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Class II correction in patients treated with Class II elastics and with fixed functional appliances: A comparative study
ORIGINAL ARTICLE Class II correction in patients treated with Class II elastics and with fixed functional appliances: A comparative study Birgitta Nelson, DDS,a Ken Hansen, DDS, Odont Dr,b and Urban Hägg, DDS, Odont Drc Malmö, Sweden and Hong Kong The aim of the present study was to evaluate quantitatively the skeletal and dental changes contributing to Class II corrections in subjects treated with Class II elastics (Begg technique) compared with subjects treated with fixed functional appliances (Herbst appliance). Thirty-six male patients with Class II, Division 1 malocclusions whose treatment had not included extraction were investigated. Eighteen were treated with the Begg technique, and eighteen were treated with Herbst appliance for an average period of 1.3 and 0.5 years, respectively. Lateral radiographs in habitual occlusion were taken at the start of treatment and 12 months afterwards. In the Begg group, the maxilla moved forward 1 mm more than in the Herbst group, and the mandible moved 1 mm more in the Herbst group than in the Begg group. The skeletal improvement in the Herbst group exceeded the changes in the Begg group by, on average, 2.0 mm (P < .01). The overjet reduction in the Begg group was larger (2.1 mm; P < .01) than in the Herbst group, mostly because of dental movements. The skeletal part of the overjet reduction was 4% in the Begg group compared with 51% in the Herbst group. The molar correction was similar in both groups, but in the Begg group, the skeletal improvement was 10%, compared with 66% in the Herbst group. The overbite correction and the increase in the anterior lower facial height and in the NSL/ML angle were larger in the Begg group (P < .05). The conclusions of this study were that the changes contributing to the Class II corrections in Begg and Herbst therapy were skeletal and dental. The skeletal changes were, however, larger in the Herbsttreated group. On the other hand, favorable and unfavorable vertical changes were more pronounced in the group treated with Class II elastics. (Am J Orthod Dentofacial Orthop 2000;118:142-9)
omparative studies of the effects of Class II treatment with fixed appliances and various kinds of functional appliances have been presented in the literature.1-6 However, in most of those studies, there is a variation among the appliance groups regarding sampling procedures and treatment and observation time. The design of this study was prospective: patients of the same sex and somatic maturity were selected, and the observation time was a year.7 The purpose of this study was to compare the skeletal and dental changes contributing to the Class II corrections in subjects treated with Class II elastics (Begg technique) but not extraction with matched subjects treated with a fixed functional appliances (Herbst appliance) during a limited period of time when Class II elastics were worn by all patients in the Begg group.8,9 The total treatment effects of each appliance have been presented in detail elsewhere.
C
Supported by the Swedish Dental Society. aConsultant, Orthodontic Clinic, Public Dental Health Service. bAssociate Professor, Department of Orthodontics, Faculty of Odontology, Lund University. cProfessor, Department of Orthodontics, Faculty of Odontology, The University of Hong Kong. Reprint requests to: Dr Birgitta Nelson, Specialistkliniken för ortodonti, Claesgatan 12, S-214 26 Malmö, Sweden; e-mail, [email protected] Submitted, July 1999; Accepted, November 1999. Copyright © 2000 by the American Association of Orthodontists. 0889-5406/2000/$12.00 + 0 8/1/104489 doi.10.1067/mod.2000.104489
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SUBJECTS
From two male patient samples of Class II, Division 1 malocclusions, 18 pairs of subjects were identified. The patients were treated with either Class II elastics (Begg technique) or a fixed functional appliance (Herbst appliance).10,11 The Herbst-treated patients were selected to match the Begg sample with respect to malocclusion, age, and somatic maturation. The total sample consisted of 36 male patients with Class II, Division 1 malocclusion whose treatment did not include extraction and who were observed for a period of 12 months. The average active treatment period was 1.3 years for the Begg patients and 0.5 year for the Herbst patients. Because the observation period was a year, the patients in the Begg group were at the end of active treatment at the time of the second registration. All of the Herbst patients had a fixed sectional arch wire in the maxillary anterior segment, and 11 of the patients had a corresponding arch wire in the mandible, in combination with the telescope mechanism. After the active Class II treatment, the Herbst patients were treated or retained with a multibracket appliance (1 patient), an activator (13 patients), a retention plate (1 patient), or a bonded retainer in the upper jaw (1 patient). No posttreatment or retention was performed in 2 patients. An outline of the patient details is given in Table I.
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Table I. Distribution
of 36 male Class II Division 1 patients*
Begg age at start of treatment (y)
Begg age at end of observation (y)
Begg observation period† (y)
Herbst age at start of treatment (y)
13.5 1.1 11.2 15.1
14.5 1.1 12.2 16.1
1.0 0.0 1.0 1.1
13.7 1.0 12.0 15.8
Mean SD Minimum Maximum
Herbst age at end of observation (y) 14.7 1.0 13.0 16.9
Herbst treatment period‡(y)
Herbst observation period§ (y)
0.5 0.1 0.4 0.8
1.1 0.1 0.9 1.3
*Eighteen patients were treated with fixed appliance (Begg), nonextraction, and 18 patients were treated with the Herbst appliance. †Start of treatment to 12 months after start. ‡Start of treatment to end of Herbst treatment. §Treatment period and 6-month settling period.
