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 Table of Contents  
Year : 2023  |  Volume : 15  |  Issue : 4  |  Page : 398-403

Posteroanterior cephalometric immediate assessment of infrazygomatic crest mini-implants: A retrospective study

Department of Orthodontics, Saveetha Dental College, Saveetha Institute of Medical and Technical Science, Saveetha University, Chennai, Tamil Nadu, India

Date of Submission18-Nov-2022
Date of Decision17-Apr-2023
Date of Acceptance17-May-2023
Date of Web Publication31-Aug-2023

Correspondence Address:
Dr. Aravind Kumar Subramanian
Department of Orthodontics, Saveetha Dental College, Saveetha Institute of Medical and Technical Science, Saveetha University, Chennai 600 050, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jioh.jioh_243_22

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Aim: There are wide variations in placement of extra-alveolar bone screws that can occur in angulation, the height of placement, and other operator-related factors. The aim of this study is to comparatively evaluate the position of bilaterally placed infrazygomatic crest (IZC) mini-implants factors such as height, angulation, the length outside the bone, if any sinus penetration and the depth of penetration into the sinus. Materials and Methods: The study is a retrospective pilot study collected from the hospital records over the time period study was conducted. Posteroanterior cephalograms taken for patients after bilateral placement of IZC were collected. The comparison of the variations in placement for the right and left side was done. Results: There is wide variation among the sample and comparison to the right and left sides in the same sample. The height of placement above the buccal tube ranged from 7 to 8 mm. There were wide variations in angulation of the implant to the buccal bone ranging from 15° to up to 50°. Of the total size of the IZC mini-implant 6–7 mm of the implant was left outside the bone and an average of 2.5 mm of sinus penetration was commonly observed. Conclusion: Postplacement assessment of IZC can be done with a posteroanterior cephalogram. The implant was placed at a height of 6–10 mm above the buccal tube; there were wide variations in angulations between right and left side; 4–7 mm of the mini-implant did not engage the IZC, and there was a high incidence of sinus penetration ranging from 1 mm to 3.5 mm.

Keywords: Anchorage, diagnosis and treatment planning, extra-alveolar anchorage, IZC mini-implant, posteroanterior cephalogram

How to cite this article:
Sreenivasagan S, Subramanian AK, Ramasamy N. Posteroanterior cephalometric immediate assessment of infrazygomatic crest mini-implants: A retrospective study. J Int Oral Health 2023;15:398-403

How to cite this URL:
Sreenivasagan S, Subramanian AK, Ramasamy N. Posteroanterior cephalometric immediate assessment of infrazygomatic crest mini-implants: A retrospective study. J Int Oral Health [serial online] 2023 [cited 2023 Sep 25];15:398-403. Available from:

  Introduction Top

Infrazygomatic crest (IZC) mini-implants are a commonly used extra-alveolar anchorage in maxilla. The site of insertion of the mini-implants are located on the buccal surface on the zygomatic process of the maxilla.[1] The site is located away from the tooth roots and hence does not cause any interference and can be efficiently used for en masse distalization, anterior retraction, intrusion, and distalization.[2],[3],[4],[5] The length of the mini-implants placed in this site range between 8 and 12 mm in length depending on the site of placement either distal to the first molar or the second molar. Considering the potential for soft tissue irritation and the growth pattern, the implant is usually placed in an area of attached gingiva with a minimum of 1.5-mm clearance from the soft tissue.[6]

Numerous studies have focused on bone thickness, anatomy, failure rate, and complication such as distance of IZC rest region from the sinus floor and other associated factors with this category of extra-alveolar mini-implants.[7],[8],[9],[10] There is often a high risk of penetration of the mini-implant into the sinus.[9] Chang et al.[10] have reported up to 7% failure of IZC mini-screws, whereas Uribe et al.[11] have reported a failure rate of 21.8%. Very minimal to no data can be found on the technique of evaluation of the IZC mini-implant postplacement. Cone-beam-computed tomography postinsertion of the IZC screw will be a gold standard for evaluation of placement-associated risk factors. The efficient radiation dose of cone-beam-computed tomography (CBCT) of various machines available in market can range from 19 to 1,073 μSv depending on the image detector, voxel side, and field of view.[12] It would, therefore, be unethical and potentially harmful. Periapical radiographs cannot be used in this region. Posteroanterior cephalograms (PA cephalograms) can be an efficient way to radiographically assess the placement technique postplacement for extra-alveolar screws.

In posteroanterior cephalograms, the radiation exposure from one cephalogram will be as low as 5.1 μSv with photostimulable phosphor storage.[13],[14] The PA cephalogram will allow us to visualize the right and left side IZC mini-implants at the same time. The aim of this study is to comparatively evaluate the position of bilaterally placed IZC mini-implants using posteroanterior cephalograms for factors such as height above the buccal tube, angulation of the mini-implant from the buccal bone, the length of mini-implant outside the bone, if any sinus penetration and the depth of penetration of the mini-implant into the sinus.

