Introduction
The purpose of this study was to quantitatively evaluate the infrazygomatic bone parameters (buccal bone thickness and buccal bone height) for miniscrew placement. An additional aim was to compare and contrast the infrazygomatic bone parameters in growing and nongrowing males and females with hyperdivergent, normodivergent, and hypodivergent skeletal patterns.
Methods
Cone-beam computed tomography scans were obtained from 718 deidentified orthodontic patients and categorized by growth status (growing and nongrowing), sex (male and female), and skeletal pattern (hyperdivergent, hypodivergent, and normodivergent). Buccal bone thickness and buccal bone height were measured at 3 locations: 2P-1M (between the maxillary second premolar and first molar), 1M (between the mesial and distal roots of the maxillary first molar), and 1M-2M (between the maxillary first and second molars) and at 3 levels above base plane (BP): 5BP, 8BP, and 11BP, which were 5, 8, and 11 mm above the alveolar crest, respectively.
Results
Males had significantly greater buccal bone thickness than females at 5BP and 8BP ( P <0.05). Males also had greater buccal bone height than females at the 1M-2M location. Buccal bone thickness increased, and buccal bone height decreased significantly as it moved posteriorly from the 2P-1M location to the 1M-2M location. Buccal bone thickness was higher in growing females and males than in nongrowing females and males. Multiple linear regression demonstrated a significant relationship between buccal bone thickness and the prediction variables: skeletal pattern and sex. Buccal bone thickness was greater in the hypodivergent skeletal pattern than in the hyperdivergent skeletal pattern at the level of 8BP in the location of 2P-1M and at the level of 11BP in the locations of 2P-1M and 1M. Buccal bone height was greater in the hyperdivergent skeletal pattern at the 2P-1M and 1M locations than in the hypodivergent and normodivergent skeletal patterns.
Conclusions
Because of adequate buccal bone thickness and acceptable buccal bone height, the 1M-2M location was considered the optimal insertion site for the placement of infrazygomatic miniscrews. Patients with a hyperdivergent skeletal pattern showed reduced buccal bone thickness and increased buccal bone height. Buccal bone thickness was significantly greater in males than in females in all skeletal patterns.
Highlights
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A total of 718 cone-beam computed tomographies were evaluated to identify the infrazygomatic bone thickness and bone height for miniscrew placement in growing and nongrowing males and females with different skeletal patterns, such as hyperdivergent, normodivergent, and hypodivergent.
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Growing males and females had significantly greater buccal bone thickness than nongrowing males and females.
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Multiple linear regression demonstrated a significant relationship between buccal bone thickness and the prediction variables: skeletal pattern and sex.
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Buccal bone thickness increased and buccal bone height decreased as we moved posteriorly from the 2P-1M location to the 1M-2M location.
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Patients with a hypodivergent skeletal pattern showed a significantly higher buccal bone thickness than those with a hyperdivergent skeletal pattern.
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Because of adequate buccal bone thickness and height, the region of the infrazygomatic crest between the first molar and the second molar was considered to be the optimal insertion site for placement of miniscrews.
Anchorage is one of the most important factors in planning orthodontic treatment and achieving the desired treatment objectives. This is particularly important with certain treatment modalities, such as intrusion and distalization of maxillary posterior teeth, as well as retraction of the maxillary arch. When such treatment modalities are undertaken using dental anchorage, it results in side effects on the anchor teeth unless extraoral anchorage is used. Headgear can provide extraoral anchorage to distalize and prevent eruption of maxillary molars, but has decreased in popularity because of esthetic and compliance concerns. Skeletal anchorage using miniplates and miniscrew implants inserted in the infrazygomatic crest provide near absolute anchorage for distalization, intrusion, and retraction of maxillary teeth. ,, The ease of insertion and removal of the miniscrew implants, lower cost, and versatility have made infrazygomatic miniscrews a popular choice over miniplates in recent years.
