The effect of treatment of skeletal open bite with two

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European Journal of Orthodontics 14 (1992) 489-499 t 1992 European Orthodontic Society

The effect of treatment of skeletal open bite with two types

of bite-blocks

Robert Kuster and Bengt IngervallOrthodontic Clinic, University of Bern, Switzerland

SUMMARY The treatment of anterior skeletal open bite was studied in two groups of children.The children of one group wore a removable spring-loaded bite-block in the lower jaw for oneyear. The bite-block exerted an intrusive force on the upper and lower posterior teeth. Thechildren of the other group were treated for 3 months with bite-blocks with repelling magnets.These bite-blocks were cemented on the posterior teeth of both jaws.

The effects of treatment were monitored by measurement of the bite-force (group with springbite-blocks only), by electromyographic recording of the activity of the temporal and massetermuscles, and by X-ray cephalometry. Recordings were made before, during, and at the end ofthe treatment, and at a follow-up observation.

The bite-force increased during the first months of treatment, but was then unchanged. Theactivity of the masseter muscle during maximal bite also increased in the first part of the periodof treatment with a spring bite-block. In the group treated with magnetic bite-blocks, there wasan increase in the resting activity of the masseter muscle and in the chewing activity of theanterior temporal muscle.

The effects of the treatment on bite and facial morphology were less marked in the groupwith spring bite-blocks than in the group with magnetic bite-blocks, with an average improvementof the overbite of 1.3 mm with the spring bite-block therapy. In the group with magnetic bite-blocks, the average improvement in overbite was 3 mm. This was thought to be due to anteriorrotation of the mandible and increased eruption of the incisors. The mandibular rotation was aresult of intrusion of the upper and lower posterior teeth and possibly also increased mandibulargrowth. A follow-up of the cases treated with magnetic bite-blocks revealed a tendency for thebeneficial effects of the treatment to relapse which possibly could be counteracted by a longphase of active retention.

Introduction

Individuals with a skeletal open bite have along-face morphology characterized by a largeanterior face height and a steep inclination ofthe mandible (Fields et al., 1984; Ellis et ai,1985). The orthodontic treatment of this maloc-clusion is difficult. Camouflage of the underlyingskeletal anomaly by the elongation of theincisors results in too much incisor exposureand does not improve the excessive anteriorface height. A causal type of treatment, i.e.growth modification, has until recently beenregarded as impossible. Attempts to treat askeletal open bite by growth modification withthe use of a posterior bite-block have, however,lately been described (Dellinger, 1986; Woodside

and Linder-Aronson, 1986) and shown promis-ing results. Dellinger used bite-blocks withrepelling magnets on the upper and lowerposterior teeth while Woodside and Linder-Aronson used bite-blocks fastened in the lowerjaw and exerting an intrusive force on the upperand lower posterior teeth through a springmechanism.

Bite-blocks could have several beneficialtherapeutic effects. They could intrude the pos-terior teeth and, thus, make possible autorot-ation of the mandible to produce bite closure.This would be equivalent to the effect of aposterior maxillary set-up procedure in orthog-nathic surgery. In patients with ongoing verticalgrowth in the posterior part of the face (in theposterior cranial base and in the mandibular

490 R. KUSTER AND B. INGERVALL

condyles), retardation of the eruption of theposterior teeth would have the same effect.Another possibility is that the bite-blocks wouldincrease the condylar growth. Such an effectwould be conceivable through unloading of thetemporomandibular joints and/or protrusion ofthe condyles during the wearing of the bite-blocks and would be comparable to the effectof an activator or a Herbst appliance. Increasedvertical condylar growth would rotate themandible anteriorly and tend to close the bite.A maximal effect of bite-block therapy wouldbe achieved by simultaneous intrusion of theposterior teeth and an increased posterior ver-tical growth. All these effects of bite-blocks havebeen described in the relatively few reportshitherto published. Intrusion or retarded erup-tion of the posterior teeth was demonstrated inmonkeys by McNamara (1977), Carlson andSchneiderman (1983), Altuna and Woodside(1985), and Woods and Nanda (1988). Inhumans, intrusion of posterior teeth induced bythe use of bite-blocks was demonstrated byDellinger (1986), Woodside and Linder-Aronson (1986), Kalra et al. (1989), Kiliaridiset al. (1990), and Barbre and Sinclair (1991).Enhancement of mandibular growth was dem-onstrated by Kalra et al. (1989), who treatedpatients with open bite with cemented magneticbite-blocks for 4 months.

