A clinical evaluation of techniques to determine the combined width of the maxillary anterior teeth and the maxillary central incisor

A clinical evaluation of techniques to determine the combined width of the maxillary anterior teeth and the maxillary central incisor Forrest R. Scandrett, D.D.S., M.S.,* Zerxis R. Umrigar, B.D.S.

Paul E. Kerber,

M.A., Ph.D.,**

and

University of Iowa, College of Dentistry, Iowa City, Iowa, and Bombay, India

I

t is difficult to determine the dimensions of the maxillary anterior teeth for an edentulous patient when preextraction records are not available. While various methods may enable dentists to select teeth that are generally suitable for the patient, the most esthetic result is probably obtained by the dentist who believes that anterior tooth selection is as much an art as it is a science.“? It requires a knowledge and an understanding of a number of physical and biological factors that are directly related to each patient as an individual. In the early part of this century, most methods involved “hunt and peck” or “trial and error” until the patient and dentist were satisfied with the particular size of a tooth.3 Later methods revealed a dependence on physical characteristics of the dentofacial form.4-8 While numerous methods have been suggested for estimating the combined width of the maxillary anterior teeth and the central incisor, there seem to be few reliable guidelines and many conflicting views.9“8 The purpose of this study was to evaluate the following methods for predicting the width of the maxillary anterior teeth and central incisors. They were intercommissural width, interalar width, bizygomatic width, sagittal cranial diameter, interbuccal frenum distance, philtrum width, and age. It was hypothesized that two or more of these predictor variables would provide a better prediction of maxillary tooth width than any of them individually.

MATERIAL

AND METHODS

Ninety subjects (45 women and 45 men) who met the following criteria were included in this study: (1)

Fig. 1. Cast with facial screens prepared from temporary splint material. they were all Caucasians; (2) they had permanent maxillary anterior and premolar teeth; (3) they had no history of orthodontic treatment; (4) they did not have more than one full or one three-fourths crown in the maxillary anterior and premolar teeth; (5) they did not have proximal restorations that grossly affected the width of the maxillary anterior teeth; (6) they were all above 18 years of age, so facial growth was essentially complete; and (7) the corner of the mouth was situated superiorly to the horizontal occlusal plane. At the first visit, an irreversible hydrocolloid impression of the maxillary arch was made with extra care to record the buccal frena. All impressions were poured immediately in Class I dental stone. On this cast, two removable facial screens were fabricated using an Omnivac vacuum adaptor (Omnidental Corp., Harrisburg, Pa.) and 0.02-inch temporary splint material. Each screen covered the canine

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Fig. 2. Facial screens covered with film of inlay casting wax. Fig. 5. Interalar width

measurement.

Fig. 3. Sagittal cranial diameter measurement with caliper aligned above midline of subject’s cranium. Fig. 6. Width of philtrum level.

Fig. 4. Bizygomatic width

measurement.

and premolars and the facial alveolar mucosa with relief for the buccal frenum (Fig. l), and each screen was covered with a film of inlay wax so that the corners of the mouth and buccal frena could be clearly marked (Fig. 2). At the second visit, measurements of the following items were obtained with anthropometric calipers and 16

measurement

for inferior

Fig. 7. Corner of mouth marked on facial screen with pointer. a Boley gauge: (1) sagittal cranial diameter (Fig. 3), (2) bizygomatic width (Fig. 4), (3) interalar width (Fig. 5), and (4) philtrum width, superior and inferior (Fig. 6). The measurements were repeated four times in the above order and recorded on a tape recorder. The buccal screens were placed in the subjects’ mouths, and JULY

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Fig. 8. Location screen.

WIDTHS

of buccal

frenum

marked

on facial

Fig. 11. Dental tape sectioned by Bard Parker No. 21 (Bard-Parker, Rutherford, N.1.)

blade

frenum(arrorc5).

