Evaluation of the nasolabial angle of the Komarapalayam population

Abstract

Esthetic features are different from one race to another, and this should be considered during the treatment planning. The great variance in soft tissue drape of the human face complicates accurate assessment. The nose–lip–chin relationships are exceedingly important in determining the facial esthetics. One important soft tissue parameter in orthodontic diagnosis is the nasolabial angle. The purpose of this study was to establish norms for nasolabial angle as proposed by Fitzgerald for the Komarapalayam population. Normative data for the three nasolabial parameters were produced from a sample of 40 (20 male and 20 female) adults determined by the authors to have well-balanced faces. Mean and standard deviation values from this pooled sample demonstrated a lower border of the nose to Frankfort horizontal plane angle of 18° ± 7°, upper lip to Frankfort horizontal plane angle of 98° ± 5°, and nasolabial angle of 116° ± 10°. No statistically significant difference was demonstrated between the values for men and women in this study, but men did have a slightly larger nasolabial angle.

Comprehensive orthodontic diagnosis and treatment includes facial harmony as a primary goal. Orthodontic treatment planning has evolved from considering previously good occlusion toward the assessment of the soft tissue as well.

In orthodontics, various pretreatment soft tissue analyses have always been used to determine facial esthetics, thus offering an important tool to clinicians. A frequently used soft tissue parameter in orthodontic diagnosis is the nasolabial angle, which is formed by a line from lower border of the nose to the one representing the inclination of the upper lip. But the nasolabial angle alone is not always reliable because it has been drawn differently by various investigators and it is affected by the position of upper incisors and nose. For example, angular measurement of the patient may be within the normal range and yet there is presence of protrusion of the maxillary incisors and the upper lip. The reason for the normal nasolabial angle is an upturned nose. Such variations may lead to erroneous conclusions in orthodontic diagnosis.

Fitzgerald et al.[1] developed a new method of constructing the nasolabial angle, which also evaluated the relative inclination of lower border of the nose and upper lip, as well as their relationship to each other.

The purpose of this study was to evaluate the nasolabial angle using the method advocated by Fitzgerald[1] in Komarapalayam population.

Materials and Methods

This study used the cephalometric radiographs of 40 adults above 18 years (20 men and 20 women), collected from the Department of Orthodontics, JKK Nataraja Dental College, Komarapalayam. The cephalograms were collected from the pretreatment records of patients who exhibited class I occlusion with good facial balance. There was no history of orthodontic treatment or orthognathic surgery. All 28 permanent teeth were intact excluding the third molars. All cephalometric radiographs were traced on a transparent cellulose acetate sheet of 0.003 inch thickness by two clinicians separately. For all the 40 samples, ANB angle was measured to confirm class I skeletal base. Dental measurements were not included since all subjects used in this study presented with balanced faces.

Nasolabial angle evaluation

A three-step approach was used to draw the nasolabial angle [Figure 1]. The most posterior point of the lower border of the nose at which it begins to turn inferiorly to merge with the philtrum of the upper lip was located and was called posterior columella point or PCm. A tangent was drawn from PCm anteriorly along the lower border of nose at its approximate middle third and was called PCm tangent. The posteroinferior angle of this line extending anteriorly and intersecting the Frankfort horizontal plane was considered the relative inclination of the nose and was termed the lower nose to Frankford horizontal plane angle or N/FH. The line drawn from PCm to labrale superius (Ls) was termed the PCm–Ls line; when extended superiorly, it intersects the Frankfort horizontal plane. The anteroinferior angle formed at this intersection was considered the relative inclination of the upper lip and was termed the upper lip to Frankfort horizontal plane angle or L/FH. The anteroinferior angle formed by the intersection of PCm tangent and PCm–Ls line was the nasolabial angle. This angle is the sum of angles N/FH and L/FH or is the component of the triangle formed by these two lines with the FH plane.

Figure 1.

Cephalometric landmarks: Sella (S), Nasion (N), Porion (P), Orbitale (Or), Subspinale (A), Supramentale (B), Pogonion (Pog), Posterior columella point (PCm), and Labrale superius (Ls). The soft tissue angular measurements used in the study: lower border of the nose to Frankfurt horizontal plane angle or N/FH, upper lip to Frankfurt horizontal plane angle or L/FH nasolabial angle

To estimate the error of tracing, the location of landmarks and measurements, and thus the inherent deviation within the study, all the 40 cephalometric radiographs were traced by two orthodontists. The means and standard errors were calculated for the difference between the two recordings. The mean error was averaged less than 1.0° for the entire sample. For purposes of this study, the average of first and second measurements was used.

The mean standard deviation was determined from the standard deviation produced by the two examiners for each angle over the entire sample of 40 subjects and was also calculated to provide a comparison of the reproducibility among each of the three nasolabial parameters.

