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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 14  |  Issue : 1  |  Page : 1-6

Evaluation of chin morphology after two-jaw orthognathic surgery: A retrospective study using stereophotogrammetry


1 Department of Oral and Maxillofacial Surgery and Periodontology, School of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil
2 Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil

Date of Submission31-May-2021
Date of Acceptance23-Sep-2021
Date of Web Publication04-Jan-2022

Correspondence Address:
João Lisboa de Sousa Filho
Av do Café s/n, Monte Alegre, Faculdade Odontologia De Ribeirão Preto, Universidade De São Paulo, Ribeirão Preto 14040-904, São Paulo
Brazil
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jorr.jorr_42_21

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  Abstract 


Background: The mandibular advancement or setback achieved by bilateral sagittal osteotomy can generate significant changes in the soft tissues of the mandible and chin. This was a retrospective study of patients who underwent bimaxillary orthognathic surgery in the Oral and Maxillofacial Surgery Residency Training Program, School of Dentistry of Ribeirão Preto, University of São Paulo.
Objective: The aim of this study was to retrospectively evaluate changes in chin morphology in patients with orthognathic surgery of two jaws using Three-dimensional (3D) photography. Based on inclusion and non inclusion criteria, 11 records including 9 women (81.1%) and 2 men (18.9%), with a mean age of 33.5 years, were incorporated in the study. 3D images were analyzed with Vectra M3® software (Canfield Scientific, Fairfield, NJ, USA), after marking reference points on the face, determining linear measurements, and performing area and angle calculations. We analyzed 3D photographs obtained preoperatively (T0), 6 months (T1), and 1 year (T2) after surgery.
Results: Chin height (Li-Me) and surface (Li-Me) demonstrated an average increase of 9.2 mm and 8.8 mm, respectively, after 6 months. In addition, chin prominence (Go-Pg), chin-to-neck distance (C-Gn), and lower jaw area increased on average by 12.1 mm, 15.0 mm, and 34.6 mm2, respectively, after 6 months. However, the mentolabial angle (Li-Si-Pg) decreased on average by 18.8° after 6 months. All results remained stable after 12 months.
Conclusion: In conclusion, 3D photography was very useful for the evaluation of facial soft-tissue changes after orthognathic surgery. Our study demonstrated a decrease in mentolabial angle and increases in chin prominence, chin height and surface, chin-to-neck distance, and lower jaw area.

Keywords: Chin, orthognathic surgery, stereophotogrammetry


How to cite this article:
de Sousa Filho JL, Rodrigues da Silva AM, Trivellato AE, Rodrigues da Silva MA, Sverzut CE. Evaluation of chin morphology after two-jaw orthognathic surgery: A retrospective study using stereophotogrammetry. J Oral Res Rev 2022;14:1-6

How to cite this URL:
de Sousa Filho JL, Rodrigues da Silva AM, Trivellato AE, Rodrigues da Silva MA, Sverzut CE. Evaluation of chin morphology after two-jaw orthognathic surgery: A retrospective study using stereophotogrammetry. J Oral Res Rev [serial online] 2022 [cited 2022 May 25];14:1-6. Available from: https://www.jorr.org/text.asp?2022/14/1/1/334832




  Introduction Top


Orthognathic surgery enables the correction of dentofacial deformities associated with dental malocclusion by repositioning the maxilla and mandible for an adequate occlusal relationship, resulting in facial harmony. Notably, changes in facial appearance depend on how skeletal repositioning is performed, and understanding this relationship is crucial for predicting postoperative facial changes and planning treatment.[1] Previous reports indicate that beauty indices[2] and facial attractiveness[3] are directly related to the lower third of the face.

Several distinct methods for analysis of ideal chin prominence based on soft tissues have been described, however, none are complete or ideal.[4] Stereophotogrammetry, or 3D photography, is a noninvasive method that provides accurate, three-dimensional (3D) reproduction of facial structures. Analysis with 3D technology may yield favorable results and facilitate better approaches;[5] however, achieving adequate accuracy may be difficult.