The infrazygomatic crest is a bony ridge around the first and second molar region in the maxilla, which borders the maxillary zygomatic buttress inferiorly. Miniscrews are often placed in the infrazygomatic crest as it offers a thick bone, which allows greater miniscrew biting depth, more bone contact, and better primary stability. , Infrazygomatic miniscrews have the advantage of being inserted extra-alveolarly, therefore minimizing the root contact issues that occur with interradicular miniscrews. Furthermore, although miniscrews remain intact once inserted, they may be displaced during orthodontic loading; therefore, careful selection of insertion sites is crucial to avoid anatomical structures.
Cone-beam computed tomography (CBCT) scans allow orthodontists to accurately evaluate and quantitatively measure different parameters of the craniofacial skeleton in 3-dimensions, as it provides a 1:1 visualization of the head and neck structures. Determining the optimal sites for the placement of miniscrews in the infrazygomatic region in different skeletal patterns remains crucial to avoid increased failure rates. Although the bone parameters of the mandibular ramus region have been evaluated in detail in both sexes, the studies evaluating the bone parameters of the infrazygomatic region in patients with different growth status, sex, and skeletal patterns are limited. Previous studies investigating maxillary bone trends have provided valuable knowledge regarding infrazygomatic crest miniscrews, but the limited sample size makes it difficult to have meaningful conclusions that can be applied clinically. ,,
Therefore, this study was undertaken with the objective of comparing infrazygomatic bone parameters (buccal bone thickness and buccal bone height) in growing and nongrowing males and females with different skeletal patterns, such as hyperdivergent, hypodivergent, or normodivergent. Our null hypothesis was that there is no significant difference in buccal bone thickness and buccal bone height between the growing and nongrowing males and females in the 3 skeletal patterns.
Material and methods
This study was conducted at Texas A&M University College of Dentistry, and the Institutional Review Board determined that this research met the criteria for exemption (STUDY2024-0174) for evaluating the CBCT scans archived in the Department of Oral and Maxillofacial Radiology. A total 718 CBCTs of patients referred for orthodontic treatment were assessed retrospectively ( Fig 1 ). All CBCT scans were recorded with the following protocol: 3 mA, 120 kVp, 0.3-mm voxel size, 17 x 23 cm field of view with 0.3-mm slice thickness, and 26.9-second acquisition time using the iCAT Next Generation machine (Imaging Sciences International, Hatfield, Pa). Digital imaging and communications in medicine format was used to reconstruct CBCTs using Dolphin software (version 12; Dolphin Imaging and Management Solutions, Chatsworth, Calif).
Distribution of the CBCT scans enrolled, excluded, and included in the study.
Dolphin Imaging was used to generate lateral cephalometric radiographs from the CBCTs with perspective projection (9.7% magnification, 1550 mm emitter-to-patient distance, 100 mm ruler, and 150 mm midplane to film distance [Bolton Broadbent dimensions]). , Patients were categorized by growth status (growing or nongrowing) based on their cervical vertebral maturity index.
Based on the skeletal pattern, the patients were further categorized into 3 subgroups: (1) hyperdivergent, (2) hypodivergent, and (3) normodivergent. The skeletal pattern was determined through analyses of lateral cephalograms, evaluating the following: (1) facial height index, (2) Frankfort mandibular plane angle, and (3) mandibular plane angle, outlined in Table I . , Based on the classification, 2 main groups were created: growing (n = 289) and nongrowing (n = 429). The growing group was further categorized into hyperdivergent (n = 141; females n = 69, males n = 72), hypodivergent (n = 71; females n = 32, males n = 39), and normodivergent (n = 77; females n = 37, males n = 72). The nongrowing group was further categorized into hyperdivergent (n = 185; females n = 128, males n = 57), hypodivergent (n = 147; females n = 105, males n = 42), and normodivergent (n = 97; females n = 60, males n = 37) ( Table II ). The cervical vertebral maturity index of the patients included in the study is described in Table III .
