January, 2012

Treatment Effects in an Anterior Open Bite Class II Malocclusion with Two Different Functional Appliances

 

Abstract

AIM: The aims of this study were to determine whether the modified bionator appliance  and open bite bionator by Balters encourages correction of an anterior open bite and Class II maloclusion, whether there is any superiority of one appliance over other.

MATERIALS AND METHODS: 58 patients with open bite, Class II division I malocclusion and functional disorders were selected. 31 patiens (15 boys and 16 girls,  mean age of 8 years 9 months) were treated with the modified bionator appliance and  27 patients (12 boys and 15 girls, mean age of 9 years 1 month) with open bite bionators by Balters. The dentoalveolar and skeletal changes that occured were compared on lateral cephalograms taken before treatment  (T1) and after active treatment (T2).

RESULTS: The modified bionator appliance demonstrated a statistically significant increase in upper incisor retraction (U1/NA  -3,5mm and U1/PP –8,1°), increase in lower incisors retraction (L1/NB –5,1°, -2,9mm and L1/MP –5,3°, 2,7mm) and interincisal angle      ( 8,6°) compared with the group treated with open bite bionator. Also, in both groups SNB angle increased and ANB angle decreased and corrected the Class II malocclusion, but without statistically significant changes between groups.

CONCLUSION: The modified bionator appliance (MBA) is a functional orthodontic-orthopedic appliance and is useful and an effective therapeutic alternative for the treatment of an anterior open bite and skeletal Class II malocclusion.

 Introduction

Malocclusions characterized by anterior open bite are often difficult to treat successfully. Anterior open bite is a malocclusion characterized by a deviation in the vertical relationship between the maxillary and mandibular dental arches, with absence of contact between the incisal edges of the maxillary and mandibular teeth in the vertical plane. The severity varies, from an almost edge-to-edge relationship to a severe handicapping open bite (1,2).

The presence of an anterior open bite is contributed by functional disorders, thumb suckling and tongue thrusting, (3,4) as well as skeletal factors (5). An anterior open bite, which is caused by a habit, has a favorable prognosis, provided that the habit is terminated (6).

The goal of early orthodontic treatment is to correct existing and developing skeletal, dentoalveolar and functional imbalances, which could help to minimize the possibility of complicated orthodontic treatment involving permanent tooth extraction or orthognatic surgery. Several types of functional appliances are currently in use for open bite treatment aimed to improving existing skeletal imbalances, arch form and orofacial function. Among contemporary functional appliances, one of the most popular is the »open bite bionator« by Balters (7).

The modified bionator appliance (MBA) is a functional orthodontic-orthopedic appliance and is useful and an effective therapeutic alternative for the treatment of an anterior open bite and skeletal Class II division I malocclusion. The modified bionator appliance is a modification by Balters bionator and was invented by Anita Fekonja and constructed and performed at Orthodontic Department in Health Centre dr. A. Drolca Maribor.

Aims of the study

The purpose of this researsh were to evaluate:

-         cephalometrically the possible effects produced by modified bionator appliance (MBA) and open bite bionator by Balters on dentoalveolar and skeletal components in patients with an anterior open bite and Class II division I malocclusion (retrognatic mandible)

-         there is any superiority of one appliance over the other

This paper describes the principle of the MBA mechanism and discusses its dentoskeletal effects as compared with an open bite bionator by Balters.

Description of the modified bionator appliance and principle of its mechanism

The MBA is a rigid appliance with a delicate design of  less bulky acrilyc base (Photos 1,2). The acrylic base of the appliance is closed in the front but it should not contact the incisors or the dentoalveolar margin so that the open bite can close. This area can be blocked out with wax before the application of the acrylic, or be trimmed free after its finishing. This part of the acrylic base prevents the intrusion of the tongue between the teeth which is very important. The acrylic base included upper and lower labial archwire that, when activated, contributed to upper and lower incisor uprighting (through palatal crown tipping). The Coffin spring is bent distally closed. The position of the tongue is influenced by the Coffin spring.

Photo 1: The modified bionator apliance

 

Photo: 2 The modified bionator apliance

Also can be incorporating a special type of jackscrew if mild compresion exist.

