Stress distribution on teeth restored with veneers using various incisal preparation designs: A 3D finite element analysis study.

STATEMENT OF PROBLEM: The type of veneer preparation is often chosen according to the patient's tooth structure and occlusion. Taking biomechanics into account in this decision-making process provides the clinician with more technical information on how to improve the clinical longevity of restorations. However, biomechanical analyses of veneer preparation designs are sparse. PURPOSE: The purpose of this 3-dimensional (3D) finite element analysis with microcomputed tomography (µCT) data obtained from realistic models was to assess the influence of different preparations for ceramic and composite resin veneers on restoration and resin layer stress distribution. MATERIAL AND METHODS: Four replicas of a central incisor were printed and prepared for laminate veneers with 4 different incisal edge designs: shoulder (SH), palatal chamfer (PC), palatal chamfer and oblique fracture involving the distal angle (OF-PC), and palatal chamfer involving horizontal incisal fracture (IF-PC). After fabrication and cementation of the veneers, the restored replicas were assessed with µCT, and 3D finite element models were built. A 100-N load was applied on the palatal surface at 60 and 125 degrees relative to the longitudinal axis. Maximum principal stress and stress distribution on the veneers, cement layer, and tooth structure were calculated and analyzed. RESULTS: The SH preparation exhibited better stress distribution than the PC preparation, and the cement layer and the veneer were subjected to lower stress. The IF-PC preparation had better stress distribution than the OF-PC. The shoulder and IF-PC showed higher stress on laminate veneers, but lower stress on the cement layer. Ceramic veneers exhibited lower stress than composite resin veneers. CONCLUSIONS: The different incisal preparations for laminate veneers influenced stress distribution on restorations and on the resin cement layer. The shoulder type preparation showed better stress distribution and the composite resin veneers showed unfavorable results compared with the ceramic veneers.

Relationship between battery level and irradiance of light-curing units and their effects on the hardness of a bulk-fill composite resin.

Objectives: This study evaluated the relationship between the battery charge level and irradiance of light-emitting diode (LED) light-curing units (LCUs) and how these variables influence the Vickers hardness number (VHN) of a bulk-fill resin. Materials and Methods: Four LCUs were evaluated: Radii Plus (SDI), Radii-cal (SDI), Elipar Deep Cure (Filtek Bulk Fill, 3M Oral Care), and Poly Wireless (Kavo Kerr). Irradiance was measured using a radiometer every ten 20-second activations until the battery was discharged. Disks (4 mm thick) of a bulk-fill resin (Filtek Bulk Fill, 3M Oral Care) were prepared, and the VHN was determined on the top and bottom surfaces when light-cured with the LCUs with battery levels at 100%, 50% and 10%. Data were analyzed by 2-way analysis of variance, the Tukey's test, and Pearson correlations (α = 5%). Results: Elipar Deep Cure and Poly Wireless showed significant differences between the irradiance when the battery was fully charged versus discharged (10% battery level). Significant differences in irradiance were detected among all LCUs, within each battery condition tested. Hardness ratios below 80% were obtained for Radii-cal (10% battery level) and for Poly Wireless (50% and 10% battery levels). The battery level showed moderate and strong, but non-significant, positive correlations with the VHN and irradiance. Conclusions: Although the irradiance was different among LCUs, it decreased in half of the devices along with a reduction in battery level. In addition, the composite resin effectiveness of curing, measured by the hardness ratio, was reduced when the LCUs' battery was discharged.

In-office dental bleaching with violet light emitting diode: bleaching efficacy and pulpal temperature rise.

Objectives: This study evaluated the bleaching efficacy of different in-office protocols associated with violet light emitting diode (V-LED), and measured the pulpal temperature rise caused by V-LED with or without gel application. Materials and Methods: Bovine incisors were distributed in 4 groups (n = 10): VL - V-LED; HP - 35% hydrogen peroxide (control); HYB - hybrid protocol, V-LED applied without gel for 10 irradiation cycles followed by V-LED applied with gel for another 10 irradiation cycles; and HPVL - gel and V-LED applied for 20 irradiation cycles. Three bleaching sessions were performed with 7-day intervals. Bleaching efficacy was evaluated with Δ E a b * , ΔE 00 and ΔWID . Data were recorded at baseline, 7, 14, 21 and 70 days. For pulpal temperature rise, thermocouples were placed inside the pulp chamber of human incisors. To determine intrapulpal temperature, the teeth were irradiated with V-LED with or without application of bleaching gel. Color difference data were analyzed by 2-way repeated measures ANOVA and Tukey's test. Pulpal temperature was analyzed by t-test (α = 5%). Results: VL exhibited lower color ( Δ E a b * and ΔE 00) and whiteness changes (ΔWID ) than the other groups. HPVL presented higher color change values than HYB. HYB and HPVL showed not different ΔWID values; and HP showed the highest whiteness changes at all times. There were significant differences comparing ΔT with gel (8.9°C) and without gel application (7.2°C). Conclusions: HPLV was more efficient than HYB. The 2 protocols with VL showed similar results to control. Gel application combined with VL promoted higher pulpal temperature than to the no gel group.

