Photogrammetric Analysis of Nasolabial Angle and Mentolabial Angle norm in Malaysian Adults

Photogrammetric Analysis of Nasolabial Angle and Mentolabial Angle norm in Malaysian Adults Lin CS, Shaari R, Alam MK, Rahman SA Abstract Introduction: While measurement of nasolabial angle and mentolabial angle is an important clinical examination in pre-orthognathic surgery assessment, data on non-western population is limited. This study was therefore conducted to determine the range of nasolabial angle and mentolabial angle in normal Malaysian adult with comparison of males and females. Materials and Methods: A total of 50 Class I males and 52 Class I females aged 19-30 years from three main ethnic groups were randomly selected from dental students, medical students and staffs in dental clinic of Hospital Universiti Sains Malaysia (HUSM). The photographic set-up consisted of a 50mm Nikon DAT camera held in position by a tripod. The photos taken in JPEG format were digitalized and analysed using ProVixwin software. Independent t-test was used to compare any possible gender difference in nasolabial and mentolabial angles. Results: The mean of nasolabial angle and mentolabial angle for male was 92.99? and 130.44? whereas for females it was 95.04? and 130.73? respectively. Gender differences were found to be insignificant for both nasolabial angle and mentolabial angle.Conclusion: Despite having great variation in our population, the nasolabial angle and mentolabial angle are gender independent.


Introduction
Physical appearance has gained its importance in this modern society.Social acceptance, psychological well-being, and self-esteem of one are in close relation to his/her physical appearance 1 ."Being esthetic is ordinary in our society" 1 .A pleasing and attractive face is a balanced and complimentary match of the nose, lips, eyes, and ears, together with a harmony of the jaws and teeth accentuated by the color and texture of the skin and hair 2 .
In order to have a pleasing physical appearance which is acceptable by the society, people are willing to change their facial proportion.Unattractive facial proportions can be modified through dentofacial orthopedics, orthognathic surgery, and esthetic soft tissue and/or hard tissue surgery, either alone or in various combinations 3 .Malkoc et   al suggested that analysis of the soft tissue should be taken into consideration for correct evaluation of an underlying skeletal discrepancy because of individual differences in soft tissue thickness 4 .

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highlighted possible anomalies in the hard tissues could be masked or exaggerated by the overlying soft tissues.In other words, facial soft tissues did not always follow the underlying dentoskeletal profile 5 .Comprehensive soft tissue analysis is vital in the pre-orthognathic surgery assessment as the soft tissue profile may differ between different age group, sexes and ethnic groups.The pilot study conducted before this study, it showed no significant difference in photogrammetric angular measurement of images taken using 35mm camera or 50mm camera.30 subjects (15males and 15 females) were examined in the pilot study; two images were taken with 35mm and 50mm respectively.The nasolabial angle was reported to be 93.92 ± 8.64 degrees for 50mm camera and 93.95 ± 8.71 degrees for 35mm camera respectively with p=0.988.On the other hand, the mentolabial angle was found to be slightly wider in with using 35mm camera.However, the p-value was found to be 0.87.The result showed insignificant difference in angular measurement for images taken using 50mm camera and 35mm camera, therefore 50mm camera was chosen in this study to determine the norms of nasolabial angle and mentolabial angle in Malaysian adult due to the fact that it provides a closer view of the subject and thus measurement can be made with higher accuracy.

Photographic set-up
The photographic set-up was consisted of a tripod (Manfrotto 141RC) holding a 50mm Nikon DAT camera.Manual setting of the camera was used by a single operator.The subjects were standing on a line marked on the floor which is 100cm from the camera and were asked to relax the face.Photographs of the subjects were taken from the front and from the side.Photographs taken in JPEG format were then being digitalised and analysed using Provixwin software (Figure I).In order to minimize intra-operator variability, for each photograph of the subject, it was analysed twice with one week apart and mean of the two measurements was used as the result for the particular subject.
The following landmarks and angular measurements are shown in Statistical analysis was done using SPSS 18.0.Independent t-test was used to compare the angular measurements between males and females.

