Summary :
Objectives: To evaluate the removal of subgingival calculus and dental hard tissues depending on the threshold level of a fluorescence feedback-controlled Er:YAG laser. Material and Methods: Twenty teeth with calculus on the root surface were treated with an Er:YAG laser. Laser settings were 140 mJ and 10 Hz. The initial fluorescence threshold level of 5 [U] was reduced at intervals of 1 [U] for every laser treatment. Areas of residual calculus (RC) were evaluated using a surface analysis software. Loss of dental hard tissues was assessed by histomorphometric analysis of undecalcified ground sections. Results: Using a threshold value of 5 [U], the median amount of RC was 11% (0–78%). By lowering the threshold levels, the amount of RC decreased [level 1 [U]: 0% (0–26%)]. The laser-treated root surfaces revealed a statistically significant reduction of the cementum thickness [median: 80 mm (0–250)] compared with the nontreated opposite side [median: 90 mm (30–250)] ( po0.05). Conclusion: The amount of RC following laser irradiation depends on the fluorescence threshold level for a feedback-controlled Er:YAG laser. It might be suggested that this laser system may be used with a threshold level even lower than 5 [U] without removing a clinically relevant amount of root cementum.

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