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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 5  |  Issue : 2  |  Page : 99-104

Digital analysis of facial landmarks in determining facial midline among Punjabi population


1 Department of Prosthodontics and Crown and Bridge, Christian Dental College, CMC, Ludhiana, Punjab, India
2 Conservative Dentistry and Endodontics, Christian Dental College, CMC, Ludhiana, Punjab, India

Date of Web Publication9-Apr-2018

Correspondence Address:
Nirmal Kurian
Christian Dental College, CMC, Ludhiana, Punjab
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/cjhr.cjhr_97_17

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  Abstract 


Introduction: Prosthodontic rehabilitation aims to achieve the best possible facial esthetic appearance for a patient. Attaining facial symmetry forms the basic element for esthetics, and knowledge of the midline of face will result in a better understanding of dentofacial esthetics. Currently, there are no guidelines that direct the choice of specific anatomic landmarks to determine the midline of the face or mouth. Most clinicians choose one specific anatomic landmark and an imaginary line passing through it. Thus, the clinician is left with no established guidelines to determine facial midline. Objective: The purpose of the study is to digitally determine the relationship of facial landmarks with midline of face and formulate a guideline for choosing anatomic landmark among Punjabi population. Materials and Methods: Three commonly used anatomic landmarks, namely nasion, tip of the nose, and tip of the philtrum, were marked clinically on 100 participants (age range: 21–45 years). Frontal full-face digital images of the participants in smile were then made under standardized conditions. Midline analysis was carried out digitally using an image analyzing software. The entire process of midline analysis was done by a single observer and repeated twice. Reliability analysis and one-sample t-tests were conducted. Results: The results indicated that each of the four landmarks deviated uniquely and significantly (P < 0.001) from the midlines of the face as well as the mouth. Conclusions: Within the limitations of the study, the hierarchy of anatomic landmarks closest to the midline of the face in smile was as follows: (1) Intercommissural midlines, (2) Tip of philtrum, (3) Nasion, (4) Tip of the nose, and (5) Dental midlines. The hierarchy of anatomical landmarks closest to the intercommissural/mouth midline was: (1) Tip of philtrum, (2) Tip of the nose, (3) Nasion, and (4) dental midline.

Keywords: Anatomical landmarks, digital analysis, facial midline, philtrum, photographs


How to cite this article:
Kurian N, Gandhi N, Daniel AY, Varghese VS, Daniel S, Mehdiratta S. Digital analysis of facial landmarks in determining facial midline among Punjabi population. CHRISMED J Health Res 2018;5:99-104

How to cite this URL:
Kurian N, Gandhi N, Daniel AY, Varghese VS, Daniel S, Mehdiratta S. Digital analysis of facial landmarks in determining facial midline among Punjabi population. CHRISMED J Health Res [serial online] 2018 [cited 2019 Mar 21];5:99-104. Available from: http://www.cjhr.org/text.asp?2018/5/2/99/229594




  Introduction Top


Driven by an increased interest in dentistry and greater patient awareness outside the profession, facial esthetics and the desire of patients to improve their appearance have grown in importance. The dental profession has even seen greater emphasis on esthetic communication for improved diagnosis and treatment planning with the use of attractiveness/self-image satisfaction scales intended to enhance esthetic outcomes.[1],[2],[3]

Symmetry and normalcy have been considered the classical elements of facial beauty. By definition, symmetry is the “correspondence in size, shape, and relative position of parts on opposite sides of a dividing line or median plane or about a center or axis.” This dividing line, which is used to attain symmetry, is known as the midline. It is the fundamental reference for all esthetic deviations. Therefore, knowledge of the midline will result in a better understanding of dentofacial esthetics, and prosthodontic rehabilitation aims to attain the best possible facial esthetic appearance for a patient.[4]

Historically, a number of facial anatomical landmarks located on the middle third of face have been used to determine the facial and dental midlines; such as bisector of pupils, nasion, tip of nose, tip of philtrum, and chin. Limitations such as inaccuracies in transposing bisector of pupils, deviations in nasal forms, and low coincidence rates of maxillary and mandibular midlines make the need of specific anatomic landmarks vital for midline determination.[5],[6]

Based on convention and dogma, most clinicians choose one specific anatomic landmark and an imaginary line passing through it. Thus, the clinician is left with no established guidelines to determine facial midline.[6]

Variations in anthropological indices have been found with regard to various populations and regions;[7] yet, most of the literatures available regarding the relationship of facial and dental midlines is in relation to Western population and studies have not been done in reference to the Indian population.

