Occlusal Stability of Ceramic Veneered Implant Restorations

Objectives: In implant prosthodontics, two fixation modes are generally applied i.e. cement fixation and screw retention. Besides passivity of fit, esthetics and retrievability, the occlusal opening of the screw access hole (SAH) is a major difference between the two restoration types. In veneered fixed partial dentues (FPDs), the SAH is considered to be a weak point of the ceramic layer. The objective was to investigate whether under dynamic loading more chipping fractures occur on the occlusal table of screw retained ceramic veneered implant FPDs than in cementable restorations. Methods: Ten cementable and ten screw retained ceramic veneered five-unit FPDs were manufactured to fit a situation with three implants. A chewing simulator was utilized for loading the FPDs above the implant positions for a total of 20000 cycles with a force of 100N applied for 1s followed by 1s of unloading. For analysis, three clinicians evaluated the FPDs using a light microscope and a dental probe. Statistical analysis (two sample t-test; a =.075) was performed based on the number of chipping fractures in each sample. Results: Independently, all investigators found significantly more chipping fractures in the group of screw retained FPDs with p-values ranging from .065 to .072. Conclusions: It could be shown that the SAH of screw retained implant FPDs forms a weak point of the ceramic layer. It was demonstrated in this in vitro study that under cyclic loading, more chipping fractures occur on the occlusal table of screw retained implant restorations with unfilled screw access holes when compared to cemented ones.