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Palatal implant versus zygoma plate anchorage for distalization of maxillary posterior teeth

Burçak Kaya, Çağla Şar, Ayça Arman-Özçırpıcı, Ömür Polat-Özsoy
DOI: http://dx.doi.org/10.1093/ejo/cjs059 507-514 First published online: 11 September 2012

SUMMARY

This study aimed to examine the skeletal, dental, and soft tissue effects of the implant-supported pendulum (ISP) and the zygoma anchorage system (ZAS) used for the distalization of maxillary posterior teeth. Among 30 patients showing Angle class II malocclusion, 15 patients with a mean age of 14.3±1.6 years and treated with ISP were included in the first group; 15 patients with a mean age of 14.7±2.5 years and treated with ZAS were included in the second group. The predistalization and postdistalization lateral cephalograms were analysed. Statistical evaluation was carried out using SPSS. Point A and upper incisors protruded in the ISP group, retruded in the ZAS group. Upper posterior teeth were distalized in both groups, but more in the ZAS group. Significant differences were observed between the groups for the sagittal movements of Point A, incisors, and posterior teeth. Overbite decreased in the ISP group, overjet decreased in the ZAS group, upper and lower lips retruded only in the ZAS group. Both methods provided absolute anchorage for distalization of posterior teeth, but the skeletal and soft tissue outcome and distalization obtained was greater in the ZAS group. Both methods can be used as alternatives to extraoral traction and conventional molar distalization appliances with different patient requirements.

Introduction

Distalization of maxillary molars into a class I relationship is often obligatory for treatment of class II malocclusion (Gelgor et al., 2007). Extraoral appliances are frequently used for molar distalization, but they require substantial patient cooperation. Hence, orthodontic mechanics requiring minimal patient cooperation are desirable. Intraoral maxillary molar distalization appliances such as magnets, push coils, superelastic nickel-titanium wires, Jones jig, pendulum, distal jet, first class and Keles slider do not require extensive cooperation from patients (Gianelly et al., 1989; Gianelly et al., 1991; Hilgers, 1992; Jones and White, 1992; Locatelli et al., 1992; Carano and Testa, 1996; Fortini et al., 1999; Keles, 2001). Both first and second molars can be effectively distalized with these tooth-supported appliances. However, the distalization force produces a reactive force on the other teeth from which anchorage is supplied from (Oberti et al., 2009). Hence, mesialization of premolars, protrusion of incisors, and increase of overjet occurs due to anchorage loss.

Implant-supported intraoral molar distalization systems have been introduced to provide suitable anchorage and to reduce these side effects recently (Kaya et al., 2009). Therefore, molar distalization appliances have been combined with various implants to obtain osseous anchorage and to get through the inadequacy of tooth-supported appliances (Oberti et al., 2009). Palatal miniscrews, alveolar microscrews, or zygoma plates were used as anchorage units with these systems (Mannchen, 1999; Karaman et al., 2002; Keles et al., 2003; Park et al., 2005; Sugawara et al., 2006; Kaya et al., 2009). Thus, the molars were distalized without reciprocal movements at premolars and incisors.

A fair amount of studies examining dentofacial outcome of various implant-supported molar distalization systems can be found in the orthodontic literature lately (Mannchen, 1999; Karaman et al., 2002; Keles et al., 2003; Gelgör et al., 2004; Park et al., 2005; Kircelli et al., 2006; Sugawara et al., 2006; Cornelis and De Clerck, 2007; Escobar et al., 2007; Gelgor et al., 2007; Polat-Ozsoy et al., 2008; Kaya et al., 2009; Oberti et al., 2009; Choi et al., 2011; Fudalej and Antoszewska, 2011; Oh et al., 2011; Ohura et al., 2011; Yu et al., 2011). Nevertheless, there isn’t adequate number of researches comparing the effects of implant-supported molar distalization mechanics which obtain anchorage from different anatomical regions. Thus, the aim of this study is to investigate and compare the skeletal, dental, and soft tissue effects of implant-supported pendulum (ISP) and zygoma anchorage system (ZAS) used for distalization of maxillary posterior teeth. The H 0 hypothesis is that comparable effects will be obtained with ISP and ZAS systems, whereas the H 1 hypothesis is that skeletal, dental, and soft tissue effects obtained with ZAS will be more extensive.