METHODS
Longitudinal growth records were available for all subjects, and the somatic maturation was assessed by analyzing the distance curve of the standing height according to the method of Karlberg et al.12 In the Begg group, treatment was started by 5 patients before the maximum of pubertal growth (prepeak), by 8 patients at the maximum (peak), and by 5 patients after the maximum (postpeak). The corresponding numbers for the Herbst sample were 4 patients before the maximum (prepeak), 9 patients at the maximum (peak), and 5 patients after the maximum (postpeak). Lateral skull radiographs in habitual occlusion were analyzed at 2 stages: at the start of treatment and 12 months after the start of treatment. The cephalometric changes occurring during the observation period were analyzed. The anatomical landmarks were marked directly on the radiographs with an All-stabilo pencil (Schwan-Stabilo). The radiographs were digitized with a Scriptel RDT digitizer (Scriptel Corporation), and the measurements and calculations were performed by a computer. No corrections were made for linear radiographic enlargement (approximately 7% in the median-plane). The analysis of sagittal skeletal and dental changes was performed according to the method of Pancherz.13 The posttreatment radiographs were superimposed on the radiographs from the start of treatment, using the NSL with sella as a registration point. The measuring points and reference lines used are those defined by Björk,14 Jacobson,15 and Pancherz13 (Fig 1). Sagittal relations: • A-Olp position of the maxillary jaw base • pg-Olp position of the mandibular jaw base • A-pg to Olp jaw base relationship: position of the maxilla in relation to the mandible (A-Olp minus pg-Olp) • is-A position of the central maxillary incisor in relation to the maxillary base (is-Olp minus A-Olp)
• ii-pg position of the central mandibular incisor in relation to the mandibular base (ii-Olp minus pg-Olp) • ms-A position of the first maxillary molar in relation to the maxillary base (A-Olp minus ms-Olp) • ms-pg position of the first mandibular molar in relation to the mandibular base (pg-Olp minus mi-Olp) • Overjet: is-Olp minus ii-Olp • Molar relationship: ms-Olp minus mi-Olp. Vertical relations: • NSL/NL inclination of the maxilla in relation to the cranial base • NSL/ML inclination of the mandible in relation to the cranial base (mandibular plane angle) • NL/ML inclination of the maxilla in relation to the mandible • sp´-me lower anterior facial height • Overbite: is-NSL minus ii-NSL Statistical methods
The arithmetic mean (mean) and SD for each variable were calculated. For the assessment of the statistical significance of the changes occurring during the observation period, t tests for paired samples were performed. For the assessment of differences between the groups, t tests for independent samples were used. The associations between variables were evaluated with the Pearson’s correlation coefficient (r). The levels of significance used were P < .001 (***), P < .01 (**), and P < .05 (*). P > .05 was considered not significant (NS). The size of the combined method error in locating the landmarks, the superimposition of the radiographs, and the measuring procedure were evaluated by calculating the SD of a single measurement (± ∑ /3 d2n is the difference between 2 registrations of a pair, and n is the number of double registrations).16 The analysis was therefore repeated in 10 randomly selected subjects at an interval of 2 months. The combined method error did not exceed 0.8 units for any of the variables investigated.
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Table II. Standard
cephalometric records of 18 male patients treated with fixed appliance (Begg) and 18 male patients treated with the Herbst appliance Start of treatment Begg
Fig 1. Measuring points and reference lines used in cephalometric analysis. Reference grid (Ol and Olp) was used to measure sagittal changes during observation period. RESULTS
Before treatment, no statistically significant difference existed between the 2 groups for any of the variables investigated, except for the inclination of the upper incisors (ILs/NL), which on average were more proclined (P < .05) in the Begg subjects (Table II).