The functional action of the appliance is effected through the way that removable part desirable mandibular position. The construction bite determines the position of the mandible: the mandible is brought by the clinician to Class I  position and 2-3 mm of opening at the vertical. The maximum permissible mandibular protrusion is considered to be 7mm in order to avoid stomatognathic dysfunction. Appropriate activation of both labial arch provides retrusion of upper an lower incisors for the proper alignment of the teeth in their apical bases (Fig 1); furthermore, transverse dentoalveolar intermaxillary relationship can corrected with the jackscrew.

Figure 1. Principles of orthodontic-orthopedic mechanism

 

 

Indication of the MBA functional appliances:

-         the patient must still be growing, preferably approaching a phase of rapid growth

-         the labial tipping of the upper and lower incisors is evident

-         the patient must be well motivated

Orthodontic treatment goals for this patient treated with MBA included:

-         achivement of normal dental occlusion through correction of  overbite and overjet

-         rehabilitation of jaw relationship in the sagital plane

-         improvement of function and facial esthetics

 

Material and methods

The material used in this clinical study comprised the clinical examination, interview, and lateral cephalometric radiographs of 58 patients with an anterior open bite, Class II malocclusion and abnormal tongue function. Patients treated at the Orthodontic Department of Health Centre dr. A. Drolc Maribor between 2004- 2009

Selection criteria included:

-         no previous orthodontic treatment

-         lateral cephalograms were available pretreatment and post treatment

-     anterior open bite, Class II division I malocclusion, abnormal tongue function

-         complete eruption of upper and lower incisors

-         no craniofacial deformities

Based on this criteria, records of 58 patients were colected. The 31 patiens (15 boys and 16 girls, with initial mean age of 8 years 9 months)  treated with MBA and 27 patients (12 boys and 15 girls, with initial mean age of 9 years 1 month) treated with open bite bionator by Balters.

The patients were instructed to wear the appliance for a minimum of 14 hours a day.

 

Methods

Data on tongue thrust swallowing was obtained at the time of clinical examination. In order to examine the presence of tongue thrusting, the patients were asked to swallow their saliva three times during the same visit. Tongue thrust was defined as protrusion of the tongue between the upper and lower incisors or during swallowing.

For each patient, lateral cephalometric radiographs at the start and end of active treatment were taken. Lateral cephalograms were taken under standard conditions: distance from the focus to the median plane of the patient’s head was 150cm, and the median plane-film distance was 10cm. The cephalograms were taken with the subject standing and the head positioned in the cephalostat and orientated to the Frankfort horizontal plane with the teeth in maximum intercuspidation.

Cephalometric angular and linear measurements:

Skeletal cephalometric variables

- SNA: sella-nasion-point A angle

- SNB: sella-nasion-point B angle

- ANB: point A- nasion-point B angle

- SNPg: sella-nasion-pogonion angle

- SN/PP: angle formed by SN line and palatal plane (Sna-Snp)

- SN/MP: angle formed by SN line and mandibular plane(Go-Gn)

- LAFH: lower anterior facial height

Dentoalveolar cephalometric variables

- U1/PP: angle between maxillary incisor long axis and palatal plane

- U1-PP: perpendicular distance between incisal edge of maxillary central incisor and palatal plane ( maxillary incisors dentoalveolar height )

- U1/NA:  angle between maxillary incisor long axis and NA line

- U1-NA: distance between most anterior point of the maxillary central incisor and the NA line

- L1/NB: angle between mandibular incisor long axis and NB line

- L1-NB: distance between most anterior point of the mandibular incisor and NB line

- L1/MP: mandilular incisor long axis to mandibular plane angle

- L1-MP: perpendicular distance between incisal edge  of mandibular central incisor and mandibular plane ( mandibular incisors dentoalveolar height )

- overbite: distance between incisale edges of maxillary and mandibular central incisors, perpendicular to functional occlusal plane

- overjet: horizontal distance between incisal edges of maxillary and mandibular central incisors in sagital plane

-  interincisal  angle: angle between maxillary incisor long axis and mandibular incisor long axis

 

Statistical analysis

All radiographs were traced on good quality acetate paper using a 3H pencil under optimum lighting conditions by the same orthodontist (AF), twice, at different times to eliminate measurement  errors, and the mean findings were statistically evaluated. 15 landmarks and 18 parameters (linear and angular) were measured in the study.

