Masking ability of gingiva-colored resin-based composites over different tooth-colored substrates.

The purpose of the study was to investigate the influence of different tooth-colored substrates and restoration thicknesses on the final color of gingiva-colored resin-based composites (GCRBCs). Five different shades of GCRBCs [light pink (LP), dark pink (DP), orange (Or), brown (Br), and purple (P)] were used to prepare disc-shaped specimens with 2 different thicknesses: 1.0 mm, and 2.0 mm. GCRBC discs (n = 5) were placed over 3 different tooth-colored substrates (ND1, ND5, and ND9) and color parameters were assessed using a spectroradiometer. Color differences (∆E*ab and ∆E00) were calculated using CIELab and CIEDE2000 formulas and compared to 50:50% perceptibility (PT: ∆E*ab = 1.7, ΔE00 = 1.1) and acceptability (AT: ∆E*ab = 3.7, ΔE00 = 2.8) visual thresholds. Color variation data were statistically analyzed using two-way ANOVAs followed by Bonferroni's post hoc tests (a = 05). The ∆E*ab and ΔE00 values of GCRBCs placed over ND9 substrates were significantly higher in the LP-1.0 mm and Or-1.0 mm groups that presented values above AT (p< .001).Regardless of the substrate color and GCRBC thickness applied, ∆E*ab and ΔE00 values below AT were recorded in the gingival color groups of P. Substrate color significantly affected the color differences in the gingival color groups of LP, DP, and Or with a restoration thickness of 1.0 mm (p < .05). Gingival color, restoration thickness, and substrate color influenced the color differences of GCRBCs. When the gingival color was a lighter gingival color, rather than dark purple, the masking ability was decreased, especially with a restoration thickness of 1.0 mm.

Effect of preparation design and scan pattern on the accuracy of intraoral scans for complete arch laminate veneers under simulated intraoral variables.

PURPOSE: The purpose of the study was to investigate the influence of different preparation designs and scan patterns on the accuracy of intraoral scans for complete-arch maxillary laminate veneers. MATERIALS AND METHODS: Three maxillary typodonts were used to obtain reference models with three different laminate veneer preparation designs: windows (W), beveled (B), and incisal overlap (IO). Reference scans were obtained with a desktop scanner. A total of 90 complete arch intraoral scans were made with an intraoral scanner (Medit i700) following three different scan patterns: straight motion (SM), zigzag motion (ZM), and combined motion (CM). Ten scans were made in each subgroup and exported as standard tessellation language (STL) files. Assessment of accuracy was conducted with a 3D software analysis program (Geomagic Control X). Each STL file was individually aligned with the reference scan using the best fit algorithm tool, and 3D differences were calculated using the root mean square (RMS) value. Two-way analysis of variance (ANOVA) followed by post hoc comparison tests were applied to analyze precision and trueness data (α = 0.05). RESULTS: Two-way ANOVA and post hoc comparison tests revealed significant differences among different preparation designs and scan patterns (p < 0.05). Regarding trueness, the IO when scanned with SM presented higher mean RMS than the other preparation designs (W and B) scanned with the same scanning pattern (p < 0.05). Regarding precision, the groups of W and IO presented significantly higher mean RMS than the group of B when scanned with ZM (p < 0.05). CONCLUSIONS: Accuracy of intraoral scans for complete-arch laminate veneers was affected by different laminate veneer preparation designs and scan patterns. CLINICAL SIGNIFICANCE: Modifying scan pattern according to preparation design helps to improve scan accuracy for complete-arch laminate veneers.

Influence of gingival color on the color differences of dental laminate veneers.

STATEMENT OF PROBLEM: The effect of various gingival colors on the color differences of laminate veneers is unclear and comparative evaluations should be documented. PURPOSE: The purpose of this in vitro study was to investigate the influence of different gingival colors on the color differences of laminate veneers. MATERIAL AND METHODS: Five maxillary typodonts were used to obtain study models using 5 different gingival colors: light pink (LP), dark pink (DP), orange (Or), brown (Br), and violet (V). A total of 45 laminate veneers were milled using A1-shaded lithium disilicate ceramic and cemented on natural tooth-colored substrates. Color parameters were assessed using a spectroradiometer at 3 measurement areas (cervical third, mid-third, and incisal third) along the midline of laminate veneer with a focus measuring diameter of 1 mm. Color differences (∆E*ab and ∆E00) were calculated and compared with perceptibility (PT: ∆E*ab=1.22, ΔE00=0.81) and acceptability (AT: ∆E*ab=2.66, ΔE00=1.77) visual thresholds. Color variation data were statistically analyzed using 2-way ANOVA and Tukey HSD tests (α=.05). RESULTS: Two-way ANOVA results of the ∆E*ab values revealed significant interaction between the gingival color and the measurement area (P=.002). The ∆E*ab and ΔE00 values of laminate veneers were significantly higher in the LP-V group that presented values above AT (P<.001). Measurement area significantly influenced ∆E values of laminate veneers (P<.001). Greater ∆E values were registered at the measurement area of the cervical third in the groups of LP-DP, LP-Br, LP-V, and Or-V. Regardless of the measurement area, ∆E00 values below AT were obtained for the gingival color groups of LP-Or, DP-Or, DP-Br, and DP-V. CONCLUSIONS: Gingival color influenced the color differences of laminate veneers. When the gingival color was a darker gingival color, rather than light pink, the color difference increased, especially at the measurement area of the cervical third.

