Strength and fracture mode of CAD/CAM all-ceramic resin bonded bridges

Objectives: Resin-bonded bridges (RBBs) are a conservative treatment option for the replacement of missing teeth. All-ceramic RBBs have been introduced as a more aesthetically pleasing alternative. However, the use of high strength ceramic materials is associated with certain disadvantages including demanding processing, the need for veneering and compromised bonding to tooth tissues. The purpose of this study was to examine the fracture strength and mode of fracture of all-ceramic RBBs fabricated from a recently introduced machinable glass ceramic material and to examine the influence of two different preparation designs on the fracture strength of the prostheses.

Methods: Twenty human central incisors were used for this study, which were randomly divided into two groups. Teeth in Group I had a minimal preparation design (palatal veneer preparation) while teeth in Group II had a more extended preparation design beyond the proximal area. The CEREC InEos Scanner and the CEREC 3D software were used for scanning, designing and milling of the restorations. The material used was lithium disilicate (IPS e.max CAD, Ivoclar-Vivadent). The bridges were adhesively bonded on their abutments (Variolonk II, Ivoclar-Vivadent) and loaded until fracture. Load data was analyzed using ANOVA. The mode of fracture was also recorded.

Results: The mean fracture strength for the minimal design group was 744N (± 473) and for the extended preparation group 804N (± 614). No statistically significant difference was found between the two designs (p > 0.05). The mode of failure was fracture at the connector area between the pontic and the retainer wing.

Conclusion: The conclusion drawn from this in vitro study was that the fracture strength of the RBBs fabricated with IPS e.max CAD was within range of clinical acceptance. The two preparation designs employed in this study did not have a significant influence on the fracture strength of the all-ceramic RBBs.