ANAHTAR KELİMELER Servikal headgear, alt utility ark, Sınıf II bölüm 1 ÖZET KEYWORDS Cervical headgear, lower utility arch, Class II division 1 ABSTRACT Amaç: Sınıf II bölüm 1 malokluzyona sahip low- angle hastalarda servikal headgear ve alt utility ark (CHG+LUA) uygulamasının etkilerini incele- mek ve üst birinci molar distalizasyonu sırasında mandibulada “ters yanıt” etkisinin olup olmadığını araştırmaktır. Bireyler ve Yöntem: Tedaviye dahil edilen toplam 30 birey iki gruba ayrılmış, birinci gruba CHG+LUA, diğer gruba sadece CHG uygulanmıştır. Angle sınıf I molar ilişkisi elde edildikten sonra lateral sefalog- ramlar alınmıştır. Bulgular: Sefalometrik değerlendirmelerden elde edilen bulgular, her iki grupta da maksiller protrüz- yonda azalma, molar distalizasyonu ve ekstrüzyonu elde edildiğini göstermektedir. Alt utility ark, alt molarda anlamlı dikleşmeye ve alt kesicilede anlamlı intrüyona neden olmuştur. Mandibuler rotasyon CHG grubunda anlamlı şekilde artarken, CHG+LUA grubunda sabit kalmıştır. Sonuç: Araştırma sonuçları, mandibular rotasyonun kontrolünde etkin bir yol olan “ters yanıt” etkisinin CHG+LUA uygulaması ile elde edilebileceğini gös- termiştir. Objective: A prospective study was performed to evaluate the effects of cervical headgear and lower utility arch (CHG+LUA) in Class II division 1 low- angle patients and to determine whether reverse response occurred during the upper first molar dis- talization period. Subjects and Methods: Thirty patients were included in the study and were divided in two groups. The first group was treated with CHG+LUA while the second group was treated only with cervical headgear (CHG). After achieving Angle class I molar relation, the cephalograms were taken. Results: The assessment of cephalometric findings showed that significant reduction of maxillary protru- sion, molar distalization, and extrusion were obtained in both groups. LUA influenced the lower molar uprighting and the lower incisor intrusion significant- ly. The rotation of the mandible showed a significant increase in CHG group while it remained constant in CHG+LUA group. Conclusion: These results showed that reverse response effect, which may be an effective way of controlling the mandibular rotational response, could be achieved by CHG+LUA. Hacettepe Dişhekimliği Fakültesi Dergisi Cilt: 30, Sayı: 3, Sayfa: 74-84, 2006 Treatment Effects of Cervical Headgear and Lower Utility Arch Mechanics in Angle Class II Division 1 Low-Angle Patients Angle Sınıf II Bölüm 1 Malokluzyona Sahip Low-angle Hastalarda Servikal Headgear ve Alt Utility Ark Mekaniğinin Tedavi Üzerine Etkileri *Müge AKSU DDS, PhD, *Filiz YUKAY DDS, PhD *Hacettepe University, Faculty of Dentistry, Department of Orthodontics ARAŞTIRMA (Research)
Transcript
ANAHTAR KELİMELERServikal headgear, alt utility ark, Sınıf II bölüm 1
ÖZET
KEYWORDSCervical headgear, lower utility arch, Class II division 1
ABSTRACT
Amaç: Sınıf II bölüm 1 malokluzyona sahip low-angle hastalarda servikal headgear ve alt utility ark (CHG+LUA) uygulamasının etkilerini incele-mek ve üst birinci molar distalizasyonu sırasında mandibulada “ters yanıt” etkisinin olup olmadığını araştırmaktır.Bireyler ve Yöntem: Tedaviye dahil edilen toplam 30 birey iki gruba ayrılmış, birinci gruba CHG+LUA, diğer gruba sadece CHG uygulanmıştır. Angle sınıf I molar ilişkisi elde edildikten sonra lateral sefalog-ramlar alınmıştır.Bulgular: Sefalometrik değerlendirmelerden elde edilen bulgular, her iki grupta da maksiller protrüz-yonda azalma, molar distalizasyonu ve ekstrüzyonu elde edildiğini göstermektedir. Alt utility ark, alt molarda anlamlı dikleşmeye ve alt kesicilede anlamlı intrüyona neden olmuştur. Mandibuler rotasyon CHG grubunda anlamlı şekilde artarken, CHG+LUA grubunda sabit kalmıştır.Sonuç: Araştırma sonuçları, mandibular rotasyonun kontrolünde etkin bir yol olan “ters yanıt” etkisinin CHG+LUA uygulaması ile elde edilebileceğini gös-termiştir.