Microstructural, physical, and optical characterization of high-translucency zirconia ceramics.

STATEMENT OF PROBLEM: The microstructural, physical, and optical properties of newly available highly-translucent zirconia ceramics have not been thoroughly investigated. PURPOSE: The purpose of this in vitro study was to evaluate the microstructural, physical, and optical properties of current zirconia ceramics with different degrees of translucency and to compare the optical properties with lithium disilicate glass-ceramic at different thicknesses. MATERIAL AND METHODS: Disk-shaped specimens (N=108) were prepared from 3 different monolithic zirconia ceramics: VITA YZ HT (YZ-HT), VITA YZ ST (YZ-ST), and VITA YZ XT (YZ-XT) and lithium disilicate glass-ceramic (IPS e-max CAD LT [IPS]) with a diameter of 14 mm and 3 different thicknesses (0.5, 1.0, and 1.5 mm ±0.02 mm). The microstructural features (grain size, elemental composition, phase identifications, and quantifications), physical properties (Vickers hardness and fracture toughness), and optical properties (translucency parameter and contrast ratio) were investigated. Data were analyzed using 1-way ANOVA, followed by the post hoc Tukey tests or Kruskal-Wallis and Mann-Whitney U tests (α=.05). RESULTS: Differences in grain size, phase assemblages, fracture toughness, translucency parameter, and contrast ratio were found to be significant (P<.05). The average grain size was different for the 3 zirconia specimens with the following order: YZ-XT>YZ-ST>YZ-HT. The fracture toughness of YZ-HT was higher than that of YZ-ST and YZ-XT (P<.05). IPS with 0.5-mm thickness had the highest TP followed by YZ-XT and YZ-ST. The CR values were in the range of 0.54 to 0.91 (YZ-HT), 0.43 to 0.61 (YZ-ST), 0.29 to 0.45 (YZ-XT), and 0.27 to 0.53 (IPS), and all decreased with an increase in thickness. CONCLUSIONS: Based on the results of the present study, the microstructural, physical, and optical properties of zirconia ceramics were affected by the changes in chemical composition and sintering parameters.

Fatigue survival and failure resistance of titanium versus zirconia implant abutments with various connection designs.

STATEMENT OF PROBLEM: Data regarding the effect of connection design and abutment material on the fatigue survival and failure resistance of implant abutments are scarce. PURPOSE: The purpose of this in vitro study was to investigate the effect of connection design and abutment material on the fatigue survival and failure resistance of implant abutment assemblies. MATERIAL AND METHODS: Three types of implants (n=18, N=54) and 6 groups of abutments (n=9, N=54) with different connection designs-internal conical (IC), internal tri-channel (IT), and external hexagonal (EH)-and abutment materials-titanium (T) and zirconia (Z)-were investigated. All the abutments were restored with identical central incisor crowns. Fatigue testing, including thermal and mechanical aging, was performed in a mastication simulator (Esetron Smart Robotechnologies) for up to 1.2×106 cycles with a load of 50 N at an angle of 45 degrees. Then, the surviving specimens were subjected to failure resistance testing in a universal testing machine (Shimadzu AG-IS; Shimadzu Corp) at a crosshead speed of 1.0 mm/min. The maximum loads to failure (N) were recorded. Survival performance of the specimens throughout the fatigue testing was examined by the Kaplan-Meier survival analysis. The failure loads were analyzed by using the Kruskal-Wallis test followed by the Mann-Whitney U tests with Bonferroni-Holm correction (α=.05). RESULTS: All the specimens of groups ICT, ITT, ITZ, and EHT survived fatigue testing, whereas 2 specimens from group ICZ and 3 specimens from EHZ failed. Statistically significant differences were found among the groups, based on the results of maximum failure loads (P<.05). The highest mean failure load was obtained in the ICT group (1069 ±182 N), followed by the ITT (926 ±197 N), EHT (873 ±126 N), ITZ (568 ±81 N), EHZ (311 ±45 N), and ICZ (287 ±63 N) groups. CONCLUSIONS: Abutment material and connection design affected the fatigue survival of implant abutment assemblies. Implant abutment assemblies with a titanium-titanium interface revealed higher failure resistance than the implant abutment assemblies with a titanium-zirconia interface.

