Bone depth and thickness of different infrazygomatic crest miniscrew insertion paths between the first and second maxillary molars for distal tooth movement: A 3-dimensional assessment

Optimizing Infrazygomatic Miniscrew Insertion Parameters: Systematic Review and Meta-Regression Analysis of Bone Thickness by Insertion Height, Angulation, and Anatomical Position

Introduction: Infrazygomatic crest (IZC) miniscrews are widely used for skeletal anchorage in orthodontics. Despite their growing popularity, the optimal insertion parameters-such as height, angulation, and anatomical position-remain controversial, with existing studies offering inconsistent and fragmented data. Aim: To determine the optimal insertion position, height, and angulation of infrazygomatic miniscrews to maximize bone insertion using cone-beam computed tomography (CBCT) analysis and to investigate the influence of facial skeletal patterns on IZC bone morphology. Methods: This review was conducted according to the PRISMA 2020 guidelines. A comprehensive electronic search was performed across six databases: PubMed, Scopus, Web of Science, Cochrane, EBSCO, and Google Scholar. Studies reporting CBCT-based IZC bone thickness were included. A meta-analysis was conducted using a random-effects model, and meta-regression was applied to assess the relationship between insertion height, angulation, and bone thickness. The STROBE checklist was used to assess the quality of the included observational studies. Results: Seventeen studies comprising a total of 1840 CBCT-based measurements were included. The meta-regression revealed a significant inverse relationship between insertion height and bone thickness (β = -0.53; p < 0.001) and a positive correlation with angulation (β = 0.09; p < 0.001). The U67 region refers to the anatomical area between the maxillary first and second molars, adjacent to the infrazygomatic crest and zygomatic buttress, which with an insertion height of 9.9 mm and 80° angulation, demonstrated the highest mean cortical bone thickness (3.52 mm). There was no evidence of a significant association between facial pattern and bone thickness (p = 0.878). Conclusions: This review presents the first predictive model for IZC miniscrew placement based on meta-regression. The findings support the U67 site at 9.9 mm height and 80° angulation as the optimal insertion protocol. These data-driven guidelines provide clinicians with practical, evidence-based direction for improving miniscrew stability and minimizing complications.

Optimizing the Anatomical Location and Procedural Parameters for Miniscrew Placement in the Infrazygomatic Region- A CBCT Study

This study evaluates the integration of anatomical and procedural guidelines to develop realistic protocols for successful miniscrew insertion in the infrazygomatic crest (IZC) region, using CBCT measurements. A total of 720 measurements were collected from 30 adult patients, focusing on the upper first molar (U6) region. A grid system was created in the sagittal plane, including 12 reference points around the U6, with horizontal and vertical measurement points. A 12-mm virtual IZC miniscrew was inserted at each reference point, with the angle adjusted for 1 mm of sinus penetration and 5 mm of projection beyond the bone surface. Insertion success was defined as maintaining a minimum 0.5 mm safe distance from the roots, classified as system-compatible (SC), while root contact (RC), failure to achieve sinus penetration (SF), or sinus perforation (SP) exceeding 1 mm were classified as failures. No significant differences were found among the reference regions (p > 0.05). The 15 mm-U6MB region, with an insertion angle of 41.22°±8.67° apically and 12.36°±2.48° mesially, had the highest success rate of 55.0 %. The 15 mm-U6DB region, while aligning with the guidelines, had a higher incidence of root proximity (56.9 %). At the 17 mm region, sinus perforations exceeded 1 mm in 96.8 % of cases. The recommended placement height of 15 mm above the POP, with a 40° apical and 10° mesial angle at U6MB, offers the best balance of stability and safety, in line with literature guidelines. This study provides clinicians with evidence for effective miniscrew placement, ensuring stability while avoiding critical anatomical structures.

Optimal sites for mini-implant insertion into the infrazygomatic crest according to different craniofacial morphologies: A cross-sectional cone-beam computed tomography study

INTRODUCTION

The infrazygomatic bone crest and other extraalveolar regions represent a viable option for the placement of temporary anchorage devices when distalizing the maxillary arch. This approach allows for the movement of the dentition without concern for potential collisions among dental structures. Nevertheless, it is of the utmost importance to conduct a thorough examination of the anatomy of this region before the placement of mini-implants to prevent potential injuries, such as maxillary sinus perforations. The objective of this study was to quantify the depth of the infrazygomatic crest and evaluate its correlations with age, gender, skeletal classification, and vertical pattern.

METHODS

The study sample of this cross-sectional, retrospective study consisted of 201 cone-beam computed tomography scans collected from patients treated at the Master's program in orthodontics at the University of Valencia and at a private dental clinic. The cone-beam computed tomography scans were collected for 5 years, from January 2017 to May 2022. The total and intraalveolar lengths were defined and measured at 3 points: the distal roots of the maxillary second molars, the distal roots of the maxillary first molars, and the mesial roots of the maxillary first molars. These measurements were taken on both the right and left sides using the Carestream 3D Imaging System (Atlanta, Ga).

