Stepwise advancement versus maximum jumping with headgear activator
* Orthodontics, University of Hong Kong, Hong Kong, SAR and
** Private Practice, Houston, Texas
Address for correspondenceProfessor Urban Hägg, Faculty of Dentistry, The University of Hong Kong, 2/F Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong SAR, E-mail: euohagg{at}hkusua.hku.hk
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Summary |
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The aim of this study was to compare the effects of stepwise mandibular advancement versus maximum jumping and extended treatment versus early retention. The material was obtained prospectively and consisted of lateral cephalograms taken at the start (T0), after initial (T1), and at the end (T2) of treatment, from two groups of consecutively treated skeletal Class II patients who had undergone therapy with headgear activators. The first headgear activator group, HGA-S (n = 24; mean age 11.9 ± 1.2 years), was treated for 13 months and had 4-mm mandibular advancement every 3 months. The second headgear activator group, HGA-M (n = 31; mean age 11.2 ± 1.5 years), had maximum jumping, 6–8 mm interincisal opening, for a total of 15.4 months, and with reduced wear for the last 6.9 months. The dropout over 12 months was 41 and 46 per cent, respectively. Pre-treatment growth changes were obtained as a reference. An independent t-test was used to determine differences in baseline dentofacial morphology between the groups, a paired t-test for intra-group comparisons, and an independent t-test to evaluate differences between the groups.
The results, in both groups, showed enhanced mandibular prognathism during the initial phase (T0–T1), followed by normal growth (T1–T2), and lower face height enhancement throughout treatment (T0–T2). For both groups, the mandibular plane and occlusal angle increased, possibly enhanced by ‘extrusion’ of the lower molars. For both groups, maxillary forward growth was restrained only during the initial phase, but the effect remained significant at T2 for the HGA-S group. In the HGA-M group, the lower incisors were protruded, while in the HGA-S group, they were unaffected. The findings indicate that both modes of mandibular jumping resulted in skeletal and dental effects. The length of active treatment seemed to be decisive in maintaining the treatment effects; stepwise advancement had less dental effects.
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Introduction |
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There has been growing interest in the subject of orthopaedic correction of Class II malocclusions in recent years (Graber et al., 1997
; Meikle, 2005). Some studies have demonstrated no significant effect, while others have shown enhanced mandibular growth with functional appliance treatment (Pancherz, 1979; Jakobsson and Paulin, 1990; Ghafari et al., 1998; Illing et al., 1998; Keeling et al., 1998; Tulloch et al., 1998, Ruf et al., 2001; Basciftci et al., 2003; Haralabakis et al., 2003; O'Brien et al., 2003a; Phan et al., 2006). The addition of high-pull headgear to the functional appliance possibly combines restraint and redirection of maxillary growth with potentially more forward positioning of the mandible (van Beek, 1982; Dermaut et al., 1992; Wieslander, 1993; Ömblus et al., 1997; Altenburger and Ingervall, 1998; Bendeus et al., 2002; Hägg et al., 2003).
Recent experimental studies demonstrated that condylar growth was enhanced with mandibular advancement, and significantly more so with stepwise advancement than with maximum jumping (Rabie et al., 2003a,b). Two clinical studies using fixed or removable functional appliances in combination with headgear have shown that mandibular stepwise advancement tended to result in larger enhancement of mandibular prognathism than maximum jumping (Ömblus et al., 1997; Du et al., 2002), whereas a study using a removable functional appliance without headgear was unable to demonstrate any significant difference between the mode of mandibular jumping (Banks et al., 2004).
It has been reported that after enhancement of mandibular prognathism in a shorter active period with functional appliances, mandibular prognathism became ‘subnormal’ during the immediate post-treatment period (Pancherz and Hansen, 1986). However, others have found a return to normal mandibular forward growth rate during extended treatment (Hägg et al., 2002). An experimental study has demonstrated that the enhancement of mandibular growth was maintained where the active treatment time was not too short (Chayanupatkul et al., 2003).
The aim of this study was to compare the treatment effects of stepwise advancement versus maximum jumping of the mandible, and extended treatment time versus early retention.
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Subjects and methods |
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The material consisted of the lateral cephalograms from two separate groups of consecutively treated patients with a skeletal Class II malocclusion, obtained at the start (T0), after the initial phase (T1), and at the end of treatment (T2). Inclusion criteria were age 8–16 years, overjet
6 mm, ANB 4 degrees, molars at least half unit Class II bilaterally, and no previous orthodontic treatment. For both groups, ethical approval was obtained from the Ethics Committee, Faculty of Dentistry, University of Hong Kong. The subjects had been treated by postgraduate students under the supervision of two designated supervisors. The length of the treatment was predetermined to approximately 12 months in both groups.