Sagittal SNA (degrees) SNB (degrees) ANB (degrees) ILs/NL (degrees) ILi/ML (degrees) Overjet (mm) ms-mi (mm) Vertical NSL/NL (degrees) NSL/ML (degrees) NL/ML (degrees) n-me (mm) n-sp´ (mm) sp´-me (mm) Overbite (mm)
Mean
SD
Mean
SD
Diff
81.3 76.0 5.3 116.2 98.5 8.8 1.6
4.7 3.6 1.8 5.8 6.4 1.3 1.0
83.4 77.2 6.2 111.6 102.0 8.1 1.2
3.6 3.6 2.2 6.9 7.1 2.3 1.4
–2.2 –1.2 –0.8 4.6* –3.5 0.7 0.2
7.4 32.5 25.1 115.2 52.5 62.7 5.9
2.6 5.8 5.2 7.2 3.6 5.2 2.3
5.3 30.2 24.9 115.8 52.0 63.8 6.6
3.7 7.6 5.8 6.4 3.2 5.1 2.2
2.2 2.4 0.2 –0.6 0.5 –1.1 –0.7
*Indicates significant changes at P < .05 level. Diff, Difference. Table III. Treatment
changes in 18 male patients treated with fixed appliance (Begg) and 18 male patients treated with the Herbst appliance Changes during the observation period Begg
Sagittal Changes
The maxillary (A-Olp) and mandibular (Pg-Olp) jaw bases moved forward in both groups. In the Begg group, the maxilla moved, on average, 1.3 mm anteriorly. In the Herbst group, the maxilla moved 0.3 mm anteriorly (Begg > Herbst, NS). The sagittal mandibular growth was, on average, 1.6 mm in the Begg subjects and 2.6 mm in the Herbst subjects (Begg < Herbst, NS). The improvement in sagittal jaw base relationship was, on average, 0.3 mm in the Begg group and 2.3 mm in the Herbst group (Begg < Herbst; P < .01). The overjet reduction was larger in the Begg group than in the Herbst-treated group: on average, 6.7 mm and 4.6 mm (P < .01), respectively. The maxillary incisors moved, on average, 5.0 mm posteriorly in the Begg group and 2.2 mm in the Herbst group (Begg > Herbst; P < .01). The mandibular incisors proclined in the Begg group (1.4 mm) but remained unchanged in the Herbst group (Begg > Herbst; P < .05) (Table III, Figs 2 and 3). The molar correction was almost similar in both groups (Begg 3.2 mm, Herbst 3.5 mm). The movements of the molars differed because of the larger skeletal improvement in the Herbst group.
Herbst
Mean Sagittal A-Olp (mm) 1.3 pg-Olp (mm) 1.6 A-pg (mm) –0.3 is-A (mm) –5.1 ii-pg (mm) 1.4 A-ms (mm) 0.4 pg-mi (mm) –2.3 Overjet reduction (mm) 6.7 ms-mi correction (mm) 3.1 Vertical NSL/NL (degrees) 0.7 NSL/ML (degrees) 1.3 NL/ML (degrees) 0.5 Lower facial height (mm) 4.2 Overbite reduction (mm)–4.1
Herbst SD
Mean
SD
Diff
1.7 2.9 2.2 2.5 2.3 1.9 2.6 1.6 1.3
0.3 2.6 –2.3 –2.2 0.0 0.3 –0.9 4.6 3.5
1.7 2.9 1.7 3.0 1.1 1.1 1.3 2.6 1.5
1.0 –1.0 2.0* –2.8* 1.3† 0.1 –1.5† –2.1* 0.4
1.7 1.0 1.8 1.4 2.2
0.4 0.0 –0.3 3.2 –2.4
1.2 1.8 1.5 1.3 2.1
0.3 1.3† 0.8 1.1† –1.7†
*Indicates significant changes at P < .01 level. †Indicates significant changes at P < .05 level. Diff, Difference.
Vertical Changes
The overbite reduction in the Begg group and in the Herbst group was, on average, 4.1 mm and 2.4 mm,
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Fig 2. Overjet reduction (mm) in male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 3. Correction in molar relationship (mm) in male Class II Division 1 patients. Eighteen patients were treated with Class-II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
respectively (Begg > Herbst; P < .05). The anterior lower facial height increased more in the Begg group (4.2 mm) than in the Herbst group (3.2 mm; Begg > Herbst; P < .05). In the Begg group, the mandibular plane angle increased, on average, 1.3°, but the angle remained unchanged in the Herbst group (Begg > Herbst, P < .05). There were no statistically significant changes found regarding the NSL/NL and the NL/ML angles (Table III, Fig 4). The only significant association between changes in the jaw base relationship and changes in the mandibular plane angle was found in the Begg group (r = 0.50; P < .05)(Figs 5 and 6). DISCUSSION
When the effects of different orthodontic appliances on the dentofacial development are compared, groups should be comparable, not only with respect to malocclusion and age, but also with the level of
somatic maturation of the individuals. The length of the observation period is also important because the longer the observation period is, the more difficult it is to analyze small changes induced by active treatment (because of the longer influence of normal growth). The treatment period with fixed appliances is normally between 18 and 24 months. During this period, Class II elastics are used for various periods of time. The purpose of this investigation was to analyze the effects of Class II elastics, compared with a fixed functional appliance, during a limited period when Class II elastics were used by all patients. The observation period was somewhat longer in the Herbst group than in the Begg group. The active treatment period in the Herbst group was 6 to 7 months, and the follow-up period after treatment was 6 months. In the Begg group the observation period was 12 months after the start of treatment, irrespec-
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Fig 4. Rotational changes of the NSL/NL and NSL/ML angles in male Class II, Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 5. Association between changes in jaw base relationship and changes in mandibular plane angle in male Class II, Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), without extraction.