RESULTS

The total length (TL) at the mesiobuccal level of the first molars was found to be significantly longer on both sides (P = 0.001). The intraalveolar length exhibited statistically significant differences between the right and left sides, with those of the left side exhibiting greater length (P <0.001). The normodivergent patterns demonstrated lower TL values than hypodivergent (P = 0.006) and hyperdivergent patterns (P = 0.033).

CONCLUSIONS

A statistically significant inverse relationship was observed between the distance from the cementoenamel junction to the vestibular bone crest and the total and intraalveolar lengths in the studied regions. The TL was greatest in the region of the mesiobuccal root of the maxillary first molars, followed by the region of the distal root of the second molars, and finally, the region of the distobuccal root of the maxillary first molars. Patients with normodivergent patterns exhibited the lowest total infrazygomatic ridge height.

An in vitro study of a combined patient-specific device for safe and accurate insertion of infrazygomatic crest miniscrews

OBJECTIVES

To develop and assess the efficacy of a novel combined patient-specific device (CPSD) for the accurate and safe insertion of infrazygomatic crest miniscrews in orthodontic procedures.

MATERIALS AND METHODS

Twenty-eight miniscrews were placed in the infrazygomatic crest region of 28 cadaver maxillae using the direct manual method (n = 14) or the CPSD (n = 14) based on preset trajectories. The CPSD, designed based on the integration model, included a positioning guide, an insertion guide, and a depth-limiting groove. Deviations in the insertion site, tip location, insertion angle, and biting depth between the preset and real insertion trajectories were calculated to evaluate the accuracy of miniscrew insertion. Classification frequencies of root proximity, sinus penetration depth, and biting depth of the miniscrew after insertion were also calculated to evaluate the safety of miniscrew insertion.

RESULTS

Regarding evaluation of accuracy, significant differences were observed in the deviation values of the insertion site, tip location, insertion angle, and biting depth between the CPSD and freehand groups (P = .001, P < .001, P < .001, P = .039, respectively). Regarding evaluation of safety, a significant difference was observed in the classification frequencies of root proximity between the two groups (P = .016).

CONCLUSIONS

Compared with manual insertion, CPSD could be a preferred method for safe and accurate insertion of infrazygomatic crest miniscrews for orthodontists.

Effects of exposure length, cortical and trabecular bone contact areas on primary stability of infrazygomatic crest mini-screws at different insertion angles

BACKGROUND

The infrazygomatic crest mini-screw has been widely used, but the biomechanical performance of mini-screws at different insertion angles is still uncertain. The aim of this study was to analyse the primary stability of infrazygomatic crest mini-screws at different angles and to explore the effects of the exposure length (EL), screw-cortical bone contact area (SCA), and screw-trabecular bone contact area (STA) on this primary stability.

METHODS

Ninety synthetic bones were assigned to nine groups to insert mini-screws at the cross-combined angles in the occlusogingival and mesiodistal directions. SCA, STA, EL, and lateral pull-out strength (LPS) were measured, and their relationships were analysed. Twelve mini-screws were then inserted at the optimal and poor angulations into the maxillae from six fresh cadaver heads, and the same biomechanical metrics were measured for validation.

RESULTS

In the synthetic-bone test, the LPS, SCA, STA, and EL had significant correlations with the angle in the occlusogingival direction (rLPS = 0.886, rSCA = -0.946, rSTA = 0.911, and rEL= -0.731; all P < 0.001). In the cadaver-validation test, significant differences were noted in the LPS (P = 0.011), SCA (P = 0.020), STA (P = 0.004), and EL (P = 0.001) between the poor and optimal angulations in the occlusogingival direction. The STA had positive correlations with LPS (rs = 0.245 [synthetic-bone test] and r = 0.720 [cadaver-validation test]; both P < 0.05).

CONCLUSIONS

The primary stability of the infrazygomatic crest mini-screw was correlated with occlusogingival angulations. The STA significantly affected the primary stability of the infrazygomatic crest mini-screw, but the SCA and EL did not.

An evaluation of bone depth at different three-dimensional paths in infrazygomatic crest region for miniscrew insertion: A cone beam computed tomography study

Objective

To investigate the difference and distribution of bone depth at different three-dimensional simulated paths to help optimize the insertion path for miniscrew placement in the infrazygomatic crest.

Methods

Cone beam computed tomography scans of 80 adults (38 males and 42 females; mean age, 27.0 years) were assessed. For each subject, bone depth of 81 simulated insertion paths at different insertion points and three-dimensional angulations was measured in 160 infrazygomatic crests; the differences were evaluated using the adjusted Friedman test. The bone deficiency ratio for each path was calculated. Distributions of measurements were analyzed and reported as specially designed colormaps.

