Ultra-morphological and analytical-chemical changes of lased carious dentin and adhesive properties of resin bonding systems

激光[Er：YAG（Erwin^R，60 mJ，10 pps），CO_2（Topal^R，1 W，0.3sec）]烧蚀牙本质可降低树脂粘接系统的粘接性能。所谓的“激光蚀刻”可能不能有效地促进粘附。未脱钙标本的透射电镜观察表明，酸蚀牙本质表面的形态变化在激光照射牙本质的次表层没有表现出来。由于结构缺陷和热变性层的形成，它在机械上被削弱，从而导致相当低的粘合性能。与平坦表面相比，在楔形缺陷中获得了显著较低的粘结强度。结构因子（C-factor）可能是影响牙本质粘接强度的一个重要因素，而高能激光（Er：YAG：250 mJ，10 pps，CO_2：3 W，0.3sec）对牙本质粘接强度几乎没有影响。低功率激光（Er：YAG：60 mJ，1 pps，CO_2：1 W，0.3sec）照射牙本质后，脱钙牙本质表面形成无定形基质（Er：YAG：3 ~ 4μm，CO_2：1 ~ 2μm），基质中含有变性胶原纤维。而高功率激光（Er：YAG：250 mJ，1 pps，CO_2：3 W，0.3sec）处理牙本质，其形态结构与正常牙本质（Er：YAG）或牙本质表层（CO_2）几乎没有区别，牙本质表层有少量无定形基质和胶原纤维断裂，并有横纹。认为高能激光烧蚀的效果可能仅限于表层。CO_2激光照射（1 W，0.3sec）龋坏牙本质后，牙本质表面几乎没有热变性层，与低速钢布尔斯钻的牙本质表面几乎没有热变性层。龋病影响的牙本质作为树脂粘接系统的粘接剂时，需要进一步的研究。

Laser ablation [Er:YAG (Erwin^R, 60mJ, 10pps), CO_2 (Topal^R, 1W, 0.3sec)] of dentin reduced adhesive properties of resin bonding systems. The so-called "laser-etching" might not be effective in promoting the adhesion. By the TEM observations of non-decalcified specimens, such morphological changes as observed in the acid-etched dentin surface could not be detected in the subsurface layer of the lased dentin. It was mechanically weakened due to the formation of structural defects and heat-denatured layer, leading to considerably lower adhesive properties. Significantly lower bond strength was obtained in the wedge-shaped defects, as compared with the flat surfaces. Configuration factor (C-factor) might be an important factor especially for the adhesion to lased dentin.However, high-energy laser ablation of dentin (Er:YAG : 250mJ, 10pps, CO_2 : 3W, 0.3sec) hardly reduced the bond strength. In the subsurface layer of low-power lased dentin (Er:YAG : 60mJ, 1pps, CO_2 : 1W, 0.3sec), TEM observations of decalcified specimens revealed that the amorphous matrix substances containing denatured collagen fibers were generated (Er:YAG : 3〜4μm, CO_2 : 1〜2μm). On the other hand, in the high power lased dentin (Er:YAG : 250mJ, 1pps, CO_2 : 3W, 0.3sec), such morphological structure as hardly distinguished from sound dentin (Er:YAG) or the subsurface dentin layer having both little amorphous matrix and torn collagen fibers with cross-striation (CO_2) was observed. It was considered that the effects of high-energy laser ablation might be limited to superficial layer. CO_2 laser irradiation (1w, 0.3 sec) of carious dentin produced almost the same morphology with little heat-denatured layer as that by low-speed steel burs.It was concluded that the amount of irradiation energy and/or the value of c- factor had to be considered when evaluating the adhesive properties. Further investigation was necessary when caries-affected dentin was used as an adherent of resin bonding systems.