Two-component mini-implant as an efficient tool for orthognathic patients

A finite element analysis of stress distribution with various directions of intermaxillary fixation using orthodontic mini-implants and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy

OBJECTIVE

This finite element analysis (FEA) aimed to assess the stress distribution in the mandible and fixation system with various directions of the intermaxillary fixation (IMF) using mini-implants (MIs) and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy (BSSRO).

MATERIALS AND METHODS

A total of nine mandibular advancement models were set according to the position of the MIs (1.6 mm in diameter, 8 mm in length) and direction of the IMF elastics (1/4 inch, 5 oz). Major and minor principal stresses in the cortical and cancellous bones, von Mises stresses in the fixation system (miniplate and monocortical screws), and bending angles of the miniplate were analysed.

RESULTS

Compressive and tensile stress distributions in the mandible and von Mises stress distributions in the fixation system were greater in models with a Class III IMF elastic direction and a higher IMF elastic force than in models with a Class II IMF elastic direction and a lower IMF elastic force. The bending angle of the miniplate was negligible.

CONCLUSIONS

Stress distributions in the bone and fixation system varied depending on the direction, amount of force, and position of IMF elastics and MIs. Conclusively, IMF elastics in the Class II direction with minimal load in the area close to the osteotomy site should be recommended.

Comparison of the Anchorage Value of the First Molars Supported with Implant and First Molars Supported with Second Molar during En Masse Retraction

Aims and Objectives:

The aim of this study was to determine the efficacy of mini-implants as adjuncts for intraoral anchorage units for en masse retraction of maxillary anterior teeth in bimaxillary dentoalveolar protrusion cases.

Materials and Methods:

The study sample consisted of 15 patients (10 females and 5 males). The samples were compared for anchorage loss with the implant-supported molar and conventional molar contralaterally in both the maxilla and mandible after six months of retraction period. The mini-implants used were 1.5 mm in diameter and 8 mm in length and were inserted in the first and third quadrant between the roots of second premolar and first molar under local anesthesia at an angle of 45°. For en masse retraction, active tiebacks with ligating (100g) were used bilaterally extending from molar hooks to J-hook on a 0.019” × 0.025” stainless steel arch wire. Lateral cephalograms were taken before and after retraction for assessing the loss of anchorage in maxillary and mandibular first molars.

Results:

Anchorage loss of 1.46 mm in the maxilla and 1.36 mm in mandible was found with conventional molar anchorage, whereas no statistically significant anchorage loss was found in the implant-supported molar side.

Conclusion:

Implant-supported molar side showed better anchorage compared with the conventional molar side. Hence, implant-supported molar can be used as an absolute anchorage unit in the en masse retraction of anterior teeth.

Gene profiling of bone around orthodontic mini-implants by RNA-sequencing analysis

This study aimed to evaluate the genes that were expressed in the healing bones around SLA-treated titanium orthodontic mini-implants in a beagle at early (1-week) and late (4-week) stages with RNA-sequencing (RNA-Seq). Samples from sites of surgical defects were used as controls. Total RNA was extracted from the tissue around the implants, and an RNA-Seq analysis was performed with Illumina TruSeq. In the 1-week group, genes in the gene ontology (GO) categories of cell growth and the extracellular matrix (ECM) were upregulated, while genes in the categories of the oxidation-reduction process, intermediate filaments, and structural molecule activity were downregulated. In the 4-week group, the genes upregulated included ECM binding, stem cell fate specification, and intramembranous ossification, while genes in the oxidation-reduction process category were downregulated. GO analysis revealed an upregulation of genes that were related to significant mechanisms, including those with roles in cell proliferation, the ECM, growth factors, and osteogenic-related pathways, which are associated with bone formation. From these results, implant-induced bone formation progressed considerably during the times examined in this study. The upregulation or downregulation of selected genes was confirmed with real-time reverse transcription polymerase chain reaction. The RNA-Seq strategy was useful for defining the biological responses to orthodontic mini-implants and identifying the specific genetic networks for targeted evaluations of successful peri-implant bone remodeling.

A novel designed screw with enhanced stability introduces new way of intermaxillary fixation

INTRODUCTION

This article represents new design of a fixation screw-spike screw-for the intermaxillary elastic fixation application after the first surgery in orthognathic surgery. This new type called spike screw is easily placed and provides enough rigidity for the intermaxillary fixation (IMF) with increased stability that was a common problem using screw-type fixation.

