JICDRO is a UGC approved journal (Journal no. 63927)

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Year : 2021  |  Volume : 13  |  Issue : 2  |  Page : 129-134

A gender-based study on the hierarchical correlation of various anatomical landmarks with the midline of face and commissure

1 Department of Conservative Dentistry and Endodontics, Hitkarini Dental College and Hospital, Jabalpur, India
2 Department of Prosthodontics and Crown and Bridge, Hitkarini Dental College and Hospital, Jabalpur, India
3 Department of Orthodontics, Private Practitioner and Consultant Orthodontist, Jabalpur, India
4 Department of Prosthodontics and Crown and Bridge, Government Dental College and Hospital, Medical Campus, Nagpur, Maharashtra, India

Date of Submission06-May-2021
Date of Decision08-Jun-2021
Date of Acceptance21-Jun-2021
Date of Web Publication17-Jan-2022

Correspondence Address:
Dr. Sneha Shivkumar Mantri
8 Gulmohur duplex, Ivory Towers, South Civil Lines, Jabalpur, Madhya Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jicdro.jicdro_24_21

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Background: The position of the dental midline is significant to enhance dentofacial esthetics. This study aimed to assess the closest anatomical landmark to the facial and mouth's midline applicable to dentate male and female Indian youths. Materials and Methods: A full-face photo of 100 males and 100 females with a broad smile showing visible anterior dentition was taken. An esthetic facial frame was developed digitally on the photographs taking the reference of facial anatomical landmarks. Relative facial midline values for nasion, the nose tip, the philtrum tip, and dental midline were obtained. The relative commissural midline value was obtained by dividing the variables by the constant. Statistical analysis: Data were statistically analyzed using the t-test. Results and Conclusions: Anatomic landmarks correlated with facial midline and with the inter-commissural midline (P < 0.01). The nasion is nearest to the facial midline, followed by dental midline, commissure, tip of the philtrum, and nose tip in that order. The anatomic landmarks nearest to the inter-commissural midline are the tip of the philtrum, followed by the dental midline, nasion, and nose tip. The nose tip was the farthest landmark from the face's midline and the inter-commissural midline. In gender-wise comparison, landmarks did not differ significantly (P > 0.05). All the measurements were almost equal in males and females.

Keywords: Commissure, dental midline, facial midline, nasion, philtrum, the tip of the nose

How to cite this article:
Mantri SP, Mantri SS, Bal AS, Deogade S, Bhasin A, Khatri M. A gender-based study on the hierarchical correlation of various anatomical landmarks with the midline of face and commissure. J Int Clin Dent Res Organ 2021;13:129-34

How to cite this URL:
Mantri SP, Mantri SS, Bal AS, Deogade S, Bhasin A, Khatri M. A gender-based study on the hierarchical correlation of various anatomical landmarks with the midline of face and commissure. J Int Clin Dent Res Organ [serial online] 2021 [cited 2022 May 28];13:129-34. Available from: https://www.jicdro.org/text.asp?2021/13/2/129/335873

   Introduction Top

Artists, philosophers, and poets have defined beauty since ancient times. They have tried to contemplate its ambiguous quality in their perspective manner. However, as dentists, a more scientific approach is must formulate a treatment plan for a successful outcome. Common reference points are essential guidelines in communicating to achieve a favorable esthetic result.

Specific characteristics that deviate from the norm should be accurately defined to help identify congenital anomalies and facial deformities. The midline of the face is an essential reference for all esthetic deviations. At present, there is no consensus to suggest the option of particular anatomical landmarks to ascertain the facial midline.[1]

The inceptive assessment of the face appraises symmetry. Symmetry often complements beauty in facial features. Upright and parallel balance is crucial, and a relevant guideline is to parallel the incisal plane with a horizontal reference plane, such as an inter-pupillary line. Paralleling the midline of the teeth with the facial midline helps to achieve vertical symmetry. Symmetry gives a sense of unity and perfection if focused on the midline. The closer to the midline, the more critical the esthetic guideline becomes.

Photogrammetry was developed as an alternative to direct measurements, using two-dimensional (2D) and three-dimensional methods to obtain distances between the facial landmarks. Obtaining measurements from images is less invasive to the patient, and cost-effective offers a permanent face record that can be retrieved later, and provides continuity in longitudinal studies in which multiple researchers with different direct measuring techniques may participate.[2] It is very important to standardize the photographs, as they are valuable for tangible analysis and assessment of the preserved data. Systematized photography is important and appropriate since it helps maintain patient data concerning groups of procedures.

