Cephalometric evaluation of skeletal alterations induced by Herbst appliance during mixed dentition

Methods: The sampling consisted of 15 pre-pubertal individuals (12 boys and 3 girls; initial age 9 years and 6 months), who were treated with Herbst appliance for a period of 7 months. The effects of the treatment were compared to a group of 15 individuals with Class II, division 1 malocclusion (8 boys and 7 girls, initial age averaged 9 years and 1 month), orthodontically untreated, who were followed up for a period of 12 months. Statistical analysis was performed with Student’s t-test with significance level at 5%.

as retainers until the end of the growth period, in order to minimize the potential relapse. 25uring the past 20 years, many studies have been conducted to assess the effects of Herbst appliance over craniofacial skeleton, during the Class II treatment.However, only a few studies have evaluated the effects of Herbst appliance in mixed dentition stage. 1,3,28,29The vast majority of researches investigated the effects of treatment in permanent dentition.For these reasons, this prospective clinical study aimed to measure the horizontal and vertical skeletal effects induced by Herbst appliance in the early treatment of Angle Class II malocclusion.

Characterization of the sample
The treated group was composed of 15 Caucasian children (12 boys and 3 girls), ranging in age from 8 to 10 years (average initial age of 9.4 years and standard deviation of 0.64; average final age of 10.1 years and standard deviation of 0.64).Individuals were selected based on the following criteria: Class II facial pattern, associated with mandibular retrusion; Class II division 1 malocclusion; permanent maxillary and mandibular central and lateral incisors erupted or in eruption; mixed dentition; absence of severe crowding in the lower arch and the absence of transverse problems.Facial morphological pattern was determined by the Facial Height Ratio of Jarabak.In this study, 60% of individuals presented mesofacial pattern, 33.33% brachyfacial pattern and 6.66% dolichofacial pattern.This study has been approved by the Ethics Committee in Research (protocol 73/04).
To determine the Class II facial pattern and the Class II malocclusion, both face and occlusion were clinically analyzed.In this way, there was a certain subjectivity, because measurable data obtained from facial radiographs were not used.In facial analysis were observed some characteristics that helped to determine the Class II facial pattern, like morphological evaluation of the nasolabial angle (straight, obtuse and acute) and length of mentocervical line.In this way, individuals who have a convex profile, straight nasolabial angle or slightly acute and short mentocervical line, were classified as Class II facial pattern (Figs 1A and 1B).The Class II division 1 malocclusion was determined by the sagittal position of permanent Patients were treated with modified Herbst appliance (Fig 3 ), where permanent maxillary first molars were banded and united to each other by a transpalatal bar, welded to bands with a 2 mm distance from palate 7 (Fig 4A).For mandibular anchorage was used a Nance modified lingual arch, constructed with 1.2 mm steel wire welded to permanent mandibular first molars bands.A cantilever with extension up to the region of deciduous or permanent canines was welded in the buccal surface of the mandibular first molars bands.The link between the cantilever and the lingual arch was made in the region of canines and deciduous first molars or permanent canines and first premolars, using a 0.9 mm wire in order to avoid occlusal interferences 18 (Fig 4B).The anterior projection of the mandible with the Herbst appliance, was performed according to Pancherz, 14 i.e., single mandibular advancement until the incisors were in an end-to-end relationship (Fig 4C).The appliance was used for a period of 7 months (Fig 5).At the end of the active stage of treatment it was verified that the centric occlusion was coinciding with the maximal intercuspation in all patients.
The control group, selected from the files of Burlington Growth Centre, located at the University of Toronto, Canada, involved 15 children (7 girls and 8 boys).The criteria for selection of the control group were: Class II facial pattern, associated with mandibular retrusion; Class II division 1 malocclusion; erupted permanent maxillary and mandibular central incisors; mixed dentition and absence of previous orthodontic treatment.The mean initial age of the control group was 9 years and 1 month (standard deviation 0.09) and the mean final age was 10 years (standard deviation 0.05).In relation to facial morphological standard of the control group, 73% of individuals presented mesofacial pattern, 20% brachyfacial pattern and 7% dolichofacial.
The skeletal age of both groups was verified through radiographs in lateral standard, determining skeletal maturation stage using cervical vertebrae. 10The determination of bone age was performed by the same operator blind to the patient status, which reduces the effect of subjectivity of this evaluation.Individuals in this study were located in the stages 1 and 2 of maturation, i.e., before the peak of pubertal growth. 2,12wo profile radiographs in maximal habitual intercuspation were obtained for each individual in the experimental group, named T 1 , at the beginning of treatment and T 2 , 7 months after the treatment.The X-rays were carried out using an X-ray machine (Rotograph Plus, model MR05, regulated to 85 Kvp and 10 mA and exposure time of 0.5 seconds).For the control group were obtained two profile radiographs in maximal intercuspation, named: T 1 , at 9 years of age and T 2 , at 10 years of age.The radiographs were obtained with equipment of brand Keleket™ set to 120 Kpv, 25 mA and exposure time of 0.3 seconds.
Although these radiographs were obtained by different X-ray machines, the correction of image magnification was not conducted.The magnification of the image, i.e., the percentage of magnification on the experimental sample was 10%, representing a magnification of 0,1000 cm (1,000mm) 23 .In the control group, the percentage of magnification reported was of 9.84%, according to the records of Burlington Growth Centre. 17The magnification percentage difference between samples would be 0.16%, what would not affect the comparison of variables obtained from radiographs taken in the different X-ray machines.This difference in magnification would correspond to a difference in magnification between X-rays of 0.0016 cm (0.016 mm).All radiographs were traced manually by a single operator.The points were typed into Numonics AccuGrid digitizer and evaluated by means of Dentofacial Planner Plus 2.01 computer software to obtain the cephalometric measurements (Fig 6).