Another approach to the treatment of skeletalopen bite has involved training of the masticat-ory muscles. It is known that individuals witha long-face morphology have weak masticatorymuscles (Ringqvist, 1973; Ingervall and Helk-imo, 1978; Proffit et al., 1983; Ingervall et al.,1989). It was shown that training of the mastic-atory muscles in children with skeletal open biteby the chewing of a special type of toughchewing-gum increased the muscle strength.This resulted in an excessive anterior rotationof the mandible with closure of the open bite(Ingervall and Bitsanis, 1987; Bakke andSiersbaek-Nielsen, 1990).

Because of the difficulties in the treatment ofskeletal open bite, the relatively new treatmentmethod with bite-blocks should be furtherevaluated for its therapeutic possibilities. Notonly the effect of the treatment on the morpho-logy of the face and the dentition, but also thepossible effect on the muscle strength should bestudied. An increase of the muscle strengthwould be a benefit of the treatment that could

help to maintain the treatment result. The aimof this investigation is to study the effect onfacial morphology and on masticatory musclestrength of two types of bite-blocks in thetreatment of skeletal open bite.

Subjects and methods

The investigation included two series of patients.One series comprised 22 children (11 boys and11 girls) aged 7 years 5 months to 11 years 7months (median age 9 years 4 months) whowere treated with a bite-block with springs(spring bite-block) as described by Woodsideand Linder-Aronson (1986). The 11 children ofthe other series (four boys and seven girls), aged9 years 9 months to 14 years 5 months (medianage 10 years 9 months), were treated withmagnetic bite-blocks in the upper and lowerjaws.

The children of both series were selected fromamong those enrolled for orthodontic treatmentat the orthodontic clinic, University of Bern,Switzerland. The children had a long face mor-phology with a varying degree of anterior openbite which was treated with one of the two typesof bite-blocks. Clinically, a neutral or a distalocclusion was present. Variables describing thefacial morphology are given in Table 5.

During the first part of the time-span of theinvestigation, only spring bite-blocks were triedfor the treatment of a skeletal anterior openbite. This type of treatment was abandonedand replaced by magnetic bite-blocks for thechildren enrolled at a later date.

The spring bite-blocks (Fig. 1) were worn atnight for 1 year. The height of the bite-blocks(with compressed springs) at the first permanentmolars varied between 6.5 and 9 mm (median7 mm). The upper and lower parts of the bite-blocks were joined by steel springs on the labialand lingual sides. The springs (wire diameter0.9 mm) were designed to exert an intrusiveforce on the upper and lower posterior teeth.The force needed to compress the springs untilcontact between the two halves of the bite-blocks was measured in eight cases. The follow-ing forces (in g) were found: 264, 304, 339, 480,501, 527, 560, and 672 (mean of right and leftsides). The patients wearing the spring bite-blocks came to the clinic for monthly checks.The springs were then activated so that a pres-sure on the posterior teeth was exerted when

TREATMENT OF SKELETAL OPEN BITE 491

Figure 1 Spring bite-block.

the mandible was in rest position. Brokensprings had to be replaced in 12 patients. Nosubject had any problem wearing the bite-blockat night and all reported consistent use of theappliance. One patient who removed his bite-block from his mouth during the night wasexcluded from the study at an early stage.

Samarium-cobalt magnets (Ugimag RecomaAG, Lupfig, Switzerland) were used for themagnetic bite-blocks. Two round repelling mag-nets, 2 mm thick and with a diameter of 12 mm,were embedded in the acrylic over the posteriorteeth in the upper and lower bite-blocks (Fig. 2).The bite-blocks on the right and left sides ofthe dental arch were joined by a steel bar. Themagnets were electrolytically covered with goldand thereafter with hardening glaze (PermaLink, G-C Dental Industrial Corp., Japan). Thiswas to protect the magnets from corrosion andprevent the leakage of possibly poisonous prod-ucts. The combined height of the upper andlower bite-blocks at the first permanent molarsvaried between 6 and 9 mm (median 7 mm).