Fig. 10. Commissure and buccal frenum ferred to cast furrows).

marks trans-

the corners of the mouth and buccal frena were marked (Figs. 7 and 8). The screens were then repositioned onto the cast (Fig. 9), and the marks were transferred to the cast with the aid of a sharp pointer (Fig. 10). The width of the six maxillary anterior teeth, intercommissural width, and interbuccal frenum distance on the cast were measured with dental tape and a Boley gauge. When measuring the width of the anteriTHE

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Fig. 13. Dental num distance.

tape placed

to obtain

interbuccat

fre-

or teeth, the tape was placed at the greatest facial curvature superoinferiorly and was sectioned and measured (Fig. 11). This was repeated four times (Fig. 12). The intercommissural width and interbuccal frenum distance were measured in a similar manner, but only one tape was used since the marks were relatively definite (Figs. 13 and 14). This tape was then measured four times. The greatest width of :he right and 17

SCANDRETT,

KERBER,

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.45

.40

.30

Fig. 14. Dental tape sectioned to obtain intercommissural width. .20

left central incisors individually was measured four times with a Boley gauge. RESULTS The Pearson Product Moment correlation coefficients were calculated for all predictor variables with the width of the maxillary anterior teeth and the left and right central incisor. For the purposesof this study, PI .05 for all statistical analyses was accepted as being statistically significant. The width of the maxillary anterior teeth was significantly correlated with all the predictor variables in this study except age (Fig. 15). However, none of the significant correlations was significantly different from any other. The largest significant correlation was 0.444 with intercommissural width, and the lowest significant correlation was 0.287 with bizygomatic width. The right central incisor was significantly correlated with the intercommissural width, interalar width, interbuccal frenum distance, and the sagittal cranial diameter (Fig. 16). The largest significant correlation coefficients were not statistically different from each other. The correlation with bizygomatic width was 0.185 and was not consideredsignificant. The left central incisor was significantly correlated with the intercommissural width, interalar width, and interbuccal frenum distance (Fig. 17). The largest significant correlation was 0.299 with interbuccal frenum distance.These three correlations were not significantly different from eachother. Again, the correlation with bizygomatic width was small, 0.153, and not significant. All predictor variables with significant correlations lacked sufficient magnitude, and their standard errors of prediction were too large to justify their usealone as

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.lO

!

4

Inslgnificant

Y

Fig. 15. Correlations for width of maxillary anterior

teeth with intercommissural width, interalar width, interbuccal frenum distance, sagittal cranial diameter, width of philtrum (superior and inferior levels), bizygomatic width, and age, arranged in order of magnitude of correlation. predictors for estimating the width of the maxillary anterior teeth or central incisors. Therefore, a stepwise multiple regressionprocedure was instituted. Predictor variables were combined until the addition of another variable did not make a statistically significant contribution to the prediction. For the width of the maxillary anterior teeth, the best model of predictor variables was interalar width, intercommissural width, age, and interbuccal frenum distance.For the left central incisor, the bestmodel was interbuccal frenum distance and interalar width. For the right central incisor, the best model was intercommissural width and interbuccal frenum distance. Each model had its own equation (Fig. 18). The hypothesis that two or more of the predictor variables would provide a better prediction of the width of the maxillary anterior teeth and maxillary central

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.40 401

.3c

.2( 2G

. 11

t Statistically

Significant

Insignificant

Statistically

Siznificant

Insioniticant

Fig. 16. Correlations for width of right maxillary central incisor with intercommissural width, interbuccal frenum distance, interalar width, sagittal cranial diameter, bizygomatic width, width of philtrum (superior and inferior levels), and age, arranged in order of magnitude of correlation.

Fig. 17. Correlations for width of left maxillary central incisor with interbuccal frenum distance, interalar width, intercommissural width, ssgittal cranial diameter, bizygomatic width, width of phi&rum (superior and inferior levels), and age, arranged in order of magnitude of correlation.

incisors was accepted as true. The correlation coefficient was increased from 0.444 to 0.596 for the width of the maxillary anterior teeth, while the correlations for the left and right maxillary central incisors were increased from 0.299 to 0.362 and from 0.334 to 0.394, respectively (Fig. 19). The standard error of prediction for the regression equations was 2.4 mm for the maxillary anterior teeth, 0.5 mm for the left central incisor, and 0.6 mm for the right central incisor. Sixty-six percent of the time, the predicted values will be within these distances of the actual width of the patient’s natural maxillary anterior teeth (Fig. 20).

mean (Fig. 21). The superior and inferior width of the philtrum were found to have the largest percentage standard error. This confirmed the difficuhy in clinically obtaining the measurement. Consequently, the width of the philtrum did not appear as part of a predictor model in any multiple regression equation. All the other variables showed a comparatively minimum error of measurement. The intercommissural width had the highest correlation, 0.44, with the width of the maxillary anterior teeth. This was in agreement with the study by Lieb et al.,‘” who found a significant correlation of +0.45. Yet, in our study, the intercommissural width was not significantly higher than other predictors. Therefore, with a replication of this study, its position as the best predictor might not be retained. The biometric ratio of 16: 1 for the relationship

