The Orthodontic CYBERjournal
Effects of Premolar Extractions
Effects of Premolar Extraction on the Facial Profile of African Americans and Caucasians: A Comparative Study.
by Siobhan M. Sheehan, D.D.S., M.S.
Previous studies have considered changes in the integumental profile with orthodontic treatment.5- 9,21,25 Few studies have been concerned with the esthetic consequences of these changes or with differences in these changes between races. The objectives of this study were to quantify soft-tissue profile changes in Caucasians and African Americans treated orthodontically with extraction of four first premolars and compare results based on groupings by both race and sex.
In this investigation 16 linear and angular measurements were made from pre- and post-treatment lateral cephalometric radiographs of 40 Caucasian and 40 African American patients to analyze the soft-tissue profile. While it was shown that the upper and lower lips in all groups became less protrusive with treatment, comparison between groups found significant differences. It was found that the soft-tissue profile of the Caucasians and African Americans respond differently to first premolar extraction treatment. Comparison of male and female subgroups demonstrated differences with the Caucasian male showing the greatest soft tissue profile change. Caucasian patients displayed a greater amount of reduced lip protrusion than African Americans, shown to be significant (p<0.05) in the mean changes of A, Ls, Li, and B to E line, Li to S line, Li to H line, and LL to Sn-Pog plane. The mean changes in the measurements of the nasolabial angle were shown to increase 2.067 degrees and 1.495 degrees in the Caucasian and the African American patient, respectively. When profile changes were compared to values representing facial esthetic norms for each race, it was shown that a greater percentage of African American patients had soft-tissue profile measurements that remained satisfactory or improved. Excessive reduction was seen in 27% of the Caucasian group and 12.5% in the African American group.
A well-balanced and harmonious soft-tissue profile is an important consideration in orthodontic diagnosis and treatment planning. Extraction of premolar teeth is often necessary to achieve treatment goals. This often changes the soft-tissue profile which can be enhancing, or in some instances, detrimental.
The integumental profile of the African American demonstrates a greater protrusiveness when compared with the American Caucasian.1,2,3,4 Maxillary and mandibular arch protrusiveness in the African American is frequently treated by extraction of four first premolars to provide space for incisor retraction. This is usually accompanied by changes in the soft-tissue profile.
Although many studies have considered changes in the soft-tissue profile concomitant with four first premolar extraction treatment 5,6,7,8,9 , few have been directly concerned with whether these changes are desirable or undesirable. Further, there is little information comparing soft-tissue profile changes between Caucasians and African Americans. Since it is the responsibility of the orthodontist to treat each patient individually, post-treatment effects on the soft- tissue profile must be considered in the diagnosis. Therefore, a thorough knowledge of the individual's facial type is necessary for proper and comprehensive treatment planning.
The objectives of this study were to quantify then compare and evaluate soft-tissue profile changes in Caucasian patients and African American patients treated with extraction of four first premolars.
MATERIALS AND METHODS
A total of sixteen linear and angular measurements were made from pre- and post-treatment lateral cephalometric radiographs of 40 Caucasian patients (20 males, 20 females) and 40 African American patients (20 males, 20 females) treated in the Department of Orthodontics at the State University of New York at Buffalo School of Dental Medicine. Age range of patients at the beginning of treatment was 8 years 11 months to 22 years 11 months. Age range of patients upon completion of treatment was 12 years 5 months to 25 years 2 months.
Patients were selected according to the following criteria:
Quality of treatment results was not considered in case selection.
All pre- and post-treatment lateral cephalometric radiographs were taken by the same technician using a standard Broadbent-Bolton Cephalometer. A standard distance of 5 feet from the tube head to the sagittal plane of the patient's head was maintained. Radiographs were taken with attention to a relaxed lip posture and teeth in occlusion. Burstone10 advocates the relaxed position headplate as the most useful when evaluating anteroposterior lip position following orthodontic treatment. The closed lip position complicates prediction of soft-tissue profile changes as attempting to achieve closure may stretch and flatten the lips. Hillesund, Fjeld, and Zachrisson11 in a study addressing difficulties regarding the reproducibility of the soft-tissue profile, concluded that cephalograms taken with the lips relaxed and the teeth in occlusion appear to exhibit the most correct lip position and morphology.
Soft-tissue profile and hard tissue landmarks were traced from each lateral cephalometric radiograph by a single investigator utilizing 0.003 inch matte translucent acetate tracing paper and a 0.5 mm lead pencil.
