Stress singularity analysis in the restorations of premolar class ii cavities

Abstract

This paper presents the singular stress analysis near the apex of a structure formed during dental restoration of a premolar class II cavity. Based on the elasticity theory, the stresses may go to infinity at the junctions of different materials (e.g. dentine, enamel, restoration materials). Tensions will cause material separation and then material fracture. In order to reduce the failure probability, the degree of stress concentration has to be reduced. The stress singularity order and the stress intensity factor are two parameters, which are often used in fracture analysis. The objective of this paper is to find conditions such that non-singular stress fields are possible.Three critical positions in the restoration structure are discussed. They are the tips of interface between (1) enamel and restoration; (2) dentine and restoration; and (3) enamel, dentine and restoration. In the last two cases, the restoration may be bonded or debonded to enamel or dentine. After employing Kolosov-Muskhelishvili complex functions together with the eigenfunction expansion method, the singularity orders are computed theoretically. Weak stress singularity conditions can be sought by properly selecting cutting angles or restoration materials.

Effects of enamel anisotropy on stress singularities in restorations of premolar class II cavities

“…In this case (R = 1), the recommended cutting angle is θ 1 > 120 0 for resin composite and θ 1 > 130 0 for amalgam. Chue et al, (2003) and Hubsch and Middleton (2000) have obtained the same conclusion. As R decreases, the recommended angle will be shifted to the other angle region.…”

“…6(d) for isotropic an case (R = 1). The same result can be seen in Chue et al, (2003). The weakest stress singularity occurs at θ 1 .…”

“…In previous studies (Hubsch andMiddleton, 2000 andChue et al, 2003), some suggestions for restoration design have been made. The reader may refer to the Fig.…”

“…The r λ -1 type stress singularity is assumed, where r is the distance measured from the tip and λ -1 is defined as the singularity order. Chue et al (2003) studied the same problem with bonded and debonded interfaces between the polymer restoration and dental materials.…”

“…Spears et al (1993) pointed out that enamel has greater rigidity along the prismatic direction as compared with the direction perpendicular to it. We extend the same problem as the studies of Hubsch and Middleton (2000) and Chue et al (2003) and take the enamel anisotropy into consideration. The anisotropy effect on the stress singularities at the apex of the wedge or junction structures will be investigated.…”