Success of infrazygomatic crest bone screws: patient age, insertion angle, sinus penetration, and terminal insertion torque

Abstract

The aim of this study was to assess the 6-month survival (success) rate for infrazygomatic crest (IZC) bone screws relative to patient age, insertion angle, sinus penetration, and terminal insertion torque. One hundred consecutive patients (27 males, 73 females; mean age 25.8 years; age range, 11.0-53.8 years) received IZC temporary anchorage devices (TADs) bilaterally (n= 200). Each TAD was routinely loaded with up to 14 oz (397 g or 389 cN), reactivated monthly, and followed for 6 months. Terminal insertion torque was measured, and radiographs were assessed to determine the length of the TAD engaged in bone and depth of penetration into the maxillary sinus. Compared with nonpenetrating IZC TADs, the mean results for the 96 (48%) TADs that did penetrate the sinus were: 3.23 mm of sinus penetration, 21.3% decrease in terminal insertion torque, and 31.5% less bone contact at the TAD osseous interface. Perforation prevalence increased with age from 35.7% (11-19 years) to 62.5% (>30 years) (P<0.01). Terminal insertion torque increased from 11-19 years to 20-29 years because of increasing bone density with age but then decreased at>30 years because of increased incidence of sinus penetration (P<0.05). Sinus penetration had no significant effect on IZC TAD survival. About 5% of the devices did fail when the final insertion torque was significantly (P<0.05) decreased to 7.37 N-cm compared with the mean torque of 11.63 N-cm for successful TADs. Both sinus perforation and IZC bone quality increased with age. Sinus penetration did not significantly affect the 6 month survival rate of IZC TADs because the loss of bone quantity at the interface was offset by the age-related increase in bone quality at the IZC site.