Three-dimensional finite element analysis of stress distribution in peri-implant bone with relined dentures and different heights of healing caps.

The purpose of this study was to evaluate the influence of height of healing caps and the use of soft liner materials on the stress distribution in peri-implant bone during masticatory function in conventional complete dentures during the healing period by using finite element analysis. Three-dimensional models of a severely resorbed mandible with two recently placed implants in the anterior region were created and divided into the following situations: (i) submerged implants, (ii) healing cap at gingival level and (iii) 1·5-mm supragingival. All these situations were also analysed for a conventional complete denture and a denture relined with a 3-mm-thick layer of soft liner material. The models were exported to mechanical simulation software that presented two simulations, one with load in the inferior right canine (35 N) and the other in the inferior right first molar (50 N). Data were evaluated using Maximum Principal Stress provided by the software. All models showed a stress concentration in the cortical bone corresponding to the cervical part of the implant. The simulations with non-submerged implants showed higher values of stress concentration than those that were submerged. Likewise, soft liner materials presented better results than when the denture base was not relined. The height of the healing caps seems to have a direct influence on the stress distribution in the peri-implant bone during the healing period. Considering the values obtained in this study, the use of soft liners with submerged implants seems to be the most suitable method to use during the period of osseointegration.

Comparison between two methods to evaluate temperature changes produced by composite light curing units and polymerization techniques.

AIM: This study evaluated the temperature change into the pulp chamber during the light curing of composite resin by direct (bovine tooth) and indirect (matrix) methods. METHODS: Direct method: fifty standardized cavities (2x2x2 mm) were prepared in bovine incisors, which were randomly assigned to evaluation of the temperature changes in the pulp chamber. Indirect method: temperature changes were evaluated through a dentine slice of 1.0 mm thickness in a elastomer cubic mold (2x2x2 mm). Filtek Z250 composite resin (3M/ESPE) was photo-activated using three light curing units: quartz-tungsten-halogen (QTH) by continuous, soft-start or intermittent light modulations; light emitting diode (LED); and plasma arc-curing (PAC). Ten groups (N.=10) were established according to technique evaluation and photo-activation methods. All experiments were carried out in a controlled environment (37 °C and 50 ± 10% relative humidity). The temperature changes were recorded using a digital thermometer attached to a type-K thermocouple in contact with the dentin slice (indirect method) or in contact with the axial wall (dentin) of pulp chamber (direct method). The results were submitted to ANOVA and Tukey's test (α=0.05). RESULTS: Temperature changes were statistically higher for the matrix indirect method (2.56 ºC) than bovine teeth direct method (1.17ºC). The change temperature was statistically higher for the PAC (1.77 ºC) when compared to other photo-activation modes in bovine teeth direct method. CONCLUSION: The two methods of temperature evaluation were different, however indirect method detected the higher temperature increase. Higher energy density arising from the light curing units and polymerization techniques promoted higher temperature increase.

Efeito das técnicas de inserção de compósitos odontológicos sobre a infiltração marginal / Effect of techniques of composit resin on microleakage

O objetivo deste estudo foi avaliar o efeito de duas técnicas de inserção do compósito sobre o nível de infiltração marginal na interface dente/compósito restaurador. Foram preparadas 40 cavidades circulares medindo 4 mm de diamêtro por 3 mm de profundidade em dentes bovinos, que foram divididos em 4 grupos (n=10): Grupo 1 - Único encremento + P60; Grupo 2 - Único encremento + Definite; Grupo 3 - Três incrementos + P60 ; e Grupo 4 - Três incrementos + Definite. Todas as amostras foram armazenadas em água destilada a 37°C, por 24 horas e submetidas a 500 ciclos térmicos (5° e 55°) por 30 segundos em cada banho. Em seguida, os dentes foram imersos em solução de azul de metileno a 2 por cento, por 4 horas, e a microinfiltração avaliada. Os resultados submetidos ao teste estatístico de Kruskal-Wallis mostraram que a técnica de inserção em 3 incrementos para o Definite com 1 incremento; o P60 com 3 incrementos apresentou níveis de infiltração marginal estatisticamente menores em relação ao P60 e Definite, ambos com 1 incremento