Is the clinical performance of composite resin restorations in posterior teeth similar if restored with incremental or bulk-filling techniques? A systematic review and meta-analysis.

OBJECTIVES: A systematic review was performed to analyze the clinical performance of class I and II restorations in posterior teeth placed with the incremental or the bulk-filling techniques. The primary outcome was retention/fracture rate, and the secondary outcomes evaluated were anatomical form, surface texture, color match, marginal adaption, marginal discoloration, caries, and postoperative sensitivity. METHODS: Electronic and manual searches were performed for randomized clinical trials comparing the clinical performance of composite resin restorations in posterior teeth placed with the incremental or the bulk-filling techniques. The Cochrane Collaboration risk of bias tool was used to assess the quality of the studies and the GRADE tool was used to access the quality of the evidence. RESULTS: Fourteen studies were included in this systematic review and most of them had unclear risk of bias. The risk difference (RD) for retention/fracture was 0.00 (95%CI = - 0.01, 0.01; p = 0.86) for 1-1.5 years of follow-up; 0.00 (95%CI = - 0.02, 0.02; p = 0.88) for 2-3 years of follow-up; 0.05 (95%CI = - 0.08, 0.18; p = 0.46) for 5 or more years of follow-up. The RD for postoperative sensitivity was 0.04 (95%CI = - 0.02, 0.10; p = 0.18) for up to 30 days; 0.00 (95%CI = - 0.01, 0.02; p = 0.63) for 1-1.5 years of follow-up; and 0.00 (95%CI = - 0.01, 0.02; p = 0.71) for 2-3 years of follow-up. For the other secondary outcomes, no significant differences were observed (p > 0.05) between the restorative techniques. The certainty of evidence was graded as moderate. CONCLUSIONS: The clinical performance of class I and II restorations in posterior teeth is similar when placed with the incremental and bulk-filling techniques. CLINICAL RELEVANCE: Based on the results of this study, posterior restorations placed with bulk-filling technique present satisfactory clinical performance, which is similar to direct restorations placed with the conventional incremental technique, considering various follow-up periods evaluated. TRIAL REGISTRATION:  CRD42018108450.

Extended glaze firings for porcelain-veneered zirconia: Effects on the mechanical and optical behavior.

OBJECTIVE: This study evaluated the effect of dwell time (conventional or extended) and cooling protocol (fast or slow) of self-glaze firings on the mechanical (flexural strength and crack propagation) and optical (color and translucency) properties of a porcelain-veneered zirconia system. METHODS: Bilayer disc-shaped samples were prepared (Vita VM9 + In-Ceram YZ) and divided according to the final thermal treatment: glaze firing followed by slow cooling (furnace opening at 200 °C) (G-S) or fast cooling (furnace opening at 600 °C) (G-F, manufacturer-recommended protocol), extended glaze firing (15 min of dwell time) followed by slow cooling (EG-S) or fast cooling (EG-F), or no thermal treatment (CTRL). Porcelain roughness (Ra and Rz) was measured before and after glaze firings. Color (ΔE00) and translucency (TP00) alteration were also evaluated. Flexural strength was measured with the piston-on-three-ball test and crack propagation analysis was performed after Vickers indentations. Complementary analyzes of crystalline phase and scanning electron microscopy were carried out. RESULTS: Significant effect of dwell time was observed, with extended glaze leading to higher flexural strength and shorter crack lengths. Cracks of EG groups were observed to end in clusters of crystals. Color and translucency changed below perceptibility thresholds. All treatments led to a smoother surface and EG groups reached the lowest Rz values. An extra SiO2 peak was revealed in control and EG groups. No effect of cooling protocol was found. SIGNIFICANCE: Extended glaze firing was able to improve the resistance to crack initiation and propagation of porcelain-veneered zirconia without clinically perceptible changes in optical properties.

Novel speed sintered zirconia by microwave technology.

