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Success of infrazygomatic crest bone screws: patient age, insertion angle, sinus penetration, and terminal insertion
Chris H Chang1, Jia-Hong Lin1, W Eugene Roberts2
1Private practice, Hsinchu, Taiwan.
Introduction:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
