title: Designed experiment evaluation of key variables affecting the cutting performance of rotary instruments.
abstract: BACKGROUND
  Laboratory studies of tooth preparation are often performed under a limited range of conditions involving single values for all variables other than the 1 being tested. In contrast, in clinical settings not all variables can be tightly controlled. For example, a new dental rotary cutting instrument may be tested in the laboratory by making a specific cut with a fixed force, but in clinical practice, the instrument must make different cuts with individual dentists applying a range of different forces. Therefore, the broad applicability of laboratory results to diverse clinical conditions is uncertain and the comparison of effects across studies is difficult.
  
  
  OBJECTIVE
  The purpose of this study was to examine the effect of 9 process variables on dental cutting in a single experiment, allowing each variable to be robustly tested over a range of values for the other 8 and permitting a direct comparison of the relative importance of each on the cutting process.
  
  
  METHODS
  The effects of 9 key process variables on the efficiency of a simulated dental cutting operation were measured. A fractional factorial experiment was conducted by using a computer-controlled, dedicated testing apparatus to simulate dental cutting procedures and Macor blocks as the cutting substrate. Analysis of Variance (ANOVA) was used to judge the statistical significance (α=.05).
  
  
  RESULTS
  Five variables consistently produced large, statistically significant effects (target applied load, cut length, starting rpm, diamond grit size, and cut type), while 4 variables produced relatively small, statistically insignificant effects (number of cooling ports, rotary cutting instrument diameter, disposability, and water flow rate).
  
  
  CONCLUSIONS
  The control exerted by the dentist, simulated in this study by targeting a specific level of applied force, was the single most important factor affecting cutting efficiency. Cutting efficiency was also significantly affected by factors simulating patient/clinical circumstances as well as hardware choices. These results highlight the importance of local clinical conditions (procedure, dentist) in understanding dental cutting procedures and in designing adequate experimental methodologies for future studies.
authors: Professor, Department of Mechanical Engineering, Hajim School of Engineering and Applied Sciences, University of Rochester, New York. Electronic address: paul.funkenbusch@rochester.edu.
authors: Paul D
authors: PD
authors: Funkenbusch
authors: Former Resident and Implant Fellow, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester, and Instructor, University of Toronto, Canada.
authors: Mario
authors: M
authors: Rotella
authors: Associate Professor, Chair and Program Director, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester, New York.
authors: Carlo
authors: C
authors: Ercoli
mesh_terms: D002516:Ceramics / Q000737:chemistry; D017076:Computer-Aided Design; D003754:Dental High-Speed Equipment / Q000592:standards*; D003764:Dental Materials / Q000737:chemistry; D018130:Diamond / Q000737:chemistry; D004209:Disposable Equipment; D004867:Equipment Design; D017743:Equipment Reuse; D006801:Humans; D008422:Materials Testing / Q000379:methods; D011312:Pressure; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D019246:Tooth Preparation / Q000295:instrumentation*; D014867:Water / Q000737:chemistry
chemical_list: D003764:Dental Materials; D014867:Water; D018130:Diamond; C023506:Glass ceramics