"Safe zones" for miniscrew implant placement in different dentoskeletal patterns

Evaluation of safe areas for miniscrew use according to various skeletal anomalies with CBCT

OBJECTIVES

We aimed to determine safe areas to apply miniscrews in the interradicular region of the maxilla and mandible in individuals with various sagittal skeletal malocclusions.

MATERIALS AND METHODS

Cone beam-computed tomography images of 159 individuals were used. Individuals were divided into three groups: Class I, Class II, and Class III. In the sagittal plane, 3-6-9-mm apical sections were determined from the alveolar crest apex. The buccal cortical bone thickness, interradicular distance, and buccolingual bone distances were measured.

RESULTS

In the buccal cortical bone thickness, we observed statistically significant differences between the classes except for the 1-1 region in the maxilla and all regions and sections in the mandible (p < 0.05). The differences in the buccolingual bone distance between classes were statistically significant, except for the 3-mm and 6-mm sections in the 3-4 and 4-5 regions of the maxilla, the 9-mm sections in the 1-2 and 2-3 regions, the 6-mm and 9-mm sections in the 3-4 region, and the 6-mm section in the 4-5 regions of the mandible (p < 0.05). The differences in the interradicular bone distance were statistically significant between the classes in all regions and sections of the mandible except the 6-mm sections in the 1-2 region and in all sections of the maxilla except the 6-mm sections in the 3-4 region (p < 0.05).

CONCLUSIONS

We observed significant differences in the buccal cortical bone thickness, interradicular bone distance, and buccolingual bone distance among individuals.

CLINICAL RELEVANCE

Understanding the anatomy of interradicular regions and preventing complications.

Assessment of cone beam computed tomography for determining position and prognosis of interradicular mini-implants

OBJECTIVE

To investigate the influence of dynamic visualization of cone beam computed tomography (CBCT) scans on orthodontist's assessment of positioning status and prognosis of interradicular mini-implants (MI).

METHODS

Three MI positions were virtually simulated in thirty CBCT volumes: (1) MI 1 mm from the lamina dura (LD), (2) MI touching the LD and (3) MI overlapping the LD. Each position was exposed to orthodontists (n = 35) as panoramic reconstruction, sagittal reconstruction and a sequence of axial slices. Each orthodontist evaluated the MI position (relationship with the LD) and scored the prognosis using a four-point scale (the higher the score, the better the prognosis). Kappa, Friedman and Nemenyi statistics were used.

RESULTS

Statistically significant associations were detected between the prognosis scores and the type of image visualized (p<0.05). The dynamic visualization of the CBCT volume (axial slices) was associated with higher scores for prognosis and more reliable evaluation of MI positioning. Inconsistent outcomes were more frequently associated with panoramic and sagittal reconstructions.

CONCLUSION

The dynamic visualization of axial slices allowed orthodontists to perform better assessment of MI position and considerably affected prognosis judgment.

[Evaluation of the morphology of the nasopalatine canal using cone beam computed tomography]

OBJECTIVE

High precise evaluation of the nasopalatine canal morphology is essential to perform detailed diagnosis and treatment plans in implantology and the orthodontic field. We aimed to study morphometric analysis measurements of the nasopalatine canal.

MATERIAL AND METHODS

In this cross-sectional study, maxillary CBCT images from 125 patients were evaluated in the Maxillofacial Radiology department between 2014-2021. Sagittal views were assessed to determine nasopalatine canal morphology and dimensions. The difference in canal diameter and length between genders was evaluated using an One Way ANOVA test.

RESULTS

There was no significant sex difference among all 125 cases in nasopalatine canal diameter, length, anterior bone plate width. The average length of the nasopalatine canal was 16.49±2.8 mm in male, 16.20±2.9 mm in female, incisive foramen diameter in the sagittal plane was 4.04±0.9 mm in male, 4.02±0.9 mm in female, nasopalatine foramen diameter was 4.63±1.4 mm in male, 4.75±1.2 mm in female. The width of the bone anterior to the canal was 5.89±1.4 mm in males, 5.69±1 mm in females.

