Insertion torque and success of orthodontic mini-implants: a systematic review

In this systematic review, we analyzed whether recommended maximum insertion torque values of 5 to 10 Ncm were associated with higher success rates of orthodontic mini-implants compared with mini-implants inserted with maximum insertion torque values beyond this range. Objective assessments of stability, variables that influence maximum insertion torque values, and adverse effect of interventions were also assessed in the studies selected for our PICO (patient problem or population, intervention, comparison, and outcomes) question.

Computerized and manual searches of the literature were conducted up to February 24, 2012, for human studies that assessed these objectives. Our eligibility criteria selected studies that (1) used sample sizes of 10 or more, (2) recorded maximum insertion torque during the insertion of orthodontic mini-implants, (3) inserted implants with a diameter smaller than 2.5 mm, and (4) applied orthodontic forces for a minimum duration of 4 months. Confounding was assessed through the analysis of risk of bias, and the validity of outcomes was rated according to the GRADE approach. The Cochrane Handbook for Systematic Reviews of Interventions was our main guideline for the methodology.

Seven nonrandomized studies met the eligibility criteria. All associations between specific maximum insertion torque values and success were based on literature rated as having low quality. The reasons for these judgments included subjective definitions of success, poor-quality torque sensors, and high risks for selection, performance, detection, and reporting biases. A risk of multiple publication bias was also suspected. All associations between maximum insertion torque and factors related to implant, patient, location, and surgery were rejected; few studies reported on adverse effects.

Currently, no evidence indicates that specific maximum insertion torque levels are associated with higher success rates for orthodontic mini-implants. Additional research on this topic is therefore necessary. The following guidelines for future studies are suggested: (1) systematically review the animal and laboratory literature, (2) perform maximum insertion torque tests on artificial bone, (3) test associations in animal studies before conducting clinical trials, (4) test associations between maximum insertion torque and the stability of orthodontic mini-implants with objective quantitative recordings rather than subjective qualitative measures, (5) measure maximum insertion torque with digital sensors rather than with mechanical devices, (6) assess the stability of orthodontic mini-implants at preestablished times, (7) consult our risk-of-bias analysis, and (8) analyze the adverse effects of interventions.