Fatigue behavior of multilayer ceramic structures in traditional and reverse layering designs.

PURPOSE: This study evaluated the fatigue failure load (FFL) and the number of cycles for fatigue failure (CFF) of traditional (porcelain layer up) and reversed (zirconia layer up) designs of porcelain-veneered zirconia samples prepared with heat-pressing or file-splitting techniques. MATERIALS AND METHODS: Zirconia discs were prepared and veneered with heat-pressed or machined feldspathic ceramic. The bilayer discs were bonded onto a dentin-analog according to the bilayer technique and sample design: traditional heat-pressing (T-HP), reversed heat-pressing (R-HP), traditional file-splitting with fusion ceramic (T-FC), reversed file-splitting with fusion ceramic R-FC), traditional file-splitting with resin cement (T-RC), and reversed file-splitting with resin cement (R-RC). The fatigue tests were performed using the stepwise approach at 20 Hz, 10,000 cycles/step, step-size of 200 N starting at 600 N, and proceeding until failure detection or up to 2600 N if enduring. The failure modes (from radial and/or cone cracks) were analyzed in a stereomicroscope. RESULTS: The reversed design decreased the FFL and CFF of bilayers prepared with heat-pressing and file-splitting with fusion ceramic. The T-HP and T-FC reached the highest results, which were statistically similar between them. The bilayers prepared by the file-splitting with resin cement (T-RC and R-RC) were similar to the R-FC and R-HP groups regarding FFL and CFF. Almost all reverse layering samples failed by radial cracks. CONCLUSIONS: The reverse layering design did not improve the fatigue behavior of porcelain veneered zirconia samples. The three bilayer techniques behaved similarly when used in the reversed design.

Effect of seating forces on cement-ceramic adhesion in microtensile bond tests.

OBJECTIVES: The aim of this study was to evaluate the effect of different seating forces during cementation in cement-ceramic microtensile bond strength (µTBS). MATERIALS AND METHODS: Forty-five blocks (5 × 5 × 4 mm(3)) of a glass-infiltrated alumina-based ceramic (In-Ceram Alumina) were fabricated according to the manufacturer's instructions and duplicated in resin composite. Ceramic surfaces were polished, cleaned for 10 min in an ultrasonic bath, silica coated using a laboratory type of air abrasion device, and silanized. Each treated ceramic block was then randomly assigned to five groups (n = 9) and cemented to a composite block under five seating forces (10 g, 50 g, 100 g, 500 g, and 750 g) using a dual-cured resin cement (Panavia F). The ceramic-cement-composite assemblies were cut under coolant water to obtain bar specimens (1 mm × 0.8 mm(2)). The µTBS tests were performed in a universal testing machine (1 mm/min). The mean bond strengths values were statistically analyzed using one-way ANOVA (α ≤ 0.05). RESULTS: Different seating forces resulted in no significant difference in the µTBS results ranging between 13.1 ± 4.7 and 18.8 ± 2.1 MPa (p = 0.13) and no significant differences among cement thickness. CONCLUSIONS: Excessive seating forces during cementation seem not to affect the µTBS results. CLINICAL RELEVANCE: Excessive forces during the seating of single all-ceramic restorations cementation seem to display the same tensile bond strength to the resin cement.

Repair bond strength of microhybrid, nanohybrid and nanofilled resin composites: effect of substrate resin type, surface conditioning and ageing.

OBJECTIVES: This study evaluated the microtensile bond strength (MTBS) of non-aged and aged resin-based composites (RBC) (nanohybrid and nanofilled) after two surface conditioning methods, repaired using the composite of the same kind or a microhybrid composite. MATERIALS AND METHODS: Nanohybrid (Tetric EvoCeram--TE) and nanofilled (Filtek Supreme--FS) RBC blocks (5 × 5 × 6 mm) (N = 128) were fabricated and randomly divided into two groups: (a) no ageing (control group) and (b) ageing (5.000 thermocycling, 5-55 °C). RBC surfaces were polished by up to 1,200-grit silicone carbide papers and conditioned with either (a) air abrasion with 30-µm SiO2 particles (CoJet Sand) for 4 s + silane coupling agent (ESPE-Sil) + adhesive resin (VisioBond) (n = 16) or (b) adhesive application only (Multilink A+B for TE; Adper ScotchBond 1XT for FS) (n = 16). In half of the groups, repair resin of the same kind with the RBC and, in the other half, a different kind of composite (microhybrid, Quadrant Anterior Shine--AS) with its corresponding adhesive (Quadrant UniBond) was used. The specimens were submitted to MTBS test (0.5 mm/min). Data were analysed using three-way ANOVA and Tukey's tests. Degree of conversion (DC) of non-aged and aged resin composites (TE, FS) (n = 3 per group) was measured by micro-Raman analyses. RESULTS: RBC type (p = 0.001) and ageing affected the MTBS results significantly (p = 0.001). Surface conditioning type did not show significant difference (p = 0.726), but less number of pre-test failures was experienced with the CoJet system compared to adhesive resin application only. Repair strength on aged TE showed significantly less (p < 0.05) MTBS than for FS. FS repaired with the same kind of RBC and adhesive resin presented the highest cohesive failures (43 %). DC was higher for TE (71 %) than for FS (58 %) before ageing. CONCLUSION: On the aged RBCs, less favourable repair strength could be expected especially for nanohybrid composite. For repair actions, RBC surface conditioning could be accomplished with either adhesive resin application only or with CoJet system, providing that the latter resulted in less pre-test failures. CLINICAL RELEVANCE: Clinicians could condition the resin surface prior to repair or relayering with either CoJet system or adhesive resin application only, depending on the availability of the system.