CONCLUSION

16-48 aged Mongolian average length of the nasopalatine canal was 16.3 mm, and average incisive foramen width was 4.08 mm, the average width of the bone anterior to the canal was 5.76 mm. Anterior retraction treatment for upper incisor root can be done safely without root resorption around 5.5 mm in the premaxillary alveolar bone.

Interradicular distance and alveolar bone thickness for miniscrew insertion: a CBCT study of Persian adults with different sagittal skeletal patterns

Background

This study aimed to assess the interradicular distance and alveolar bone thickness of Persian adults with different sagittal skeletal patterns for miniscrew insertion using cone-beam computed tomography (CBCT).

Methods

This cross-sectional study was conducted on maxillary and mandibular CBCT scans of 60 patients (18–35 years) in three groups (n = 20) of class I, II and III sagittal skeletal pattern. Anatomical and skeletal parameters were measured at 2, 4 and 6 mm apical to the cementoenamel junction (CEJ) by one examiner. The intra- and inter-class correlation coefficients were calculated to assess the intra, and interobserver reliability. Data were analyzed by ANOVA and Tukey’s test (alpha = 0.05).

Results

The intra- and interobserver reliability were > 0.9 for all parameters. The largest inter-radicular distance in the maxilla was between the central incisors (1–1) in classes I and III, and between premolars (4–5) in class II patients. The largest inter-radicular distance in the mandible was between molar teeth (6–7) in all three classes. The buccal cortical plate thickness was maximum at the site of mandibular first and second molars (6–7). The posterior maxilla and mandible showed the maximum thickness of cancellous bone and alveolar process. Wide variations were noted in this respect between class I, II and III patients.

Conclusions

The area with maximum inter-radicular distance and optimal alveolar bone thickness for miniscrew insertion varies in different individuals, depending on their sagittal skeletal pattern.

Zygomatic-maxillary cortical bone thickness in hyper, normo and hypodivergent patients

Objective:

The aim of this study was to evaluate the thickness of the zygomatic-maxillary cortical bone using computed tomography in different skeletal patterns.

Methods:

A total of 54 patients of both sexes, divided into three groups according to the vertical skeletal pattern, were evaluated for cortical bone thickness of the anterior slope of the zygomatic process of the maxilla, using cone beam computed tomography. Measurements were made at 2mm, 4mm, 6mm, 8mm and 10mm above from first molar mesial root apex. Vertical skeletal pattern was determined by Frankfurt mandibular angle (FMA).

Results:

The hyperdivergent pattern had the lowest cortical thickness value, nevertheless, no patient in the hyperdivergent group presented cortical thickness exceeding 2mm, and no patient in the hypodivergent group presented cortical thickness less than 1mm. However, the correlation between cortical thickness and mandibular plane angle was weak and not significant.

Conclusion:

Although higher prevalence of thick cortical was observed in the hypodivergent patients, and thin cortical groups in the hyperdivergent group, the vertical skeletal pattern could not be used as determinant of the zygomatic-maxillary cortical thickness.

Mini-implant and Modified Nance Button Assisted Alignment of a Horizontally Impacted Maxillary Canine - A Case Report

Orthodontic alignment of a horizontally impacted canine placed high and deep in the maxilla represents a challenging clinical scenario. This article describes a case report of a 16-year-old postpubertal male patient who was concerned about an unesthetic smile. The clinical and radiographic investigations revealed that the patient had retained deciduous canines and bilaterally impacted maxillary canines. The right impacted canine had a good prognosis. The left canine was horizontally impacted in the labial side with a Kau-Pan-Gallerano index score of 19, which indicates a "difficult" degree of treatment. The initial treatment plan was application of distal traction to the impacted left canine from reinforced anchorage unit to change its inclination from horizontal to vertical before erupting it toward occlusion. In this case report, we demonstrated the use of a mini-implant and a modified Nance button-assisted forced eruption of an impacted canine. The 12-month follow-up review showed that the results were maintained during the time, and the previously impacted teeth showed intact gingival attachments. A conservative surgical exposure of the impacted canine and well-planned biomechanics helped us achieve a desirable, esthetic outcome.

