A novel measurement method for the morphology of the mandibular ramus using homologous modelling

Specific pelvic shape in patients with developmental dysplasia of the hip on 3D morphometric homologous model analysis

PURPOSE

To clarify the morphological factors of the pelvis in patients with developmental dysplasia of the hip (DDH), three-dimensional (3D) pelvic morphology was analyzed using a template-fitting technique.

METHODS

Three-dimensional pelvic data of 50 patients with DDH (DDH group) and 3D pelvic data of 50 patients without obvious pelvic deformity (Normal group) were used. All patients were female. A template model was created by averaging the normal pelvises into a symmetrical and isotropic mesh. Next, 100 homologous models were generated by fitting the pelvic data of each group of patients to the template model. Principal component analysis was performed on the coordinates of each vertex (15,235 vertices) of the pelvic homologous model. In addition, a receiver-operating characteristic (ROC) curve was calculated from the sensitivity of DDH positivity for each principal component, and principal components for which the area under the curve was significantly large were extracted (p<0.05). Finally, which components of the pelvic morphology frequently seen in DDH patients are related to these extracted principal components was evaluated.

RESULTS

The first, third, and sixth principal components showed significantly larger areas under the ROC curves. The morphology indicated by the first principal component was associated with a decrease in coxal inclination in both the coronal and horizontal planes. The third principal component was related to the sacral inclination in the sagittal plane. The sixth principal component was associated with narrowing of the superior part of the pelvis.

CONCLUSION

The most important factor in the difference between normal and DDH pelvises was the change in the coxal angle in both the coronal and horizontal planes. That is, in the anterior and superior views, the normal pelvis is a triangle, whereas in DDH, it was more like a quadrilateral.

The online attention analysis on orthognathic surgery research

OBJECTIVES

Altmetrics is one of the fields of bibliometrics that seeks to assess the impact and interest of a given subject through Internet users. The aim of this study is to make an altmetric analysis of the orthognathic surgery literature.

METHODS

A literature search was conducted using Dimensions app up to December 2023. A list of the 100 most mentioned articles on the topic was compiled. A Google Trends search was performed with same strategy to visualize important data regarding internet search. Charts and tables were created using Microsoft Excel and VOSviewer software to allow bibliometric visualization.

RESULTS

There was a very poor correlation between the number of mentions and the number of citations (r = 0.0202). Most articles discussed on technical innovations associated to orthognathic surgery, majority related to virtual planning (n = 26). Other topics considered interesting to internet readers were complications (n = 18), surgical technique (n = 14), and psychological aspects/quality of life (n = 13).

CONCLUSION

Online interest in orthognathic surgery closely aligns with the level of academic interest but is also influenced by factors such as location and economic status. The internet is a powerful tool for disseminating scientific research to a broad audience, making it more accessible and engaging than traditional academic channels.

Objective evaluation of tooth carving using homologous models

PURPOSE/OBJECTIVES

Tooth carvings are evaluated subjectively. However, subjective evaluations are associated with low intra- and inter-evaluator reliability in providing feedback for the fabrication of better tooth carvings. Therefore, this study aimed to analyze the relationship between subjective evaluation and the morphological characteristics of tooth carvings and their morphological characteristics using the feedback method in the low-scoring group.

METHODS

Between April 2013 and September 2021, 120 maxillary left first molar carvings fabricated by undergraduate students were subjectively evaluated by an experienced instructor using a five-point scale. The tooth carvings were scanned to obtain three-dimensional shape data and divided into two groups, the high- and low-scoring groups, for principal component analysis. Homologous models with dimensions matching those of the average model were created, and principal component analysis was performed to evaluate the morphological characteristics of the tooth.

RESULTS

Principal component analysis indicated that an objective evaluation was possible using homologous model. On increasing the subjective evaluation, the occlusal inclination angle and the cervical region of the tooth became steeper, and the shape of the occlusal surface resembled a parallelogram. In addition, large morphological differences were observed in the position of the cervical region of the tooth, height of contour, and shape of the occlusal surface in the low-scoring group, whereas no such difference was observed in the high-scoring group.

CONCLUSION

Objective evaluation of tooth carving was possible using homologous model. The evaluation of tooth morphological characteristics could be effective in providing feedback to undergraduate students.

