1

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.

2

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.

2

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.