Mechanical Evaluation of the Stability of One or Two Miniscrews under Loading on Synthetic Bone

The aim of the present study was to evaluate the primary stability of a two-miniscrew system inserted into a synthetic bone and to compare the system with the traditional one. Forty-five bi-layered polyurethane blocks were used to simulate maxillary cancellous and cortical bone densities. Samples were randomly assigned to three groups—one-miniscrew system (Group A, N = 23), two-miniscrew system (Group B, N = 22) and archwire-only (Group C, N = 10). A total of 67 new miniscrews were subdivided into Group A (23 singles) and Group B (22 couples). 30 mm of 19″ × 25″ archwires were tied to the miniscrew. The load was applied perpendicularly to the archwire. Maximum Load Value (MLV), Yield Load (YL) and Loosening Load (LL) were recorded for each group. The YL of Group B and C had a mean value respectively of 4.189 ± 0.390 N and 3.652 ± 0.064 N. The MLV of Group A, B and C had a mean value respectively of 1.871 ± 0.318N, of 4.843 ± 0.515 N and 4.150 ± 0.086 N. The LL of Group A and B had a mean value respectively of 1.871 ± 0.318 N and of 2.294 ± 0.333 N. A two- temporary anchorage device (TAD) system is on average stiffer than a one-TAD system under orthodontic loading.

Interradicular sites and cortical bone thickness for miniscrew insertion: A systematic review with meta-analysis

INTRODUCTION

Safe zone maps are useful for the clinician to plan miniscrew insertion and possibly reduce radiation exposure. This study aimed to investigate the available evidence regarding the presence of sufficient interradicular space and adequate cortical bone thickness in patients with a complete permanent dentition, in the vestibular and palatal or lingual interradicular sites, mesial to the second molar.

METHODS

PubMed, Scopus, Web of Science, Cochrane Library, and OpenGrey databases were searched up to January 2019 for observational studies involving patients with fully erupted second molars that investigated the amount of interradicular space and/or the cortical thickness of the alveolar processes using 3-dimensional data sets. A custom tool was prepared and used to assess the risk of bias in individual studies. A meta-analysis was performed when at least 4 different studies evaluated 1 identical parameter homogeneously. Publication bias was assessed with the Egger linear regression test.

RESULTS

Twenty-seven observational articles were included in the qualitative synthesis. Only 11 articles were at low risk of bias. Fifteen articles were included in the meta-analysis. The results were graphically reported in "safe-zone" maps.

CONCLUSIONS

In the maxilla, the most suitable insertion sites are those from mesial to the first molar to distal to the first premolar, and between the canine and the lateral incisor, all at 6 mm from the cementoenamel junction. In those areas, the cortical bone has adequate thickness, not requiring predrilling. In the mandible, the preferable vestibular interradicular spaces are those between first and second molars and between first and second premolars, both at 5 mm from the cementoenamel junction, and predrilling is suggested in these areas.

TRIAL REGISTRATION NUMBER

PROSPERO CRD42016042081.

Simulation of miniscrew-root distance available for molar distalization depending on the miniscrew insertion angle and vertical facial type

Objective

The purpose of this study was to evaluate the effects of miniscrew insertion angle and vertical facial type on the interradicular miniscrew–root distance available for molar distalization.

Materials and methods

Cone-beam computed tomography images of 60 adults with skeletal Class I occlusion exhibiting hyperdivergent (n = 20), normodivergent (n = 20), and hypodivergent (n = 20) facial types were used. Placement of a 6-mm long, 1.5-mm diameter, tapered miniscrew was simulated at a site 4 mm apical to the cementoenamel junction, with insertion angles of 0°, 30°, 45°, and 60° relative to the transverse occlusal plane. The shortest linear distance between the miniscrew and anterior root at four interradicular sites was measured: maxillary second premolar and first molar (Mx 5–6), maxillary first and second molars (Mx 6–7), mandibular second premolar and first molar (Mn 5–6), and mandibular first and second molars (Mn 6–7).

Results

Miniscrew–root distance significantly increased as the insertion angle increased from 0° to 60°. In the mandible, the distances significantly differed among vertical facial types, increasing in the following order: hyperdivergent, normodivergent, and hypodivergent. The minimum mean distance was found in the Mx 6–7 (30°; 0.86±0.35 mm), and the maximum mean distance was found in the Mn 5–6 (60°; 2.64±0.56 mm). The rates of miniscrews located buccally outside the root distalization path were up to 70% and 55% when the miniscrews were placed at 60° insertion angles in the Mx 5–6 and Mn 5–6 regions, respectively.