Tibial morphology of symptomatic osteoarthritic knees varies according to location: a retrospective observational study in Japanese patients

This study analyzed 31 patients with symptomatic osteoarthritic knees scheduled to undergo knee arthroplasty or high tibial osteotomy and demonstrated shape variations in their proximal tibia using an average three-dimensional (3D) bone model. Preoperative computed tomography of the affected knees was reconstructed as 3D bone models using a triangle mesh of surface layers. The initial case was defined as the template, and the other models were reconstructed into homologous models with the same number of mesh vertices as that in the template. The corresponding mesh vertices of the other models were averaged to evaluate the spatial position on the particular mesh vertex of the template. This was applied to all the mesh vertices of the template to generate the average 3D model. To quantify the variation in surface geometry, average minimum distance from the average bone model to 31 models was recorded. The medial proximal tibial cortex (1.63 mm) revealed lesser variation compared to the tibial tuberosity (2.50 mm) and lateral cortex (2.38 mm), (p = 0.004 and p = 0.020, respectively). The medial tibial plateau (1.46 mm) revealed larger variation compared to the lateral tibial plateau (1.16 mm) (p = 0.044). Understanding 3D geometry could help in development of implants for arthroplasty and knee osteotomy.

Comparison of the three-dimensional bone morphology of the first proximal phalanx and first metatarsal between normal and hallux valgus foot using the homologous model technique

Bone morphology is one of the factors involved in hallux valgus development. However, previous studies have not evaluated the overall bone shape in three dimensions. This study aimed to compare the overall shape of the first proximal phalanx and first metatarsal in hallux valgus with those of normal feet.Homologous models were created from computed tomography data of the first proximal phalanx and first metatarsal of 75 healthy men and 53 women in the control group and 10 men and 71 women in the hallux valgus group. Principal component analysis was performed to examine the differences in bone morphology between the control and hallux valgus groups. In men and women with hallux valgus, the proximal articular surface of the first proximal phalanx was characterized by a more lateral inclination and torsion of the pronated first metatarsal. Additionally, the first metatarsal head was characterized by a more lateral inclination in male hallux valgus. This study is the first to reveal the morphological characteristics of the first metatarsal and first proximal phalanx in hallux valgus as a whole bone using a homologous model technique. These characteristics are considered possible causes of hallux valgus development. The shapes of the first proximal phalanx and first metatarsal in hallux valgus were different from those in normal feet. This finding should be useful when considering the pathogenesis and treatment development for hallux valgus.

Application of the Homologous Modeling Technique for Precision Medicine in the Field of Oral and Maxillofacial Surgery

In the field of oral and maxillofacial surgery, establishment of a new method for predicting morphology is desirable. Therefore, the purpose of the present study was to establish a new method for predicting the original shape of a mandibular defect site using the homologous modeling technique. This study used data from 44 patients who underwent computed tomography in the Department of Oral Surgery at Osaka Medical College. Two types of homologous models were constructed: total mandible (TM) and half mandible (HM). Principal component analysis (PCA) was performed using point cloud data of the homologous model M and homologous model HM, and a multiple regression equation was created using the PC value of TM as the object variable and PC value of HM as the explanatory variable. The predicted PC (M) was created from PC (HM) using a regression formula, back-calculated from point cloud data from PC (M), to create the predicted mandible model. Finally, the original image (TC-M) and estimated mandible were superposed and examined. The mean absolute error between the predicted mandible and actual mandible was 1.04 ± 1.35 mm. We believe that this method will be applicable in actual clinical practice.

Global patterns of the cranial form of modern human populations described by analysis of a 3D surface homologous model

This study assessed the regional diversity of the human cranial form by using geometric homologous models based on scanned data from 148 ethnic groups worldwide. This method adopted a template-fitting technique for a nonrigid transformation via the iterative closest point algorithm to generate the homologous meshes. Through the application of principal component analysis to 342 sampled homologous models, the largest variation was detected in overall size, and small South Asian crania were clearly verified. The next greatest diversity was found in the length/breadth proportion of the neurocranium, which showed the contrast between the elongated crania of Africans and the globular crania of Northeast Asians. Notably, this component was slightly correlated with the facial profile. Well-known facial features, such as the forward projection of the cheek among Northeast Asians and compaction of the European maxilla, were reconfirmed. These facial variations were highly correlated with the calvarial outline, particularly the degree of frontal and occipital inclines. An allometric pattern was detected in facial proportions in relation to overall cranial size; in larger crania, the facial profiles tend to be longer and narrower, as demonstrated among many American natives and Northeast Asians. Although our study did not include data on environmental variables that are likely to affect cranial morphology, such as climate or dietary conditions, the large datasets of homologous cranial models will be usefully available for seeking various attributions to phenotypic skeletal characteristics.

Average Models and 3-dimensional Growth Patterns of the Healthy Infant Cranium

Treatment of cranial deformity is often performed during infancy in cases such as craniosynostosis and deformational plagiocephaly. To acquire morphologic standards for the treatment goals of these conditions, we created cranial average models and elucidated the growth patterns of the cranium of healthy infants in 3-dimension (3D) using homologous modeling.