Mean and standard deviations (SD) for the two groups were calculated for all cephalometrics variables at T1 an T2. To apply the t test, the results showed that all variables were normally distributed in both groups. Therefore, independent t test were used for comparison of the changes during treatment (T2-T1). The results were regarded as significant at P<0.05

 

Results

The results of the pre-treatment lateral cephalograms measurements are shown in Table 1 and describe the initial values for each groups. Compararisons of the changes occurring during the treatment period are shown in Table 2 .

 

 

Table 1. Comparison of pre-treatment cephalometric measurements

                     variable

Modified bionator appliance (MBA)                                mean      DS

Open bite bionator by Balters          mean                        SD

SNA (°)

80,5

3,7

80,1

3,9

SNB (°)

76,8

3,5

76,4

3,3

ANB (°)

2,9

2,2

2,7

2,3

SNPg (°)

78,1

3,4

78,3

4,4

SN/PP (°)

7,7

3,3

7,6

2,3

SN/MP (°)

36,1

4,6

35,9

5,6

LAFH(mm)

55,5

5,7

55,3

4,5

U1/NA (°)

28,5

4,3

29,3

5,7

U1/NA (mm)

7,5

1,9

6,8

2,2

U1/PP (°)

115,8

7,1

115,4

6,8

U1/PP (mm)

 26,6

1,9

27,3

1,8

L1/NB(°)

28,2

6,5

28,4

5,6

L1/NB(mm)

6,5

2,1

5,4

1,9

L1/MP (°)

94,5

5,6

93,4

5,5

L1/MP(mm)

38,4

2,7

38,2

2,9

Overbite (mm)

-2,7

1,8

-2,8

1,6

Overjet (mm)

6,1

2,1

5,8

2,7

Interincisal angle degrees

129,3

11,5

127,3

5,7

 

 

Table 2. Difference in mean changes ( T1 to T2 ) standeardized to 18 months

                     Variable

Modified bionator appliance                                        mean              SD

Open bite bionator by Balters                                mean              DS

                       P

SNA (°)

0,1

1,6

0,3

1,8

NS

SNB (°)

1,8

1,3

1,4

1,1

NS

ANB (°)

-1,5

1,3

-1,2

1,1

NS

SNPg (°)

1,6

1,4

1,5

0,9

NS

SN/PP (°)

0,2

1,6

0,3

1,3

NS

SN/MP (°)

0,4

2,2

0,5

1,9

NS

LAFH(mm)

1.9

1,6

2,1

1,8

NS

U1/NA (°)

-6,3

5,5

-4,2

4,8

NS

U1/NA (mm)

-3,5

3,4

-0.9

2,1

*

U1/PP (°)

-8,1

5,2

-4,1

4,7

*

U1/PP (mm)

2,1

1,6

2,3

1,3

NS

L1/NB (°)

-5,1

3,8

-1,2

3,7

*

L1/NB(mm)

-2,9

1,3

0,7

1,5

*

L1/MP(°)

-5,3

4,1

-1,1

4,8

*

L1/MP (mm)

2,7

1,3

1,4

1,4

*

Overbite (mm)

2,2

1,2

1,8

1,9

NS

Overjet (mm)

-4,2

2,4

-3,8

2,2

NS

Interincisal angle degrees

8,6

5,6

2,1

4,5

*

 

* statistically significant P<0.05

 

Of the 18 variables analysed,  7 were statistically significant. All of these were dentoalveolar measurements.

The MBA group showed statistically significant differences with the open bite bionator group in the distance of the upper incisor to the NA line, in the inclination from upper incisor tip to the palatal plane, in the inclinacion and distance of the lower incisor to the mandibular plane, and the inclinacion and distance of the lower incisor to the NB line, indicating uprighting of the incisors and deepening bite.

Point B appeared to have moved forward as a result of orthodontic-orthopedic therapy in both treatment groups, but without statistically significant differences.

In the group treated with MBA, the mean anterior open bite closure was 2,2mm. Treatment provided closure of the anterior open bite in all 31 individuals. However, in the group treated with open bite bionator by Balters the mean change in overbite was 1,8mm and treatment provide closure of anterior open bite in 23 of the 27 individuals.

The maxillary and mandibular incisors showed in MBA group greater extrusion and  retrusion ( uprighting ) than in open bite bionator group.