Headgear activator with stepwise advancement and extended treatment (HGA-S) group
The appliance consisted of a high-pull headgear combined with a modified activator using a screw to advance (by the operator) the mandible 4 mm every 3 months (Figure 1A). All subjects had the mandible advanced 8 mm during the initial phase (T0–T1). Thereafter, the amount of mandibular advancement was dependent on the size of the remaining overjet at T1. The majority of the patients had a third advancement and two subjects had a fourth advancement. The average mandibular advancement was 12 mm. The interincisal opening was 3–4 mm. Extraoral force of approximately 350 g each side was used. The patients were instructed to wear the appliance, with the headgear, 10–14 hours per day during the whole treatment period and compliance was evaluated from a written report. Thirty-four (83 per cent) of the 41 subjects completed the first stage of treatment (T0–T1). Twenty-four patients (6F and 18M; 59 per cent; mean age = 11.9 ± 1.2 years) completed the later phase of treatment (T0–T2) after 13.0 months, and were included in the analysis (Table 1; Figure 2). The dropout (n = 17; 41 per cent) was due to failure (resulting in no advancement of the mandible) of the appliance screw mechanism (n = 5), poor compliance (n = 9), self-discontinuation from treatment (n = 2), and poor attendance (n = 1).
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Headgear activator with maximum jumping and early retention (HGA-M) group
The HGA-M, with extraoral high-pull traction, had a construction bite edge-to-edge with 6–8 mm interincisal opening and an extraoral force of approximately 500 g at each side (van Beek, 1982; Figure 1B). The amount of mandibular advancement varied from 9 to 15 mm (average 12 mm). The patients were instructed to wear the appliance 10–14 hours per day during active treatment (T0–T1) and compliance was evaluated from the patients’ written reports. During retention (T1–T2), the headgear was removed and the appliance was worn at night only. Forty-three (75 per cent) of 57 subjects completed the first stage of treatment (T0–T1), while 31 (11F and 20M; 54 per cent; mean age = 11.2 ± 1.5 years) completed the retention phase (T1–T2) after a total of 15.4 months, and were subsequently included in this study (Table 1). The dropout (n = 26; 46 per cent) was due to poor compliance in the first 2 months of treatment (n = 12), respiratory problems (n = 6), poor compliance (n = 7), and emigration (n = 1).
Untreated growth data
Growth changes were obtained from lateral cephalograms of the HGA-M group 6 months prior to treatment.
Method of analysis
All radiographs were manually traced twice by one examiner (MCW) with an interval of at least 2 weeks before being digitized and measured by CASSOS software (CASSOS 2001, City University, Hong Kong) using the analysis of Björk (1947) and Pancherz (1982a, b; Figure 2). Data from the two tracings of the same radiographs were then averaged. As the treatment periods differed significantly between the groups, interpolation was undertaken on the results to represent exactly the same length of compared periods, i.e. 6 and 12 months, respectively (Table 1). Growth changes obtained from the untreated growth data were deducted from treatment changes to obtain the net treatment effects.
Statistical analysis
Statistical analysis was carried out using the Statistical Package for Social Science (SPSS Inc., Chicago, Illinois, USA) software. An independent t-test was used to determine differences in baseline dentofacial morphology between both groups. A paired t-test was used for intra-group comparisons and differences between groups were evaluated by an independent t-test.
Method error
Two weeks after the first measurement, 10 sets of radiographs were selected at random and retraced twice, redigitized, and remeasured. The combined method errors for landmark identification and measurement were tested using two-tailed paired t-tests. Differences between the first and second measurements were insignificant.
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Results |
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Comparison of dentofacial morphology
At T0, the HGA-S group had a statistically significantly more severe Class II jaw base relationship and deeper overbite, but at T2 there was no difference in dentofacial morphology between the two groups (Table 2).
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There were no statistically significant gender differences for normal growth and treatment changes in either group, except for lower permanent first molar extrusion, which was greater in males in the HGA-S group at T2. Data for both genders were therefore pooled for analysis.
‘Growth changes’ over 6 months were significant for linear measurement of mandibular forward growth (OLp-Pg), lower incisor, and upper molar eruption (Table 3).