OBJECTIVE: Continuous efforts have been made to hasten the zirconia densification process without compromising properties. This study evaluated the long-term structural durability of microwave speed-sintered zirconia (MWZ) relative to a conventionally sintered zirconia (CZ). METHODS: As-machined dental 3Y-TZP discs (Ø12 × 1.2 mm) were speed sintered at 1450 °C for 15 min using an industrial microwave oven, while conventional sintering was conducted in a standard dental furnace at 1530 °C for 2 h. Both were followed by natural cooling. The total sintering time was 105 min for MWZ and 600 min for CZ. Groups were compared regarding density, grain size, phase composition, and fracture resistance. Structural durability was investigated employing two fatigue protocols, step-stress and dynamic fatigue. RESULTS: Compared to CZ, MWZ exhibited a slightly lower density (MWZ = 5.98 g/cm3, CZ = 6.03 g/cm3), but significantly smaller grain sizes (MWZ = 0.53 ± 0.09 µm, CZ = 0.89 ± 0.10 µm), lower cubic-zirconia contents (MWZ = 15.3%, CZ = 22.7%), and poorer translucency properties (TP) (MWZ = 13 ± 1, CZ = 29 ± 0.8). However, the two materials showed similar flexural strength (MWZ = 978 ± 112 MPa, CZ = 1044 ± 161 MPa). Additionally, step-stress testing failed to capture the fatigue effect in 3Y-TZP, whereas dynamic fatigue revealed structural degradation due to moisture-assisted slow-crack-growth (SCG). Finally, MWZ possessed a slightly higher Weibull modulus (MWZ = 7.9, CZ = 6.7) but similar resistance to SCG (MWZ = 27.5, CZ = 24.1) relative to CZ. SIGNIFICANCE: Dental 3Y-TZP with similar structural durability can be fabricated six-times faster by microwave than conventional sintering.

The bleaching efficacy of carbamide peroxide gels containing potassium nitrate desensitizer.

BACKGROUND: To evaluate the bleaching efficacy of at-home carbamide peroxide (CP) gels in two concentrations, containing or not a desensitizing agent. MATERIAL AND METHODS: Forty incisors were divided into four groups (n=10), according to gel concentrations (10% or 22%), and presence or not of 3% potassium nitrate in the gel. A thin layer of gel was applied to the buccal surface of each tooth for 2h/day for 4 weeks. Bleaching efficacy was measured using a spectrophotometer, and ∆E*ab, ∆E00 and ∆WID were calculated. Measurements were performed at baseline, 7, 14, 21, 28, and 35 days following the first gel application. Data were analyzed by two-way RM-ANOVA and Tukey's test (α=0.05). RESULTS: Regarding gel concentration or potassium nitrate inclusion, both gels resulted in color change above the perceptibility thresholds, which were similar between gels. Regarding time, significant differences were observed between color change values at 7 days and other time periods. ∆WID ranged from 3.8 to 9.6. Significant moderate to strong positive correlation was observed among the parameters. CONCLUSIONS: Nor the CP concentration, neither the inclusion of potassium nitrate in the gel, had influence on bleaching efficacy. All gels were effective and showed good results from the first weeks' application. Key words:Tooth bleaching, carbamide peroxide, desensitizer, potassium nitrate, color.

Do thermal treatments affect the mechanical behavior of porcelain-veneered zirconia? A systematic review and meta-analysis.

OBJECTIVES: A systematic review of in vitro studies was conducted to assess the effect of thermal treatments on flexural strength or critical load to failure of porcelain-veneered zirconia (PVZ). SOURCES: Literature searches were performed up to June 2018 in PubMed/MEDLINE, Scopus and Web of Science databases, with no publication year or language limits. DATA: From 393 relevant studies, 21 were selected for full-text analysis, from which 7 failed to meet the inclusion criteria. The 14 remaining papers were included in the systematic review: 8 for meta-analysis and 6 restricted to descriptive analyses. Hand searching of reference lists resulted in no additional papers. STUDY SELECTION: In vitro studies using PVZ specimens testing the influence of thermal treatments on the fracture resistance to monotonic or cyclic loading. Papers evaluating cooling rate were divided into those applying fast cooling from above the porcelain glass transition temperature (Tg), or from below it. Meta-analyses were performed separately for flexural strength and critical load to failure, using random effects at a 5% significance level. CONCLUSIONS: Delaying furnace opening at a temperature below the porcelain Tg is advised for PVZ restorations, in order to improve their fracture resistance. Additional information is required to confirm the apparent beneficial effect of self-glaze and repeated veneer firings on the mechanical properties of these restorations. Finally, in order to obtain conclusive and relevant evidence regarding thermal treatments and the fracture resistance of PVZs, future studies should concentrate on anatomically-correct crown specimens.

