Er,Cr:YSGG 雷射製備牙本質窩洞之形態分析及複合樹脂填補後鍵結關係之探討

Abstract

For many years, dentists have used conventional mechanical high speed systems to remove diseased dental hard tissues and prepare cavities for restoration. This process is efficient but uncomfortable for the patient. Therefore, lots of investigators tried hard to obtain a new model to solve these problems. Research concerning dental applications of lasers has been undertaken for more than 40 years. Recently, Er:YAG and Er,Cr:YSGG lasers, with wavelengths corresponding to absorption peaks for water and hydroxyapatite, have been shown to remove dental hard tissue effectively without causing undesirable thermal effects. Based on the literature reviews, the dentin surface after Er,Cr:YSGG laser irradiation was very clean, with patent tubule orifices and lacked of smear layer coverings. So it might be a favorable technique for the removal of carious dentin and cavity preparation, followed by composite resin restoration. However, surprisingly little attention has given to the evaluation of the quality of the Er,Cr:YSGG laser irradiated dentin surface for composite resin bonding. Thus the aim of this study was to investigate bonding between human dentin and composite resins in cavities prepared with an Er,Cr:YSGG laser, compared with high-speed drills. The morphological features of the irradiated dentin after acid etching were also observed. This study consisted of three parts. The first part compared the morphological analysis of the prepared dentin surface between Er,Cr:YSGG laser irradiation and high speed bur drilling, before and after 37% phosphoric acid etching. The laser was set at 3.0 W with 80% water and 80% air, in non-contact mode. The 2 x 2 mm square and 1 mm deep cavities, which were prepared on approximate 3 mm thick dentin disks, were then observed under light stereoscopy and scanning electron microscopy. The second part of our study was to observe the resin-dentin bonding interfaces. The cavities grouped as the first part were treated with adhesive (One Coat Bond, Coltener) followed by composite resin (Palfique Estelite Paste) restoration. After splitting, the dentin discs were observed under scanning electron microscopy after dentin-resin interface demineralization (10N HCl) and deproteinization (1% NaOCl). The final component of this study was to estimate the tensile bond strength of the groups just like the above. The INSTRON Universal Testing Machine was chosen with testing speed set at 0.5 mm/min. After test, the data was computed by Kruskall-Wallis statistics and the fracture modes were recorded, followed by scanning electron microscopy observation. The Er,Cr:YSGG laser beam produced cavities without signs of thermal damage of dentin. Undesirable thermal effects such as surface cracking or carbonization were not observed. In cavities prepared with high-speed drills, resin tags were more frequent and thicker in dentin subjected to acid etching then without etching. Bonding to laser irradiated dentin resulted in more and thicker resin tags in cavities compared with high speed drills; moreover, the removal of intertubular dentin was more prominent than peritubular dentin. Acid etching resulted in hybrid layers that could be detected under SEM observation. The tensile bond strength of the high speed bur preparation after acid etching was 5.37 MPa, which is not significantly different (p > 0.05) to that of Er,Cr:YSGG laser irradiation after acid etching, 5.17 MPa. The tensile bond strength of the Er,Cr:YSGG laser irradiation without acid etching was 3.29 MPa, which is significantly lower (p < 0.05) than the above two. As for the fracture modes, 5 adhesive failures (type 1), as well as 4 partial adhesive and partial cohesive failure (type 2) and 1 cohesive failure in resin (type 3) were noted in the group treated with high speed bur preparation with acid etching. 3 type 1 and 7 type 2 failure modes were in the teeth irradiated with Er,Cr:YSGG laser with acid etching. Without acid etching, 7 type 1 and 3 type 2 failure modes were recorded. These findings indicated that it is possible to remove dentin using Er,Cr:YSGG laser irradiation with minimal thermal damage. Bonding between resin and dentin after laser irradiation was equivalent to the conventional technique. Further studies should be conducted in order to obtain more information about the characteristics of Er,Cr:YSGG laser irradiated dentin.