Effect of connector size and design on the fracture resistance of monolithic zirconia fixed dental prosthesis

Designing a high strength all-ceramic fixed partial denture with favorable esthetics can be challenging for clinicians; this study aims to evaluate the effect of connector size and design on fracture resistance of monolithic zirconia fixed dental prosthesis.

Two groups of twenty 3-unit monolithic zirconia (Sirona inCoris TZI, Sirona Dental Systems GmbH) bridges extending from mandibular first premolar to the first molar with different connector size (9 mm2, 12 mm2) were divided into two subgroups with different connector design (round and sharp). The specimens were subjected to the 3-point bending test to obtain the fracture-bearing load. The results were reported using descriptive statistics (mean ± standard deviation). To compare the fracture load in two types of designs for each connector size, and two types of connector size for each connector design, Mann- Whitney U test was used. The significance level was considered as p<0.05.

The minimum failure load was related to the group with 9 mm2 connector dimension and sharp embrasure design (1054.4±133.89 N), and the highest mean value belonged to the group with 12 mm2 connector dimension and rounded embrasure design (1599.8±167.09N). Mann-Whitney U test indicated a significant difference between the mean failure load of the rounded and sharp embrasure designs in 9 mm2 connector dimension (p=0.007). However, the difference was insignificant in 12 mm2 connector dimension (p=0.075).

Sharp embrasure design is not recommended for high-stress areas with restricted occlusogingival height. Nine mm2 connector dimension for 3-unit monolithic zirconia FDP, which is recommended by the manufacturer should be used more cautiously.