Primary failure rate for 1680 mandibular buccal shelf miniscrews placed in movable mucosa or attached gingiva
Chris Chang; Sean S-Y Liu; W. Eugene Roberts
ABSTRACT
Objective: Compare the initial failure rate (≺ 4mo) for mandibular buccal shelf (MBS) miniscrews placed in movable mucosa (MM) or attached gingiva (AG).
Materials and Methods:
1680 consecutive stainless steel (SS) 2X12mm MBS miniscrews were placed in a total of 840 patients (405 males 435 females, mean age 16±5 yr). All screws were placed buccal to the lower 1st and 2nd molars roots and the screw heads were at least 5 mm superior the soft tissue. Loads from 8-14 oz (227-397g, 231-405cN) were used to retract mandibular buccal segments for at least 4 months.
Result
Overall, 121 miniscrews out of 1680 (7.2%) failed: 7.31% were in MM and 6.85% were in AG, but that difference was statistically insignificant. Failures were divided into 89 unilateral and 16 that were bilateral (32 screws). Failures on the left side (9.29%) was significantly greater (P≺.001) compared to those on the right (5.12%). Average age for failure patients was 14+3yr.
Conclusion
MBS miniscrews were highly successful (~93%), and there was no significant difference between MM or AG. The right-handed clinician experienced more failures on the left side and in younger patients (~14yr). About 13% of failures were bilateral suggesting an inherent susceptibility in some patients.
KEY WORDS:
Mandibular buccal shelf (MBS); Miniscrews; Skeletal anchorage; Attached gingiva; Movable mucosa; Extra-alveolar orthodontics anchorage