To evaluate the validity of Recurring Esthetic Dental proportion in natural dentition

Abstract

Background:

Different proportions are described in the literature for smile designing, such as Golden proportion, Golden percentage, Preston's proportion, and recently, Recurring Esthetic Dental (RED) proportion.

Aims and Objectives:

To evaluate the existence of RED proportion in natural dentition. To determine the relative height of maxillary lateral incisor and canine occurring in natural dentition so that it can be used in any of the above proportions.

Materials and Methods:

Fifteen male subjects and 15 female subjects in each of the different age groups of 18–23 years, 24–29 years and 30–35 years were selected for this study (total 90). Photographs of the subjects were taken using Nikon D200 camera with 135 mm lens and analyzed using Adobe Photoshop CS4 extended software. The height and width of maxillary central incisors, lateral incisors and canines were found out using the measuring tool provided in the software.

Results:

Average width ratio and height ratio of maxillary lateral incisor to central incisor and maxillary canine to lateral incisor were calculated to check the existence of RED proportion in natural dentition. Average lateral incisor to central incisor height ratio for “small”- and “medium”-sized teeth was found to be 88% and for “tall”-sized teeth was found to be 84%. Average canine to lateral incisor height ratio for “small”- and “medium”-sized teeth was found to be 106% and for “tall”-sized teeth was found to be 105%.

Conclusions:

Within the limitations of the study, RED proportion was not seen in natural dentition.

INTRODUCTION

The smile design theory can be broken down into four parts: facial esthetics, gingival esthetics, microesthetics and macroesthetics. Facial esthetics involves lips and soft tissue curvature during smiling, speech and laughter. Gingival esthetics involves health of the gingiva, shape of the interdental papilla and the presence or absence of black triangles. Microesthetic features involve the anatomy of the anterior teeth, incisal translucency, characterization and lobe development. Macroesthetic features involve facial midline, size and shape of the teeth.

Different proportions are described in the literature for the size of maxillary anterior teeth. Golden proportion[1,2] is based on the theory that a relationship exists between the beauty in nature and mathematics. It states that the width of maxillary lateral incisor, when viewed from front, should be in Golden proportion to the width of maxillary central incisor. Thus, the width of maxillary lateral incisor should be 62% the width of maxillary central incisor and the width of maxillary canine should be 62% the width of resulting lateral incisor. Golden Percentage proportion given by Snow[3,4] states that the width of maxillary central incisor should be 25% the intercanine distance, when measured from distal of canine on one side to the distal of canine on the contralateral side in the frontal view. Width of maxillary lateral incisors and canines should be 15 and 10%, respectively, of the intercanine distance [Figure 1].

Figure 1.

Golden proportion: Calculating the width of maxillary anterior teeth using the Golden Proportion

Preston[3,5] in 1993 studied the existence of Golden proportion in natural dentition and found that only 17% of the maxillary lateral incisors’ width was in Golden proportion with the width of maxillary central incisors and none of the canines’ width were in Golden proportion to the width of maxillary lateral incisor. He proposed Preston's proportion, that is, the width of maxillary lateral incisor should be 66% the width of central incisors and the width of maxillary canines should be 55% the width of maxillary central incisors in the frontal view [Figure 2].

Figure 2.

Preston's proportion: Calculating the width of maxillary anterior teeth using Preston's proportion

Ward[6–8] in 2000 proposed Recurring Esthetic Dental (RED) proportion based on the different heights of the maxillary anterior teeth, which had not been considered in any of the proportions mentioned above. RED proportion is shown in Table 1.

Table 1.

Tooth height and desired recurring esthetic dental proportion

Golden proportion is one of the RED proportions for “tall”-sized maxillary teeth.

MATERIALS AND METHODS

Fifteen male subjects and 15 female subjects in each age group of 18–23 years, 24–29 years and 30–35 years were selected for this study (total 90).

Inclusion criteria

Well-aligned anterior dentition is the inclusion criterion.

Exclusion criteria

Restorations in anterior teeth

Midline diastema

Malalignment of anterior teeth

Congenital or acquired facial and dental defects

History of orthodontic treatment

Photographs of the subjects were taken from the frontal view with Nikon D200 camera, 135 mm lens with a tripod, at a distance of 1 m, and by the same and single investigator throughout the study. Photographs were analyzed using Adobe Photoshop CS4 extended software. The width and height of maxillary central incisors, lateral incisors and canines were measured using the scale tool provided in the software [Figure 3].

Figure 3.