Conclusions

Miniscrew–root distance increased significantly with the increased insertion angle, and the amount of increase was affected by the miniscrew placement site and vertical facial type. To ensure adequate distalization of the posterior segment, the miniscrew should be inserted at an angle in the interradicular area between the second premolar and first molar.

Oblique Plane Cutting of Cone Beam Computed Tomography Analysis on the Safe Zone for Micro-Implants of Maxillary Molar Region

OBJECTIVE

To explore the safe zone for micro-implants of the maxillary molar region by oblique plane cutting mode of cone beam computed tomography (CBCT).

METHODS

Thirty-nine patients with orthodontic alignment were enrolled with CBCT. In this study, the areas between the maxillary second premolar and the first molar were analyzed by the image reconstruction with CS 3D Imaging Software. The alveolar ridge bone width and the minimum interradicular space were measured at the height of 8, 10, and 12 mm from archwire under the 2 cutting modes of the oblique plane and coronal plane, respectively. The statistical analysis was performed.

RESULTS

The bone widths of alveolar ridge between the maxillary second premolar and the first molar were statistically significant under the 2 cutting modes of the oblique plane and coronal plane. The bone width was gradually decreased to the cranial side with the fixed measurement point and the interradicular space was gradually increased. The differences were statistically significant.

CONCLUSION

The oblique plane cutting of CBCT is more representative of the alveolar bone than the coronal plane. There is sufficient safe zone between the maxillary second premolar and the first molar for most patients to implant the micro-implants. However, the individual differences present large and CBCT needs to be taken before the implantation.

X-ray beam angulation can compromise 2-dimensional diagnosis of interradicular space for mini-implants

INTRODUCTION

The aim of this research was to evaluate the influence of x-ray projection geometry on interradicular space of the posterior maxillary arch.

METHODS

Cone-beam computed tomography (CBCT) scans of 32 patients (16.85 ± 4.93 years) who met the selection criteria were enrolled. One hundred ninety-two interradicular sites of the posterior maxillary arch were evaluated. Before measurements, each side of the maxillary arch was orientated in all 3 planes of space to obtain CBCT synthesized periapical radiographs with 0° projection geometry (orthogonal x-ray beam-orthogonal X-ray angulation [OX]). Standardized CBCT axial rotations (10°, 20°, -10°, and -20°) were used to simulate periapical radiographs taken with mesial and distal angulation of the x-ray beam (mesial x-ray angulation [MX] and distal x-ray angulation [DX]). Interradicular space widths were measured on OX, MX, and DX CBCT synthesized periapical radiographs. Measurements were performed parallel to the occlusal plane at 3 mm and 6 mm apical to the midpoint of the alveolar crest. Interradicular distances were statistically compared (P <0.05).

RESULTS

Interradicular distances measured on MX and DX CBCT synthesized periapical radiographs were significantly smaller than those measured on OX. Interradicular distance was significantly correlated with the horizontal angulation of the x-ray beam. X-ray projection angle was the most influential variable on interradicular distance. About 30% reduction in interradicular space was observed for every 10° of deviation from orthogonal x-ray.

CONCLUSION

Two-dimensional radiographs obtained away from the 0° projection geometry can reduce the actual interradicular space for mini-implants, inducing misdiagnosis.

Canine substitution of congenitally missing maxillary lateral incisors in Class I and Class III malocclusions by using skeletal anchorage

INTRODUCTION

This prospective cohort study aimed to evaluate canine substitution supported by skeletal anchorage as a viable treatment protocol for patients with maxillary lateral incisor agenesis (MLIA) and skeletal Class I or Class III.

METHODS

Patients (n = 30) who met the following criteria were recruited: (1) bilateral MLIA or unilateral MLIA with a riziform contralateral incisor with a planned extraction; (2) skeletal Class I or Class III; and (3) dentoalveolar discrepancy in the mandible <5 mm. The archwire sequence routine was administered, combined with a rapid palatal expander, temporary intraoral skeletal anchorage device, and intermaxillary traction with Class III elastics. The results of the cephalometric analyses, peer assessment rating indexes, and the patient's smile self-evaluation using the visual analog scale were compared between initial and final treatments.

