Role of buccal corridor in smile esthetics and its correlation with underlying skeletal and dental structures :[PAUTHORS], Indian Journal of Dental Research (IJDR)

ORIGINAL RESEARCH
Year : 2012 | Volume : 23 | Issue : 2 | Page : 187--194

Role of buccal corridor in smile esthetics and its correlation with underlying skeletal and dental structures

Tripti Tikku, Rohit Khanna, RP Maurya, Nabeel Ahmad
Department of Orthodontics and Dentofacial orthopaedics, Uttar Pradesh Dental College and Research Centre, Lucknow, India

Correspondence Address:
R P Maurya
Department of Orthodontics and Dentofacial orthopaedics, Uttar Pradesh Dental College and Research Centre, Lucknow
India

Abstract

Purpose: This study was designed to evaluate the buccal corridor in smile esthetics and to correlate it with underlying hard tissues. Materials and Methods: Posed smiling frontal photographs, digital posterior-anterior (PA) cephalograms, and study models of 25 males and 25 females in age range of 18-25 years were taken. Photographs were evaluated for smile esthetics by eight orthodontists, eight plastic surgeons, eight beauticians and eight lay people to group them into three groups with least attractive, average and attractive smile and buccal corridor width was measured. Digital PA cephalograms were transferred on Nemo-tech software for frontal facial analysis. Intercanine and intermolar widths were measured on upper study model with the help of a digital calliper. Results: The buccal corridor width was least in attractive smile group and maximum in least attractive smile group. The buccal corridor width had a negligible correlation with hard tissues and a mild to moderate inverse correlation with intercanine and intermolar widths within the groups. Conclusion: As the amount of buccal corridor display was increased, smiling images were scored less attractive by the evaluators. The buccal corridor is not influenced by underlying skeletal hard tissues but have mild to moderate inverse correlation with the intercanine and intermolar width.

How to cite this article:
Tikku T, Khanna R, Maurya R P, Ahmad N. Role of buccal corridor in smile esthetics and its correlation with underlying skeletal and dental structures.Indian J Dent Res 2012;23:187-194

How to cite this URL:
Tikku T, Khanna R, Maurya R P, Ahmad N. Role of buccal corridor in smile esthetics and its correlation with underlying skeletal and dental structures. Indian J Dent Res [serial online] 2012 [cited 2023 Jun 6 ];23:187-194
Available from: https://www.ijdr.in/text.asp?2012/23/2/187/100424

Full Text

Smile plays a significant role in facial attractiveness. It influences mating success, kinship opportunities, personality evaluations, performance, employment prospects and also influences personality development. The upper and lower lips frame the display zone of the smile, bordering the dentition, the gingival scaffold, and the space in the oral cavity. Smiles can be either posed or spontaneous. [1],[2],[3] The posed smile is voluntary and static in the sense that it can be sustained and need not be elicited or accompanied by an emotion. The spontaneous smile is involuntary and natural which expresses authentic human emotion and dynamics. Lip elevation in the unposed smile is often more animated, as seen in the laughing smile. [4]

The buccal corridor is more commonly referred by orthodontists as negative space present between the lateral aspects of maxillary posterior teeth and the corner of the mouth during smile which appears as a black or dark space. Frush and Fischer demonstrated that the presence of buccal corridors added the illusion of a natural dentition, whereas its absence gave the patient an artificial appearance. Again, the orthodontist's eye for beauty is an important factor in creating appropriately sized buccal corridors. In smiling, the width of the mouth increases by as much as 30%, therefore, an excessive transverse lip extension in smiling would produce a wider buccal corridor. [5]

The purpose of this study was to evaluate the presence of buccal corridor in smile esthetics as judged by a panel of judges constituting of orthodontists, laymen, beauticians and plastic surgeons and to correlate it with underlying hard tissues.

