Ceramics in dentistry: historical roots and current perspectives

Influence of additives and binder on the physical properties of dental silicate glass-ceramic feedstock for additive manufacturing

OBJECTIVES

The aim of the study was to investigate the impact of organic additives (binder, plasticizer, and the cross-linking ink) in the formulation of water-based feedstocks on the properties of a dental feldspathic glass-ceramic material developed for the slurry-based additive manufacturing technology "LSD-print."

MATERIAL AND METHODS

Three water-based feldspathic feedstocks were produced to study the effects of polyvinyl alcohol (AC1) and poly (sodium 4-styrenesulfonate) (AC2) as binder systems. A feedstock without organic additives was tested as the control group (CG). Disc-shaped (n = 15) and bar (n = 7) specimens were slip-cast and characterized in the green and fired states. In the green state, density and flexural strength were measured. In the fired state, density, shrinkage, flexural strength (FS), Weibull modulus, fracture toughness (KIC), Martens parameters, and microstructure were analyzed. Disc-shaped and bar specimens were also cut from commercially available CAD/CAM blocks and used as a target reference (TR) for the fired state.

RESULTS

In the green state, CG showed the highest bulk density but the lowest FS, while the highest FS in the green state was achieved with the addition of a cross-linking ink. After firing, no significant differences in density and a similar microstructure were observed for all slip-cast groups, indicating that almost complete densification could be achieved. The CAD/CAM specimens showed the highest mean FS, Weibull modulus, and KIC, with significant differences between some of the slip-cast groups.

SIGNIFICANCE

These results suggest that the investigated feedstocks are promising candidates for the slurry-based additive manufacturing of restorations meeting the class 1a requirements according to DIN EN ISO 6871:2019-01.

A comparative evaluation of the variations on the shades of pressable ceramic system with the layering technique after different number of firing cycles: An in vitro study

AIM

The main aim of the present study was to compare and evaluate the effect of repetitive firings on different shades of a pressable all ceramic system layered with veneering porcelain.

SETTING AND DESIGN

In-vitro comparative study.

MATERIALS AND METHODS

An in vitro comparative study was conducted, and a total of 60 disc shaped specimens (15 mm in diameter and 0.8 mm in thickness) were made of heat pressed ceramic of shades A2, A3, and B2 (20 discs of each shade) grouped as Group I, II, and III, respectively, using the lost wax technique. The discs were subsequently layered with veneering porcelain followed by glazing and overglazing and underwent a firing cycle at each step until six times combined. CIE L*a*b* measurements were noted on each sample after the third, fourth, fifth, and sixth firing using VITA Easyshade Advance 4.0 spectrophotometer.

STATISTICAL ANALYSIS USED

Statistical Analysis was done by SPSS 17.0 software. One way analysis of variance, multiple comparisons using the Tukey test, and descriptive statistical analysis were done for all the groups in the study. P <0.05 was statistically significant.

RESULTS

The mean color differences for the repeated firings were imperceptible (ΔE <1.67) to the human eye for all ceramic samples tested except between the fourth and fifth firing of Group II (shade A3).

CONCLUSION

The analysis revealed that although repeated firings lead to changes in L*, a*, and b* values, the mean color difference was below the clinically acceptable color change (ΔE <3.7).

Materials and Methods for All-Ceramic Dental Restorations Using Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) Technologies-A Brief Review

The materials used in dentistry for the fabrication of all-ceramic restorations have undergone great and rapid developments over the last two decades. Among the most common ceramic materials in dentistry are those based on zirconium and lithium disilicate. Due to the properties of these materials, they are in great demand in the field of dental restoration production. Thus, dental restorations that will use those materials are commonly machined in CAD/CAM systems, which offer the possibility of manufacturing all-ceramic dental restorations in a very short period of time. This article reviews the modern materials in the field of all-ceramic dental restorations, their manufacturing processes, as well as what determines which ceramic materials are used for the production of CAD/CAM blanks and their production technology.

Effect of Hydrothermal Degradation on Flexural Fatigue Strength of Various Cubic-Containing Translucent Zirconia

OBJECTIVE

 The aim of this study is to investigate the fatigue and hydrothermal degradation behavior among the cubic-containing translucent yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP).

MATERIALS AND METHODS

 Four groups of commercial Y-TZP (T, ST, XT, and P), containing different amount of cubic crystal, were examined. Artificial aging was accomplished by autoclaving at 122°C under 2 bar pressure for 8 hours. Fatigue simulation parameters were set using an axial 50 N load, a total of 240,000 cycles. Flexural fatigue strength was evaluated.

STATISTICAL ANALYSIS

 Two-way analysis of variance with Tukey's honestly significant difference test was used to determine the difference in fatigue strength values between various type of zirconia materials within control and aging with a significant level of 5%. Weibull analysis was conducted on the fatigue strength data.

RESULTS

 All groups showed the mean flexural fatigue strength had no significant difference in hydrothermally aged specimens compared with specimens without aging (p = 0.154). Group T showed significantly higher flexural fatigue strength followed by group ST, XT, and P. Group XT and P showed no significant difference in strength value (p > 0.05). Group T demonstrated a lower probability of failure than group ST, XT, and P whether with or without aging. Weibull modulus in group T and ST with aging condition was increased and higher than all the experimental groups.

CONCLUSION

 Cubic-containing zirconia materials (group ST, XT, and P) exhibited lower flexural fatigue strength than non-cubic 3Y-TZP zirconia (group T). However, various cubic-containing translucent zirconia was assumed to have high resistance to hydrothermal degradation.

The Influence of Hydrofluoric Acid Temperature and Application Technique on Ceramic Surface Texture and Shear Bond Strength of an Adhesive Cement

All-ceramic restorations are the foundation of modern esthetic dentistry. Clinical approaches for preparation, durability, aesthetics, and repair have been reformed by the idea of adhesive dentistry. The aim of the study and the objective question was to evaluate the impact of heated hydrofluoric acid pretreatment and the application technique's influence on the surface morphology and roughness of leucite-reinforced glass-ceramic materials (IPS Empress CAD, Ivoclar Vivadent), which is fundamental for understanding the adhesive cementation process. Scanning electron microscopy was used to observe the effectiveness of the two HF (Yellow Porcelain Etch, Cerkamed) application techniques and the HF's temperature impact on the surface topography of the ceramic. Based on surface conditioning methods, the adhesive cement (Panavia V5, Kuraray Noritake Dental Inc., Tokyo, Japan) was applied to the conditioned ceramic samples and light-cured. Shear bond strength values were correlated with the micro-retentive surface texture of the ceramic. With universal testing equipment at a 0.5 mm/min crosshead speed, SBS values between the resin cement and the ceramic material were assessed until failure. Analyzing the fractured surfaces of the specimens by digital microscopy, the failure modes were divided into three categories: adhesive, cohesive, and mixed failure. Analysis of variance (ANOVA) was used to statistically analyze the collected data. The results show that alternative treatment methods affected the material's surface characteristics and have an influence on the shear bond strength.

An investigation on fatigue, fracture resistance, and color properties of aesthetic CAD/CAM monolithic ceramics

OBJECTIVES

To evaluate and compare fracture resistance, translucency, and color reproducibility, as well as the effect of aging on the fracture load and color stability of novel monolithic CAD/CAM ceramics.

MATERIALS AND METHODS

One hundred crowns of uniform thickness were milled from five ceramic blocks (n = 20): partially crystallized lithium disilicate (PLD) and fully crystallized lithium disilicate (FLD), lithium metasilicate (LMS), 4Y-TZP (SMZ), and 5Y-TZP (UMZ) monolithic zirconia. PLD crowns were glazed, LMS was fired, and FLD was polished. SMZ and UMZ crowns were sintered and polished. Crowns were adhesively cemented to epoxy dies. Half of the crowns (n = 10) were subjected to 1.200.000 load cycles with thermal cycling. Color space values L, a, b defined by the Commission Internationale de l´Eclairage (CIELAB) were measured before and after aging, and (∆E) was calculated. Both aged and non-aged specimens were loaded until fracture in a universal testing machine and the fracture load was recorded. X-ray diffraction (XRD) and scanning electron microscope (SEM) fractographic analysis were carried out on fractured fragments of representative samples. For translucency and color reproducibility, 50 rectangular-shaped specimens were fabricated and processed as described previously. Color values were measured over black and white backgrounds, and the translucency parameter (TP) was computed. Using the shade verification mode, (∆E) to shade A3 was calculated. Data were statistically analyzed using one-way and two-way ANOVA, and t-test.