tive of how far the treatment had proceeded. However, the longer observation period in the Herbst sample was during a period of settling, when there was no active stimulation on mandibular growth. It has been shown that wearing an activator during this settling period does not result in increased mandibular growth.17 The Herbst appliance was used in this
investigation because it is one of the few appliances where an increased mandibular growth has been shown to occur during treatment.18 The Herbst appliance had a larger skeletal impact (P < .01), although the active treatment time was shorter. The size of the improved sagittal jaw base relationship in the Herbst sample was in accordance
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Nelson, Hansen, and Hägg 147
Fig 6. Association between changes in jaw base relationship and changes in mandibular plane angle in male Class II, Division 1 patients. Eighteen patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 7. Overjet reduction and correction in molar relationship in percentage of male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
with previous investigations.9,11,13 The overjet reduction was larger in the Begg group than in the Herbst group (P < .01), probably because of more proclined upper incisors in the Begg group before treatment. The skeletal part of the overjet correction was, on average, 4% in the Begg group, compared with 51% in the Herbst group (Fig 7). The molar correction, on the other hand, was the same in both groups. In the
Begg group, a more forward movement of the mandibular molars could be noted (P < .05) because the skeletal part of the molar correction was smaller in the Begg group then in the Herbst group (10% and 66%, respectively) (Fig 7). The individual values varied between the 2 groups. In Fig 8, it is shown that the sagittal skeletal jaw base relationship improved in almost all Herbst
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American Journal of Orthodontics and Dentofacial Orthopedics August 2000
Fig 8. Changes in jaw relationship (mm) in male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 9. Changes in mandibular plane angle in male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
patients and that the improvement was more than 2 mm in 72% of the Herbst cases (13 subjects). In the Begg group only 4 (22%) of the subjects had a greater improvement of the jaw bases than 2 mm, and the relationship remained unchanged or worsened in 50% of the cases (Fig 8). The NSL/ML angle and the anterior lower facial height increased and the overbite decreased signifi-
cantly more in the Begg subjects (P < 0.05). There was also an association between the changes in the jaw base relationship and the changes in the mandibular plane angle (r = 0.50; P < .05) for the Begg group (Fig 5). It seemed as if the Class II elastics caused a downward and backward rotation of the mandible, and this could perhaps explain the decreased forward movement of the pogonion in the Begg group, as well the
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increased anterior facial height. The NSL/ML angle in the Herbst group remained unchanged, which was in agreement with previous studies, and there was no association between changes in NSL/ML angle and sagittal mandibular growth (Fig 6).5,19,20 In all Begg subjects except one, the mandibular plane angle increased. In the Herbst group, 9 patients (50%) had an increase in the mandibular plane angle, and 9 patients (50%) had a decrease (Fig 9). This investigation studied the effects during a limited period of time when the amount of natural growth is rather small. If the time period is longer (ie, 2-3 years), the amount of natural growth increases and could, to some extent, mask the effects of the appliances. However, the long-term results are interesting because the continuing growth and development might wipe out the effects of treatment and perhaps make the 2 groups comparable again. This will be studied in a forthcoming follow-up study.
5.
6.
7.
8. 9. 10.
11.
12.
CONCLUSIONS
The changes that contributed to Class II corrections in Begg and Herbst therapy were skeletal and dental. The skeletal changes were larger in the Herbst-treated group. On the other hand, favorable and unfavorable vertical changes were more pronounced in the group treated with Class II elastics (ie, Begg). REFERENCES 1. Gianelly AA. A comparison of Class II treatment changes noted with the light wire, edgewise and Fränkel appliances. Am J Orthod 1984;86:269-762. 2. Remmer KR, Mamandras AH, Hunter WS, Way DC. Cephalometric changes associated with treatment using the activator, the Fränkel appliance, and the fixed appliance. Am J Orthod 1985;88:363-72. 3. Adenvalla ST, Kronman JH. Class II, division 1 treatment with Fränkel and Edgewise appliances. Angle Orthod 1985;55:281-97. 4. Pancherz H, Malmgren O, Hägg U, Ömblus J, Hansen K. Class II correction in Herbst and Bass therapy: the mechanism of Class
13. 14. 15. 16. 17. 18.
19.
20.
