INTRODUCTION

Large individual variation in children's growth patterns and growth potential is usually considered to favor an individualized approach in orthodontic therapy. However, attempts have been made to apply more generalized interceptive measures in the community to reduce or eliminate malocclusion.12

Väkiparta et al2 studied the effects of an early treatment oriented orthodontic program for which a systematic screening at the age of 8 years was followed by early interceptive treatment. Examination of the children at the age of 12 years showed that the treatment need was significantly reduced. Al Nimri and Richardson1 investigated the effectiveness of an interceptive program that targeted selected unfavorable features of the developing occlusion and showed that the change in the dental health component of the Index of Orthodontic Treatment Need (IOTN) was significantly greater in the treated children compared to the controls.1

Neither of the studies cited above12 included Class II occlusion or Class II tendency to select children in the interceptive program. This seems to be in line with the recent findings suggesting that only minor benefits can be obtained by early treatment in Class II patients.3–6 However, other studies have reported considerably better results after an early intervention.7–9 A recent clinical trial investigated the occlusal effects of the eruption guidance appliance.9 Complete age cohorts of children were screened in the deciduous dentition, and orthodontic intervention with the eruption guidance appliance was carried out in the mixed dentition in children showing a tendency to Class II occlusion, crowding, increased overjet or overbite with lack of tooth-to-tooth contact between the incisors, anterior crossbite, and/or buccal crossbite (scissors bite). A comparison with an untreated control group with similar malocclusions revealed that an efficient Class II correction, along with a general normalization of the occlusal development, was achieved in the majority of the patients.9

The purpose was to cephalometrically analyze craniofacial and dentoalveolar morphology in children who had undergone orthodontic intervention with the eruption guidance appliance in the early mixed dentition.

MATERIALS AND METHODS

The study population was collected from three rural municipalities in western Finland: Jalasjärvi, Kurikka, and Seinäjoki. The treatment sample of 115 children was derived from the 1992 and 1993 age cohorts in Jalasjärvi and from the 1992 age cohort in Kurikka. All children in these age cohorts were screened during the late deciduous dentition period, and those diagnosed as needing treatment received a full clinical examination at the onset of the mixed dentition period.10 Children were included in the treatment group if they showed one or more of the following occlusal characteristics: (1) distal step (≥1 mm), (2) Class II canine relationship (≥1 mm), (3) excess overbite (>3 mm and lack of tooth-to-tooth contact between the incisors), (4) deep bite (>3 mm with gingival contact of the incisors), (5) crowding, (6) anterior crossbite, and (7) scissors bite (buccal crossbite). The treatment group was treated using the eruption guidance appliance only (Figure 1). Children who had a moderately or severely constricted maxilla or a skeletal Class III relationship were first treated with an expansive arch and/or facemask. These children as well as those who refused the treatment or did not cooperate were excluded from the present analyses.9 The mean active treatment time was 3.3 years (range 5.1 to 8.4 years).

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The control group was a random sample of 104 children from Seinäjoki (population 30,000) who fulfilled the same criteria, ie, they represented the 1992 and 1993 age cohorts, were screened during the late deciduous dentition period, and had similar occlusal deviations. The children in the control sample received a full clinical examination, including collection of dental casts and lateral cephalograms at the onset of the mixed dentition period; but their treatment was not started until the late mixed dentition in accordance with the treatment protocol that was followed in the dental clinics of Seinäjoki. The treatment and control samples were all healthy Finnish children and none had undergone orthodontic treatment previously. Children and their parents were free to decline participation in the study at any time.

The timing of the examinations and interventions was based individually on the stage of dental development of each child and not on chronologic age. Treatment was started at the beginning of the mixed dentition period, ie, when the first deciduous incisor was exfoliated (T1). Active treatment was completed after all permanent incisors and first molars were fully erupted (T2). The present investigation evaluates the skeletal changes that occurred from T1 to T2 in 115 consecutively treated children in the treatment group (62 boys and 53 girls) and 104 children in the control group (52 boys and 52 girls).