Images should be obtained with a proper camera lens, arrangement, illumination, film, and set patient posture to have accurate and unbiased assessments of the treated patients by clinical photographs.[3] In the literature, many authors have described in detail the method of facial photography. Freehe,[4] Gordon and Wander,[5] and Bengel[6] described the basic principles of facial photography and mentioned the need for standardization. They gave basic principles on the head position, the position of the camera, and lighting. Williams[7] describes the position and lighting and mentioned specific anatomic references for the head position. Larrabee et al.[8] described the standard photogrammetric method.

Facial symmetry refers to a complete harmony in shape, size, location, and arrangement of each facial component about the sagittal plane. Perfect symmetry does not exist in nature. It would convey an artificial appearance. Symmetry is a critical biologically based determining factor of facial attractiveness, and its evaluation in a patient's face is crucial to developing a complete dentofacial diagnosis.[9]

The facial and dental midline harmony significantly affects tooth esthetics. The midline should be parallel to the face's midline and perpendicular to the incisal and occlusal plane.[10] Spear suggested that the facial midline is the beginning point of esthetic management in smile designing.[11] Morley and Eubank[12] stated that nasion and the philtrum's base (denoted as a Cupid's bow) are two critical reference points for determining the midline. A line joining these two landmarks locates the facial midline, also known as the facial vertical axis.

It is an imperative reference position for determining many design criteria[12] with the maxillary midline position in relation to the facial midline, especially in esthetic and restorative treatment planning,[13] as it is an essential functional component of occlusion.[14] In a symmetric face, the dental and the facial midline should coincide, but often they do not. Scanty data are available regarding positioning the maxillary dental midline for patients with asymmetrical faces to optimize dentofacial esthetics.

Miller et al.[15] indicated that, in approximately 70% of people, the midline matches the exact middle of the mouth and in about three-fourth of the population, the maxillary and mandibular midlines do not coincide. In a study of dental students, Soares et al.[16] observed that the midline of face coincided with the arch midline in only one-half of the subjects. Recommended guidelines are available for a symmetrical patient whose nose, Cupid's bow, mouth, and chin are coincident with the midsagittal plane. However, all patients do not have symmetrical faces. This asymmetry has led to the perplexity of positioning the dental midline in patients with deviated facial structures and bafflement regarding the most reliable method for describing the position of the teeth relative to symmetrical and asymmetrical faces.

The perception of beauty is highly subjective and is the most significant challenge in achieving the perfect smile for the patient. The Indian population ranges with a wide diversity of races, mixed cultures, and ethnicity often poses a problem for the selection/restoration of anterior teeth.

Literature is not unanimous regarding the method used for determining the facial midline. Smile esthetics are restricted to the teeth (dental components) and influenced by facial morphological factors. As there is no universally accepted method, dentists must seek guidance from various techniques to attain an acceptable result. Hence, this cross-sectional correlational photographic study was designed to assess the closest anatomical landmark to the midline of face and the mouth applicable to dentate males and females of the Central Indian population.

The objectives were

  1. To determine the hierarchical order of the anatomical facial landmark nearest to the midline of face
  2. To determine the hierarchical order of the facial anatomical landmark nearest to the oral commissure's midline.

   Materials and Methods Top

The target population was scholars of Dental and Engineering College in the city of Madhya Pradesh in Central India. The accessible population was aged 18 years to 35 years. A total of 367 individuals were screened. Two hundred dentate subjects, 100 males and 100 females, who fulfilled the inclusion criteria were selected. Based on the results of pilot study, the sample size was calculated to be 180.To avoid attrition, we took the round figure of 200 samples,100 males and 100 females, according to convenience sampling. The power of study was 80%, and acceptable error was 5%. The Institutional Review Board approved the study. The intended participant was selected who provided written consent to participate in the study. Individuals were included if they were male or female, had no record of trauma or hereditary disorders altering facial shape and form, had no ophthalmic asymmetry, had no past orthodontic treatment, had no anterior maxillary teeth that had been replaced, and could understand the written informed consent.

Photographs with rotated head positions, apparent asymmetry involving eyes, and incorrect clinical markings were excluded.

Materials Required

Digital camera (Canon 700 D Digital SLR Camera, Canon India Pvt.Ltd.), Auto CAD software (version 2014), a tripod stand (BENRO T660EX, China), erasable marker, and measuring tape.

Standardization of photographs

A single observer marked the nasion, nose tip, and the philtrum tip of all participants using a fine-tipped 0.5 mm diameter erasable marker to imitate a clinical situation.