Objective: A prospective study was performed to evaluate the effects of cervical headgear and lower utility arch (CHG+LUA) in Class II division 1 low-angle patients and to determine whether reverse response occurred during the upper first molar dis-talization period.Subjects and Methods: Thirty patients were included in the study and were divided in two groups. The first group was treated with CHG+LUA while the second group was treated only with cervical headgear (CHG). After achieving Angle class I molar relation, the cephalograms were taken.Results: The assessment of cephalometric findings showed that significant reduction of maxillary protru-sion, molar distalization, and extrusion were obtained in both groups. LUA influenced the lower molar uprighting and the lower incisor intrusion significant-ly. The rotation of the mandible showed a significant increase in CHG group while it remained constant in CHG+LUA group.Conclusion: These results showed that reverse response effect, which may be an effective way of controlling the mandibular rotational response, could be achieved by CHG+LUA.
Hacettepe Dişhekimliği Fakültesi DergisiCilt: 30, Sayı: 3, Sayfa: 74-84, 2006
Treatment Effects of Cervical Headgear and Lower Utility Arch Mechanics in Angle
Class II Division 1 Low-Angle Patients
Angle Sınıf II Bölüm 1 Malokluzyona SahipLow-angle Hastalarda Servikal Headgear ve Alt
Utility Ark Mekaniğinin Tedavi Üzerine Etkileri
*Müge AKSU DDS, PhD, *Filiz YUKAY DDS, PhD
*Hacettepe University, Faculty of Dentistry, Department of Orthodontics
ARAŞTIRMA (Research)
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IntrODUctIOn
Extraoral traction is the most reliable method for management of maxillary protrusion and still continues to be a major treatment alternative for the orthodontists.
The decision as to which type of headge-ar to use in the treatment of growing patients with skeletal and dental class II malocclusion has been discussed by many investigators1-6. Cervi-cal headgear has been most frequently used in cases of skeletal maxillary protrusion, producing distal displacement of the maxilla, increasing the vertical dimension and generating mandi-bular clockwise rotation7,8. Because some studi-es have shown the upper molar extrusion and the opening rotation of the mandible besides the distalization effect of cervical headgear5,910, many orthodontists tend to avoid using cervical headgear when a patient with class II maxillary protrusion has a vertical growth pattern. Some investigators have stated that mandibular plane angle opens with the cervical headgear11,12, while others have disagreed with this statement, beli-eving that mandibular plane closes or does not change with treatment1,13. Many authors have reported significant changes in vertical parame-ters when patients treated with cervical headgear compared to patients treated without the use of headgear14-16, or patients treated with occipital or high-pull headgear4,12,16,17. However, Ricketts et al18 suggested that the effect of cervical he-adgear did not occur as it has been accepted in the literature. According to the authors18, when a cervical headgear is used in high-angle patients, the extrusion of both maxillary molar and maxil-la causes a reciprocal clockwise rotation of the mandible, resulting in a higher face height. On the contrary, in low-angle patients, the authors stated that the extrusive forces of cervical head-gear cause changes in the dentition rather than in the facial proportions. In those cases, where a cervical headgear is used in combination with a lower utility arch, the mandible may rotate in a counterclockwise direction. This effect is called
“reverse response” of the mandible and the man-dibular arch. This is almost entirely a functional response and adverse to the common concepts.
