Fracture resistance of human teeth with mesial-occlusal-distal cavities prepared with sharp and round internal line...

Conservative MOD amalgam-type preparations of similar dimensions were cut in extracted contralateral maxillary first premolars; one preparation for each pair had sharp internal line angles and the other had a rounded internal form. The data do not demonstrate a statistically significant difference in resistance to fracture between the two groups. The difference in preparation produced by the use of a flat-end bur vs. a rounded-end bur does not appear to produce a great enough concentration of stress to significantly weaken teeth with conservative preparations.