Effect of bonding amalgam on the reinforcement of teeth

Extensively weakened maxillary premolars may be more prone to fracture due to their small size. The weakening may be due to excessive demineralization of supporting tooth structure caused by dental caries or nonconservative or traumatic tooth preparation.

The purpose of this study was to determine the effect of a bonded amalgam restoration on reinforcement of weakened tooth structure.

Forty extracted noncarious maxillary premolars were collected. The teeth were prepared individually with mesio-occluso-distal (MOD) cavities with specific dimensions (cavity width buccolingually, 1.8 to 2.1 mm; palatal cusp width, 1.7 to 2.2 mm; cusp height, 4.7 to 5.0 mm) and divided into 4 groups (n=10). The first group was prepared and not restored (control). The other 3 groups were restored with amalgam (Megalloy), bonding agent (Syntac) with amalgam, and amalgam with an adhesive resin luting agent (Resinomer), respectively. Fracture load (in kg) for specimens in all groups was determined by applying a vertical splitting load through a specially shaped steel rod at a crosshead speed of 1 mm/min. The data were analyzed by 1-way analysis of variance and least significant difference statistical tests (alpha=.01).

The mean force and standard deviation values required to fracture the cusp of the control and amalgam groups were 25.2+/-3.27 kg and 26.1+/-3.07 kg , respectively, with no significant difference between the 2 groups (P>.01). Significant differences were found between control and Syntac groups (29.8+/-2.80 kg), as well as between control and Resinomer groups (37.9+/-3.55 kg). Significant difference was also noted between Syntac and Resinomer groups (P>.01)

It was concluded that the use of resin cement increased the fracture resistance of the tooth with an MOD amalgam restoration.