Grinding of composite cores using diamond burs with different grit sizes: the effects on the retentive strength of zirconia crowns

Aim: To evaluate the retention of Y-TZP crowns cemented in aged composite cores ground with burs of different grit sizes. Methods: Sixty composite resin simplified full-crown preparations were scanned, while 60 Y-TZP crowns with occlusal retentions were milled. The composite preparations were stored for 120 days (wet environment-37°C) and randomly distributed into three groups (n=20) according to the type of composite core surface treatment. The groups were defined as: CTRL (control: No treatment), EFB (extra-fine diamond bur [25µm]), and CB (coarse diamond bur [107µm]). The grinding was performed with an adapted surveyor standardizing the speed and pressure of the grinding. The intaglio surfaces on the crowns were air-abraded with silica-coated alumina particles (30 µm) and then a silane was applied. The crowns were cemented with self-adhesive resin cement, thermocycled (12,000 cycles; 5/55°C), stored (120 days) and submitted to a retention test (0.5mm/min). The retentive strength data (MPa) were analyzed using one-way analysis of variance and Tukey test, as well as Weibull analysis. Failures were classified as 50C (above 50% of cement in the crown), 50S (above 50% of cement in the substrate) and COE (composite core cohesive failure). Results: No statistical difference was observed among the retention values (p=0.975). However, a higher Weibull modulus was observed in the CTRL group. The predominant type of failure was 50S (above 50% of cement in the substrate composite). Conclusion: The retention of zirconia crowns was not affected by grinding using diamond burs with different grit sizes (coarse/extra-fine) or when no grinding was performed

Adhesive cementation of zirconia posts to root dentin: evaluation of the mechanical cycling effect

This study evaluated the effect of mechanical cycling on the bond strength of zirconia posts to root dentin. Thirty single-rooted human teeth were transversally sectioned to a length of 16 mm. The canal preparation was performed with zirconia post system drills (CosmoPost, Ivoclar) to a depth of 12 mm. For post cementation, the canals were treated with total-etch, 3-steps All-Bond 2 (Bisco), and the posts were cemented with Duolink dual resin cement (Bisco). Three groups were formed (n = 10): G1 - control, no mechanical cycling; G2 - 20,000 mechanical cycles; G3 - 2,000,000 mechanical cycles. A 1.6-mm-thick punch induced loads of 50 N, at a 45° angle to the long axis of the specimens and at a frequency of 8 Hz directly on the posts. To evaluate the bond strengths, the specimens were sectioned perpendicular to the long axis of the teeth, generating 2-mm-thick slices, approximately (5 sections per teeth), which were subjected to the push-out test in a universal testing machine at a 1 mm/min crosshead speed. The push-out bond strength was affected by the mechanical cycling (1-way ANOVA, p = .0001). The results of the control group (7.7 ± 1.3 MPa) were statistically higher than those of G2 (3.9 ± 2.2 MPa) and G3 (3.3 ± 2.3 MPa). It was concluded that the mechanical cycling damaged the bond strength of zirconia posts to root dentin.

Prótese adesiva em resina composta reforçada por fibra: relato de caso clínico / Inlay bridge made with fiber reinforced composite: a case report

As restaurações adesivas feitas com resinas compostas reforçadas por fibras têm sido propostas para a fabricação de próteses parciais fixas adesivas metal-free com retentor inlay. No entanto, em prótese com pequena extensão (três elementos), o desenho e as características de cada retentor da infra-estrutura de fibra são importantes e requerem critério. O reforço com as fibras é fundamental para que a prótese suporte ao máximo possível as cargas mastigatórias. Este artigo descreve um caso clínico em que se utilizou uma prótese parcial fixa de resina composta e alto volume de fibras como reforço da estrutura, para a reposição de um primeiro molar superior.

Surface roughness of glazed feldspar, alumina, and zirconia-based ceramics

A proposta deste estudo foi comparar a rugosidade superficial de cerâmicas feldspáticas, cerâmicasa base de zircônia e outra de alumina, avaliandoa hipótese que cerâmicas feldspáticas apresentammenor rugosidade superfi cial que cerâmicas de infraestrutura. Oito discos (diâmetro: 5mm; espessura:2mm) de cada cerâmica foram fabricados conformeas recomendações dos fabricantes: V7- cerâmicafeldspática (Vita VM7); VA- cerâmica feldspática (Vitadur-α); IA- cerâmica de alumina infiltrada porvidro (Vita In-Ceram Alumina); IZS- cerâmica dezircônia-alumina infi ltrada por vidro (Vita In-CeramZirconia); IZB- cerâmica de zircônia-alumina infi ltradapor vidro (Vita In-Ceram Zirconia 2000 for CerecInLab). Todos os materiais foram glazeados conformeas recomendações do fabricante. Quatro leituras derugosidade Ra (Mitutoyo SJ 400) por espécime foramfeitas, obtendo a média por espécime (n=8). Os dadosforam analisados pelo teste de ANOVA 1-fator e deTukey. (α=0,05). V7 apresentou a mais baixa médiade rugosidade (0,43±0,07 µm) comparada às outrascerâmicas. Não houve diferença estatística entre osvalores de VA (0,94±0,2 µm), IA (0,7±0,13 µm), IZS (0,98±0,3 µm) e IZB (0,75±0,4 µm). A hipótese foiparcialmente aceita. V7 teve uma superfície mais lisaque VA. Os valores de rugosidade das cerâmicas altamentecristalinas para infra-estrutura (IA, IZS, IZB)não foram diferentes estatisticamente.