The effect of working tip angulation on root substance removal using Er:YAG laser radiation:: an in vitro study

Objectives: The present investigation attempted to determine the amount of cementum and/or dentin removal with Er:YAG laser radiation, dependent on the angulation of a specially-developed application tip. Material and methods: Subject of the study were 150 extracted incisors, canines, premolars, and molars. Source of laser radiation was an Er:YAG laser device emitting pulsed infrared radiation at a wavelength of 2.94 mum with a pulse duration of 250 mus and a pulse repetition rate of 10 pps. The samples of the 3 study groups were irradiated with 380 laser pulses at radiation energies of 60 mJ (group A), 100 mJ (group B), or 180 mJ (group C). In each group, 10 samples were treated at working tip angulations of 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees. The substance removal was determined 3-dimensionally using a newly developed laser scanning system (100,000 surface points per sample, accuracy 5 mum) and a special image-analysing software (Match 3D). Statistical analysis was completed with ANOVA followed by multiple comparisons using the Scheffe-test and with linear regression analysis according to Pearson-Bravais (p < 0.05). Results: Strong dependance of substance removal, both determined as maximum depth of the defects (0.5% quantil) as well as defect volume, on the angulation of the working tip was shown. At 60 mJ, the depth of the defects was 41.39 (<plus/minus>32.55) mum at an angulation of 15 degrees and that at 90 degrees was 181.39 +/- 74.42) mum (R-2 = 0.921. For the radiation energy at 100 mJ, the depth of the defects ranged from 51.96 (+/- 26.86) mum at 15 degrees to 306.64 (+/- 62.44) mum at 90 degrees (R-2 = 0.983). Choosing radiation energies at 180 mJ, the depth of the defects ranged from 64.73 (+/- 27.73) mum at 15 degrees to 639.89 (+/- 47.28) mum at 90 degrees, on average (R-2 = 0.853). Conclusions: The results of the present study provide clear evidence that besides the physical radiation parameters, also the parameters of clinical handling, in particular the angulation of the application tip, has a strong influence on the amount of root substance removal using Er:YAG laser radiation.