title: Multivariate evaluation of the cutting performance of rotary instruments with electric and air-turbine handpieces.
abstract: BACKGROUND
  Laboratory studies of tooth preparation often involve single values for all variables other than the one being tested. In contrast, in clinical settings, not all variables can be adequately 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 different forces. Therefore, the broad applicability of laboratory results to diverse clinical conditions is uncertain and the comparison of effects across studies difficult.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to examine the effects of 9 process variables on the dental cutting of rotary cutting instruments used with an electric handpiece and compare them with those of a previous study that used an air-turbine handpiece.
  
  
  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 an electric handpiece in a computer-controlled, dedicated testing apparatus to simulate dental cutting procedures with Macor blocks as the cutting substrate. Analysis of variance (ANOVA) was used to assess the statistical significance (α=.05).
  
  
  RESULTS
  Four variables (targeted applied load, cut length, diamond grit size, and cut type) consistently produced large, statistically significant effects, whereas 5 variables (rotation per minute, number of cooling ports, rotary cutting instrument diameter, disposability, and water flow rate) produced relatively small, statistically insignificant effects. These results are generally similar to those previously found for an air-turbine handpiece.
  
  
  CONCLUSIONS
  Regardless of whether an electric or air-turbine handpiece was used, 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 and hardware choices. These results highlight the greater importance of local clinical conditions (procedure, dentist) in understanding dental cutting as opposed to other hardware-related factors.
authors.affiliation: Professor, Department of Mechanical Engineering, Hajim School of Engineering and Applied Sciences, University of Rochester, Rochester, NY. Electronic address: paul.funkenbusch@rochester.edu.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Funkenbusch
authors.affiliation: Former Resident and Implant Fellow, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester, and Instructor, University of Toronto, Toronto, Ont., Canada.
authors.forename: Mario
authors.initials: M
authors.lastname: Rotella
authors.affiliation: Assistant Professor, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester, Rochester, NY.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Chochlidakis
authors.affiliation: Professor, Chair and Program Director, Division of Prosthodontics, Eastman Institute for Oral Health, University of Rochester, Rochester, NY.
authors.forename: Carlo
authors.initials: C
authors.lastname: Ercoli
mesh_terms: D003754:Dental High-Speed Equipment; D003762:Dental Instruments / Q000592:standards*; D006801:Humans; D066298:In Vitro Techniques; D019246:Tooth Preparation / Q000295:instrumentation