With newer developments in digital technologies, we have superior means of assessing the relationship of facial landmarks and facial midline. Various authors [4],[8],[9] have utilized digital approach in evaluating hard- and soft-tissue alignments in helping in widening our understanding of facial landmarks.

Hence, the purpose of this study is to digitally determine the relationship of facial landmarks with the midline of the face and dental midline and formulate a guideline for choosing anatomic landmark during clinical practice among Punjabi population.


  Materials and Methods Top


Materials for the study comprised of the following: digital camera (Canon 1100 D Digital SLR Camera, Canon India Pvt., Ltd.), imaging software (Adobe Photoshop CS3, Adobe system Inc., San Jose, California, USA), tripod stand (BENRO T660EX, China), erasable marker, and measuring tape.

Inclusion criteria included 100 individuals of both sexes of Punjabi ethnic origin and age group of 20–45 years.

Exclusion criteria comprised of patients with any of the following conditions: history of congenital or acquired conditions affecting facial form and appearance, history of orthodontic treatment, missing maxillary anterior teeth, restored maxillary anterior teeth, interdental spacing or severe malocclusion in maxillary teeth, ophthalmic asymmetry, and severe periodontal problems.

Each participant had three small marks placed by a single observer using a fine-tipped erasable marker, with a tip approximately 0.5 mm in diameter on the nasion, the tip of the nose, and the tip of the philtrum, to simulate a clinical situation. A digital camera (Canon 1100 D Digital SLR Camera, Canon India Pvt. Ltd.) was mounted on a tripod stand, with a standardized focus and at a standardized distance of 5 feet (1.5 m) from the individual. The lighting conditions remained the same for all the photographs. The head position was standardized with the help of cephalostat [Figure 1]. The height of the lens of the camera was adjusted on the tripod to match the eye level of the individual when seated upright with shoulders and head held straight and facing forward [Figure 2]. Full-face digital photographs were taken of the individuals in seated position and analyzed in imaging software.
Figure 1: A participant's position standardized with a cephalostat

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Figure 2: Camera positioned on a tripod stand at standardized distance from the participant

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The “Esthetic Frame” was then constructed over this photograph digitally. Its superior border was defined by a line originating at the exocanthion of one eye and meeting the exocanthion of the other eye. The two lateral borders of the frame were drawn as perpendicular lines from the exocanthion of each eye and parallel to each other. The inferior border of the frame was parallel to the superior border and was drawn at the most inferior border of the lower lip.

The facial midline was established by bisecting the distance between the two lateral borders on the frame. Three vertical lines were drawn along each of the anatomic points, which had been marked clinically. A fourth line was drawn along the individual's existing dental midline. The dental midline was defined as the vertical line through the tip of the incisal embrasure between the two maxillary central incisors and parallel to the vertical lines of the esthetic frame of the face [Figure 3].
Figure 3: Esthetic frame illustrating lines drawn along each anatomic landmark

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Relative facial midline value (RFV) was defined as the relative closeness of an anatomic landmark to the facial midline.

  1. The measured distance from the lateral border of the frame to the defined facial midline was considered as a constant – “F
  2. The measured distance from the lateral border of the frame to the nasion was considered a variable – “n
  3. The measured distance from the lateral border of the frame to the philtrum was considered a variable – “p"
  4. The measured distance from the lateral border of the frame to the tip of nose was considered a variable – “t[Figure 4].
Figure 4: Method of determination of relative facial midline value and relative commissural midline value values for each anatomic landmark

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The RFV was then obtained by dividing n by F. Similarly, RFVs were obtained for all anatomic landmarks as follows:

Nasion (n) = n/F, Tip of the nose (t) = t/F, Tip of philtrum (p) = p/F, and Dental midline (d) = d/F.

Numerical values for nasion, the tip of the nose, the tip of philtrum, and dental midline represented by RFVn, RFVt, RFVp, and RFVd, respectively, were obtained.

The relative commissural midline value (RCV) was defined as the relative closeness of an anatomic landmark to the midline of the oral commissures (center of the mouth). The measured distance from the midpoint of the intercommissural line to the right/left cheilion was considered a constant termed C.