  Materials and Methods Top

Setting and design

The study is a retrospective study collected samples of posteroanterior cephalograms obtained from the record-keeping software of patients for whom IZC mini-implants were placed bilaterally at the Saveetha Dental College. The sample was collected between June and December 2022.

Sampling criteria

The IZC mini-implants placed in these patients were from Favanchor company and were made of titanium had a long collar and were of the size 2 × 12 mm. A total of 17 PA cephalograms were obtained and analyzed to comparatively evaluate the position of the bilaterally placed mini-implant. Samples when any bone pathology or facial asymmetry was observed were excluded from the study.

Ethical approval and informed consents

The study was approved by the institutional review board of the university and the approval number is SRB/SDC/ORTHO-1804/21/04.


All the PA cephalograms were oriented by reference line perpendicular to the line passing through bilateral orbitale point and a midsagittal reference line from the crista galli.[15],[16] The factors analyzed in the study include height and angulations of insertion and length of mini-implant not engaged in the bone and sinus penetration. All the PA cephalograms were taken at a stage when leveling and aligning of the arches were completed and each of the patients were in 17 × 25 or 19 × 25 SS arch form. The leveling of the bracket slots thus aided in standardization and thus the leveled slot of the maxillary first molar was used a landmark in the cephalometric measurements.

Observational parameters

The height of the head of the IZC mini-implant was measured from the buccal tube of maxillary first molar to the head of the mini-implant [Figure 1]. The angulation of the mini-implant was assessed by drawing a perpendicular to the buccal bone and measuring the angulation of the implant from this horizontal line [Figure 2]. Length of the mini-implant not inserted into the bone was measured from the head of the IZC mini-implant to the point where it engaged the bone [Figure 3]. From the PA cephalogram, we evaluated if there is any penetration of the mini-implant within the sinus, if there was penetration, it was measured from the sinus floor to the tip of the mini-implant within the sinus.
Figure 1: Height of IZC mini-implant head above the buccal tube

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Figure 2: Angulation of mini-implant to the buccal bone

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Figure 3: Length of mini-implant outside the bone

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All the values were tabulated using excel sheet. Statistical analysis was performed IBM SPSS Statistics 20 (headquartered in Chicago and incorporated in Delaware). Descriptive analysis was done and independent t-test was done to compare the variations in right and left side for the four factors assessed in this study. Confidence interval was kept at 95%. P value less than 0.05 was taken as statistically significant.

  Results Top

The results of the statistical analysis are represented in [Table 1]. The confidence interval was kept at 95%. P value less than 0.05 was taken as statistically significant.
Table 1: Factors analyzed using posteroanterior cephalogram

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The height of the head of the mini-implant was inserted at 7.57 ± 3 on the right side and at 6.59 ± 2.4 mm on the left side. The angle of mini-implant from the buccal bone was inserted at 27.2° ± 11.5° in the right side and 38.5° ± 12° in the left side. The length of the mini-implant that did not engage the bone in the right side was 6 ± 2.4 mm and 6.9 ± 2.5 mm in the left side. Sinus penetration was observed in both the right and the left side; 2.6 ± 1.5 mm in the right side and 2.4 ± 1.7 mm. All the values were statistically significant.

  Discussion Top

The results from the study showed that the implant was placed at an average of 7.6 mm on the right side and at 7 mm on the left side when measured from buccal tube. There was a difference in placement angulation between the right and left side by almost 10°. The mini-implants were angulated more in the left side. The angulation of placed mini-implants varied from as low as 10° from the buccal bone. The length of the mini-implant used in this study is 12 mm, in both the right and left side at an average of 6–7 mm did not engage the bone. Sinus penetration had not occurred in 3 of the 24 sites assessed. In the sites where the sinus was penetrated an average of 2–2.7 mm penetration was observed. The site of insertion of height difference can vary between the brachycephalic and dolicocehalic patients.[16] These findings indicated that there is variation between placing in the same patient in the right and left side. The findings of this study are an eye-opener that suggests there is huge variation among clinicians when they place bone screws in the IZC. The use of template and guides could assist in better placement and immediate postplacement assessment with the help in assessing factors for optimum placement and success.

PA cephalometric measurements using midsagittal reference plane that is perpendicular to the midpoint of the right and left orbitale were closest in measurements to a 3D-computed tomography.[17] CBCT could be an indication of the amount of the bone available in the IZC site and if needed can be used for planning and diagnostic purpose prior to placement.[8] Immediate postplacement of posteroanterior cephalogram can be useful in evaluating the protocol with which the mini-implant was placed and to determine the potential risk of sinus penetration.

