Assessment of biomechanical strength of titanium versus unsintered-hydroxyapatite/poly-L-lactic acid (u-HA/PLLA) osteosynthesis screws in bilateral sagittal split ramus osteotomy

Abstract

Titanium osteosynthesis is considered to be stable for the bilateral sagittal split ramus osteotomy (BSSRO) procedure in orthognathic surgery but is disregarded owing to a multitude of complications, the most significant necessitating a secondary surgery for removal. Bioresorbable osteofixation devices, especially third-generation unsintered-hydroxyapatite/poly-L-lactic acid (u-HA/PLLA), are increasingly used in the mandibular region because of their strength and bioactive/osteoconductivity. To date, three titanium bicortical screws has been the standard for the rigid fixation of BSSRO. As data on the use of u-HA/PLLA bicortical screws are limited, we conducted an in vitro biomechanical strength test to evaluate the performance of 12-mm bicortical u-HA/PLLA screws in comparison with titanium screws using mandibular bone models. BSSRO was performed on all specimens, followed by fixation with either three titanium screws or three, four, or five u-HA/PLLA screws, and loading was performed using a clinically presumed occlusal force. Displacement forces (measured in newton ‘N′) of 50 N, 130 N, and 220 N were applied. Our results showed that the use of three u-HA/PLLA screws was unstable, that of four u-HA/PLLA screws was comparable, and that of five u-HA/PLLA screws provided stability equal to that of the three titanium bicortical screws. Although further clinical assessment is needed, our study demonstrated that the five u-HA/PLLA bicortical screws are viable alternatives to titanium in BSSRO osteofixation.