ASSESSMENT OF MEAN DISTANCE BETWEEN CENTRAL INCISOR AND INCISIVE PAPILLA WITH RESPECT TO STANDARDIZED ARCH FORM IN DENTATE SUBJECTS

BACKGROUND & OBJECTIVE: Edentulous patients require accurate positioning of artificial maxillary anterior teeth in complete dentures to recover the esthetic and phonetic characteristics. This positioning is guided by measuring distance between central incisor (CI) and incisive papilla (IP) in dentate subjects which varies according to the ovoid, square and tapered maxillary arch forms. Objectives of the study is to determine the frequency of three different arch forms in dentate patients; and to assess the mean distance between central incisor and incisive papilla in each of the three maxillary arch forms. METHODOLOGY: 130 cases were selected by non-probability consecutive sampling, which included both genders and age range of 20-40 years. Impressions of maxillary arches were recorded and their casts photocopied. Arch form template was used to standardize the assessment of arch forms by best-fit method on the photocopies. The distance between mesio-incisal edge of CI and posterior border of IP was measured with digital verniercalipers (SparkFun,Colorado). RESULTS: Out of 130 subjects, 54 males and 76 females were present. The ovoid arch form was the most frequent form recorded at 67% (n=87) while the tapered arch was the least at 14% (n=18). The overall mean distance between central incisor (CI) and incisive papilla (IP) was 11.34mm (7.58mm 16.45mm). The mean distance was the highest for ovoid arch form (11.58mm) and lowest for square (10.49) with a statistically significant difference (p=0.016) between the two arch forms. CONCLUSION: The ovoid arch was the most frequent arch form found in dentate subjects. The mean distance recorded was highest for ovoid arch followed by tapering arch and least for square arches.

Maxillary teeth with surface loss, malalignment, diastemata, fixed prosthesis, mobility and/or history of orthodontic treatment were excluded from the study. An informed consent was taken from participants ensuring confidentiality of their data and this data was recorded in a specially designed proforma. The study comprised of 130 cases. This sample size was calculated with 95% confidence interval, 7% margin of error and with expected percentage [13] of square arch form i.e. 21 After three measurements of each cast, the mean distance was recorded. Data collected was entered in SPSS version 20 and analyzed. The qualitative data was presented in the form of frequency and percentages i.e. gender and arch forms. The quantitative data was presented in the form of mean and standard deviation i.e. age and distance between CI and IP. Data was stratified for gender to address the effect of modifiers. One-way ANOVA was applied to compare mean values of distance between CI and IP with respect to arch form and also poststratification, where result with p-value of 0.05 or less was considered significant.

RESULTS:
One hundred and thirty patients models were made for this study.   Data was stratified to check the significance between the two groups of genders. There was no statistically significant difference between the groups (p= 0.981). Table III demonstrates the mean distance according to arch forms. Data was stratified to check the significance between the three groups of arch forms. There was a statistically significant difference between the groups (p=0.022). Table IV shows post-stratification for gender with arch form and CI-IP distance. One-way ANOVA was applied to compare mean values of distance (between CI and IP) in the 3 different arch forms. There was a statistically significant difference between the groups ovoid and square arches (p= 0.016).