DISCUSSION The standard error of measurement was calculated for each measurement procedure as a percentage of the

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SCANDRETT,

Dependent

variable

Best

predictor

models

Multiple

regression

KERBER,

0.314 (interalar) + 0.195 (intercommissural) - 0.018 (age) + 0 -096 (interbuccal frenum) + 3.247

of left incisor

interbuccal frenum distance, interalar width

0.023 (interbuccal + 0.035 (interalar) + 0.601

of right incisor

intercommissural width, rnterbuccal frenum distance

0.033 (intercommissural) + 0.024 (interbuccal frenum) + 0.560

of

Width central

Width central

maxillary teeth

UMRIGAR

equation

interalar width, intercommissural width, age, interbuccal frenum dist ante

Width anterior

AND

frenum)

Fig. 18. Stepwise multiple regression procedure results.

Dependent

Variable

Highest correlation coefficient of any single bred.

Multiple R

Teeth

0.444

0.596

0.299

0.362

0.334

0 -394

Maxillary

Anterior

Maxillary

Left Central

Maxillary

Right Central

All

statistically

Incisor Incisor

significant

at P <

0.05

Fig. 19. Evidence for acceptanceof major hypothesis.

between the width of the central incisor and the bizygomatic width was verified in this study. It was found to be 16: 1 for the left central incisor and 15.97: 1 for the right central incisor. Young,3 House and Loop, Berry,* and Wavrin” have previously reported this ratio to be 16: 1. However, theseauthors did not report standard deviations, correlation coefficients, or confidence limits. This ratio is the basis for the Trubyte Tooth Selector (Dentsply International, Inc., York, Pa.). Our study did not demonstratestatistically significant correlations of large magnitude, 0.185 and 0.153, between the bizygomatic width and the width of the central incisors. The biometric ratio of 16: 1 has little predictive value for a given individual because the

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magnitude of the correlation was small, indicating little individual relationship between bizygomatic width and central incisor width. If the correlation between these variables approached 1, the use of the biometric ratio would be justified for prediction, as the error of prediction would be quite small. Numerous biometric ratios between maxillary central incisor width and various parts of the body could be established, e.g., height, waist circumference, foot length, and chestsize. Yet, unlesstheir correlations are sufficiently large, they are of little value for predicting central incisor width for a given individual. A ratio does not estimate the error of prediction, nor doesit provide confidencelimits on the prediction. Thus, the use of the biometric ratio

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In % of thepatient’s

1.

would be within of the predicted

the population natural teeth

Maxillary

Anterior

Maxillary

Left

Central

Maxillary

Right

Central

of prediction

Variable

Interalar

width

width

Bi-zygomatic

width

Interbuccal Sagittal

frenum cranial

distance diameter

m.m. m.m. m.m. m.m.

0.2 0.4 0.6 1.1

m.m. m.m. m.m. m.m.

applied

to population.

Mean

S.E. of Measurement as o/, of Mean

0.1

48.5

0. lo%,

0.1

34.4

0.29%

0.7

136.5

0.53%

0.1

55.9

0.12%

1.2

105.3

C.63%

of philtrum

(supr)

0.5

8.2

h .45a

Width

of philtrum

(infr)

0.5

11.1

4.72%

Max.

anterior

teeth

0.2

53.61

0.27%

Max.

central

inc.

width

(rt)

0.0(4)*

8.6

0.46%

Max.

central

inc.

width

(It)

0 .o (4) *

8.5

0.467

a significant

width

digit

Fig. 21. Standard

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Width

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Standard Error of Measurement

Intercommissural

m.m. m.m. m.m. m.m.

Incisor

32% 50% 66% 95%

Fig. 20. Accuracy

1.0 1.6 2.4 4.7

Incisor

32% 50% 66% 95%

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m.m.

Teeth

32% 50% 66% 95%

2.

__ value.

error

of measurement

for all variables.

21

SCANDRETT,

of 16 : 1 to estimate the width of the central incisors is not based on sound statistical procedure and therefore should not be used. The inclusion of age as a predictive factor for the width of the maxillary anterior teeth was quite interesting. The relationship was inverse, indicating that, with an increase in age, there was a decrease in tooth size. This could possibly be attributed to interproximal wear and loss of tooth structure at the incisal edge through attrition and abrasion.

