A Prospective Clinical Investigation of the Failure Rate of Immediately Loaded Mini-implants Used for Orthodontic Anchorage

Aim: To evaluate the failure rate of immediately loaded mini-implants used for orthodontic anchorage.

Materials And Methods: 140 mini-implants were inserted in 98 patients and immediately loaded with 50cN super-elastic coil springs. 99 devices were inserted in the lower jaw and 41 in the upper jaw in the following sites: mandibular symphusis (n=17), mandibular alveolar process (n=72), maxillary alveolar process (n=32), retromolar area (n=10), and palate (n=9). The mini-implants were used to perform the following dental movements: molar uprighting, molar uprighting and mesial movement, molar mesial movement, incisor intrusion and proclination, incisor retraction, premolar intrusion, midline correction, premolar distal movement, and molar intrusion. All devices that showed complete absence of mobility after 120 days of continuous load were scored as successful. Those that showed minimum mobility but stayed in place and could resist further load were scored as partial failures, while those that were lost were scored as failures.

Results: 13 of the mini-implants failed (9.3%), 9 were partial failures (6.4%). The upper jaw had a greater failure rate (12.2%) than the lower jaw (8.0%). The palate was the anatomic location with the greatest risk of failure, while in the mandibular alveolar process the lowest failure rate was observed.

Conclusions: The overall failure rate was similar to other investigations where a healing period had been performed, suggesting that immediate loading with light forces should not be considered a risk factor. Other factors such as inflammation of the surrounding soft tissues, bone characteristics, thickness of the mucosa and incorrect surgical procedure should be considered determinants of clinical failure.