Materials and methods

This study is organized retrospectively as a parallel group design with 1:1 ratio between the groups. A power analysis was performed to calculate the sample size required for the study. The power analysis revealed that a total sample size of 28 (14 per group) was needed to detect statistically significant differences between the groups with medium effect size and a power of 90 per cent at 0.05 significance level. Sample size estimation was performed by using NCSS and PASS software (Number Cruncher Statistical Systems. Version 2000. Kaysville, Utah, USA).

The predistalization and postdistalization radiographs of all patients who were treated in Başkent University Faculty of Dentistry Department of Orthodontics with distalization of maxillary posterior teeth either by using ISP or ZAS were evaluated. Within the 39 patients (22 ISP, 17 ZAS) evaluated, five patients (three ISP, two ZAS) with poor quality or nonstandard radiographs and four patients (four ISP) who did not match for gender, age or dentoskeletal characteristics were excluded. Hence, the study sample consisted of 30 patients (20 females, 10 males). The inclusion criteria are shown below:

  1. Skeletal class I or class II, dental class II (at least end to end) relationship

  2. All permanent teeth present and erupted, except for the third molars

  3. No supernumerary teeth exist

  4. Crowding in the upper dental arch and/or increased overjet

  5. Minimum or no crowding in the lower dental arch

  6. Presence of high quality and standard lateral cephalometric radiographs

Fifteen patients (10 females, 5 males) with a mean age of 14.3±1.6 years and treated with ISP were included in the first group. Fifteen patients (10 females, 5 males) with a mean age of 14.7±2.5 years and treated with ZAS were included in the second group. The study was conducted retrospectively on 60 lateral cephalometric radiographs obtained from these patients. The study was ethically approved by Başkent University Research and Ethical Committee for all orthodontic, cephalometric and surgical stages. All patients and parents were informed about the surgical and orthodontic procedures that would be applied throughout the study and signed a consent form. All palatal screws or zygoma plates were placed under local anesthesia by the same oral surgery team and the orthodontic mechanics were applied by the same group of orthodontists in cooperation.

In the ISP group, two titanium intraosseous screws (IMF intermaxillary fixation screw; Stryker, Leibinger, Germany) were used as rigid bone anchors. The screws were 2.0mm diameter, 8mm length and placed in the paramedian region of the anterior palate, 4–6mm posterior to the incisive foramen and 3–4mm lateral to the median palatal suture. One week after the screws were placed, their clinical stability was checked, and then impressions and dental stone casts were obtained with the screws in place. The screw head was blocked out with wax on the stone model. The pendulum appliance was constructed as prescribed by Hilgers (1992) with the exception of supplementary wires extending to the occlusal surfaces of upper premolars. The 0.032" titanium molybdenum alloy springs (TMA; Ormco, Glendora, Calif) of the appliance were activated 60°–70° posteriorly to apply approximately 230g distalization force bilaterally. The acrylic plate of the appliance was connected to the head of the screws by using cold-curing, methyl methacrylatefree acrylic resin (Ufi Gel hard; Voco GmbH, Cuxhaven, Germany). Lastly, activated springs were placed in the lingual sheaths of the upper first molar bands (Figure 1). The springs were reactivated at monthly appointments if necessary. Uprighting bends were incorporated to the springs after the initiation of 1–2mm of distalization, in order to minimize the amount of tipping.

Figure 1

Implant-supported pendulum appliance (ISP).