1. More than one variable was needed to predict the width of the maxillary anterior teeth and central incisors since no best single predictors were accurate enough for clinical application. 2. Multiple regression equations were calculated to predict maxillary anterior teeth width and central incisor width:

1

Boucher, C. 0.: Swenson’s Complete Dentures, ed 6. St. Louis, 1970, The C. V. Mosby Co., p 312. Fenn, H. R. B., Liddelow, K. P., and Gimson, A. P.: Clinical Dental Prosthetics, ed 2. London, 1961, Staples Press, pp 224-234. Young, H. A.: Selecting the anterior tooth mold. J PROSTHET DENT 4:748, 1954. Sears, V. H.: The art side of denture construction. Dent Digest 29:764, 1923. DeVan, M. M.: The appearance phase of denture construction. Dent Clin North Am 1:225, 1957. Kra,jicek, D. D.: Natural appearance for the individual denture patient. J PROSTHET DENT 10:205, 1960. House, M. M., and Loop, J. L.: Form and Color Harmony in the Dental Art. 1939, Whittier. Berry, F. H.: Is the theory of temperatures the foundation of the study of prosthetic art? Dent Mag 1:405, 1905-1906. Williams, L. J.: A New Classilication of Natural and Artificial Teeth. New York, 1914, Dentists Supply Co. Clapp. G. N.: Prosthetic Articulation. New York, 1914, Dentists Supply Co. Wnvrin, J. A.: A simple method of classifying face form. Dent Digest Z&331-335, June 1920; 414-419, July 1920; 531-537, August 1920. Nelson, A. A.: Aesthetic triangle in arrangement of teeth, face form, tooth form, and alignment form. Harmonious or grotesque? J Am Dent Assoc 9:392, 1922. Sears, V. H.: An analysis of art factors in full denture construction. J Am Dent Assoc 25~3, 1938. Justi, H. D. and Sons: A Manual for Plastic Teeth, ed 6. Philadelphia, 1964. H. D. Justi and Sons. Dentists Supply Co.: Trubyte Bioform Teeth. New York, 1955, Dentists Supply Co. Swenson’s Mould Selector: Swenson’s Complete Dentures, ed 4. St. Louis, 1959, The C. V. Mosby Co., p 339. Stein, hI. R.: Co-ordinate system of specification of artificial teeth. J .4m Dent Assoc 30:276, 1943. Dentists Supply Co.: Trubyte Tooth Indicator. New York, 1951, Dentists Supply Co. I,ieb, N., Silverman, S., and Garlinkel, L.: An analysis of soft tissue contours of the lips in relation to the maxillary cuspids. J Ptwsrm’r DENT 18:292, 1967.

2

3 4 5 6 7 8

IO 1 I.

12

13.

Width of maxillary anterior teeth

= 0.314 (interalar) +0.195 (intercommissural) -0.018 (age) +0.096 (interbuccal frenum) +3.247

14. IS. I6

Width of left maxillary central incisor

= 0.023 (interbuccal +0.035 (interalar)

Width

= 0.033 (intercommissural) +0.024 (interbuccal frenum) +0.56

of right

maxil-

lary central incisor

frenum) +0.601

All measurementsare in millimeters, and the intercommissural width and interbuccal frenum distance are measuredaround the occlusion rim. 3. The useof the biometric ratio of 16: 1 to estimate the width of the maxillary central incisor from the bizygomatic width in the edentulous patient, e.g., the

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UMRIGAR

REFERENCES

9

CONCLUSIONS

AND

Trubyte Tooth Selector, is not basedon sound statistical procedures. The ratio was reconfirmed, but the correlation was not of sufficient magnitude to justify the use of the 16: 1 ratio for an individual edentulous patient.

SUMMARY In this study, techniques to determine the combined width of the maxillary anterior teeth and the maxillary central incisor widths were evaluated. Measurements were obtained from the dental casts of 45 men and 45 women and related to their intercommissural width, interalar width, bizygomatic width, sagittal cranial diameter, interbuccal frenum distance, philtrum width, and age. Correlation coefficients were calculated for all relationships.

KERBER,

17. 18. 19.

lic~/ll-rrll

DR.

,‘c’qrtc’\l\

FORREST

UNIVERSITY COLLEGE IOWA

10: R. SCANDRETT

OF IOWA 0~

CITY,

DENTISTRY

IA 52242

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