Failure Strength of Four Veneered Stainless Steel Crowns

Department of Pediatric Dentistry
Lutheran Medical Center

Resident’s Name: Anna Haritos Date: February 13, 2009
Article title: Failure strength of four veneered primary stainless steel crowns
Author(s): Waggoner, William et al
Journal: Pediatric Dentistry
Volume (number): 17:1
Month, Year: 1995
Major topic: failure of the facings of veneered primary SSC
Minor topic(s): n/a
Type of Article: research article
Main Purpose(s): (1) to determine the amount of shear force required to fracture or dislodge the veneered facings of four commercially available veneered primary incisor stainless steel crowns; (2) to determine which of the veneers demonstrate the greatest resistance to dislodgement and to characterize the bond failures.
Overview of method of research: Forty size #4 primary left central incisor stainless steel crowns from Unitek were obtained and shaped to fit an incisor master die. Ten of each of the 40 crowns were mailed to four commercial manufacturers who were asked to veneer the crowns with their normal process ensuring that they did not overlap the incisal edge. The commercial manufacturers were Kinder Krowns, Whiter Biter Crown II, NuSmile Primary Crowns, and Cheng Crowns. Each veneered crown was cemented with polycarboxylate cement (Durelon Espe/Premiere) to a cast die (that had been duplicated from a master cast die). 24 hours after cementation, the crowns were thermo-cycled at 4 degrees Celsius and 55 degrees Celsius for five hundred one-minute cycles. After this, each crown was placed in a holder of a machine that applied a force to the incisal edge of the veneer at 1 mm/min until the veneer fractured or dislodged. The force was designed to be stronger than that of a 5-10 year old child biting down on the incisal edge. The force at which this occurred was then recorded. An adhesive failure occurred when the entire veneer dislodged in one piece. A cohesive failure occurred when the veneer remained bonded to the metal but had cracks within it. A mixed failure occurred when part of the veneer chipped from the metal-resin surface.
Findings: The Whiter Biter crowns required significantly more force for failure than the other three groups. Although it was not significant, the Kinder Krowns required the least amount of force to fail. All of the White Biter veneers failed adhesively (no breakage, chipping). None of the NuSmile, Cheng of Kinder crowns experienced adhesive failures. The Whiter Biter crown is different in both material and attachment from the other three crowns; The Whiter Biter uses a thermoplastic material facing while the other three types use a composite resin or a dimethylacrylate resin for the facing. The thermoplastic material is flexible while the resins are brittle under force. The White Biter crown is spot welded to the SSC and then melted onto the mesh where it is retained by spots of plastic incorporated into the mesh. The failures from the Whiter Biter were from the spot weld site and did not involve the meshwork. The failure of the Cheng crowns had to do with the veneer material and not with the welded meshwork. NuSmile and Kinder crowns do not use a metal meshwork but directly bond to the stainless steel.
Key points/Summary: It is probably likely that the breakage of these crowns is due to traumatic forces and not incisal forces. $18/veneered crown versus $2/nonveneered crown! You can not heat sterilize veneered SSC. Since this study was published, Kinder Krowns had produced a second generation of crowns
Assessment of article: Very interesting article – I want to try the Whiter Biters! Would be a good resident research project (repeat investigation!)