Materials and Methods

The sample for this study consisted of 50 orthodontically untreated subjects (25 males and 25 females) in the age groups of 18 to 25 years (21.11±0.85 years). The subjects were selected from various colleges, namely, Northern India Engineering College, Babu Banarasi Das Engineering College and Uttar Pradesh Dental College and Research Centre, Lucknow.

Criteria for subject selection

No history of previous orthodontic treatment or maxillofacial surgery;Complete permanent dentition except for 3 rd molars with no missing or supernumerary teeth or any abnormality, irrespective of any malocclusion;No active periodontal disease and no periodontal treatment except for routine scaling and polishing; andNo craniofacial anomalies or other pathologies.

The samples for this correlation study consisted of frontal smile photographs, posterior-anterior (PA) cephalograms, and study models of all subjects. Approval was taken from all the subjects as per the format of ethical committee of our dental college affiliated to Agra University.

A digital camera (Fuji HD 200 with 10.1 megapixels) was used to capture photographs of all subjects. To standardize the technique, photographs were taken after positioning the subject's head on a digital cephalometric machine (Planmeca Proline XC, Finland) [Figure 1], a cephalometric head holder, a calibrating scale (sticked to cephalostat), and natural head position were used with a fixed patient camera distance of 60 inches. Before taking the photographs, each subject was asked to rehearse the following word "cheese" and smile, showing his/her teeth. Subsequently, two to three photographs of each subject were taken which were imported into a commercially available photograph editing program (Adobe Photoshop, version 7). The image that best represented the patient's natural unstrained social smile was selected [Figure 2]. In addition, the image was cropped with vertical (nose tip and soft tissue pogonion) and transverse (perpendicular drawn down from the zygomatic prominence) limits to eliminate most of nose, cheeks, and chin to minimize the influence of background facial attractiveness. The images were adjusted to a standardized image size (3 × 5 inch) and saved as JPEG files format [Figure 3].{Figure 1}{Figure 2}{Figure 3}

The facial photographs were evaluated by a panel of judges comprising of eight plastic surgeons, eight beauticians, eight orthodontists, and eight lay persons. The judges were later asked to rate the smile on a scoring sheet using a scoring scale (0-10) [Figure 4].{Figure 4}

Each panel member made its evaluation separately without any knowledge of the subject's identity and the ratings given by the other panel members. They were given the following instructions: "Please complete the following survey by evaluating the smiles for the esthetic value of the teeth and lip appearance. Disregard facial blemishes, any variation in teeth shade, or picture quality. The purpose of this survey was (the evaluator) to assess the attractiveness of your entire smile and how the teeth appear within the lips. The smiles are to be graded using the scales from unattractive to attractive. You may give score from 0 to 10. Please examine several smiles in the album first to calibrate you for the evaluation process, but once you have started, please do not flip back and please do not compare any of the photographs or score to one another." The scores were calculated manually and entered onto an Excel spread sheet (Windows 7, Microsoft Office 2007, Microsoft Corp.).

Digital PA cephalogram of the subjects were taken on a digital cephalometric machine (Planmeca Proline XC, Finland) by positioning the subject's head in natural head position. The receptor -source distance was fixed at 60 inches. The exposure values were set at 66 kV, 9 mA, and exposure time of 18 sec. All PA cephalograms were then transferred to a computer loaded with Planmeca software from where the digital PA cephalograms were saved in bitmap files and taken onto a compact disc, read only memory (CD ROM) (Moserbaer Aqua). The PA cephalograms of 50 subjects were transferred to Nemotech digital imaging software cephalometric landmarks and cephalometric planes were identified and marked and analyzed by norms as established by Rickett's for frontal analysis [Figure 5].{Figure 5}

Also, study models of all the subjects were made by taking an upper and lower impression with alginate (Zelgan 2002, Dentsply ISO 9001, and ISO 13485) and poured in dental stone (Denstone). Intercanine and intermolar widths on each upper study model were measured by using a digital calliper (Yamayo Co.).

