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American Journal of Orthodontics and Dentofacial Orthopedics Kinzinger et al 581 Volume 136, Number 4 6. S-Go:N-Me: the facial height ratio (posterior face height to anterior face height). 7. U1-CEJ/PTV: the distance from the maxillary central incisor to the pterygoid vertical. 8. U4-CEJ/PTV: the distance from the maxillary first premolar to the pterygoid vertical. 9. U5-CEJ/PTV, the distance from the maxillary second premolar to the pterygoid vertical. 10. U6-CEJ/PTV: the distance from the maxillary first molar to the pterygoid vertical. 11. U1/ANS-PNS: the angle between the maxillary central incisor and the palatal plane. 12. U1/SN: the angle between the maxillary central incisor and the anterior cranial base. 13. U4/ANS-PNS: the angle between the maxillary first premolar and the palatal plane. 14. U4/SN: the angle between the maxillary first premolar and the anterior cranial base. 15. U5/ANS-PNS: the angle between the maxillary second premolar and the palatal plane. 16. U5/SN: the angle between the maxillary second premolar and the anterior cranial base. 17. U6/ANS-PNS: the angle between the maxillary first molar and the palatal plane. 18. U6/SN: the angle between the maxillary first molar and the anterior cranial base. 19. U1-CEJ/ANS-PNS: the distance from the maxillary central incisor to the palatal plane. 20. U4-CEJ/ANS-PNS, the distance from the maxillary first premolar to the palatal plane. 21. U5-CEJ/ANS-PNS: the distance from the maxillary second premolar to the palatal plane. 22. U6-CEJ/ANS-PNS: the distance from the maxillary first molar to the palatal plane. SNA, SNB, S-N/ANS-PNS, ANS-PNS/Go-Me, Björk’s summation angle, and the facial height ratio were measured or computed to verify any skeletal changes. In the sagittal plane, the relative incisor and first premolar mesial movement, hence the anchorage loss, and the relative second premolar and first molar distal movement in relation to the pterygoid vertical (U1-CEJ/PTV, U4-CEJ/PTV, U5-CEJ/PTV, and U6-CEJ/PTV) were determined. The respective points of reference for the measurements were the cementoenamel junction (CEJ) on the longitudinal axis of the teeth. Growthinduced changes (increase of 1 mm per year) were taken into account. The amounts of labial tipping of the incisors and first premolars and distal tipping of the second premolars and first molars were determined based on the angles between the longitudinal tooth axis and, respectively, the palatal plane or the anterior cranial base (U1/ ANS-PNS, U1/SN; U4/ANS-PNS, U4/SN; U5/ANS- PNS, U5/SN; U6/ANS-PNS, U6/SN). Potential tooth intrusions and extrusions were verified in the palatal plane (U1-CEJ/ANS-PNS, U4-CEJ/ ANS-PNS, U5-CEJ/ANS-PNS, and U6-CEJ/ANS- PNS). Statistical analysis Statistical computations were performed with SPSS software (version 14, SPSS, Chicago, Ill). Casts and lateral cephalographs were traced twice at a 4-week interval. If values deviated, the means of both measurements were fed into the statistical analysis. Then the arithmetic mean and the standard deviation were computed for every variable used in the in-vivo measurements, and the changes of each variable from T1 to T2 were statistically analyzed with a 1-sample t test. Thereby, we determined which effective changes were therapeutically induced by the treatment as evidence against the null hypothesis. Differences with a probability of error less than 5% (P \0.05) were considered statistically significant. RESULTS Metrical assessment of the maxilla casts before and after molar distalization with a skeletonized distal jet appliance showed the following dental position changes of the permanent first molars (Table I). The supporting zones increased by 4.01 6 0.63 mm in the first quadrant and 3.64 6 0.69 mm in the second quadrant. The transverse widths of the dental arch increased by means of 1.79 6 1.08 mm between the mesiobuccal cusps, 2.58 6 0.69 mm between the central fossae, and 3.03 6 0.68 mm between the distobuccal cusps; this indicates both expansion and mesial inward rotation of the permanent first molars. When we looked more closely, the permanent first molars of the first quadrant had rotated mesiopalatally and distobuccally by a mean 8.35 6 7.66 and those of the second quadrant, by 7.88 6 5.50 . All position changes of the permanent first molars were significant. Skeletal assessments showed that the cranial base remained constant, with changes of the SNA angle of only a mean 0.19 6 0.80 and the SNB angle of only a mean 0.13 6 0.82 . The positional relationships of the palatal plane to the anterior cranial base and to the mandibular plane were virtually unchanged. Björk’s summation angle changed by only 0.73 6 1.26 during molar distalization, and the facial height ratio changed by 0.58% 6 1.51%. All registered skeletal changes during treatment were not significant (Table II).