Thus, the aim of this study was to retrospectively evaluate changes in chin morphology in patients with orthognathic surgery of two jaws using 3D photography.


  Materials And Methods Top


Sample selection

The medical records of all patients undergoing orthognathic surgery in the Oral and Maxillofacial Surgery Residency Training Program, School of Dentistry of Ribeirão Preto, University of São Paulo, from August 2013 to August 2019, were analyzed.

In this article, we use a methodology developed and previously published by our research group. Our research group has a sampling criterion protocol, clinical methodology, surgical methodology, postoperative orientation, postoperative follow-ups and guidelines, capturing photos, protocol for marking landmarks, and digital marking of landmark. This methodology is published in the article by Osborne et al., 2021.[29]

Procurement of three-dimensional images

Aiming to evaluate the possible changes in the chin-to-neck distance, the point C (cervical) was added to the LAPESE protocol.[6],[7],[8],[9] In order to determine the accuracy between the manual and virtual marked points, a pilot study was developed involving 12 patients. Six patients received point manually marked, and six patients received marks directly on the 3D (digital) images. Subsequently, linear measurements were made to evaluate if there were any differences between manual and direct markings on 3D photographs, and the data were submitted for statistical analysis (Kolmogorov, Smirnov, and Shapiro). Initially, Wilk tests were performed to verify whether the sample exhibited a normal distribution, followed by the Student's t-test. Results showed that there were no statistically significant differences between marking the C point directly on the already existing digital photograph and manually on the patient. Scheideman et al.[10] initially defined the C point as the most concave point on the chin to neckline.

After all the images had been appropriately marked, a single evaluator selected the points and obtained the areas, linear measurements, and angle are described below:

Area (mm2)

Jaw area: Passing by Go (r), Ch (r), Li, Ch (l), Go (l), Me, and Go (r) points [Figure 1] and [Figure 2].
Figure 1: Mandible area, front view

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Figure 2: Mandible area, side view

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Linear measurements (mm)

  • Chin height: Distance between Li and Me
  • Chin surface: Distance between Li and Me running across the soft-tissue surface
  • Chin prominence: Distance between Go (right side) and Pg
  • Chin to neckline: Distance between C and Gn.


Angle (degrees)

Mentolabial angle: Angle formed by points Li, Sl, and Pg.

Aiming to evaluate the changes caused by the surgery, the preoperative (T0) and postoperative (T2) images were superimposed [Figure 3] applying the points not altered by the surgical procedure that were tragus (T[r] T[l]), trichion (Tr), glabella (G), Exocanthion (Ex[r] Ex[l]), Endocanthion (En[r] En[l]), orbitale superius (Os[r] Os[l]), and orbitale (Or[r] Or[l]).
Figure 3: Green mesh represented as changes after orthognathic surgery, pre-operative and post-operative image overlapping

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Statistical analysis

Statistical analyses including Pillai's trace, Wilks' lambda, Hotelling's trace, and Roy's largest root multivariate statistical tests were applied to verify whether there was a change over time (T0, T1, and T2) in the measurements; a 5% significance level was used. Subsequently, we conducted a Bonferroni test to verify at what times changes had been observed.


  Results Top


The final study sample of 11 patients, from an initial total of 92 records, was selected by application of the inclusion and noninclusion criteria. The group of 11 adults was 21–55 years of age (mean 33.5 years) and included 9 (81.1%) women and 2 (18.9%) men. The ethnic composition of the study group included 10 White (90.9%) and 1 Afro-American (9.1%). Patients were assigned to different malocclusion types, according to the Angle classification; 8 (72.7%) patients were placed in class II and 3 (27.2%) in class III. The average maxillary movements proposed by surgical planning consisted of an advancement of 4.09 mm (±1.94 mm) in the anteroposterior (AP) direction, an anterior intrusion of 3.0 mm (±3.68 mm), and a posterior intrusion of 2.13 mm (±3.27 mm). The mean mandibular movements incorporated an advancement of 2.9 mm (±3.2 mm) in the AP direction and a mean mandible counterclockwise rotation of 3.5 mm (±3.7 mm).

