Intrusion in implant-tooth-supported fixed prosthesis: an in vitro photoelastic stress analysis

Intrusion of natural teeth is a very common and interesting problem associated with implant-assisted fixed partial prostheses. Various theories have been put forth to explain this phenomenon, most of which revolve around the philosophy of exertion of excessive forces onto the natural tooth in a combination fixed partial denture. This photoelastic study examines the current theories revolving around intrusion and evaluates whether natural tooth intrusion is a definite possibility in an implant-tooth-connected fixed partial prosthesis.

A two-dimensional photoelastic method was employed for testing and analysis. Two sets of photoelastic models were fabricated, one depicting a totally tooth-supported situation and the other an implant-tooth-supported situation. A rigid type and non-rigid type of connection were also incorporated into the fixed partial denture used in the both the situations in the study. Loads were applied on the anterior and posterior abutments and the pontic regions in both sets of models and the fringe patterns were photographically recorded for analysis.

The forces were proportionately consistent with the increase in applied loads in both the situations. The use of a non-rigid connection did not show any major significance but in fact may be erroneous. The forces were considerably higher in the implant-tooth-connected situation. The results indicated that the differences in the forces exerted were not light and continuous and may not cause tooth intrusion. Natural tooth intrusion may be caused by reasons other than excessive forces and needs further investigation.