The purpose of this prospective study was (1) to evaluate the skeletal and dental effects of cer-vical headgear and lower utility arch (CHG+LUA) in Class II division 1 low-angle patients whet-her reverse response occurs (2) and to compa-re the dental and skeletal differences between CHG+LUA and CHG during the upper first mo-lar distalization.
SUbjectS and MetHOD
The sample consisted of thirty patients (14 boys and 16 girls) either in the late mixed or per-manent dentition ranging in age from 9.08 to 13 years. The inclusion criteria for the patients in the study were as follows: (1) Class II division 1 skeletal maxillary protrusion with a low-ang-le growth pattern (SNA>80o, ANB>4o, maxil-lary depth angle>90o, lower facial height< 47o, FMA<25o, GoGnSN < 32o) (2) Half to one full cusp upper molar deviation (3) None or minimal crowding (4) Good cooperation
The subjects were divided into two groups randomly. The first group consisted of 15 pa-tients (8 boys and 7 girls) with a mean age of 10.54 ± 1.05 years, whose treatment included an orthopedic cervical headgear in conjunction with a lower utility arch18,19. The second group consisted of 15 patients (6 boys and 9 girls) with a mean age of 10.52 ± 0.96 years, whose treat-ment included an orthopedic cervical headgear only. These patients did not wear any other app-liances during the distalization. The first group was closely matched for age and dentoskeletal characteristics with the patients in the second group (Table I).
The headgear used for both groups was Klo-ehn type (GAC International, Bohemia, NY) with a long outer bow. All the patients were instructed to wear the CHG 14-16 hours per day with an orthopedic force of 500 gm18.
The lateral cephalograms were taken at the start of treatment (T1) and after molar distaliza-
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tion was completed (T2). The radiographs were traced by one investigator (M.A.) to verify anato-mic landmarks (Figure 1A). The duration of dista-lization was 1.23 ± 0.42 years in the CHG+LUA group and 1.17 ± 0.30 years in the CHG group. The skeletal and dentoalveolar effects of CHG + LUA and CHG were then compared by cephalo-metric analysis.
Maxillary and mandibular skeletal responses were documented by comparing the means of cephalometric measurements at T1 and T2 (Fi-gure 1B).
The dental measurements (Figures 1C and 1D) were obtained through maxillary and mandi-bular superimpositions, respectively18-20. Maxilla was superimposed on the palatal plane at ANS and mandible was superimposed on the cor-pus axis at Pm. The long axis of maxillary and
FIGURE 1a
1 Nasion 14 L6 mesial apex2 Sella 15 L6 bifurcation 3 Orbitale 16 B point4 Porion 17 Pm5 A point 18 Pogonion6 U1 crown 19 Menton7 U1 apex 20 Gonion8 U6 mesiobuccal cusp tip 21 Xi point9 U6 mesiobuccal apex tip 22 R1 10 U6 trifurcation 23 R311 L1 crown 24 ANS12 L1 apex 25 PNS 13 L6 mesiobuccal cusp
1 Palatal plane2 Line perpendicular to palatal plane from ANS3 U6, distalization of the crown (mm) 4 U6,distalization of the trifurcation (mm) 5 U6, angulation (°) 6 U6, vertical displacement (mm)7 U1, horizontal displacement of the crown (mm)8 U1, horizontal displacement of the apex (mm)9 U1, angulation (°)10 U1, vertical displacement (mm)
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mandibular first molar teeth were constructed by drawing a line through the apexes and the me-siobuccal and mesial cusp tips for the upper and lower first molars. The long axes of incisor teeth were constructed through the incisal edge and apex. The angular differences in teeth positions were measured as the angles between the long axis of each maxillary and mandibular tooth and the lines perpendicular to palatal plane and cor-pus axis at T1 and T2. To determine the amount of molar distalization, the distances between the cusp tip of the maxillary first molar and the line perpendicular to palatal plane from ANS and the cusp tip of the mandibular first molar and the line perpendicular to corpus axis from Pm were used. The distances of the trifurcation and the bifurcation were also measured to determi-ne the amount of tipping after distalization. The amount of horizontal displacements of maxil-lary and mandibular incisors was measured on a line parallel to the palatal plane and corpus
axis respectively. The vertical movements of the maxillary and mandibular first molars and inci-sors were determined by measuring the perpen-dicular distances between the mesiobuccal cusp tip of the maxillary molar, mesial cusp tip of the mandibular first molar and incisal edges of the maxillary and mandibular incisor teeth relative to the palatal plane and corpus axis at T1 and T2.
