Marginal bone loss influence on the biomechanics of single implant crowns.

Marginal bone loss, whether it is physiological or pathological, is one of the implant treatment complications. The biomechanical consequences of marginal bone loss could be catastrophic particularly when the abutment screw is at supraosseous level. This study aimed at investigating marginal bone loss influence on the biomechanics of single implant crown using finite element (FE) analysis. Four FE models for a 3.5 x 13 mm implant supported by 4 bone levels (8.5 mm, 10 mm, 11.5 mm, and 13 mm) were subjected to 3 loading conditions: vertical, oblique, and horizontal. The results indicated 5-10 times increase in maximum von Mises stresses under oblique and horizontal loading. The maximum stresses within the fixture were concentrated at the bone/fixture interface with highest value under horizontal loading at 10 mm bone support. Abutment screw was most susceptible to fracture as the highest stress was concentrated at the screw/fixture interface. Cortical bone suffered its greatest stress level at the fixture/bone interface at 10 mm bone support. However, increasing bone support to 11.5 mm has improved the fracture resistance of the abutment screw to a great extent especially under oblique and vertical loading. Severe marginal bone loss might be attributed for abutment screw and fixture head fracture especially under horizontal loading.