II correction in Herbst appliance treatment. Eur J Orthod 1989; 11:17-30. McNamara JA, Howe RP, Dischinger TG. A comparison of the Herbst and Fränkel appliances in the treatment of Class II malocclusion. Am J Orthod Dentofacial Orthop 1990;98:134-44. Weichbrodt L, Ingervall B. Treatment of Class II, division 1 malocclusion with the activator and with the Begg technique. Schweiz Monatsschr Zahnmed 1992;102:1037-45. Tulloch JFC, Medland W, Tuncay OC. Methods used to evaluate growth modification in Class II malocclusion. Am J Orthod Dentofacial Orthop 1990;98:340-7. Begg PR, Kesling PC. Begg orthodontic theory and technique. 3rd ed. Philadelphia: WB Saunders Co; 1977. Pancherz H. The Herbst appliance—its biological effects and clinical use. Am J Orthod 1985;87:1-20. Nelson B, Hansen K, Hägg U. Overjet reduction and molar correction in fixed appliance treatment of Class II, division 1 malocclusions: sagittal and vertical components. Am J Orthod Dentofacial Orthop 1999;115:13-23. Hansen K. Post-treatment effects of the Herbst appliance: a radiographic, clinical and biometric investigation. Swed Dent J Suppl 1992;88;5-49. Karlberg J, Hägg U, Pancherz H. Growth analysis using the infancy-childhood-puberty (ICP) model: assessing the age at pubertal maximum and the pubertal path of growth. In: Hernandez M, Argente J, editors. Human growth: basic and clinical aspects. New York: Excerpta Medica; 1992. Pancherz H. The mechanism of Class II correction in Herbst appliance treatment. Am J Orthod 1982;82:104 –13. Björk A. The face in profile [thesis]. Swed Dent J Suppl 1947;40:30-50. Jacobson SO. Cephalometric evaluation of treatment effect on Class II, division 1 malocclusions. Am J Orthod 1967;53:446-55. Dahlberg G. Statistical methods for medical and biology students. London: Allen and Unwin; 1940. Pancherz H, Hansen K. Occlusal changes during and after Herbst treatment: a cephalometric study. Eur J Orthod 1986;8:215-28. Aelbers CM, Dermaut LR. Orthopedics in orthodontics, part I: fiction or reality—a review of the literature. Am J Orthod Dentofacial Orthop 1996;110:513-9. Pancherz H. Vertical dentofacial changes during Herbst appliance treatment: a cephalometric investigation. Swed Dent J Suppl 1982;15:189-96. Ruf S, Pancherz H. The effect of Herbst appliance treatment on the mandibular plane angle: a cephalometric roentgenographic study. Am J Orthod Dentofacial Orthop 1996;110:225-9.
omparative studies of the effects of Class II treatment with fixed appliances and various kinds of functional appliances have been presented in the literature.1-6 However, in most of those studies, there is a variation among the appliance groups regarding sampling procedures and treatment and observation time. The design of this study was prospective: patients of the same sex and somatic maturity were selected, and the observation time was a year.7 The purpose of this study was to compare the skeletal and dental changes contributing to the Class II corrections in subjects treated with Class II elastics (Begg technique) but not extraction with matched subjects treated with a fixed functional appliances (Herbst appliance) during a limited period of time when Class II elastics were worn by all patients in the Begg group.8,9 The total treatment effects of each appliance have been presented in detail elsewhere.
C
Supported by the Swedish Dental Society. aConsultant, Orthodontic Clinic, Public Dental Health Service. bAssociate Professor, Department of Orthodontics, Faculty of Odontology, Lund University. cProfessor, Department of Orthodontics, Faculty of Odontology, The University of Hong Kong. Reprint requests to: Dr Birgitta Nelson, Specialistkliniken för ortodonti, Claesgatan 12, S-214 26 Malmö, Sweden; e-mail, [email protected] Submitted, July 1999; Accepted, November 1999. Copyright © 2000 by the American Association of Orthodontists. 0889-5406/2000/$12.00 + 0 8/1/104489 doi.10.1067/mod.2000.104489
142
SUBJECTS
From two male patient samples of Class II, Division 1 malocclusions, 18 pairs of subjects were identified. The patients were treated with either Class II elastics (Begg technique) or a fixed functional appliance (Herbst appliance).10,11 The Herbst-treated patients were selected to match the Begg sample with respect to malocclusion, age, and somatic maturation. The total sample consisted of 36 male patients with Class II, Division 1 malocclusion whose treatment did not include extraction and who were observed for a period of 12 months. The average active treatment period was 1.3 years for the Begg patients and 0.5 year for the Herbst patients. Because the observation period was a year, the patients in the Begg group were at the end of active treatment at the time of the second registration. All of the Herbst patients had a fixed sectional arch wire in the maxillary anterior segment, and 11 of the patients had a corresponding arch wire in the mandible, in combination with the telescope mechanism. After the active Class II treatment, the Herbst patients were treated or retained with a multibracket appliance (1 patient), an activator (13 patients), a retention plate (1 patient), or a bonded retainer in the upper jaw (1 patient). No posttreatment or retention was performed in 2 patients. An outline of the patient details is given in Table I.
