Introduction
Prosthodontics is a continuously evolving field of dentistry that replaces teeth or tooth structure via multiple types of prosthesis. The stakes are especially high when the prosthesis involves the aesthetic zone or more specifically the anterior maxillary region.
The maxillary anterior teeth are not just responsible for the aesthetics but also the phonetics, the lip support and a harmonious incisal guidance. For patients who are completely edentulous, setting the teeth as close to their original position can fulfill the abovementioned factors. However, it may be a challenging task in absence of pre-extraction records.1 Over the years, many moulds, shade guides and templates have been proposed for selection of complete denture teeth. 2, 3 Also a number of anthropometric studies have been carried out in different population groups using intra-oral or extraoral landmarks for selecting size and shape of teeth. But in absence of a fundamental approach which may be applied universally irrespective of the ethnicity or gender, selection of appropriate teeth for fixed or removable prosthesis relies solely on the perception and judgement of the clinician and laboratory technician.
Aim
The current study was conducted involving 50 fully dentulous Gujarati individuals to analyse the correlation between width of dental arch (via the inter-molar distance) and inter-hamular notch distance with the combined width of the maxillary anterior teeth and straight distance between canine cusp tips.
Materials and Methods
The study was conducted in the Dept. of Prosthodontics and Crown & Bridge, College of Dental Sciences and Research Centre, Bopal. It was carried out in accordance with the protocols reviewed and approved by the Institutional Ethical Board. The study also adhered to the Declaration of Helsinki.
Study design
50 participants (39 females and 11 males) between the ages of 18-35 participated in the study and an informed consent was obtained from each of them. The participants met the inclusion criteria of presence of all maxillary teeth from central incisor to second molar. Participants with dental malposition, diastema, attrition or history of orthodontic treatment were excluded from the study.
Procedure
A full arch maxillary impression was made in each of the participants in a metal tray with irreversible hydrocolloid impression material (Tropicalgin, Zhermack). Then, the impressions were poured in Type III dental stone (Goldstone, Asian chemicals) and casts were obtained.
The following points were marked on the cast with a fine tip graphite marker:
Both cusp tips of Left and right maxillary canine.
The point of Contact of left and right maxillary canines with their respective first premolar.
Left and right maxillary first molar mesiopalatal cusp tips.
Center of left and right hamular notches.
With help of an electronic digital caliper (Zhart Company) with an accuracy of ±0.02 mm, the following measurements were made:
A flexible ruler was used to measure the curved distance between the distal contact points of left and right maxillary canines with first premolar (CCC). (Figure 4)
Statistical analysis
SPSS software (version 22.0; IBM Corp.; U.S.) was used for the statistical analysis. The intermolar and the inter-hamular notch distances were compared with the linear distances between canine cusp tips and the curved distance of 6 maxillary anterior teeth each. Karl Pearson’s correlation coefficient was derived for each comparison and p value was obtained to check for significance of correlation.
Results
The study sample comprised of 78% females and 22% males.
The descriptive statistics namely mean, range and standard deviation of each of the measured parameters are listed in Table 1.
Table 1
Descriptive statistics for the measured parameters
Comparison via correlation analysis was done between the different parameters to derive the Karl pearson correlation coefficient.
Correlation coefficient was obtained with the formula:
r = nΣxy - Σx * Σy / √nΣx2 – (Σx)2 * √nΣy2 – (Σy)2
where x = actual value, y = predicted value and n = total number of subjects
Interhamular notch distance and intercanine cusp tip distance as well as combined maxillary anterior width is shown in Table 2.
Table 2
Correlation of Interhamular notch distance (IHND) with intercanine cusp tip distance (CCS) and combined maxillary anterior width (CCC)
|
Correlation parameters |
Correlation coefficient (r) |
Coefficient of determination (R2) |
P value |
|
IHND –CCS |
0.34 |
0.11 |
0.02* |
|
IHND-CCC |
0.35 |
0.12 |
0.01* |
Correlation analysis done between Intermolar distance and intercanine cusp tip distance as well as combined maxillary anterior width is shown in Table 3.
Table 3
Correlation of Intermolar distance (IMD) with intercanine cusp tip distance (CCS) and combined maxillary anterior width (CCC)
|
Correlation parameters |
Correlation coefficient (r) |
Coefficient of determination (R2) |
P value |
|
IMD – CCS |
0.24 |
0.05 |
0.09 |
|
IMD-CCC |
0.33 |
0.11 |
0.02* |
Figure 5
A scatter plot and the corresponding regression line and regression equation for the correlation between the dependent CCS and the independent IHND
Figure 6
A scatter plot and the corresponding regression line and regression equation for the correlation between the dependent CCC and the independent IHND
Figure 7
A scatter plot and the corresponding regression line and regression equation for the correlation between the dependent CCC and the independent IMD
Hence, it was observed that a statistically significant and positive correlation existed between the distance between the 2 hamular notches (IHND) and inter canine cusp tip distance (CCS) and also with combined mesiodistal width of the anterior teeth (CCC). In addition, a statistically significant positive correlation was obtained between the inter molar distance (IMD) and combined anterior teeth width (CCC).