I. The landmarks used in the study are defined as described by Scheideman and associates.11:
A. Hard Tissue:
B. Soft Tissue:
The lower lip is indicated as either Li or LL and the upper lip as Ls or UL in accordance with the abbreviation commonly used for a certain measurement. Legan and Burstone13 define Ls (Labrales Superius) as a point indicating the mucocutaneous border of the upper lip and Li (Labrale Inferius) as a point indicating the mucocutaneous border of the lower lip.
II. Four analytical lines were used in the study and drawn on the tracing paper. Specific measurements were made to these lines:
III. The angles used in the study were:
B. Soft Tissue:
The skeletal plane, Sella-Nasion, was utilized. A horizontal reference plane was constructed by drawing a line through Nasion 7 degrees up from the Sella-Nasion plane. (Figure 1) Measurements in the horizontal and vertical components were made to the various analytical reference lines with the lateral cephalometric radiograph oriented perpendicular to the horizontal reference plane. Linear measurements were made utilizing a Helios dial caliper measured to the nearest 0.025 mm. Angular measurements were measured to the nearest 0.1 degree with an Ormodent protractor.
ERROR OF METHOD:
Thirty-two radiographs, balanced over the four groups and of Caucasian females, Caucasian males, African American females, and African American males, were retraced and remeasured to evaluate tracing and measuring errors. A paired Student's t test with a p<0.05 level of significance was used to test stability significant differences between the reproducibility of measurements.
The first part of the statistical analysis measured changes in the sort-tissue profile during treatment. The values reported in this section were calculated by subtracting the pre-treatment measurement of each variable from the post-treatment measurement. Therefore, retraction of the lips relative to the E line, S line, H line, and Sn-Pog plane would have negative values and increased protrusion would be positive. A change in the lower lip to E line from a pre-treatment measurement of -1.975 mm to a post-treatment measurement of -4.275 mm would be recorded as (-4.275) - (-1.975) = -2.3mm. A change in the nasolabial angle from a 114.0 degree pre-treatment value to a 117.0 degree post-treatment value would be recorded as 117.0-114.0=3.0. Thus, a nasolabial angle that becomes more obtuse during treatment would exhibit a positive value for the change. The results for this section of the analysis are reported as descriptive statistics. Frequency distributions are used to evaluate the proportions of each group. Four groups: 20 Caucasian females, 20 Caucasian males, 20 African American females, and 20 African American males are compared utilizing a two-way analysis of variance. A p<0.05 level of significance between Caucasians and African American, males and females, and among a race-gender combination.
The second part of the statistical analysis concerns the esthetic outcome of soft-tissue profile changes, therefore, the establishment of norms for pleasing and harmonious soft-tissue profiles of both Caucasians and African Americans is necessary. Pleasing facial esthetics appear to change with age22and measurements of various soft-tissue landmarks can be age related. Measurement of the upper and lower lips to the E line can differ in early adolescence and adulthood.16 Therefore, three measurements less influenced by age have been selected to evaluate facial esthetics: the nasolabial angle, the measurement of the upper lip to the Sn-Pog plane and the measurement of the lower lip to the Sn-Pog plane.
The Sn-Pog plane is a plane of minimal variation in the area of the face10: unlike the E plane, the S line, or the H line. For upper and lower lip protrusion to the Sn-Pog plane, values of +3.5mm with a standard deviation of 1.4mm for the upper lip, and +2.2mm with a standard deviation of 1.6 for the lower lip, have been shown to be esthetic in the Caucasian.10 This establishes a desirable range for upper lip to Sn-Pog of +2.1 to +4.9 mm and lower lip to Sn-Pog of +0.6mm to +3.8mm for Caucasian patients. Norms for upper and lower lip protrusion to the Sn-Pog plane in African American patients have been established by Flynn and associates.23 For upper and lower lip protrusion to the Sn-Pog plane, values of +8.6mm and +6.9mm, respectively, have been found to be ideal; with a standard deviation of +1.8mm and +2.7mm. Thus, a desirable range for the African American orthodontic patient is defined as +6.8mm to +10.4mm for the upper lip to Sn-Pog, and +4.2mm to +9.6 for the lower lip to Sn-Pog plane.
From an esthetic viewpoint, the measurement of the nasolabial angle is clinically useful10. Several studies of normal faces or pleasing profiles have established desirable values for the nasolabial angle.12,13,23,24 Ranges used in this study for a desirable nasolabial angle for both the Caucasian and the African American have been established utilizing the means and standard deviations of the nasolabial angles for Caucasian females, Caucasian males, African American females, and African American males as indicated by Connors and Moshiri.24 These ranges are: 94.352 to 114.178 degrees for the Caucasian patient, and 59.973 to 93.347 for the African American patient.