Each participant was seated in a natural head position against a white background. The natural head position is a consistent and repeatable upright posture of the head; the eyes are focused at eye level on a point in the space, which means that the optical axis is horizontal on a white background.[17] A digital camera was placed on a tripodal stand five feet (1.5 m) away from the participant with a standardized focus.

The position of the head was adjusted so that the F–H plane and camera lens were parallel to the floor. The focal center was projected near the glabella, keeping the eyes and the mouth also in focus. A full-face photo with a broad smile showing visible anterior dentition was taken. The lighting conditions were similar for all the photographs.

Digital analysis of the photographs for different midlines

The photographs were duplicated in two sets – one for facial midline and the other for commissural midline to avoid overlapping lines. The esthetic frame, as adapted from Bidra et al.,[1] was used to delineate the facial midline objectively. An esthetic facial frame was developed digitally on the photographs taking the reference of facial anatomical landmarks. The frame's lateral borders were drawn as perpendicular bisectors from each eye's exocanthion, parallel to each other. The superior margin was drawn by a line that ran from one eye's exocanthion (the point at the eye's outer corner) to the exocanthion of the other eye.

The inferior border of the frame was defined at the most inferior border of the lower lip, parallel to the superior border. These four borders comprised the rectangular frame, which enclosed all the factors of smile parameters that were perceivable and confirmable.

The midline was determined by bisecting the distance between the frame's two lateral boundaries. The frame's midline was regarded as the face's midline. Three vertical lines, namely the nasion, nose tip, and philtrum, were drawn along the anatomic points.

A fourth line was drawn matching to the vertical lines of the face's esthetic frame along the dental midline. The relative proximity of the landmark to the face midline was characterized as relative facial midline value (RFV).

The distance between the frame's lateral border and the designated facial midline was deemed constant “F.” The distance to the nasion was deemed as variable “n.” The distance to the philtrum was regarded as variable “p.” The distance to the tip of the nose was considered a variable “t.” [Figure 1] and [Figure 2].
Figure 1: relative facial midline values F: Facial midline/esthetic midline; n: Distance between nasion and lateral border of esthetic frame; t: Distance between the nose tip and esthetic frame's lateral border; p: Distance between the philtrum tip and lateral margin of esthetic frame; d: Distance between dental midline and esthetic frame's lateral border

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Figure 2: relative commissural values C: Midline of oral commissures; nx: The distance between nasion and oral commissures; tx: The distance between the nose tip and oral commissures; px: The distance between the philtrum tip and oral commissures; dx: The distance between dental midline and oral commissures

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By dividing n by F, the RFV was acquired. RFVs were also obtained for all anatomic landmarks in the same way: Dental midline (d) = d/F, Nasion (n) = n/F, Nose tip (t) = t/F, Philtrum tip (p) = p/F, and Nasion (n) = n/F. The numerical values for nasion, the nose tip, the philtrum tip, and the dental midline were estimated using RFVn, RFVt, RFVp, and RFVd. The landmark's proximity to the oral commissures midline is defined as the relative commissural midline value (RCV). The distance between the midpoint of the inter-commissural line and the right/left cheilion was considered a constant termed C, from nasion (nx), from the nose tip (tx), from the philtrum tip (px), and the dental midline (dx). By dividing the variables by the constant (nx/C, tx/C, px/C, and dx/C), the RCV was computed. Cx was defined as the estimated distance between the esthetic frame's lateral border and the midway of commissures. Cx/F, therefore, acquired the relation between the commissure's midline and the face's midline.

The purpose of using RFV and RCV was to forge a commensurable association between an anatomic landmark and the midline in query. As a result, all the landmarks within the esthetic frame had a common denominator, negating the requirement for the images to be size-matched to the individual's face. In complete symmetry, all five RFVs and all four RCVs, as well as the number 1, would be identical. The right or left lateral border of the esthetic frame, and the commissures, was selected based on anatomic landmark deviations. As a result, the shortest distance to the frame's lateral boundary was always chosen.

The same value for RFV or RCV was recorded if a line sketched alongside one landmark corresponded with other landmarks. If the landmark coincided with the midline of the face or commissure, it was assigned a value of 1 for RFV or RCV. Nine values were recorded for each subject, and the data were statistically assessed using the t-test.

