title: In vitro influence of ultrasonic stress, removal force preload and thermocycling on the retrievability of implant-retained crowns.
abstract: OBJECTIVE
  The main goals of this in vitro study were to evaluate the influence of thermocycling, ultrasonic stress and the removal force preload on the retrievability of cemented implant crowns using a clinical removal device (Coronaflex) and evaluating the tensile strength using a universal testing machine (UTM).
  
  
  METHODS
  Thirty-six crowns were cast from a Co-Cr alloy for 36 tapered titanium abutments (5° taper, 4.3 mm diameter, 6 mm height, Camlog, Germany). The crowns were cemented with a glass-ionomer (Ketac Cem) or a polycarboxylate (Durelon) cement, followed by 3 days of storage in ionized water without thermocycling or 150 days of storage with 37,500 thermal cycles between 5°C and 55°C. Before removal, the crowns were subjected to ultrasonic stress for 0, 5 or 10 min with a contact pressure of either 50 or 500 g. The Coronaflex was used with a removal force preload of 50 or 400 cN, respectively, applied on the point of loading. Scanning electronic microscopy (SEM) was used to evaluate the impact of the removal on the abutment screws.
  
  
  RESULTS
  Crowns cemented with the glass-ionomer cement were significantly easier to remove with the Coronaflex or the UTM than crowns cemented with the polycarboxylate cement (P≤0.05). Ultrasonic stress showed no significant impact on the retrievability regardless of the contact pressure or duration applied (P>0.05). No significant differences could be found for both cements when removed with the Coronaflex or the UTM (P>0.05) after thermocycling was applied. A removal force preload of 400 cN resulted in significantly reduced removal attempts in comparison with 50 cN for both cements (P≤0.05).
  
  
  CONCLUSIONS
  Ultrasound and thermal cycling did not result in reduced cement strength, but to retrieve the crowns, the full impact of a removal instrument has to be applied. Ketac Cem can be used as a "semipermanent" solution, whereas Durelon might serve for permanent cementation. None of the abutment screws showed signs of wear caused by the removal process.
authors: Department of Prosthodontics, Propaedeutics and Dental Materials, Dental School, Christian-Albrechts University at Kiel, Kiel, Germany. cmehl@proth.uni-kiel.de
authors: Christian
authors: C
authors: Mehl
authors: Sönke
authors: S
authors: Harder
authors: Dorothee
authors: D
authors: Schwarz
authors: Martin
authors: M
authors: Steiner
authors: Oliver
authors: O
authors: Vollrath
authors: Matthias
authors: M
authors: Kern
mesh_terms: D000704:Analysis of Variance; D002484:Cementation; D002857:Chromium; D003035:Cobalt; D003442:Crowns; D000044:Dental Abutments; D017268:Dental Prosthesis Retention; D019094:Dental Prosthesis, Implant-Supported; D020878:Device Removal / Q000295:instrumentation*; D005899:Glass Ionomer Cements; D006358:Hot Temperature; D066298:In Vitro Techniques; D008277:Magnesium Oxide; D008855:Microscopy, Electron, Scanning; D011076:Polycarboxylate Cement; D018709:Statistics, Nonparametric; D013499:Surface Properties; D013718:Tensile Strength; D014025:Titanium; D014465:Ultrasonics; D015034:Zinc Oxide
chemical_list: D005899:Glass Ionomer Cements; D011076:Polycarboxylate Cement; D002857:Chromium; C031374:zinc polyacrylate; D008277:Magnesium Oxide; D003035:Cobalt; C040235:Ketac-cem; D014025:Titanium; D015034:Zinc Oxide