A direct comparison of pre- and post-treatment values of the nasolabial angle, upper lip to Sn-Pog and lower lip to Sn-Pog were made since a single measurement cannot, itself, be interpreted as desirable or undesirable, The chi-square distribution was used.
Table I lists results of the paired Student's t test for retracing and remeasuring errors. There were no statistically significant differences between first and second measurements for 15 of the 16 variables. The measurement of lower lip to the H line was significant
at p=0.006. Hillesund, Fjeld, and Zachrisson11 state that sources of errors of measurement are likely to be greater for cephalometric soft-tissue landmarks than for hard, due to the less well defined anatomic structures and variations introduced by facial expressions. They found that the reproducibility of Steiner's S point was very good. Both the S line and E line were equally reproducible and exhibited less variability than Holdaway's H line. This finding appears to apply to this present investigation. A consistently smaller measure was obtained when lower lip to H line was measured a second time. Since the other measurements of lower lip to various soft tissue reference lines were reproducible, it appears that an error in redrawing the H line may have contributed to the error in measurement.
Descriptive statistics for changes in the soft-tissue profile following orthodontic treatment with extraction of four first premolars were calculated form observed values for each measurement and are listed in Tables II-VI. Data is presented for nine separate groups as follows: 40 Caucasian subjects and 40 African American subjects(Table II); 40 female subjects and 40 male subjects(Table III); 20 Caucasian female subjects and 20 Caucasian male subjects(Table IV); 20 African American female subjects and 20 African American male subjects(Table V);and all 80 subjects as a single group(Table VI).
The mean changes in measurements of lip protrusion indicate the lips became less protrusive as a result of orthodontic treatment. The upper and lower lips moved back relative to the E line an average of 2.97 mm and 3.22 mm in the Caucasian group and 1.95 mm and 1.71 mm in the African American sample. In regard to the S line, the lips of both the Caucasian and African American samples retracted. The Caucasian group displayed upper lip retrusion averaging 1.70 mm and lower lip 2.40 mm. Retraction in the African American group averaged 1.51 mm and 1.41 mm respectively. The lower lip moved back in both groups when measured against the H line. The Caucasian group displayed 1.12 mm lower lip movement and the African American group an average of 0.41 mm. Finally, upper and lower lips of both groups moved back relative to the Sn-Pog plane.
Frequency distribution of changes of these measurements for the Caucasian and African American samples were listed in Tables VII and Table VIII. In the Caucasian sample frequency distribution percentages for these seven measurements were highly skewed toward negative values (reduction in protrusion). It was shown that 91.8 % of the this group exhibited reduced lip protrusion while only 7.5% displayed an increase in lip protrusion. Frequency distribution percentages for the African American sample were also skewed toward negative values, but not as highly as the Caucasian group. A reduction in lip protrusion was displayed in 73.93 % while 25.71% exhibited an increase.
The nasolabial angle had a mean increase of 1.78 degrees in the total sample population. The Caucasian group exhibited a mean increase of 2.07 degrees while the African American group displayed a mean increase of 1.5 degrees. Variability in the magnitude of changes in individuals was evident as frequency distributions for the Caucasian sample revealed that 23 patients (57.5 %) had nasolabial angles that became more obtuse during treatment, 14 patients (35 %) the angle became more acute, and 3 patients (7.5 %) remained unchanged. In African American patients the nasolabial angle became more obtuse during treatment in 26 (65%) while 14 patients (35 %) became more acute.
The labiomental angle exhibited a mean decrease of 2.8 degrees in the total population sample. Caucasians displayed an average decrease (closing of the angle) of 1.6 degrees while African Americans showed a mean decrease of 3.9 degrees. Again the variability in response to treatment was exhibited. Twenty Caucasians (50 %) had angles which became more acute, 18 (45 %) displayed angles which became more obtuse, and 2 patients (5 %) no change. Twenty-five African Americans (62.5 %) had labiomental angles which became more acute while in 15 patients (37.5 %) angles became more obtuse with treatment.
The H angle exhibited a mean decrease in the Caucasian and the African American populations by 2.81 degrees and 3.1 degrees respectively.
