Introduction: The aims of this study were to assess the type of trauma incurred on tooth roots after contact or close approximation with mini-implants during insertion, and to observe the healing responses via histological analysis.
Methods: Four male minipigs were used. Twenty mini-implants (1.6 mm x 8 mm) were implanted in each minipig into the buccal sides of all four quadrants between roots of teeth so that contact or approximation between the mini-implant and root surface occurred, with the aid of dental fluoroscopy. All mini-implants on the left side of the mouth were left in situ, while those on the right side were removed immediately after insertion. The minipigs were sacrificed at 4-week intervals, and histological sections made.
Results: When mini-implants were left in-situ, the root surface was mostly resorbed away from the mini-implant thread. Partial repair started from 8 weeks. When the mini-implant thread is left touching the root, there was no normal healing response. If the mini-implant was inserted less than 1 mm away from the periodontal ligament, resorption was evident on the root surface. Abnormal healing responses were seen when the pulp tissue was ruptured, mostly through osteodentine formation. In all instances after mini-implant removal immediately after insertion, varying degrees of cementum repair occurred.
Conclusion: Immediate removal of the mini-implant will lead to cementum repair, whereas leaving the mini-implant in place will cause either a delay in repair or no repair. Inserting mini-implants less than 1 mm away from the root surface will cause surface root resorption.