MATERIALS AND METHODS

Spike screw has a unique design: a washer with soldered stainless hook that adds stability and fixation to the screw done by a miniscrew. It increases stability by reducing the high peak stress-often occurs in miniscrew-and obtaining the advantage of miniplate system with miniscrew fixation. It allows noninvasive screw placement unlike miniplate. The 8 spike screws were placed on the posterior lesion to provide secure IMF, and 2 I-type C-tubes were placed on the anterior lesion.

RESULTS

By modifying the length of the hook attached to a washer can accommodate each patient's IMF length variation like a custom-made screw. The stability of the screw was kept well for 6 weeks even with minor gingival irritation in some of the area. This proved that spike screw could be one of the methods for IMF. The closeness of the hook to the teeth eliminated further gingival irritation around the elastic attachment site. Finally, it provided easy manipulation of the hook to change vectors of the elastic force application.

CONCLUSIONS

The novel design of the screw permits easy placement and removal for the IMF. In addition, its advantages include increased stability with unique design, less gingival irritation, and simple vector modification of the IMF elastics by adjusting the hook length and shape.

Retreatment of a transfer patient with bialveolar protrusion with mini bone-plate anchorage

A 40-year-old black woman, with pretorqued, preangulated appliances on the maxillary teeth, transferred with chief concerns of missing teeth and her orthodontic progress. She had bialveolar protrusion and edentulous areas in both the maxilla and the mandible. After records were made and her desires assessed, she was retreated with the extraction of 3 premolars. Her protrusion was reduced and all edentulous spaces were closed. The facial change was evident due to the reduction of the protrusion.

Replacing a failed mini-implant with a miniplate to prevent interruption during orthodontic treatment

INTRODUCTION

When mini-implants fail during orthodontic treatment, there is a need to have a backup plan to either replace the failed implant in the adjacent interradicular area or wait for the bone to heal before replacing the mini-implant. We propose a novel way to overcome this problem by replacement with a miniplate so as not to interrupt treatment or prolong treatment time.

METHODS

The indications, advantages, efficacy, and procedures for switching from a mini-implant to a miniplate are discussed. Two patients who required replacement of failed mini-implants are presented. In the first patient, because of the proximity of the buccal vestibule to the mini-implant, it was decided to replace the failed mini-implant by an I-shaped C-tube miniplate. In the second patient, radiolucencies were found around the failed mini-implants, making the adjacent alveolar bone unavailable for immediate placement of another mini-implant. In addition, the maxillary sinus pneumatization was expanded deeply into the interradicular spaces; this further mandated an alternative placement site. One failed mini-implant was examined under a scanning electron microscope for bone attachment.

RESULTS

Treatment was completed in both patients after replacement with miniplates without interrupting the treatment mechanics or prolonging the treatments. Examination under the scanning electron microscope showed partial bone growth into the coating pores and titanium substrate interface even after thorough cleaning and sterilization.

CONCLUSIONS

Replacement with a miniplate is a viable solution for failed mini-implants during orthodontic treatment. The results from microscopic evaluation of the failed mini-implant suggest that stringent guidelines are needed for recycling used mini-implants.

Resistance to immediate orthodontic loading of surface-treated mini-implants

OBJECTIVE

To test the hypothesis that there is no difference in the stability and resistance to orthodontic forces of immediately loaded sandblasted and acid-etched (SAE) mini-implants and those of machined-surface implants of the same size and shape.

MATERIALS AND METHODS

Two types of mini-implants were used in the tibiae of 44 rabbits; some had an SAE surface and some had machined surfaces. Orthodontic loading of 150 g was applied immediately after placement. The success rates and maximum removal torque values (RTVs) of 412 mini-implants were recorded and compared immediately after placement, 3 days after placement, and 1, 6, and 10 weeks after placement. The RTV data were analyzed using multiple regression analysis to evaluate differences with respect to surface treatment, loading, and loading periods (P < .05). Multiple comparisons using the Scheffé method were performed to evaluate the RTVs for the subsequent loading periods.

RESULTS

Thirteen mini-implants failed during the experimental period. The SAE group had a higher RTV than the machined group, and there was significant difference in RTVs in accordance with loading periods (P < .001). However, there was no significant RTV difference between loaded and unloaded mini-implants.

CONCLUSIONS

The hypothesis was supported. Both SAE mini-implants and machined mini-implants can be loaded immediately and experience similar success rates. RTVs were higher for the SAE mini-implants than for the machined mini-implants. The latter finding suggests that, for immediate loading, SAE mini-implants may provide more stable retention than machined mini-implants.