Fracture origins in twenty-two dental alumina crowns.

OBJECTIVES

The causes of in vivo fractures of all-ceramic dental crowns are not yet fully understood. The fracture origins often occur in the cervical margin in the approximal area, but the reason for this is unclear. The aim of this study was to evaluate the fracture origin of 22 of clinically-failed alumina crowns.

METHODS

The fracture surfaces of alumina crowns fractured in vivo were inspected by optical microscopy to evaluate the fracture patterns and identify the cause of fracture. Fracture maps were constructed as needed to interpret the patterns of breakage and to back track to a fracture origin area. A scanning electron microscope (SEM) was used to characterize the fracture origins of the 22 cases where the origin site was available.

RESULTS

The most common fracture origins were marginal defects either in the alumina core or in the veneer. The defects included thin, chipped, cracked or uneven crown margins and excess veneer on the inside of the crown. Multiple flaws were present along the margins in most specimens, but fracture origins were usually located in the region of the shortest axial wall. A few crowns had pores, contamination, or incomplete sintering that acted as fracture origins.

SIGNIFICANCE

Production method, handling, design and material insufficiencies influence the fracture of dental ceramic crowns. Machining defects and other margin flaws seem to be the most detrimental factors for alumina crowns. Feather-edge or sharp margins should be avoided. Smooth and moderately thick crown margins would probably dramatically improve the durability.