Effects of handpiece speed, abrasive characteristic, and load during polishing of dental ceramics
Date
1999
DOI
Authors
Ahmad, Rohana
Version
OA Version
Citation
Abstract
Polishing of dental ceramics has become an increasingly important procedure in restorative dentistry as all-ceramic restorations, which require post-cementation occlusal adjustment, are gaining in popularity. There are numerous studies in both dental and ceramic literature on polishing of dental ceramics and the effects of polishing on their mechanical properties. However, lack of standardization in polishing parameters, precludes comparison among these studies. This study aimed to: characterize three silicone-based dental ceramic polishing systems (diamond, silicon carbide, and alumina abrasives); determine the average clinical polishing loads; determine the effects of speed and abrasive characteristics on clinical polishing load profiles; and evaluate the effects of handpiece speed, abrasive characteristics, and polishing load on polishing efficacy of two dental ceramics (aluminous, and low fusing). Polishing efficacy was evaluated based on mechanical properties and surface smoothness of the polished ceramics. Mechanical strength was determined by four-point bending, and surface roughness was evaluated qualitatively by scanning electron microscopy. Controlled polishing was performed on a customized set-up that allowed independent control over the relevant polishing parameters. Results indicated that the use of clinical polishing instruments, under simulated clinical parameters [load (58 gf for a coarse polisher, 101 gf for a medium grit polisher and 136 gf for a fine grit polisher), workpiece speed (499 mm / min), and rotational velocity (10,000 and 20,000 rpm)] did not affect the flexural strengths of both dental ceramics. At low polishing speed (10,000 rpm), rough (as-ground) and smooth (polished, ground & annealed, and ground & overglazed) surfaces produced statistically similar flexural strength for aluminous porcelain. At higher polishing speed (20,000 rpm), diamond polishers produced statistically weaker (P <.05) specimens (from 74.77 ± 6:28 to 68.41 ± 4.07 MPa) than those which had been ground and annealed (from 74.77 ± 6.28 to 80.27 ± 9.97 MPa. Annealing of the high speed polished group improved the flexural strength by 10.2% (from 68.41 ± 4.07 to 75.40 ± 1 1.46 MPa) to be statistically similar to the ground-and-annealed group. High speed polishing of the ground-and-annealed group reduced the flexural strength by 7.3% (from 80.27 ± 9.97 to 74.77 ± 6.28 MPa) to be statistically similar to the high speed polished group. Bonded fine diamond abraSive significantly reduced the flexural strength of aluminous ceramic by 12.11% (from 74.77 ± 6.28 MPa to 65.69 ± 8.20 MPa; P <.05). No reduction was observed when aluminous ceramic bars were polished with a felt wheel and 6-[mu]m diamond paste (75.46± 9.41 MPa). Overglazing did not change the flexural strength of aluminous ceramic. For low fusing ceramics, annealing significantly reduced the flexural strength by 25% (from 72.18 ± 6.06 MPato 53.49 ± 10.88 MPa; P<.05). Additional annealing cycles (3x) did not further reduce the flexural strength. Electron micrographs of annealed specimens etched with hydrofluoric acid revealed the presence of crystals which were not found in the single firing group. The additional annealing cycles may be associated with crystal formation, and these crystals may be associated with the degradation of strength.
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Thesis (M.Sc.D.)--Boston University, Henry M. Goldman School of Dental Medicine, 1999 (Prosthodontics).
Includes bibliographical references (leaves 58-59).
Thesis (M.Sc.D.)--Boston University, Henry M. Goldman School of Dental Medicine, 1999 (Prosthodontics).
Includes bibliographical references (leaves 58-59).
License
This work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.