A comparative animal experimental study of differently dimensioned osteosynthesis screws used in the mid-face

The soft tissue covering most of the midfacial skeleton is relatively thin. On account of this plates and screws of the 2 mm systems used in the osteosynthesis of this region can bulge and/or be palpable through the thin integument. This shortcoming has prompted the need to develop smaller systems. The present study was designed to investigate whether these more delicate systems are capable of withstanding the midfacial forces that come to bear during functional mastication. For the study a Le Fort I osteotomy was carried out in 10 sheep. The mobile maxilla was fixed with osteosynthesis plates and screws. This paper reports on 40 plates and 170 screws of two AO titanium systems. It compares the strength of 1.5 mm and 2.0 mm AO screws. The anchorage of the screws was assessed by evaluating the nature of contact between the screw and interfacial bone. The loaded screws showed no discernible differences in postoperative bone remodelling that could be correlated to the osteosynthesis systems. Although the experimental situation may not be directly comparable to the trauma or osteotomy case, this study lends credibility to the assumption that the 1.5 mm screw system could be used instead of the 2.0 mm system, even in mid-face areas associated with high masticatory loads.