The theoretical maximum repelling force of themagnets was, because of the distance betweenthem and their coverage, reduced. In six casesthe repelling force of the bite-blocks was meas-ured when they were placed on dental castsmounted on an articulator (corresponding totheir use in the mouth) and was found to be299, 356, 413, 417, 440, and 483 g, respectively.The magnetic bite-blocks were cemented ontothe upper and lower posterior teeth and wereleft in place 3 months. The patients werechecked every 3-4 weeks during this period.

Recordings

The sequence of the recordings is given inTable 1.

Measurement of bite-force

In the group with spring bite-blocks, the bite-force at the right and left first permanent molarswas measured as described earlier (Ingervall andBitsanis, 1987) with the bite-force recorder ofFloystrand et al. (1982). The mean of the bite-

R. KUSTER AND B. INGERVALL

Figure 2 Magnetic bite-blocks.

force on the two sides was calculated. Measure-ments were made at each control visit. Thus,altogether 13 measurements (at the start of thetreatment and each month during the 12 monthsof treatment) were made.

Electromyography (EMG)

The activity of the anterior portion of thetemporal muscle and of the masseter musclewas recorded bilaterally. Bipolar hook elec-trodes were used as described earlier (Ingervalland Egermark-Eriksson, 1979). Recordingswere made as in an earlier study (Ingervall andBitsanis, 1987) in the rest position of the mand-ible, during maximal bite in the intercuspalposition and during chewing of apple and pea-nuts with a Disa electromyograph (Disa Elek-tronik, Copenhagen) and a Gould electrostaticwriter (Gould Elektronik, Zurich). The meanvoltage amplitude in the rest position and duringmaximal bite was measured. The maximal meanvoltage amplitude during the closing phase ofthe chewing cycle was determined as the mean

of six randomly selected cycles during an actof chewing. The mean of the recordings fromthe muscles on the right and left sides wascalculated.

Cephalometry

Cephalograms were taken with the mandible inthe intercuspal position. The reference pointsand lines used in the analysis of the profilecephalogram (linear enlargement 3.6 per cent)are shown in Figs 3 and 4. The variablesrecorded are given in Table 5. The reference lineOL was defined as a line from mo bisecting thedistance is-ii. The point io was constructed asthe perpendicular projection of the point ii onthe line mo-is (upper occlusal line). The dis-tances is-io and ii—io give the overjet andoverbite, respectively, and were measured fromthe central incisor in the most extreme position.The quotients s-tgo/n-mex 100 and n-sp'/sp'-me x 100 express the relationship between theposterior and anterior face heights, and theupper and lower anterior face heights, respect-

TREATMENT OF SKELETAL OPEN BITE

Table 1 Recordings at different times in the two series of patients.

493

Spring bite-blocks

Magnetic bite-blocks

Recording 1Before the start ofthe treatment

Profile cephalogramEMGBite-force

Recording 1Before the start ofthe treatment

Profile cephalogramEMG

Recording 2After 6 months

EMGBite-force

Recording 2After 3 months (endof treatment)

Profile cephalogramEMG

Recording 3After 12 months(end of treatment)

Profile cephalogramEMGBite-force


Profile cephalogram


EMG

9O

Figure 3analysis.

Reference points used in the cephalometric

ively. The total rotation of the mandible duringthe period of observation was analysed by thesuperimposition of the profile cephalogramsusing the natural reference structures of themandible as described by Bjork and Skieller(1983). An arbitrary reference line (approxi-mately parallel to ML) was drawn on the mand-ible (Fig. 4) and transferred from the first tothe second cephalogram by the superimpositionon the natural reference structures of the mand-ible. The difference of the angle between themandibular reference line (MRL) and the NSLbetween the two cephalograms expresses thedegree of mandibular rotation during the timeinterval. The MRL was also used to record the

Figure 4 Reference lines used in the cephalometricanalysis.

vertical position of the lower molar cusp (lmc)and of the edge of the lower incisor (ii) by themeasurement of the perpendicular distance tothe MRL.