In the total sample, three vertical measurements of lip length: Sn-St; St-Me; and Sn-Me were shown to demonstrate an average increase, however, the Caucasian sample exhibited a mean decrease in upper lip length, Sn-St, by 0.19 mm. while the African American group revealed an average increase of 0.87 mm. Lower lip length, as measured by St-Me, was shown to increase in both the Caucasians and the African Americans by an average of 3.56 mm 3.16 mm respectively.
From Table II it can be seen that profile changes seem to be most substantial for the Caucasian group, particularly the Caucasian males.
Statistical differences for each variable between Caucasians and African Americans; males and females; and among a combination of all, are listed in Table IX. Interpretation of the data reveals significant differences between Caucasians and African Americans for 9 of the 16 variables. Five of these variables directly concern lip protrusion, one concerns upper lip length. The angle of convexity was shown to be significant between the two races. Significance was demonstrated between males and females in only 5 of the 16 variables. The three vertical measurements of lip length were significant as well as the angle of convexity. Significance among the combined group was evident only in the measurement of the lower lip to S line and the angle of convexity.
To evaluate the effects of changes in facial profile on facial esthetics pre- and post-treatment values of the nasolabial angle were analyzed using chi-square distribution (Table X) . In the Caucasian sample (N=40) 10 patients (25 %) began and finished treatment with values in the defined ideal range (94.35 degrees and 114.18 degrees). Six patients (15 %) had pretreatment values that were outside the normal range but were improved by treatment. Twenty-two patients (55 %) began and finished treatment with values outside the normal range; 2 of these individuals started and completed treatment with excessively acute nasolabial angles while 20 patients both began and finished with angles that were more obtuse than ideal. Two patients (5 %) started orthodontic treatment with nasolabial angles in the normal range, yet finished with angles more obtuse than the ideal.
In the African American sample (N=40) 10 patients (25 %) both began and finished treatment in the ideal range of 59.97 degrees and 93.35 degrees for the nasolabial angle. Nine individuals (22.5 %) exhibited pre-treatment values outside the ideal range but improved with treatment. Sixteen patients (40 %) began and finished treatment with nasolabial angles that were considered to be excessively obtuse. Finally, 5 patients (12.5 %) who began treatment with angles in the normal range, completed treatment with angles more obtuse.
The chi-square distribution for the upper lip to the Sn-Pog plane (Table XI) revealed that for the Caucasian sample, 9 patients (22.5 %) began and ended treatment in the ideal range of +2.1 - +4.9 mm. Seven patients (17.5 %) whose pretreatment values were outside the ideal improved with treatment. Thirteen individuals (32.5 %) exhibited pre- and post-treatment values that fell outside the ideal range. Ten of these individuals began and ended treatment below the normal range. Thus they started and finished with a less than ideal lip protrusion. Three patients both began and ended treatment with above normal measurements and therefore a greater amount of lip protrusion than normal. Finally, 11 Caucasians (27.5 %) who began treatment in the normal range, finished with measurements below normal; upper lips became less protrusive with treatment.
The chi-square distribution for the African American sample for the same measurement showed that 16 patients (40 %) began and finished treatment with upper lip to Sn-Pog plane values that were within the desired ideal range of +6.8 - =10.4 mm. In 8 patients (20 %) pre-treatment values were improved with treatment. Nine individuals (22.5 %) started and finished treatment out of the normal range, 7 (17.5%) of which both began and completed treatment with upper lips that exhibited less than the ideal protrusion. Two individuals began and finished treatment with a greater amount of upper lip protrusion that ideal. Seven (17.5 %) demonstrated pre-treatment values that were within the normal range, yet post-treatment values were not, 5 of these completed treatment with lips that were less protrusive than the ideal range, while 2 individuals finished with a greater lip protrusion than ideal.
Results for the chi-square distribution for the measurement of the lower lip to Sn-Pog plane for both the Caucasians and African Americans are listed in Table XII.
The two studies found in the literature with which this present investigation can be directly compared 6,7 concern only the Caucasian patient, thus, specific comparative remarks cannot be made about the African American patient. Drobocky and Smith7, in their investigation on changes in the facial profile of 160 Caucasian patients orthodontically treated with the extraction of four first premolars, found mean changes of -2.58 mm of A to E line, -3.44 mm for Ls to E line, -1.83 mm for B to E line, -2.24 mm for UL to Sn-Pog plane, -2.66 mm for LL to Sn-Pog plane, 2.15 mm for St-Me, and 2.78 mm for Sn-Me. These changes are all close to the values reported in Table II for the Caucasian group as were values reported by Finnoy, Wisth, and Boe6 for A, Ls, Li, and B to E line.