PNS ANS
Cephalometric evaluation of skeletal alterations induced by Herbst appliance during mixed dentition original article

ReSultS
To assess the possible occurrence of measurement errors, all tracings were typed again and measured by the same operator, with a range of 2 weeks between the first and second evaluation.It was used intraclass correlation coefficient (ICC) to evaluate the error of method (reproducibility).The results indicated that the measurement process was highly accurate because the expected value of the ICC was, at least, 0.983 and for most variables the ICC was above 0.99.
To compare the measurement changes, with and without treatment, it was necessary to eliminate the time difference effect between measurements made in the experimental and control group.To do so, measurement changes were annualized.
To assess the data, the following statistical tests have been conducted: a) Student's t-test for the average equality of two independent populations -to examine the hypothesis that the average of each measurement of control group is equal to the experimental group at the beginning of treatment (Table 1).
b) Student's t-test for average equality of two populations with independent samples -to examine the hypothesis that the mean changes observed in a cephalometric measurements between times 1 and 2 are equal in the control group and the experimental group (Table 2).
The assessment of equivalence between control and experimental groups, regarding the measurements of interest at the beginning of the study, (Table 1) showed that there is little cephalometric difference before treatment between groups, with only 3 of 14 variables showing statistically significant differences.

dISCuSSIOn a) Sagittal skeletal changes
After the one-year assessment period of the treated group, we noticed that the maxillary growthrelated variables (SNA and A-Nperp) presented a decrease of 1.3°/year and 1.2 mm/year, respectively, which was not statistically significant.When comparing these changes with those observed in the control group, that was just 0.21°/year and 0.26 mm/year, it can be stated that the Herbst appliance presented a tendency to restrict the anterior growth of maxilla.These data are in accordance with other studies in the literature 13,15,18,27,30 , since they have shown that the Herbst appliance provides a limited skeletal effect on the maxillary complex.However, when one considers the variable Co-A, we noted that there was a significant growth constraint of 2,23 mm/year in maxillary growth, while in the group without treatment there was a tendency to increase the effective length of the maxilla.This result confirms the fact that there was a restriction of the maxillary growth.Another study 29 reported that the maxilla was affected by the treatment with the Herbst appliance associated with the extraoral appliance, since the position of the point A was changed in the posterior direction about 1.5 mm in individuals with mixed dentition.Similarly, other authors 3 concluded that early treatment with Herbst appliance restricted the anterior sagittal displacement of point A about 1.2 mm.
Even considering the probable skeletal changes, SNB, Pog-Nperp and Co-NG measurements were assessed, to identify the effect of the appliance in the mandibular bone.While the control group showed a decrease on SNB angle (0.06°/year), the experimental group showed a statistically significant increase of 1.8°/year, which indicated that the use of this orthopedic appliance intensified the effect of the forward displacement of the mandible in relation to the base of the skull.When assessing the measurement Pog-Nperp, we found a significant reduction in the degree of retrusion of pogonion to the Nperp line of 3.01 