The samples were placed under three groups-group I, group II, and group III according to mean scores and were divided into three subgroups - a (males), b (females), and a+b (overall) [Table 1] and [Table 2].{Table 1}{Table 2}

Method

The following points and landmarks and planes were taken on photographs, cephalograms and study models.

Photographic points - [Figure 2] and [Figure 3]

Outer commisure- outer junction of upper and lower lips lateral to the angle of the mouth;

Inner commisure- inner junction of upper and lower lips lateral to the angle of the mouth; and

Buccal corridor- the distance from the most visible posterior teeth in the smile to the inner commissures of the lips.

Cephalometric points and landmarks - (Rickett's, [Figure 6]) {Figure 6}

ZL zygomatic- most medial point of the frontozygomatic suture in the external margin of the orbital rim on left side.ZR zygomatic - most medial point of the frontozygomatic suture in the external margin of the orbital rim on right side.ZA zygomatic- center of the root of the zygomatic arch on left side.AZ zygomatic- center of the root of the zygomatic arch on right side.ANS maxilla- center of anterior nasal spine, located on the intermaxillary suture just below the nasal cavity.JL maxilla- deepest point on the jugular process on left side.JR maxilla - deepest point on the jugular process on right side.AG mandible- deepest point of the antegonial notch on left side.GA mandible- deepest point of the antegonial notch on right side.Me menton - midpoint of the inferior border of the symphysis. It is located inferior to the center of trigonium mentalis below the genial tubercles.

Cephalometric planes - (Rickett's; [Figure 6])

[INLINE:1]

Points taken on upper study models

Canine cusp tipMesiobuccal cusp tip of first maxillary molar

Method of measurements

Measurements on photograph

[Figure 2] and [Figure 3] to calculate the buccal corridor width ratio on the photograph, the sum of outer commisure, and the most distal tooth visible was subtracted from the sum of outer and inner commisure.

Buccal corridor width = (outer commissure + most distal tooth visible) − (outer commisure + inner commisure)

This was measured for each side and an average buccal corridor width was taken for each subject. For this purpose, vertical lines were drawn passing through outer commisure, inner commisure, and most distal tooth visible on each side. These lines were extended to pass through calibrating scale attached linearly so that exact measurements were made.

Measurements on cephalogram

The following measurements were done on a digital cephalogram for Ricketts frontal analysis with the help of Nemoceph software.

Linear measurements on cephalogram [Figure 6]

Left and right maxillomandibular width = perpendicular distance between maxilla (point J) and frontal facial plane (ZR-GA/ZL-AG).Maxillary width = distance between J points (JL-JR).Mandibular width = the distance between points AG and GA.Facial width = the distance between points ZA and AZ.

Angular measurement on cephalogram [Figure 6]

Postural symmetry angle = difference between angles ZL-AG-ZA and ZR-GA-AZ.

Measurements on study models

The following measurements were done on upper study models with the help of a digital calliper.

Intercanine width = from canine tip of one side to other on maxillary arch.

Intermolar width = from mesiobuccal cusp tip of first molar on one side to another side on maxillary arch.

Statistics

Descriptive statistics included mean and standard deviation. Non parametric tests i.e., Kruskall Wallis test and Chi- square test were done to compare the test values in different groups and subgroups. Mann-Whitney U test was applied wherever the differences were significant on Kruskall-Wallis test.

Results

The mean buccal corridor width in group I was observed to be maximum followed by group II and minimum in group III in all the subgroups. The mean intercanine and intermolar width in group III was observed to be maximum followed by group II and minimum in group I in all the subgroups. For subgroup a (males), subgroup b (females), and subgroup a+b (overall) none of the parameters except buccal corridor width, intercanine and intermolar width showed a statistically significant intergroup difference [Table 3], [Table 4] and [Table 5]. [Table 6] shows multiple comparisons between the smile esthetic groups.{Table 3}{Table 4}{Table 5}{Table 6}

