The influence of varying maxillary incisor shape on perceived smile aesthetics

Abstract

Objectives

This paper aims to determine the influence of varying the maxillary incisor shape of an individual on perceived smile aesthetics.

Methods

A photograph of a female smile displaying maxillary teeth only was digitally altered to produce five different incisor shapes. They consisted of three basic shapes: square (S), ovoid (O), triangular (T) and two variations, tapered-ovoid (TO) and square-tapering (ST). The images were ranked from the most to the least attractive by 30 dentists, 30 technicians and 30 patients.

Results

The TO maxillary incisor shape was perceived to be the most attractive smile overall (50%), and amongst dentists (70%), technicians (50%) and patients (30%). The O shape maxillary incisors were ranked the second most attractive overall (36.7%) and the most attractive amongst patients (56%). The S shape maxillary incisors were perceived as the least attractive overall (43.3%), and amongst dentists (47%), technicians (50%) and patients (33%).

Conclusions

The tapered-ovoid incisor tooth form for females is preferred to the square form, which corresponds with the findings in the dental literature. However, the results also suggest that there is not one ‘ideal’ incisor shape and that dental professionals are more critical than patients with respect to the shapes of maxillary incisors. Dental professionals should take the individual variability in patient response into consideration during treatment planning, to produce an aesthetic outcome that is acceptable for the patient.

Clinical significance

As a general rule, the tapered-ovoid tooth form is perceived to be more desirable than the square tooth form. The dental team should therefore keep this finding in mind and liaise with the patients accordingly, in order to help to produce desirable aesthetic clinical outcomes.

Introduction

The maxillary incisors are the most dominant teeth displayed during a smile. According to Phillips , the shape of the anterior teeth has a significant influence on smile aesthetics. The crown shape was also ranked the highest from all the various features that contribute to the overall dental attractiveness in a study by Ong et al. . Patients are becoming increasingly more conscious of their dental appearance. For many, aesthetic concerns have become one of the main reasons for seeking dental treatment. Treatment that restores function and controls active disease, without delivering optimal aesthetics, is often not perceived by patients to be a complete success.

The morphology of the maxillary anterior teeth is a combination of three basic shapes; ovoid, square and triangular. The unique morphology of teeth allows individuality and diversity. The size and shape of tooth crowns are genetically pre-determined during embryogenesis . As shapes of faces are different from one another, so is the morphology of the teeth.

Tooth shapes are very unique and no two teeth are ever identical. In addition to the three basic shapes, there are six further variations (square-tapering, ovoid-tapering, reverse-tapering, ovoid-square, ovoid-reverse-tapering and square-reverse tapering). This classification was based on the facial outline of crowns and their mesio-distal and gingivo-incisal contours .

The shape of the maxillary anterior teeth has been reported in many studies. The most prominent are by Williams and Frush and Fisher . Williams suggested that the shape of the central incisor was the inverted frontal view of the face, a square face merited square teeth and an ovoid face merited ovoid teeth. Although this theory was proposed some time ago, it is still the most common theory for the choice of artificial teeth by dental supply companies, such as Dentsply (York, PA, USA) and their Trubyte ® plastic shade guide. Williams and Frush and Fisher both proposed that there are four basic face forms (square, square tapering, tapering and ovoid).

This theory was later invalidated by subsequent studies which looked into Williams’s geometric theory to find similarity between the face and tooth form. Results concluded that William’s theory relating tooth shape to the shape of the face was not necessarily true.

The shape of a tooth requiring restoration can be determined from the adjacent teeth, previous study casts and photographs. If no such records are available, it has been suggested to consider age, sex, and personality . According to this concept, women should be given rounder, softer and more delicate teeth for proper harmony. In contrast, men are perceived as angular and square, and should be given tooth shapes that harmonise with their appearance.

In another study, it was shown that the ovoid shape was the most prevalent for anterior teeth (47.06%) in a sample of 51 Caucasian individuals , whereas 30% of this tooth shape was found in 2000 individuals studied by Ibrahimagic et al. .

Measurements of width/length ratios of normal clinical crowns represent the most stable reference point for aesthetics. For example, the height-to-width ratio of the central incisor should range from 0.75 to 0.8, a value less than 0.6 creates a long narrow tooth, and a value beyond this ratio results in a short wide tooth .

As defined by the golden proportion, a ratio of 1 is given to the lateral incisor with regard to mesio-distal width. The central incisors will then have a 1.616 ratio and the canines will have a 0.618 ratio when compared with the lateral incisors. Studies have shown that clinically the Golden proportion is not always apparent and variations are often evident. In one study, measurements of plaster casts of natural teeth revealed that only 17% conformed to the Golden proportion and can cause narrowing of the lateral incisors when applied .

In a previous similar study where the contribution of tooth shape to the aesthetic smile was evaluated, orthodontists preferred round and square-round incisors in women whereas general dentists preferred square-round incisors. Lay people in the study did not discriminate between incisor shapes for women but unlike the orthodontist group, they preferred square-round and square-square incisor shapes for men .

Dental appearance was also assessed using a questionnaire completed by dentists,technicians and patients. The images of smiles varied in tooth size,tooth form,tooth colour,smile line and the presence of a diastema. The triangular tooth form for both male and female images was the least popular,whereas the oval form for the female image and the rectangular form for the male image were the most popular .

Brisman compared dentists’ and patients’ perceptions of attractiveness. Photographs of three shapes – square ovoid, ovoid and tapered ovoid were presented to 293 subjects. Ovoid was found to be the first choice in three of the four groups.

It is therefore clear that some individual components of smile aesthetics have received more attention than others. There has been research on the influence of tooth shape on smile aesthetics which focused on the incisal edge morphology of maxillary incisors. There have been few studies that have focused on the influence of the geometric shape of incisor teeth.

