A study on the fracture strength of collarless metal-ceramic fixed partial dentures

PURPOSE. The objective of this study was to evaluate fracture strength of collarless metal-ceramic FPDs according to their metal coping designs. MATERIALS AND METHODS. Four different facial margin design groups were investigated. Group A was a coping with a thin facial metal collar, group B was a collarless coping with its facial metal to the shoulder, group C was a collarless coping with its facial metal 1 mm short of the shoulder, and group D was a collarless coping with its facial metal 2 mm short of the shoulder. Fifteen 3-unit collarless metal-ceramic FPDs were fabricated in each group. Finished FPDs were cemented to PBT (Polybutylene terephthalate) dies with resin cement. The fracture strength test was carried out using universal testing machine (Instron 4465, Instron Co., Norwood MA, USA) at a cross head speed of 0.5 mm/min. Aluminum foil folded to about 1 mm of thickness was inserted between the plunger tip and the incisal edge of the pontic. Vertical load was applied until catastrophic porcelain fracture occurred. RESULTS. The greater the bulk of unsupported facial shoulder porcelain was, the lower the fracture strength became. However, there were no significant differences between experimental groups (P>.05). CONCLUSION. All groups of collarless metal-ceramic FPDs had higher fracture strength than maximum incisive biting force. Modified collarless metal-ceramic FPD can be an alternative to all-ceramic FPDs in clinical situations. [J Adv Prosthodont 2010;2:134-41]

Confronto tra la precisione marginale di corone in disilicato di litio monolitiche (full-contour) e stratificate

OBJECTIVES. Monolithic all-ceramic fixed partial dentures are reported to be cost-effective and more resistant than layered counterparts. Monolithic crowns are more resistant to a type of failure called chipping and also aesthetically acceptable.Lithium disilicate blocks can be milled to obtain aesthetic, stronger and cheaper prosthetic manufacturing: without layering, lead times and costs are highly reduced.Although monolithic crowns seem to be more advantageous, during the layering process, crowns are submitted to the same thermic cycle as the monolithic, but this may yield different results as to marginal gaps. The aim of this study is to compare the fitting of monolithic and layered lithium disilicate all-ceramic crowns using the replica technique.MATERIALS AND METHODS. An upper incisor and a canine were prepared to receive ceramic restoration. For each tooth, 6 monolithic and 6 layered crowns were replicated using CAD/CAM technology and IPS e. max (R) CAD lithium disilicate blocks (Ivoclar-Vivadent, Shaan, Liechtenstein), thus obtaining 24 crowns divided into 4 groups: Group A, layered incisors; Group B, layered canines; Group C, monolithic incisors; Group D, monolithic canines. In order to determine the marginal gap, materials of two different colours were used for the replica technique. When the replica was obtained, it was cut into four pieces and observed through the microscope and the four marginal points could be measured thanks to the two different material colours.RESULTS. All crowns showed a marginal gap of over 100 mu m with different valuves in each group; such differences, however, are not statistically significant and are neither correlated with the fabrication technique, nor with the type of tooth.CONCLUSIONS. There is no statistical significance in the difference between monolithic and layered crowns marginal gaps. Although both types of crowns were obtained with the same CAD/CAM technology, the layering process is not involved in the precision level of marginal gaps

Marginal fit of anterior 3-unit fixed partial zirconia restorations using different CAD/CAM systems

PURPOSE: Few studies have investigated the marginal accuracy of 3-unit zirconia fixed partial dentures (FPDs) fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) system. The purpose of this study was to compare the marginal fit of zirconia FPDs made using two CAD/CAM systems with that of metal-ceramic FPDs. MATERIALS AND METHODS: Artificial resin maxillary central and lateral incisors were prepared for 3-unit FPDs and fixed in yellow stone. This model was duplicated to epoxy resin die. On the resin die, 15 three-unit FPDs were fabricated per group (45 in total): Group A, zirconia 3-unit FPDs made with the Everest system; Group B, zirconia 3-unit FPDs made with the Lava system; and Group C, metal-ceramic 3-unit FPDs. They were cemented to resin dies with resin cement. After removal of pontic, each retainer was separated and observed under a microscope (Presize 440C). Marginal gaps of experimental groups were analyzed using one-way ANOVA and Duncan test. RESULTS: Mean marginal gaps of 3-unit FPDs were 60.46 µm for the Everest group, 78.71 µm for the Lava group, and 81.32 µm for the metal-ceramic group. The Everest group demonstrated significantly smaller marginal gap than the Lava and the metal-ceramic groups (P<.05). The marginal gap did not significantly differ between the Lava and the metal-ceramic groups (P>.05). CONCLUSION: The marginal gaps of anterior 3-unit zirconia FPD differed according to CAD/CAM systems, but still fell within clinically acceptable ranges compared with conventional metal-ceramic restoration