Statistical analysis
The means and standard deviations were cal-culated for each cephalometric variable. Paired t-test was performed in each group to analyze the changes from T1 to T2. Student t-test was used to evaluate intergroup differences at diffe-rent periods (T1-T2). To determine the accuracy of the method, 15 cephalograms were retraced and recalculated by the same investigator. The reliability coefficients were between 0.93 and 0.99 for linear measures, and between 0.91 and 0.97 for angular measures, indicating a high le-vel of consistency.
reSUltS
Maxillary depth angle decreased significant-ly in CHG+LUA and CHG groups with a mean change of 1.87o and 1.93o respectively (p<0.05, Table II). The mean changes in SNA angle did not indicate a significant reduction in both groups (p>0.05, Table II) while palatal plane angle dec-reased significantly in CHG group (p<0.05, Tab-le II).
The upper first molar (U6) in CHG + LUA and CHG groups moved distally with respect to its crown (4 mm, and 1.77 mm respectively, p< 0.05, Table III). However, the distalization of the trifurcation of the upper first molar showed signi-ficant difference in CHG + LUA group (2.4 mm, p< 0.05, Table III), while there was no signifi-cant difference in the CHG group (0.77 mm, p> 0.05, Table III) during cervical headgear therapy. The change in the angulation of the U6 was sta-tistically different in the CHG+LUA group, in-dicating that the tooth was distalized by tipping of the crown rather than the bodily movement.
FIGURE 1d
1 Corpus axis 2 Line perpendicular to corpus axis from Pm3 L6, distalization of the crown (mm) 4 L6, distalization of the bifurcation (mm) 5 L6, angulation (°)6 L6, vertical displacement (mm)7 L1, horizontal displacement of the crown(mm)8 L1, horizontal displacement of the apex (mm)9 L1, angulation (°)10 L1, vertical displacement (mm)
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(5.6º, p< 0.05, Table III). On the other hand, the angulation of the U6 in CHG group did not change significantly (-0.17º, p> 0.05, Table III). In both groups, the upper first molar showed sig-nificant vertical change (1.07 mm, and 1. 43 mm respectively, p< 0.05, Table III). The only signi-ficant change of the upper incisor (U1) in the
CHG +LUA group was found in the horizontal displacement of the upper incisor’s apex (0.93 mm lingually, p< 0.05, Table III). The horizontal, the angular and the vertical changes in the po-sition of the U1 did not differ in the CHG group (p>0.05, Table III).
T1 (pretreatment) and T2 (after the distalization period) values of maxillary skeletal measurements
cHG+lUA (n=15)
cHG(n=15)
Variables Mean SD P Mean SD P
Maxillary depth (º) t1 91.60 ± 2.53 81.90 ± 3.34
0.008* 0.000*
t2 89.73 ± 2.56 89.20 ± 1.69
SnA (º) t1 81.90 ± 3.34 81.33 ± 3.02
nS nS
t2 80.80 ±3.78 80.50 ±2.63
Palatal plane-FH (º) t1 1.97 ±3.07 3.07 ±3.58
nS 0.002*
t2 0.93 ±3.22 0.87 ±3.59
* p<0.05
SD: standard deviation NS: not significant
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The mandibular skeletal measurements showed no statistically significant changes in both groups (SNB, facial depth angle) (p>0.05, Table IV). The measurements such as GoGnSN, FMA, lower facial height did not show any signifi-
cant difference in the CHG+LUA group (p>0.05, Table IV) while there was a significant increase in FMA, and lower facial height in the CHG group (p<0.05, Table IV).