Effectiveness of Combination of Dentin and Enamel Layers on the Masking Ability of Porcelain

This study evaluated the masking ability of different porcelain thicknesses and combination of enamel and/or dentin porcelain layers over simulated background dental substrates with higher (A2) and lower (C4) color values. Combination of the enamel (E) and dentin (D) monolayer porcelain disks with different thicknesses (0.5 mm, 0.8 mm, and 1 mm) resulted in the following bilayer groups (n=10): D1E1, D1E0.8; D1E0.5; D0.8E0.8; D0.8E0.5, and D0.5E0.5. CIELAB color coordinates were measured with a spectrophotometer. The translucency parameter of mono and bilayer specimens and the masking ability estimated by color variation (ΔE*ab) of bilayer specimens over simulated dental substrates were evaluated. Linear regression analysis was used to investigate the relationships translucency parameter × ΔE*, translucency parameter × porcelain thickness, and ΔE* × porcelain thickness. Data were analyzed statistically (α= 0.05). Thinner porcelain disks were associated with higher translucency. Porcelain monolayers were considerably more translucent than bilayers (enamel + dentin). Dentin porcelain was less translucent than enamel porcelain with same thickness. ΔE* was always lower when measured over A2 background. Higher ΔE* was observed for the C4 background, indicating poorer masking ability. Increased ΔE* was significantly associated with increased translucency for both backgrounds. Decreased translucency and ΔE* were associated with increased total porcelain thickness or increased dentin thickness for both backgrounds. In conclusion, increased porcelain thickness (particularly increased dentin layer) and increased porcelain opacity resulted in better masking ability of the dental backgrounds.

Resumo Este estudo avaliou a capacidade de mascaramento de diferentes espessuras de porcelana e a combinação de camadas de porcelana de esmalte e/ou de dentina sobre substratos dentais simulados de fundo com cores de maior (A2) e menor (C4) valor. Combinação de discos de porcelana em monocamadas de esmalte (E) e dentina (D) com diferentes espessuras (0,5 mm, 0,8 mm e 1 mm) resultou nos seguintes grupos bicamadas (n=10): D1E1, D1E0,8; D1E0,5; D0,8E0,8; D0,8E0,5 e D0,5E0,5. Coordenadas de cor CIELAB foram mensuradas com um espectrofotômetro. O parâmetro de translucidez de espécimes mono e bicamadas e a capacidade de mascaramento estimada pela variação de cor (ΔE*ab) dos espécimes bicamadas sobre os substratos dentais simulados foram avaliados. Análise de regressão linear foi utilizada para investigar as relações parâmetro de translucidez x ΔE*, parâmetro de translucidez x espessura da porcelana, e ΔE* x espessura da porcelana. Os dados foram analisados estatisticamente (α=0,05). Discos de porcelana mais finos foram associados a maior translucidez. Monocamadas de porcelana foram consideravelmente mais translúcidas que bicamadas (esmalte + dentina). Porcelana de dentina foi menos translúcida que porcelana de esmalte com mesma espessura. ΔE* foi sempre menor quando mensurado sobre fundo A2. Maior ΔE* foi observado para o fundo C4, indicando pior capacidade de mascaramento. Maior ΔE* foi significativamente associado à maior translucidez para ambos fundos. Menor translucidez e ΔE* foram associados ao aumento da espessura total da porcelana ou aumento da espessura de dentina para ambos fundos. Em conclusão, aumento da espessura da porcelana (particularmente aumento da camada de dentina) e aumento da opacidade da porcelana resultaram em melhor capacidade de mascaramento dos fundos dentários.

Effectiveness of Combination of Dentin and Enamel Layers on the Masking Ability of Porcelain.

This study evaluated the masking ability of different porcelain thicknesses and combination of enamel and/or dentin porcelain layers over simulated background dental substrates with higher (A2) and lower (C4) color values. Combination of the enamel (E) and dentin (D) monolayer porcelain disks with different thicknesses (0.5 mm, 0.8 mm, and 1 mm) resulted in the following bilayer groups (n=10): D1E1, D1E0.8; D1E0.5; D0.8E0.8; D0.8E0.5, and D0.5E0.5. CIELAB color coordinates were measured with a spectrophotometer. The translucency parameter of mono and bilayer specimens and the masking ability estimated by color variation (ΔE*ab) of bilayer specimens over simulated dental substrates were evaluated. Linear regression analysis was used to investigate the relationships translucency parameter × ΔE*, translucency parameter × porcelain thickness, and ΔE* × porcelain thickness. Data were analyzed statistically (α= 0.05). Thinner porcelain disks were associated with higher translucency. Porcelain monolayers were considerably more translucent than bilayers (enamel + dentin). Dentin porcelain was less translucent than enamel porcelain with same thickness. ΔE* was always lower when measured over A2 background. Higher ΔE* was observed for the C4 background, indicating poorer masking ability. Increased ΔE* was significantly associated with increased translucency for both backgrounds. Decreased translucency and ΔE* were associated with increased total porcelain thickness or increased dentin thickness for both backgrounds. In conclusion, increased porcelain thickness (particularly increased dentin layer) and increased porcelain opacity resulted in better masking ability of the dental backgrounds.