In the ZAS group, 0.018" slot brackets (Roth Omni C-PM / Hook, GAC International Inc., Bohemia, NY, USA) and molar bands (Ideal Molar Bands, GAC International Inc., Bohemia, NY, USA) were bonded on upper premolars and molars. After leveling, maxillary posterior teeth were distalized segmentally on 0.016×0.022" stainless steel continuous arch wire with an anterior vertical step for ease of tooth cleaning. The zygoma anchor (Bollard Zygoma Anchor: Surgi-Tec, Bruges, Belgium), which is a titanium miniplate with three screw holes, a round bar, and a cylindrical terminal unit, was used for distalization of maxillary premolars and molars together. The zygoma anchor was placed to the inferior crest of the zygomaticomaxillary bone, after a mucoperiosteal flap was elevated under local anesthesia. After bending the cylindrical unit distally, the anchor was fixed with miniscrews and covered with mucoperiosteum. One week after the operation, 450g distalization force was applied bilaterally with nickel-titanium closed coil springs from the zygoma anchors to the crimpable hooks placed mesial to the first premolar brackets (Figure 2).

Figure 2

Zygoma anchorage system (ZAS).

Distalization was finished when class I molar relationship was obtained in all patients.

Cephalometric analysis

The lateral cephalometric radiographs of each patient were taken at the beginning and immediately after the end of distalization of maxillary posterior teeth with a Planmeca cephalometer (PM 2002 EC; Proline, Helsinki, Finland). All the predistalization (T0) and postdistalization (T1) lateral cephalometric radiographs obtained from these patients were hand-traced on orthodontic tracing paper on a conventional negatoscope using 0.3mm lead pencil and measured by the same examiner (BK). A horizontal reference (HR) line with 7° angle to SN line and a vertical reference (VR) line perpendicular to horizontal reference line were constructed. A total of 28 parameters (9 skeletal, 17 dental, 2 soft tissue) were evaluated (Figure 3).

Figure 3

1: SNA°, 2: SNB°, 3: ANB°, 4: A-VR mm, 5: B-VR mm, 6: SN/GoMe°, 7: N-Me mm, 8: N-ANS mm, 9: ANS-Me mm, 10: U1-VR mm, 11: U4-VR mm, 12: U5-VR mm, 13: U6-VR mm, 14: U7-VR mm, 15: U1/HR°, 16: U4/HR°, 17: U5/HR°, 18: U6/HR°, 19: U7/HR°, 20: U1-HR mm, 21: U4-HR mm, 22: U5-HR mm, 23: U6-HR mm, 24: U7-HR mm, 25: Overjet mm, 26: Overbite mm, 27: ULip-VR mm, 28: LLip-VR mm.

Statistical analysis

Data analysis was performed by using SPSS for Windows, version 11.5 (SPSS Inc., Chicago, IL, United States). The normality of distribution of the continuous variables was determined by using Shapiro Wilk test. Descriptive statistics were shown as mean ± standard deviation for continuous variables. The mean differences between pre-treatment and post-treatment measurements within the groups were analysed by Bonferroni Adjusted Paired Samples-t test for normally distributed variables and by Bonferroni Adjusted Wilcoxon’s signed test for not normally distributed variables. A P value less than 0.025 was considered statistically significant. The mean treatment changes obtained in the groups were compared by Unpaired-t test for normally distributed variables and by Mann Whitney-U test for not normally distributed variables. A P value less than 0.05 was considered statistically significant.

Intra-observer reliability

Three weeks after the first measurements, 20 lateral cephalometric films from 10 randomly selected patients were repeated by the same examiner (BK). Intra-class correlation coefficients (r) were calculated on pre-treatment and post-treatment cephalometric films for evaluation of reliability. The intra-class correlation coefficients (r) calculated for each variable ranged between 0.950 and 1.000 and was considered statistically reliable.

Results

The distalization was successfully completed with a mean of 8.1±4.2 months in the ISP group and with a mean of 9.0±2.4 months in the ZAS group. There was no significant difference between the groups for gender, age, or distalization time (Table 1). The groups were comparable at T0, since only two parameters showed significant differences (Tables 24). All the miniscrews and miniplates remained stable throughout the distalization period.