Table I
Categorization of skeletal pattern based on 3 criteria
| Method of measurement | Hypodivergent | Normodivergent | Hyperdivergent | |
|---|---|---|---|---|
| Facial height index | Ratio between the posterior facial height (sella to gonion) and the anterior facial height (nasion to menton) | >69% | 61%-69% | <61% |
| Mandibular plane angle | Angle between the anterior cranial base and the mandibular plane (menton to gonion) | <27° | 27°-37° | >37° |
| Frankfort mandibular plane angle | Angle between the Frankfort-Horizontal plane (FH plane-porion to orbitale) and the mandibular plane | <21° | 21°-29° | >29° |
Table II
Age of the patients in the different groups
| Groups | Age mean (SD) | ||
|---|---|---|---|
| Hyperdivergent | Hypodivergent | Normodivergent | |
| Growing female | 14 y 6 mo (1 y 4 mo) | 14 y 6 mo (1 y 6 mo) | 14 y 5 mo (1 y 2 mo) |
| Growing male | 14 y 9 mo (1 y 4 mo) | 14 y 5 mo (1 y 2 mo) | 14 y 2 mo (1 y 1 mo) |
| Nongrowing female | 28 y 7 mo (8 y 4 mo) | 28 y 8 mo (8 y 3 mo) | 27 y 2 mo (8 y 5 mo) |
| Nongrowing male | 28 y 6 mo (8 y 5 mo) | 27 y 3 mo (6 y 8 mo) | 28 y 1 mo (9 y 9 mo) |
SD , standard deviation.
Table III
CVMI of patients in the different groups
| CVMI | Hyperdivergent | Hypodivergent | Normodivergent | |||||
|---|---|---|---|---|---|---|---|---|
| Frequency | Percentage (%) | Frequency | Percentage (%) | Frequency | Percentage (%) | |||
| Growing female | ||||||||
| 1 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 2 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 3 | 3 | 4.17 | 4 | 12.90 | 5 | 14.29 | ||
| 4 | 55 | 76.39 | 21 | 67.74 | 26 | 74.29 | ||
| 5 | 14 | 19.44 | 6 | 19.35 | 4 | 11.43 | ||
| 6 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| Growing male | ||||||||
| 1 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 2 | 10 | 13.16 | 8 | 20.51 | 5 | 14.29 | ||
| 3 | 35 | 46.05 | 20 | 51.28 | 16 | 45.71 | ||
| 4 | 30 | 39.47 | 11 | 28.21 | 14 | 40.00 | ||
| 5 | 1 | 1.32 | 0 | 0.00 | 0 | 0.00 | ||
| 6 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| Nongrowing female | ||||||||
| 1 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 2 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 3 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 4 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 5 | 15 | 15.00 | 9 | 10.47 | 7 | 20.59 | ||
| 6 | 85 | 85.00 | 77 | 89.53 | 27 | 79.41 | ||
| Nongrowing male | ||||||||
| 1 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 2 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 3 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 4 | 0 | 0.00 | 0 | 0.00 | 0 | 0.00 | ||
| 5 | 21 | 22.34 | 9 | 23.68 | 9 | 26.47 | ||
| 6 | 73 | 77.66 | 29 | 76.32 | 25 | 73.53 | ||
CVMI, cervical vertebral maturity index.
The exclusion criteria were established as the conditions that may affect the infrazygomatic parameters, such as patients with anomalies in the infrazygomatic region, patients with missing teeth, pathology such as cyst, supernumerary teeth, radiographic signs of periodontal disease, or other abnormalities in the region of interest, and patients with craniofacial and genetic differences.
Dolphin software (version 12; Dolphin Imaging and Management Solutions) was used to import the CBCT scans, which were standardized by orienting the occlusal plane, defined by a horizontal line in the sagittal plane intersecting the incisal edge of the maxillary central incisor and the mesiobuccal cusps of the maxillary first molars. The base plane (BP), parallel to the occlusal plane, was constructed at the alveolar crest and used as a reference for the 3 planes that were 5, 8, and 11 mm above the BP, named as 5BP, 8BP, and 11BP, respectively ( Fig 2 , A and B ). The evaluation of the infrazygomatic region for the optimal site of insertion for miniscrews was performed at 3 apical regions: between the maxillary second premolar and the maxillary first molar (2P-1M), between the mesial root and distal roots of the maxillary first molar (1M), and between the maxillary first molar and the maxillary second molar (1M-2M).
