Failure strength of four veneered primary stainless steel crowns

The purpose of this study was 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 (SSC) and to characterize the veneer failures. Forty Unitek SSCs (#4 left central incisor) were shaped to fit a master die and then 10 each were mailed to four commercial dental laboratories that produce veneered SSCs. The resulting four types of crowns tested were: Cheng Crowns (CC), [Peter Cheng Orthodontic Laboratory]; Kinder Krowns (KK) [Mayclin Dental Studio, Inc]; NuSmile Primary Crowns (NC), [Orthodontic Technologies, Inc]; and Whiter Biter Crown II (WB), [White Bite Inc]. Each crown was cemented onto a standardized die and then thermocycled at 4 degrees C and 55 degrees C for 500 1-min cycles. Each die was then placed into a custom holder on the Instron (Model 4204) testing machine. A force was applied at the incisal edge of the veneer at 148 degrees, (the primary inter-incisal angle), with a crosshead speed of 1 mm/min until the veneer fractured or was dislodged. The mean force (N) required +/- SD to produce failure was, respectively: KK (397.2 +/- 53.0); NC (447.2 +/- 78.5); CC (511.9 +/- 83.4); WB (686.5 +/- 181.4). Analysis of variance (ANOVA) indicated significance at P < 0.0001. A Scheffe's post hoc comparison demonstrated that the Whiter Biter (WB) group required significantly (alpha = 0.05) more force for failure than the other three groups.(ABSTRACT TRUNCATED AT 250 WORDS)