RESULTS

This study indicated that closing the space in patients with Class I or Class III malocclusion by using temporary intraoral skeletal anchorage devices in the mandible, along with Class III elastics, yielded satisfactory outcomes. Proper occlusion was established by mesialization of the maxillary teeth and correction of the intermaxillary discrepancy, thereby yielding beneficial and significant cephalometric changes after the treatment. The soft tissue profile was maintained when it was harmonious before the treatment and improved posttreatment in patients in whom the profile was initially inharmonious. All occlusions improved, as evidenced by the peer assessment rating index. Smile esthetics were also enhanced after orthodontic treatment for all patients.

CONCLUSIONS

Canine substitution may be safely offered to patients with Class I and Class III skeletal pattern and MLIA.

Nonextraction Treatment of a Class III Malocclusion Case Using Mini-Screw-Assisted Lower Molar Distalization

Mini-screw assisted lower molar distalization was planned for a present mild Class III malocclusion case. Two mini-screws were inserted into the available inter-root area: one on the left, and the other on the right side in the posterior region in the mandible. Distalization of lower molars, premolars and canines were achieved. Orthodontic treatment lasted approximately 2.5 years with 1 year of molar distalization. Minimal relapse was seen in the postretention period. Dentoalveolar changes with mini-screw assisted lower molar distalization are reported in the present case.

Anatomical study of the maxillary tuberosity using cone beam computed tomography

OBJECTIVES

To examine the dimensions (width, length, and height) of the maxillary tuberosity (MT) and their correlations with age and sex, and to identify different anatomical types for adequate positioning of miniscrews in this area.

METHODS

The study enrolled 39 patients attending the University of Valencia. The patients comprised 21 males and 18 females with a mean age of 39.7 ± 8.4 years. The dimensions of all 78 MTs were measured on cone beam computed tomography (CBCT) images using Invivo Dental 5 software.

RESULTS

The intraobserver and interobserver errors were good for all measurements. A total of 858 MT measurements were taken. The widths were greater in men than in women, with significant differences. The MT dimensions showed correlations with patient age, whereby older patients presented with greater widths and lengths, but reduced heights. Three different anatomical types were detected according to patient age.

CONCLUSIONS

The dimensions (width, length, and height) of the MT vary according to patient age and sex. The MT dimensions conform to particular anatomical types, which should be taken into account when placing miniscrews in this region.

Correlation between tooth size-arch length discrepancy and interradicular distances measured on CBCT and panoramic radiograph: an evaluation for miniscrew insertion

INTRODUCTION

The selection of appropriate sites for miniscrew insertion is critical for clinical success.

OBJECTIVES

The aim of the present study was to evaluate how interradicular spaces measured on panoramic radiograph compare with Cone-Beam Computed Tomography (CBCT), and how crowding can influence the presence of available space for miniscrew insertion, in order to define a new "safe zones" map.

METHODS

A total of 80 pre-treatment panoramic radiographs and 80 CBCT scans with corresponding digital models were selected from the archives of the department of Dentistry, Aarhus University. Crowding was measured on digital models, while interradicular spaces mesial to the second molars were measured on panoramic radiographs and CBCTs. For panoramic radiographs, a magnification factor was calculated using tooth widths measured on digital models. Statistical analyses were performed to investigate the correlation between the amount of crowding and the available interradicular space. Visual maps showing the amount of interradicular spaces measured were drawn.

RESULTS

The most convenient interradicular spaces are those between the second molar and the first premolar in the mandible, and between the central incisors in the maxilla. However, some spaces were revealed to be influenced by crowding.

CONCLUSIONS

Calibration of panoramic radiographs is of utmost importance. Generally, panoramic radiographs underestimate the available space. Preliminary assessment of miniscrew insertion feasibility and the related selection of required radiographs can be facilitated using the new "safe zone" maps presented in this article.

Average interradicular sites for miniscrew insertion: should dental crowding be considered?

Objective:

To define a map of interradicular spaces where miniscrew can be likely placed at a level covered by attached gingiva, and to assess if a correlation between crowding and availability of space exists.