Examination of new parameters for sex determination of mandible using Japanese computer tomography data

OBJECTIVE

In the field of forensic science, sex discrimination of skeletons is an important identification item for personal identification. The individual sex discrimination method using skeletons includes a determination method using measurement values and a macroscopic form observation method. Both methods have advantage and disadvantage. In this study, we used the homologous model technique and principal component (PC) analysis to determine gender difference from morphology of the mandible.

METHODS AND MATERIALS

45 patients (23 males and 22 females) of CT imaging for tooth extraction from January 2018 to March 2019 at department of oral surgery, Osaka Medical College. The mean age was 43.1 ± 14.6. Patients with less than 14 remaining teeth were excluded because the number of remaining teeth may affect the shape of the mandible. 3D images were constructed, and 20 landmarks plotting on the 3D model surfaces. We generated template models of the mandible consisting of approximately 8434 polygons. The template model automatically fitted into the individually scanned point cloud of the mandible by minimising external and internal energy functions. As described above, the mandibles were constructed for each sample by using the Homologous Body Modeling software (HBM, Digital Human Technology, Inc.) and the mHBM-Rugle (Medic Engineering Corporation). The mandibles were analysed using the PCA.

RESULTS

The contribution of the most important PC was found to be 27.2%. 12 PCs explained over 75% of the total variance. That is, it was able to express 75% or more of the mandible expression with 12 PCs. A significant difference between male and female was observed in the first PCs (Wilcoxon test, p < 0.05). Visualising the result of the first PC showed that the mandibular branch of male was larger than that of female, and the mandible angle was overhanging outside.

CONCLUSION

This method is a combination of the determination method using the previous measurement values and the determination using macroscopic observation, and is considered to be innovative method.

Identifying Differences Between a Straight Face and a Posed Smile Using the Homologous Modeling Technique and the Principal Component Analysis

Recently, a homologous modeling method was developed to simulate 3D human body forms, which can visualize principal component analysis (PCA) results and facilitate its detailed comparison with results of previous method. Herein, we aimed to construct a homologous model of the face to identify differences between a straight face and a posed smile. Thirty-eight volunteers (19 males and 19 females, 38 straight faces and 38 posed smiles) with no medical history associated with a posed smile were enrolled. Three-dimensional images were constructed using the Homologous Body Modeling software and the HBM-Rugle; 9 landmarks were identified on the 3D-model surfaces. The template model automatically fitted into an individually scanned point cloud of the face by minimizing external and internal energy functions. Faces were analyzed using PCA; differences between straight faces and posed smiles were analyzed using paired t tests. Contribution of the most important principal component was 23.8%; 8 principal components explained >75% of the total variance. A significant difference between a straight face and a posed smile was observed in the second and the fourth principal components. The second principal component images revealed differences between a straight face and a posed smile and changes around the chin area with regard to length, shape, and anteroposterior position. Such changes were inclusive of individual differences. However, the fourth principal component image only revealed differences between a straight face and a posed smile; observed differences included simultaneous shortening of upper and lower eyelid length, evaluation of the nasal ala ase, swelling of the cheek area, and elevation of the mouth angle. Although these results were clinically apparent, we believe that this article is the first to statistically verify the same.Consequently, the homologous model technique and PCA are useful for evaluation of the facial soft-tissue changes.

Analysis of Cranial Morphology of Healthy Infants Using Homologous Modeling

OBJECTIVE

Data on cranial morphology of healthy individuals can be used as the guide in the treatment of cranial deformity. There are many reports analyzing the cranial morphology of healthy children in the past. But most of them focus on 2-dimensional values, and there are only a few reports, which analyzed the cranial morphology of Japanese healthy infants. We report a novel method that enables the comprehensive analysis of cranial morphology of Japanese healthy infants in 3D.

METHODS

Craniofacial CT data of 20 healthy infants (9 males, 11 females) ranging in age from 1 to 11 months were collected. Based on the CT data, we created 20 homologous models of cranium using software specifically designed to support homologous modeling. We averaged vertex coordinates of the homologous models to create average model. We further performed principal component analysis, and created virtual models based on each principal component. The contribution rate was calculated, and the features described by each principal component were interpreted.

RESULTS

We created the average cranial model of Japanese healthy infants. Seven principal components (cumulative contribution rate: 89.218%) were interpreted as to which part of the cranial shape each component was related to. The elements were extracted that may characterize the cranial morphology of some of the clinical conditions such as dolico/brachycephaly and deformational plagiocephaly. Some of these elements have not been mentioned in the past literature.

CONCLUSION

Homologous modeling was considered to be valid and strong tool for comprehensive analysis of cranial morphology.