Chin height (Li-Me) and chin surface (Li-Me) increased by an average of 9.2 mm (standard deviation [SD] =0.8) and 8.8 mm (SD = 1.8), respectively, after 6 months. Chin prominence (Go-Pg) and chin-to-neck distance (C-Gn) increased by an average of 12.1 mm (SD = 1.9) [Table 1] and 15.0 mm (SD = 1.4) [Table 2], respectively, after 6 months. The mandible area (Go[r]-Ch[r]-Li-Ch[l]-GO[l]-Me-GO[l]) displayed an average increase of 34.6 mm2 (SD = 1.4) after 6 months [Table 3], and the mentolabial angle (Li-Si-Pg) showed an average decrease of 18.8° (SD = 2.2) after 6 months [Table 4]. All measurements remained stable from T1 to T2 [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6].
Table 1: Means, standard deviations, and time-related confidence intervals (t0<t1=t2)

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Table 2: Means, standard deviations, and time-related confidence intervals (t0<t1=t2)

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Table 3: Means, standard deviations, and time-related confidence intervals (t0<t1=t2)

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Table 4: Means, standard deviations, and time-related confidence intervals (t0>t1=t2)

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Table 5: Means, standard deviations, and time-related confidence intervals (t0<t1=t2)

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Table 6: Means, standard deviations, and time-related confidence intervals (t0<t1=t2)

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  Discussion Top


A significant part of the population has some types of dentofacial deformity associated with malocclusion. Dias and Gleiser[11] observed that of 407 children aged 9–12 years who had never undergone orthodontic treatment, one-third needed the treatment.

Some malocclusions initially manifesting in childhood will require treatment with orthognathic surgery when the individual is in adulthood.[12] Unfortunately, published reports on the epidemiology of dentofacial deformities in the Brazilian population are scarce.[13] Sato et al.[14] analyzed 251 medical records of patients undergoing orthognathic surgery and found that the most prevalent malocclusion pattern was class III (55%), followed by class II (29.5%) and class I (15.5%). In our study sample, the most prevalent malocclusion type was class II (72.7%), followed by class III (27.2%).

The final esthetic result obtained with orthognathic surgery is a key concern for patients and professionals. Ambrizzi et al.[15] analyzed the main motivation for treatment and observed that esthetic complaints were predominant in 58.5% of patients undergoing orthognathic surgery, followed by 20.0% indicating orofacial pain. However, Sato et al.[14] observed that for 52% of patients, the main motivation was functional, followed by 27% reporting esthetics.

The influence of gender on soft-tissue changes in individuals undergoing orthognathic surgery was examined in several studies.[16],[17],[18] Mobarak et al.[17] reported that soft-tissue changes in response to skeletal repositioning were slightly higher in women than in men. Part of this response may be due to the greater thickness of soft tissues in men, which may absorb more skeletal modifications, and result in fewer final facial changes compared to women.[16],[18] Our study sample consisted of 9 (81.1%) women and 2 (18.9%) men. The Ambrizzi et al.[15] study included 87 (66.9%) female and 43 (33.1%) male patients, whereas the Sato et al.[14] study involved 153 (60.9%) female and 98 (39.0%) male patients.

Naini et al.[3] reported that facial harmony and beauty patterns are highly influenced by soft tissues in the lower third of the face. They observed that individuals with a convex profile (decreased chin prominence) resulted in the worst beauty indexes, whereas individuals with straighter profiles resulted in better indexes. Jong et al.[19] evaluated the effect of orthognathic surgery on a class III malocclusion patient using the same methods applied in our study. The authors observed not only a decrease in the length of the lower third of the face but also a significant decrease in the average surface of the middle and lower third of the face. Our study demonstrated the opposite results, i.e. we not only observed an increase in chin height and surface but also an average increase in chin prominence of 12.1 mm (SD = 1.9) and a jaw area of 34.6 mm2 (SD = 1.4) after 6 months. We may have observed this result because 8 (72.7%) patients in our study were class II and therefore underwent mandibular advancement. It is important to emphasize that the mean mandibular movements in the AP and vertical directions proposed in presurgical planning for our study group included an advancement of 2.9 mm (±3.2 mm) and a counterclockwise rotation of 3.5 mm (±3.7 mm).