(a) Subject with well-aligned dentition, Measuring the (b) height and (c) width of maxillary central incisors using the Adobe Photoshop CS4 extended software

Magnification was calculated by finding out the ratio between the actual height of central incisors measured on the subject's cast and height of the central incisors measured using the photograph. Once the magnification was calculated, the actual height of the central incisors was found out. Depending on the maximum and minimum values for the height of central incisors, central incisors were divided into three categories – “small”, “medium” and “tall”. Then, the following ratios were computed: 1) RA1 (ratio of the width of maxillary lateral incisors to central incisors), 2) RA2 (ratio of the width of maxillary canines to lateral incisors), 3) RA3 (ratio of the height of maxillary lateral incisors to central incisors), and 4) RA4 (ratio of the height of canines to lateral incisors) [Figure 3].

RESULTS

We can see from Table 2 that the mean RA1 (lateral incisor to central incisor width ratio) for “small” category teeth was 73% (proposed ratio 80%), for “medium” teeth was 72% (proposed 76%) and for “tall” teeth was 71% (proposed 62%). Similarly, the mean RA2 (canine to lateral incisor width ratio) for teeth of all the three categories was found to be different as compared to that proposed by Ward in RED proportion.

Table 2.

Comparison of mean values of ratio of the various tooth

Also, the mean RA1 (lateral incisor to central incisor width ratio) for “small” category teeth was not similar to RA2 (canine to lateral incisor width ratio) and similar results were obtained for “medium”- and “tall”-sized teeth. Thus, the two ratios were not recurring in the natural dentition.

The average lateral to central incisor height ratio was found to be 84% in “tall”-sized teeth and 84% for “small”- and “medium”-sized teeth. Average canine to lateral incisor height ratio was 105–107%.

DISCUSSION

Golden proportion was given by Levin[1,9–11] based on the principle that there exists a relationship between the beauty in nature and mathematics and the same principle was applied in designing the width of maxillary anterior teeth. Preston[5] in 1993 studied the existence of Golden proportion in natural dentition with pleasant smiles and found that Golden proportion was hardly seen in the natural dentition and proposes his own Preston's proportion.

Stephen Rosenstiel and Ward[6] in 2000 in their web-based study were the first to consider the importance of length of teeth in determining the width of maxillary anterior teeth. In case of tall central incisors, lesser width of lateral incisors and canines is desired for an esthetic smile so that the width proportion is less, while in case of “small”-sized central incisor teeth, greater width of lateral incisors and canines is desired so that the width proportion is more. Golden proportion of 62% is one of the RED proportions for “tall”-sized teeth.

The study was conducted to evaluate the existence of RED proportion proposed by Rosenstiel and Ward in a small section of Indian population with pleasant smiles. The teeth were divided into three categories, and it was found that in none of the three categories the maxillary lateral incisor to central incisor width ratio was similar to that proposed, and the maxillary lateral incisor to central incisor width ratio was also not similar to maxillary canine and lateral incisor width ratio, the two ratios were not seen recurring. The reason for such a finding could be that the proportions proposed by Ward and Rosenstiel in 2000 were basically computer and software based and no efforts were made to check if these proportions really exist in the natural dentition.

The results obtained were similar to that obtained in the study done by Shreenivasan[12] in 2008. The study was conducted on 56 subjects and RED proportion was not seen in the natural dentition. It was also concluded that the width of maxillary anterior teeth follows more closely the Golden Percentage proportion given by Snow in 1999. The height of the teeth was not taken into consideration in the study.

None of the proportions mentioned in the literature describe about the relative height of lateral incisors and canines to be used along with the widths during the smile designing. In this study, relative heights of lateral incisors and canines were also determined to estimate the height of lateral incisor and canine in cases of esthetic reconstruction.

The term “medium” has been used for the second category of central incisors instead of “normal” as proposed by Ward, as the “tall”-sized teeth may be normal for subjects with long faces.

As a general rule, while designing smile, neither of the proportions can be taken as a sole criterion to determine the width of maxillary anterior teeth. Modifications need to be done according to age, sex, personality and profession. Heights of the lateral incisors and canines can be roughly determined (not mentioned in any proportions) using results obtained from this study. Again, these need to be modified according to age, sex, personality and profession as the width of maxillary anterior teeth.

Major limitation of this study was the small sample size and further studies need to be undertaken with a large sample size. Second limitation is the lack of definitive sizes according to which the central incisors were divided into three categories that is “small”, “medium” and “tall”, which is not mentioned in the original article proposed by Ward. In this study, the central incisors were divided accordingly based on the highest and lowest values for the height (central incisors) obtained.

CONCLUSIONS

Within the limitations of the study, RED proportion was not seen in the natural dentition.

Average lateral incisor to central incisor height ratio for “small”- and “medium”-sized teeth was found to be 88% and for “tall”-sized teeth was found to be 84%.

Average canine to lateral height ratio for “small”- and “medium”-sized teeth was found to be 106% and for “tall”-sized teeth was found to be 105%.