Statistical methods

Differences between observations on thedifferent occasions and between the duplicatedeterminations were tested with Wilcoxon'smatched-pairs, signed-ranks test. The accidentalerrors (si) were calculated with the formula


si= sf'Ld2/2n, where d is the difference betweenthe two determinations.

Errors of the method

The errors of the cephalometric analysis, includ-ing the procedure of superimposition, weredetermined by duplicate measurements of 20randomly selected cephalograms. A systematicdifference between the two measurements wasfound for two variables. Variable 8 (s-tgo/n -mex 100) was greater at the second than atthe first measurement (mean difference 0.97,0.001 <P<0.01) and variable 28 (ii-io) waslikewise greater at the second measurement(mean difference 0.32 mm, 0.01</ )<0.05). Theaccidental errors of the method are given. inTable 2.

Results

Bite-force

The bite-force increased during the first monthsof the treatment with the spring bite-blocks(Fig. 5), but did not change in the interval from6 months to the end of the treatment (Table 3).

Electromyography

The muscle activity in the rest position or duringchewing did not change during the treatmentwith the spring bite-blocks (recordings 1-3,Table 2). The activity of the masseter muscleduring maximal bite increased from the first tothe second recording (a numerical increase was

Table 2 Accidental errors of the method of thecephalometric variables in degrees (variables 1-7,10-14) and in mm (variables 15-28).

Variable

1 s-n-ss2 s-n-sm3 ss-n-sm4 NSL/NL5 NSL/OL6 NSL/ML7 NL/ML8 s-tgo/n-me x 1009 n-sp'/sp'-me x 100

10 NSL/MRL11 RL/ML12 n-s-gn13 ILs/NL14 ILi/ML

Error

0.530.370.270.600.840.430.781.080.361.241.020.511.101.37

Variable

15 s-go16 s-tgo17 n-me18 se-pm19 gn-cd20 gn-ar21 NL-umc22 NL-is23 ML-lmc24 ML-ii25 MRL-lmc26 MRL-ii27 is-io.28 ii-io

Error

0.420.400.430.621.070.340.400.320.450.660.450.430.380.44

also found for the anterior temporal muscle)with no further change to the recording at oneyear.

In the group treated with magnetic bite-blocks, electromyographic recordings weremade before the start of the treatment and oneweek after the removal of the bite-blocks at 3months. Between these two recordings, theactivity of the masseter muscle at rest and ofthe anterior temporal muscle during chewing ofapple increased (Table 4).

Cephalometry

The values of the cephalometric variables atthe start of the treatment and the change to thefollowing recording are given in Table 5. Thetable also gives the annual changes during nor-mal growth in the untreated longitudinal sampleof Riolo et al. (1974). The values of Riolo et al.were matched with those of the present subjectswith respect to sex and age, and reduced to thesame degree of linear magnification.

In the group with spring bite-blocks, themandibular prognathism (var. 2, Table 5)increased and the angle for sagittal jaw relation(var. 3) decreased slightly during the year ofobservation. The inclination of the jaws (vars.4 and 6) and the vertical jaw relation (var. 7)did not change.

There were also no changes of the quotientsbetween the posterior and anterior face heights(var. 8) or between the upper and lower anteriorface heights (var. 9). The gonial angle (var. 11)increased and the j>-axis angle (var. 12)decreased slightly. The linear dimensions of theface (vars. 15-26) increased significantly withthe exception of the distances from the lowermolar cusp to ML (var. 23) and to MRL (var.25), which were constant. The lower incisorsuprighted (var. 14) and the overbite (var. 28)increased.

In the group with magnetic bite-blocks(observed for 3 months), there was a greaterincrease of the mandibular prognathism (var.2) and a greater decrease of the sagittal jawrelation angle (var. 3, Table 5) than in the groupwith spring bite-blocks. In addition, there wasin the group with magnetic bite-blocks a slightanterior rotation of the mandible expressed asa decrease of the angles NSL/ML and NSL/MRL and an increase of the quotient betweenthe posterior and anterior face heights (var. 8).

The upper posterior face height (var. 18) and


[N]

500.