View this table:
Table 1

Demographic assessment of the sample.

ParametersISP (n = 15)ZAS (n = 15) P value
Gender (female/male)10/510/5NS
Chronological age (year)14.3±1.614.7±2.5NS
Treatment period (month)8.1±4.29.0±2.4NS
  • NS: Nonsignificant, *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001

Point A did not move significantly in the ISP group and significantly retruded (P ≤ 0.05) in the ZAS group. Point B did not move significantly in the ISP group and significantly retruded (P ≤ 0.05) in the ZAS group. ANB angle increased in the ISP group and decreased in the ZAS group. Significant differences were observed between the groups for SNA angle (P ≤ 0.01), A-VR distance (P ≤ 0.05), and ANB angle (P ≤ 0.05). Lower and total anterior facial heights significantly increased and a minor amount of mandibular posterior rotation occurred in both groups, but there were no significant differences between the groups (Table 2).

View this table:
Table 2

Skeletal comparisons within and between the groups.

ParametersPredistalization (T0) P valueaPostdistalization (T1) P valuebChange (T1–T0) P valuec
SNA° NS **
ISP79.77±4.49 80.23±4.62NS0.47±1.13
ZAS79.27±3.25 78.03±3.94*−1.23±1.97
SNB° NS NS
ISP75.23±3.12 75.00±2.54NS−0.23±1.46
ZAS74.50±2.59 73.63±3.43*−0.87±1.27
ANB° NS *
ISP4.53±2.29 5.23±2.84NS0.70±1.50
ZAS4.77±1.66 4.40±1.55NS−0.37±1.14
A-VR mm NS *
ISP65.67±3.77 66.23±4.11NS0.57±1.65
ZAS68.47±5.02 67.07±5.93*−1.40±2.38
B-VR mm NS NS
ISP55.37±4.34 55.30±4.59NS−0.07±1.90
ZAS56.93±5.98 55.40±7.32*−1.53±2.14
SN/GoMe° NS NS
ISP35.10±4.03 35.60±4.00NS0.50±0.93
ZAS35.13±4.89 36.13±5.67*1.00±1.40
N-Me mm ** NS
ISP115.03±8.36 117.73±8.75*2.70±3.64
ZAS124.90±6.11 126.17±6.42*1.27±1.77
N-ANS mm NS NS
ISP53.43±3.70 53.83±3.90NS0.40±1.57
ZAS56.37±3.82 56.77±3.79NS0.40±0.51
ANS-Me mm NS NS
ISP65.30±5.50 66.93±5.65***1.63±1.01
ZAS69.40±6.28 70.30±6.78*0.90±1.67
  • aComparison of T0 measurements between the groups (NS: Nonsignificant, *P ≤ 0.025, **P ≤ 0.01, ***P ≤ 0.001).

  • bComparison of the T0 and T1 measurements within the groups (NS: Nonsignificant, *P ≤ 0.025, **P ≤ 0.01, ***P ≤ 0.001).

  • cComparison of the T1–T0 changes that were obtained between the groups (NS: Nonsignificant, * P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001).

Upper incisors protruded in the ISP group and significantly retruded (P ≤ 0.01) in the ZAS group. Upper posterior teeth were significantly distalized (P ≤ 0.001) in both groups, but more in the ZAS group. Significant differences (P ≤ 0.001) were observed between the groups for the sagittal movements of incisors and posterior teeth (Table 3).

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Table 3

Dental comparisons within and between the groups.

