The effect of anterior tooth retraction on lip position of orthodontically treated adult Indonesians

ORIGINAL ARTICLE

The effect of anterior tooth retraction on lip position of orthodontically treated adult Indonesians Joko Kusnoto, DDS, MS,a and Hendro Kusnoto, DDS, PhDb Jakarta, Indonesia This study was conducted to determine upper and lower lip changes after orthodontic treatment of bimaxillary dental protrusion in adult Indonesians. Pretreatment and posttreatment cephalograms of 40 patients (6 males and 34 females) who required extraction of 4 premolars, were traced, superimposed, and measured. The changes of anterior tooth position (measured as the horizontal distance from the incisal tip to a constructed vertical through sella) were correlated with changes in the upper and lower lip positions with the Pearson correlation method. Significant positive correlation was found between changes of the maxillary and mandibular incisors with the changes in both the upper lip (rU1 = 0.39, P < .05; rL1 = 0.44, P < .01) and the lower lip (rU1 = 0.44, P < .01; rL1 = 0.51, P < .01) positions. By using stepwise multiple regression, it was found that for every millimeter of mandibular incisor retraction, 0.4 mm of upper lip retraction and 0.6 mm of lower lip retraction were produced. This study concluded that, for this Indonesian sample, a strong correlation exists between mandibular anterior tooth retraction and the position of both lips. (Am J Orthod Dentofacial Orthop 2001;120:304-7)

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oft tissue profile changes as a result of orthodontic reduction of bimaxillary protrusion are expected when the main treatment objective is to decrease convexity of the lower face and fullness of the lips. To achieve that objective, retraction of the maxillary and mandibular anterior teeth becomes a very important factor, and extractions are often planned to create room for retraction of the anterior teeth. This study examines the effect of maxillary and mandibular anterior teeth retraction on reduction of soft tissue bimaxillary protrusion in the Indonesian population. This information is of interest because Indonesia’s population is the fourth largest in the world and shares many common facial characteristics with Southeast Asian populations. Most Indonesians have similar facial features except for those from the eastern region who have Aboriginal traits. Bimaxillary protrusion is a common facial characteristic, but the effect of orthodontic treatment on bimaxillary protrusion for Southeast Asian populations has only limited documentation.1,2 It is also necessary to have this information to form a baseline for creating computer simulations of treatment results for Southeast Asian patients. Hard tissue changes involving the lower third of the face affect the soft tissue drape, namely the lips, the

From the College of Dentistry, Trisakti University, Jakarta, Indonesia. aFormer student. bProfessor, Department of Orthodontics. Reprint requests to: Joko Kusnoto, Musi 27, Jakarta 10150, Indonesia. Submitted, July 2000; revised and accepted, January 2001. Copyright © 2001 by the American Association of Orthodontists. 0889-5406/2001/$35.00 + 0 8/1/116089 doi:10.1067/mod.2001.116089

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nasolabial angle, and the labiomental angle.3,4 In white individuals, soft tissue changes follow the extraction of 4 premolars. In one study, 95% of patients with 4 premolars extracted had decreased lip protrusion, whereas the nasolabial angle increased by 5.2°, the upper lip retracted 3.4 mm to the E-line, and the lower lip retracted 3.6 mm to the E-line.5 In another study of white subjects, a 1:3.8 ratio was found between upper lip retraction and incisor retraction.6 It was also found that maxillary incisor retraction caused upper lip retraction, increased lower lip length, and increased the nasolabial angle,7 whereas the mandibular incisor position determined lower lip position and shape.4 In African Americans, a ratio of 1.75:1 between mandibular incisor retraction and retraction of the lower lip was reported (r = 0.70, P < .05). A weak relationship was found between upper lip retraction and retraction of the maxillary incisors (r = 0.42, P < .05). It was also concluded that the mandibular incisor was the only hard tissue variable that could be used as a predictor in a regression model to explain lip response to orthodontic therapy.8 In 18- to 26-year-old Chinese subjects, a significant correlation existed between maxillary incisor retraction and upper lip retraction (r = 0.73, P < .01), as well as between mandibular incisor retraction and lower lip retraction (r = 0.80, P < .01). The nasolabial angle increased by 10°.1 In most of these studies, horizontal changes in dentoskeletal structure and soft-tissue profile were assessed by using a reference line through sella perpendicular to the line sella-nasion minus 7° to approximate the true horizontal.2,7-11 The similarity in methods facilitates comparison between studies.