Multidisciplinary Management of a Severe Maxillary Midline Diastema: A Clinical Report.

A maxillary midline diastema (MMD) is a common form of incomplete occlusion and often is a primary complaint of patients during dental consultations. MMD is considered to be a multifactorial phenomenon and can therefore be best restored with a multidisciplinary approach. This clinical report presents a multidisciplinary approach to the management of a 4.0-mm MMD by using limited orthodontics combined with periodontal and prosthodontic treatments.

Mechanical and optical properties of monolithic CAD-CAM restorative materials.

STATEMENT OF PROBLEM: Achieving natural tooth appearance with sufficient mechanical strength is one of the most challenging issues of computer-assisted design and computer-assisted manufacturing (CAD-CAM) materials. However, limited evidence is available regarding their optical and mechanical properties for proper and evidence-based material selection in clinical practice. PURPOSE: The purpose of this in vitro study was to assess and compare the translucency and biaxial flexural strength of 5 monolithic CAD-CAM restorative materials. MATERIAL AND METHODS: Disk-shaped specimens (n=30) of each material (Lava Ultimate [LU], Vita Enamic [VE], Vitablocs Mark II [VMII], Vita Suprinity [VS], and IPS e.max CAD [IPS]) with a diameter of 12 mm and a thickness of 1.2 ±0.05 mm were prepared. A spectrophotometer was used to measure the translucency parameter. The specimens were then subjected to a biaxial flexure test using 3 balls and loaded with a piston in a universal testing machine at a cross-head speed of 0.5 mm/min until failure occurred (International Organization for Standardization standard 6872). Weibull statistics were used to evaluate the characteristic strength and reliability of each material. Chemical compositions were analyzed using an energy dispersive spectrometer, and microstructural analysis was conducted using scanning electron microscopy. Data were analyzed using 1-way ANOVA and the Tukey honest significant difference test (α=.05). RESULTS: Significant differences were found among the materials concerning translucency and biaxial flexural strength (P<.05). The highest mean transparency value was obtained in the VS group, whereas the lowest mean value was obtained in the VE group. The VS group produced the highest mean biaxial flexural strength, followed by the IPS, LU, VE, and VMII groups. CONCLUSIONS: Based on the results of the present study, zirconia-reinforced glass-ceramic revealed higher mean translucency and biaxial flexural strength than resin nanoceramic, feldspathic ceramic, lithium disilicate ceramic, and dual-network ceramic.

Effect of coloring and sintering on the translucency and biaxial strength of monolithic zirconia.

STATEMENT OF PROBLEM: The influences of coloring and sintering procedures on the optical and mechanical properties of monolithic zirconia have not been thoroughly investigated. PURPOSE: The purpose of this in vitro study was to investigate the effects of the coloring procedure and of varying final sintering temperatures on the translucency parameter (TP) and biaxial flexural strength (BFS) of monolithic zirconia. MATERIAL AND METHODS: Disk-shaped specimens (N=210) of 2 different monolithic zirconia brands (Vita YZ HTWhite [VYZa]; Vita YZ HTColor A2 [VYZb]; Prettau Zirkonzahn [PZ]; Prettau Anterior Zirkonzahn [PZA]) with a diameter of 15 mm and a thickness of 1.0 ±0.05 mm were prepared. Half of the specimens prepared from noncolored blocks (VYZa, PZ, and PZA) received coloring liquid application. Then, the specimens were divided into 3 subgroups (n=10) according to the final sintering temperatures (1350°C, 1450°C, and 1600°C). The TP was determined by using a reflection spectrophotometer, and the BFS was tested with the piston-on-3-ball method in a universal testing machine. Data were statistically analyzed by multivariate multiple regression and Bonferroni tests (α=.05). RESULTS: Significant differences were obtained among the groups based on the results of the TP and BFS (P<.05). The TP was affected by the changes in final sintering temperature. The varying final sintering temperatures demonstrated no significant effect on the BFS, except in group PZ (noncolored) that produced lower BFS when sintered at 1350°C than the subgroups sintered at 1450°C and 1600°C (P<.05). Coloring liquid application significantly decreased the TP of VYZa (sintered at 1350°C) but produced no significant effect on the groups PZ and PZA. Additionally, the coloring procedure had no significant effect on the BFS of tested materials (VYZa, PZ, and PZA) (P>.05). CONCLUSIONS: Increased sintering temperature leads to increased translucency with minimal impact on the BFS. The coloring procedure should be considered at the time of material selection to avoid possible reduction in translucency.