The measured distances (variables) were as follows: from the nasion (nx), from the tip of the nose (tx), from the tip of philtrum (px), and from the dental midline (dx). The RCV was then obtained by dividing the variables by the constant (nx/C, tx/C, px/C, and dx/C). The measured distance from the lateral border of the esthetic frame to the midpoint of the commissures was described as a variable called Cx. Thus, the relationship between the midline of the commissures and the midline of the face was obtained by Cx/F. The primary reason to use RFV and RCV was to develop a proportional relationship between an anatomic landmark and the midline in question. This was done to ensure a standard common denominator for all anatomic landmarks within the esthetic frame and negate the need for size matching the images with the individual's face.

The assignments for relativity of landmarks for both midlines were as follows:

  • RFVn and RCVn: Relativity of nasion to midline of the face and commissures
  • RFVt and RCVt: Relativity of tip of the nose to midline of the face and commissures
  • RFVp and RCVp: Relativity of tip of the philtrum to midline of the face and commissures
  • RFVd and RCVd: Relativity of dental midline to midline of the face and commissures
  • RFVc: Relativity of the midline of the commissures with the midline of the face.


Thus, in perfect symmetry, all five of the RFVs and all four of the RCVs would be equal to each other and to the numeral 1. The right or left lateral border of the esthetic frame or the commissures was chosen, based on the direction of deviation of the anatomic landmark.

Therefore, the shorter distance to the lateral border of the frame was always chosen. If a line drawn along one anatomic landmark coincided with any of the other landmarks, the same RFV or RCV value was recorded for both. If an anatomic landmark was coincident with the facial or the commissural midline, then it was assigned an RFV or RCV value of 1.

A total of nine values were recorded per individual. To determine whether the selected landmarks significantly differed from the midline of the face, a series of one-sample t-tests was conducted.


  Results Top


Two separate sets of data were formed:

  1. Measurements for marked anatomic landmarks in relation to midline of face (RFV)
  2. Measurements for marked anatomic landmarks in relation to intercommissural midline/midline of mouth (RCV).


Results are depicted in [Table 1] and [Table 2].
Table 1: One-sample t-test for hierarchy of landmarks for midline of face

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Table 2: One-sample t-test for hierarchy of landmarks for midline of mouth

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The analysis indicated that the difference between the mean ratio of each anatomic landmark and the midline of the face was statistically significant (P< 0.001).

[Table 1] shows mean values of RFVs for each anatomical landmark chosen.

The hierarchical order so obtained is intercommissural line followed by tip of philtrum, nasion, tip of the nose, and dental midline, which is represented in [Graph 1].



The analysis indicated that the difference between the mean ratio of each anatomic landmark and the midline of the face was statistically significant (P< 0.001).

[Table 2] shows that the philtrum ranked highest, followed by tip of the nose, soft-tissue nasion, and dental midline, which is represented in [Graph 2].




  Discussion Top


Esthetic dentistry is a delicate combination of scientific principles and artistic abilities. Mathematical parameters used by the dentist and the laboratory technician combine to produce an attractive esthetic appearance. However, these geometric laws must not be used mechanically; instead, they must act as guidelines for each clinical restoration.[10],[11],[12]

The midline is the fundamental reference for all esthetic deviations. Therefore, knowledge of the midline will invariably result in a better understanding of facial and dental esthetics. In smile designing, the starting point of the esthetic treatment plan is the facial midline. Thus, it is vital for a dentist to be able to determine the midline of a patient.[4]

The present study was conducted to evaluate the relationship of the facial anatomic landmarks with respect to the facial midline and intercommissural midline in dentate individuals in the population of Indian state of Punjab. The anatomic landmarks included nasion, tip of the nose, philtrum, and dental midline which are commonly used clinically.

Photography has been used as an adjunct to direct measurements in anthropologic studies, which was further confirmed by Sheldon (1940) who suggested that accurate anthropometric measurements could be recorded from standardized photographs.[13] Tanner and Weiner examined the reliability of the approach and cited several advantages of using photogrammetry over direct measurements including the fact that photographs provide a permanent record of the patient on which an indefinite number of measurements may be made at the investigator's leisure.[14] Previous studies [4],[15],[16],[17],[18],[19] have used various standard photo documentation techniques for digital analysis to derive a variety of facial proportions.