Further statistical analysis was done by carrying out regression analysis between the above mentioned parameters to derive the regression formula between the independent (IHND and IMD) and the dependent (CCS and CCC) variables. The results are described in Figure 5, Figure 6, Figure 7.
Hence, the distance between left and right hamular notches (IHND) and dental arch width measured via the inter-molar distance (IMD) can be used to accurately determine the combined mesiodistal width of the six maxillary anterior teeth (CCC) by the regression equations:
CCC = 40.901 + 0.2726*IHND and CCC =41.09 + 0.3334* IMD
On the other hand only the distance between left and right hamular notches (IHND) can predict the straight distance between the left and right canine cusp tips (CCS) by the regression equation:
CCS = 19.058 +0.2924*IHND
Discussion
In dentistry, the difference between the natural and the artificial is decreasing rapidly with advancements in techniques and materials.
In the absence of pre extraction records, a dentist has to rely on the clinical judgement and the patient’s preferences in teeth selection. Non judiciously chosen anterior teeth, especially maxillary may lead to patient dissatisfaction and esthetic compromise. The color of artificial teeth can be reliably selected via a patient’s complexion and in combination with clinician’s judgement and patient’s preference. Also the patients’s photographs taken before extraction can aid in the shade selection of teeth. Hovewer, the selection of size of teeth is not as easy in cases where there are no pre-extraction records.
A literature review on the current subject reveals that a number of methods have been proposed over the years to select appropriate size and form of maxillary anterior teeth. As early as in 1815, Madame Schimmelpeinik proposed the geometric classification that categorized the face form and profile for use of artists which was also utilized in dentistry for teeth selection.4 Later, the “Typal Form Concept” was projected by Hall which was essentially a classification based on the various parameters of the anterior tooth namely, the outline form, labial surface and the width of the necks. 5 Another measure suggested was the Berry Biometric Ratio Method which said that a1:16 biometric ratio can be used to describe the relationship of the width of the maxillary central incisor to the bizygomatic width.6 Kern conducted the ‘Skull Study Project’ in 1967 that compared cranial parameters to the tooth measurements.7 Many such previous studies indicate that while some anatomical landmarks have a correlation with the mesiodistal width of all 6 maxillary anterior teeth, some others are more closely related to the mesiodistal width of maxillary central incisors. Extraoral parameters like the innercanthal distance,8, 9, 10 interalar width, 9, 10 interpupillary distance,11 intercommissural width, 11, 12 and palatal width 13 along with incisive papilla 1, 14, 15 which is an intraoral landmark have been proposed to establish width and position of the maxillary anterior teeth.
The hamular notch or the pterygomaxillary notch is one such landmark. Previously carried out studies have concluded that a correlation exists between the inter-hamular notch distance and the dimensions of the six maxillary anterior teeth 16, 17 It is a stable landmark and has the advantage of being clearly located intraorally as well as on the dental cast.
The present study was carried out with the purpose of determining if the inter-hamular notch distance and the mesiodistal width of the maxillary anterior teeth along with the linear distance between the cusp tips of the two maxillary canines were correlated in the considered Gujarati participants.
It was noted that within the limitations of the study, there was a statistically significant correlation of the interhamular notch distance with both the mesiodistal width of the six maxillary anterior teeth (p value=0.02) as well as with the straight distance between the cusp tips of the two maxillary canines (p value =0.01). This is in accordance with study conducted by Guldag et al 16 in the Turkish population and Shrestha et al 18 in the Nepalese population.
In cases where just the maxillary anteriors are missing or are to be rehabilitated for the purpose of esthetics (proclined, spaced or crowded anteriors), choosing the teeth size which is in harmony with rest of the dentition is important. Therefore, the arch width was taken up as another parameter which was measured via the intermolar distance (IMD) measured between the mesiopalatal cusp tips of left and right first maxillary molar. This parameter was also compared with the mesiodistal width of the maxillary anterior teeth as well as with the straight distance between the cusp tips of the two maxillary canines.
The results of the current study concluded that although the inter-molar distance had a statistically significant correlation with the mesiodistal width of the six maxillary anterior teeth (p value=0.02), there wasn’t a significant correlation found with the linear distance between maxillary cusp tips. This observation is similar to the results found in a study conducted by Ellakwa 11 et al that concluded that the average dental arch width along with arch length and inter alar distance could be used to accurately determine the maxillary anterior teeth width.
Conclusion
Within the constraints of the study, it can be concluded that for the Gujarati population taken into consideration:
The inter-hamular notch distance (IHND) may serve as an accurate predictor for determining the combined mesiodistal width of maxillary anterior teeth (CCC) and also the straight distance between the maxillary canine cusp tips(CCS) by using the following regression equations:
However, the dental arch width assessed by measuring the intermolar distance(IMD) possessed a statistically significant correlation with only the combined mesiodistal width of six maxillary anterior teeth(CCC) and can be calculated using the following regression equation:
CCC =41.09 + 0.3334* IMD