 

Discussion

The study was conducted on growing patients, and the groups should nacessarily present similar chronological and skeletal ages to allow reliable comparison. The initial cephalometric characteristic of both groups should also be similar.

At the start of treatment all cephalometric measurements were comparable in both groups.

This study compared the effect of the appliances over a 18 months period. The modified bionator appliance (MBA) is a functional orthodontic-orthopedic appliance and is useful and effective therapeutic alternative for the treatment of anterior open bite with abnormal tongue function and skeletal Class II malocclusion.

It is reported that functional appliance therapy increases the lenght of the mandible and results in an anterior relocation of point B and pogonion (8, 9). In the present study, the values of SNB and SN-Pg support these findings, demonstrating that the mandible moved forward as a result of active therapy in both treatment groups with no statistically significant differences.

Both study groups demonstrated a small increase in SN/PP, SN/MP and LAFH, although the appliances for patients for both treatment groups were designed to prevent further increase of facial height, i.e. use of an untrimmed interoclusal acrylic prevent eruption of the buccal segment.

During treatment, there were only significant differences in the maxillary and mandibular dentoalveolar components between the groups. Retroinclination of the maxillary incisors is a consistent finding in many Bionator studies. In the present study, the upper incisors were more retracted in the MBA group. The more pronounced retrusion in the MBA group may be due to the upper labial archwire control. This is expected treatment outcome of functional appliance therapy due to their Class II »traction effect« and the findings support those of Op Heij et al.(10) and Bolmgren and Moshiri (11). The effect of appliance therapy on the position of lower incisors varied statistically significant between the appliance groups. Statistically significant  reduction in the proclination of the lower incisors was seen in the MBA group. This effect was expected as the labial bow may come into contact with the incisors during appliance wear. It would apper that the MBA is a more logical treatment approach in Class II patients with protrusive upper and lower incisors and anterior open bite.

As a result of therapy, the overjet decreased in both groups. The greatest reduction was observed in the MBA group. As the open bite bionator appliance showed effect on the upper incisors retroinclinacion and minimal effect on the lower incisors, this would account for incomplete correction Class II molar relationship. It could be speculated that the Bionator appliance did not show such rapid anteroposterior correction, the changes may be superior in terms of the effect on incisor inclinacion.

 

Conclusion

This paper demonstrates that a modified bionator appliance can be succesfully used to treat an anterior open bite and Class II division I malocclusions.

The success of treatment lies in correction of the anterior-posterior, vertical and mild transverse discrepancies and the most important also correction irregular function. The importance of correcting the inter- incisal angle is paramount for stability. It is essential to reduce the interincisal angle towards 125 degrees, bringing the upper and lower incisor into correct axial position. This avoids the need for an another appiance.

From a clinical impresion, the MBA appeared to be the most readily tolerated and was advantageous in terms of rapidity of correction of the effects on the lower incisors. It must be stressed that this study reports the initial effects and no conclusions can be drawn about stability.

 

References

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  7. Graber TM, Rakosi T, Petrovic AG. The bionator – a modigied activator. In: Graber TM, Rakosi T, Petrovic AG, eds. Dentofacial orthopedics with functional appliances. St. Louis: CV Mosby, 1985: 209-218.
  8. Bastiftci FA, Uysal T, Büyükerkmen A, Sari Z. The effect of activator treatment on the craniofacial structures of Clacc II division I patients. Eur J Orthod 2003;25: 87-93
  9. Ruf S, Baltromejus S, Pancherz H. Effective condylar growth and chin position changes in activator treatment: a cephalometric roentgenographic study. Angle Orthod 2001;71: 4-11.
  10. Op Heij DG, Callaert H,Opdebeeck HM. The effect of the amount of protrusion built into the bionator on condilar grovth and displacement: a clinical study. Am J Orthod  Dentofac Orthop 1989; 95:401-409.
  11. Bolmgren GA, Moshiri F. Bionator treatment in Class II division 1. Angle Orthod 1986; 56:255-262.

 

 

Author and address for correspondence:

Anita Fekonja

Department of Orthodontics

Health Centre dr.A. Drolc Maribor

Partizanska 14a

2000 Maribor

e-mail: anita.fekonja1@guest.arnes

 

 

Comments One Response

  1. Janko Grosek

    01. Aug, 2012

    Čestitam zanimiv in dober članek.

    Reply to this comment

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