The factors that influence the height of placement of the IZC mini-implant include the cortical bone thickness, the soft tissue interference in this site. Chang et al.[10] had reported that there is no significant difference in the success of mini-implant when placed in the attached gingiva or the movable mucosa. Cortical bone thickness of 1–1.6 mm is found in this site in relation to the first and second molar.[18],[19] Adequate primary stability can be achieved when the mini-implant is placed as perpendicular as possible to the cortical bone thus engaging a maximum cortical bone.[20] The thickness of the cortical bone thickness increases as we move away from the cementoenamel junction and a study by Ono et al.[18] have found a thickness of 2.4 mm at a 15-mm mark from the alveolar crest. The height at which implants were placed in our study was placed at 7–8 mm above the molar tube which is an adequate height to engage cortical bone and achieve primary stability.

On an average, 6–7 mm of the length of the mini-implant did not engage the IZC and was outside the bone in both the right and left side among the samples we had evaluated. A recent study by Murugesan et al.[21] states that the required length of IZC mini-implant in Indian population should be 9–11 mm where 6–7 mm of the treated portion will be engaging the bone and thus still leaving 3–4 mm of collar length needed for this site.

Liou et al.[7] recommend a height of 14–16 mm from the maxillary occlusal plane and an angulation of 55°–70° of angulation from the buccal bone or horizontal plane in order to achieve maximal bone engagement. Lin and Roberts[22] suggest placing the IZC mini-implants distal to the maxillary second molar as there is more cortical bone available in this site. In a previous finite element analysis conducted by our team, we observed maximum efficient distalization by IZC mini-implant and when it was at an angulation of 70°.[23] Uribe et al.[11] suggested placement at an angle of 40°–70° to the maxillary occlusal plane by palpating the key ridge above the maxillary first molar in the IZC region. Benedict Wilmes[24] in his work had reported that when the implant was placed less oblique at an angle of 60°–70° for the purpose of engaging more cortical bone, it required a high-insertion torque value, whereas angles like 30°–40° would not be beneficial for achieving primary stability. The placement angulation in our studies widely varied among the samples ranging from 20° to 50°. Very low angulation to the buccal bone will be disadvantageous and interfere with achieving primary stability; angulations of 70°–90° will cause severe irritation to the cheek mucosa and can cause the mucosa to get fibrosed.

There is high incidence reported in literature where the sinus is penetrated during the IZC mini-implant placement. When mini-implant run through adequate layer of cortical bone, then the tip of the implant would have penetrated into the sinus.[9] Studies have shown evidence to indicate a penetration of 1–2 mm would be covered with newly formed membrane and partially covered new bone.[25] The relative height of the sinus floor for the Indian population from the alveolar crest is at 8.1 mm for men and 7.8 mm for woman.[26] Motoyoshi et al.[27] reported that there is no case of sinusitis in cases where there was sinus perforation and no clinical symptoms or screw mobility. The sinus floor was thinner in cases where there was perforation. Sinus penetration was observed in most of the sites we observed but the average depth of penetration was more than 2 mm in both the right and left side which is more than the acceptable depth of perforation across the various literatures available.

The findings of this study suggest that the practitioner may not always be precise in placement of the temporary anchorage devices in the correct position. The authors suggest that proper planning of extra-alveolar screws with clinical and radiographic aid will help in precise positioning. The evaluation of immediate postplacement will be beneficial in assessing if the long IZC mini-implant has penetrated the sinus floor as well as assessing its position and site and height of insertion.

The implications for further research are that the IZC mini-implants should be placed with stents or navigation system. The use of CBCT post-treatment can be used as a standard and to compare with immediate postplacement evaluation with posteroanterior cephalogram to evaluate the efficiency of this technique.

The limitation of this study is that it is a pilot retrospective study where we could assess only 24 sites. Further studies need to be conducted with larger sample size, immediate follow-up postplacement of IZC along with a clinical follow-up. As indicated by this study, there is definite variation in placement between the right and left side IZC and thus stents designed according to the specific requirement of the patient would be beneficial in having a thorough placement protocol.

  Conclusion Top

Postplacement assessment of IZC can be done with posteroanterior cephalogram. This immediate assessment will help in avoiding the placement variations between the right and left side. Sinus penetration and the depth of the placement can be evaluated thus minimizing the risk of complications like sinusitis. The implant was placed at a height of 6–10 mm above the buccal tube; there were wide variations in angulations between right and left side; 4–7 mm of the mini-implant did not engage the IZC and there was high incidence of sinus penetration ranging from 1 to 3.5 mm.


The authors would like to extend their sincere gratitude to the operators for the collection of radiographs.

Financial support and sponsorship


Conflict of interest

There are no conflicts of interest.