Results
Descriptive data for mean, maximum, minimum, range, and standard deviation together with the result of comparison between male and female using independent t-test for nasolabial angle and mentolabial angle norm determination are shown in .Subsequently, soft tissue profile of the face is changed.Hence, extraction of teeth can increase the nasolabial angle 6 .Likewise, Cummins highlighted that upper and lower lips were more retrusive after the extraction of premolars.In addition, the nasolabial angle was significantly larger among the female extraction group 8 .
In order to get the norm of nasolabial and mentolabial angles for normal Malaysian adult, subjects who had previously undergone orthodontic treatment, maxillofacial surgery or facial plastic surgery were excluded.This is because orthodontic and orthognathic surgical treatment can influence significantly the cranial hard-tissue structures and lead to adaptions of the facial musculature 9,10 .
Furthermore, Eggensperger et al stated that surgical procedures to correct skeletal deformities result in changes in shape and position of the overlying soft tissue 11 .
From this study, the nasolabial angle showed wider measurement in females (95.04 ± 8.17 degrees) in comparison to the males (92.99 ± 8.82 degrees).
Fariaby et al. 12 reported a nasolabial angle of 98 ± 10 degrees for females and 97 ± 11 degrees for males.Likewise, Malkoc et al.CS Lin, R Shaari, MK Alam, SA Rahman Females have a wider nasolabial angle generally 1,4,11,12 .The mean of nasolabial angle for both sexes is more acute for Malaysian compare with other western countries.Gender difference was found to be insignificant, this is coincided with the report of Fernandez-Riveiro et al. 1 and Fariaby et al 12 .However, the result obtained was contradictory to that in Croatia where significant sexual dimorphism was concluded 13 .
The .Prior to surgery, a thorough examination on both dentoskeletal pattern and soft tissue should be carried out.The soft tissue covering the teeth and bones can vary so greatly that the dentoskeletal pattern may be an inadequate guide in evaluating facial disharmony 6 .Nasolabial and mentolabial angles are two important guides in orthognathic surgery.Any deviation of these angles from the norm should be noted in pre-orthognathic surgery assessment.McCollum and Evans 2 had emphasized on the importance to predict not only the occlusal and skeletal relationships but importantly the soft-tissue outcome.Thus, restoring these angles to its norm is one of the aims of treatment for the patient.By knowing the norm of these angles in a population, outcome of the surgery can be more perfect and social-acceptable accordingly.The weakness of this study was the result is not specific to any ethnic groups as the subjects were randomly chosen from three main ethnic groups in Malaysia.Scavone mentioned that every ethnic group showed specific dentofacial characteristics in each ethnic group 17 .Different ethnic group groups may have different skeletal base pattern and facial features, which in turn, may reflect changes in the soft tissue profile of the face.For example, lip prominence and facial divergence are strongly influenced by racial and ethnic characteristics [18][19][20] .
Therefore, in the future, attention should be focused on each ethnic group in effort to obtain the precise result and to avoid any possible ethnicity difference.

Conclusion
Soft tissue profile of the face especially the nasolabial angle and mentolabial angle should be revised in planning of orthognathic surgery and orthodonthic treatment as it contributes to the success of the treatment.The parameters obtained from this sample can be used in comparison with records of other subjects with the same characteristics and following the same photogrammetric technique.The results showed slightly wider nasolabial angle in females and similar measurement in mentolabial angle for both sexes.Large variability was found for both nasolabial and mentolabial angle.However, the impact of sex was insignificant for both these angles.
Bangladesh Journal of Medical Science Vol. 12 No. 02 April '13 Figure I: Columella (Cm): the most inferior and most anterior point of the nose Subnasale (Sn): the point where the nasal septum meets the upper lip in the midsagittal plane Labial superior (Ls): the most anterior point of the upper lip Labial inferior (Li): the most anterior point of the lower lip Supramental (Sm): the deepest point in the concavity between the lower lip and the pogonion Pogonion (Pg): the most anterior point of the chin Cm-Sn-Ls: the nasolabial angle Li-Sm-Pg: the mentolabial angle Figure I: Landmarks and angular measurements used in this study.(Cm, columella; Sn, subnasale; Ls, labial superior; Li, labial inferior; Sm, supramental; Pg, pogonion; Cm-Sn-Ls, nasolabial angle; Li-Sm-Pg, mentolabial angle) Bangladesh Journal of Medical Science Vol. 12 No. 02 April'13 angle of 102.94 ± 10.43 degrees for females and 101.09 ± 10.19 degrees for males.