three crowns was fabricated with the participant's casts virtually mounted utilizing a different method. An impression was taken of the crown in place before occlusal adjustment. The occlusal adjustment was then performed and timed with the three crowns in the different groups. After the occlusal adjustment, an impression of the adjusted crown was taken. The pre-adjustment and post-adjustment impressions were digitally superimposed and the volume difference was measured. The Kruskal-Wallis test was used to compare the groups.

RESULTS

Group A showed the shortest mean adjustment time (3:44.59 ± 3:39.07) followed by group F (4:30.09 ± 2:01.50) and group B (4:35.30 ± 2:32.33). The mean adjustment volume for group A was (28 ± 19.1 mm³) followed by group F (30.5 ± 18.8 mm³) and group B (40.6 ± 29.5 mm³). Different virtual mounting methods had no statistically significant effect on adjustment time (P-value = 0.538) or adjustment volume (P-value = 0.490).

CONCLUSIONS

A simplified approach in virtual articulator mounting appears to be justified in the construction of a single full-coverage prosthesis. Added labor, time and cost of more elaborate virtual mounting methods seem to be counterproductive.

Accuracy of four recent intraoral scanners with respect to two different ceramic surfaces

OBJECTIVES

To investigate the complete arch accuracy of intraoral scanners (IOS) on two different ceramic surfaces.

METHODS

Two maxillary master cast samples were prepared. The bases of both the master casts were made from zirconium oxide. The difference between the two casts was that the teeth of the [ZR] cast were produced from zirconium oxide and that of the [LD] cast were made of lithium disilicate glass-ceramic. Unlike the zirconia teeth of the [ZR] cast, the lithium disilicate teeth of the [LD] cast were glazed. The two master casts were digitized using a high-resolution scanner (Atos Compact Scan 5 M, GOM GmbH, Braunschweig, Germany) to obtain digital reference casts. Subsequently, each master cast was scanned 15 times using four IOSs. The IOSs were the Cerec Omnicam [OM], Primescan [PR], Trios 4 [TR4], and VivaScan [VS]. On surface comparison, the absolute mean deviation values were obtained for trueness and precision. For multiple comparisons, statistically significant differences were analyzed using one-way ANOVA and the Kruskal-Wallis H test. The p-value was adjusted to control for the increased risk of type I error (p < 0.0083). To compare the two means, the t-test and Mann-Whitney U test were used (p < 0.05).

RESULTS

Trueness values for [ZR] ranged from 24.6 (±6.3) µm for [PR] and 77.1 (±8.3) µm for [OM]. Trueness values for [LD] were between 28.3 (±6.3) µm for [PR] and 72.8 (±15.6) µm for [OM]. Precision values for [ZR] ranged from 17.6 (±3.7) µm for [PR] to 37.3 (±9.9) µm for [OM]. Precision values for [LD] ranged from 17.5 (±3.6) µm for [PR] to 41.8 (±8.7) µm for [OM]. Statistically significant differences were found among all the IOSs (p < 0.0083). The trueness values of the four IOSs did not differ significantly (p < 0.05) with respect to either the [ZR] or [LD] cast. The precision values of [OM] and [VS] differed significantly with respect to the scanned surface.

CONCLUSIONS

Complete arch scans achieved with the four IOSs showed significantly different trueness and precision results. [VS] and [OM] were more sensitive in terms of the scanned material.

CLINICAL SIGNIFICANCE

The latest IOSs showed the required accuracy for complete arch digital impressions in-vitro investigations. These findings should be implemented under conditions relevant to complete arch deviations, such as the construction of occlusal splints, analysis of occlusal relationships, and long-span restorations. Clinicians should be aware that the clinically acceptable threshold varies depending on the purpose of the IOS.

Should finishing, polishing or glazing be performed after grinding YSZ ceramics? A systematic review and meta-analysis

The present systematic review and meta-analysis aimed to assess the characteristics and consequences of post-processing methods after grinding procedures in YSZ ceramics on its surface roughness and flexural strength. The protocol of this review was made prospectively and is available online in the PROSPERO database (link). Literature searches on PubMed/MEDLINE, EMBASE, Lilacs, Web of Science and Scopus were conducted on December 2022 to select in vitro studies written in English, without publishing-date restrictions, that considered surface characteristics and mechanical properties of YSZ ceramics submitted to grinding and subsequent post-processing surface treatments as an attempt to revert the effect induced by grinding. Two authors independently selected the studies, extracted the data and assessed the risk of bias. Mean differences (Rev-Man 5.1, random effects model, α= 0.05) were obtained by comparing flexural strength and surface roughness values of ground surfaces with at least one post-processing surface treatment (global analysis). Subgroup analyses were performed considering the most prevalent categories of post-processing methods. A total of 33 (out of 4032) studies were eligible and included in the analysis. In the global analysis, ground surfaces showed higher flexural strength than when post-processing methodologies were employed (p< 0.0001). The subgroup analysis showed that only polishing was able to enhance the flexural strength after grinding (p= 0.001); however, when other protocols were used, the ground surface was always superior in terms of flexural strength (p< 0.0001). Post-processing techniques in both the global and sub-group analyses were able to reduce the surface roughness after grinding in YSZ ceramics (p< 0.00001). High heterogeneity was found in all the meta-analyses. Concerning the risk of bias analysis, the included studies had mixed scores for the considered factors. In conclusion, in terms of improving flexural strength and restoring surface roughness after grinding, polishing protocols can be considered the best indication as post-processing treatment after YSZ ceramics adjustments/grinding.

Indirect restorative systems-A narrative review

OBJECTIVE

The background and clinical understanding of the properties of currently available indirect restorative systems and fabrication methods is, along with manufacturer and evidence-based literature, an important starting point to guide the clinical selection of materials for tooth and/or implant supported reconstructions. Therefore, this review explores most indirect restorative systems available in the market, especially all-ceramic, along with aspects of manufacturing process, clinical survival rates, and esthetic outcomes.

OVERVIEW

Progressive incorporation of new technologies in the dental field and advancements in materials science have enabled the development/improvement of indirect restorative systems and treatment concepts in oral rehabilitation, resulting in reliable and predictable workflows and successful esthetic and functional outcomes. Indirect restorative systems have evolved from metal ceramics and polymers to glass ceramics, polycrystalline ceramics, and resin-matrix ceramics, aiming to improve not only biological and mechanical properties, but especially the optical properties and esthetic quality of the reconstructions, in attempt to mimic natural teeth.

CONCLUSIONS

Based on several clinical research, materials, and patient-related parameters, a decision tree for the selection of indirect restorative materials was suggested to guide clinicians in the rehabilitation process.

CLINICAL SIGNIFICANCE

The pace of materials development is faster than that of clinical research aimed to support their use. Since no single material provides an ideal solution to every case, professionals must continuously seek information from well designed, long-term clinical trials in order to incorporate or not new materials and technological advancements.