RESULTS

Aging did not affect fracture resistance significantly (p > 0.05). The highest mean fracture load was obtained for the SMZ and UMZ. A significant color change was observed after aging in all groups. The highest TP was noted for FLD. SMZ and UMZ had the best shade match.

CONCLUSIONS

Zirconia showed higher fracture resistance and color stability than lithium silicate ceramics. Lithium silicate ceramics were more translucent. The experimental FLD demonstrated high translucency.

CLINICAL RELEVANCE

Tested ceramics showed sufficient stability to withstand masticatory forces. Characterization of final restorations might be mandatory for better color match.

Pre-cementation treatment of glass-ceramics with vacuum impregnated resin coatings

OBJECTIVE

The study aimed to investigate the effectiveness of a vacuum impregnation process to eliminate the porosity at the ceramic-resin interface to optimize the reinforcement of a glass-ceramic by resin cementation.

METHODS

100 leucite glass-ceramic disks (1.0 ± 0.1 mm thickness) were air-abraded, etched with 9.6 % HF acid, and silanated. Specimens were randomly allocated to 5 groups (n = 20). Group A received no further treatment (uncoated control). Groups B and D were resin-coated under atmospheric pressure, whereas groups C and E were resin-coated using vacuum impregnation. The polymerized resin-coating surfaces of specimens in groups B and C were polished to achieve a resin thickness of 100 ± 10 µm, while in groups D and E no resin-coating modification was performed prior to bi-axial flexure strength (BFS) determination. Optical microscopy was undertaken on the fracture fragments to identify the failure mode and origin. Comparisons of BFS group means were made by a one-way analysis of variance (ANOVA) and post-hoc Tukey test at α = 0.05.

RESULTS

All resin-coated sample groups (B-E) showed a statistically significant increase in mean BFS compared with the uncoated control (p < 0.01). There was a significant difference in BFS between the ambient and vacuum impregnated unpolished groups (D and E) (p < 0.01), with the greatest strengthening achieved using a vacuum impregnation technique.

SIGNIFICANCE

Results highlight the opportunity to further develop processes to apply thin conformal resin coatings, applied as a pre-cementation step to strengthen dental glass-ceramics.

Effect of crystal orientation on flexural strength of pressable lithium disilicate glass-ceramics

This study examined the crystal orientation of four kinds of pressable lithium disilicate glass-ceramics and evaluated the effect of crystal orientation on flexural strength. Bar-shaped (24 mm in length, 1.2 mm in thickness, 4.0 mm in width), disk-shaped (12 mm in diameter, 0.5 mm in thickness), and crown-shaped (maxillary first molar) specimens were prepared according to the manufacturer's instructions. Three-point and biaxial flexural strengths were measured for bar- and disk-shaped specimens. Microstructure analysis was performed using X-ray diffractometry and scanning electron microscopy. Three-point flexural strength was improved by parallel crystal orientation along the longitudinal direction of the bar-shaped specimen. There was no relationship between two-dimensional crystal orientation and biaxial flexural strength. The results of this study assumed that biaxial flexural strength was improved by the crystal orientation in the cross-sectional direction. Pressed restorations are expected to possess higher strength than milled restorations due to their crystal orientation.

Influence of Thickness of Opaque Porcelain and Alloy Color on the Final Color of Porcelain-Fused-to-Metal Restorations

Despite the advent of metal-free solutions, porcelain-fused-to-metal restorations (PFM) are still widely used. Particularly for the latest ceramic systems, scarce information is present in the scientific literature about the ideal opaque layer thickness and the alloy color impact to achieve the desired final color of PFM restorations. This study aimed to evaluate the influence of opaque thickness variation layered on different metal alloys on the final color of PFM restorations. Opaque porcelain of one metal−ceramic system (VITA VM13) was layered in four different thicknesses (0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm) on three differently colored dental alloys: a gold−platinum alloy (yellowish), a gold−palladium alloy (light grayish), and a nickel−chromium alloy (dark grayish). The veneering porcelain layered over the opaque was kept constant (Base Dentine 0.45 mm, Transpa Dentine 0.50 mm, and Enamel 0.20 mm). Sixty specimens were fabricated, five samples for each combination of alloy/opaque thickness. The color difference (ΔE) between specimen and reference was measured using a clinical spectrophotometer. The two-way ANOVA revealed that the thickness of both the opaque (p < 0.001) and the metal alloy (p < 0.001) significantly influenced the ΔE values. Gray-colored alloys covered by a 0.10 mm thick opaque layer enabled the closest color match, whereas this occurred for yellow-color alloys covered by a 0.15 mm thick opaque layer. In contrast, the samples covered by a 0.25 mm thick opaque layer obtained the worst ΔE.

Influence of ZrO2 Nanoparticle Addition on the Optical Properties of Denture Base Materials Fabricated Using Additive Technologies

This study investigated the translucency of 3D-printed denture base resins modified with zirconium dioxide nanoparticles (ZrO₂NPs) under thermal cycling. A total of 110 specimens were fabricated and divided into 3 groups according to the materials, i.e., heat-polymerized resin, and 3D-printed resins (NextDent, and ASIGA). The 3D-printed resins were modified with 0, 0.5, 1, 3, and 5 wt.% of ZrO₂NPs. All the specimens were subjected to 5000 thermal cycles. The translucency was measured using a spectrophotometer. The results showed that the heat-polymerized resin had considerably higher translucency than the 3D-printed resins. Compared to the unmodified group, the translucency decreased significantly after adding 5% ZrO₂NPs to NextDent and 3% ZrO₂NPs to ASIGA resins. The highest translucency was achieved for NextDent by adding 0.5% ZrO₂NPs and for ASIGA without any ZrO₂NPs. It was found that the average concentration level in ASIGA was significantly higher than that in NextDent. These findings revealed that 3D-printed resins have lower translucency than heat-polymerized acrylic resin, and adding ZrO₂NPs at low concentrations did not affect the translucency of the 3D-printed resins. Therefore, in terms of translucency, 3D-printed nanocomposite denture base resins could be considered for clinical applications when ZrO₂NPs are added at low concentrations.

Factory Crystallized Silicates for Monolithic Metal-Free Restorations: A Flexural Strength and Translucency Comparison Test

Flexural strength (FS) and translucency (Contrast Ratio-CR) of three different factory crystallized silica-based glass ceramics, Celtra Duo (CD), N!ce (NI) and Li-Si Block, a lithium disilicate, IPS e.max CAD (LD), and a leucite-reinforced feldspathic ceramic, Empress CAD (EM), in two different translucencies (HT and LT) for use in chairside dental restorations have been compared. CAD blocks of the materials were cut into beams and tiles and processed following manufacturers’ instructions. The beams were tested (3-PBT) to determine flexural strength, Weibull characteristic strength, and Weibull modulus; and tiles were tested to determine CR. All data were statistically analyzed. In addition, SEM analysis of the materials was performed. Differences in flexural strength (FS) and translucency (CR) between the materials were found to be statistically significant. FS decreased as follows (MPa): LDHT 350.88 ± 19.77 (a) = LDLT 343.57 ± 18.48 (a) > LSLT 202.15 ± 17.41 (b) = LSHT 196.93 ± 8.87 > NIHT 186.69 ± 13.06 (c) = CDLT 184.73 ± 13.63 (c) = CDHT 174.15 ± 21.76 (c) = NILT 172.12 ± 11.98 (c) > EMHT 131.16 ± 13.33 (e) = EMLT 127.65 ± 11.09. CR decreased as follows (mean ± sd): CDLT 74.1 ± 1.1 (a); LSLT 74.0 ± 1.1 (ab); NILT 73.3 ± 0.8 (ab); EMLT 73.0 ± 1.5 (ab); NIHT 72.4 ± 1.0 (bc); LDLT 71.3 ± 1.1 (bc); LTHT 65.2 ± 0.9 (de); LSHT 63.8 ± 1.1 (def); EMHT 636 ± 1.2 (ef); CDHT 62.2 ± 0.8 (f). Our findings show that factory-crystallized lithium silicate glass ceramics fulfill ISO standards for Classes 1 and 2. Therefore, they can be considered viable alternatives to produce single-unit restorations with a chairside procedure not requiring thermal treatment.

