title: Effect of rotatory instrument speed on its capacity to remove demineralized and sound dentin.
abstract: OBJECTIVE
  The aim of this study was to evaluate the capacity of two rotatory instruments (controlled speed electric motor [CSEM] - 300 rpm; conventional slow handpiece [CSHP] - 18,000 rpm) to remove sound and demineralized dentin, by examining prepared cavity walls using the scanning electron microscopy (SEM) and assessing loss of mass.
  
  
  METHODS
  A total of 40 blocks of human occlusal dentin, measuring 5 mm × 5 mm × 4 mm (L × W × H), were divided into two groups according to the substrate type in which the cavity preparation was performed: D - demineralized dentin; and S - sound dentin (control group). The groups were subdivided according to the rotatory instrument used for cavity preparation (n = 10): CSEM (300 rpm); and CSHP (18,000 rpm). In half of the dentin blocks, caries lesion induction was performed for 6 weeks. The preparation of the cavities was performed on a standardizing machine, using a cylindrical tungsten carbide burr. Before and after the preparation, specimens were dehydrated in an incubator at 60°C for 30 min. The initial and final mass (in mg) of each dentin block was measured 3 times using the digital precision balance to obtain the mean weight Following cavity preparation, all specimens were hemisected and SEM was used to blindly assess each half so that the lateral walls of the prepared cavity were measured in μm, accepting the average of two measurements as the total depth of the preparation. Non-parametric Mann-Whitney analysis was performed with a 5% of significance level.
  
  
  RESULTS
  Regarding the weight difference (mg), no significance was detected between the groups. Regarding depth (μm), a significant difference was found between the groups, so that the CSRM showed lower cavity depth when compared with CSHP, both in sound and demineralized dentin.
  
  
  CONCLUSIONS
  Controlled speed rotatory instruments were found to be more conservative in removing both sound and demineralized dentin, in terms of preparation and depth.
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Institute and Research Center, Campinas, São Paulo, Brazil.
authors.forename: Mariana
authors.initials: M
authors.lastname: Cortes
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Institute and Research Center, Campinas, São Paulo, Brazil.
authors.forename: Vanessa Galego
authors.initials: VG
authors.lastname: Arias Pecorari
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Institute and Research Center, Campinas, São Paulo, Brazil.
authors.forename: Roberta Tarkany
authors.initials: RT
authors.lastname: Basting
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Institute and Research Center, Campinas, São Paulo, Brazil.
authors.forename: Fabiana Mantovani
authors.initials: FM
authors.lastname: Gomes França
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Institute and Research Center, Campinas, São Paulo, Brazil.
authors.forename: Cecília Pedroso
authors.initials: CP
authors.lastname: Turssi
authors.affiliation: Department of Restorative Dentistry, São Leopoldo Mandic Institute and Research Center, Campinas, São Paulo, Brazil.
authors.forename: Flávia Lucisano
authors.initials: FL
authors.lastname: Botelho do Amaral
keywords: Dentin; demineralized; removal; rotatory instrument