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Published on: December 20, 2024
Dental Composite Offers Comparable or Greater Pullout and Shear Strength to Lateral Mass Screw Fixation in a Human
Harsh Wadhwa1, Javier Castro1, Olivia Okoli2
1Department of Orthopaedic Surgery, Stanford University Medical Center, Stanford, CA, USA.
Background:
Lateral mass screw fixation is the common method of fixation for an instrumented posterior fusion of the subaxial cervical spine. While screws have established efficacy, adhesive material that can be applied to the bony surface may be a promising alternative strategy owing to ease of application, size, and avoidance of screw loosening, malposition, or fracture.
Methods:
Eighteen fresh frozen human cadaveric subaxial cervical vertebrae were prepared for biomechanical testing. In each vertebra, 1 side underwent lateral mass screw fixation, and the contralateral side underwent composite fixation. On the screw side, a 12 × 3.5-mm lateral mass screw was inserted using a standard free-hand technique by a spine surgeon. For the dental composite side, the lamina was treated with etching acid solution and a dental bonding agent over a 10-mm diameter area before an orthodontic metal bracket was attached using dental composite. Nine specimens in each group were subjected to an axial load to failure (pullout) test, where the load was perpendicular to the vertebral surface. The remaining specimens were subjected to cyclical testing, where the load was applied cranially (shear) relative to each vertebra and gradually increased with each cycle until failure occurred. Differences were assessed with paired t tests with a 2-sided level of significance of α = 0.05.
Results:
Under axial load (pullout), the dental composite (203.4 ± 43.4 N) showed higher ultimate load than the screws (127.7 ± 21.2 N; P < 0.001). The predominant failure mode under axial load was the composite pulling off the cortical bone surface, whereas the screw pulled through the cancellous and cortical bone. In cyclical testing, the ultimate shear load of dental composite (163.7 ± 48.4 N) did not differ from lateral mass screws (173.6 ± 65.5 N; P = 0.7). The composite failure mechanism under shear loading for half of the specimens was composite separation from bone, whereas the rest failed due to fractures distant from the composite site, indicating robust fixation integrity of composite to bone.
Conclusions:
Dental composite displayed similar shear strength and greater pullout strength compared with lateral mass screws.
Clinical Relevance:
An adhesion-based fixation strategy may serve as a viable alternative to traditional screws in specific clinical scenarios that are worthy of further investigation.