Current Protocols for Resin-Bonded Dental Ceramics

Resin-bonded ceramic restorations are common treatment options. Clinical longevity of resin-bonded ceramic restorations depends on the quality and durability of the resin-ceramic bond. The type and composition of the specific ceramic determines the selection of the most effective bonding protocol. Such protocol typically includes a surface pretreatment step followed by application of a priming agent. Understanding of fundamental ceramic properties and chemical compositions enables the clinician to make proper material selection decisions for clinically successful and long-lasting restorations. Based on research accrued over the past decades, this article reviews and discusses current resin-bonding protocols to most commonly used dental ceramics.

Effect of yellow anodization of titanium on the shade of lithium disilicate ceramic with different thicknesses

STATEMENT OF PROBLEM

The color of the titanium abutment can affect the shade of the definitive restoration. Methods such as anodic oxidation, which changes the gray color of implant abutment to yellow, have been advocated to mask the unesthetic gray color of the abutment. However, whether a yellow anodized titanium abutment can prevent discoloration of translucent ceramic restorations is uncertain.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of the yellow anodization of titanium on the shade of lithium disilicate ceramic with different thicknesses by using CIEDE 2000 formulas.

MATERIAL AND METHODS

Sixty grade V titanium backgrounds were fabricated and divided into 2 test groups (n=30): group A was anodized to a yellow color, and group U was unanodized. Each group was subdivided into 3 subgroups (n=10) according to the thickness of the lithium disilicate ceramic cemented over it: subgroup 1 with 1-mm-thick lithium disilicate, subgroup 1.5 with 1.5-mm-thick lithium disilicate, and subgroup 2 with 2-mm-thick lithium disilicate. Each titanium background was cemented to its corresponding lithium disilicate block by using translucent resin cement. For the control group, 5-mm-thick lithium disilicate specimens were fabricated. Color measurements of the specimens were made with a spectrophotometer, and differences were calculated by using CIEDE 2000 formulas (ΔE₀₀). Comparisons between the 2 study groups were done by using independent samples t test. Two-way ANOVA was used to assess the effect of anodization and thickness on ΔE₀₀ with calculation of adjusted means and 95% confidence intervals (α=.05).

RESULTS

Statistically significant differences were found among the mean values between yellow anodized and unanodized groups in all ceramic thicknesses (P<.001 for 1 mm, P<.001 for 1.5 mm, and P<.046 for 2 mm). Yellow anodization of titanium and increasing the ceramic thickness from 1 to 2 mm decreased the ΔE₀₀ values.

CONCLUSIONS

The restoration shade appeared to be improved by titanium anodization to a yellow color and by increasing the thickness of the machinable high-translucent lithium disilicate.

TiO2 nanoparticles added to dense bovine hydroxyapatite bioceramics increase human osteoblast mineralization activity

OBJECTIVES

This study evaluated the effect of TiO₂ nanoparticles + dense hydroxyapatite (HA) on human osteoblast cells (SAOS-2).

METHODS

Particulate bovine HA powder with or without the addition of either 5 or 8 % TiO₂ (HA, HA/TiO₂Np5 % or HA/TiO₂Np8 %) were pressed into disks (Ø = 12.5 mm; thickness = 1.3 mm) uniaxially (100 MPa) and isostatically (200 MPa/1 min) and sintered at 1300 °C. Y-TZP disks were used as control. The following tests were performed: Scanning Electron Microscopy and Dispersive Energy Spectroscopy (SEM/EDS), Atomic Force Microscopy (AFM), cell viability assay (Alamar Blue-AB) and mineralized matrix deposition (Alizarin Red-AR). AB and AR data were submitted to 2-way ANOVA/Tukey tests and ANOVA/Tukey tests, respectively.

RESULTS

SEM revealed that the surface of HA/TiO₂Np5% resembles DPBHA surface, but also contains smaller granules. HA/TiO₂Np8% characteristics resembles HA/TiO₂Np5% surface, but with irregular topography. Y-TZP showed a typical oxide ceramic surface pattern. EDS revealed Ca, O, and P in all samples. C, O, and Zr appeared in Y-TZP samples. AFM data corroborates SEM analysis. AB test revealed excellent cellular viability for HA/TiO₂Np5% group. AR test showed that all groups containing TiO₂np had more mineralized matrix deposition than all other groups, with statistically differences between HA/TiO₂Np8% and HA cultivated in non-osteogenic medium. Culture in osteogenic medium exhibited much more mineralized matrix deposition by TiO₂np groups.

SIGNIFICANCE

In conclusion, the addition of TiO₂np showed chemical, superficial, and biological changes in the reinforced materials. HA/TiO₂Np5% showed the best results for cell viability and HA/TiO₂Np8% for mineralized matrix deposition.

Digital image analysis of fluorescence of ceramic veneers with different ceramic materials and resin cements

The objective of this study was to analyze the effect of the type of ceramics and resin cements on the fluorescence of ceramic veneers under the 405 nm UV-light by digital imaging. One hundred and ninety-two veneers were fabricated using three types of ceramics (IPS e.max CAD, IPS Empress CAD, and Zenostar). Eight pieces of substrates were made of resin-nano-ceramic (Lava Ultimate). The level of fluorescence for each sample cemented with the substrate using three kinds of resin cements (RelyX U200, Variolink N, and Choice 2) was analyzed by using histogram data of luminosity from Adobe Photoshop software. Furthermore, the fluorescence values were evaluated by two-way ANOVA and Tukey's test. The highest fluorescence values were observed for the IPS e.max CAD cemented with Choice 2 cement, followed by IPS Empress CAD, and Zenostar the lowest. The final fluorescence intensity of ceramic veneer is affected by ceramic materials and resin cements.

Color alteration with ceramic veneers according to the tooth type and preparation step: A clinical analysis

STATEMENT OF PROBLEM

Achieving accurate tooth color is important in esthetic dental treatments; however, clinical studies evaluating how ceramic veneer procedures affect color alterations are lacking.

PURPOSE

The purpose of this clinical study was to assess the color alteration during treatment with ceramic veneers and to correlate these changes with the tooth treated and veneer thickness.

MATERIAL AND METHODS

Ten patients who underwent esthetic treatment were enrolled as participants. Color analysis with the VITA spectrophotometer was performed at baseline, after tooth preparation, immediately after cementation (Final 1), and after 6 to 12 months of follow-up (Final 2). Data of L∗, a∗, b∗, shade guide unit (SGU), ΔEab, ΔE00, and variation in SGU (ΔSGU) were obtained. Thickness of the veneer was also recorded. Each participant was considered as a statistical block, and the mean results for each tooth (maxillary central incisors, lateral incisors, and canines) were presented. Data were evaluated by the mixed model for repeated measures and Tukey-Kramer post hoc test (L∗, a∗, b∗), generalized linear models (thickness, ΔEab, ΔE00, SGU), Friedman test (ΔSGU), and the Pearson test was used to correlate veneer thickness and color change (ΔEab, ΔE00, ΔSGU) (α=.05).

RESULTS

Among the teeth treated, no differences were found in ceramic thicknesses. The mean thickness was 1.03 mm for central incisors, 0.96 for lateral incisors, and 0.89 for canines. The b∗ values increased significantly after preparation and decreased after cementation (P<.001). For ΔEab, ΔE00, and ΔSGU, there was no statistically significant difference between the types of tooth at each respective time of analysis (P>.05). Regardless of the tooth, a decrease in the SGU score was detected after cementation (P=.015). After tooth preparation, there was significant correlation (P<.05) between ceramic thickness and ΔSGU (r=0.36).

CONCLUSIONS

Treatment with ceramic veneers resulted in color change, mainly with respect to the b∗ axis (yellow), producing objective differences in the ΔE analysis. Although ceramic thickness correlated with the VITA scale change (ΔSGU) after tooth wear or preparation, ceramic thickness did not differ among tooth types and did not correlate with changes in color parameters after cementation. (P>.05).

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

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.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-022-04611-w.

