Silvando Vieira dos Santos

Dentin deproteinization effect on bond strength of self-adhesive resin cements

This study examined the effect of deproteinization on the bond strength between self-adhesive resin cements and dentin surfaces that were untreated (control), acid-etched, or acid-etched and subjected to a post-etch deproteinization treatment. Cylinders of RelyX Unicem or BisCem (n = 6) cement were build-up on the dentin surfaces and tested to determine shear strength. The results were analyzed using two-way ANOVA and Tukeys test (5%). While neither dentin pretreatment improved the bond strength for RelyX Unicem, deproteinization treatments resulted in greater bond strength in BisCem specimens while acid etching alone did not improve the performance of the material.

Análise da resistência à fadiga entre pilares retos sólidos e anatômicos do sistema cone morse

Contexto O estudo do fenomeno de fadiga e essencial porque as falhas de implantes geralmente sao causadas por este processo. Objetivo O objetivo deste estudo foi analisar a resistencia a fadiga de conjuntos de pilares retos e anatomicos que foram submetidos a cargas ciclicas. Material e metodo Foram utilizados 37 implantes cone Morse e 37 pilares, divididos em dois grupos (n = 16: pilares retos, n = 21: pilares anatomicos). Os conjuntos foram submetidos a carga ciclica (5.000.000) usando o equipamento servo-hidraulico. Tres conjuntos de cada grupo foram submetidos a testes de flexao para determinar a resistencia de carga maxima, o que serviu de parâmetro para comparacao dos testes ciclicos. Foram avaliados numero de ciclos, carga e momento de flexao. Resultado Dos 31 pilares ciclicamente testados, 17 (54,8%) fraturaram em menos de 5 milhoes de ciclos; 8 (25,8%) destes eram pilares retos, e 9 (29%) eram anatomicos. Um total de 14 amostras (45,2%) resistiu a carga ciclica. De acordo com o teste exato de Fisher, nao houve diferenca entre os grupos quanto a fratura. Conclusao Apesar dos pilares retos terem maior carga media e momento de flexao que os anatomicos, os dois tipos de pilares apresentaram desempenho semelhante quanto a resistencia a fratura in vitro.

Experimental evaluation of cyclic stresses on axially loaded bolted joints

The bolted joints fatigue behavior was analyzed by using torque as tightening method and steel and aluminum as members’ material. The bolt used in the current study was the M6 class 8.8. The bolt preload value was calculated based on the bolts’ elongation in each applied torque. The fatigue limit increases as the torque increases up to the torque limit to fracture the bolt. This behavior was seen in both members’ material. Steel members support higher torque before bolt fracture. An analytical study also evaluated the relationship between the cyclic stress amplitude and the mean stress experienced by fatigue-tested bolts based on the available models for joint stiffness. The results were compared to the bolt fatigue diagram by Burguete and Patterson. The herein studied linear elastic theoretical models showed wide range in the correlation between stress amplitude and mean stress.

Análise da resistência à fratura entre pilares retos e angulados do sistema cone Morse

Objective The aim of this study was to verify the fatigue fracture resistance of the implant-abutment joint, in straight and angled types, subject to cyclic loads similar to chewing. Material and method It was used 32 implants system (3.75 × 11mm) with Morse taper and 32 abutment, divided in two groups: abutment straight and angled (n = 16) (Neodent, Curitiba, PR, Brazil). The sets were submitted to cyclic testing using servo-hydraulic equipment, fixing the number of cycles at 5 million. It was evaluated the number of cycles, load and moment force of the samples. The Fisher test and ANOVA were applied (p<0,005). Fractured samples were analyzed in the scanning electron microscopy (SEM). Result Straight abutment, four resisted the cycles number established, supporting loads between 470N and 510N. Angled abutment: nine resisted to loads between 570N and 890N. Regarding the fractured samples below the number of cycles, in the straight abutment, nine fractured with loads between 470N and 630N. In the angled abutment, five fractured with loads ranging from 760N and 890N. The moment of the force was calculated for each joint implant-abutment (Averages: Straight Group - 4335,23Nmm, angled Group - 3923,37Nmm). Conclusion Two types of abutments (straight and angled), in vitro conditions, statistically behaved similarly, and accepts the null hypothesis that there is no difference in fracture resistance between groups.