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Table I. Results of t test between 2 operators’ measurements

Maxillary incisor change (mm) Mandibular incisor change (mm) Upper lip change (mm) Lower lip change (mm) Nasolabial angle change (°) Labiomental angle change (°)

Mean

SD

SE

P

r

–0.13

0.46

0.07

.10*

0.98

–0.08

0.27

0.04

.08*

0.99

–0.15

2.97

0.47

.75*

0.76

0.55

3.28

0.52

.30*

0.76

–0.70

8.74

1.38

.62*

0.55

–0.55

3.00

0.47

.25*

0.88

*No significant differences (P > .05).

Table II. Results

of t test between pretreatment and posttreatment measurements Pretreatment Mean

SD

Posttreatment Mean

Change

SD Mean

SD

P

Maxillary incisor 78.6 5.22 72.9 5.15 5.70 distance (mm) Mandibular incisor 74.9 5.13 69.9 5.20 5.00 distance (mm) Upper lip distance 89.5 5.05 85.0 5.13 4.48 (mm) Lower lip distance 86.9 6.10 80.8 5.90 6.08 (mm) Nasolabial 97.0 13.29 104.8 14.08 –7.75 angle (°) Labiomental 129.1 17.37 136.4 17.52 –7.25 angle (°)

2.32

.00*

2.63

.00*

2.43

.00*

3.15

.00*

7.08

.00*

5.80

.00*

*Significant changes (P < .05).

MATERIAL AND METHODS

Records of 40 orthodontic patients, 6 males and 34 females who had their 4 first premolars extracted, were obtained. The selection criteria for those patients were as follows: 1. Indonesian ethnic group with a Class I malocclusion and skeletal bimaxillary protrusion 2. A minimum age at the beginning of treatment of 15 years (mean age 18 years) to reduce growth effects 3. Availability of a good quality pretreatment lateral cephalogram taken immediately before the active orthodontic treatment started and a posttreatment lateral cephalogram taken immediately after active orthodontic treatment ceased All patients who accepted extraction treatment for profile reduction and fulfilled the other selection crite-

Fig 1. Reference line and landmarks: R, Reference line; 1, most anterior point of upper lip to reference line; 2, maxillary incisor tip to reference line; 3, mandibular incisor tip to reference line; 4, most anterior point of lower lip to reference line; 5, nasolabial angle; 6, labiomental angle.

ria were included in this study. All patients were treated by 1 operator (H.K.) who planned to reduce lip fullness by using continuous maxillary and mandibular preadjusted 0.018 slot edgewise appliances with sliding mechanics and no extraoral anchorage. Both pretreatment and posttreatment lateral cephalograms were taken in a natural head position with the lips relaxed. Each lateral cephalogram was traced and a reference line was established (a constructed line perpendicular to sella-nasion minus 7° through sella) (Fig 1). Linear measurements were made with a millimeter ruler from 4 landmarks—the maxillary incisor tip, the mandibular incisor tip, the most anterior point of the upper lip, and the most anterior point of the lower lip to the reference line. Two angular measurements (the nasolabial and labiomental) were measured with a protractor (Fig 1). Two operators (H.K. and J.K.) carried out this process on 2 separate occasions; a paired 2-tailed t test, at the P = .05 level, to assess measurement error, as recommended by another author, showed no significant difference between the 2 operators’ measurements (Table I).12 RESULTS

The means, SDs, and P values between pretreatment and posttreatment measurements are given in Table II. All linear and angular measurement showed

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American Journal of Orthodontics and Dentofacial Orthopedics September 2001

Table III. Correlations between hard tissue and soft tissue

changes Maxillary incisor changes r Upper lip changes Lower lip changes Nasolabial changes Labiomental changes

0.39* 0.44** 0.01 0.04

Mandibular incisor changes

P

r

P

.01 .01 .97 .78

0.44** 0.51** –0.02 0.15

.01 .00 .92 .36

*Correlation significant at 0.05 level; **correlation significant at 0.01 level.