Full Digital Workflow in the Esthetic Dental Restoration

This case report presented a fully digital workflow in esthetic dental restoration. A 51-year-old female patient was referred to BDMS Wellness Clinic due to a fracture of the maxillary left central incisor. An immediate dental implant was planned to restore tooth 21 with esthetic crown lengthening of upper front teeth and new zirconia crowns for teeth 11, 12, 13, 21, 22, and 23. Digital impression was made using a digital scanner (PRIMESCAN®, Dentsply Sirona, Bensheim, Germany); surgical guide (Cerec Guide 3, Dentsply Sirona, Bensheim, Germany) was designed by using a designing software (Galileos Software, Dentsply Sirona, Bensheim, Germany) and was milled by using a milling machine (MCXL milling machine, Dentsply Sirona, Bensheim, Germany) to create a precise surgical guide. 3D smile design was done by using the Digital Smile Design (DSD) program, the crown lengthening guide was designed according to DSD designed by using a designing software (Inlab 19 Software, Dentsply Sirona, Bensheim, Germany), and the guide was fabricated by a 3D printer (FormLabs Form 2, Formlab, MA, USA). Provisional crowns (splinted) for teeth 11, 12, 13, 21, 22, and 23 were milled by using polymer (VIPI BLOCK TRILUX®, VIPI Industria, Pirassununga, SP, Brazil) using a milling machine (MCX5, Dentsply Sirona, Bensheim, Germany). The zirconia crowns were designed by using software (Inlab19 Software, Dentsply Sirona, Bensheim, Germany) and milled using the same milling machine. At the implant position, Ti-base is cemented by using an abutment (Multilink Hybrid Abutment, Ivoclar Vivadent, Schaan, Lichtenstein, Germany) with zirconia coping (Cercon base white shade, Dentsply Sirona, Bensheim, Germany) utilized as the abutment. The zirconia crowns (Cercon Xt, Dentsply Sirona, Bensheim, Germany) were sintered and characterized and then cemented. The patient was satisfied with the esthetic outcome of the treatment.

Translucency of a Dental Porcelain Mixed by Two Ceramic Slurry Methods: A Bayesian Comparison

Background

The ceramics industry produces porcelain pastes using a controlled ratio of water and porcelain powder. Two methods are used to produce a dental porcelain paste: one-step mixing or incremental mixing.

Objective

To evaluate the optical properties of a feldspathic dental ceramic using two different ceramic paste preparation methods using a Bayesian approach.

Materials and Methods

Two groups of feldspathic porcelain discs, an incremental mixing group (n = 40) and a one-step mixing group (n = 40), were assessed. Groups were evaluated using spectrophotometry, and the translucency parameter (TP) of each sample was calculated. Surfaces were characterized by AFM and SEM. Statistical analysis was performed using a Bayesian approach.

Results

Translucency parameter values of the incremental mixing group ranged from 1.65 to 3.41, while values for the one-step mixing group ranged from 3.62 to 5.74, this difference being statistically significant. The lowest roughness was obtained on the surface of discs in the one-step mixing group.

Conclusions

Feldspathic porcelain with lower translucency and higher roughness was obtained using the incremental mixture method.

Evaluation of marginal adaptation and microleakage of differant all-ceramic porcelain systems

ABSTRACT Purpose: This study evaluated the marginal adaptation and microleakage of the İn-Ceram Alumina, In-Ceram Zirconia and Finesse press all-ceramic porcelain systems. Material and methods: Thirty maxillary Central teeth extracted for periodontal reasons without caries and cracks were divided equally into three group and there was no control group; only the three systems were compared. Sample teeth cemented were stored in distile water for 24 hours. Then, they were applied to a repeated thermal cycle for 500 times. The samples were left in %5 of basic fuchsin dye for 24 hours. For the marginal adaptation rankings, all of the sample teeth for which cross-sections were made were moved into the metal microscope (Scherr Turico St. James/ Minn./ USA) and the marginal adaptation degrees were measured in both the palatinal and vestibul regions by measuring twice with x10 enlargement at micron level. For the statistical evaluations of marginal adaptation and microleakage values, Kruskal Wallis test has been used (p>0.05). Results: The differences between the three all-ceramic porcelain systems are not significant (p>0.05), α=0.05). Conclusion: The Finesse porcelain system caused the least leakage in both regions. In second place in both regions was In-Ceram Alumina, In-Ceram Zirconia caused the most leakage in both regions. The biggest margin gap in the palatal region was seen in the Finesse porcelain system, In-Ceram Zirconia in second place. The least marginal gap was caused by the In- Ceram Alumina porcelain system.

Ceramic Toughening Strategies for Biomedical Applications

Aiming at shortage of metal materials, ceramic is increasingly applied in biomedicine due to its high strength, pleasing esthetics and good biocompatibility, especially for dental restorations and implants, artificial joints, as well as synthetic bone substitutes. However, the inherent brittleness of ceramic could lead to serious complications, such as fracture and disfunction of biomedical devices, which impede their clinical applications. Herein, several toughening strategies have been summarized in this review, including reinforcing phase addition, surface modification, and manufacturing processes improvement. Doping metal and/or non-metal reinforcing fillers modifies toughness of bulk ceramic, while surface modifications, mainly coating, chemical and thermal methods, regulate toughness on the surface layer. During fabrication, optimization should be practiced in powder preparation, green forming and densification processes. Various toughening strategies utilize mechanisms involving fine-grained, stress-induced phase transformation, and microcrack toughening, as well as crack deflection, bifurcation, bridging and pull-out. This review hopes to shed light on systematic combination of different toughening strategies and mechanisms to drive progress in biomedical devices.

Wear Behavior of Different Generations of Zirconia: Present Literature

Objective. The wear behavior of the novel zirconia generation is less well understood and may be affected by compositional modifications compared to the conventional zirconia. Materials and Methods. Combinations of keywords such as “zirconia,” “high translucent,” and “wear” were searched in PubMed and Google Scholar databases up to May 2021. The total of 23 relevant articles was selected according to inclusion criteria. Results. Reports show comparable wear resistance of translucent zirconia to the conventional zirconia despite an increased cubic phase content and lower mean flexural strength. A meticulously polished surface creates the lowest surface roughness, producing favorable zirconia wear resistance and antagonist wear compared to a glazed surface. In comparison to other ceramic materials, zirconia produces the least wear on an enamel antagonist and almost undetectable wear when opposed by zirconia. Wear when paired against resin materials yields a favorable outcome, whereas wear behavior against a metal antagonist varies with the surface hardness of the metal. Conclusions. All zirconia generations are considered wear-friendly to all types of antagonists. Nonetheless, comparative studies on antagonist wear opposing zirconia of different compositions are still limited and further investigation is required.

Surface Roughness and Translucency of Various Translucent Zirconia Ceramics after Hydrothermal Aging

OBJECTIVE

 This study investigated the effect of hydrothermal aging on surface roughness and translucency of various translucent zirconia materials.

MATERIALS AND METHODS

 Four types of zirconia were tested. Group 1 was translucent zirconia with no cubic structure. Group 2, 3, and 4 included cubic-containing zirconia with different amounts of cubic structures (less than 30%, 30-50%, and more than 50%, respectively). Each group contained 15 disk-shape specimens with dimensions of 15 mm in diameter and 1 mm in thickness. As-sintered surface roughness, translucency parameter, and contrast ratio were evaluated in the two different sessions, before and after aging.

STATISTICAL ANALYSIS

 Two-way repeated measures ANOVA with Bonferroni test was used to analyze statistically significant difference in those tested parameters. Phase structure before and after aging was analyzed by X-ray diffraction analysis (XRD).

RESULTS

 Groups 1 and 2 showed significant increased surface roughness after aging while groups 3 and 4 showed no alteration of surface. There was no effect of aging on translucency in all groups. After aging, group 1 and 2 presented monoclinic structure (16.63 and 5.01%, respectively).

CONCLUSION

 Hydrothermal aging caused phase transformation and increasing surface roughness in group 1 and 2 but did not affect translucency in all groups.

The Effect of Translucency and Surface Treatment on the Flexural Strength of Aged Monolithic Zirconia

Aims

This in vitro study aimed to evaluate the effect of the degrees of translucency in different types of monolithic zirconia as well as the aging and surface treatment with airborne particle abrasion on the flexural strength of monolithic zirconia.

Materials and Methods

Sixty bar-shaped specimens were fabricated from three different types of presintered monolithic zirconia (n = 20 per group) including low translucent (LT) (DD Bio ZW iso, high strength zirconia, Dental Direkt, Germany), high translucent (HT) (DD Bio ZX² 98, high translucent zirconia, Dental Direkt, Germany), and multilayered system (ML) (DD cubeX2®ML, multilayer, cubic zirconia system, Dental Direkt, Germany). Each monolithic zirconia group was equally subdivided according to be either air-abraded with 110 µm aluminium oxide particles or left untreated (control). After thermocycling, the flexural strength was measured by using a universal testing machine. Two-way ANOVA followed by Tukey's post hoc and independent samples t-test were used for the statistical analyses (P < 0.05).

Results

Surface treatment and types of zirconia were found to have a significant interaction (P = 0.010). Having controlled the effect of surface treatment, the flexural strength of HT and LT zirconia was found to be significantly higher than the ML zirconia system (P ≤ 0.001). Airborne particle abrasion could significantly decrease the flexural strength of monolithic zirconia only in ML zirconia (P = 0.002).