A quantitative morphological analysis of three-dimensional CT coxal bone images of contemporary Japanese using homologous models for sex and age estimation

Sexual dimorphisms and age-dependent morphological features of the human coxal bone were quantitatively analyzed using homologous models created from three-dimensional (3D) computed tomography images of the pelvis (male: 514 samples, female: 388 samples, age 16-100). Bilateral average coxal images of each sex and age decade were generated separately through principle component analyses (PCA). By measuring average point-to-point distances of 8472 corresponding points (average corresponding point differences [ACPDs]) between each homologous coxal image and the average images, the sex of more than 93% of the samples was correctly assigned. Some principal components (PCs) detected in PCA of the homologous models of the samples correlated fairly well with age and are affected by features of the curvature of the iliac crest, the arcuate line and the greater sciatic notch. Moreover, separate PCA using the average images of each age decade successfully detected the first PCs, which were strongly correlated with age. However, neither multiple regression analysis using PCs related to age nor comparison of ACPDs with the average images of each age decade could produce accurate results for age decade assignment of unknown (blind) samples. Therefore, more detailed analysis of age-dependent morphological features would be necessary for actual age estimation. In addition, some laterality or left and right shape difference of the coxal bone images was also elucidated, and was more significant in females. Analysis of 3D structures using homologous models and PCA appears to be a potential technique to detect subsistent morphological changes of bones.

Effect of Measurement Technique on TMJ Mandibular Condyle and Articular Disc Morphometry: CBCT, MRI, and Physical Measurements

PURPOSE

Accurate description of the temporomandibular size and shape (morphometry) is critical for clinical diagnosis and surgical planning and the design and development of regenerative scaffolds and prosthetic devices and to model the temporomandibular loading environment. The study objective was to determine the 3-dimensional morphometry of the temporomandibular joint (TMJ) condyle and articular disc using cone-beam computed tomography (CBCT), magnetic resonance imaging (MRI), and physical measurements of the same joints using a repeated measures design and to determine the effect of the measurement technique on temporomandibular size and shape.

MATERIALS AND METHODS

Human cadaveric heads underwent a multistep protocol to acquire physiologically meaningful measurements of the condyle and disc. The heads first underwent CBCT scanning, and solid models were automatically generated. The superficial soft tissues were dissected, and intact TMJs were excised and underwent MRI scanning, with solid models generated after manual segmentation. After MRI, the intact joints were dissected, and physical measurements of the condyle and articular disc were performed. The CBCT-based model measurements, MRI-based model measurements, and physical measurements were standardized, and a repeated measures study design was used to determine the effect of the measurement technique on the morphometric parameters.

RESULTS

Multivariate general linear mixed effects models showed significant effects for measurement technique for condylar morphometric outcomes (P < .001) and articular disc morphometric outcomes (P < .001). The physical measurements after dissection were larger than either the CBCT-based or MRI-based measurements. Differences in imaging-based morphometric parameters followed a complex relationship between imaging modality resolution and contrast between tissue types.

CONCLUSIONS

Physical measurements after dissection are still considered the reference standard. However, owing to their inaccessibility in vivo, understanding how the imaging technique affects the temporomandibular size and shape is critical toward the development of high-fidelity solid models to be used in the design and development of regenerative scaffolds, surgical planning, prosthetic devices, and anatomic investigations.

Evaluation of natural mandibular shape asymmetry: an approach by using elliptical Fourier analysis

OBJECTIVES

The purpose of this study was to demonstrate that asymmetry is a natural occurring phenomenon in the mandibular shape by using elliptical Fourier analysis.

METHODS

164 digital orthopantomographs from Colombian patients of both sexes aged 18 to 25 years were collected. Curves from left and right hemimandible were digitized. An elliptical Fourier analysis was performed with 20 harmonics. In the general sexual dimorphism a principal component analysis (PCA) and a hotelling T² from the multivariate warp space were employed. Exploratory analysis of general asymmetry and sexual dimorphism by side was made with a Procrustes Fit. A non-parametric multivariate analysis of variance (MANOVA) was applied to assess differentiation of skeletal classes of each hemimandible, and a Procrustes analysis of variance (ANOVA) was applied to search any relation between skeletal class and side in both sexes.

RESULTS

Significant values were found in general asymmetry, general sexual dimorphism, in dimorphism by side (p < 0.0001), asymmetry by sex, and differences between Class I, II, and III (p < 0.005). However, a relation of skeletal classes and side was not found.

CONCLUSIONS

The mandibular asymmetry by shape is present in all patients and should not be articulated exclusively to pathological processes, therefore, along with sexual dimorphism and differences between skeletal classes must be taken into account for improving mandibular prediction systems.