A, CBCT Volume; B, Sagittal view showing the reference lines for the occlusal plane, BP (edge of alveolar crest), 5 mm (5BP), 8 mm (8BP), and 11 mm (11BP) above the measurement BP.
The buccal bone thickness was measured from the alveolar crest parallel to the occlusal plane for 5BP, 8BP, and 11BP as shown in Figure 3 , A , B , and C . The buccal bone height was measured from the edge of the alveolar crest to the floor of the maxillary sinus with the reference planes in the middle of 1P-1M, 1M, and 1M-2M as shown in Figure 4 , A , B , and C . All the measurements were performed by one researcher (W.L.). A total of 108 CBCTs (9 CBCTs from each group) were randomly selected and remeasured by the same investigator after a washout period of 2 weeks for the intrarater reliability.
Measurements for buccal bone thickness for the right and left sides are performed in axial view. The landmarks are identified in the multiplanar view, and then the measurements are performed in the axial view. Buccal bone thickness is measured at 3 locations, 2P-1M, 1M, and 1M-2M: A, Measurement of buccal bone thickness at the plane 5BP; B, Measurement of buccal bone thickness at the plane 8BP; C, Measurement of buccal bone thickness at the plane 11BP.
Measurements for buccal bone height were performed at 3 locations, 2P-1M, 1M, and 1M-2M: A, Axial view showing the reference lines between 2P-1M, 1M, and 1M-2M; B, Buccal bone height was measured as the distance between the alveolar edge of the crest and the sinus floor at the buccal side; C, CBCT volume showing the measurement of buccal bone height.
Statistical analysis
Simple descriptive statistics were used to summarize the data. Mean, standard deviation, minimum, maximum, and confidence intervals were calculated for buccal bone thickness and buccal bone height at 5BP, 8BP, and 11BP for the different groups: (1) skeletal pattern (hyperdivergent, hypodivergent, and normodivergent), (2) growth type (growing and nongrowing), and (3) sex (males and females). Intraclass coefficients and Dahlberg’s analysis for method error were used to measure intrarater reliability. One-sample Kolmogorov-Smirnov test was used to analyze the normality of distributions. The parameters were found to be normally distributed. The analysis of variance test was used for the analysis of buccal bone thickness and buccal bone height, and Tukey’s honest significant difference tests were used for multiple comparisons. Multiple linear regression analyses were performed to test the best relationships between sex, growth, and skeletal pattern for predicting bone thickness and buccal bone height. The statistical analyses were performed using SPSS (version 28.0; IBM, Chicago, Ill), and graphs were generated using GraphPad Prism (version 10; GraphPad Software, La Jolla, Calif). All statistical tests were 2-sided and a P < 0.05 was considered to be statistically significant.
Results
The intraclass correlation coefficient showed values of greater than 0.9, indicating good reliability for the measurements. Dahlberg’s analysis showed that the method error ranged 0.027-0.126.
The descriptive statistics, including mean and standard deviation of buccal bone thickness, are shown in Table IV for growing females and males and nongrowing females and males. Buccal bone thickness increased significantly as we moved posteriorly from 2P-1M to 1M to 1M-2M region in hyperdivergent, hypodivergent, and normodivergent skeletal patterns in females and males.
