Multiple Use of Diamond Burs and Restoration Leakage

Objectives: Diamond burs are claimed to maintain cutting efficiency with repeated use. This was tested by cutting a series of 5 preparations and then assessing the leakage following conditioning and restoration. Methods: 60 extracted anterior and premolar teeth were used. 30 teeth were prepared with 3x2x2 mm Class V preparations ½ in enamel and ½ in cementum. 10 teeth were prepared with a new diamond bur for each tooth. The burs were then used to cut a Cl V preparation in spare teeth before being used to prepare a 2nd series of 10 teeth, i.e. the 3rd use of the bur. The burs were used to cut Cl V preparations in spare teeth before preparing a 3rd set of 10 teeth, i.e. the 5th use of each bur. The existing restorations in a 2nd group of 30 teeth, previously used in leakage studies, were removed and the preparations extended using the same regimen of 1, 3 and 5 uses of each bur. Thereafter all preparations were etched, conditioned and restored with composite resin. Leakage was followed electrochemically in 1% NaCl for 30 days using a 20 V dc power source and a stainless steel counter electrode. Results: Freshly prepared and restored teeth showed markedly less leakage than re-prepared teeth. Tooth leakage was similar for the 1st and 3rd time bur use but it was far greater with the 5th bur use (p<0.01). With previously restored teeth, those cut with 1st and 5th use burs leaked less than with 3rd usage burs (p<0.01). Conclusion: Re-use of a bur had little effect on leakage of teeth that were re-prepared and restored. With freshly prepared teeth, greater leakage was found with repeated use of burs. Restoration removal and re-preparation of teeth resulted in greater leakage than for freshly prepared teeth.