mm/year.Meanwhile, the control group showed a reduction of only 0.21 mm/year.With respect to the effective length of the maxilla (Co-NG) is was noticed that both experimental and control groups showed a significant increase of this measure.Nevertheless, the experimental group (4 mm/year) showed an increase 2.5 times greater than the control group (1,57 mm/year).Thus, in our study of Herbst appliance was able to induce an additional mandibular growth.These results confirm the findings found in the literature 4,9,11,13,14,15,18,26,27,28,30 with regard to immediate mandibular skeletal effects induced by Herbst appliance.
One of the questions of this study was the possible interference of the Herbst appliance in the mandibular growth potential of individuals in early stages of occlusion development, i.e., does the amount of increase in mandibular length is similar to that of those individuals treated with the Herbst appliance at the adolescence period?Significant short term increases in the length of the mandible have been reported in adolescents in approximately 2.2 mm 13,14 and 3.4 mm. 30The literature has shown favorable and clinically significant mandibular growth in individuals treated with the Herbst appliance, who started the treatment in stages 3 and 4 of skeletal maturation of cervical vertebrae, i.e., at the peak of pubertal growth. 5According to the analysis of skeletal maturation using cervical vertebrae in our study, all patients started treatment before the outbreak of pubertal growth.Thus, it is worth mentioning that the magnitude of skeletal mandibular effects in our study was similar to that found in individuals treated around the peak of pubertal growth, when one might expect a more significative orthopedic effect. 8,9,15,16,19ephalometric evaluation of skeletal alterations induced by Herbst appliance during mixed dentition original article Due to the restriction of maxillary growth and the effect of mandibular growth stimulus, we observed a significant reduction in maxillomandibular relationship (ANB: 3.09º/year; AO-BO: 4.6mm/year).When the results of the evaluated groups were compared, we noticed that the experimental group presented a similar alteration to the control group, however in a larger magnitude, what denotes a positive effect of use of this device in terms of improving sagittal maxillomandibular relationship.Croft et al 3 when comparing the ANB angle change in mixed dentition patients treated with Herbst appliance and others monitored without treatment, they obtained a reduction of maxillomandibular relationship of 1.4° greater than the experimental and control group.Reduction in ANB angle of 3.26° and of 1.3° in 12 months of treatment with the Herbst appliance has been described in the literature. 9,18hen evaluating the behavior of facial skeletal convexity, it was identified an increase in the NAPog angle of 6.03º/year, leading to a decrease in the facial convexity.The changes observed in the experimental group were similar to the control group, nevertheless, on a larger scale.Our result is in agreement with other studies 3,18 that observed a reduction of 4.23 and 2.2º in this angle in a sample treated with Herbst appliance.
Thus, according to the results of our study, there was a significant improvement in the sagittal relation between apical bases.The reduction of about 4.6 mm in the maxillomandibular relationship (AO-BO) can be explained by the significant restriction of 1.2 mm in the maxillary growth (A-Nperp) and by the anterior displacement of 3.01 mm of Pogonion (Pog-Nperp).This fact is confirmed when assessing the ANB angle, that showed a decrease of 3.09º, represented by maxillary growth inhibition (SNA: -1.3º) and by the anterior displacement of the mandible (SNB: 1.8º).