Table IV
Descriptive statistics for buccal bone thickness of hyperdivergent, hypodivergent, and normodivergent skeletal patterns in growing female and male and nongrowing female and male groups at 3 levels: 5 mm above BP (5BP), 8 mm above BP (8BP), and 11 mm above BP (11BP)
| Site | Hyperdivergent | Hypodivergent | Normodivergent | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean | SD | Min | Max | Mean | SD | Min | Max | Mean | SD | Min | Max | ||
| Growing female | |||||||||||||
| Buccal bone thickness | 2P-1M | 1.86 | 0.62 | 0.00 | 3.85 | 1.86 | 0.62 | 0.10 | 3.20 | 2.03 | 0.89 | 0.10 | 4.70 |
| 1M | 1.84 | 0.63 | 0.40 | 3.80 | 1.95 | 0.69 | 0.50 | 3.45 | 1.95 | 0.80 | 0.40 | 4.30 | |
| 5BP | 1M-2M | 2.13 | 0.69 | 0.50 | 4.10 | 2.19 | 0.70 | 0.70 | 3.90 | 2.21 | 0.89 | 0.00 | 4.50 |
| Buccal bone thickness | 2P-1M | 1.61 | 0.80 | 0.25 | 3.70 | 1.90 | 1.03 | 0.00 | 4.50 | 2.07 | 0.90 | 0.55 | 4.45 |
| 1M | 1.85 | 1.07 | 0.00 | 6.20 | 2.13 | 0.98 | 0.45 | 4.45 | 2.06 | 1.00 | 0.60 | 5.00 | |
| 8BP | 1M-2M | 2.48 | 0.84 | 0.95 | 5.75 | 2.64 | 0.97 | 0.90 | 5.05 | 2.67 | 0.97 | 1.35 | 5.80 |
| Buccal bone thickness | 2P-1M | 2.21 | 1.26 | 0.00 | 7.10 | 2.97 | 1.84 | 0.65 | 8.20 | 3.14 | 1.51 | 0.30 | 6.15 |
| 1M | 2.80 | 1.76 | 0.40 | 10.10 | 3.15 | 1.40 | 1.25 | 6.85 | 3.29 | 1.72 | 0.90 | 7.85 | |
| 11BP | 1M-2M | 3.49 | 1.56 | 1.35 | 9.70 | 3.60 | 1.35 | 2.00 | 7.80 | 3.79 | 1.38 | 1.10 | 8.35 |
| Growing male | |||||||||||||
| Buccal bone thickness | 2P-1M | 2.10 | 0.78 | 0.20 | 3.90 | 2.34 | 0.82 | 1.10 | 5.20 | 2.08 | 0.70 | 0.75 | 3.60 |
| 1M | 2.16 | 0.77 | 0.80 | 4.20 | 2.33 | 0.74 | 0.95 | 4.85 | 2.20 | 0.71 | 0.30 | 3.60 | |
| 5BP | 1M-2M | 2.47 | 0.80 | 1.00 | 4.40 | 2.49 | 0.75 | 0.50 | 4.90 | 2.35 | 0.68 | 1.05 | 4.05 |
| Buccal bone thickness | 2P-1M | 1.85 | 0.89 | 0.00 | 5.55 | 2.22 | 0.99 | 0.45 | 4.85 | 1.90 | 0.99 | 0.25 | 4.15 |
| 1M | 2.00 | 1.07 | 0.00 | 6.50 | 2.28 | 0.96 | 0.40 | 5.50 | 2.26 | 0.98 | 0.40 | 4.15 | |
| 8BP | 1M-2M | 2.66 | 1.01 | 0.60 | 5.80 | 2.65 | 1.01 | 0.65 | 5.70 | 2.72 | 0.80 | 0.90 | 4.85 |
| Buccal bone thickness | 2P-1M | 2.08 | 1.13 | 0.00 | 6.00 | 2.97 | 1.22 | 0.35 | 5.20 | 2.56 | 1.44 | 0.00 | 5.45 |