A cephalostat keeps the head of a patient in a well-defined position throughout the photographic session.[20] Cephalostats are mostly used in radiology and for anthropometric studies, but they can also be used to standardize clinical light photographs.[20] When applied to healthy individuals with no gross facial asymmetry, grids and cephalostats may lead to interindividually comparable and reproducible photographs. This holds true even though a certain asymmetry is common in individuals without apparent craniofacial deformities.[20]

[Table 1] shows the mean values of RFVs for each anatomical landmark chosen. It indicates intercommissural line of the closest landmark to facial midline followed by philtrum. The present study showed that the tip of the philtrum ranked second in the hierarchy of facial midlines, superseded only by the midline of the commissures. This reinforces the integrity of the tip of the philtrum as a dependable landmark in the determination of the midlines of the face and mouth. The hierarchical order so obtained is intercommissural line followed by tip of philtrum, nasion, tip of the nose, and dental midline. The relative closeness of philtrum to intercommisural midline which ranks first in the hierarchy makes philtrum the closest anatomical landmark among the clinical landmarks made on individuals. The second part of the study evaluated the proximity of these anatomical landmarks to the midline of the mouth (commissures). [Table 2] and [Graph 2] show that the philtrum ranked highest, followed by tip of the nose, soft-tissue nasion, and dental midline.

Facial midline is frequently coupled with dental midline on the matter of human perception, and any disparity or deviations of >2 mm are more likely to be observed or perceived.[21],[22] Philtrum being closest to intercommissural and dental midlines among other landmarks has an inherent advantage of having a closer association with the same and thus can be used as a dependable landmark in locating facial midline.

A common procedure to establish the facial midline is to take a piece of dental floss and connect points at glabella or nasion, subnasale, and pogonion.[19] This can lead to invalid results because of inaccuracy in identifying the points and the parallax required in visualizing the points. In addition, if there is any type of mandibular asymmetry, the three points would not correspond. The literature recommends the use of floss/thread to form a straight line from nasion to mouth to mark midline. Such a technique can produce inconsistent results owing to the subjective nature of identification of nasion and dropping a perpendicular from nasion. Furthermore, its distant location from the dental midline may not result in easy determination.

Nose being the central and prominent structure of face is prone to cosmetic or functional deformity. These deformities can be congenital or traumatic in origin. A cosmetic or functional nasal deformity may occur secondary to a crooked septum, an asymmetric nasal bone, scar tissue, collapse or weakening of nasal structures, or a specific portion of the nose being disproportionate to the remainder of the nose and face.[23] With estimates of 80% of all nasal septums being skewed, the probability of tip of nose being off center is relatively high. Considering the poor reliability and inconsistency in nasal anatomy, the tip of the nose becomes a poor choice in marking facial or dental midline.

The facial midline can be used as a guide for establishing the dental midline. Miller et al. used the midline of the philtrum as a guide for the facial midline and they found that 70% of their patients had maxillary dental midlines that coincided with the midline of the philtrum. Based on Miller's study and results from the present study, establishing the maxillary dental midline at the exact position of the facial midline, or slightly at variance from it, can be considered to restore the natural appearance and philtrum can be considered as a reliable anatomical landmark in achieving the same.

From a clinical standpoint, it becomes vital for the clinician to know the hierarchy or best choice of anatomic landmarks that could be used in the determination of the midline for a particular patient. A study among local population will aid in proposing a guideline for midline determination, tailor-made for the specific population which could be adapted in esthetic rehabilitation. The present study among Punjabi population fulfills the aforementioned advantages. Similar studies in different geographical areas including larger population can be done to confirm the results of the present study.


  Conclusions Top


Within the limitations of the present study, it can be concluded that:

  1. There was a significant difference between the mean ratios of the chosen anatomic landmarks and the midlines of the face and mouth
  2. The hierarchy of anatomic landmarks closest to the midline of the face is: (1) intercommissural midlines, (2) tip of philtrum, (3) nasion, (4) tip of the nose, and (5) dental midlines
  3. The hierarchy of anatomical landmarks closest to the intercommissural/mouth midline is: (1) tip of philtrum, (2) tip of nose, (3) nasion, and (4) dental midline.


The hierarchy derived which is simple, authoritative, and population centered can be used as a guideline for determining facial midline among Punjabi population. Similar studies in different geographical areas including larger population can be done to confirm the results of the present study.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Vegter F, Hage JJ. Standardized facial photography of cleft patients: Just fit the grid? Cleft Palate Craniofac J 2000;37:435-40.  Back to cited text no. 20
    
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Miller EL, Bodden WR Jr., Jamison HC. A study of the relationship of the dental midline to the facial median line. J Prosthet Dent 1979;41:657-60.  Back to cited text no. 21
    
22.
Williams RP, Rinchuse DJ, Zullo TG. Perceptions of midline deviations among different facial types. Am J Orthod Dentofacial Orthop 2014;145:249-55.  Back to cited text no. 22
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2]



 

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