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Treatment changes and effects in the HGA-S group
At the end of treatment (T0–T2), the statistically significant treatment effects in the HGA-S group were a reduction of overjet and overbite, restraint of maxillary forward growth, increase of mandibular prognathism and lower face height, improvement of jaw base and molar relationship, retrusion and intrusion of upper incisors, and extrusion of lower molars (Tables 3 and 4; Figures 3 and 4). The mandibular plane angle increased, while the maxillary and mandibular occlusal plane angles decreased and increased, respectively. Most of these effects were pronounced in both the initial (T0–T1) and the late (T1–T2) phases of treatment, except for mandibular prognathism and retrusion of the upper incisors. There were no differences in treatment effects between either treatment phase except for a greater improvement in overjet and molar relationship in the initial treatment phase.
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Treatment changes and effects in the HGA-M group
At the end of treatment (T0–T2), the statistically significant effects in the HGA-M group were a reduction of overjet and overbite, increased mandibular prognathism (OLp-Pg) and lower face height, improvement of jaw base and molar relationship, protrusion of lower incisors and molars, and eruption of lower molars (Tables 3 and 4; Figures 3 and 4). The mandibular plane and occlusal plane angles increased. There were statistically significant effects in the initial (T0–T1) treatment phase for these variables, and also for restraint of maxillary forward growth, retrusion of upper incisors and molars, and intrusion of upper incisors. There were statistically significant effects in the retention phase (T1–T2) for increase of lower face height, forward movement and eruption of upper incisors and molars, and eruption of lower molars. Most variables improved during T0–T1, while from T1–T2 some effects rebounded, but mostly normal growth returned.
Comparison of the treatment effects between the HGA-S and HGA-M groups
There were some statistically significant differences in the treatment effects after therapy (T0–T2) between the HGA-S and HGA-M groups (Table 4). The HGA-S group showed a more pronounced reduction in overbite, improvement of jaw base (ANB) and molar relationship, upper incisor intrusion, and less lower incisor protrusion. The upper occlusal plane closed and the mandibular plane angle increased more in the HGA-S group. During T0–T1, there was a greater improvement in jaw base relationship (ANB), less upper incisor retrusion and lower incisor protrusion, and the upper occlusal plane closed in the HGA-S group. During the later treatment phase in the HGA-S group and the retention phase in the HGA-M group (T1–T2), there were statistically significant differences since treatment effects continued in the HGA-S group, while some treatment effects rebounded in the HGA-M group. The skeletal contribution to the reduction of overjet at T2 was 70 per cent in the HGA-S group and 59 per cent in the HGA-M group (Figure 3). There was no significant difference in treatment changes between the two groups for maxillary and mandibular prognathism, jaw base relationship, and lower face height (Figure 4A–D). The upper incisors were more retruded during T0–T1 in the HGA-M group, but rebounded and became more protruded at T2 than in the HGA-S group (Figure 4E). The lower incisors became protruded but only in the HGA-M group (Figure 4F).
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Discussion |
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This was a prospective study based on two separate groups of consecutive skeletal Class II patients treated with a headgear activator, with two different modes of mandibular jumping. The sampling criteria used were similar but the dentofacial morphology of the groups differed at the start of treatment (T0) for jaw base relationship and overbite, which was more severe in the HGA-S group (Table 3). However, these differences were probably not clinically relevant, and consequently do not affect the validity of this study. The dentofacial morphology of the patients was generally in agreement with that of Caucasian samples treated with the HGA-M appliance (Dermaut et al., 1992
; Altenburger and Ingervall, 1998; Bendeus et al., 2002), except that the protrusion of the upper and lower incisors was more pronounced in the present Chinese subjects, which is a documented ethnic difference, also in Class II subjects (Lau and Hägg, 1999).
Interpolations were made to represent intervals of exactly 6 and 12 months, which enables a direct comparison to be made between the two groups and age with the results of previous studies on functional appliances (Ömblus et al., 1997; Bendeus et al., 2002; Du et al., 2002; Hägg et al., 2002, 2003), and a general comparison to be made with other studies on the headgear activator, where the patients were treated on average for 9–11 months (Dermaut et al., 1992; Altenburger and Ingervall, 1998).