Comparing the nasolabial angle of the Caucasian sample in this study to Drobocky and Smith, one finds measurements of 2.067 and 5.23 degrees respectively. Although this change differs, it is consistent with their study and with Finnoy, Wisth, and Boe in that the angle increased with treatment. The increased nasolabial angle in the African American sample is consistent with the findings of Nelson5. The labiomental angle in this investigation had a mean change of -1.598 degrees in the Caucasian sample while the mean reported by Drobocky and Smith was 2.04 degrees. Mean changes for Sn-St also differed. This investigation found a mean decrease of 0.19 mm in Caucasians while Drobrocky and Smith had a mean increase of 0.77 mm. One possible reason for the difference is that the sample they used was four times the Caucasian sample used in this study. In this study the labiomental angle exhibited great variability in response to treatment in both races and does not appear to offer a reliable assessment of soft-tissue changes.
It was found in both the Caucasian and the African American groups, the upper and lower lips became less protrusive as a result of treatment. The Caucasian sample displayed the greater decrease in protrusion of both upper and lower lips. This was shown to be significant in seven of the nine variables that were utilized in evaluation. The lips of the African American population have been found to be normally more protrusive than those of Caucasians.1-4 It has been suggested that a strong tongue may contribute to the greater procumbency of the African American dentition.2 A significant difference in lip thickness has been reported in the two populations, with African Americans possessing thicker and longer lips.23,24,25 Thus, it would appear that response to treatment should differ. Thicker lips and stronger tongues may be contributing factors in the differing lip changes found in the Caucasian and African American groups in this investigation. The observation that 91.8 % of the Caucasian sample exhibited reduced lip protrusion as compared with 73.93 % of the African American sample indicates that orthodontic treatment in the African American does not produce as dramatic a result in lip changes as with the Caucasian. This observation is in agreement with Hambleton.18
Several studies have found significant lip length differences between the two groups, with African Americans displaying larger upper and lower lip lengths than Caucasians.23,24 In the present investigation, the mean changes of vertical lip length due to treatment differed between Caucasians and African Americans with the change in the upper lip length being statistically significant. The African American group showed a slight mean increase in upper lip length while the Caucasian group displayed a slight mean decrease with treatment. Statistically significant changes in all three measurements of vertical lip length were found between males and females.
A quantitative method was utilized in this investigation to evaluate the esthetic consequences of soft tissue changes due to orthodontic treatment with extraction of four first premolars. Although this study compared obtained values with established normal values for desirable esthetics for the Caucasian and the African American, results must be interpreted carefully. Investigations involving subjective evaluations of pleasing and non-pleasing soft tissue profiles have revealed differences in preference between the lay public and the orthodontic community. Therefore, normal values established by orthodontic research may not represent ideal esthetic values for everyone. Also, growth of the chin and nose in adolescents can serve to further change completed cases.
According to the findings in this study 27.5 % of Caucasian patients completed treatment with upper lips that were flattened, while 25 % completed treatment with flattened lower lips. These findings are considerably greater than those of Drobocky and Smith.7 These investigators reported that 15 % of the 160 patients completed treatment with flattened lip profiles. This occured even though their defined desirable ranges for upper and lower lip to Sn-Pog plane were slightly greater than used in this study. Again, sample size of the two investigations may contribute to the difference in findings. It was shown that 12.5 % of the American Black group displayed flatter lips after treatment, while just 7.5 % exhibited flatter lower lips. In those individuals whose initial UL to Sn-Pog measurements were out of the desired range, 32.5% of the Caucasians and 22.5% of the African Americans remained outside the desired range after treatment. In the lower lip measurement LL to Sn-Pog, 42.55 in the Caucasians and 22.5% of the African Americans remained outside the desired range. They may have moved closer but failed to fall within the range.
In the nasolabial angle measurements excessively obtuse angles (possibly due to over flattened upper lips) were seen in 5% of the Caucasian and 12.5% of the African American groups. In those individuals with initial nasolabial angles outside the desired range, 55% of the Caucasians and 40% of the African Americans remained outside the desired range. Again, they may have improved but still did not reach the desired range of measurements..