Fig 2. Typical pretreatment and posttreatment profile views.

statistically significant changes (P < .05). The Pearson correlation test (Table III) showed significant positive correlation between changes in the maxillary and mandibular incisor position with the changes in the upper lip position (rU1 = 0.39, P < .05; rL1 = 0.44, P < .01) and lower lip (rU1 = 0.44, P < .01; rL1 = 0.51, P < .01) position. Stepwise multiple regression showed that a 1-mm mandibular incisor tip retraction will produce a 0.4-mm retraction of the most anterior point on the upper lip and a 0.6-mm retraction of the lower lip. DISCUSSION

The assessment of horizontal changes in dentoskeletal and soft tissue relationships was performed with the use of a reference line through sella perpendicular to sellanasion minus 7°, a technique commonly used to approximate true horizontal and minimize variability. 2,7-11 Accurate prediction of changes in the soft tissue profile after orthodontic treatment is desired, especially for malocclusions characterized by bimaxillary protrusion. Wide variability exists between racial groups, but most of the studies regarding soft tissue profiles have been carried out with white subjects. The findings of this study can be used as a source of quantitative information for the orthodontist, the patient, and the patient’s family about profile changes that may occur as a result of orthodontic treatment in Indonesian patients or other Southeast Asian groups. When treating malocclusions with bimaxillary protrusion, it is assumed that the upper and lower lips will move back, while the nasolabial and labiomental angles increase as a result of the orthodontic retraction of the maxillary and mandibular incisors. In this study, significant posterior movement of the upper and lower lips occurred with simultaneous significant increases of the nasolabial and labiomental angles. Clinical obser-

vation showed that, after treatment, bimaxillary protrusion was reduced, as was lip strain (Fig 2). The results showed that only mandibular incisor retraction correlated with upper and lower lip change, a result that agrees with several other studies of white and African American samples.4,8,9 This study failed to show a correlation between maxillary or mandibular incisor retraction with nasolabial or labiomental angle changes, which is in agreement with Waldman’s study of a white sample.6 This study also failed to show a correlation between maxillary incisor retraction and upper lip retraction in a Chinese population.1,2 As expected, mandibular incisor retraction was found to influence lower lip retraction. Curling of the lower lip may support the upper lip and influence upper lip changes. If the lower lip moves back, curling of the lower lip will be reduced, and the upper lip may follow. Movement of the upper lip is less predictable because it may be influenced by the lower lip and may also be related to the attachment of the lip to the nose. CONCLUSIONS

Significant posterior movement of the upper and lower lips and increased nasolabial and labiomental angles after orthodontic treatment of bimaxillary protrusion were found in this study. For this Indonesian sample, a strong correlation existed between mandibular anterior tooth location and changes in the positions of both lips. REFERENCES 1. Lew K. Profile changes following orthodontic treatment of bimaxillary protrusion in adults with Begg appliance. Eur J Orthod 1989;11:375-81. 2. Tan TJ. Profile changes following orthodontic correction of bimaxillary protrusion with a preadjusted edgewise appliance. Int J Adult Orthod Orthognath Surg 1996;11:239-51. 3. Kusnoto H. Soft tissue profile changes after orthodontic treatment in class III malocclusion. Ind Dent Assoc J 1994;43:72-6. 4. Roos N. Soft tissue profile changes in class II treatment. Am J Orthod 1977;72:165-75.

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5. Drobocky OB, Smith RJ. Changes in facial profile during orthodontic treatment with extraction of four first premolars. Am J Orthod Dentofacial Orthop 1989;95:220-30. 6. Waldman BH. Change in lip contour with maxillary incisor retraction. Angle Orthod 1982;52:129-34. 7. Talaas MF, Talaas F, Baker RC. Soft-tissue changes resulting from retraction of maxillary incisors. Am J Orthod Dentofacial Orthop 1987;91:385-94. 8. Caplan MJ, Shivapuja PK. The effect of premolar extractions on the soft tissue profile in adult African American females. Angle Orthod 1997;129-36.

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9. Assuncao ZLV, Cappelli J, Almeida MA, Bailey LJ. Incisor retraction and profile and profile changes in adult patients. Int J Adult Orthod Orthognath Surg 1994;9:31-6. 10. Kokodynski RA, Marshall SD, Ayer W, Weintraub NH, Hoffman DL. Profile changes associated with maxillary incisor retraction in the postadolescent orthodontic patient. Int J Adult Orthod Orthognath Surg 1997;12:129-34. 11. Rains MD, Nanda R. Soft tissue changes associated with maxillary incisor retraction. Am J Orthod 1982;81:481-8. 12. Houston WJB. The analysis of errors in orthodontic measurements. Am J Orthod 1983;83:382-90.

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