A negative correlation was observed to exist between buccal corridor width, intercanine and intermolar width in subgroup-a (males), subgroup-b (females), and subgroup- a+b (overall) [Table 7], [Table 8] and [Table 9].{Table 7}{Table 8}{Table 9}

[Figure 7] shows negligible correlation between buccal corridor width and maxillomandibular width, maxillary width, mandibular width and facial width (r<0.3). A mild inverse correlation between buccal corridor width and postural symmetry angle (r=0.3 to 0.5) and moderate inverse correlation between buccal corridor width, intercanine width and intermolar width (r=0.5 to 0.7) were also observed.{Figure 7}

Discussion

The impact of buccal corridor on smile esthetics has been studied in recent years. [6] Reports show that buccal corridor has an effect on the esthetic evaluation of smiles. Knowledge of the correlations between hard and soft tissue anatomy and smile esthetics might add important clinical meaning to orthodontic diagnosis and treatment planning. [7]

This study was undertaken with an aim of evaluating buccal corridor in different smile esthetics and to clarify the relationships between specific skeletal and dental structures as compared to buccal corridor width while smiling. The present study was conducted on 50 adult orthodontically untreated subjects. The age range of the sample was above 18 years so as to ensure that complete growth had taken place as stated by Genecov J.S. et al.[8] and Subtelny J.D. [9] In this study, eight orthodontists, eight plastic surgeons, eight beauticians, and eight lay people evaluated the smiling photographs of the subjects one by one to rank the smiles. The subjects were put into three groups as least attractive smile (group I), average smile (group II), and attractive smile (group III) according to scores which were further subdivided into subgroups a, b, a+b on the basis of gender.

In previous studies by Rigsbee et al.[10] and Peck and Peck, [11] the difference in smile between males and females had been noted.

Quantitative measurements were made by using images of the posed smile of all the subjects focussing on buccal corridor width, transverse parameters on frontal cephalograms, and the transverse parameters on upper study models.

The result of the present study showed that the smile with least buccal corridor display was considered to be most attractive and the smile with more buccal corridor display was considered to be least attractive by the raters. In the present study, the overall calculated mean buccal corridor width for group I was 2.00+0.59 mm was maximum followed by group II 1.22+0.53 mm and group III was 0.96+0.30 mm which was found to be statistically highly significant (P<0.001). This result is also supported by the study of Moore.T, Southard.K.A. et al.[12] , Parekh.S.M et al., [13] Ker A.J., Chan.R et al.[14] and Ioi.H et al., [15] who found that a broader smile (minimal buccal corridors) was judged by lay people and orthodontists to be more attractive than a narrow smile (larger buccal corridors). On the contrary, Johnson D.R., Gallerano.R et al.[16] Rittera D.E. et al.[2] Zangea S.E. et al.[17] and Janson.G et al.[6] who found that the presence of buccal corridor space did not influence the smile esthetics. Yang. I.H. et al.[7] found that for achieving a better esthetic smile after fixed orthodontic treatment the amount of buccal corridor area should be controlled. Similar trend was observed in both males and females. On comparison of smile esthetic groups group I, II, and III to subgroup-a and b (males and females), no statistically significant difference was found (P=0.757). Southard.T.E. and Casko.J.S. et al.[12] also found no significant difference in judging smile esthetics between male and female subjects.

Most of the studies done previously correlated underlying hard tissue in lateral cephalogram with the buccal corridor. Since the buccal corridor is visible on frontal photographs, its correlation to hard tissue on the lateral cephalogram is a questionable issue; hence, it was decided to correlate hard tissue parameters on frontal cephalograms to buccal corridor width. Yang.I.H [7] compared the lateral cephalogram to frontal photograph and found that when vertical length in the lower half of soft tissue profile increased then buccal corridor space decreased i.e., long faces have a tendency for less buccal corridor and hard tissue variables like FMA and lower facial height ratio also behave in a similar fashion. Panossian Antoine J et al.[18] and Krishnan.V et al.[19] in their study tried to correlate facial widths measured clinically to modified smile index, but not to the buccal corridor width. Hence, there were not many studies for direct comparison. Within these limitations of this study, it can be suggested that it is mainly the soft tissue drape that governs the buccal corridor display while smiling rather than underlying hard tissues.