   Results Top

One set of five t-tests with an alpha value of 0.05 was conducted for five specified landmarks to check their correlation with the facial midline. The second set of four paired t-test was performed to check the hierarchy of the anatomical landmarks with the inter-commissural midline [Figure 3].
Figure 3: hierarchical correlation of anatomic landmarks with the midline of mouth and face

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The analysis revealed a statistically significant difference (P < 0.001) between the mean ratio of specified landmarks and the face's midline or inter-commissural midline [Table 1].
Table 1: One-sample t-test for the anatomic landmarks of the midline of face and mouth

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Further, a gender-wise comparison shows that similar to landmarks for the midline of the face, the landmarks for the midline of mouth also did not differ statistically significantly (P > 0.05), and all the measurements were almost equal in males and females [Table 2].
Table 2: Comparison of landmarks for the midline of face and midline of mouth among males and females by unpaired t-test

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   Discussion Top

The present study aimed to acquire the norm and determine the propinquity of different landmarks of the face nearest to the midline of face and commissures among the males and females.

The mid-facial or skeletal midline is a vertical reference line that facilitates the visual coordination of the midline of the face relative to the dental midline. In the literature, there is no established method for determining facial midline. As suggested by Bidra et al.[1] using the esthetic frame, a computer-based approach was followed. Unfortunately, existing facial 3D analysis devices are expensive, making them unsuitable for normal clinical use. In addition, they also need dedicated spaces. Morphometric measuring has become a simple and cost-effective approach for precisely measuring changes in soft tissue as the use of digital photography, and computer imaging has grown. Other advantages are that it is a simple, noninvasive, cost-effective, and efficient procedure involving limited time and equipment in soft tissue measurement, provided such images are taken in uniform environments.[2]

The mean ratio of each anatomical landmark to the facial midline differs significantly in the current study (P < 0.001).

The hierarchical pattern showed that nasion was nearest, then the dental midline, commissure, the philtrum tip, and nose tip in that order. Similar studies done by Bidra et al.[1] support the difference in the mean ratio. However, the hierarchical pattern was different, with the commissure midline being nearest, followed by the dental midline, the philtrum tip, nasion, and nose tip. Gender-wise comparison of landmarks for the midline of face among males and females showed that RFV1 in males was 0.983 ± 0.014 and in females was 0.984 ± 0.010, which was statistically insignificant. Similarly, the other landmarks for the midline of the face were also almost similar in males and females (P > 0.01).

There is a statistically significant difference (P < 0.001) between the mean ratio of each anatomic landmark and the commissure midline. The philtrum was the closest, followed by dental midline, nasion, and nose tip. This result agreed with the result of previous studies conducted by Moshkelgosha et al.[18] According to earlier studies, the philtrum or the vermillion border tip represents the midline of the face.[14],[19]

In the chosen study population, the tip of the nose was the most strayed landmark regarding the facial midline and the midline of the commissures. The nose, being the most prominent and central feature of the face, is susceptible to cosmetic and functional deformation. The cause of these deformities can be congenital or traumatic. A crooked septum, an asymmetric nasal bone, scar tissue, collapse or weakening of nasal tissues, or a specific part of the nose that is disproportionate to the rest of the nose and face can cause a cosmetic or functional nasal deformity.[20],[21],[22]

With estimates of 80% of all nasal septum being skewed, the probability of the tip of the nose being off-center is relatively high.[23] Considering the poor reliability and inconsistency in nasal anatomy, the tip of the nose becomes an inappropriate choice in marking facial or dental midline. Therefore, in locating either midline, this landmark is not advised. A study among the local population will help propose a guideline for midline determination, customized for the particular geographic location to aid esthetic rehabilitation. The present study results can be used as a guide to provide symmetry and harmony and thus eliminate visual tensions while restoring the smile. Similar studies can be conducted in the same geographical area, taking a larger population to corroborate the present study results. This study did not explore the intraoral landmark like incisive papilla, which is also used as a guide to determine the midline. The participants were of Indian origin; hence, the outcomes are not generalized for the population from other cultural backgrounds and different ethnicity. Another limitation of the research is that it uses a 2-dimensional approach based on photographic images. Future studies can be carried out with a 3D approach using digital face scanning.

   Conclusions Top

The current findings suggest a considerable variation in the average ratios of the landmarks (nasion, a dental midline, nose tip, and the philtrum tip) and the midlines of the face and the mouth.

The nasion is closest to the facial midline, followed by dental midline, commissure, philtrum tip, and nose tip in that order. The tip of philtrum is the nearest landmark to the inter-commissural midline, followed by the dental midline, nasion, and the nose tip. The tip of nose was the farthest landmark from the midline of the face and commissure.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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