The mean age in both treatment and control groups was 5.1 years (SD ± 0.5) at T1 and 8.4 years (SD ± 0.5) at T2. During active treatment, each child wore two to three prefabricated eruption guidance appliances of different sizes (Nite-Guide or Occlus-o-Guide, Ortho-Tain Inc).11 The appliances were worn during sleeping hours only. If difficulties were encountered, daytime wear of 1 hour was recommended until the problems with night-wear disappeared.9 The average duration of active treatment was 3.3 years. At point T2 all treated children entered a retention period during which the last of the appliances was used as a retainer, two nights per week. The retention was continued until all permanent canines, premolars, and second molars were fully erupted. No further treatment was normally required or planned.

The lateral cephalograms were taken with standard cephalostats.12 Computer assisted analysis of the cephalograms was carried out by the first author. The landmarks and measurements used in the analysis are listed in Table 1. The cephalometric assessment was carried out as described previously.12 Occlusal characteristics were measured as described earlier.10 The differences between the sample means were tested with Student's t-test. The relationships between continuous variables were further tested with simple linear regression and correlation analysis. A P-value difference < .05 was interpreted as statistically significant.

Table 1.  Landmarks and Measurements

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RESULTS

No statistically significant differences were detected between the treatment and control groups in the occlusal or cephalometric variables at the beginning of the study (Table 2). From T1 to T2, overjet and overbite decreased in the treatment group and increased in the control group (Table 2). In the treatment group, the sagittal relationship of molars improved by 1.9 mm and the canines by 1.5 mm. In the control group, the molar and canine relationship remained virtually unchanged showing a tendency to a Class II occlusion. Differences between the groups in overjet, overbite, and molar and canine relationship were statistically significant at T2.

Table 2.  Occlusal and Cephalometric Variables in the Treatment and Control Groups at T1 and T2. The Differences Between the Groups at T1 Were Nonsignificant

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In most skeletal variables an equal amount of growth took place in the treatment and control children during the observation period (Table 2). In addition, the growth direction of the mandible, measured by the facial axis angle, was similar on both groups. In midfacial length, mandibular length, and maxillomandibular differential, the treatment children showed a significantly greater increase compared with the controls. In mandibular length, the growth increment was 11.1 mm in the treatment group and 7.2 mm in the control group. The greater mandibular growth in the treatment group also largely explains the difference in midfacial length and the maxillomandibular differential. The Wits appraisal was significantly smaller in the treatment group at T2, indicating a better intermaxillary relationship in comparison to the control group.

The treatment did not seem to have any effects on the protrusion or angulation of the upper incisors (Table 2). The lower incisors, on the other hand, became more protruded and more labially inclined in the treatment group. At the same time, the interincisal angle decreased.

Correlations between the occlusal characteristics at T1 and skeletal variables at T2 were analyzed in the control group where no intervention was carried out. In general, the correlations were low and of little clinical relevance. However, a moderate and statistically significant positive correlation (r = .4, P < .0001) was found between the width of the upper dental arch at T1 and the length of the mandible at T2. This suggests that a narrow upper deciduous dental arch was associated with less growth of the mandible. Tracings of two treatment children and one control are shown as Figures 2, 3, and 4 respectively.

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DISCUSSION

The eruption guidance appliance has been shown to be capable to correct many aspects of the developing occlusion including overjet and overbite, openbite, spatial deficiencies, and Class II molar relationship.913–16 The present results are consistent with earlier findings indicating that the skeletal changes induced by the eruption guidance appliance are largely restricted to the dentoalveolar region.1415 However, treatment with the eruption guidance appliance seems to significantly enhance mandibular growth. The mandibular length, measured from condylion to gnathion, increased 3.9 mm more in the present treatment sample compared to the controls during the study period; this is equivalent to extra growth of 1.2 mm per year. Janson et al15 studied a group of 30 patients who were treated with the eruption guidance appliance for 26 months and reported a similar annual enhancement in mandibular length. The present results are in agreement with the earlier findings15 in that the maxillary growth is not affected. Similarly, direction of the facial growth remained unaffected.