ParametersPredistalization (T0) P valueaPostdistalization (T1) P valuebChange (T1–T0) P valuec
U1-VR mm NS ***
ISP67.63±5.59 68.73±6.53NS1.10±2.44
ZAS70.03±5.94 66.70±7.86**−3.33±3.52
U4-VR mm NS ***
ISP54.10±4.46 53.20±4.81*−0.90±1.26
ZAS57.70±5.38 53.10±6.24***−4.60±1.70
U5-VR mm NS ***
ISP46.83±4.38 45.00±4.99***−1.83±1.14
ZAS50.80±5.36 45.63±6.00***−5.17±1.52
U6-VR mm NS ***
ISP39.97±4.55 36.97±4.87***−3.00±1.70
ZAS43.73±5.19 38.47±5.91***−5.27±1.53
U7-VR mm NS ***
ISP20.83±3.43 18.40±3.69***−2.43±1.24
ZAS21.23±5.16 16.80±5.61***−4.43±1.47
U1/HR° NS **
ISP105.27±11.75 107.27±11.43NS2.00±5.29
ZAS103.97±8.19 98.57±9.29**−5.40±6.51
U4/HR° NS NS
ISP90.23±4.94 85.70±4.98***−4.53±3.25
ZAS90.50±4.95 89.37±6.62NS−1.13±6.63
U5/HR° NS NS
ISP84.23±6.16 78.13±7.62***−6.10±5.80
ZAS82.40±4.47 80.13±5.58NS−2.27±5.70
U6/HR° NS NS
ISP79.07±6.88 70.27±7.47***−8.80±6.54
ZAS80.23±5.18 74.47±7.34***−5.77±4.99
U7/HR° NS **
ISP62.80±7.24 50.50±8.81***−12.30±6.66
ZAS67.73±5.12 62.03±7.39**−5.70±6.21
U1-HR mm NS *
ISP72.87±5.64 73.03±6.15NS0.17±1.13
ZAS77.43±5.25 78.57±5.03**1.13±1.30
U4-HR mm NS ***
ISP69.13±5.09 69.70±4.86NS0.57±1.13
ZAS73.80±5.31 72.63±5.12***−1.17±0.86
U5-HR mm NS ***
ISP68.03±4.89 68.53±5.05NS0.50±0.89
ZAS72.60±5.43 71.30±5.19***−1.30±1.21
U6-HR mm NS **
ISP66.27±4.99 66.20±5.43NS−0.07±1.02
ZAS70.30±5.52 68.90±5.24***−1.40±1.24
U7-HR mm * NS
ISP58.80±6.47 57.23±7.15**−1.57±1.90
ZAS64.67±5.39 62.17±5.72***−2.50±1.75
  • aComparison of T0 measurements between the groups (NS: Nonsignificant, *P ≤ 0.025, **P ≤ 0.01, ***P ≤ 0.001).

  • bComparison of the T0 and T1 measurements within the groups (NS: Nonsignificant, * P ≤ 0.025, **P ≤ 0.01, ***P ≤ 0.001).

  • cComparison of the T1–T0 changes that were obtained between the groups (NS: Nonsignificant, *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001).

Upper incisors did not show significant tipping in the ISP group and significantly retroclined (P ≤ 0.01) in the ZAS group. Upper posterior teeth showed significant distal tipping (P ≤ 0.001) in the ISP group and less considerable distal tipping in the ZAS group. Significant differences (P ≤ 0.01) were observed between the groups for upper incisor and second molar tipping (Table 3).

Minor vertical movements were observed at upper incisor and posterior teeth except for significant intrusion (P ≤ 0.01) at upper second molars in the ISP group. On the other hand, significant extrusion (P ≤ 0.01) of upper incisors and significant intrusion (P ≤ 0.001) of upper posterior teeth were observed in the ZAS group. Significant differences were observed between the groups except for upper second molars (Table 3).

Overbite significantly decreased (P ≤ 0.01) in the ISP group, overjet significantly decreased (P ≤ 0.05) in the ZAS group. Significant differences (P ≤ 0.01) were observed between the groups for overbite and overjet. Upper and lower lips did not move significantly in the ISP group and significantly retruded (P ≤ 0.05) in the ZAS group. Significant differences (P ≤ 0.05) were observed between the groups for lips (Table 4).

