Â© 2006 - The Charles H. Tweed International Foundation

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The more protrusive the lip profile, the less the Z-angle. The more retrusivethe lip profile, the more the Z-angle. In general, as the lip profile position becomesmore protrusive in its relationship to the chin, the Z-angle will decrease and the E-valuewill become more positive. As the lip profile position becomes more retrusive in itsrelationship to the chin, the Z-angle will increase and the E-value will become morenegative. In this study, pretreatment and posttreatment measurements were comparedwithin the nonextraction and extraction groups and between each of the two groups.THE SAMPLEIn the nonextraction group, the posttreatment Z-angle ranged from 68° to 90°.Fig. 2. E-value measurement.The posttreatment E-value ranged from +1.5 mm to -10 mm. Only one patient in thenonextraction group had a positive posttreatment E-value (+1.5 mm). The averageposttreatment Z-angle for the nonextraction group was 79.01°. The average posttreatment E-value for the nonextractiongroup was -4.05 mm.Several different extraction protocols were used in the extraction group. The most common ones were (1)maxillary and mandibular second premolars (14 patients), (2) maxillary first premolars (7 patients), (3) maxillaryfirst premolars and mandibular second premolars (27 patients), and (4) maxillary and mandibular first premolars (36patients). The remaining patients (24) in this group required various other extraction combinations.Characteristics of the maxillary and mandibular second premolar extraction subgroup were (1) mild tomoderate arch length discrepancy, (2) good soft tissue facial pattern or mild facial imbalance, and (3) good skeletalpattern. An example of this extraction protocol is shown (Fig. 3A, Fig. 3B).Characteristics of the maxillary first premolar extraction subgroup were (1) Class II dental relationship, (2)maxillary protrusion, maxillary anterior crowding, or both, and (3) good mandibular incisor position with little or nocrowding. An example of this extraction protocol is shown (Fig. 4A, 4B).Characteristics of the maxillary first premolar and mandibular second premolar extraction subgroup were (1)Class II dental relationship and mild to moderate Class II skeletal pattern, (2) mild to moderate mandibular archlength discrepancy, (3) soft tissue facial imbalance, and (4) low to medium Frankfort mandibular plane angle. Anexample of this extraction protocol is shown (Fig. 5A, 5B).Characteristics of the maxillary and mandibular first premolar extraction subgroup were (1) severe archlength discrepancy, dental (bialveolar) protrusion, or both, (2) Class I or Class II dental relationship, and (3) mediumto high Frankfort mandibular plane angle. An example of this extraction protocol is shown (Fig. 6A, 6B).RESULTSThe facial profiles of the extraction group and the nonextractiongroup were within the normal range of Z-angle and E-values at theconclusion of treatment. On average, the nonextraction group completedtreatment with a slightly more retrusive lip profile position than did theextraction group (Fig. 7A). The posttreatment Z-angle average for thenonextraction group was 79.01° (Fig. 7B) compared with 73.74° for theFig. 3. A, Facial photographs: extractionof four second premolars (pretreatment-left;posttreatment-right).Fig. 3. B, Tracings: extraction of four second premolars (pretreatment-left;posttreatment-right).21
extraction group, a 5.27° difference. The posttreatment E-value average for the nonextraction group was -4.05 mmcompared with -2.58 mm for the extraction group. Therefore, the nonextraction group finished treatment with the lowerlip 1.47 mm further behind the esthetic line than did the extraction group (Table I).The extraction group began treatment with significantly more lip-chin imbalance; the pretreatment Z-angle ofthe extraction group was 66.61° compared with 73.38° for the nonextraction group, a 6.77° difference. Thepretreatment E-value for the extraction group was +.74 mm compared with -2.93 mm for the nonextraction group, a 3.67mm difference. A note of interest is the fact that the posttreatment Z-angle and E-values of the extraction group (Z =73.74°; E = -2.58 mm) are very close to the pretreatment Z-angle and E-values of the nonextraction group (Z = 73.38°;E = -2.93 mm). In other words, the extraction group finished treatment approximately where the nonextraction groupbegan treatment.DISCUSSIONWithin the extraction group, the least amount of pretreatment lip-chin profile imbalance occurred in the foursecond premolar extraction subgroup (Z= 71.64°; E = -1.29 mm), and the most pretreatment lip-chin profile imbalanceoccurred in the four first premolar extraction subgroup (Z= 62.78°; E = +2.31 mm). These subgroups had a Z-angledifference of 8.86° and an E-value difference of 3.60 mm (Table II).The four second premolar extraction subgroup, the maxillary first premolar extraction subgroup, and themaxillary first premolar – mandibular second premolar extraction subgroup finished treatment fairly close together(Table II). The posttreatment Z-angle values were within 1.81° of eachother, and the E-values were within .25 mm. These posttreatment valuesare the result of a predictable diagnostic measurement analysis andtreatment plan.The four first premolar extraction subgroup finished treatmentwith a Z-angle value of 70.89° and an E-value of -1.46 mm, becausethe patients in this subgroup started treatment with more arch lengthdiscrepancy, facial imbalance, or both. When the nonextraction groupwas compared with the four first premolar extraction subgroup, theFig. 4. A, Facial photographs: extraction ofmaxillary first premolars (pretreatment-left;posttreatment-right).Fig. 4. B, Tracings: extraction of maxillary first premolars (pretreatment-left;posttreatment-right).22
Page 1 and 2: © 2006
Page 5 and 6: Chairman of the Board Report 2006Ja
Page 7 and 8: Tribute: Dr. Herbert A. Klontz, Twe
Page 9 and 10: He was not only generous in Toronto
Page 11 and 12: Director of Education — Herb Klon
Page 13 and 14: Orthodontic Treatment of a Low Angl
Page 15: Fig. 5. McNamara’s NasionFrankfor
Page 19: REFERENCES1. Horn AJ. Facial height
Page 24 and 25: Fig. 5. B, Tracings: extraction of
Page 26 and 27: The Extraction/Nonextraction Dilemm
Page 28 and 29: Fig. 6. Baxter’s posttreatment ce
Page 30 and 31: Fig. 16. Adams’ posttreatment cep
Page 32 and 33: The Extraction/Nonextraction Dilemm
Page 34 and 35: Fig. 12. Pretreatment dental castsF
Page 36 and 37: Microimplant Anchorage (MIA) in Ort
Page 38 and 39: Recently, with the rapid developmen
Page 40 and 41: Fig. 5. Molar intrusion: A) Maxilla
Page 43 and 44: Two Phase Treatment for Deep Bite P
Page 45 and 46: Fig. 7a. Post orthopedic cephalomet
Page 47: References:1. Dale J.G.. Longitudin

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