title: Using an Er,Cr:YSGG laser to remove lithium disilicate restorations: A pilot study.
abstract: BACKGROUND
  The use of lasers is growing widely in dentistry. Despite its clinical implications, most information and clinical data related to the removal of ceramic restorations with the aid of a laser is either anecdotal or in the form of clinical reports.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to establish a parameter on the removal of lithium disilicate crowns with a laser and conduct an in vitro trial of crown removal based on the wattage and time of application.
  
  
  METHODS
  Twenty extracted molars were prepared to accommodate a lithium disilicate disk specimen, which was cemented with resin cement. An erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser was applied at different wattages (3, 3.5, 4, and 5 W) to determine the optimal wattage for the removal of the lithium disilicate specimens. Once the optimal wattage was established, 25 extracted teeth were mounted in stone, then prepared to receive milled lithium disilicate computer-aided design/computer-aided manufacturing complete coverage crowns. The crowns were cemented with a dual-polymerizing resin cement. The groups comprised 3.5 and 4 W output with 30-, 60-, and 90-second application time (n=5), and 5 crowns were removed using traditional handpiece and electric handpiece with coarse grit diamond rotary instruments. The results and time required to remove the crown were recorded. The chi-square test was performed to assess any significant differences in removing the crown with the laser according to wattage or time of application (α=.05).
  
  
  RESULTS
  Laser application at 3.5 and 4 W was best for removing crowns conservatively. Eight crowns (40%) of 20 specimens were successfully removed at the first attempt. The majority of the crowns came off during the second attempt. The chi-square test revealed no significant difference between the combination of wattage and time of application (P= .92). The mean time to remove the lithium disilicate crown with a diamond rotary instrument was 6 minutes, and removal required 1.8 instruments on the average.
  
  
  CONCLUSIONS
  An Er,Cr:YSGG laser can safely remove lithium disilicate crowns with the settings used this study.
authors.affiliation: Former resident, Advanced Prosthodontics Program, Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, Columbus, Ohio.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Gurney
authors.affiliation: Clinical Assistant Professor, Division of General Practice and Material Science, The Ohio State University College of Dentistry, Columbus, Ohio.
authors.forename: Stanley D
authors.initials: SD
authors.lastname: Sharples
authors.affiliation: Former resident, Advanced Prosthodontics Program, Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, Columbus, Ohio.
authors.forename: Wesley B
authors.initials: WB
authors.lastname: Phillips
authors.affiliation: Program Director and Assistant Professor, Advanced Prosthodontics Program, Division of Restorative Science and Prosthodontic, The Ohio State University College of Dentistry, Columbus, Ohio. Electronic address: lee.6221@osu.edu.
authors.forename: Damian J
authors.initials: DJ
authors.lastname: Lee
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain; D053844:Lasers, Solid-State; D010865:Pilot Projects; D019279:Resin Cements
chemical_list: D019279:Resin Cements; C493120:lithia disilicate; D003776:Dental Porcelain