Conclusions

Multilayered zirconia system had the lowest flexural strength among all groups. Moreover, the flexural strength of this system was attenuated by surface treatment with airborne particles abrasion.

Faculty versus Student Repeatability on Evaluating Translucency of the Anterior Dentition

The objective was to compare the repeatability between dental faculty, whose clinical practice was primarily restorative dentistry, and final year dental students in categorizing the inherent translucency of images selected at random using either a 3- or 7-point scale (translucent to opaque). Digital images of anterior dentition were randomly selected based on inherent translucency. Thirty images (five were repeated) were randomized and categorized by 20 dental students and 20 faculty on their inherent translucency. Statistical analysis was performed using an F test for analysis of variance at 95% confidence interval. A covariance parameter estimate (CPE) was accomplished to compare the inter-rater variability of the dental faculty and dental students. Statistically, more variability occurred between Slides (CPE of 0.185 (p = 0.001)) and between Subject and Slide (CPE of 0.122 (p = 0.0002)) than within subjects (CPE of 0.021 (p = 0.083)). Viewing repeat Slides, Students (CPE = 0.16) were more consistent (p < 0.05) than faculty (CPE = 1.8) using the 3- point scale, while the CPE was the same (CPE = 0.669) using 7-point scale. Dental students and faculty were consistent using the 7-point scale to judge repeat slides, while dental students in this limited pilot study were more consistent when viewing a repeat slide using the 3-point scale.

The Flexural Strength and Flexural Modulus of Stereolithography Additively Manufactured Zirconia with Different Porosities

PURPOSE

Additive manufacturing (AM) technologies are capable of fabricating complex geometries with different porosities. However, the effect of such porosities on mechanical properties of stereolithography (SLA) AM zirconia with different porosities is unclear. The purpose of this in vitro study was to investigate the mechanical properties namely flexural strength, and flexural modulus of AM zirconia with different porosities.

MATERIALS AND METHODS

A bar (25 × 4 × 3 mm) for flexural strength test (ISO standard 6872/2015) was designed by CAD software program and standard tessellation language (STL) file was obtained. The STL file was used to fabricate a total of 80 bars in four groups. Three experimental groups each containing 20 samples were manufactured using an SLA ceramic printer (CeraMaker 900; 3DCeram Co) and zirconia material (3DMix ZrO₂ paste; 3DCeram Co) with different sintering post processing to achieve different porosities including 0%-porosity (AMZ0), 20%-porosity (AMZ20), and 40%-porosity (AMZ40). The same STL file was used for subtractive manufacturing or milling of 20 zirconia bars as control group (CNCZ) with the same dimensions using a commercial zirconia. Three-point bending tests were performed for all groups following ISO standard 6872/2015 specification using a universal testing machine. Outcomes measured included load at fracture, mean flexural strength, and flexural modulus and they were compared across the experimental groups using a one-way ANOVA. Post hoc pair wise comparison between each pair of the groups were performed using Tukey test.

RESULTS

There was a significant difference between the four groups, in terms of fracture load, flexural strength and flexural modulus using one-way ANOVA. AM zirconia with 0% porosity (AMZ0) showed the highest value for fracture load (1132.7 ± 220.6 N), flexural strength (755.1 ± 147.1 MPa) and flexural modulus (41,273 ± 2193 MPa) and AM zirconia with 40% porosity (AMZ40) showed the lowest fracture load (72.13 ± 13.42 N), flexural strength (48.09 ± 8.95 MPa) and flexural modulus (7177 ± 506 MPa). Tukey's pairwise comparisons detected a significant difference between all the possible pairs for all variables except flexural modulus between AMZ0 and CNCZ. The Weibull moduli presented the lowest value for AMZ20 (4.4) followed by AMZ40 (6.1), AMZ0 (6.1), and the highest value was for CNCZ (8.1).

CONCLUSION

AM zirconia with 0% porosity showed significantly higher flexural strength and flexural modulus when compared to milled and AM zirconia with 20% and 40% porosities.

Optical Properties and Color Stability of Denture Teeth-A Systematic Review

PURPOSE

To systematically review past studies to determine the effect of various solutions on the color of denture teeth, thus answering the question in regards to which type of denture teeth has the best optical properties after exposure to various solutions. The method of measuring the color of artificial teeth was also evaluated as a secondary outcome.

MATERIALS AND METHODS

A search of studies that quantitatively investigated the influence of immersion solutions on the color change of denture teeth was conducted. Ovid MEDLINE, PubMed and Scopus databases were searched from 1997 to April 2021. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used during article selection. Data regarding the effect of immersion solutions, accelerated aging and surface treatments on color change were gathered. Methodologies used to assess optical properties were also summarized and compared. The modified CONSORT checklist was used to determine the risk of bias of past studied included in this review.

RESULTS

One hundred thirty-three studies were identified after removing duplicates. Forty-one studies were selected for full-text analysis, and 35 remaining papers met the inclusion criteria and were therefore included in this systematic review. Thirty-two in vitro studies and 3 in vivo studies were included in the review. All studies reported that immersion in various solutions has a significant influence on the change in color and optical properties of denture teeth. However, the discoloration of denture teeth is still clinically acceptable in most studies. Exposure to various solutions also affected the translucency parameter of denture teeth. Most studies also investigated the surface roughness and hardness along with the optical properties, and reported that immersion cycles did not cause changes in surface roughness of denture teeth, while hardness was affected. The optical properties of PMMA denture teeth have been studied extensively, whereas that of CAD/CAM and 3D printed denture teeth is limited.

CONCLUSIONS

Color stability of CAD/CAM milled denture teeth is comparable to conventional PMMA denture teeth. There are contradictory findings in terms of color stability of 3D printed denture teeth as compared to conventional PMMA denture teeth. Staining by coffee is worst among the common beverages and solutions investigated. Denture teeth can show color changes after immersion in staining beverages as early as one week. The degree of discoloration of denture teeth after immersion is time dependent, with the larger extent in the initial phase.

Color and masking properties of translucent monolithic zirconia before and after glazing

Purpose 1. to assess the ability of four brands of translucent monolithic zirconia with different thicknesses to mask discolored substrates; 2. to assess the influence of glazing upon their color coordinates and masking properties.Methods Sixty samples of shade A1 (0.8, 1.5, and 2.0 mm thickness) from: ZirCAD/MT, Katana/HT, Vita YZ/HT, Cercon/HT were fabricated and glazed using a standardized laboratory procedure. CIE L*a*b* parameters were recorded on composite substrates, (IPS Natural Die Material Kit) (ND1=reference; ND2, ND3, ND4, ND5=test backgrounds), before and after glazing. The color changes of zirconia samples induced by glazing were analyzed. Masking properties was calculated as the color difference between CIE L*a*b* parameters of the samples placed on reference and test substrates with CIEDE2000(1:1:1) formula. The effect of material, thickness, substrate, and glazing on the color of monolithic zirconia was analyzed with ANOVA test and the multiple comparisons were analyzed with Tukey HSD tests (α=0.05).Results After glazing, lightness L* significantly increased, while chromatic coordinates a* and b* decreased (p<0.05). Significant differences in the masking properties of the four materials (p<0.001) were found, with IPS e.max ZirCAD/MT having the lowest masking effect (p<0.001). Thickness, substrate and glazing had a significant effect on the color masking properties of monolithic zirconia (p<0.001).Conclusions Masking properties of translucent zirconia were significantly influenced by the materials, the thickness and the color of the substrate; moreover, glazing improved the masking ability for all zirconia samples.

Optical properties of a novel glass-ceramic restorative material

OBJECTIVE

To examine the optical properties of a dental restorative material manufactured from lithium aluminosilicate ceramic and reinforced with lithium disilicate. Translucency and the optical effects of various supporting materials on color were the primary focus.

METHODS

Five 10 × 10 mm samples were prepared in thicknesses of 0.5, 1.0, 1.5, and 2.0 mm of both high translucency (HT) and low translucency (LT) versions of the material in shade A3. A spectrophotometer was used to measure the illuminance of the samples with black and white backings in order to calculate contrast ratio (CR) and relative translucency parameter (RTP). A baseline relationship between translucency and material thickness was examined and the effects of composite, titanium, and zirconia abutments on color change were studied.

