Biologic evaluation of a hollow-type miniscrew implant: an experimental study in beagles

Comparison between microporous and nanoporous orthodontic miniscrews : An experimental study in rabbits

PURPOSE

Surface characteristics of orthodontic miniscrews might affect survival rates and removal torque values (RTVs). This experimental study aimed to clarify whether and why a microporous or nanoporous surface promotes higher survival rates and RTVs for orthodontic miniscrews.

METHODS

Using a split-leg design, one set each of nonporous (sham control, n = 24) and microporous (control, n = 6), and three sets of nanoporous (experimental, n = 6 per set) miniscrews were implanted in the tibias of 12 New Zealand rabbits and immediately loaded with 1.5 N nickel-titanium coil springs for 12 weeks. The surface morphology, micropores, and nanotube diameters of the miniscrews were examined using scanning electron microscopy and field-emission scanning electron microscopy. The surface composition and thickness were determined using Auger electron spectroscopy. The survival rates and RTVs of each set were assessed.

RESULTS

The nanoporous miniscrews had higher survival rates, RTVs (p < 0.001), and thicker nanotube oxide thicknesses (p < 0.001) than the nonporous and microporous miniscrews. The nonporous and microporous miniscrews had no nanotube structures. The surface oxide composition was titanium dioxide (TiO2). The threshold RTV, TiO2 thickness, and nanotube diameter of nanoporous miniscrews needed to promote the experimental survival rate to 100% was determined to be 6.6 ± 0.8 N-cm (p < 0.05), 22.5 ± 4.8 nm (p < 0.05), and 17.6 ± 2.3 nm or above, respectively.

CONCLUSION

Nanoporous surfaces promoted higher survival rates and RTVs than microporous miniscrews. This could be due to TiO2 nanotube structures with thicker oxide layers in nanoporous miniscrews.

A comparative histomorphological and micro computed tomography study of the primary stability and the osseointegration of The Sydney Mini Screw; a qualitative pilot animal study in New Zealand rabbits

Objective

The aim of this study was to assess the potential of improving orthodontic miniscrews’ (MSs) primary stability in vivo by evaluating the dispersion capacity of an injectable bone graft substitute (iBGS) through a newly designed hollow MS [The Sydney Mini Screw (SMS)] and its integration with the cortical and trabecular bone by using the femur and tibia in a New Zealand rabbit animal model.

Methods

In total, 24 MSs were randomly placed in each proximal tibia and femur of 6 New Zealand rabbits with an open surgery process. Aarhus MSs were used as controls and the effect of injection of iBGS was studied by implanting SMSs with and without iBGS injection. The dispersion of iBGS and the integration of the SMS were studied by using micro Computed Tomography (μCT) and histochemical analysis at two time points, 0 day and 8 weeks post-implantation.

Results

iBGS was successfully injected through the SMS and hardened in situ. After 8 weeks, μCT results revealed that the iBGS particles were resorbed and bone tissue was formed around the SMS and within its lateral exit holes.

Conclusions

This pilot animal study showed the high potential of the combined use of iBGS and SMS as a newly developed technique to promote the primary stability of MSs.

Histomorphometric evaluation of the bone surrounding orthodontic miniscrews according to their adjacent root proximity

Objective

This study was conducted to perform histomorphometric evaluations of the bone surrounding orthodontic miniscrews according to their proximity to the adjacent tooth roots in the posterior mandible of beagle dogs.

Methods

Four male beagle dogs were used for this study. Six orthodontic miniscrews were placed in the interradicular spaces in the posterior mandible of each dog (n = 24). The implanted miniscrews were classified into no loading, immediate loading, and delayed loading groups according to the loading time. At 6 weeks after screw placement, the animals were sacrificed, and tissue blocks including the miniscrews were harvested for histological examinations. After analysis of the histological sections, the miniscrews were categorized into three additional groups according to the root proximity: high root proximity, low root proximity, and safe distance groups. Differences in the bone–implant contact (BIC, %) among the root proximity groups and loading time groups were determined using statistical analyses.

Results

No BIC was observed within the bundle bone invaded by the miniscrew threads. Narrowing of the periodontal ligament space was observed in cases where the miniscrew threads touched the bundle bone. BIC (%) was significantly lower in the high root proximity group than in the low root proximity and safe distance groups. However, BIC (%) showed no significant differences among the loading time groups.