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Table 4

Interdental and soft tisue comparisons within and between the groups.

ParametersPredistalization (T0) P valueaPostdistalization (T1) P valuebChange (T1–T0) P valuec
Overjet mm NS **
ISP6.10±1.92 6.83±2.74NS0.73±1.57
ZAS5.20±1.74 4.00±1.79*−1.20±2.00
Overbite mm NS **
ISP4.33±2.17 3.03±2.53**−1.30±1.51
ZAS3.07±1.97 3.53±1.75NS0.47±1.26
ULip-VR mm NS *
ISP82.63±4.92 83.23±5.31NS0.60±1.65
ZAS86.80±5.88 85.20±7.30*−1.60±2.81
LLip-VR mm NS *
ISP77.40±4.66 77.53±5.26NS0.13±1.68
ZAS81.00±5.86 79.07±7.55*−1.93±3.03
  • aComparison of T0 measurements between the groups (NS: Nonsignificant, *P ≤ 0.025, **P ≤ 0.01, ***P ≤ 0.001).

  • bComparison of the T0 and T1 measurements within the groups (NS: Nonsignificant, *P ≤ 0.025, **P ≤ 0.01, ***P ≤ 0.001).

  • CComparison of the T1–T0 changes that were obtained between the groups (NS: Nonsignificant, *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001).

Discussion

Implant-supported molar distalization systems have been widely used in orthodontic practice lately. The number of studies examining the dentofacial effects of these systems have been published in the recent years (Mannchen, 1999; Karaman et al., 2002; Keles et al., 2003; Gelgör et al., 2004; Park et al., 2005; Kircelli et al., 2006; Sugawara et al., 2006; Cornelis and De Clerck, 2007; Escobar et al., 2007; Gelgor et al., 2007; Polat-Ozsoy et al., 2008; Kaya et al., 2009; Oh et al., 2011; Ohura et al., 2011; Yu et al., 2011). Most of these papers separately evaluated an implant-supported molar distalization system without a control group (Mannchen, 1999; Karaman et al., 2002; Keles et al., 2003; Gelgör et al., 2004; Park et al., 2005; Kircelli et al., 2006; Sugawara et al., 2006; Cornelis and De Clerck, 2007; Escobar et al., 2007; Oh et al., 2011; Ohura et al., 2011) and a few papers compared these systems with conventional methods (Polat-Ozsoy et al., 2008; Kaya et al., 2009). Two papers compared different implant-supported molar distalization systems with each other (Gelgor et al., 2007; Yu et al., 2011). However, one of them was a finite element study without clinical assessment (Yu et al., 2011) and the other one was comparison of similar distalization methods obtaining anchorage from the same anatomical region (Gelgor et al., 2007).

In this study, we examine and compare the skeletal, dental, and soft tissue effects of two different implant-supported molar distalization systems that are assumed to provide absolute bone anchorage from different anatomical regions of the oral cavity. Hence, implant-supported pendulum (ISP), which provides anchorage from the anterior palate, and zygoma anchorage system (ZAS), which provides anchorage from the zygomatic buttress, were compared for distalization of maxillary posterior teeth in two groups of patients with similar age, gender distribution, and dentofacial characteristics. Thus, the implant-supported distalization methods applied in this study were chosen with an attempt to substitute each other if one of the methods is not available due to anatomical or physiological conditions of patients.

It can be argued that the force applied in the ZAS group was two times greater than the ISP group, which causes unequal conditions. However, the resistance of these two systems to the reactive forces would naturally be different due to the anchorage unit and appliance design, leading to an important advantage of being able to apply higher distalization forces with ZAS. Since this is the major concern in most distalization systems and can be achieved only with a system that requires invasive surgical procedures, then there is a necessity to compare its effects with a less invasive, easily applied and common alternative, to define the specific area of use of both systems.