The findings suggest that during the actual period neither growth rate nor treatment response differed between the genders, which might indicate that the majority of the patients were pre-pubertal when treated (Pancherz and Hägg, 1985). Since the growth reference data were obtained prior to treatment, the average basic growth rate measured might differ slightly to that observed during the respective treatment periods, but probably to a negligible extent, since the observation periods were short. Growth data obtained prior to treatment of the HGA-M group showed growth in respect of mandibular prognathism and face height, which is consistent with that observed in controls in some previous studies on functional appliances (Nelson et al., 1993; Wieslander, 1993; O'Brien et al., 2003a). However, it should be noted that in other studies the controls showed practically no mandibular growth (Ömblus et al., 1997; Illing et al., 1998).
Metric cephalometric measurements are demonstrably more accurate (Bookstein, 1997), but angular measurements are more commonly reported in the orthodontic literature, and have therefore been included.
In any functional appliance treatment, whether with fixed or removable devices, there is a dropout rate. The dropout figure sometimes represents only patients who have left the study (Tulloch et al., 1998) but it often includes, as in the present research, non-compliant patients (Ömblus et al., 1997; Ghafari et al., 1998; Bendeus et al., 2002; O’Brien et al., 2003a,b). The dropout rate in the initial treatment phase of this study (T0–T1) was 17 per cent in the HGA-S group and 25 per cent in the HGA-M group. These figures are comparable with other investigations with similar observation periods (Ömblus et al., 1997; Illing et al., 1998; Bendeus et al., 2002; Banks et al., 2004). However, the dropout rate at the end of the present study (T2) was over 40 per cent in both samples. This was towards the higher end of that reported in other studies on removable functional appliances, which varied from 6 to 40 per cent (Nelson et al., 1993; Ömblus et al., 1997; Altenburger and Ingervall, 1998; Illing et al., 1998; Keeling et al., 1998; Bendeus et al., 2002). Dropout usually increases with time, but the age of the sample seems to be an important factor, as observed from a comparison between two recent studies on the Twin Block (TB; O'Brien et al., 2003a,b). In that investigation, the younger sample had a dropout rate of 18 per cent, whereas 3-year-old subjects had a dropout rate almost twice as large. In the later study, it was also reported that the dropout rate of patients treated with the fixed functional Herbst appliance was approximately half that of those treated with the TB appliance. There might be fewer dropouts in a patient sample treated by a single, ‘committed’, clinician than in a one treated by a larger number of clinicians. The patients analysed in this study were definitely compliant and submitted written reports throughout the study, but still it has to be borne in mind that orthodontic patients have been stated to over report compliance (Brandão et al., 2006).
The treatment effect on overjet was statistically significant with both devices after both 6 (T1) and 12 (T2) months of treatment (Table 4), which is consistent with previous studies of the HGA-M appliance (Dermaut et al., 1992; Altenburger and Ingervall, 1998; Bendeus et al., 2002). However, the overjet continued to decrease in the late phase in the HGA-S group only, and at the end of treatment (T2) there was no difference between the two groups (Figure 4G). Restraint on maxillary forward growth was found with both devices after 6 months (T1) and while this disappeared, after 6 months of retention (T2) in the HGA-M group, it became more pronounced in the HGA-S group after extended treatment. In one study, there was no restraint of maxillary growth after 6 months of treatment, whereas after a further 6 months of treatment there was an effect (Bendeus et al., 2002) similar to that reported after 9–11 months of treatment (Dermaut et al., 1992; Altenburger and Ingervall, 1998). In the present study, mandibular growth was accelerated with both devices after 6 and 12 months of treatment, which is in agreement with all but one of the other studies, which indicated that mandibular growth was unaffected (Bendeus et al., 2002). However, the enhancement of mandibular prognathism reached a statistically significant level only during T0–T1 similar to that reported for the Herbst appliance (Hägg et al., 2002). The upper incisors were retruded with both devices during T0–T1, but relapsed during T1–T2 in the HGA-M group. This was similar to the pattern observed by Bendeus et al. (2002) that there was no lasting effect after 12 months of treatment with HGA-M. At T2, the upper incisors were retruded in the HGA-S group, which is in agreement with the observations made after 9 and 11 months with the HGA-M appliance in two previous studies (Dermaut et al., 1992; Altenburger and Ingervall, 1998). The mandibular incisors became protruded with the HGA-M appliance in this study at T1 and T2, but no such effect was observed in the HGA-S group or with HGA-M in previous studies (Dermaut et al., 1992; Altenburger and Ingervall, 1998; Bendeus et al., 2002). This difference in effect on the lower incisors might depend on the degree of labial lower incisor capping rather than stepwise advancement. The skeletal changes contributing to the overjet reduction was larger with the HGA-S than the HGA-M, being 70 and 59 per cent, respectively, after treatment (Figure 3).