582 Kinzinger et al American Journal of Orthodontics and Dentofacial Orthopedics October 2009 Table I. Changes in permanent first molar position induced by distal jet therapy in the horizontal plane Cast analysis n T1 mean T1 SD T2 mean T2 SD DT1-T2 mean DT1-T2 SD Significance UR2 distal-UR6 mesial (mm) 10 20.80 2.04 24.81 2.34 –4.01 0.63 UL2 distal-UL6 mesial (mm) 10 21.17 1.90 24.81 2.08 –3.64 0.69 ‡ Mesiobuccal cusp tips UR6-UL6 (mm) 10 50.80 2.16 52.59 1.28 –1.79 1.08 † Central fossa UR6-UL6 (mm) 10 45.80 2.36 48.39 2.04 –2.58 0.69 ‡ Distobuccal cusp tips UR6-UL6 (mm) 10 53.06 1.70 56.09 1.49 –3.03 0.68 ‡ Tooth UR6 rotation ( ) 10 12.86 6.15 21.21 6.28 –8.35 7.66 * Tooth UL6 rotation ( ) 10 13.43 4.29 18.93 5.94 –7.88 5.50 * Determination of type of molar rotation: angle between midpalatal raphe and a line running through the mesiobuccal and distobuccal cusps of the molars; for DT1-T2 (value before distalization) – (value after distalization): positive value 5 mesiobuccal and distopalatal rotation, negative value 5 mesiopalatal or distobuccal rotation. *P \0.05; † P \0.01; ‡ P \0.001. ‡ Table II. Skeletal angular and linear measurements Cephalometric analysis n T1 mean T1 SD T2 mean T2 SD D T1-T2 mean D T1-T2 SD Significance Skeletal-angular SNA ( ) 10 83.55 2.63 83.36 2.78 0.19 0.80 NS SNB ( ) 10 79.83 3.42 79.70 3.27 0.13 0.83 NS S-N/ANS-PNS ( ) 10 5.56 1.92 5.18 1.53 0.38 1.18 NS ANS-PNS/Go-Me ( ) 10 24.20 4.31 25.08 4.14 –0.88 1.09 NS Björk’s summation angle ( ) 10 389.61 3.29 390.34 3.49 –0.73 1.26 NS Skeletal-linear S-Go:N-Me (%) 10 67.49 2.79 66.91 2.60 0.58 1.51 NS NS, Not significant. In the area of the CEJ, the permanent first molars were distalized by a mean of 3.92 6 0.53 mm and intruded by a mean of 0.16 6 0.26 mm. At the same time, they experienced distal tipping of 2.79 6 2.51 in relation to the palatal plane and 3.00 6 2.31 in relation to the anterior cranial base. The second premolars, which were not part of the anchorage setup, drifted distally after the molars by 1.87 6 0.74 mm, elongating by 0.42 6 0.41 mm and tipping, in relation to the respective reference planes, by 3.00 6 2.69 and 3.21 6 2.86 . The first premolars, included in the anchorage setup, mesialized by 0.72 6 0.78 mm, extruded by 0.14 6 0.14 mm, and, at the same time, tipped by 1.15 6 2.98 in relation to the palatal plane and by 0.79 6 2.23 in relation to the anterior cranial base. The central incisors were protruded by 0.36 6 0.32 mm and extruded by 0.14 6 0.29 mm, and showed slight labial tipping of 0.57 6 0.79 in relation to the palatal plane and 0.64 6 0.75 to the anterior cranial base. All linear dental movements in relation to the pterygoid vertical, the extrusion of the premolars, and the angular dental position changes of the second premolars and first molars were significant (Table III). The total movement in the sagittal plane was 4.28 6 0.51 mm (cumulating molar distalization and central incisor protrusion) or 4.64 6 1.06 mm (cumulating molar distalization and first premolar mesialization). Based on the values obtained for the permanent first molars— distalization length of a mean 3.92 6 0.53 mm—molar distalization represents 91.71% 6 7.32% and 86.56% 6 13.21%, respectively, of the total sagittal movement (Table IV). DISCUSSION The outcomes confirm the efficiency of the distal jet in clinical applications. Cast registrations showed that the supporting zone had increased, and that a therapeutically desired widening of the dental arch, as well as mesial inward and distal outward rotations of the molars, had occurred. The biomechanical explanation of this effect is that force is applied palatally from the center of resistance of the molars. In theory, a toe-in bend would be appropriate to compensate for this effect, but it results in friction in the guide tubes of the appliance. This effect was verified with the casts used and by an in-vitro registration. The resultant adhesive effect expressing this friction reduced the distalization force substantially and, accordingly, would be an obstacle for distalization of the molars. Therefore, a toe-in bend should not be used, although it would be therapeutically desirable. 4 After the distal jet treatment, the molars
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