Watson T F, Cook R J
Department of Conservative Dentistry, United Medical School of Guy's Hospital, Guy's Dental School, London, United Kingdom.
J Dent Res. 1995 Nov;74(11):1749-55. doi: 10.1177/00220345950740110601.
This study aimed to determine the degree of eccentricity between different tungsten carbide bur manufacturing techniques and to study the effect of bur inaccuracy on dental enamel. Error in bur concentricity may arise from malalignment of the steel shaft and carbide head in a two-piece construction bur. Cutting blades rotate at multiple radii from the shaft axis, potentially producing vibrations and damage to the cut substrate. Techniques now allow for the manufacture of one-piece tungsten carbide burs with strength adequate to withstand lateral loading. A comparison of tungsten carbide dental cutting tools revealed the true extent of concentricity errors. Variation in alignment of the cutting head and shaft in the two-part constructions incurred between 20 and 50 microns of additional axial error. High-speed cutting interactions with dental enamel between carbide burs were studied by means of a video-rate confocal microscope. A cutting stage fitted to a Tandem Scanning Microscope (TSM) allowed for real-time dynamic image acquisition. Images were captured and retrieved by means of a low-light-level camera recording directly to S-VHS videotape. Videotape showing the interactions of high-speed rotary cutting instruments (at 120,000 rpm) were taken under simulated normal wet-cutting environments, and the consequent damage to the tooth tissue was observed as it occurred. Concentrically engineered bur types produced a superior quality cut surface at the entry, exit, and advancing front aspects of a cavity, as well as less subsurface cracking. Imaging of the coolant water film local to recent cutting operations showed regular spherical cutting debris of 6 to 18 microns diameter from the concentric tools, whereas the less-well-engineered burs produced ragged, irregular chips, with 25-40 microns diameter debris, indicating far more aggressive cutting actions. This study has shown that there is reduced substrate damage with high-concentricity carbide burs.
本研究旨在确定不同碳化钨车针制造工艺之间的偏心程度，并研究车针精度误差对牙釉质的影响。两件式结构车针中，钢轴与硬质合金头部未对准可能导致车针同心度出现误差。切割刀片围绕轴的轴线在多个半径上旋转，可能会产生振动并对切割的基底造成损伤。现在的技术能够制造一体式碳化钨车针，其强度足以承受侧向载荷。对碳化钨牙科切割工具的比较揭示了同心度误差的真实程度。两部分结构中切割头与轴的对准偏差会产生20至50微米的额外轴向误差。借助视频速率共聚焦显微镜研究了碳化钨车针与牙釉质之间的高速切割相互作用。安装在串联扫描显微镜（TSM）上的切割台可进行实时动态图像采集。图像通过低光水平相机直接记录到S-VHS录像带上进行捕捉和检索。在模拟正常湿切环境下拍摄了显示高速旋转切割器械（转速为120,000转/分钟）相互作用的录像带，并观察了对牙齿组织随之产生的损伤。经过同心设计的车针类型在窝洞的入口、出口和推进前沿处产生的切割表面质量更高，并且表面下裂纹更少。对近期切割操作局部的冷却液水膜成像显示，同心工具产生直径为6至18微米的规则球形切割碎屑，而设计欠佳的车针产生的碎屑参差不齐、不规则，直径为25 - 40微米，表明切割作用更为剧烈。本研究表明，高同心度碳化钨车针可减少对基底的损伤。