Conclusions

Regardless of the loading time, the stability of an orthodontic miniscrew is decreased if it is in contact with the bundle bone as well as the adjacent tooth root.

Effects of recycling on the biomechanical characteristics of retrieved orthodontic miniscrews

Objective

The aim of this study was to compare recycled and unused orthodontic miniscrews to determine the feasibility of reuse. The comparisons included both miniscrews with machined surfaces (MS), and those with etched surfaces (ES).

Methods

Retrieved MS and ES were further divided into three subgroups according to the assigned recycling procedure: group A, air-water spray; group B, mechanical cleaning; and group C, mechanical and chemical cleaning. Unused screws were used as controls. Scanning electron microscopy, energy-dispersive X-ray spectrometry, insertion time and maximum insertion torque measurements in artificial bone, and biological responses in the form of periotest values (PTV), bone–implant contact ratio (BIC), and bone volume ratio (BV) were assessed.

Results

Morphological changes after recycling mainly occurred at the screw tip, and the cortical bone penetration success rate of recycled screws was lower than that of unused screws. Retrieved ES needed more thorough cleaning than retrieved MS to produce a surface composition similar to that of unused screws. There were no significant differences in PTV or BIC between recycled and unused screws, while the BV of the former was significantly lower than that of the latter (p < 0.05).

Conclusions

These results indicate that reuse of recycled orthodontic miniscrews may not be feasible from the biomechanical aspect.

Evaluation of primary stability of innovated orthodontic miniscrew system (STS): An ex-vivo study

BACKGROUND

Stability is determined as one of the requirements in use of Temporary Anchorage Devices (TAD) in orthodontics. Miniscrew has been a widely used Bone Anchor. Compared with mini-implant that necessitates osseointegration; mechanical retention is a determining factor for primary stability of miniscrew. Studies investigated various ways to increase primary stability. The aim of this study is to introduce a new configuration of miniscrew system which is believed to obtain more primary stability.

MATERIAL AND METHODS

Freshly ovine mandibles were cut in blocks. Twenty-seven miniscrews (diameter 1.6 × 8 mm; G2, Dual Top Anchor System, Jeil Medical, Seoul, Korea) were inserted in the blocks and divided in 2 experimental groups: single miniscrew and the innovated design "Seifi Twin Screw (STS)". Primary stability was evaluated by Periotest "M"® device.

RESULTS

Independent t-test showed a significant difference between 2 experimental groups in periotest evaluation (p< 0.05). STS demonstrated higher primary stability due to its mechanical configuration and design.

CONCLUSIONS

The STS provides higher primary stability and was found to be effective in increased success rate of miniscrew systems from the standpoint of primary stability.

KEY WORDS

Anchorage procedures, anchorage techniques, orthodontic anchorage procedures, miniscrews, temporary anchorage device.

Evaluation of the surface characteristics of anodic oxidized miniscrews and their impact on biomechanical stability: An experimental study in beagle dogs

INTRODUCTION

In this study, we aimed to assess the surface characteristics and the biomechanical stability of miniscrews with an anodic oxidized surface compared with machined surface miniscrews in beagle dogs.

METHODS

Self-drilled, titanium-aluminum-vanadium alloy miniscrews with an anodic oxidized surface (n = 48) or a machined surface (n = 48) were placed into the mandibles of 12 beagle dogs. The surface characteristics of both types of miniscrews were analyzed before implantation with scanning electron microscopy and atomic force microscopy. Insertion torque was measured during placement of all 96 miniscrews. Half of the implants in each group (24 specimens per subgroup) received 200 to 250 g of tensile force for 3-week or 12-week loading periods. Removal torque was measured in 12 specimens of each subgroup, and bone-implant contact and bone volume were quantified in the other 12 specimens of each subgroup.

RESULTS

Atomic force microscopy measurements demonstrated that the anodic oxidized surface miniscrews had significantly higher roughness parameters than did the machined surface miniscrews (P < 0.001). The 2 types of miniscrews were not significantly different in insertion and removal torque values or in bone-implant contacts and bone volumes, regardless of the loading period.

CONCLUSIONS

Anodic oxidized miniscrews have different surface roughness profiles but no clinically significant superiority in biomechanical stability compared with machined surface miniscrews.