b) Vertical Skeletal Changes
The influence of functional or fixed appliances in the vertical relation of the bone bases is a controversial subject in literature. 3,9,18,20,21,28In cases of hyperdivergent growth pattern patients, functional appliances are not recommended because these appliances can cause a subsequent clockwise mandibular rotation 20 and, consequently, may worsen the facial esthetics.On the other hand in patients with mesofacial growth pattern, the mandibular plane angle, on average, does not seem to be affected with the Herbst appliance. 1,3,9,11,18,19,28,30However, some authors found no significant differences regarding the magnitude of vertical skeletal changes in hypodivergents and hyperdivergents patients treated with the Herbst appliance 21,24,30 .
Our study showed a significant increase in the anterior (N-Me: 4.11 mm/year) and in posterior facial height (S-Go:3.53mm/year).The changes observed in the experimental group were similar to the control group, however, in a larger magnitude.Increase of facial height as a result of treatment with the Herbst appliance was found on some researches. 9,28However, a study 1 related the absence of significant changes in anterior and inferior facial height in individuals treated with Herbst appliance.It is interesting to observe that despite the increased facial height in our study that is favorable to the esthetic of the patient, the mandibular plane angle (SN.GoMe) did not change significantly in the treated (0.16°/year) and in the untreated group.These data are in accordance with the findings of literature. 1,3,4,9,11,18,19,26,28,30The results of this study showed that the use of the Herbst appliance did not change the pattern of rotation of mandibular plane.
In relation to the palatal plane, our results showed that the treated group did not show a significant increase (0.59°/year) of this plane from the base of the skull.The change observed in the experimental group was not similar to the control group.This variable in the control group also presented a significant change.Our results are consistent with other papers 1,5,6,13,19 that also did not observe changes in palatal plane in patients treated with the Herbst appliance.
According to the results of vertical skeletal changes in our study, we could verify that the mandibular plane presented a similar behavior to the palatal plane, that is, a tendency toward maintenance of initial values, in a comparable way to the control group.As for anterior and posterior facial heights, our study showed that there was a significant increase in the use of this appliance, indicating a harmony in the increase of vertical dimensions.These data suggest that the use of Herbst appliance in patients with excessive facial height should be performed with caution, since this appliance might increase even more the facial height.In this way, when a professional uses the Herbst appliance in patients with increased facial height, it would be wise to use an anchorage structure with occlusal coverage in order to obtain a better control of the vertical growth of bone bases. 5,9,24,27,30he results of this study showed that the Herbst appliance was able to satisfactorily treat Class II malocclusion in pre-puberty subjects.However, it is worth to notice that the choice of the ideal time to begin the treatment of Class II it is still a critical point in orthodontic planning.Therefore, the advantages and disadvantages of early treatment should be carefully considered before starting treatment.In case of early treatment, it is worth to notice the importance of the prolonged monitoring these patients to mitigate the potential for relapse. 3,25,29Thus, this makes necessary the use of functional removable appliances as retainer until the end of the growth stage, 3,25,29 with the goal of keeping the orthopedic correction and lead the tooth eruption during the transition from mixed to permanent dentition.

COnCluSIOn
Skeletal effects produced by Herbst appliance at the stage of mixed dentition in this study were: -Restriction of maxillary growth.
-Greater anterior position and increase of the mandibular length.
Cephalometric evaluation of skeletal alterations induced by Herbst appliance during mixed dentition original article molars and permanent or deciduous canines, and by the overjet.Individuals with molar and canines in Class II, equal to or higher than the half of a cusp, and overjet equal to or greater than 4 mm, were included in the sample (Fig2).

H
Cephalometric evaluation of skeletal alterations induced by Herbst appliance during mixed dentition original article

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Positive change in relation to facial convexity and the maxillomandibular relationship.-No significant change in mandibular and palatal plane.-Significant increase in anterior and posterior facial height.

Table 1 -
Mean and standard deviations in the experimental and control groups and mean differences between measurements before treatment, and Student's t-test for the difference between measures.

Table 2 -
Means and results of Student's t-test of equality of means in the Experimental group and control group, each of the variables under study.