There was an increase of lower face height during both the initial and the late phases with both devices in this study, whereas two previous reports found no effect on lower face height with high-pull headgear (Dermaut et al., 1992; Bendeus et al., 2002). The increase in lower face height may be partly due to the lower molars having been extruded during treatment with both devices and in both treatment phases, whereas in one previous study (Bendeus et al., 2002) they were unaffected. The extrusion of the lower molars in the HGA-S group could be explained by the fact that this two-piece device did not prevent eruption, while in HGA-M group, there was no occlusal stop at the lower first molars. The maxillary occlusal plane angle closed in the HGA-S group only, due to continuous intrusion of the upper incisors, but in the HGA-M group there was no net effect on intrusion of the upper incisor and no lasting effect on the maxillary occlusal plane. In both groups, the mandibular occlusal plane angle increased due to extrusion of the lower molars, whereas there was no significant effect on the lower incisors in the vertical plane. Stepwise versus maximum jumping of the mandible produced no significantly different skeletal effect on mandibular prognathism compared with maximum jumping.
There were fewer dental effects in the HGA-S group, which might be a reflection of the lower force transmitted to the dentition when the mandible was gradually advanced by 8 mm (2 x 4 mm) over the first 6 months, compared with an average jumping of the mandible of 12 mm in the HGA-M group at the start of treatment. A comparison of two groups treated with the TB for 7 months (Banks et al., 2004) found no difference in sagittal maxillary and mandibular treatment changes between stepwise advancement and maximum jumping of the mandible. This was in general agreement with the findings of Illing et al. (1998) who compared the effects of stepwise versus maximum jumping using Bass versus Bionator and TB. A tendency to a greater increase in mandibular prognathism was observed with gradual advancement (3 x 2 mm) of the mandible with the Bass appliance compared with maximum jumping with the Herbst appliance after 6 months of treatment (Ömblus et al., 1997) and with stepwise advancement (3 x 2 mm) with the Herbst appliance (Hägg et al., 2002). In an experimental study, it has been demonstrated that stepwise advancement of the mandible resulted in significantly more condylar bone formation (2 + 1.5 mm) than a similar amount of single advancement (3.5 mm), even though fixed appliances were used in both cases (Rabie et al., 2003b).
It has been claimed, from a survey of clinical studies, that increased mandibular growth during active treatment will be followed by a period of subnormal growth, and that this ‘enhancement effect’ is merely temporary (Pancherz and Michailidou, 2004). In many studies on functional appliances, the active treatment period was comparatively short, e.g. 5–7 months (Pancherz, 1979; Pancherz and Hansen, 1986; Wieslander, 1993; Ömblus et al., 1997; Wong et al., 1997), i.e. a potentially unfavourable growth pattern was affected for a brief period but then returned to its original pattern (Pancherz and Fackel, 1990). In the present study, the HGA-M treatment lasted for 8.6 months (T0–T1), and was followed by retention (T1–T2) using the same device at night only and without the headgear for nearly 6 months. During the retention period, there were no further significant positive effects, and the skeletal changes did not differ from those of normal growth, but relapse of dental effects and increase in lower face height continued. With continued treatment with the HGA-S, the effects achieved during the initial phase of treatment were maintained, and some further improvement occurred, which is in agreement with previous studies of extended treatment with the HGA-M and Herbst appliance, respectively (Bendeus et al., 2002; Hägg et al., 2002). It has also been demonstrated that early removal of a functional appliance does not allow the new condylar bone to mature, and subsequently the treatment gain in bone is not fully maintained, whereas prolonged use of the functional appliance results in permanent gain of the newly formed condylar bone (Chayanupatkul et al., 2003). Consequently, the length of active treatment seems to be a crucial factor in achieving more pronounced and lasting effects.
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Conclusions |
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The findings indicate that stepwise mandibular advancement does not affect mandibular prognathism differently from maximum mandibular jumping. With both modes of mandibular jumping, there is enhanced mandibular growth in the initial phase only, and the effect is maintained in the late phase, indicating that extended treatment is of importance. There was a significant increase in lower face height with both devices but neither device prevented extrusion of the lower molars. With stepwise advancement, the dental effects were less pronounced, and there was no protrusion of the lower incisors. The length of active treatment tended to be decisive in maintaining and further enhancing the treatment effects.
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Acknowledgement |
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We wish to thank Mr Shadow Yeung for his valuable statistical guidance and support, and Ms Zinnia Pang for her secretarial work.
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References |
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