Methods:

Panoramic radiographs and digital models of 40 patients were selected according to the inclusion criteria. Interradicular spaces were measured on panoramic radiographs, while tooth size-arch length discrepancy was assessed on digital models. Statistical analysis was performed to evaluate if interradicular spaces are influenced by the presence of crowding.

Results:

In the mandible, the most convenient sites for miniscrew insertion were in the spaces comprised between second molars and first premolars; in the maxilla, between first molars and second premolars as well as between canines and lateral incisors and between the two central incisors. The interradicular spaces between the maxillary canines and lateral incisors, and between mandibular first and second premolars revealed to be influenced by the presence of dental crowding.

Conclusions:

The average interradicular sites map hereby proposed can be used as a general guide for miniscrew insertion at the very beginning of orthodontic treatment planning. Then, the clinician should consider the amount of crowding: if this is large, the actual interradicular space in some areas might be significantly different from what reported on average. Individualized radiographs for every patient are still recommended.

Comparación de distancias interradiculares y grosor del hueso cortical en dos sectores del maxilar inferior para colocación de mini implantes

Introducción: la colocación de mini implantes interradiculares, como alternativa para el anclaje de aparatología ortodóntica, varía acorde a la clasificación esquelética del paciente Clase I o II. Es necesario realizar la correcta identificación de la ubicación radicular y grosor cortical como parte del análisis estratégico del área a intervenir. Objetivo: comparar tomográficamente las distancias interradiculares y grosor del hueso cortical en dos sectores del maxilar inferior para colocación de mini implantes. Materiales y métodos: estudio transversal que incluyó 120 tomografías computarizadas de haz cónico, pertenecientes a pacientes Clase I (60) y Clase II (60) esquelética. Se identificó tomográficamente la distancia interradicular, el ancho bucolingual y el grosor del hueso cortical bucal, a partir de la cresta alveolar entre el segundo premolar y primer molar inferior derecho y entre el canino y lateral del mismo lado. Un análisis estadístico con prueba t Student al 95% de confianza comparó la ubicación de las estructuras anatómicas para clase I y II esquelética. Resultados: en la distancia interradicular, comparativamente entre clase I y II, se encontró significancia entre canino y lateral derecho (p=< 0.054) a los 8 mm. En este mismo sector, en el ancho bucolingual, se encontró diferencia significativa  a  6mm de altura (p=<.04). En el grosor del hueso cortical no se encontraron diferencias estadísticas al comparar los  valores para la Clase I y II. Conclusiones: en Clase I y II, el mayor espesor para la colocación de mini implantes se registró en el espacio interradicular a 8 mm de altura y en  el ancho bucolingual a 6 mm.

Comparison of interradicular distances and cortical bone thickness in Thai patients with Class I and Class II skeletal patterns using cone-beam computed tomography

Purpose

This study evaluated and compared interradicular distances and cortical bone thickness in Thai patients with Class I and Class II skeletal patterns, using cone-beam computed tomography (CBCT).

Materials and Methods

Pretreatment CBCT images of 24 Thai orthodontic patients with Class I and Class II skeletal patterns were included in the study. Three measurements were chosen for investigation: the mesiodistal distance between the roots, the width of the buccolingual alveolar process, and buccal cortical bone thickness. All distances were recorded at five different levels from the cementoenamel junction (CEJ). Descriptive statistical analysis and t-tests were performed, with the significance level for all tests set at p<0.05.

Results

Patients with a Class II skeletal pattern showed significantly greater maxillary mesiodistal distances (between the first and second premolars) and widths of the buccolingual alveolar process (between the first and second molars) than Class I skeletal pattern patients at 10 mm above the CEJ. The maxillary buccal cortical bone thicknesses between the second premolar and first molar at 8 mm above the CEJ in Class II patients were likewise significantly greater than in Class I patients. Patients with a Class I skeletal pattern showed significantly wider mandibular buccolingual alveolar processes than did Class II patients (between the first and second molars) at 4, 6, and 8 mm below the CEJ.

Conclusion

In both the maxilla and mandible, the mesiodistal distances, the width of the buccolingual alveolar process, and buccal cortical bone thickness tended to increase from the CEJ to the apex in both Class I and Class II skeletal patterns.