Statistical analysis

The measurements recorded from the sample of 40 cephalometric radiographs were tabulated. The mean and standard deviation and coefficient of reproducibility were calculated for each measurement to establish normative data.

Results

The mean value of the nasolabial angle was 116.1° ± 10°, with men showing a value of 116.51° ± 8.01° and women showing 115.701° ± 4°. This difference was found to be statistically insignificant.

The N/FH angle had a mean value of 18.50° ± 7.90°. Men had a mean value of 18.011° ± 7.9° and women had 18.981° ± 7.9°, with no statistically significant difference between them.

The mean value of the L/FH angle was found to be 98.781° ± 5.98°. Men demonstrated a mean value of 98.041° ± 5.8° and women showed 99.531° ± 6.02°, with the difference being statistically insignificant.

Discussion

Beauty is an ill-defined concept that is obvious to observer and recognized cross-culturally. However, it is difficult to quantify and it may vary in its perception across different ethnic groups. To achieve high levels of patient satisfaction consistently after orthodontic treatment, the orthodontist must have an idea of appropriate esthetic norms. This has yet to be satisfactorily defined for all racial groups.

Many authors have emphasized on soft tissue evaluation before contemplating orthodontic or orthognathic treatment modalities in which nasolabial soft tissue is an important factor in determining the patients’ facial esthetics. Consistent and reproducible methods of evaluating the nasolabial region are lacking. The nasolabial angle is formed by two lines, one from the nose and another from the upper lip, and both are independent of each other. The angular measurement described by these two lines is a resultant of their individual inclinations. The nasolabial angle of a person may be within normal range, small, or large. The measurement of this angle alone provides inadequate information as it does not reveal which component is responsible for the variability. It could be the nose, the lip, or both. Therefore, it is important to analyze each component of this angle to assist in the differential diagnosis of normal from its variation.

Fitzgerald et al. proposed a consistent and reproducible method not only for constructing the nasolabial angle on a lateral cephalometric radiograph, but also to evaluate and develop standards for the inclination of the nose and the upper lip. The proposed method of locating the posterior columella point onto which a tangent was drawn to the lower border of the nose, as well as the line from this point to labrale superius proved to be a reliable technique for constructing the nasolabial angle. The posteroinferior angle formed by the intersection of the Frankfurt horizontal plane with the line drawn tangent to the lower border of the nose provided a representative inclination of the nose. The anteroinferior angle formed by the intersection of the Frankfurt horizontal plane with the line drawn from the posterior columella point tangent to labrale superius provided a representative inclination of the upper lip.

When the individual measurements of the three nasolabial parameters, as recorded by two orthodontists, were statistically evaluated by a single-factor repeated measure analysis of variance, a very high coefficient of reliability was revealed for the N/FH angle, the L/FH angle, and the nasolabial angle.

The reproducibility among the three nasolabial parameters was also examined. This was accomplished by calculating a mean standard deviation of the individual measurements produced by the two examiners for each of the three angles throughout the sample. The greatest difference between the average standard deviations for the three angles was less than 0.22°. This suggested that all of the three nasolabial parameters were equally reproducible.

The mean value of the nasolabial angle in this sample was similar to the one reported by Fitzgerald et al. It also correlates with the values reported by Nanda et al.[2] They reported that the nasolabial angle changes little, if any, after 7 years. The nasolabial angle decreased slightly from 7 to 18 years of age in both sexes, with the mean being 107.8° for boys and 114° for girls. At 18 years, the means were 105.81° for men and 110.7° for women.

Owen et al.[3] have reported a smaller nasolabial angle value of 105° ± 8°, as compared with the results of this study. The probable reason for the difference could be to the different locations of the vertices of the two nasolabial angles. Their vertex, subnasale, was constructed by bisecting tangents to both the columella of the nose and the upper lip. This placed the vertex considerably posterior to the posterior columella point.

Much research demonstrates that soft tissues, which vary considerably in thickness, are a major factor in determining a patient's profile.[4–6] The soft tissues of the face are independent of the thickness and size of the underlying facial skeleton,[7,8] and thus greater emphasis needs to be placed on their evaluation in formulating treatment plans for dentofacial disharmonies.

Conclusion

A cephalometric study of 40 subjects from Komarapalayam population (20 men and 20 women) with class I occlusions and good facial balance was conducted. Standardized lateral cephalograms were taken in natural head position. All cephalograms were traced and the nasolabial angle was evaluated as proposed by Fitzgerald et al.

The results show that the mean nasolabial angle was 116.11° ± 10°, N/FH was 18.501° ± 7.90°, and L/FH was 98.781° ± 5.98°. The mean nasolabial angle for men was slightly higher than the female group by 0.81°, which was statistically insignificant.