On comparison of buccal corridor width to maxillomandibular width (right and left), maxillary width and facial width, a weak positive statistically insignificant correlation was found (r<0.3) and an inverse statistically insignificant correlation (r<0.3) was found between buccal corridor and mandibular width. Considering these facts, we can assume that there was weak correlation between the buccal corridor width and maxillomandibular width, maxillary width, mandibular width, and facial width, but this was not statistically significant. Hence, it reveals that the buccal corridor is a defined space which has negligible affect from underlying hard tissues.

On evaluating the postural symmetry angle, an inverse correlation between buccal corridor width and postural symmetry angle was observed which was not statistically significant. This further suggested that the adjoining hard tissue structures had limited or practically no affect on buccal corridor.

Another aspect to the present study was to find correlation between dental widths (intercanine and intermolar widths) to the buccal corridor width. In order to eliminate the possible errors in measurement of dental arch width in frontal cephalograms, the measurements were made directly on dental cast of the subjects were done. Smile with least intermolar and intercanine width was rated as least attractive. However, the intercanine width and intermolar width had mild to moderate inverse correlation to buccal corridor width which was statistically significant in all groups. Attractive smile had least buccal corridor display and maximum intercanine and intermolar width. The reason for this mild to moderate inverse correlation between buccal corridor width and intercanine and intermolar width could be that this dentoskeletal parameter was only one boundary of the buccal corridor space, the other boundary of buccal corridor space being governed by soft tissue drape which is a combination of lining mucosa, submucosal fat, and muscular attachment and pull. This was also observed by Dusten Roden-Johnson et al.[16] who found that broader arch forms were considered esthetically pleasing by dentists, orthodontists, and lay people with no buccal corridor space. Yang.I.H. [7] observed statistically significant inverse correlation between the interpremolar width and buccal corridor space. On contrary, Laurie McNamara, Marc B. Ackerman [1] found that there was no correlation between the widths of the right and left buccal corridors and the intermolar and intercanine widths of the maxillary arch as measured from the casts.

Reduced buccal corridor dimension or display was pleasing to the raters suggesting the importance of buccal corridor width in influencing the smile esthetics of an individual. Underlying hard tissue parameters on frontal radiographs did not show statistically significant difference in subjects with least, average and attractive smile and also had a negligible correlation with buccal corridor width. Intercanine and intermolar width was found to maximum in subjects with attractive smile and minimum in subjects with least attractive smile in both the sexes and had mild to moderate inverse correlation with buccal corridor widths irrespective of sex. Finally, inference thus drawn from the above study was that the buccal corridor space was not influenced by facial widths because of soft tissues compensation and camouflage of underlying hard tissue structures.

This study was the first attempt to correlate facial widths in transverse dimension to buccal corridor space; further studies could be directed on clinical measurements of the facial widths as this will add the soft tissue dimension to the underlying hard tissue. A more in depth research on correlation of buccal corridor with underlying skeletal and dental structures is needed with a sample of larger size for more reliable information.

Conclusion

The following conclusions were drawn from the present study-

Buccal corridor width was found to be least in subjects with attractive smile and maximum in subjects with least attractive smile irrespective of sex.Maxillomandibular width (right and left), maxillary width, mandibular width, facial width, and postural symmetry angle (right and left) on frontal radiographs did not show statistically significant difference in subjects with least, average and attractive smile and also had a negligible correlation with buccal corridor.Buccal corridor had mild to moderate inverse correlation with intercanie and intermolar widths irrespective of sex.Intercanine and intermolar width was found to maximum in subjects with attractive smile and minimum in subjects with least attractive smile in both the sexes.

From these findings, it was concluded that the buccal corridor is influenced by dental structures and soft tissue structures rather than underlying skeletal structures.

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