Author contribution

S.S. performed data collection, writing the manuscript, and statistics. A.K.S. formulated the study design and helped in proofreading the manuscript. N.R. assisted in data collection and verifying the calculations, any difference of opinion by the first two authors was clarified by discussion with author N.R.

Ethical policy ad institution review board statement

The study was approved by the institutional review board of the university and the approval number is SRB/SDC/ORTHO-1804/21/04.

Patient declaration of consent

Not applicable.

Data availability statement

The authors will provide the raw data that was collected during the study upon request.

  References Top

Baumgaertel S, Hans MG Assessment of infrazygomatic bone depth for mini-screw insertion. Clin Oral Implants Res 2009;20:638-42.  Back to cited text no. 1
Ghosh A, Infra-Zygomatic C, Buccal S Orthodontic bone screws: a leap ahead of micro-implants—Clinical perspectives. J Indian Orthod Soc 2018;52:127-41.  Back to cited text no. 2
Seres L, Kocsis A Closure of severe skeletal anterior open bite with zygomatic anchorage. J Craniofac Surg 2009;20:478-82.  Back to cited text no. 3
Nanda R, Uribe FA, Yadav S Temporary Anchorage Devices in Orthodontics E-Book. United States of America: Elsevier Health Sciences; 2019.  Back to cited text no. 4
Cornelis MA, De Clerck HJ Maxillary molar distalization with miniplates assessed on digital models: A prospective clinical trial. Am J Orthod Dentofacial Orthop 2007;132:373-7.  Back to cited text no. 5
Goaslind GD, Robertson PB, Mahan CJ, Morrison WW, Olson JV. Thickness of facial gingiva. J Periodontol 1977;48:768-71.  Back to cited text no. 6
Liou EJW, Chen P-H, Wang Y-C, Lin JC A computed tomographic image study on the thickness of the infrazygomatic crest of the maxilla and its clinical implications for miniscrew insertion. Am J Orthod Dentofacial Orthop 2007;131:352-6.  Back to cited text no. 7
Murugesan A, Sivakumar A Comparison of bone thickness in infrazygomatic crest area at various miniscrew insertion angles in Dravidian population—A cone beam computed tomography study. Int Orthod 2020;18:105-14.  Back to cited text no. 8
Jia X, Chen X, Huang X Influence of orthodontic mini-implant penetration of the maxillary sinus in the infrazygomatic crest region. Am J Orthod Dentofacial Orthop 2018;153:656-61.  Back to cited text no. 9
Chang CH, Lin JS, Roberts WE Failure rates for stainless steel versus titanium alloy infrazygomatic crest bone screws: A single-center, randomized double-blind clinical trial. Angle Orthod 2018;89:40-6.  Back to cited text no. 10
Uribe F, Mehr R, Mathur A, Janakiraman N, Allareddy V Failure rates of mini-implants placed in the infrazygomatic region. Prog Orthod 2015;16:1-6.  Back to cited text no. 11
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Ordobazari M, Al-Hosseini AAN, Zafarmand AH A novel approach for craniofacial symmetry evaluation: Using the midsagittal reference line drawn from “Crista Gali” with NHP technique. Nov Biomed 2013;1:48-53.  Back to cited text no. 15
Matias M, Flores-Mir C, de Almeida MR, da Silva Vieira B, de Freitas KM, Nunes DC, et al. Miniscrew insertion sites of infrazygomatic crest and mandibular buccal shelf in different vertical craniofacial patterns: A cone-beam computed tomography study. Kor J Orthodont 2021;51:387-96.  Back to cited text no. 16
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Ono A, Motoyoshi M, Shimizu N Cortical bone thickness in the buccal posterior region for orthodontic mini-implants. Int J Oral Maxillofac Surg 2008;37:334-40.  Back to cited text no. 18
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Lakshmikantha HT, Ravichandran NK, Jeon M, Kim J, Park H-S Three-dimensional characterization of cortical bone microdamage following placement of orthodontic microimplants using optical coherence tomography. Sci Rep 2019;9:1-3.  Back to cited text no. 20
Murugesan A, Jain RK A 3D comparison of dimension of infrazygomatic crest region in different vertical skeletal patterns: A retrospective study. Int Orthod 2020;18:770-5.  Back to cited text no. 21
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Sreenivasagan S, Subramanian AK, Chae JM, Chadwick SM Comparison of infrazygomatic crest mini-implant and inter-radicular mini-implant as skeletal anchorage when used for en masse anterior retraction and en masse distalization—A FEM study. Int J Dentistry Oral Sci. 2020;7:976-81.  Back to cited text no. 23
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Motoyoshi M, Sanuki-Suzuki R, Uchida Y, Saiki A, Shimizu N Maxillary sinus perforation by orthodontic anchor screws. J Oral Sci 2015;57:95-100.  Back to cited text no. 27


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1]


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