A CBCT atlas of buccal cortical bone thickness in interradicular spaces

OBJECTIVE

To provide a road map of buccal cortical bone thickness in interradicular locations where miniscrew implants are commonly placed.

MATERIALS AND METHODS

Cone-beam computed tomography images from 100 study quadrants (50 maxillary and 50 mandibular) were studied. Cortical bone thickness was measured at the most mesial point, the midpoint, and the most distal point in interradicular areas from the canine to the first molar in both arches at 4 mm and 6 mm from the alveolar ridge. Indicator variables of whether the cortical bone thickness was thinner than 1 mm and thicker than 1.5 mm were constructed and analyzed in a general linear mixed model.

RESULTS

Buccal cortical bone was significantly thinner at a point bisecting two teeth than the bone adjacent to the teeth (P < .0001). The site with the greatest percentage of measurements <1 mm (20%) was at the midpoint bisecting the mandibular canine and the first premolar. The site with the highest percentage of measurements >1.5 mm (50%) was in the mandible adjacent to the first molar (distal to the midpoint of the second premolar and first molar) at 6 mm from the alveolar crest.

CONCLUSION

Cortical bone thickness is significantly thinner centrally between two teeth than in the areas adjacent to the roots.

Comparative photoelastic study of dental and skeletal anchorages in the canine retraction

Objective

To compare dental and skeletal anchorages in mandibular canine retraction by means of a stress distribution analysis.

Methods

A photoelastic model was produced from second molar to canine, without the first premolar, and mandibular canine retraction was simulated by a rubber band tied to two types of anchorage: dental anchorage, in the first molar attached to adjacent teeth, and skeletal anchorage with a hook simulating the mini-implant. The forces were applied 10 times and observed in a circular polariscope. The stresses located in the mandibular canine were recorded in 7 regions. The Mann-Whitney test was employed to compare the stress in each region and between both anchorage systems. The stresses in the mandibular canine periradicular regions were compared by the Kruskal-Wallis test.

Results

Stresses were similar in the cervical region and the middle third. In the apical third, the stresses associated with skeletal anchorage were higher than the stresses associated with dental anchorage. The results of the Kruskal-Wallis test showed that the highest stresses were identified in the cervical-distal, apical-distal, and apex regions with the use of dental anchorage, and in the apical-distal, apical-mesial, cervical-distal, and apex regions with the use of skeletal anchorage.

Conclusions

The use of skeletal anchorage in canine retraction caused greater stress in the apical third than the use of dental anchorage, which indicates an intrusive component resulting from the direction of the force due to the position of the mini-implant and the bracket hook of the canine.

Nonsurgical correction of a Class III malocclusion in an adult by miniscrew-assisted mandibular dentition distalization

This article reports the successful use of miniscrews in the mandible to treat a 20-year-old Mongolian woman with a chief complaint of anterior crossbite. The patient had a skeletal Class III malocclusion with a mildly protrusive mandible, an anterior crossbite, and a deviated midline. In light of the advantages for reconstruction of the occlusal plane and distal en-masse movement of the mandibular arch, we used a multiloop edgewise archwire in the initial stage. However, the maxillary incisors were in excessive labioversion accompanied by little retraction of the mandibular incisors; these results were obviously not satisfying after 4 months of multiloop edgewise archwire treatment. Two miniscrews were subsequently implanted vertically in the external oblique ridge areas of the bilateral mandibular ramus as skeletal anchorage for en-masse distalization of the mandibular dentition. During treatment, the mandibular anterior teeth were retracted about 4.0 mm without negative lingual inclinations. The movement of the mandibular first molar was almost bodily translation. The maxillary incisors maintained good inclinations by rotating their brackets 180° along with the outstanding performance of the beta-titanium wire. The patient received a harmonious facial balance, an attractive smile, and ideal occlusal relationships. The outcome was stable after 1 year of retention. Our results suggest that the application of miniscrews in the posterior area of the mandible is an effective approach for Class III camouflage treatment. This technique requires minimal compliance and is particularly useful for correcting Class III patients with mild mandibular protrusion and minor crowding.