The aim of this paper was to determine the influence of varying maxillary incisor shape on perceived dental aesthetics amongst dentists, dental technicians and patients.

Materials and methods

A photograph of a female smile displaying only maxillary teeth, was digitally altered using an iPad Smile Guide Touch application and Adobe Photoshop (Creative Cloud, San Jose, CA, USA) to produce five different incisor shapes. They consisted of three basic shapes, square (S), ovoid (O), triangular (T) and two variations namely, tapered-ovoid (TO) and square-tapering (ST). This follows similar approaches reported by Cooper et al. , Foulger et al. and Bukhary et al.

Final images used for this study

(The colour coded reference for the above tooth shapes used in Figs. 6–9 are as follows:

  • 1.

    Square incisors (S)

  • 2.

    Ovoid incisors (O)

  • 3.

    Triangular incisors (T)

  • 4.

    Square tapering incisors (ST)

  • 5.

    Tapered-ovoid incisors (TO) )

The square shape ( Fig. 1 ) was digitally manipulated to produce mesio- and disto-incisal angles that approximate to a right angle. They typically have a long proximal contact area, the longest of the three basic morphologies and a straight incisal outline. The mesial and distal proximal surfaces are parallel to each other and perpendicular to the incisal edge.

Fig. 1
Image for square incisors (S).

The square shape was also manipulated to produce characteristics typical of an ovoid tooth shape ( Fig. 2 ), having rounded incisal edges, proximal contact areas in the middle of the proximal outline and curved mesial and distal proximal outlines.

Fig. 2
Image for ovoid incisors (O).

The triangular shape ( Fig. 3 ) had the sharpest incisal angles of the three morphologies. The contact areas were near the incisal edge within the proximal outline. It had a straight outline with a prominent convergence from incisal to cervical aspects with a V-shaped cervical line.

Fig. 3
Image for triangular incisors (T).

The tapering ovoid shape ( Fig. 4 ) had rounded incisal edges. The lines following the proximal surfaces converged to meet at a point near the root apex. In contrast, the square tapering shape ( Fig. 5 ) had similar incisal angles and proximal surfaces to the square shape, however the lines following the proximal surfaces converged to meet at a point near the root apex.

Fig. 4
Image for tapered ovoid incisors (TO).

Fig. 5
Image for square tapering incisors (ST).

The numbers of confounding variables in the images were reduced by only including the maxillary teeth and eliminating other parts of the face, lips or lower teeth.

The height-to-width ratios of the maxillary central incisor were kept consistent within the 78–82% range proposed in the dental literature . 0.8–0.81 was chosen as the center-stage of the images to eliminate this confounding variable, so that the perception of attractiveness would only be influenced by the variation of tooth shape.

The square image was used as a baseline, which was then digitally manipulated using Photoshop ® to produce the different tooth shapes. The overall size of the images were standardised to 10.7 cm × 3.8 cm, in order to accommodate the five images onto one A4 sized gloss finished photographic paper.

The requisite research ethics approval was applied for and granted. Ninety participants aged 25 years or older were recruited into this study, including 30 patients, 30 general dental practitioners and 30 dental technicians.

The images were ranked in order of attractiveness (1 for the most attractive and 5 for the least attractive) by 30 dentists (15 male, 15 female), 30 technicians (24 male, 6 female) and 30 patients (12 male, 18 female). The colour temperature (background lighting) was standardised to a white fluorescent light for the entire study.

In order to elicit qualitative responses, the study participants were additionally asked to express why and how they made their choices.

In order to determine consistency, the participants were then asked to repeat the study after an interval of 60 min. Previous studies used a wash out period of 10 min . However, this was increased in this study to prevent the results being influenced by the effects of memory. Cohen’s kappa values were calculated to test the reliability of participants in their ability to rank the images in the same order of attractiveness.

The data was tabulated on a spreadsheet, which was then transferred to SPSS software (version 22: SPSS Inc, Chicago, Illinois, USA) for data analysis. The level of significance was set at 5%. Pearson’s chi-squared was used to compare the most and least attractive tooth shape overall and between the three cohorts. The effect of potential confounding factors (such as gender & age) on the most and least attractive tooth shape, was evaluated using Logistic regression.

Materials and methods

A photograph of a female smile displaying only maxillary teeth, was digitally altered using an iPad Smile Guide Touch application and Adobe Photoshop (Creative Cloud, San Jose, CA, USA) to produce five different incisor shapes. They consisted of three basic shapes, square (S), ovoid (O), triangular (T) and two variations namely, tapered-ovoid (TO) and square-tapering (ST). This follows similar approaches reported by Cooper et al. , Foulger et al. and Bukhary et al.

Final images used for this study

(The colour coded reference for the above tooth shapes used in Figs. 6–9 are as follows:

  • 1.

    Square incisors (S)

  • 2.

    Ovoid incisors (O)

  • 3.

    Triangular incisors (T)

  • 4.

    Square tapering incisors (ST)

  • 5.

    Tapered-ovoid incisors (TO) )

The square shape ( Fig. 1 ) was digitally manipulated to produce mesio- and disto-incisal angles that approximate to a right angle. They typically have a long proximal contact area, the longest of the three basic morphologies and a straight incisal outline. The mesial and distal proximal surfaces are parallel to each other and perpendicular to the incisal edge.

Fig. 1
Image for square incisors (S).

The square shape was also manipulated to produce characteristics typical of an ovoid tooth shape ( Fig. 2 ), having rounded incisal edges, proximal contact areas in the middle of the proximal outline and curved mesial and distal proximal outlines.

Fig. 2
Image for ovoid incisors (O).
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Jun 19, 2018 | Posted by in General Dentistry | Comments Off on The influence of varying maxillary incisor shape on perceived smile aesthetics
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