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Table I. Distribution
of 36 male Class II Division 1 patients*
Begg age at start of treatment (y)
Begg age at end of observation (y)
Begg observation period† (y)
Herbst age at start of treatment (y)
13.5 1.1 11.2 15.1
14.5 1.1 12.2 16.1
1.0 0.0 1.0 1.1
13.7 1.0 12.0 15.8
Mean SD Minimum Maximum
Herbst age at end of observation (y) 14.7 1.0 13.0 16.9
Herbst treatment period‡(y)
Herbst observation period§ (y)
0.5 0.1 0.4 0.8
1.1 0.1 0.9 1.3
*Eighteen patients were treated with fixed appliance (Begg), nonextraction, and 18 patients were treated with the Herbst appliance. †Start of treatment to 12 months after start. ‡Start of treatment to end of Herbst treatment. §Treatment period and 6-month settling period.
METHODS
Longitudinal growth records were available for all subjects, and the somatic maturation was assessed by analyzing the distance curve of the standing height according to the method of Karlberg et al.12 In the Begg group, treatment was started by 5 patients before the maximum of pubertal growth (prepeak), by 8 patients at the maximum (peak), and by 5 patients after the maximum (postpeak). The corresponding numbers for the Herbst sample were 4 patients before the maximum (prepeak), 9 patients at the maximum (peak), and 5 patients after the maximum (postpeak). Lateral skull radiographs in habitual occlusion were analyzed at 2 stages: at the start of treatment and 12 months after the start of treatment. The cephalometric changes occurring during the observation period were analyzed. The anatomical landmarks were marked directly on the radiographs with an All-stabilo pencil (Schwan-Stabilo). The radiographs were digitized with a Scriptel RDT digitizer (Scriptel Corporation), and the measurements and calculations were performed by a computer. No corrections were made for linear radiographic enlargement (approximately 7% in the median-plane). The analysis of sagittal skeletal and dental changes was performed according to the method of Pancherz.13 The posttreatment radiographs were superimposed on the radiographs from the start of treatment, using the NSL with sella as a registration point. The measuring points and reference lines used are those defined by Björk,14 Jacobson,15 and Pancherz13 (Fig 1). Sagittal relations: • A-Olp position of the maxillary jaw base • pg-Olp position of the mandibular jaw base • A-pg to Olp jaw base relationship: position of the maxilla in relation to the mandible (A-Olp minus pg-Olp) • is-A position of the central maxillary incisor in relation to the maxillary base (is-Olp minus A-Olp)
• ii-pg position of the central mandibular incisor in relation to the mandibular base (ii-Olp minus pg-Olp) • ms-A position of the first maxillary molar in relation to the maxillary base (A-Olp minus ms-Olp) • ms-pg position of the first mandibular molar in relation to the mandibular base (pg-Olp minus mi-Olp) • Overjet: is-Olp minus ii-Olp • Molar relationship: ms-Olp minus mi-Olp. Vertical relations: • NSL/NL inclination of the maxilla in relation to the cranial base • NSL/ML inclination of the mandible in relation to the cranial base (mandibular plane angle) • NL/ML inclination of the maxilla in relation to the mandible • sp´-me lower anterior facial height • Overbite: is-NSL minus ii-NSL Statistical methods
The arithmetic mean (mean) and SD for each variable were calculated. For the assessment of the statistical significance of the changes occurring during the observation period, t tests for paired samples were performed. For the assessment of differences between the groups, t tests for independent samples were used. The associations between variables were evaluated with the Pearson’s correlation coefficient (r). The levels of significance used were P < .001 (***), P < .01 (**), and P < .05 (*). P > .05 was considered not significant (NS). The size of the combined method error in locating the landmarks, the superimposition of the radiographs, and the measuring procedure were evaluated by calculating the SD of a single measurement (± ∑ /3 d2n is the difference between 2 registrations of a pair, and n is the number of double registrations).16 The analysis was therefore repeated in 10 randomly selected subjects at an interval of 2 months. The combined method error did not exceed 0.8 units for any of the variables investigated.
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Table II. Standard
cephalometric records of 18 male patients treated with fixed appliance (Begg) and 18 male patients treated with the Herbst appliance Start of treatment Begg
Fig 1. Measuring points and reference lines used in cephalometric analysis. Reference grid (Ol and Olp) was used to measure sagittal changes during observation period. RESULTS
Before treatment, no statistically significant difference existed between the 2 groups for any of the variables investigated, except for the inclination of the upper incisors (ILs/NL), which on average were more proclined (P < .05) in the Begg subjects (Table II).