Avaliação in vitro da resistência à compressão de condicionadores de tecido submetidos a diferentes tempos de armazenamento / In vitro evaluation of the compressive strength of tissue conditioners submitted to different storage times

Objetivou-se avaliar in vitro a resiliência de dois condicionadores de tecido, UG - Ufigel SC (Voco) e D - Dentusoft (DMG), depois de serem submetidos a diferentes tempos de armazenamento em água destilada a 37ºC (24 horas, 14 dias, 30 dias e 180 dias). Foram confeccionadas 20 cápsulas de resina acrílica termicamente ativada, com 20 mm de diâmetro interno e 3 mm de profundidade. Os condicionadores de tecido, UG e D, foram manipulados de acordo com o fabricante, acomodados no interior das cápsulas (n = 10) e armazenados por 24 horas, 14 dias, 30 dias e 180 dias. Cada grupo foi submetido ao teste de resiliência utilizando uma ponta romba de 3 mm de diâmetro em máquina de ensaio universal (EMIC-DL 1000). Os dados foram submetidos à análise estatística two-way ANOVA e ao teste de Tukey (α = 0,05). Os valores de média para os materiais/tempo de armazenagem foram: UG/24 horas - 3,81A; D/30 dias - 5,54B; UG/14 dias - 5,58B; UG/30 dias - 5,66BC; UG/180 dias - 5,77BC; D/24 horas - 5,79BC; D/180 dias - 6,13C; D/14 dias - 6,54D. Dentusoft armazenado por 14 dias obteve valores de média de resiliência significantemente superiores em relação aos demais. Ufigel armazenado nos períodos de 1 a 14 dias apresentaram valores de resiliência menores do que D, sendo estatisticamente significante nesses períodos. Entretanto, para os períodos de avaliação de 30 e 180 dias, não se observaram diferenças significantes entre os materiais.

Dental fluorosis: exposure, prevention and management.

Dental fluorosis is a developmental disturbance of dental enamel, caused by successive exposures to high concentrations of fluoride during tooth development, leading to enamel with lower mineral content and increased porosity. The severity of dental fluorosis depends on when and for how long the overexposure to fluoride occurs, the individual response, weight, degree of physical activity, nutritional factors and bone growth. The risk period for esthetic changes in permanent teeth is between 20 and 30 months of age. The recommended level for daily fluoride intake is 0.05 - 0.07 mg F/Kg/day, which is considered of great help in preventing dental caries, acting in remineralization. A daily intake above this safe level leads to an increased risk of dental fluorosis. Currently recommended procedures for diagnosis of fluorosis should discriminate between symmetrical and asymmetrical and/or discrete patterns of opaque defects. Fluorosis can be prevented by having an adequate knowledge of the fluoride sources, knowing how to manage this issue and therefore, avoid overexposure.

Prótese parcial removível associada a implantes osseointegrados / Removable partial denture associated the osseointegrated implants: a clinical report

A prótese parcial removível (PPR) conjugada a implantes osseointegrados é um desafio na Odontologia restauradora, pois a biomecânica que envolve dois sistemas diferentes é um tanto quanto complexa. Este relato de caso expõe a instalação de uma PPR associada a dois implantes osseointegrados com encaixe do tipo ERA, fixados na região distal. Após minuciosos exames clínico, radiográfico e realização de modelos de estudo fez-se os planejamentos cirúrgico e protético. Restabeleceu-se função e estética associadas a um grande conforto e satisfação relatados pelo paciente, mas vale ressaltar que mais estudos clínicos são necessários para se ter um posicionamento mais definido em relação a esta modalidade terapêutica.

Shear bond strenght between metal alloy and a ceramic system, submitted to different thermocycling immersion times

El objetivo de este estudio fue evaluar la resistencia a cizallamiento de aleaciones metálicas de Co-Cr y Ni-Cr; con un mismo tipo de cerámica, sometidos a diferentes tiempos de inmersión en el termociclaje. Sesenta especímenes fueron confeccionados de forma standarden formato cilindrico. Tres condiciones de termociclaje fueron evaluadas: sin termociclaje, 3000 ciclos (5ºC/55ºC±1) con 30s y 3.000 ciclos (5ºC/55ºC±1) con 60s de tiempo de inmersión. El ensayo de cizallamiento fue realizado en una máquina universal usando un dispositivo para concentrar la tensión en la interfase metalocerámica durante el test. La carga fue aplicada hasta que ocurra la fractura de los especimenes. La información fue estadísticamente analizada por ANOVA(two-way) y el test de Tukey (p<0,05). Los resultados no mostraron diferencia estadísticamente significante entre las combinaciones metal-porcelana. Sin embargo, ambas combinaciones metalocerámicas sometidas a 60s de tiempo de inmersión mostraron valores más bajos en comparación con los especimenes del grupo sin termociclaje. Fue concluido que el tiempo de inmersión de termociclaje de 1 minuto afectó los valores de resistencia de cizallamiento en los grupos de Ni-Cr/porcelana y Cr-Co/porcelana.