Effect of non-thermal plasma treatment and resin cements on the bond strength of zirconia ceramics with different yttria concentrations.

OBJECTIVES: To investigate the effect of different surface treatments and resin cements on the shear bond strength of zirconia ceramics with different yttria concentrations. METHODS: Zirconia blocks characterized by different yttria concentrations [Vita YZ HT (HT), Vita YZ ST (ST) and Vita YZ XT (XT)] were used to prepare disc-shaped specimens (n=252). Specimens prepared to investigate shear bond strength (SBS), water contact angle and surface roughness (Ra) were divided into four subgroups; control (C), sandblasting (S), sandblasting + nonthermal plasma treatment (SNTP) and nonthermal plasma treatment (NTP). For SBS testing, specimens were further divided into two groups (n=108) according to the luting cement used [Panavia F2.0 (P) and Rely X U200 (R)]. The water contact angles were determined by sessile drop technique and Ra was analyzed with optical profilometer. SBS tests were performed in a universal testing machine at a crosshead speed of 0.5 mm/min. The data sets were statistically analyzed with two and three-way ANOVAs followed by post-hoc comparisons (α=0.05). RESULTS: The water contact angle and Ra data were significantly affected by surface treatments. The mean Ra values of ST and XT were significantly lower than HT for the surface treatment groups of C and NTP. The SBS values were significantly different among the groups subjected to different surface treatments. The mean SBS values of surface treatment groups (S, SNTP and NTP) when cemented with R were significantly higher than the groups of C (p<0.05). CONCLUSIONS: For the tested zirconia ceramics with different yttria concentrations, non-thermal plasma activation helps to improve SBS and is a promising tool in practical use.

Masking ability of monolithic CAD-CAM laminate veneers over different resin cement shades and substrate colors.

PURPOSE: To compare the masking ability of monolithic CAD-CAM veneers placed over different resin cement shades and substrate colors. MATERIAL AND METHODS: Veneers were milled of four different monolithic CAD-CAM restorative materials: feldspathic ceramic (VMII), lithium disilicate ceramic (Emax CAD), zirconia-reinforced lithium silicate ceramic (VS), and high translucency zirconia ceramic (YZ-XT). Veneers (n=9) were luted on natural tooth colored (ND1) or discolored substrates (ND3 or ND5) using two different resin cement shades (white opaque or translucent). Color parameters were obtained using a dental spectrophotometer before and after luting. Color differences (ΔE00) were calculated using CIEDE2000 formula and compared to perceptibility (P =0.81 ΔE00 units) and acceptability (AT=1.77 ΔE00 units) visual thresholds. Color variation data were statistically analyzed using the Kruskal-Wallis and Mann-Whitney U tests with Bonferroni-Holm correction (α=.05). RESULTS: The highest ΔE00 value was obtained in VMII group placed over discolored substrate, followed by the groups of Emax CAD, YZ-XT, and VS. The effect of material types on ΔE00 values was significantly observed when the veneers luted on discolored substrates using translucent resin cement (p<.05). CONCLUSIONS: Restorative material type, substrate color, and resin cement shade affect the masking ability of monolithic CAD-CAM laminate veneers.

Retrospective evaluation of factors affecting long-term clinical performance of CAD-CAM laminate veneers.

PURPOSE: The purpose of the study was to assess the clinical performance of CAD-CAM laminate veneers placed by a single operator and systematically evaluated for up to 10 years. MATERIAL AND METHODS: A total of 197 laminate veneers fabricated using either feldspathic ceramic (VMII) or lithium disilicate ceramic (EmaxCAD) were followed up to 10 years in 32 patients. Technical, esthetical, and biological findings of each restoration were evaluated using modified United States Public Health Service criteria. The survival and complication rates were assessed using Kaplan-Meier survival analysis and compared using the Log Rank test. Statistical significance was set at p<0.05. RESULTS: The estimated Kaplan-Meier survival rate was 91.9% after the mean observation period. According to ceramic system used, the estimated Kaplan-Meier survival rate amounted to 92.7% for Emax-CAD and to 89.1% for VMII. Survival rates were significantly affected by the location of veneer according to Log Rank test (p < 0.05). A range of survival rates between 83.3% and 98.6% were observed based on the location of veneer. CONCLUSIONS: CAD-CAM laminate veneers milled of feldspathic or lithium disilicate ceramics have comparable long-term survival rates. Oral positioning affects the survival of veneer. Veneers of incisors have higher survival rates than the veneers of maxillary canines and premolars.

