Proportions of maxillary anterior teeth relative to each other and to golden standard in Chitwan Medical College

Introduction: One of the most important aspects of aesthetic dentistry while restoring or replacing maxillary anterior teeth is the creation of harmonious proportion between the widths of them. The appearance of anterior teeth is critical for an attractive face and pleasing smile. The dimensional determination of maxillary anterior teeth is an important factor for both, esthetic and function. Materials and Methods: This study was conducted in 140 dentate subjects. Out of the 140 subjects, 70 (50%) were males and 70 (50%) were females. The age of the patients in this study ranged from 18 to 50 years. Maxillary impressions of selected subjects were made with an irreversible hydrocolloid impression material. The mesiodistal width of the maxillary anterior teeth was measured from the casts with a Boley gauge.


INTRODUCTION
Dental esthetics is a science based on the general taste of society 1 . One of the most important aspects of aesthetic dentistry while restoring or replacing maxillary anterior teeth is the creation of harmonious proportion between the width of them. 2 The appearance of anterior teeth is critical for an attractive face and pleasing smile 3 . According to Young 4 "it is apparent that beauty, harmony, naturalness and individuality are major qualities" of esthetics. The dimensional determination of maxillary anterior teeth is an important factor for both, esthetic and function. Lombardi 5 proposed that dental and facial aesthetics are optimized if central incisor-to-canine width is repeated in proportion when patient is viewed from the front. This proportion was called golden proportion and is approximately 1.618 to 1. He stated the golden proportion was too strong for use in dentistry. Preston 6 found only 17% of the samples studied actually had golden proportion between the perceived width of the maxillary central and lateral incisors. White 7 projected the concept of "Correspondence and Harmony." The basis of this concept was that the temperaments called for a characteristic association of tooth form and color, and that harmony called for a corresponding proportion and size of tooth to that of the face, and a tooth color in harmony with facial complexion; that both form and color were modified to be in harmony with sex and age. White considered the detailed line values of the teeth singly, and in the over-all composition, and thought that these were modified by age and sex. Levin 8 described a system of esthetic prediction that has been used since antiquity. The naturality of the golden proportion system was emphasized by showing examples from nature and how artists and designers used it. The relationship between the length and width of the central incisor is another important concept of esthetics. The average maxillary central incisor has a length to width ratio of 10:9.1 The recommended proportion in dental anatomy and for dental laboratory technicians is 10.5:8.5.9,10 However, there is little scientific data in the dental literature to use as a guide for defining the proper size and shape of anterior teeth or determining normal relationships for them 11 . So the aim of this study was to find out the proportions of Maxillary Anterior Teeth relative to each other and objective was to evaluate the occurrence of golden proportion in the anterior teeth and to assess the width to length proportion of maxillary central incisors.

MATERIALS AND METHODS
This hospital-based prospective observational study was conducted in 140 dentate subjects in the Department of Prosthodontics and Maxillofacial prosthetics, College of Dental Science, Chitwan Medical College, Bharatpur, Nepal. Out of the 140 subjects, 70 (50%) were males and 70 (50%) were females. The age of the patients in this study ranged from 18 to 50 years. Most of the patients, 90% were in the age group 20-30 years followed by patients in the age group of ≤20 years.
Inclusion criteria were ≥18 years old; born in Nepal; with an Angle Class I molar relationship, pleasing profile, and intact morphologically normal permanent dentition up to the second molar. Subjects with a history of orthodontic treatment; a Class II or Class III molar relationship; gingival inflammation and hypertrophy in the upper anterior region; severe attrition; crowns or proximal restorations placed in the anterior teeth; and a history of congenital anomaly, orbital disease, trauma, or facial surgery were excluded. Approval for the study was obtained from Chitwan Medical College Institutional Review Committee (CMC-IRC). Verbal consent was taken from the subjects. The subjects were comfortably seated on a dental chair in a relaxed state in an upright position with the head resting firmly against the headrest. Maxillary impressions of selected subjects were made with an irreversible hydrocolloid impression material tray (Zelgan®2002 Dustfree Alginate Impression Material, DENTSPLY DeTrey GmbH, Konstanz, Germany) and poured into a Type III dental stone (Kalstone, Kalabhai Karson Pvtd Ltd, Mumbai, India). The mesiodistal width of the maxillary anterior teeth was measured from the casts with a Boley gauge (Taurus 811-2, SS Medident Instruments [Pvt] Ltd, Sialkot, Pakistan) as shown in Figure 1.

STATISTICAL METHODS
Collected data were entered into Microsoft® Excel 2007 software. Descriptive statistics were calculated (mean and standard deviation) and also tabular presentation was done. For inferential statistics. Data were analyzed using GraphPad software (San Diego California USA). P-value was calculated using one sample t-test.

RESULTS
The data collected from the 140 subjects 70 males and 70 females were analyzed to find out proportions in the maxillary anterior teeth relative to golden proportion. According to the results of one sample t-test, ratio for maxillary LI/CI and CN/LI are shown in table 1. The mean width ratios were 0.83 for right LI/CI and 0.85 for left LI/CI, 1.12 for right CN/LI and 1.1 for left CN/LI in total population. The mean width ratios in male group were 0.83 for right LI/CI and 0.87 for left LI/CI, 1.14 for right CN/LI and 1.1 for left CN/LI. Similarly in female group the mean width ratios were 0.82 for right LI/CI and 0.83 for left LI/CI, 1.1 for right CN/LI and 1.1 for left CN/LI. There was a stastically significant difference between the proportion of the right lateral incisor width based on golden proportion (p<0.001). For the left side of the jaw, the difference was also significant (p<0.001). Therefore, considering the width of the upper teeth, no golden proportion existed. Table 2 shows WLRs of maxillary central incisors in total population, male and female on both right and left side. The mean WLRs in right CI were found to be 0.84 in total population, 0.8 in male and 0.9 in female. The mean WLRs in left CI were found to be 0.83 in total population, 0.8 in male and 0.72 in female. Table- Correlation analysis was performed using GraphPad software (San Diego California USA). P-value was calculated using one sample t-test. Table 2. Width-to-length ratio of maxillary central incisors. Correlation analysis was performed using GraphPad software (San Diego California USA). P-value was calculated using one sample t-test.

DISCUSSION
Mathematical or geometrical relation between anterior teeth is important to achieve an esthetic result. It would be helpful if statistically reliable results existed to support existing theories12. Lombardi5 stated the golden proportion was too strong for use in dentistry. Several studies were conducted to find application of golden proportion in dentistry. However, the golden proportion idea can no longer be considered since many articles found that golden proportion didn't exist. Ward in 2001 recommended using other ratios, such as 0.70 rather than 0.618 to provide more pleasing appearance. 13  Oh17 studied in 93 adult Korean and found the average W/LRs of maxillary central incisors is the greatest in patients over sixty years of age. In patients aged forty to fifty years old, the maxillary central incisor WLRs of males is higher than that of females, similar to our study.

LIMITATIONS
This study has several limitations. The accuracy in determining the dimensions of teeth was compromised in two stages-one during impression making and the other during cast making. This could have been avoided if the teeth were measured intraorally but the patients' comfort would have been compromised.