Effect of thickness of cavity wall on fracture strength of pulpotomized primary molar teeth with class II amalgam restorations

Summary

Aim: This was to evaluate the effect of different thicknesses of cavity walls on fracture strength of pulpotomized primary molar teeth with class II amalgam restorations. Methods: 80 carious extracted human primary molar teeth were selected for pulpotomy preparation. The teeth were divided into four groups. Mesio- or disto-occlusal (20 teeth) and mesio-occluso-distal (20 teeth); cavities were prepared in both first and second primary molar teeth. Each group was divided into two subgroups of ten teeth according to the thickness of their walls (1.5 or 2.5 mm). After restoring teeth with amalgam, all groups were stored in distilled water at 37°C for seven days. They were then thermo cycled 1,000 times between 5° to 55°C. The specimens were then subjected to a compressive axial load in a universal testing machine at a crosshead speed of 0.5 mm min⁻¹. The t-test was used for statistical analysis. Results: Mean fracture resistances of the first and second molar teeth were 975.5 ± 368.8 and 1049.2 ± 540.1, respectively. In the first molars, fracture resistance of 2-surface cavities was significantly more than 3-surface cavities (p=0.001), but this difference was not statistically significant in second molars. In second molars, fracture strength in 2- and 3-surface cavities with a 2.5 mm thickness in the walls was more than those with 1.5 mm thickness. However, in first molars this difference was only statistically significant in 3-surface cavities (p=0.045). Conclusions: The fracture strength in pulpotomized primary molar teeth with amalgam restorations was high, more than maximum bite forces in primary teeth, even in extensive 3-surface cavities.