Managing emerging challenges of Coronavirus disease 2019 (COVID-19) in dentistry.

Dental centers have been referred to as a hub or reservoir for infection, where healthcare professionals and other staff, patients and the public together may potentially spread pathogenic microorganisms. This may occur via saliva, skin or indirectly through air, water, and contaminated surfaces or instruments. Everyone should therefore be considered as potential sources of infection. During a pandemic, limiting unnecessary care has been adopted as a clinical measure for some patient's, to reduce the risk of cross-infection in the short term. However, in order to enable continuation of necessary and qualified care, dental processes need to follow specific infection control strategies in order to prevent transmission of emerging pandemic risks following COVID-19. In this article, we develop a tool with practical recommendations to mitigate infection risks before, during and following pandemics to enable ongoing dental care provision in primary and secondary care based on national and global recommendations.

Sealing capability and marginal fit of titanium versus zirconia abutments with different connection designs.

PURPOSE: Limited data is available regarding the differences for possible microleakage problems and fitting accuracy of zirconia versus titanium abutments with various connection designs. The purpose of this in vitro study was to investigate the effect of connection design and abutment material on the sealing capability and fitting accuracy of abutments. MATERIALS AND METHODS: A total of 42 abutments with different connection designs [internal conical (IC), internal tri-channel (IT), and external hexagonal (EH)] and abutment materials [titanium (Ti) and zirconia (Zr)] were evaluated. The inner parts of implants were inoculated with 0.7 µL of polymicrobial culture (P. gingivalis, T. forsythia, T. denticola and F. nucleatum) and connected with their respective abutments under sterile conditions. The penetration of bacteria into the surrounding media was assessed by the visual evaluation of turbidity at each time point and the number of colony forming units (CFUs) was counted. The marginal gap at the implant- abutment interface (IAI) was measured by scanning electron microscope. The data sets were statistically analyzed using Kruskal-Wallis followed by Mann-Whitney U tests with the Bonferroni-Holm correction (α=.05). RESULTS: Statistically significant difference was found among the groups based on the results of leaked colonies (P<.05). The EH-Ti group characterized by an external hexagonal connection were less resistant to bacterial leakage than the groups EH-Zr, IT-Zr, IT-Ti, IC-Zr, and IC-Ti (P<.05). The marginal misfit (in µm) of the groups were in the range of 2.7-4.0 (IC-Zr), 1.8-5.3 (IC-Ti), 6.5-17.1 (IT-Zr), 5.4-12.0 (IT-Ti), 16.8-22.7 (EH-Zr), and 10.3-15.4 (EH-Ti). CONCLUSION: The sealing capability and marginal fit of abutments were affected by the type of abutment material and connection design.

Surface deterioration of monolithic CAD/CAM restorative materials after artificial abrasive toothbrushing.

PURPOSE: The purpose of this in vitro study was to evaluate the effect of abrasive toothbrushing on the surface properties of monolithic computer-assisted design and computer-assisted manufacturing (CAD/CAM) materials stored in food-simulating liquids (FSLs). MATERIALS AND METHODS: Fourty-eight disk-shaped test specimens of each material (Paradigm MZ100/PMZ, Lava Ultimate/LU, Vita Enamic/VE, and Vita Mark II/VMII) with a diameter of 10.0 mm and a thickness of 3.0 ± 0.05 mm were prepared. Specimens were divided into 4 subgroups (n=12) and stored in air, distilled water, 0.02 M citric acid, or 75% ethanol/water solution for 7 days at 36.5℃. Then, the specimens were brushed in a multi-station brushing machine under a vertical load of 2.0 N for 3 hours. Surface gloss (GU), roughness (Ra), and hardness (Vickers [VHN]) were measured after storage and brushing simulation. The data sets were statistically analyzed with 2 and 3-way ANOVAs followed by the Tukey's post-hoc comparisons (α=.05). RESULTS: Statistically significant difference was found among the materials concerning the results of surface properties. VMII showed the highest VHN, while PMZ produced the lowest. Storage in FSLs significantly affected the VHN of PMZ and LU. VMII showed the lowest Ra and highest GU irrespective of FSLs and of abrasive toothbrushing. VE, LU, and PMZ produced significant decrease in GU and increase in Ra after toothbrushing. CONCLUSION: Surface properties of monolithic CAD/CAM restorative materials were differently affected by the storage media and abrasive toothbrushing.