Watson T F, Flanagan D, Stone D G
Division of Conservative Dentistry, Guy's, King's & St Thomas' Dental Institute, KCL, Guy's Hospital, London Bridge.
Br Dent J. 2000 Jun 24;188(12):680-6. doi: 10.1038/sj.bdj.4800576.
The aim of these experiments was to compare the cutting dynamics of high-speed high-torque (speed-increasing) and high-speed low-torque (air-turbine) handpieces and evaluate the effect of handpiece torque and bur type on sub-surface enamel cracking. Temperature changes were also recorded in teeth during cavity preparation with high and low torque handpieces with diamond and tungsten carbide (TC) burs. The null hypothesis of this study was that high torque handpieces cause more damage to tooth structure during cutting and lead to a rise in temperature within the pulp-chamber.
Images of the dynamic interactions between burs and enamel were recorded at video rate using a confocal microscope. Central incisors were mounted on a specially made servomotor driven stage for cutting with a type 57 TC bur. The two handpiece types were used with simultaneous recording of cutting load and rate. Sub-surface enamel cracking caused by the use of diamond and TC burs with high and low torque was also examined. Lower third molars were sectioned horizontally to remove the cusp tips and then the two remaining crowns cemented together with cyanoacrylate adhesive, by their flat surfaces. Axial surfaces of the crowns were then prepared with the burs and handpieces. The teeth were then separated and the original sectioned surface examined for any cracks using a confocal microscope. Heat generation was measured using thermocouples placed into the pulp chambers of extracted premolars, with diamond and TC burs/high-low torque handpiece variables, when cutting occlusal and cervical cavities.
When lightly loaded the two handpiece types performed similarly. However, marked differences in cutting mechanisms were noted when increased forces were applied to the handpieces with, generally, an increase in cutting rate. The air turbine could not cope with steady heavy loads, tending to stall. 'Rippling' was seen in the interface as this stall developed, coinciding with the bur 'clearing' itself. No differences were noted between different handpieces and burs, in terms of sub-surface enamel cracking. Similarly, no differences were recorded for temperature rise during cavity preparation.
Differences in cutting mechanisms were seen between handpieces with high and low torque, especially when the loads and cutting rates were increased. The speed increasing handpiece was better able to cope with increased loading. Nevertheless, there was no evidence of increased tooth cracking or heating with this type handpiece, indicating that these do not have any deleterious effects on the tooth.
这些实验的目的是比较高速高扭矩（增速）和高速低扭矩（气涡轮）手机的切割动力学，并评估手机扭矩和车针类型对牙釉质表面下裂纹的影响。在使用高扭矩和低扭矩手机搭配金刚石和碳化钨（TC）车针进行窝洞制备过程中，还记录了牙齿的温度变化。本研究的零假设是，高扭矩手机在切割过程中对牙齿结构造成的损伤更大，并导致牙髓腔内温度升高。
使用共聚焦显微镜以视频速率记录车针与牙釉质之间动态相互作用的图像。将中切牙安装在特制的伺服电机驱动平台上，使用57型TC车针进行切割。使用两种类型的手机，同时记录切割负荷和速率。还检查了使用高扭矩和低扭矩的金刚石和TC车针导致的牙釉质表面下裂纹。将下颌第三磨牙水平切开以去除牙尖，然后将剩余的两个牙冠通过其平坦表面用氰基丙烯酸酯粘合剂粘在一起。然后用车针和手机制备牙冠的轴向表面。然后将牙齿分开，使用共聚焦显微镜检查原始切开表面是否有任何裂纹。在使用金刚石和TC车针/高-低扭矩手机变量切割咬合面和颈部窝洞时，使用放置在拔除的前磨牙牙髓腔内的热电偶测量热量产生。
在轻载时，两种类型的手机表现相似。然而，当对手机施加更大的力时，切割机制存在明显差异，通常切割速率会增加。气涡轮无法应对稳定的重负荷，容易失速。随着这种失速的发展，在界面处可见“波纹”，这与车针“清理”自身相吻合。在牙釉质表面下裂纹方面，不同手机和车针之间未发现差异。同样，在窝洞制备过程中记录的温度升高也没有差异。
高扭矩和低扭矩手机在切割机制上存在差异，尤其是当负荷和切割速率增加时。增速手机更能应对增加的负荷。然而，没有证据表明这种类型的手机会增加牙齿裂纹或发热，这表明这些对牙齿没有任何有害影响。
