Stability of mini-screws invading the dental roots and their impact on the paradental tissues in beagles.

OBJECTIVE

To examine the stability of mini-screws that invade a dental root by measuring the retention period/failure rate, and to illustrate their effects on paradental tissues.

MATERIALS AND METHODS

Three adult male beagle dogs received 48 orthodontic mini-screws. Half of the mini-screws were implanted to invade the roots, and the rest were placed in the middle of the alveolar bone. Half of the mini-screws were loaded immediately. The retention period of the mini-screws was documented. The dogs were euthanized after 8 weeks, and tissue samples were examined histologically.

RESULTS

The failure rate of the mini-screws that invaded the roots was 79.2%, and that of the mini-screws in the middle of the alveolar bone was 8.3%. The application of force had little effect on the failed mini-screws. Moderately injured roots were repaired with osteoid and/or cementoid tissues with normal periodontal ligaments, followed by recovery of the original configuration.

CONCLUSION

Orthodontic mini-screws had a higher failure rate when placed to invade the dental roots. However, minimally damaged dental roots do not adversely affect the healing process.