Original article
Effect of longitudinal flutes on miniscrew implant stability and 3-dimensional bone formation

https://doi.org/10.1016/j.ajodo.2016.04.029Get rights and content

Highlights

  • Loaded 3-mm miniscrew implants (MSIs) placed in animal models can have very high (97%) success rates.

  • Miniscrews can be stable even when placed with maximum insertion torque values below recommended levels.

  • Adding flutes to 3-mm MSIs increases the removal torque by 37% after 6 weeks of healing.

  • There was less bone 6 to 24 μm from the MSI surface than at 24 to 42 or 42 to 60 μm from the implant surface.

  • There was more bone surrounding nonfluted than fluted MSIs after 2 and 6 weeks of healing.

Introduction

The purpose of this study was to evaluate the effects of longitudinal flutes on miniscrew implant (MSI) stability and bone healing.

Methods

Using 11 skeletally mature New Zealand white rabbits, we placed 31 longitudinally fluted and 31 nonfluted, 3-mm-long MSIs in standardized positions in their calvaria and immediately loaded them with 100 g using nickel-titanium coil springs. Insertion torque values were obtained for each MSI placed; removal torque values were obtained for 28 MSIs that had been in place for 6 weeks and 20 MSIs that had been in place for 2 weeks. The bone volume fractions at 6 to 24, 24 to 42, and 42 to 60 μm from the MSI surfaces were evaluated using microcomputed tomography with an isotropic resolution of 6 μm.

Results

The success rate was 97% for both the fluted and nonfluted MSIs. The difference in insertion torque between the fluted and nonfluted MSIs was not statistically significant (P = 0.930). After 2 weeks, there was no statistically significant (P = 0.702) difference in removal torque between the fluted and nonfluted MSIs. After 6 weeks, removal torque values were significantly (P = 0.008) higher for the fluted (3.42 ± 0.26 N.cm) than the nonfluted (2.49 ± 0.20 N.cm) MSIs. Bone volume fractions of the 6-to-24–, 24-to-42–, and 42-to-60–μm layers were significantly (P <0.05) greater for the nonfluted than the fluted MSIs.

Conclusions

Loaded 3-mm-long MSIs with and without flutes have high success rates. Longitudinal flutes placed in 3-mm MSIs increased their removal torque by 37% and decreased the amount of bone immediately surrounding them.

Section snippets

Material and methods

Eleven skeletally mature female New Zealand white rabbits, 7 to 8 months of age, were used in this study. The Institutional Animal Care and Use Committee at Texas A&M University Baylor College of Dentistry in Dallas approved the care of the animals and the experimental protocol. Each of the 62 miniscrews placed was subjected to a constant force of 100 g.

Two miniscrews were specifically fabricated for this study. They were identical except for the flutes that extended down the entire length of

Results

The overall success rate for the study was 97.0% for the fluted (1 failure out of 31 screws) and 97.0% for the nonfluted (1 failure out of 31) MSIs. Both failures were complete failures; the MSIs were not in bone, and the expansion springs were no longer active. They occurred in different animals and pertained to MSIs loaded anteroposteriorly.

Insertion torque values of the fluted MSIs ranged from 1.5 to 7.0 N.cm, with a mean of 3.98 ± 0.24 N.cm (Fig 5). For the nonfluted MSIs, insertion torque

Discussion

High success rates are attainable with loaded 3-mm-long MSIs. The fluted and nonfluted MSIs were 97% stable over the 6-week experimental period. The success rates were similar to or higher than previously reported for animal models16, 17, 18, 19, 25 and substantially higher than rates reported for humans.7, 8 This suggests that the lower clinical success of MSIs depends on confounding factors, such as root proximity24, 26 and peri-implant infection,26 that are difficult to control. The ability

Conclusions

  • 1.

    Loaded 3-mm MSIs have high (97%) success rates in rabbit calvaria.

  • 2.

    Miniscrews remained stable even when placed with maximum insertion torque values below recommended levels.

  • 3.

    Adding flutes to 3-mm MSIs increased the removal torque by 37% after 6 weeks of healing.

  • 4.

    There was less bone at 6 to 24 μm from the MSI surface than at 24 to 42 μm and 42 to 60 μm from the implant surface.

  • 5.

    There was greater bone surrounding nonfluted than fluted MSIs after 2 and 6 weeks of healing.

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    All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported.

    Partially funded by the Robert E. Gaylord Endowed Chair in Orthodontics.

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