Effects of Implant-Abutment Design and Inter-implant Distance on Inter-implant Stress

Objectives: Reconstructing the inter-dental papilla is especially difficult in the inter-implant area. To preserve the inter-implant papilla, the maintenance of the inter-implant bone is essential. The inter-implant distance should be at least 3mm, whereas it has been reported that the inter-implant bone can be maintained with the distance between 2 and 3mm in vivo by improving the design of implants. However, there are no studies on which implant-abutment connection design is the most useful for preserving the inter-implant bone when the inter-implant distance has become less than 3mm.
Methods: Three types of two-piece implant Computer Aided Designed (CAD) models were designed with CAD software: external connection (EC), internal connection (IC), and conical connection (CC). Two implants with the same design were embedded with the inter-implant distance of 2 or 3mm in the anterior maxillary bone model and a metal crown was connected to each abutment. Six kinds of analysis models were constituted: EC, IC and CC with distance of 2mm (EC2, IC2 and CC2) and 3mm (EC3, IC3 and CC3). A static load of 176N was applied to the crown. 3D FEA was performed to evaluate the maximum principal stress distribution.
Results: The stress in the inter-implant bone was higher in the order of IC2, EC2, IC3, EC3, CC2 and CC3. The stress concentration were dispersed around implant components in CC models, whereas stress was concentrated on implant-abutment connection in EC and IC models.
Conclusions: These results suggest that conical connection might be more useful for reducing the inter-implant bone resorption even if the inter-implant distance has become less than 3mm.