Ageing of silorane-based and methacrylate-based composite resins: effects on translucency.

OBJECTIVES: Verify if media and time of storage affect the translucency of a silorane-based composite (Filtek P90) compared to two methacrylate-based composites (Z350 and ROK), and compare two methods of translucency evaluation. METHODS: Specimens were divided into two groups (n=7) according to the storage media (deionized water or red wine). With a spectrophotometer (SP60) in reflectance mode, the CIE L*a*b* parameters and opacity percentage readings were conducted at baseline, 24h, 30 days, and 180 days. Data were analyzed using two-way repeated measures ANOVA and Tukey (p<0.05). Pearson correlation measured the relationship between translucency parameter and opacity percentage. RESULTS: When stored in water, P90 showed an increase, whereas Z350 decreased in translucency. ROK did not exhibit any tendency over time. When stored in wine, the translucency of all materials decreased. A negative relationship was found between translucency parameter and opacity percentage. When stored in water, the a* values for P90 decreased, whereas Z350 and ROK showed values increasing over time. When stored in wine, the L* parameter tended to decrease over time, an effect that was less intense for P90. Moreover, the b* parameter for P90 decreased, whereas methacrylate-based composites increased over time. CONCLUSIONS: P90 was more stable in red wine than the other materials and became more translucent in water whether metacrilate-based materials became more opaque. Both media as well as storage time affected the translucency of the materials tested. Translucency could be measured with both methods tested. CLINICAL SIGNIFICANCE: Silorane-based composites seemed to be more stable than methacrylate-based composites in red wine and became more translucent over time in water, which was different than methacrylate-based composites. More studies are needed to clarify silorane-based composites performance.

Dureza de resinas compostas de diferentes cores, em profundidades distintas, fotoativadas por diferentes fotopolimerizadores / Hardness of composite resins of different colors, at distinc depths, photoactivated by different light-curing units

Objetivo: Avaliar a dureza de resinas compostas (RC) de cores diferentes em duas profundidades (topo e base), fotoativadas com diferentes fotopolimerizadores. Méto-do: Utilizaram-se duas RC de cores e opacidades diferentes (Filtek Supreme A1E®, Filtek Supreme A3D®) e quatro aparelhos fotopolimerizadores LED (Ultra Blue Is 600® - 450 mW/cm2; Optilight LD III® - 250 mW/cm2; Ultraled® - 250 mW/cm2; Radii® - 700 mW/cm2). Confeccionaram-se 24 matrizes de polímero de náilon (5 mm de diâmetro e 3 mm de espessura), nas quais as RC foram inseridas em dois incrementos de 1,5 mm cada, fotoativados por 20s cada. Submeteram-se os corpos-de-prova (cp) à análise de dureza Vickers no 'topo' e na 'base', com quatro medidas em cada superfície. A média de dureza de cada cp foi calculada e aplicaram-se análise de variância e Tukey. Resultados e conclusões: Observou-se que a dureza das RC variou conforme a cor do material e os aparelhos utilizados, com o Raddi e o Ultra Blue IS proporcionando os maiores valores. De forma geral, as RC apresentaram maior dureza no topo do que na base. Na base, a resina composta com maior translucidez apresentou maior dureza do que a resina composta opaca.

Reabilitação estética e funcional associada à erosão dentária: relato de caso clínico / Aesthetic and functional rehabilitation of dental erosion: case report

Lesões dentárias não cariosas, como as associadas à erosão ácida, por exemplo, podem provocar prejuízos significativos para a estrutura dentária, gerando hipersensibilidade dentinária, desgaste do esmalte, danos estéticos e perda de dimensão vertical de oclusão. O presente trabalho consiste na apresentação de um caso clínico de reabilitação estética e funcional de uma paciente portadora de erosão dentária, evidenciando uma abordagem clínica integrada, inter-relacionando cirurgia estética periodontal, restabelecimento de dimensão vertical de oclusão, restaurações indiretas de porcelana e restaurações diretas de resina composta. Com o tratamento executado, obteve-se o equilíbrio oclusal desejado, conforto para a paciente e um resultado estético plenamente satisfatório