Miniscrew biomechanics: Guidelines for the use of rigid indirect anchorage mechanics

A novel biomechanical system to intrude the upper incisors and control overbite: Posterior miniscrew-assisted lever arm and 2 cases report

RATIONALE

Overbite control is a key factor in orthodontic treatment. In some cases, incisor intrusion is essential and could be an optimal strategy for overbite control. The aim of this article was to introduce a biomechanical system called the posterior miniscrew-assisted lever arm, which is innovative in using existing posterior miniscrews to intrude the upper incisors and to control anterior overbite while simultaneously retracting the anterior teeth. Its efficiency in incisor intrusion has been proved with 2 cases.

PATIENT CONCERNS

Two adult women who came for orthodontic treatment with the chief complaint of convex profile were included in this study.

DIAGNOSIS

Both patients had similar malocclusions of Class II molar relationship, anterior deep overjet, and anterior deep overbite.

INTERVENTIONS

Their treatment plans were to extract 4 first premolars and insert 2 maxillary posterior buccal miniscrews. After teeth aligning and leveling, en masse retraction was started in both arches. During the space-closing stage, posterior miniscrew-assisted lever arms were placed in their upper arches so as to intrude upper incisors and control the overbite.

OUTCOMES

After respectively 4 months and 3 months of incisor intrusion, the anterior overbite was successfully reduced to the normal range in each patient. Cephalometric analysis and superimposition also confirmed the treatment effect of this biomechanical system on incisor intrusion.

LESSONS

The posterior miniscrew-assisted lever arm is a valuable biomechanical system for intruding incisors and controlling anterior overbite.

Effects of Rigid and Nonrigid Connections between the Miniscrew and Anchorage Tooth on Dynamics, Efficacy, and Adverse Effects of Maxillary Second Molar Protraction: A Finite Element Analysis

Introduction

Direct, rigid indirect, and nonrigid indirect absolute anchorages using temporary anchorage devices (TADs, mini-implants/miniscrews) can provide promising opportunities for challenging, yet common, orthodontic tooth movements such as molar protraction. Rigid rectangular wire and ligature wire are the most common methods of attaching a tooth to a miniscrew in indirect anchorages. We aimed to provide a comparison of the rigidity of the connecting wire in terms of stress on the miniscrew, the anchorage loss, and the risk of root resorption using finite element analysis (FEA).

Methods

The maxillary right second molar was protracted into the proximal space at a 150 g load (1) using direct absolute anchorage with a tapered miniscrew implanted between the premolar roots and using indirect absolute anchorage with the second premolar reinforced by the miniscrew through (2) a rigid stainless steel (SS) wire or (3) a nonrigid SS ligature wire (4) at different elastic moduli. Stresses and displacements of 4 models' elements were measured. The risk of external root resorption was evaluated.

Results

Connecting the tooth to the miniscrew using rigid full-size wire (model 2) compared to ligature (model 3) can give better control of the anchorage (using the ligature wire, the anchorage loss is 1.5 times larger than the rectangular wire) and may reduce the risk of root resorption of the anchorage unit. However, the risk of miniscrew failure increases with a rigid connection, although it is still lower than with direct anchorage. The miniscrew stress when using a ligature is approximately 30% of the rigid model using the rectangular wire. The miniscrew stress using the rectangular wire is approximately 82.4% of the miniscrew stress in the direct model. Parametric analysis shows that the higher the elastic modulus of the miniscrew-tooth connecting wire in the indirect anchorage, the less the anchorage loss/palatal rotation of the premolars/and the risk of root resorption of the anchorage teeth and instead the stress on the miniscrew increases.

Conclusions

Direct anchorage (followed by rigid indirect anchorage but not nonrigid) might be recommended when the premolars should not be moved or premolar root resorption is a concern. Miniscrew loosening risk might be the highest in direct anchorage and lowest in nonrigid indirect anchorage (which might be recommended for poor bone densities).