Comparing treatment results in the Caucasian sample and the African American sample with defined normal values for soft tissue profile esthetics for each population demonstrated distinct differences between the two groups. The African American group was less likely to exhibit excessive lip flattening with treatment. Only 12.5% of this group could be defined as excessively flat after treatment. Sixty-seven and one-half percent had soft tissue measurements that suggested the profile had either improved or remained satisfactory. However, 27.5% of the Caucasian group could be classified as having excessively flattened soft tissue profiles and only 40% could be described as improved or remaining satisfactory. The esthetic outcome of orthodontic treatment involves many variables. Individual growth potential and patient compliance are two examples. Also, comparing individuals with ideal standards for specific measurements can introduce inconsistencies. Some individuals may display ideal lip position, however their nasolabial angle may be considered to be too obtuse when compared to the defined ideal. It seems that facial esthetics cannot be evaluated from a completely objective approach. Some degree of subjectivity remains necessary when evaluating the final outcome of the soft tissue profile following orthodontic treatment. The results of this study indicate that the integumental profile of Caucasians and African Americans react differently to orthodontic treatment with extraction of four first premolars. The ethnic make up of an individual as well as their presenting soft tissue features must be considered when this type of treatment is implemented.
1. Altemus LA. Comparative integumental relationships. Angle Orthod 1963; 3:217-21.
2. Drummond RA. A determination of cephalometric norms for the Negro race. Am J Orthod 1968;54:670-82.
3. Fonseca RJ, Klein WD. A cephalometric evaluation of American Negro women. Am J Orthod 1978;74:298-304.
4. Sushner NI. A photographic study of the soft-tissue profile of the Negro population. Am J Orthod 1977;72:373-85.
5. Nelson RI III. Facial soft-tissue profile changes in the North American Black with four first bicuspid extractions. Thesis, Howard University College of Dentistry, Dept. of Orthodontics, Washington, DC:1984.
6. Finnoy JP, Wisth PJ, Boe OE. Changes in soft-tissue profile during and after orthodontic treatment. Eur J Orthod 1987;9:68-78.
7. Drobocky OB, Smith RJ. Changes in facial profile during orthodontic treatment with extraction of four first premolars. Am J Orthod Dentofac Orthop 1989;95:220-30.
8. Park S, Kudlick EM, Abrahamian A. Vertical dimensional changes of the lips in the North African American patient after four first-premolar extractions. Am J Orthod Dentofac Orthop 1989; 96:152-60.
9. Roos N. Soft-tissue profile changes in Class II treatment. Am J Orthod 1977;72:165-75.
10. Burstone CJ. Lip posture and its significance in treatment planning. Am J Orthod 1967;53:262- 84.
11. Hillesund E, Fjeld D, Zachrisson BU. Reliability of soft-tissue profile in cephalometrics. Am J Orthod 1978;74-537-50.
12. Scheideman GB, Bell WH, Legan HL, Finn RA, Reisch JS. Cephalometric analysis of dentofacial normals. Am J Orthod 1980;78:404-20.
13. Legan HL, Burstone CJ. Soft tissue cephalometric analysis for orthognathic surgery. J Oral Surgery 1980;38:744-51. . 14. Ricketts RM. A foundation for cephalometric communication. Am J Orthod 1960; 46:330- 57.
15. Ricketts RM. Planning treatment on the basis of the facial pattern and an estimate of its growth. Angle Orthod 1957;27:14-37.
16. Ricketts RM. Esthetics, environment, and the law of lip relation. Am J Orthod 1966;54:272- 89.
17. Steiner OC. The use of cephalometrics as an aid to planning and assessing orthodontic treatment. Am J Orthod 1960;46:721-735.
18. Hambleton RS. The soft-tissue covering of the skeletal face as related to orthodontic problems. Am J Orthod 1964;50:405-20.
19. Holdaway RA. A soft-tissue cephalometric analysis and its use in orthodontic treatment planning. Part I. Am J Orthod 1983;84:1-28.
20. Holdaway RA. A soft-tissue cephalometric analysis and its use in orthodontic treatment planning. Part II. Am J Orthod 1984;85:279-93.
21. Lo FD, Hunter WS. Changes in nasolabial angle related to maxillary incisor retraction. Am J Orthod 1982;82:384-91.
22. Foster EJ. Profile preferences among diversified groups. Angle Orthod 1973; 43:34-40.
23. Flynn TR, Ambrogio RI, Zeichner SJ. Cephalometric norms for orthognathic surgery in Black American adults. J Oral Maxillofac Surg 1989;47:30-38.
24. Conner AM, Moshiri F. Orthognathic surgery norms for African American patients. Am J Orthod 1985;57:119-34.
25. Garner LD. Soft-tissue changes concurrent with orthodontic tooth movement. Am J Orthod 1974;66:367-77.
Dr. Sheehan is in private practice in Duxbury, Massachusetts.
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