RESULTS

No significant findings were identified for RTP or CR between the HT and LT material, regardless of the material thickness (p = 0.39, p = 0.14, respectively). Regardless of material thickness (HT vs. LT), translucencies (RTP and CR) were significantly different with composite, titanium, and zirconia backings compared to baseline values (p < 0.0001). Titanium had the most significant decrease in translucency compared to composite and zirconia. There was no difference in ΔE00 between the HT and LT materials (p > 0.05) regardless of the backing. Titanium had the most significant effect on color of both materials followed by composite then zirconia (p < 0.0001).

CONCLUSIONS

There is not a clinically significant difference in translucency between the high translucency and low translucency materials. Only zirconia supporting structures produced changes in color that are clinically acceptable.

CLINICAL SIGNIFICANCE

Understanding the optical properties of glass-ceramic restorative materials aids providers in selecting appropriate materials for optimum esthetic outcomes. The lithium-aluminosilicate reinforced with lithium disilicate material does a poor job masking supporting structures and resisting color change.

Novel CAD-CAM zirconia coping design to enhance the aesthetics and strength for anterior PLZ crowns

BACKGROUND

The aesthetics and strength of anterior porcelain layered zirconia (PLZ) crowns are mainly affected by the zirconia (Zr) coping design. There is a need for a modified design to enhance aesthetics with strength.

OBJECTIVES

The purpose of this study was to compare the fracture resistance of anterior PLZ crowns having modified CAD-CAM Zr coping designs (in terms of thickness and marginal collar designs) with standard Zr copings.

METHODS

Fifty PLZ crowns were fabricated and divided into two groups: Gr 1: Standard Zr Coping (SZC) (control gr) with 0.5 mm thickness (Facial-F, Mesial-M, Distal-D, incisal-I, and Palatal-P) without a collar; Gr 2: Collar Zr Coping (CZC) (test gr) with 2.5 mm collar height on M, D, P and 0.2 mm F and variable facial wall thickness. Subgroups: Gr 2a: (CZC-0.5 mm) facial wall thickness 0.5 mm; Gr 2b: (CZC-0.4 mm) facial wall thickness 0.4 mm; Gr 2c: (CZC-0.3 mm) facial wall thickness 0.3 mm; Gr 2d: (CZC-0.2 mm) facial wall thickness 0.2 mm. The fracture load was determined and analysed using One-way ANOVA and Dunnet test.

RESULTS

The minimum fracture load was 927.36 ± 127.80 N observed for Gr 2c (CZC at 0.3 mm) while the maximum fracture load was 1373.61 ± 146.54 N observed for Gr 2a (CZC at 0.5 mm). A highly significant difference in mean fracture load among various Zr coping groups (p< 0.001) was determined.

CONCLUSIONS

Novel Zr coping design for anterior PLZ crowns can provide better aesthetics with strength. Reducing the thickness of Zr coping in the aesthetic zone to 0.2 mm and providing a modified collar design (2.5 mm collar height on M, D, P, and 0.2 mm F) would provide strength without jeopardizing aesthetics.

Review on Polymer, Ceramic and Composite Materials for CAD/CAM Indirect Restorations in Dentistry-Application, Mechanical Characteristics and Comparison

The aim of this review article is to present various material groups, including ceramics, composites and hybrid materials, currently utilized in the field of CAD/CAM. The described technology is amongst the most important in modern prosthetics. Materials that are applicable in this technique are constantly tested, evaluated and improved. Nowadays, research on dental materials is carried out in order to meet the increasing demand on highly aesthetic and functional indirect restorations. Recent studies present the long-term clinical success of restorations made with the help of both ceramic and composite materials in the CAD/CAM method. However, new materials are developed and introduced that do not have long-term in vivo observations. We can outline a monolithic polymer-infiltrated ceramic network and zirconia teeth support that show promising results to date but require further assessment. The materials will be compared with regard to their mechanical and clinical properties, purpose, advantages and limitations.

Influence of Different Zirconia Coping Designs on the Fracture Resistance of All-Ceramic Crowns: An In Vitro Study

Background and Aim:

Increased demand for metal-free restorations in posterior areas has increased the focus on zirconia restorations because of its advantages in excellent mechanical properties, patient comfort, and acceptance. Although all-ceramic crowns have better biocompatibility and esthetic properties, there are some clinical reasons for the fracture of the veneer or the core materials in the posterior region. This study aims at comparing the influence of zirconia coping designs on the fracture resistance of all-ceramic crowns.

Materials and Methods:

A total of 32 zirconia copings (n = 8 for each group) were designed and fabricated based on the marginal collar height of zirconia coping. The groups were the following: Group 1: 0.0 mm zirconia coping; Group 2: 0.5 mm collar; Group 3: 1.0 mm collar; and Group 4: 1.5 mm collar. All these zirconia copings were veneered with porcelain. Master die with cemented ceramic-layered zirconia copings was tested using Universal testing machine. Data obtained were statistically evaluated by one-way analysis of variance and post hoc test.

Results:

There was statistically significant difference between the groups with P < 0.001. Group 4 has the highest strength (3318.89 ± 395.67) followed by Group 3 (2910.0 ± 219.22), then Group 1 (2320.02 ± 547.36) that is the control group and the least strength with Group 2 (2286.59 ± 496.66).

Conclusion:

On the basis of the results obtained from this study, it can be concluded that, the more the height of the zirconia collar, the higher the fracture strength of the all-ceramic crowns. Thus ceramic-layered zirconia coping design with 1.5 mm marginal collar height is recommended for functional long life, at least in the posterior higher load-bearing areas with lesser esthetic demands.

Fatigue performance of fully-stabilized zirconia polycrystals monolithic restorations: The effects of surface treatments at the bonding surface

This study evaluated the distinct conditioning effect of the intaglio surface of bonded fully-stabilized zirconia (FSZ) simplified restorations on the mechanical fatigue behavior of the set prior to and after aging. Ceramic disc shaped specimens (Ø= 10 mm and 1 mm thick) were randomly allocated into 14 groups considering: "surface treatments" (Ctrl: no-treatment; PM: universal primer; GLZ: low-fusing porcelain glaze; SNF: 5 nm SiO₂ nanofilm deposition; AlOx: air-abrasion with aluminum oxide; SiC: air-abrasion with silica-coated aluminum oxide; 7%Si: air-abrasion with 7% silica-coated aluminum oxide); and "aging" (baseline: 24 h at 37 °C in water; or aged: 90 days at 37 °C in water + 12,000 thermal cycles). The discs were treated, luted with resin cement onto the dentin analog, subjected to aging or not, and then tested under a step-stress fatigue test at 20 Hz, 10,000 cycles/step, step-size of 100N starting at 200N, and proceeding until failure detection. Fractographic, topographic, surface roughness, contact angle, and atomic force microscopy analyzes were performed. The surface treatments at baseline led to statistically similar fatigue failure loads (953N-1313N), except for GLZ (1313N), which was significantly higher than 7%Si (953 N). Meanwhile, Ctrl had 40% pre-test failures (debonding) after aging, and therefore the worst fatigue performance (notable decrease in fatigue results), while all the other groups presented superior and statistically similar fatigue behavior (973-1271N). In fact, when considering baseline Vs aging conditions, stable fatigue results could only be noted when using surface treatments. In conclusion, internal surface treatments of FSZ ceramic restorations are mandatory for fatigue behavior stability after aging the restorative set, while non-treatment induced unstable results.

Flexural Strength of Different Monolithic Computer-Assisted Design and Computer-Assisted Manufacturing Ceramic Materials upon Different Thermal Tempering Processes

Objective  Strength of ceramics related with sintering procedure. This study investigated the influence of different tempering processes on flexural strength of three monolithic ceramic materials.

Materials and Methods  Specimens were prepared in bar-shape (width × length × thickness = 4 × 14 × 1.2 mm) from yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP, inCoris TZI [I]), zirconia-reinforced lithium silicate (ZLS, Vita Suprinity [V]), and lithium disilicate (LS ₂ , IPS e.max CAD [E]), and sintered with different tempering processes: slow (S), normal (N), and fast (F) cooling procedure ( n = 15/group). Flexural strength (σ ) was determined using three-point bending test apparatus at 1 mm/min crosshead speed.

Statistical Analysis  The analysis of variance and Bonferroni’s multiple comparisons were determined for significant difference (α = 0.05). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristics strength (σ _o ). Microstructures were evaluated with scanning electron microscope and X-ray diffraction.