Management of Class III Extraction with the Miniscrew-Supported Orthodontic Pseudo-Ankylosis (MSOPA) Using Direct Tads

The aim of the present study is to represent the orthodontic treatment of a young patient with a skeletal Class III malocclusion(Wits Appraisal −9 mm), in which the extractions of the first lower premolars were performed to obtain a class III camouflage using direct temporary anchorage devices (TADs). The patient reported a history of three years of orthodontic treatment at another clinic and the radiographic evaluation revealed an important impairment of the upper root incisors. A treatment was performed with a fixed appliance in the upper and lower arches using an archwire sequence of 0.16 CuNiTi, 19 × 25 CuNiTi, 19 × 25 SS and was carried out in 18 months. Post-treatment records of our patient show a control of facial esthetics from the frontal and lateral perspectives, with a harmonious soft-tissue profile. A Class I canine was achieved and her overbite and overjet were normalized by retracting the mandibular anterior teeth and carrying out a bodily mesialization of the posterior sector into the extraction space. In conclusion, the “pseudoankylosis system” used in this case allowed the desired result to be achieved with minimal change to the lower incisal inclination and without overloading the anterior upper and lower sectors, thus reducing the risk of further root resorption and patient compliance.

3-D Evaluation of temporary skeletal anchorage sites in the maxilla

Background

The selection of temporary anchorage device (TAD) site can be a challenging task since one should not only consider the 2-D distances between roots, but also the entire 3-D space. Thus, the aim of this study was to evaluate the posterior maxillary region areas available for the insertion of temporary anchorage devices in reconstructed images from cone beam computed tomography (CBCT).

Material and Methods

Sample consisted of 72 patients with indication for orthodontic treatment, grouped into three distinct age groups: 11 to 14 years (age group 1), 15 to 19 years (age group 2) and aged 20 years or older (age group 3), which were further subdivided as to the type of malocclusion (Angle Class I, II and III). Orthopantomographic reconstructions and cross sections were obtained with the Dolphin Imaging software. The distance between the roots of maxillary teeth (canines, premolars and first molars) was determined at 5 mm of the cementoenamel junction, as well as the depth of bone availability at different insertion angles (90°, 75°, 60°, 45°). The influence of different angulations, age, and malocclusion on bone availability was evaluated by ANOVA, followed by the Bonferroni post-test. For the evaluation of the interaction of these factors, 2-way ANOVA was used.

Results

Bone availability was found to be poor between roots in the molar region. There was a reduction in bone availability with increasing age. With regard to angulations, greater bone availability was found in depth for 45° angulation in the canine and first premolar regions and for angulation of 75° or 90° in the molar region. However, there was no difference between bone availability in the region of the second premolars.

Conclusions

According to applied methodology it can be concluded that the region between canines and premolars accepts better vertical angular variations for TADs insertion.

Key words:Cone-Beam Computed Tomography, Orthodontic Anchorage Procedures.

Anatomical consideration for optimal position of orthodontic miniscrews in the maxilla: a CBCT appraisal

BACKGROUND

Orthodontic miniscrews are commonly used as temporary anchorage devices. Bone thickness and bone depth are important factors when placing miniscrews. There are no studies to assess the maxillary bone thickness for optimum miniscrew placement in a Saudi population.

OBJECTIVE

Assess the proximity of the maxillary sinus and nasal cavity in areas where miniscrews are usually inserted using cone beam computed tomography (CBCT).

DESIGN

Retrospective, cross-sectional.

SETTING

Department of maxillofacial radiology in a Saudi dental school.

PATIENTS AND METHODS

Using CBCT images, we measured the distance between the maxillary sinus and nasal cavity to the palatal bone, buccal intra-radicular and infrazygomatic crest areas. Mean values (SD) were compared at various locations, including by gender, and correlation with age was calculated.

MAIN OUTCOME MEASURE

Mean bone thickness at commonly used sites for orthodontic miniscrew placements in the maxilla. Secondary outcome was the insertion angle in the infrazygomatic crest area.

SAMPLE SIZE

CBCT images of 100 patients (50 males and 50 females).

RESULTS

The mean (standard deviation) age for the sample was 25.4 (6.5) years with no significant difference between males and females. In the palate, the distance to the nasal cavity and maxillary sinus was greater anteriorly and decreased significantly posteriorly (P<.001). Buccally, the interdental bone depth was significantly greater between the second premolar and first molar (11.96 mm) compared to between the central and lateral incisors (7.53 mm, P<.001). The mean bone thickness of the infrazygomatic crest area at a 45° insertion angle was 4.94 mm compared to 3.90 at a 70° insertion angle (P<.001). No correlation was found between age and bone thickness.

CONCLUSION

The distance to the nasal cavity and maxillary sinus was greater in the anterior than posterior areas. There is minimal risk of injuring the maxillary sinus or nasal cavity using the buccal approach. Caution is needed when placing miniscrews in the infrazygomatic crest area.

LIMITATIONS

Cross-sectional study from one center; hence, findings cannot be generalized to other populations.

CONFLICT OF INTEREST

None.