Experimental Study on Removal of Three Kinds of Occlusal Veneer by Er:Yag Laser.

Objectives: To analyze and compare the effect of Er:Yag laser on the microstructure of all-ceramic onlay and tooth tissue, and to provide a theoretical basis for laser non-invasive removal of all-ceramic onlay.
Methods: Freshly extracted orthodontic mandibular premolars were selected, and after standardized tooth preparation, three different thicknesses (1mm,1.5mm,2mm) and different materials (IPS e.max, Lava Esthetic, emberized porcelain) were made for adhesive. One week later, Er:Yag laser (3W,4W) was used to irradiate the all-ceramic onlays, and the time was recorded. The microscopic morphology after removal was observed by electron microscopy.
Results: The emollient porcelain occlusal veneers could not be removed even after a long time (> 20 minutes) of irradiation. The time of removing bonding in 3W power group: the 1mm Lava Esthetic group (100±10s) is greater than the 1mm e.max group (80±15s) (P < 0.05). The 1.5mm Lava Esthetic group (625±20s) was greater than the 1.5mm e.max group (245±15s) (P < 0.05). The bonding removal time of 4W power group: 2mm Lava Esthetic (381±24s) is greater than that of 2mm e.max group (341.5±26.5s).
Conclusions: With the same material and the same thickness, the greater the laser power, the shorter the removal time. When the laser power is small, it may lead to the onlay cannot be removed. Under the same thickness and the same power, the laser penetrating through the ceramic block to the bonding layer may affect the structure of the ceramic block. In the case of the same material and the same power, the thicker the porcelain block is, the longer the time required for dismantling and the higher the power required. Laser could not remove the resin-like ceramic onlays directly.