Results  The mean ± standard deviation (MPa) of σ, m, and σ _o were: 1,183.98 ± 204.26, 6.23, 1,271.80 for IS; 1,084.43 ± 204.79, 5.76, 1,170.08 for IN; 777.19 ± 99.77, 8.78, 819.96 for IF; 267.15 ± 32.71, 9.11, 281.48 for VS; 218.43 ± 38.46, 6.40, 234.23 for VN; 252.67 ± 37.58, 7.20, 269.23 for VF; 392.09 ± 37.91, 11.37, 409.23 for ES; 378.88 ± 55.38, 7.45, 403.11 for EN, and 390.94 ± 25.34, 16.00, 403.51 for EF. Thermal tempering significantly affected flexural strength of Y-TZP ( p < 0.05), but not either ZLS or LS ₂ ( p > 0.05). Y-TZP indicated significantly higher flexural strength upon slow tempering than others.

Conclusion  Enhancing flexural strength of Y-TZP can be achieved through slow tempering process and was suggested as a process for monolithic zirconia. Strengthening of ZLS and LS ₂ cannot be accomplished through tempering; thus, either S-, N-, or F- tempering procedure can be performed. Nevertheless, to minimize sintering time, rapid thermal tempering is more preferable for both ZLS and LS ₂ .

A State-of-the-Art Review on the Wear of the Occlusal Surfaces of Natural Teeth and Prosthetic Crowns

This review focuses on the wear mechanisms of natural and restorative dental materials, presenting a comprehensive description and analysis of the works published in the last two decades on the wear at the interface of occlusal surfaces. Different groups of tribological pairs were considered: tooth-tooth, tooth-restorative material (tooth-ceramic, tooth-resin-based-materials, and tooth-metal), and restorative-restorative materials. The lack of standardization of the wear tests impairs the direct comparison of the obtained results. However, it was possible to infer about the main wear mechanisms observed on the different classes of dental materials. Concerning ceramics, their toughness and surface finishing determines the wear of antagonist tooth. Abrasion revealed to be the main wear mechanisms at occlusal interface. In the case of resin-based composites, the cohesion of the organic matrix and the nature, shape, and amount of filler particles greatly influences the dental wear. The protruding and detachment of the filler particles are the main causes of abrasion of antagonist enamel. Metallic materials induce lower wear on antagonist enamel than the other classes of materials, because of their low hardness and high ductility. Most of the studies revealed plastic deformation and adhesive wear as the main wear mechanisms. Overall, more research in this area is needed for a better understanding of the mechanisms involved at the occlusal surfaces wear. This would be essential for the development of more suitable restoration materials.

Acid Effects on the Physical Properties of Different CAD/CAM Ceramic Materials: An in Vitro Analysis

PURPOSE

To evaluate the flexural strength, elastic modulus, microhardness, and surface roughness of monolithic zirconia, lithium disilicate ceramics, and feldspathic ceramics after being exposed to different acidic solutions.

MATERIALS AND METHODS

Rectangular specimens (n = 180) were prepared from three different ceramic materials: lithium disilicate, monolithic zirconia, and feldspathic porcelain. Initial Surface roughness of ninety specimens (n = 30/material) was evaluated using an optical noncontact profilometer. Thirty specimens of each material were immersed in one of the following solutions (n = 10/group): citric acid; acidic beverage; and artificial saliva, which served as the control. Post immersion surface roughness, flexural strength, and elastic modulus were determined using an optical noncontact profilometer and three-point bending test. Another thirty specimens of each material were immersed in the aqueous solutions (n = 10/group) following the same protocol and subjected to microhardness test using a Vickers diamond microhardness tester. A scanning electron microscope (SEM) was used to examine the surface characteristics changes. ANOVA and Post-hoc Tukey's Kramer tests were used for data analysis (α = 0.05).

RESULTS

Immersion in different solutions did not affect the flexural strength and elastic modulus of lithium disilicate or zirconia. Microhardness and surface roughness were significantly affected in all groups (p < 0.05). For feldspathic porcelain groups, the flexural strength and elastic modulus were significantly decreased in the citric acid group (p = 0.045 and p = 0.019). Also, there were significant differences among all feldspathic porcelain groups (p = 0.001) in terms of microhardness and surface roughness values.

CONCLUSIONS

The tested acidic agents significantly affected the flexural strength, elastic modulus, surface roughness, and microhardness of feldspathic porcelain. However, the flexural strength and elastic modulus of evaluated lithium disilicate and zirconia did not change significantly.

Evaluation of the wear of glazed and polished zirconia crowns and the opposing natural teeth: A clinical pilot study

STATEMENT OF PROBLEM

Clinical studies on the wear properties of different zirconia surfaces are lacking. Selecting a surface that causes and undergoes minimal wear will help improve clinical outcomes.

PURPOSE

The purpose of this clinical study was to evaluate and compare the wear over 1 year use of glazed zirconia (GZ) and polished zirconia (PZ) crowns opposing natural enamel and the wear of natural enamel opposing PZ and GZ crowns.

MATERIAL AND METHODS

This prospective, split mouth, randomized clinical trial included 14 participants requiring complete coverage crowns on first molars, bilaterally, in a completely dentate mandibular arch. GZ and PZ crowns were cemented according to a randomization chart. Polyvinyl siloxane impressions were made immediately and 1 year after the cementation of the crowns. The respective casts were scanned by using a 3D scanner and a software program to measure the amount of linear wear of zirconia crowns and opposing natural teeth. Wear was observed in 8 groups: PZ crowns, GZ crowns, natural enamel opposing natural enamel in the molar and premolar regions (NE-M and NE-PM), natural enamel opposing PZ crowns in the molar region (NE-PZ-M), natural enamel opposing GZ crowns in the molar region (NE-GZ-M), natural enamel opposing PZ crowns in the premolar region (NE-PZ-PM), and natural enamel opposing GZ crowns in the premolar region (NE-GZ-PM). A descriptive analysis was followed by comparison between groups by using a repeated-measure ANOVA with post hoc adjustments (α=.05).

RESULTS

The mean wear (μm) observed was as follows (in ascending order): PZ crowns (13 ±3), NE-PM (13 ±1), GZ crowns (27 ±9), NE-M (34 ±3), NE-PZ-PM (44 ±18), NE-PZ-M (63 ±22), NE-GZ-PM (69 ±21), NE-GZ-M (113 ±33). Wear of GZ and PZ crowns was less than wear of NE-M. The difference was statistically significant when comparing PZ with NE-M (P<.001, CI=-17 to -24). Wear of NE-GZ-M and NE-PZ-M was higher than wear of NE-M, with a statistically significant difference (P<.001, CI=-49 to -107 and P =.004, CI=-8 to -49, respectively). Wear of NE-GZ-M was more than that of NE-PZ-M, and the difference was statistically significant (P<.001, CI=-68 to -32). Wear of NE-PZ-PM and NE-GZ-PM was also more than the wear of NE-PM, and the difference was statistically significant (P<.001, CI=-17 to -43 and P<.001, CI=-39 to -70).

CONCLUSIONS

PZ and GZ crowns wear substantially with time, with lesser wear observed in PZ crowns. PZ and GZ crowns also cause more wear in opposing natural enamel than natural enamel antagonists, with the highest wear caused by GZ crowns.

Two-body wear test of enamel against laboratory polished and clinically adjusted zirconia

AIM

A two-body wear test experiment was performed on human enamel, in simulated chewing motion, against non-veneered zirconia ceramic. Aim-1 was to ascertain the effect of zirconia roughness on enamel wear. Aim-2 was to ascertain the relative enamel wear between enamel-zirconia wear pair and enamel-enamel control pair.

MATERIALS

Six molar and premolar human enamel cusps per group were used for a dental wear test against laboratory polished (LP) zirconia and laboratory polished and clinically adjusted (LP + CA) zirconia. Enamel antagonists were tested against incisor teeth as a control group to demonstrate laboratory enamel wear.

METHODOLOGY

Two-body wear tests were conducted in a dual-axis biomimetic dental wear simulator. 49N loading force was used for 120,000 cycles with 1 mm lateral movement of the test specimen at 1.6Hz frequency, under constant ambient temperature water flow. Surface roughness before testing was determined using 3D profilometry. Loss of enamel height and volume i.e. vertical wear and volumetric wear respectively, were measured by superimposition of before and after testing scans by 3D laser scanning. Scanning electron microscopy was used for surface morphology assessment. One-way ANOVA and Post Hoc Multiple Comparisons with Bonferroni corrections were used at the 5% significance level to determine whether surface finish affected volumetric and vertical enamel loss. The relationship between volumetric and vertical loss of enamel was assessed using Pearson's correlation test.