It was observed that Point A protruded in the ISP group and retruded in the ZAS group, whereas Point B retruded in both groups. The protrusion of Point A can be explained with the protrusion of upper incisors in the ISP group and the retrusion of Point A can be explained with the retrusion of upper incisors in the ZAS group. The retrusion of Point B can be attributed to the clockwise rotation of the mandible which is observed in both groups. ANB angle inherently increased in the ISP group due to the protrusion of Point A and decreased in the ZAS group due to the retrusion of Point A. The minor amounts of mandibular clockwise rotation and increases in lower and total anterior facial heights observed in both groups can possibly be the result of a slight change in the position of mandible due to unstable occlusion. These findings were similar with other studies in which similar mechanics were used, despite the fact that skeletal changes obtained with molar distalization systems were evaluated only in a few of them (Kircelli et al., 2006; Escobar et al., 2007; Polat-Ozsoy et al., 2008; Kaya et al., 2009).

Upper incisors slightly proclined and protruded in the ISP group while substantially retroclined and retruded in the ZAS group. The differences observed between the groups in the sagittal movements of upper incisors are definitely related with the location of bone anchorage unit used for distalization of maxillary posterior teeth. In the ISP group bone anchorage is provided from two intraosseous screws placed in the anterior paramedian region with an acrylic plate covering these screws and the anterior palate. Hence, the distalization force creates a reactive force with an anterior force vector that pushes the acrylic plate and the screws to the anterior palate. This might have resulted in some amount of anterior tipping of the screws without lack of stability accompanied by slight embedment of the acrylic plate into the gingiva leading to protrusion of upper incisors by labial tipping. On the other hand, in the ZAS group bone anchorage is provided from miniplates placed in the zygomatic buttress and no reactive force is applied to the anterior palate or upper incisors. Thus, distalization of upper posterior teeth causes retrusion of upper incisors by lingual tipping due to the tension that occurs in transseptal gingival fibers. Similar with our findings, nonsignificant movements were obtained in upper incisors with implant-supported pendulum and significant retrusion was obtained with zygoma anchorage in other studies (Kircelli et al., 2006; Escobar et al., 2007; Polat-Ozsoy et al., 2008; Kaya et al., 2009).

Upper posterior teeth were distalized with a mean amount of 1–3mm in the ISP group, increasing from the premolars to the molars. On the other hand, they were distalized with a mean amount of 5mm in the ZAS group, equally in the premolars and the molars. The gradual amount of distalization observed in the ISP group can be explained with the application point of distalization force which is the maxillary first molars. Hence, maxillary molars were distalized directly with activation of pendulum springs, and maxillary premolars were distalized indirectly with the tension of transseptal gingival fibers descending from upper second premolars to first premolars. Conversely, the application point of distalization force is maxillary first premolars in the ZAS group, which is certainly the reason of equal distalization of posterior teeth as a block. The significant difference observed between groups for the distalization amounts of upper posterior teeth can be attributed to the difference between the magnitude of distalization forces applied in the ISP and ZAS groups, which were 230 and 450g, respectively. The distalizations obtained in the ISP group were a little small compared to other implant-supported pendulum studies (Kircelli et al., 2006; Escobar et al., 2007; Polat-Ozsoy et al., 2008), which is probably the result of less distal tipping observed in our ISP group. On the other hand, the distalizations obtained in the ZAS group were somewhat greater than other zygoma anchorage studies (Sugawara et al., 2006; Cornelis and De Clerck, 2007), which is probably due to the greater distalization force and increased distalization period in our ZAS group.

