Stability of immediately loaded 3- and 6-mm miniscrew implants in beagle dogs--a pilot study.
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INTRODUCTION: We compared the stability of 3- and 6-mm long miniscrew implants (MSIs) loaded with orthopedic force levels. METHODS: Using a split-mouth experimental design, we placed MSIs into the jaws of 5 mature beagle dogs and immediately loaded them for 6 weeks. Continuous forces were applied by reciprocally loading pairs of MSIs with nickel-titanium coil springs. The mandibles had the 3-mm MSIs randomly loaded with forces of 600 or 900 g. In the maxilla, the 3- and 6-mm MSIs were randomly assigned and loaded with 600 g of force. An unloaded, control MSI was placed in each quadrant. Overall success was defined as MSIs that remained intact; net success rates excluded MSIs that had sheared off and all implants placed in a dog that frequently chewed his run bars and food bowl. RESULTS: The overall success rates of the loaded and the control 6-mm MSIs were 100%. Overall and net success rates for the 3-mm experimental MSIs were 66.7% and 95.2%, respectively. Similarly, the overall and net success rates of the 3-mm control MSIs were 66.7% and 81.8%, respectively. The overall success rates of the 3-mm mandibular MSIs loaded with 900 and 600 g of force were both 60%; their net success rates were 100% with 900 g and 85.7% with 600 g. Overall success rates of the 3-mm experimental MSIs in the maxilla and the mandible were 80% and 60%, repectively. The net success rates were 100% (maxilla) and 85.7% (mandible). There were no significant (P > 0.05) differences in stability associated with force or location. The loaded 3- and 6-mm MSI pairs demonstrated significant decreases in interimplant distance, averaging 2.2 and 1.8 mm, respectively; the 3-mm MSIs loaded with 900 g showed significantly more displacement than those loaded with 600 g. CONCLUSIONS: Success rates of immediately loaded 3-mm MSIs were significantly lower than those of immediately loaded 6-mm MSIs. Neither force nor location explained differences in the success rates. The linear displacements of the MSIs were associated with load amount rather than implant length.