Sagittal SNA (degrees) SNB (degrees) ANB (degrees) ILs/NL (degrees) ILi/ML (degrees) Overjet (mm) ms-mi (mm) Vertical NSL/NL (degrees) NSL/ML (degrees) NL/ML (degrees) n-me (mm) n-sp´ (mm) sp´-me (mm) Overbite (mm)
Mean
SD
Mean
SD
Diff
81.3 76.0 5.3 116.2 98.5 8.8 1.6
4.7 3.6 1.8 5.8 6.4 1.3 1.0
83.4 77.2 6.2 111.6 102.0 8.1 1.2
3.6 3.6 2.2 6.9 7.1 2.3 1.4
–2.2 –1.2 –0.8 4.6* –3.5 0.7 0.2
7.4 32.5 25.1 115.2 52.5 62.7 5.9
2.6 5.8 5.2 7.2 3.6 5.2 2.3
5.3 30.2 24.9 115.8 52.0 63.8 6.6
3.7 7.6 5.8 6.4 3.2 5.1 2.2
2.2 2.4 0.2 –0.6 0.5 –1.1 –0.7
*Indicates significant changes at P < .05 level. Diff, Difference. Table III. Treatment
changes in 18 male patients treated with fixed appliance (Begg) and 18 male patients treated with the Herbst appliance Changes during the observation period Begg
Sagittal Changes
The maxillary (A-Olp) and mandibular (Pg-Olp) jaw bases moved forward in both groups. In the Begg group, the maxilla moved, on average, 1.3 mm anteriorly. In the Herbst group, the maxilla moved 0.3 mm anteriorly (Begg > Herbst, NS). The sagittal mandibular growth was, on average, 1.6 mm in the Begg subjects and 2.6 mm in the Herbst subjects (Begg < Herbst, NS). The improvement in sagittal jaw base relationship was, on average, 0.3 mm in the Begg group and 2.3 mm in the Herbst group (Begg < Herbst; P < .01). The overjet reduction was larger in the Begg group than in the Herbst-treated group: on average, 6.7 mm and 4.6 mm (P < .01), respectively. The maxillary incisors moved, on average, 5.0 mm posteriorly in the Begg group and 2.2 mm in the Herbst group (Begg > Herbst; P < .01). The mandibular incisors proclined in the Begg group (1.4 mm) but remained unchanged in the Herbst group (Begg > Herbst; P < .05) (Table III, Figs 2 and 3). The molar correction was almost similar in both groups (Begg 3.2 mm, Herbst 3.5 mm). The movements of the molars differed because of the larger skeletal improvement in the Herbst group.
Herbst
Mean Sagittal A-Olp (mm) 1.3 pg-Olp (mm) 1.6 A-pg (mm) –0.3 is-A (mm) –5.1 ii-pg (mm) 1.4 A-ms (mm) 0.4 pg-mi (mm) –2.3 Overjet reduction (mm) 6.7 ms-mi correction (mm) 3.1 Vertical NSL/NL (degrees) 0.7 NSL/ML (degrees) 1.3 NL/ML (degrees) 0.5 Lower facial height (mm) 4.2 Overbite reduction (mm)–4.1
Herbst SD
Mean
SD
Diff
1.7 2.9 2.2 2.5 2.3 1.9 2.6 1.6 1.3
0.3 2.6 –2.3 –2.2 0.0 0.3 –0.9 4.6 3.5
1.7 2.9 1.7 3.0 1.1 1.1 1.3 2.6 1.5
1.0 –1.0 2.0* –2.8* 1.3† 0.1 –1.5† –2.1* 0.4
1.7 1.0 1.8 1.4 2.2
0.4 0.0 –0.3 3.2 –2.4
1.2 1.8 1.5 1.3 2.1
0.3 1.3† 0.8 1.1† –1.7†
*Indicates significant changes at P < .01 level. †Indicates significant changes at P < .05 level. Diff, Difference.
Vertical Changes
The overbite reduction in the Begg group and in the Herbst group was, on average, 4.1 mm and 2.4 mm,
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Nelson, Hansen, and Hägg 145
Fig 2. Overjet reduction (mm) in male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 3. Correction in molar relationship (mm) in male Class II Division 1 patients. Eighteen patients were treated with Class-II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
respectively (Begg > Herbst; P < .05). The anterior lower facial height increased more in the Begg group (4.2 mm) than in the Herbst group (3.2 mm; Begg > Herbst; P < .05). In the Begg group, the mandibular plane angle increased, on average, 1.3°, but the angle remained unchanged in the Herbst group (Begg > Herbst, P < .05). There were no statistically significant changes found regarding the NSL/NL and the NL/ML angles (Table III, Fig 4). The only significant association between changes in the jaw base relationship and changes in the mandibular plane angle was found in the Begg group (r = 0.50; P < .05)(Figs 5 and 6). DISCUSSION
When the effects of different orthodontic appliances on the dentofacial development are compared, groups should be comparable, not only with respect to malocclusion and age, but also with the level of
somatic maturation of the individuals. The length of the observation period is also important because the longer the observation period is, the more difficult it is to analyze small changes induced by active treatment (because of the longer influence of normal growth). The treatment period with fixed appliances is normally between 18 and 24 months. During this period, Class II elastics are used for various periods of time. The purpose of this investigation was to analyze the effects of Class II elastics, compared with a fixed functional appliance, during a limited period when Class II elastics were used by all patients. The observation period was somewhat longer in the Herbst group than in the Begg group. The active treatment period in the Herbst group was 6 to 7 months, and the follow-up period after treatment was 6 months. In the Begg group the observation period was 12 months after the start of treatment, irrespec-
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American Journal of Orthodontics and Dentofacial Orthopedics August 2000
Fig 4. Rotational changes of the NSL/NL and NSL/ML angles in male Class II, Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 5. Association between changes in jaw base relationship and changes in mandibular plane angle in male Class II, Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), without extraction.
