Abstract:

Objective：To investigate the effects of erbium:yttrium aluminium garnet (Er:YAG)laser irradiation on pulp and formation of dentin bridge. The beagle dogs' coronal pulp is amputated by Er:YAG laser. Methods: In the study, 24 premolar teeth of two one-year-old Beagle dogs were used. They were divided into 3 groups: bur group, 200 mJ laser group,100 mJ laser group. The coronal pulp were removed by traditional bur or 200 mJ/20 Hz or 100 mJ/20 Hz Er:YAG laser. Then, they were dressed with mineral trioxide aggregate (MTA) and sealed with resin. Clinical, radiological and histological analyses were performed  1 day, 2 weeks, 4 weeks and 8 weeks after treatment. The mobility and gingiva si-tuation were evaluated for clinical evaluation. Periapical films were used for radiological evaluation. The extracted teeth were preserved in 10% formalin. After decalcification, tissue processing, paraffin embedding, serial sectioning at 5 μm thickness, staining (Hematoxylin and Eosin, HE), the samples were assessed by an independent observer for calcified bridge formation and radicular pulp inflammation. The mean thickness of dental bridge was measured if there was complete dental bridge.  Results: Clinical evaluation: there were no signs of fistula or mobility or any abnormal symptoms in Er:YAG laser groups and bur group during the observation period. Radiological evaluation: there were no signs of widened pe-riodontal ligament or root absorption or periapical radiolucency in Er:YAG laser groups and bur group. Histological evaluation: there was no severe inflammation reaction in 200 mJ/20 Hz, 100 mJ/20 Hz Er:YAG laser groups and bur group-1 day, 2 weeks, 4 weeks, 8 weeks post-operation in Hematoxylin and Eosin staining. A complete dentin bridge could be observed in 200 mJ/20 Hz, 100 mJ/20 Hz Er:YAG laser groups, while no complete dentin bridge  in bur group-2 weeks post-operation. Complete dental bridge could be observed in each group-4 and 8 weeks post-operation. The mean thickness of dental bridge-4 weeks post-operation in 200 mJ laser group was 77 μm, 100 mJ laser group 87 μm, and bur group  101 μm, and-8 weeks post-operation in 200 mJ laser group was 222 μm，100 mJ laser group-160 μm，and bur group 152 μm. Conclusion: The 200 mJ/20 Hz and 100 mJ/20 Hz Er:YAG laser pulpotomies show no harm to radicular pulp and can promote the formation of dentin bridge.

Key words: Pulpotomy, Er:YAG laser, Dentin, Dogs