Haddad and Ghafari[20] observed an increase of 8.8 mm in the chin-to-neck distance in class II patients submitted for bimaxillary surgery. However, the authors did not describe the proposed or completed maxillary and mandibular adjustments. In this study, an average increase of 15.0 mm (SD = 1.4) was found after 6 months and remained stable after 12 months.

Proper surgical prediction of the mentolabial region morphology is essential during orthognathic surgery planning.[21] Naini et al.[3] evaluated the relationship of chin prominence and mentolabial angle with attractiveness and patient demand for orthognathic surgery. The authors observed that higher mandibular retrusion resulted in lower facial attractiveness and an increased patient desire to undergo surgery. Olate et al.[22] observed in a review of published reports that the mentolabial angle demonstrated a consistent correlation with point B in the horizontal direction. The mentolabial angle and point B correlations found by the authors ranged from 98% to 100%, respectively, for mandibular advancements and from 95% to 100% for retractions, respectively. No vertical references to point B were found. Naini et al.[21] observed that images with mentolabial angles between 107° and 140° were associated with increased attractiveness indexes for all groups (laypersons, clinicians, and patients). In addition, images with angles of 84° or lower and 162° or higher were considered unattractive by all groups.[21] In our study, the mean preoperative mentolabial angle was 138.9°, decreasing after 6 months to 120.1°, and stable after 12 months.

Olate[22] observed that the important esthetic change resulting from two-jaw surgery was mainly due to the new position of the lower lip. The lower lip is influenced by the position of the upper and lower incisors, as well as the perioral muscles (Lu et al. apud).[22] Therefore, overjet changes lead to changes in lower lip position.[22] The 40% difference in the correlation between soft and hard tissues in the vertical lower lip region is probably related to dental occlusion and the relationship between teeth and the lower lip.[22] Our study group showed a mean increase in chin height (Li-Me) of 9.2 mm (SD = 0.8) and chin surface (Li-Me) of 8.8 mm (SD = 1.8) after 6 months and remained stable after 12 months. In addition, it is important to note that in our sample group, the most prevalent type of malocclusion receiving mandibular advancement was class II (72.7%).

It is important not to include changes resulting directly from the surgical procedure (edema) in the soft-tissue analysis; therefore, our first postoperative analysis period was 6 months. Van der Vlis et al.[28] evaluated patients with 3D photography and observed that there was a significant reduction in edema in the first 3 weeks, however, a reduction also occurred between 6 months and 1 year. Osborne et al.[29] observed that there was a volume reduction of 52.1% up to the 1st month. In the present study, no statistically significant differences were observed between 6 months and 1 year, therefore, at 6 months, the soft tissue in the chin region would have its definitive morphology.

In summary, it is critical that surgeons obtain information about possible postoperative soft-tissue changes. Precise methods will improve predictability and improve communication with patients and other professionals. 3D photography is a valuable resource as it allows the assessment of quantitative and longitudinal soft-tissue changes, noninvasively capturing high-quality images in less than two milliseconds.[19],[23],[24],[25],[26],[27] It is worth to note that the inclusion and exclusion criteria in this study were strict in order to make our sample standardized and reliable, however limited significantly the sample size. Therefore, future studies with a larger sample should be carried out to confirm the results observed in this study.


  Conclusion Top


3D photography was very useful for the evaluation of facial soft-tissue changes after orthognathic surgery. Postoperative analysis of our sample group demonstrated a decrease in the mentolabial angle and increases in the prominence, height, and surface area of the chin, chin-to-neck distance, and the mandibular area.

Acknowledgments

The authors thank João Batista Mendes Teles for assistance with the statistical analysis.

Ethical clearance

Study approved by the Human Ethics Committee of the School of Dentistry of Ribeirão Preto, University of São Paulo (CAAE # 15829319.9.0000.5419).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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