TABLE III
T1 (pretreatment) and T2 (after the distalization period) values of maxillary dental measurements
cHG+lUA (n=15)
cHG(n=15)
Variables Mean SD P Mean SD P
U6, distalization t1 -36.17 ± 3.41 -38.87 ± 2.86
of the crown (mm) 0* 0.015*
t2 -40.17 ± 3.72 -40.63 ± 3.68
U6, distalization t1 -37.13 ± 2.69 -38.40 ± 2.48
of the trifurcation (mm) 0* nS
t2 -39.53 ± 2.76 -39.17 ± 2.91
U6, angulation (º) t1 15.27 ± 6.52 19.70 ± 2.91
0.014* nS
t2 20.87 ± 7.42 19.87 ± 9.36
U6, vertical t1 20.90 ± 2.93 20.37 ± 1.58
displacement (mm) 0.046* 0.001*
t2 21.97± 2.71 21.80 ± 1.68
U1, horizontal t1 -1.17 ± 3.26 -1.63 ± 3.11
displacement of nS nS
the crown (mm) t2 -1.70 ± 3.50 -0.83 ± 2.76
U1, horizontal t1 -10.33 ± 2.09 -11.60 ± 1.76
displacement of 0.019* nS
the apex (mm) t2 -11.27 ± 1.94 -10.93 ± 2.80
U1, angulation (º) t1 21.40 ± 6.43 23.10± 7.08
nS nS
t2 21.90 ± 7009 25.00 ± 6.71
U1, vertical t1 29.37 ± 2.62 28.47 ± 1.89
displacement (mm) nS nS
t2 30.03 ± 2.27 28.53 ± 2.46
* p<0.05
SD: standard deviation NS: not significant
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The crown of the lower first molar (L6) in the CHG+LUA group was distalized and tipped back significantly (with a mean difference of 2.5 mm and 8.3 ,̊ p< 0.05, Table V).The vertical change in the position of the L6 was not shown to be significantly different in CHG+LUA group. The crown of the lower incisor (L1) in the CHG+LUA group retroclined and intruded significantly with a mean difference of 4.73˚ and 1.13 mm res-pectively (p<0.05, Table V).The cant of occlusal plane increased 2.47˚ (p<0.05, Table V) in the CHG+LUA group while there was no significant change in the CHG group. In CHG group, all the variables determinig the L6 and L1 positi-onal changes, did not also show any significant difference during distalization (p>0.05, Table V).
Within all the skeletal measurements regar-ding the maxilla and the mandible, neither of
the variables showed any significant difference between the two groups. The distalization of the U6 was significantly different between the two groups (p<0.05, Table VI). In CHG+LUA group, both the crown and the trifurcation moved dis-tally with a mean difference of 4 mm and 2.4 mm respectively. On the other hand, in the CHG group, the distalization of the crown and the tri-furcation was 1.77 mm and 0.97 mm respecti-vely. The horizontal displacement of the U1 was significantly different between the two groups (p<0.05, Table VI). In the CHG+LUA group, U1 moved 0.53 mm lingually while in the CHG group, U1 moved 0.8 mm labially. For the L6, the distalization of the crown (2.5 mm for the CHG+LUA group and 0 mm for the CHG group) and the bifurcation (2.4 mm for the CHG+LUA group and 0.97 mm for the CHG group) and the
TABLE IV
T1 (pretreatment) and T2 (after the distalization period) values of mandibular skeletal measurements and facial pattern
T1 (pretreatment) and T2 (after the distalization period) values of mandibular dental measurements
cHG+lUA (n=15)
cHG(n=15)
Variables Mean SD P Mean SD P
l6, distalization t1 -32.80 ± 2.41 -33.77 ± 2.35
of the crown (mm) 0.006* nS
t2 -35.30 ± 2.70 -33.77 ± 2.40
l6, distalization t1 -33.80 ± 0.74 -34.37 ± 0.16
of the bifurcation (mm) nS nS
t2 -34.56 ± 2.70 -34.46 ± 0.16
