Fracture Resistance of CAD/CAM Restorations on Anterior Primary Teeth

Background:Computer Aided Design (CAD) and Computer Aided Milling (CAM) have been used to fabricate effective restorations for the past thirty years. Using CAD/CAM, dental providers can accurately capture a digital impression of a tooth preparation and fabricate a restoration without the need for impression material or stone models. The restorations can be delivered on the same day the teeth are prepared and, in most instances, this eliminates the need for a temporary restoration or a second visit for cementation. CAD/CAM restorations are durable and esthetic, yet there is limited research on the use of CAD/CAM restorations on primary teeth.Purpose:The purpose of this study is to compare fracture resistance of CAD/CAM restorations on anterior primary teeth with two different thickness and two preparation designs. The results are compared to a control group of non-restored primary teeth.Methods:Carious and non-carious extracted primary anterior teeth were collected from the UCSF Pediatric Dentistry clinics from 2013 through 2015. Based on extent and location of caries, the teeth were assigned to four groups with different depths of tooth preparation and restoration designs and one group of non-restored control teeth. Each group had ten (n=10) teeth for a total of fifty (50) teeth in the study. The five groups are: 1) 0.5mm traditional veneer, 2) 0.5mm three-quarter veneer, 3) 0.7mm traditional veneer, 4) 0.7mm three-quarter veneer, and 5) control teeth without restorations.The teeth were prepped, restorations milled and bonded, and then mounted for the fracture force testing. The universal testing machine applied compressive force along the incisal edge at increments of 1mm/min. The force at fracture was recorded in pounds. Data was collected and entered into an excel spread sheet.Results:There was a significant overall difference between the fracture resistances of the five groups (Kruskal-wallis test p=0.0007). Specifically, the 0.7mm three-quarter prep group had significantly lower fracture resistance than the control group (Wilcoxon rank sum testp=0.0443), and 0.7mm traditional veneer prep group had marginally significantly lower fracture resistance than the control group (Wilcoxon rank sum test p=0.0596) while thefracture resistances of 0.5mm three-quarter prep group and the 0.5mm tradition veneer prep group did not differ significantly compared to the control group (p>0.05).Conclusion:There was a significant overall difference between all five groups, yet a two-group comparison only found a significant difference between the 0.7mm three-quarter preparation group and control group. The trend was that 0.7mm traditional preparation group showed marginally significant difference from the control group, while both the 0.5mm traditional and 0.5mm three-quarter preparation groups showed no significant difference. Nearly all the teeth in the study groups failed with the fractured occurring within the restorations during load testing; only one sample in the study groups had damage to the underlying tooth structure