tive of how far the treatment had proceeded. However, the longer observation period in the Herbst sample was during a period of settling, when there was no active stimulation on mandibular growth. It has been shown that wearing an activator during this settling period does not result in increased mandibular growth.17 The Herbst appliance was used in this
investigation because it is one of the few appliances where an increased mandibular growth has been shown to occur during treatment.18 The Herbst appliance had a larger skeletal impact (P < .01), although the active treatment time was shorter. The size of the improved sagittal jaw base relationship in the Herbst sample was in accordance
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Nelson, Hansen, and Hägg 147
Fig 6. Association between changes in jaw base relationship and changes in mandibular plane angle in male Class II, Division 1 patients. Eighteen patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 7. Overjet reduction and correction in molar relationship in percentage of male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
with previous investigations.9,11,13 The overjet reduction was larger in the Begg group than in the Herbst group (P < .01), probably because of more proclined upper incisors in the Begg group before treatment. The skeletal part of the overjet correction was, on average, 4% in the Begg group, compared with 51% in the Herbst group (Fig 7). The molar correction, on the other hand, was the same in both groups. In the
Begg group, a more forward movement of the mandibular molars could be noted (P < .05) because the skeletal part of the molar correction was smaller in the Begg group then in the Herbst group (10% and 66%, respectively) (Fig 7). The individual values varied between the 2 groups. In Fig 8, it is shown that the sagittal skeletal jaw base relationship improved in almost all Herbst
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American Journal of Orthodontics and Dentofacial Orthopedics August 2000
Fig 8. Changes in jaw relationship (mm) in male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
Fig 9. Changes in mandibular plane angle in male Class II Division 1 patients. Eighteen patients were treated with Class II elastics (Begg), and 18 patients were treated with fixed functional appliances (Herbst), without extraction.
patients and that the improvement was more than 2 mm in 72% of the Herbst cases (13 subjects). In the Begg group only 4 (22%) of the subjects had a greater improvement of the jaw bases than 2 mm, and the relationship remained unchanged or worsened in 50% of the cases (Fig 8). The NSL/ML angle and the anterior lower facial height increased and the overbite decreased signifi-
cantly more in the Begg subjects (P < 0.05). There was also an association between the changes in the jaw base relationship and the changes in the mandibular plane angle (r = 0.50; P < .05) for the Begg group (Fig 5). It seemed as if the Class II elastics caused a downward and backward rotation of the mandible, and this could perhaps explain the decreased forward movement of the pogonion in the Begg group, as well the
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increased anterior facial height. The NSL/ML angle in the Herbst group remained unchanged, which was in agreement with previous studies, and there was no association between changes in NSL/ML angle and sagittal mandibular growth (Fig 6).5,19,20 In all Begg subjects except one, the mandibular plane angle increased. In the Herbst group, 9 patients (50%) had an increase in the mandibular plane angle, and 9 patients (50%) had a decrease (Fig 9). This investigation studied the effects during a limited period of time when the amount of natural growth is rather small. If the time period is longer (ie, 2-3 years), the amount of natural growth increases and could, to some extent, mask the effects of the appliances. However, the long-term results are interesting because the continuing growth and development might wipe out the effects of treatment and perhaps make the 2 groups comparable again. This will be studied in a forthcoming follow-up study.
5.
6.
7.
8. 9. 10.
11.
12.
CONCLUSIONS
The changes that contributed to Class II corrections in Begg and Herbst therapy were skeletal and dental. The skeletal changes were larger in the Herbst-treated group. On the other hand, favorable and unfavorable vertical changes were more pronounced in the group treated with Class II elastics (ie, Begg). REFERENCES 1. Gianelly AA. A comparison of Class II treatment changes noted with the light wire, edgewise and Fränkel appliances. Am J Orthod 1984;86:269-762. 2. Remmer KR, Mamandras AH, Hunter WS, Way DC. Cephalometric changes associated with treatment using the activator, the Fränkel appliance, and the fixed appliance. Am J Orthod 1985;88:363-72. 3. Adenvalla ST, Kronman JH. Class II, division 1 treatment with Fränkel and Edgewise appliances. Angle Orthod 1985;55:281-97. 4. Pancherz H, Malmgren O, Hägg U, Ömblus J, Hansen K. Class II correction in Herbst and Bass therapy: the mechanism of Class
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