Fracture load and failure mode of semi-direct resin composite occlusal veneers: Influence of design and mechanical cycling.

AIMS: To evaluate the influence of the type of preparation and mechanical cycling on the fracture load and failure mode of semi-direct posterior resin composite restorations. METHODS: In total, 70 healthy third molars were used; 10 belonging to the control group (C - unprepared teeth) and 60 teeth prepared and restored with nanoparticle resin composite, divided into 3 groups (n = 20): O - exclusively occlusal preparation (Table Top); OV - occlusal preparation with buccal extension (Veneerlay); OVP - Occlusal preparation with chamfer on the proximal and buccal-lingual/palatal surfaces (Overlay). The preparations were performed with diamond burs with a thickness of 1 mm. The restorations were made with nanoparticulate resin composite (Filtek Z350 XT) and subsequently received additional polymerization (thermoprocessing). Cementation was performed with the use of universal adhesive system (Single Bond Universal) on dental substrate and dual resin cement (RelyX ARC). Half of the teeth in each group (n = 10) were submitted to mechanical cycling, simulating 6 months of clinical service (5 × 105 fatigue cycles), under dynamic loading of 130 N, at a frequency of 2Hz. Fracture load tests were performed in a universal testing machine with a 200 kgf load cell. Failure mode was classified using scores. Generalized linear models and Fisher Exact tests were applied to the data (significance level of 5%). RESULTS: There were no significant differences between the types of preparation (p = 0.9435), or relative to cycling (p = 0.3764). The Fisher Exact Test showed a significant association between the groups and the type of failure (p = 0.0006), with preparations O (with cycling) and OVP (with and without cycling) exhibiting most failures with restoration fractures without involvement of the dental remnant. CONCLUSIONS: Semi-direct restorations showed resistance to fracture load similar to that of healthy teeth and were capable of withstanding functional masticatory loads. The type of preparation influenced the failure mode of teeth. The Table Top and Overlay types of preparations were those had fewer catastrophic failures, suggesting that since they are more conservative preparations, they made it possible for the tooth to receive a new restorative procedure in the future in cases of failures.

Comparação de Diferentes Técnicas de Moldagem com Silicone de Adição - Estudo in vitro / Comparison of Different Impression Techniques With Addition Silicone - in vitro Study

Objetivo: Comparar diferentes técnicas de moldagem com silicone de adição, quanto à precisão e fidelidade da cópia através de medidas manuais e sobreposição em CAD/CAM. Material e método: Foram realizadas 4 moldagens com silicone de adição de um mesmo modelo nas seguintes técnicas: T1 ­ dois passos com recorte; T2 ­ dois passos com alívio de filme PVC; T3 ­ dois passos sem alívio e T4 - simultânea. A fidelidade das 4 técnicas de moldagem foi avaliada por meio de mensurações de 5 dimensões nos modelos de gesso vazados em cada um dos moldes obtidos. Outra forma de análise foi a sobreposição de imagens no CAD/CAM, com a finalidade de verificar se há semelhanças ou diferenças dimensionais entre o modelo piloto e as amostras. As medidas obtidas foram submetidas ao teste ANOVA com comparações múltiplas pelo teste de Tukey (α=0,05). Resultados: De acordo com as mensurações, a técnica que apresentou maior discordância do modelo piloto foi a T4, não havendo diferença entre as outras técnicas. Na avaliação em CAD/CAM, as técnicas T4 e T3 apresentaram maiores diferenças em relação ao modelo original de acordo com as imagens sobrepostas. Conclusões: Todas as técnicas estudadas apresentaram alterações dimensionais, em especial a técnica simultânea e a sem alívio, tanto nas medidas obtidas quanto na análise em CAD/CAM.

Objetives: To compare different impression techniques with addition silicone, by means of copy accuracy through manual measurements and overlaping in CAD/CAM. Material and methods: Four impressions of a same pilot model were carried out with silicone addition in different techniques: T1 ­ two steps with cut-back; T2 ­ two steps with PVC film relief; T3 ­ two steps without relief; and T4 ­ one step. The accuracy of the 4 different impression techniques was assessed by measuring 5 dimensions on stone casts poured from the impressions of the pilot model. Another analysis was carried out in CAD/CAM using the overlaping of the casts and the pilot model, in order to verify dimensional similarities and differences between them. The values obtained were submitted to ANOVA and Tukey test, for multiple comparisons (α=0.05). Results: According to the measures done, the technique that generated the greatest difference from the pilot model was T4, with no difference among the other techniques. In CAD/CAM analysis, techniques T4 and T3 presented more differences from the original model. Conclusions: All studied techniques presented dimensional changes, mainly the 1 step and the 2 step without relief, in both methods, measures and CAD/CAM analysis.