l6, angulation (º) t1 -10.33 ± 10.49 11.20 ± 7.0
0* nS
t2 18.77 ± 6.15 11.0 ± 4.45
l6, vertical t1 13.23 ± 1.49 12.87 ± 1.43
displacement (mm) nS nS
t2 13.60 ± 1.65 12.77 ± 2.41
l1, horizontal t1 -6.13 ± 1.87 -5.70 ± 1.87
displacement of 0.011* nS
the crown (mm) t2 -7.53 ± 2.83 -6.27 ± 1.72
l1, horizontal t1 -8.70 ± 1.87 -7.67 ± 1.03
displacement of nS nS
the apex (mm) t2 -8.30 ± 2.83 -7.63 ± 1.16
l1, angulation (º) t1 6.47 ± 5.72 4.80 ± 4.56
0.012* nS
t2 1.73 ± 8.91 25.40 ± 1.80
l1, vertical t1 25.50 ± 2.0 26.50 ± 2.24
displacement (mm) 0.017* nS
t2 24.37 ± 2.57
cant of occlusal t1 18.13 ± 0.98 19.10 ± 3.84
plane (º) 0.019* nS
t2 20.60 ± 0.86 20.73 ± 2.63
*p<0.05
SD: standard deviation NS: not significant
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angulation (8.43o for the CHG+LUA group and -0.20o for the CHG group) were significantly dif-ferent between the study groups (p<0.05, Tab-le VI). The vertical displacement of L1 was also significantly different between the two groups (p<0.05, Table VI). (L1 intruded with a mean difference of 1.13 mm in the CHG+LUA group while extruded with a mean difference of 1.10 mm in the CHG group).
DIScUSSIOn
A prospective investigation was undertaken to determine the effects of CHG+LUA in Class II division 1 low-angle patients. The orthopedic effect of CHG has previously been the subject of many studies1-3,5-7,14. In contrast with the com-mon concepts about the mandibular rotational effects, Ricketts et al18 suggested that a reverse response could occur when a CHG was used with a LUA in low-angle patients. According to the authors,18 the extruding upper molar picks up the lower molar, uprighting that tooth in a distal rotation. This action allows the maxilla to be compressed and rotated distally without ro-tation of the mandible and is referred to as the reverse response of the LUA18. However, CHG therapy accompanying by LUA has been rarely
investigated20. The only investigation reported in the literature was the retrospective study of Cook et al20, which was performed in high-angle pati-ents. The purpose of this study was not to focus on posttreatment effects but to evaluate pure ef-fects of CHG+LUA during the molar distalization period as the overall change for the entire period of treatment may hide the CHG effect.
In this study, the maxilla moved distally in terms of maxillary depth angle. Our finding is in accordance with the finding of many studies indicating the restriction of the maxilla with the use of CHG4,9,21,22. However, SNA angle did not show any significant difference during the dista-lization while some authors interpreted differen-ces in SNA reduction7,21,23. The observation pe-riod in this study included only the distalization period, which might be insufficient to achieve an orthopedic movement.
The literature regarding the effect of CHG on the palatal plane angle is still unclear. Although many authors reported that anterior nasal spine to be positioned downward more than posterior nasal spine1,3,5,11,18,24, rotation of the palatal pla-ne was changed significantly only in CHG group. Boecler13 et al reported no change in the angu-lation of the palatal plane with CHG therapy in contrast to our finding.