DISCUSSION:
The majority of edentulous patients requiring complete dentures to restore their teeth do not have pre-extraction records to guide the placement of the prosthetic teeth. In the absence of pre-extraction records, biometric guides are useful in determining positions of [15] denture teeth . The IP is a stable landmark and the mean distance between CI and IP in dentate subjects gives a reliable guide to position the maxillary anterior teeth in complete [7] dentures . This mean distance varies with the three maxillary arch forms; tapered, square and ovoid; hence, anterior teeth positioning [13,14] should follow these arch forms . A total of 130 subjects were selected for this study out of which 54 were males and 76 females, at 41.5% and 58.5% respectively. This is contrary to other studies that had either selected equal number of subjects from both genders, or those who created equal number of [4,8,14] arch form groups . Zia et al conducted their study on 150 subjects, with 75 males and [8] females each . Saleem et al used 250 subjects, equally divided into 125 males and females [14] each .In the current study, non-probability consecutive sampling was used to select the subjects, hence the unequal distribution of gender and arch forms. To standardize the assessment of the maxillary arch forms, orthoform template was used in this study. The use of template to assess arch form is in accordance with many authors who have [8,13,14,16-recorded the frequency of these arches 18] . The template allowed accurate assessment of arch forms according to the best-fit method and helped to remove subjective bias. In the current study, ovoid arch form was the most frequent arch form recorded at 67% followed by the square arch at 19%, while the tapered arch was the least recorded form at 14%. This higher frequency of ovoid arch is concurrent with that recorded in one of the earliest studies conducted by Ehrlich and Gazit [17] at 64% . Their result for least frequent tapered arch (10%) is also in agreement. However, the results of this study are converse to those of Nojima et al (Japanese population), Olmez et al (Turkish) and Tajik et al (Pakistan), all of whom recorded a lower frequency of ovoid arch form at 38%, 27.3% and 29.2% [13,16,18] respectively . Tajik and Olmez both recorded the highest frequency for tapered arch form at 62.5% and 49.2% respectively, a stark [13,16] contrast to the result of the current study . Majority of these studies were not local which also helps to explain the difference in the frequency of arch forms recorded amongst various racial populations. In the present study, the frequency of arch forms according to gender also showed ovoid arch as the most frequent among both males and females at 59.2% and 72.4% respectively. The tapered arch was again least frequent among both genders; males at 16.7% and females at 11.8%. The higher frequency of ovoid arch form in females compared to males can be attributed to the higher frequency of overall female subjects in the study. These results are in concordance with those of Zia et al whose frequency for ovoid arch was highest among both males (57.3%) and females (68%), while the tapered arch was 10.3% for JUMDC Vol. 12, Issue 1, January-March 2021  [8] males and 13.3% for females . This validates the highest frequency of ovoid and least of tapered arch form since Zia et al's study included equal number of male and female subjects, while the distribution of genders in the present study was unequal. The current study included selection of subjects in the age range of 20-40 years. The mean age of the subjects was recorded as 25.35 years. This age range is in similarity to many studies.and provides a good number of dentate individuals since tooth loss accelerates [4,8,14,19] after 40 years of age . This study used the mesio-incisal edge of the CI and the posterior border of the IP as the anterior and posterior reference points, respectively. The overall mean distance recorded between the two references was 11.34mm ±1.76mm. No statistically significant difference was observed between gender groups as both male and female subjects showed the same reading of 11.34mm. This reading was in converse (and in a higher range) to the earliest studies of 1950-70 which recorded the distance of 8-10 mm [2,20] . However, these readings were on a lower range than those of the next generation of authors (1970-90) who recorded the distance [17,21] of 12-13mm . With the turn of the millennium, the most recent authors have recorded the mean distance as 11.96mm and [7] 11.92mm .This study is in consensus with the recent intermediate range most probably because the selected subjects fall under the same generation. Moreover, the current study recorded an unprecedented maximum distance of 16.45mm which explains the large variations present among local as well as global [22] populations . The IP to CI distance varies with respect to the three maxillary arch forms. The results of this study support the findings of a local study by Zia et al who recorded the mean distances for ovoid and square arch forms as 11.2mm and 10.5mm respectively. However, the highest mean distance recorded was for the tapered [8] arch form (13.0mm) . Moreover, the readings of the present study are in converse to an international study by Avhad et al who found the distances as 9.99mm, 9.67mm and 10.91mm for the ovoid, square and tapered [4] arches respectively .
Among the genders, the highest mean distance was recorded for the tapered arch form in the male group as 11.66mm while the lowest distance was recorded for the square arch form in the female group as 10.37mm. This was synchronous with Zia et al who also recorded the highest mean distance for the male tapered arch (13.0mm) and the lowest distance for the [8] female square arch (10.0mm) . The readings of this study were more in coherence with those of local Zia et al than those of Avhad et alsince the population [4,8] characteristics were more or less the same . Overall, the ovoid arch form showed the highest frequency, suggesting its greater need in Prosthodontics as well as the highest mean distance indicating that artificial tooth for this arch form should be positioned farther from the IP than the tooth position for tapered and square arch forms.

CONCLUSION:
The aim of a Prosthodontist is to provide esthetically pleasing complete dentures to edentulous patients, which emphasizes the need to accurately position the maxillary anterior teeth. The distance of CI to IP in dentate subjects varies with the three maxillary arch forms and provides a guide for tooth positioning in edentulous patients.In this study, ovoid arch was the most frequently occurring arch form in dentate subjects. In addition, the mean distance recorded was highest for ovoid arch followed by tapering arch and least for square arches.

CONFLICT OF INTEREST:
All authors declare no conflict of interest.

REFERENCES:
1. Valdez R, Aarabi G, Spinler K, Walther C, Seedorf U, Heydecke G, et al. Association between Subjective Well-Being and Frequent Dental Visits in the German Ageing Survey. International Journal of