| 1M | 2.49 | 1.50 | 0.25 | 9.80 | 3.33 | 1.11 | 1.40 | 5.95 | 3.18 | 1.71 | 0.15 | 7.65 | |
| 11BP | 1M-2M | 3.22 | 1.31 | 0.70 | 9.85 | 3.48 | 1.12 | 1.85 | 5.85 | 3.51 | 1.21 | 1.20 | 7.60 |
| Nongrowing female | |||||||||||||
| Buccal bone thickness | 2P-1M | 1.49 | 0.89 | 0.00 | 4.75 | 1.33 | 0.93 | 0.00 | 5.00 | 1.51 | 0.92 | 0.00 | 4.25 |
| 1M | 1.52 | 0.88 | 0.00 | 5.25 | 1.52 | 0.93 | 0.00 | 4.55 | 1.57 | 0.89 | 0.00 | 4.10 | |
| 5BP | 1M-2M | 2.06 | 0.89 | 0.00 | 5.10 | 2.10 | 1.00 | 0.45 | 5.20 | 2.08 | 0.77 | 0.00 | 3.75 |
| Buccal bone thickness | 2P-1M | 0.96 | 0.84 | 0.00 | 3.55 | 1.26 | 1.07 | 0.00 | 4.75 | 1.33 | 1.12 | 0.00 | 4.55 |
| 1M | 1.13 | 0.85 | 0.00 | 3.20 | 1.46 | 1.00 | 0.00 | 5.25 | 1.35 | 0.95 | 0.00 | 4.15 | |
| 8BP | 1M-2M | 1.95 | 0.87 | 0.30 | 4.55 | 2.19 | 0.99 | 0.45 | 4.85 | 2.15 | 0.91 | 0.00 | 4.35 |
| Buccal bone thickness | 2P-1M | 1.35 | 1.05 | 0.00 | 4.45 | 2.06 | 1.45 | 0.00 | 7.60 | 2.12 | 1.50 | 0.00 | 5.20 |
| 1M | 1.59 | 1.03 | 0.00 | 4.60 | 2.22 | 1.26 | 0.00 | 6.20 | 2.31 | 1.31 | 0.00 | 5.60 | |
| 11BP | 1M-2M | 2.49 | 1.10 | 0.50 | 6.15 | 2.83 | 1.37 | 0.75 | 7.80 | 2.99 | 1.38 | 0.55 | 6.60 |
| Nongrowing male | |||||||||||||
| Buccal bone thickness | 2P-1M | 1.69 | 0.77 | 0.00 | 4.15 | 1.65 | 1.01 | 0.00 | 4.25 | 1.42 | 0.84 | 0.00 | 3.60 |
| 1M | 1.86 | 0.84 | 0.00 | 4.05 | 1.73 | 0.86 | 0.25 | 4.25 | 1.50 | 0.85 | 0.00 | 3.55 | |
| 5BP | 1M-2M | 2.37 | 0.98 | 0.55 | 4.60 | 2.27 | 1.01 | 0.55 | 5.85 | 2.00 | 0.96 | 0.00 | 4.35 |
| Buccal bone thickness | 2P-1M | 1.41 | 0.96 | 0.00 | 3.35 | 1.54 | 1.01 | 0.00 | 5.05 | 0.96 | 0.93 | 0.00 | 3.00 |
| 1M | 1.67 | 0.93 | 0.00 | 3.90 | 1.47 | 0.77 | 0.00 | 3.15 | 1.10 | 0.95 | 0.00 | 3.80 | |
| 8BP | 1M-2M | 2.66 | 1.05 | 0.20 | 5.00 | 2.06 | 0.92 | 0.00 | 4.35 | 2.06 | 0.94 | 0.00 | 4.05 |
| Buccal bone thickness | 2P-1M | 1.68 | 1.13 | 0.00 | 4.05 | 2.22 | 1.51 | 0.00 | 7.10 | 1.43 | 1.07 | 0.00 | 3.80 |
| 1M | 1.76 | 0.95 | 0.00 | 4.75 | 2.09 | 1.29 | 0.00 | 7.10 | 1.40 | 1.16 | 0.00 | 4.80 | |
| 11BP | 1M-2M | 2.63 | 0.97 | 0.75 | 5.35 | 2.53 | 1.23 | 0.00 | 7.20 | 2.16 | 1.26 | 0.00 | 5.15 |
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