Results

Bone depth increased, and bone deficiency ratio reduced mesially to distally (P < 0.001), apically to coronally (P < 0.01), and at a greater gingival and distal inclination (P < 0.05). The maximum bone depth (10.72 mm) was observed 13 mm above the maxillary occlusal plane in the mesiobuccal root of the maxillary second molar. The minimum bone depth (3.4 mm) was observed 17 mm above the maxillary occlusal plane in the distobuccal root of the maxillary first molar. No bone deficiency was detected at the paths of 13 mm above the maxillary occlusal plane at a gingival inclination of 70° and distal inclination of 30° in the mesiobuccal root of the maxillary second molar. The highest bone deficiency ratio is present 17 mm above the maxillary occlusal plane at a gingival inclination of 60° and a distal inclination of 0° in the distobuccal root of the maxillary first molar (89/160).

Conclusion

Insertion paths located at 13 mm above the maxillary occlusal plane in the mesiobuccal root of the maxillary second molar were optimal. A gingival inclination of 70° and a distal inclination of 30° could be beneficial. The distobuccal root of the maxillary first molar region or above the 17 mm insertion plane may not be recommended.

Should Cone-Beam Computed Tomography Be Performed Prior to Orthodontic Miniscrew Placement in the Infrazygomatic Crest Area?-A Systematic Review

There is no unequivocal scientific consensus for the temporary anchorage device (TAD) positioning in the infrazygomatic crest area (IZC). The two principal aims of this systematic review were to assess bone availability in the IZC and to establish both the target site and the need for cone-beam computed tomography (CBCT) prior to miniscrew placement. The study was performed following PRISMA guidelines (PROSPERO: CRD42023411650). The inclusion criteria were: at least 10 patients, three-dimensional radiological examination, and IZC assessment for the TAD placement. ROBINS-I tool and Newcastle-Ottawa Scale were used for quality evaluation. No funding was obtained. The study was based on the information coming from: PubMed, Google Scholar, Web of Science Core Collection, MDPI, Wiley, and Cochrane Libraries. The last search was carried out on 1 August 2023. Fourteen studies were identified for analysis. A narrative synthesis was performed to synthesize the findings of the different studies. Unfortunately, it is not possible to establish the generally recommended target site for IZC TAD placement. The reasons for this are the following: heterogeneity of available studies, inconsistent results, and significant risk of bias. The high variability of bone measurements and the lack of reliable predictors of bone availability justify the use of CBCT for TAD trajectory planning. There is a need for more high-quality studies aiming three-dimensional bone analysis of the IZC.

Clinical analysis of successful insertion of orthodontic mini-implants in infrazygomatic crest

BACKGROUND

The insertion positions of mini-implant in infrazygomatic crest has been reported, but due to the anatomical variation, the precise location of this site is not clear yet. This study used cone-beam computed tomography (CBCT) to analyze the position and angle of mini-implants successfully inserted in the infrazygomatic crest, with the goal of providing reference data for clinical practice.

METHODS

CBCT was used to image 40 mini-implants and their surrounding tissues in adult orthodontic patients who successfully underwent mini-implant insertion in the infrazygomatic crest. The insertion positions and angles of mini-implants were measured, and the thicknesses of buccal and palatal bone adjacent to the mini-implants were also recorded. Then, we proposed the position and implantation angle for infrazygomatic crest insertion. According to the position and angle, the cortical bone thickness and distance to the root of another 54 randomly selected infrazygomatic crests were recorded to verify its feasibility.

RESULTS

In the coordinate system, the implantation position of the 40 successful mini-implants was (-0.4 ± 2, 8.2 ± 2.5) and the implantation angle between the long axis of the mini-implant and horizontal reference plane was 56.4° ± 7.7°. The bone thicknesses on buccal and palatal sides of infrazygomatic crest adjacent to mini-implants were 4.1 ± 2.5 mm and 7.2 ± 3.2 mm, respectively, and the cortical bone thickness was 2.4 ± 0.6 mm. Among 54 infrazygomatic crests, 75.9% of them met the safety and stability requirements. When the implantation height was increased by 1, 2, and 3 mm, the proportions of implants that met requirements for success were 81.5%, 90.7%, and 94.4%, respectively. But, the proportions of eligible implants were limited at implantation angle increases of 5° and 10°.

CONCLUSIONS

Using the long axis of the maxillary first permanent molar (U6) as the vertical reference line, mini-implants could be safely inserted in the infrazygomatic crest at a distal distance of 0.4 mm and height of 8.2 mm from the central cementum-enamel junction of U6, with an implantation angle of 56.4°. The success rate increased when the implant height increased, but the proportion of eligible implantation was limited with the increase of implantation angle.