RESULTS

No significant difference was found between LP and LP + CA zirconia in vertical and volumetric enamel wear results. Control enamel had significantly higher vertical and volumetric enamel wear than LP and LP + CA zirconia. Pearson correlation revealed a strong relationship between vertical wear and volumetric wear of enamel.

CONCLUSION

Within the constraints of the test method in this experiment, zirconia irrespective of surface preparation, was found to cause less vertical and volumetric enamel wear compared to control enamel. No statistically significant difference was seen between LP zirconia and LP + CA zirconia.

Cement opacity and color as influencing factors on the final shade of metal-free ceramic restorations

OBJECTIVE

To investigate the influence of opacity and color of luting cements on the final shade of metal-free restorations.

MATERIALS AND METHODS

Five resin cement colors in combination with four different thicknesses of CAD/CAM ceramic materials were tested, and a composite substrate was used as dentin color reference (n = 3). Specimen color was measured with a spectrophotometer equipped with an integrating sphere before and after cementation (CIELAB). Cement and ceramic color and opacity (TP) were assessed by measuring the tested ceramic thickness as a 1-mm thick disk for each of the cement shades. The differences in color were evaluated (ΔE₀₀ ). Data were statistically analyzed by a Two-Way ANOVA followed by the Tukey Test for post-hoc comparison (P < .05) and multiple comparison Pearson's test (P < .05); the acceptability and perceptibility threshold were evaluated.

RESULTS

Statistically significant influence was found for factors ceramic thickness and cement shade (P < .001). Perceptible and unacceptable color changes were induced on the final restoration by resin cements (ranging from ΔE₀₀  = 0.69 ± 0.54 to ΔE₀₀  = 5.53 ± 0.46), the correlation between factors became strong (r²  > 0.6) in case of mismatch between color and translucency of cement and ceramic. Only the clear shade in combination with the thickest ceramic, resulted in an imperceptible color change (ΔE₀₀  = 0.69 ± 0.54).

CONCLUSIONS

The final shade of ceramic restorations can be influenced by resin cements; the magnitude of influence is related to the cement optical properties.

CLINICAL SIGNIFICANCE

In order to influence the final shade of a ceramic restoration, a cement more opaque than the restorative material should be used. Conversely, in the case of a fitting shade of the restoration, a cement more translucent than the restoration should be used to avoid undesired changes.

Biomaterials and biocompatibility: An historical overview

This review focuses on the characteristics and applications of biomaterials through the ages, ranging from the prehistoric times to the beginning of the era of modern medicine, which has been arbitrarily set to the middle of the 19th century, when aseptic procedures, antiseptic substances and modern anesthetics were developed. After a brief discussion on the definition of "biomaterial" from an historical point of view and a short introduction on the general history of surgery and dentistry, each material or class of materials will be presented with references listed in chronological order and, where possible, with their real, scientifically demonstrated effects on biological tissues. Particular attention has been given to references that are nowadays considered spurious or affected by translation errors or other kinds of biases.

Flexural strength, fracture toughness, three-body wear, and Martens parameters of pressable lithium-X-silicate ceramics

OBJECTIVES

To test and compare five pressable lithium-X-silicate-ceramics on their mechanical and wear properties.

METHODS

Specimens were pressed and prepared from: i. Amber Press (AP), ii. Celtra Press (CP), iii. Initial LiSi Press (IL), iv. Livento Press (LP), and v. IPS e.max Press (IE). Four-point flexural strength (FS), SEVNB fracture toughness (K_IC), three-body wear (3BW), Martens hardness (HM) and indentation modulus (E_IT) were measured. For CP, FS and HM were measured with and without additional Power Firing. Each subgroup contained 15 specimens. Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA followed by Scheffé test, Kruskal-Wallis-H-, Mann-Whitney-U-, and Spearman-Rho-test (p < 0.05). The Weibull modulus was calculated using the maximum likelihood estimation method.

RESULTS

AP and CP presented higher FS than IL. LP presented the highest Weibull modulus. CP showed lower K_IC values than AP, and AP was not significant compared to LP and IE. The most 3BW material loss was observed for CP. CP revealed higher HM values than the remaining ceramics. IL presented lower E_IT compared to AP and CP. The following correlations were observed between the test parameters: 3BW with FS (r = 0.279, p = 0.015), with HM (r = -0.378, p = 0.001), and with E_IT (r = -0.344, p = 0.004); E_IT with FS (r = 0.203, p = 0.028); and HM with FT (r = -0.223, p = 0.027) and E_IT (r = 0.884, p < 0.001). No correlations were observed between FS and K_IC (r = 0.046; p = 0.346).

SIGNIFICANCE

AP followed by LP showed the highest and IL followed by CP the lowest properties tested. Power Firing of CP improved the flexural strength. Ceramics with high flexural strength and Martens parameters showed lower wear. Materials with high Martens hardness presented lower fracture toughness values and ones with high indentation modulus showed high flexural strength.

Fatigue Failure Load of a Bonded Simplified Monolithic Feldspathic Ceramic: Influence of Hydrofluoric Acid Etching and Thermocycling

Objective:

To evaluate the effect of hydrofluoric acid (HF) etching and thermocycling (Tc) on fatigue failure load of feldspathic ceramic restorations cemented with two resin cements.

Methods:

Disc-shaped feldspathic ceramic (Vitablocs Mark II; Ø=10 mm, 1.0-mm thick) and G10 epoxy resin (Ø=10 mm, 2.5-mm thick) specimens were made and randomly allocated considering three factors: ceramic etching (ie, with vs without 10% HF plus silane application), resin cement (ie, self-adhesive [RelyX U200; U200] or conventional [Multilink Automix; MA]), and Tc (ie, with vs without 5-55°C/12,000 cycles). Adhesive cementation followed each manufacturer's instructions. The fatigue test (n=20) was based on the staircase approach (250,000 cycles; 20 Hz). Contact angle, surface topography, and fractography analysis were also executed. Specific statistical tests were employed for each outcome (α=0.05).

Results:

The interaction of HF and Tc factors decreased the fatigue resistance for both cements (U200 542.63&gt;U200/HF-Tc 495.00; MA 544.47&gt;MA/HF-Tc 506.84). Comparing the cements associated with HF or Tc, there was statistical superiority for MA (U200-Tc 537.37&lt;MA-Tc 561.32; U200/HF 535.79&lt;MA/HF 557.11), and no statistical difference was detected when only cement type or its association with HF-Tc was compared (U200 542.63=MA 544.47; U200/HF-Tc 495.00=MA/HF-Tc 506.84). The fracture always originated from defects at the ceramic-intaglio surface as radial cracks.

Conclusion:

HF etching plus silane agent increased the ceramic surface free energy and its wettability, but it did not provide better results in terms of fatigue resistance compared with silane agent application only. The association of HF etching and aging significantly reduced the fatigue resistance of the material, regardless of the resin cement used.

Effects of accelerated artificial aging on the translucency and color stability of monolithic ceramics with different surface treatments

STATEMENT OF PROBLEM

Different surface finishing procedures can be applied to monolithic restorations. However, information is limited regarding the long-term performance of these procedures.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of aging on the translucency and color stability of monolithic ceramics with different surface finishing procedures.

MATERIAL AND METHODS

Disk-shaped (14×1.5 mm) specimens of monolithic zirconia (Zirkonzahn Prettau [ZZ]) and lithium disilicate glass-ceramic (IPS e.max Press [IPS]) were fabricated. The specimens were divided into 3 subgroups according to the surface treatments (n=9, G: glazing, R: rubber polishing system, and P: rubber polishing system followed by polishing paste). Color measurements were made by using a spectrophotometer before and after an ultraviolet aging process. L*, a*, and b* parameters were recorded. ΔE and translucency parameter (TP) values were calculated. One specimen from each subgroup was examined by scanning electron microscopy (×30 000). The data were statistically analyzed using the Mann-Whitney U, Kruskal-Wallis, and post hoc tests (α=.05).

RESULTS

ΔE values of group ZZ (5.03) exceeded the clinically acceptable level (3.5); however, the color change was not clinically perceptible for IPS (0.41). The ΔE value of the subgroup P was found to be higher than that of the others for ZZ (P<.001). The ΔE value was not affected by the surface treatment for IPS. Group IPS showed significantly higher translucency than the ZZ group (P<.001). TP values were not affected by the surface treatment in either material and decreased after aging. However, changes in the TP values were too slight to be clinically perceptible.

CONCLUSIONS

Lithium disilicate ceramic was found to be more esthetic than monolithic zirconia ceramic in terms of color stability and translucency.