TABLE VI
Comparison of pre and post-distalization differences between groups
cHG+lUA (n=15)
cHG(n=15)
Variables Mean SD Mean SD P
U6, distalization of the crown (mm) -4.0 ± 2.65 -1.77 ± 2.46 0,02*
U6, distalization of the trifurcation (mm) -2.4 ± 1.48 -0.97 ± 1.93 0,03*
U1, horizontal displacementof the crown (mm)
-0.53 ± 1.42 0.8 ± 1.80 0,03*
l6, distalization of the crown (mm) -2.5 ± 3.01 0 ± 1.57 0,008*
l6, distalization of the bifurcation (mm) -2.4 ± 1.48 0.97 ± 1.93 0,03*
The results of this study indicate that there was a significant distalization of U6 in both groups. This finding is in accordance with the findings re-ported in the literature1,9. However, the amount of distalization in CHG group was less than that of CHG + LUA group. Although the duration of distalization was almost the same, a difference between the amounts of distalization occurred. This might be due to the variation in the amount of molar cusp deviation at the start of treatment. Another possible explanation for this might be the angular changes between the two groups du-ring the distalization period. To investigate the type of molar movement, distalization of the tri-furcation of U6 was also evaluated. The amount of distalization of the trifurcation was less than the crown movement in contrast with the stu-dies reported in the literature20,25. Furthermore, Schiavon Gandini et al25 showed that the distal relocation of U6 was more significant in the apex due to the 20o upward angulation of the external bow. Additionally, Cook et al20 did not observe any distal tipping when the outer bows of the CHG were bent upward. The downward vector of the extraoral force produced a more downward movement of U6 in both groups. Cook et al20 reported the upper molar extrusion either with or without treatment, suggesting that the molar extrusion could not be attributed to only cervical headgear due to the ongoing downward growth of the maxilla.
In this study, the lower first molar moved distally and the lower incisors intruded and ret-roclined significantly in the CHG+LUA group as described by Ricketts et al.18 The bioprogressive theory of cortical anchorage hypothesizes that bends in the utility arch will move the roots of the first lower molars toward the buccal cortical bone of the mandible, leading to the extrusion of the lower first molars and the intrusion of lower incisors. The upper molar in the CHG+LUA group extruded, then uprighted the lower first molar in a distal rotation, confirmig the reverse response effect of the LUA. In contrast with our findings, Cook et al did not find any reverse res-ponse effect in their study group.
Additionally, L1 and the cant of the occlusal plane were also changed by the LUA. The LUA might have a reaction at the molar to upright it however, cortical anchorage might prevent the significant molar extrusion even when the inci-sor intrusion mechanics were used. Meanwhile, Cook et al20 did not find any molar response whi-le they found a significant intrusion and proclina-tion of the lower incisors.
Since no other appliances were worn by the patients in our study during the period of the in-vestigation, it can be stated that CHG+LUA used in this study produced Class II correction without producing an opening rotation of the mandible. GoGnSN, FMA and lower facial height angles did not demonstrate any significant changes between T1 and T2 in CHG+LUA group, confirming that when a CHG is used in conjunction with a LUA, the mandible may remain constant without any rotation. Ricketts et al18 also suggested that the extrusive forces of CHG was translated through the utility arch to the lower dentition, allowing maxilla to move distally without rotation of the mandible. Cook et al20 reported different results with our findings regarding mandibular rotation, this might be due to their study group which was different from that of our study.
A limitation of this study was that the groups were relatively small. However, the characteris-tics of the patients and the application of the appliances were highly homogeneous and the study was designed prospectively. Most of the studies pertaining to CHG are either retrospe-ctive or CHG has been combined with edgewi-se appliances; functional appliances, bite plates, extractions and the groups in these studies are not usually homogeneous. Additionally, there is only one study in the literature, investigating the speculation of Ricketts et al.18 Future studies including larger study groups and posttreatment effects should be undertaken for the long-term effects of CHG+LUA.
cOnclUSIOn
Both CHG+LUA and CHG groups restric-ted maxillary sagittal growth and resulted in an
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extrusion of upper first molars. The lower first molar uprighted and moved distally with LUA, however, it could not prevent the extrusion but might restrict the excessive extrusion of the up-per first molar. The reverse response of the LUA did not affect the mandibular rotation in low-angle patients thus, mandible remained stable without any rotation in the CHG+LUA group. However, opening rotation of the mandible oc-curred in the CHG group.
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CORRESPONDING ADDRESS
Müge AKSU DDS, PhDHacettepe University, Faculty of Dentistry, Department of Orthodontics 06100 Sıhhiye-Ankara/TURKEY
