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The effect of anterior tooth retraction on lip position of orthodontically treated adult Indonesians
Joko Kusnoto, DDS, MS,a and Hendro Kusnoto, DDS, PhDb
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)
oft tissue profile changes as a result of orthodon- tic 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 maxil- lary 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 protru- sion is a common facial characteristic, but the effect of orthodontic treatment on bimaxillary protrusion for Southeast Asian populations has only limited docu- mentation. It is also necessary to have this informa- tion to form a baseline for creating computer simula- tions 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.
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
nasolabial angle, and the labiomental angle. In white individuals, soft tissue changes follow the extraction of
4 premolars. In one study, 95% of patients with 4 pre- molars 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 posi- tion determined lower lip position and shape.
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 con- cluded that the mandibular incisor was the only hard tis- sue variable that could be used as a predictor in a regres- sion model to explain lip response to orthodontic therapy.
In 18- to 26-year-old Chinese subjects, a significant cor- relation 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 dento- skeletal 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 hori- zontal.2,7-11 The similarity in methods facilitates com- parison between studies.
Table I. Results of t test between 2 operators’ measurements
Mean SD SE P r
Maxillary incisor –0.13 0.46 0.07 .10* 0.98
Mandibular incisor –0.08 0.27 0.04 .08* 0.99
Upper lip change –0.15 2.97 0.47 .75* 0.76 (mm)
Lower lip change 0.55 3.28 0.52 .30* 0.76 (mm)
Nasolabial angle –0.70 8.74 1.38 .62* 0.55
Labiomental angle –0.55 3.00 0.47 .25* 0.88
*No significant differences (P > .05).
Table II. Results of t test between pretreatment
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