Many studies have indicated that the growth of the mandible can be influenced by functional appliances in the middle or late mixed dentition.1517–22 The present results indicate that an orthopedic effect on mandibular growth can be achieved even earlier, in the early mixed dentition. In an analysis of treatment effects of the FR-2 appliance of Fränkel, McNamara et al18 found that the growth response was greater in the older patients with a starting age of 11.5 years compared to the younger patients with a starting age of 8.5 years. The annual growth increment was 1.8 mm in the older group and 1.2 mm in the younger group.18 The growth rate in the present treatment sample was 1.2 mm per year. These figures are in line with suggestions that the best response to functional therapy in terms of mandibular growth rate is achieved at or near the peak of the pubertal growth spurt.2324 However, it seems obvious that a clinically significant orthopedic effect that contributes to the correction of the Class II molar relationship can be obtained at almost any age in growing children.

The eruption guidance appliance is designed to solve crowding by expanding the dental arches.11 Because a transverse deficiency of the upper dental arch is a common finding in Class II patients,25 it is possible that this expansion,9 in addition to the mandibular growth, enhanced the transition from a Class II to a Class I relationship. It is of interest that a moderate but significant correlation was found between the width of the upper dental arch at T1 and mandibular length at T2. This suggests that a narrow upper arch tends to restrict anterior mandibular growth in early mixed dentition.

A recent analysis of untreated Class II subjects indicated that the effect of mandibular growth that potentially could bring the lower dentition forward, seems to be lost because of intercuspal locking and subsequent adaptive movements of the dentoalveolar complex.26 Earlier, Johnston27 suggested that the key effect of a functional appliance is to displace the mandible forward and let the condyle grow into the fossae without producing maxillary dentoalveolar compensations.

In the present study, the changes in occlusion and Wits appraisal toward a Class I relationship were significantly greater in the treatment group compared to controls. On the other hand, no differences were found in measurements that describe the position of the anterior border of the maxilla and mandible in relation to the cranium. It thus seems that a major effect of the eruption guidance appliance was indeed to induce a change in the dentoalveolar component without significantly affecting the position of the basal skeletal components. Johnston27 further suggested that the forward displacement of the mandible, typical to functional appliances, would cause a relative retrusive effect on maxillary dentition. However, no such effect was evident in the present study as the maxillary dentition seemed to move forward equally in both groups. The present findings are thus in agreement with the previous results indicating that the eruption guidance appliance does not cause a significant restriction of anterior growth of maxilla.15

A significantly smaller overjet, overbite, and interincisal angle were observed in the treatment group compared to the controls at the end of the study. More pronounced labial inclination and more anterior position of the lower incisors in the treatment group seem to be the main factors that affected the incisor relationships. There seemed to be no treatment effect on inclination or protrusion of the maxillary incisors. These findings differ from those of a previous study that showed bodily protrusion, but unchanged inclination of the lower incisors and protrusion and labial inclination of the upper incisors after treatment with the eruption guidance appliance.15 Linear retrusion and lingual tipping of the maxillary incisors seem to be frequent findings also with other functional appliances.182228–31 The different response of the incisors observed in the present study may relate to the fact that the present patients were younger and that the treatment took place during the period when the permanent incisors were erupting.

On the basis of the existing literature, Proffit31 suggested that early Class II treatment is indicated only for a selected group of children. However, many studies have shown that a Class II relationship does not show spontaneous correction with growth.92632–35 Instead, the skeletal and occlusal features of Class II tend to become exaggerated with age. It would, therefore, be logical to seek a treatment modality that would offer a method to intercept and correct Class II development at an early stage of occlusal development. The eruption guidance appliance seems to be a promising candidate for such a purpose.9 Not only Class II relationships but many other signs of disturbed occlusal development such as crowding, excess overjet, deep bite, and openbite can be treated simultaneously with this appliance in the early mixed dentition.9

Long-term results of the present trial are not yet available, but clinical data, accumulated on the treatment effects of the eruption guidance appliance, suggest that an early intervention can produce results efficiently and consistently. After treatment and proper retention, children who have undergone early orthodontic therapy with the eruption guidance appliance do not normally require further treatment.

CONCLUSIONS

• Occlusal correction brought about by the eruption guidance appliance was achieved mainly through changes in the dentoalveolar region of the mandible.

• Condylar growth was enhanced resulting in a clinically significant increase in mandibular length.

• No effect was observed on maxillary position, maxillary size, inclination, or protrusion of the maxillary incisors, or facial height.