Distal tipping was observed at upper posterior teeth in both groups, but the tipping was less considerable in the ZAS group. The marked distal tipping examined in the ISP group compared with the ZAS group can be explained with the difference between the distalization mechanisms of the two systems. ISP applies distalization force with 60°–70° posterior activation of the pendulum springs passing through the crown level of upper first molar teeth that causes distal tipping at the maxillary molars naturally. A significant but less amount of distal tipping also occurs in maxillary premolars as they follow the molars with the same movement pattern. In contrast with ISP, which has no control over tipping of posterior teeth, ZAS applies distalization force passing through the center of resistance of upper posterior teeth by stretching of coil springs from the crimpable hooks to the zygoma anchors. Besides, distalization of all posterior teeth takes place on 0.016×0.022" stainless steel continuous arch wire with sliding mechanics. Thus, these characteristics of the system prevent excessive distal tipping of maxillary posterior teeth during distalization. Distal tipping observed in the ISP group was less compared with other implant-supported pendulum studies (Kircelli et al., 2006; Escobar et al., 2007), which is probably due to the uprighting bends of pendulum springs in our ISP group.

Minor vertical movements were observed at upper incisor and posterior teeth whereas significant intrusion was observed at upper second molars in the ISP group. The reason of the intrusion monitored only at upper second molars can be the excessive distal tipping detected at these teeth. On the other hand, significant extrusion of upper incisors and significant intrusion of upper posterior teeth were perceived in the ZAS group. Extrusion of upper incisors can be explained with the prominent lingual tipping of these teeth and intrusion of upper posterior teeth can be attributed to the apical position of zygoma anchors, which adds an intrusive component to the distalization force despite long crimpable hooks.

Overbite decreased in the ISP group; overjet decreased in the ZAS group. The changes obtained in these parameters are definitely related to the proclination of upper incisors in the ISP group and the retroclination of upper incisors in the ZAS group. Similarly, upper and lower lips protruded in the ISP group and retruded in the ZAS group. The differences observed between the groups for overbite, overjet, and the position of lips can also be evaluated as the most distinctive and critical findings of the study. These findings were also similar with other studies in which similar mechanics were used (Kircelli et al., 2006; Cornelis and De Clerck, 2007; Polat-Ozsoy et al., 2008; Kaya et al., 2009).

The average distalization period was 8.1 months in the ISP group and 9.0 months in the ZAS group, which were statistically comparable. The distalization periods in this study were comparable with other studies in the ISP group and a little longer than other studies in the ZAS group, in which identical treatment protocols were used (Kircelli et al., 2006; Cornelis and De Clerck, 2007; Escobar et al., 2007; Polat-Ozsoy et al., 2008). The relatively longer distalization time in the ZAS group of this study can be attributed to the full unit class II buccal segment relationship of the patients in this group which required longer time for greater amount of distalization. On the other hand, the distalization rates were 0.1–0.37mm/month in the ISP group and 0.5–0.6mm/months in the ZAS group.

The shorter distalization period may be considered as one of the most important improvements in any distalization procedure and can certainly alter the clinicians’ choice of treatment method—whether distalization or extraction. However, it must be kept in mind that distalization period must be evaluated in conjunction with the skeletal, dental, and soft tissue outcomes of the applied distalization system. The zygoma anchors can be used as anchorage to prevent relapse of buccal segment distalization and to retract the anterior segment in the second phase of treatment. Besides, uprighting of upper molars and distalization of upper premolars are not required, as all of them are distalized adequately without prominent tipping in the first phase of treatment. Therefore, despite the relatively long distalization period, the anticipated total treatment time is shorter in the ZAS group. Nevertheless, ISP is affordable and can be applied easily in an orthodontics clinic, whereas ZAS is expensive and requires complicated surgical procedures. Since the expectations and clinical requirements vary in each case, the most convenient method that each patient individually can benefit the most should be preferred.

Conclusions

  1. The H0 hypothesis is rejected and H1 hypothesis is accepted.

  2. Both methods can be used as aesthetic, noncompliant, and reliable alternatives to extraoral traction and conventional molar distalization appliances.

  3. ZAS is more advantageous in severe class II malocclusion cases with maxillary protrusion.

Acknowledgements

We would like to thank our biostatistician Dr. Salih Ergocen for his contributions.

References

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