title: Comparative study of the surface characteristics, microstructure, and magnetic retentive forces of laser-welded dowel-keepers and cast dowel-keepers for use with magnetic attachments.
abstract: BACKGROUND
  Information regarding the merits and problems associated with connecting a keeper to a dowel and coping using a laser welding technique has not been explored extensively in the dental literature.
  
  
  OBJECTIVE
  This in vitro study compared the surface characteristics, microstructure, and magnetic retentive forces for a dowel and coping-keeper mechanism fabricated using a laser welding process and a cast-to casting technique.
  
  
  METHODS
  Five cast-to and 6 laser-welded dowel and coping-keeper specimens were tested. Using 5 freestanding keepers as the control group, the surface characteristics and microstructures of the specimens were examined by means of stereomicroscopy, metallographic microscopy, and scanning electron microscopy (SEM). Energy-dispersive spectroscopic (EDS) microanalysis with SEM provided elemental concentration information for the test specimens. The vertical magnetic retentive forces (N) of the 3 groups were measured using a universal testing machine. The results were statistically compared using 1-way analysis of variance and the Newman-Keuls multiple range test (alpha =.05).
  
  
  RESULTS
  The laser-welded dowel-keeper generally maintained its original surface smoothness as well as the original microstructure. Elements diffused readily through the fusion zone. The surface of the cast dowel-keeper became rough with the formation of an oxide layer, the microstructure changed, and there was only limited elemental diffusion in the fusion zone. The average vertical magnetic retentive force of the laser-welded group, the cast group, and the control group were 4.2 +/- 0.2 N, 3.8 +/- 0.3 N, and 5.6 +/- 0.3 N, respectively. Statistically significant differences in vertical magnetic retentive force were found between the control group and both the laser-welded and cast groups (P <.01). Compared with the cast dowel-keepers, the average vertical magnetic retentive force of the laser-welded dowel-keepers was significantly higher (P <.05).
  
  
  CONCLUSIONS
  The laser welding technique had less influence on the surface characteristics, the microstructure, and the magnetic retentive forces of keepers relative to techniques that incorporate a keeper at the time of cast dowel and coping fabrication.
authors.affiliation: Department of Prosthodontics, West China College of Stomatology, Sichuan University, Chengdu, Sichuan 610041, People's Republic of China. nestcn@263.net
authors.forename: Yonglie
authors.initials: Y
authors.lastname: Chao
authors.forename: Li
authors.initials: L
authors.lastname: Du
authors.forename: Ling
authors.initials: L
authors.lastname: Yang
mesh_terms: D017268:Dental Prosthesis Retention / Q000379:methods*; D012994:Dental Soldering / Q000379:methods; D007834:Lasers; D008280:Magnetics; D011176:Post and Core Technique / Q000295:instrumentation*; D013499:Surface Properties