Marginal and internal discrepancies of zirconia copings: Effects of milling system and finish line design.

Context: Discrepancies at the abutment/crown interface can affect the longevity of zirconia restorations. Aim: The aim was to evaluate the marginal and internal discrepancies (MD and ID) of zirconia copings manufactured by two milling systems with different finish lines. Materials and Methods: Three aluminum‑master‑dies (h = 5.5 mm; Ø =7.5 mm; 6°), with different finish lines (large chamfer [LC]; tilted chamfer [TC]; rounded shoulder [RS]) were fabricated. Twenty impressions were made from each master die and poured. Sixty zirconia copings were manufactured and divided according to the factors “finish line” and “milling system” (n = 10): CADLC = Computer‑aided design/computer‑aided manufacturing (CAD/ CAM) + LC; CADTC = CAD/CAM + TC; CADRS = CAD/CAM + RS; MADLC = manually aided design/manually aided manufacturing (MAD/MAM) + LC; MADTC = MAD/MAM + TC; and MADRS = MAD/MAM + RS. For MD analysis, each coping was fixed, and the distance between the external edges of the coping and the edge of the cervical preparation was measured (50 points). Using the same copings, the ID of each coping was evaluated, by the replica technique, at 12 points equally distributed among the regions (n = 10): Ray (R), axial (A), and occlusal (Occl). The measurements were performed by optical microscopy (×250). The data (μm) were subjected to parametric and non‑parametric statistical analyses. Results: For the MAD/MAM system, the “finish line” (P = 0.0001) affected significantly the MD median values (μm): LC = 251.80a, RS = 68.40a and TC = 8.10b (Dunn’s test). For the CAD/CAM system, the median MD values (μm) were not affected by the factor “finish line” (P = 0.4037): LC = 0.82a, RS = 0.52a, and TC = 0.89a. For the ID, it was observed interaction between the finish line types and the region (P = 0.0001) and between region and milling system (P = 0.0031) (RM‑ANOVA). Conclusions: The CAD/CAM system presented lower MD values, regardless the finish line. However, the MAD/MAM system showed ID values smaller than those of CAD/CAM.

Fatores de relevância na determinaçäo e registro da relaçäo cêntrica / Relevance factors in the determination and registration of the centric relation

Säo abordados os fatores de relevância na determinaçäo do registro da relaçäo cêntrica, tais como: posiçäo e relaxamento do paciente, técnica de manipulaçäo e material para registro. Seräo demonstradas as associaçöes entre técnicas e materiais que preencham os requisitos para um registro preciso da relaçäo cêntrica

Influência dos princípios biomecânicos nos preparos extra e intra-coronários em restaurações convencionais e adesivas / Influence of biomechanicals principles on intra and extra-coronals preparations in conventional and adhesives restaurations

Os preparos mudaram substancialmente desde a introdução da cimentação adesiva. As mudanças surgidas nos preparos extra e intra-coronários são relatadas enfatizando o adequamento sofrido em virtude das características dos materiais restauradores utilizados na cimentação adesiva