450 _

400_

350 _

300 _

250 _

Mean+Std

MeanMedian

Mean-Std

200 I

Start oftreatment

10 End of Monthstreatment

Figure 5 Bite-force values in the group with spring bite-blocks during the period of observation.

Table 3 Bite-force (in N) and muscle activity (in uV) in the rest position, during maximal bite and duringchewing recorded on the various occasions in the group treated with spring bite-blocks.

Bite-force

Rest positionAnterior temporal m.Masseter m.

Maximal biteAnterior temporal m.Masseter m.

Chewing appleAnterior temporal m.Masseter m.

Chewing peanutsAnterior temporal m.Masseter m.

Recording

Median

309

3.91.2

417243

313150

393180

1

Range

170-471

0.7-12.20.0-3.8

98-138981-396

183-65880-214

187-86994-310

Recording

Median

376**

4.11.4

598301**

321149

373182

2

Range

249-520

0.7-12.20.0-5.4

194-1461128-562

219-65277-316

210-84497-330

Recording

Median

392

3.51.7

486290

347171

382199

3

Range

199-616

0.7-18.20.0-7.4

117-1729147-757

161-83585-280

205-970116-429

Recording 4

Median

4.83.4*

605319

315183*

398240

Range

1.4-14.20.0-10.1

178-129978-1068

111-94292-335

160-114748-401

*0.0I </><0.05, **0.001 </><0.0I; indicates significant difference from previous recording.

the mandibular length (vars. 19 and 20)increased and the incisors erupted (vars. 22, 24,26). In contrast to the findings in the groupwith spring bite-blocks, there was in the groupwith magnetic bite-blocks a significant intrusion

of the upper and lower molars (vars. 21 and23). In the group with magnetic bite-blocks,both the upper and the lower incisors uprighted(vars. 13 and 14) and there was a markedincrease of the overbite (var. 28).


Table 4 Muscle activity (in u.V) in the rest position, during maximal bite, and duringchewing recorded on two occasions in the group treated with magnetic bite-blocks.

Rest positionAnterior temporal m.Masseter m.

Maximal biteAnterior temporal m.Masseter m.

Chewing appleAnterior temporal m.Masseter m.

Chewing peanutsAnterior temporal m.Masseter m.

Recording I

Median

4.92.4

475215

363288

423287

Range

1.7-10.90.7-6.8

168-98342-744

165-76287-469

187-1016122-600

Recording 2

Median

4.95.4*

488267

527*301

561356

Range

2.5-6.82.4-8.1

383-725200-697

303-745209-623

239-82496-677

*0.01 </><0.05; indicates significant difference from previous recording.

Discussion

No adverse effects of the bite-blocks were seen.Thus, no pain or functional problems werenoted. No child wearing a magnetic bite-blockdeveloped cross-bite, a problem described insome studies (Kalra et al., 1989; Kiliaridis et al.,1990), but not mentioned by other authors(Barbre and Sinclair, 1991).

Before the start of the treatment, the bite-force of the group of children treated with aspring bite-block was below normal (average inrandom 9-year old children 375 N, Ding andKober, 1985). The bite-force increased duringthe period of observation. This might be due tonormal development (average in 11-year-old chil-dren 424 N, Dine and Kober, 1985), but couldalso at least partly be an effect of the treatment.The latter explanation is supported by the factthat the increase occurred during the first partof the period of treatment with no furtherincrease during the following months. The elec-tromyographically recorded muscle activity dur-ing maximal bite also increased during the firstpart of the treatment and was thereafter constant.

Similar results (increase of bite-force andmuscle activity) were achieved by the trainingof the masticatory muscles in long-face children(Ingervall and Bitsanis, 1987) and were foundto influence the facial morphology favourably.In the present investigation, the same effects onthe muscles could contribute to the treatmentresults and be a positive factor for their mainten-

ance provided the muscle strength does notdecline after treatment. The bite-force was notmeasured after the end of the treatment. Thiswas due to various types of treatment (includingthe wearing of multiband appliances) of thechildren after the phase of bite-block treatment.From the electromyographic recordings at 18months, there was, however, no evidence of adecline in muscle strength.

The changes in facial morphology in thegroup treated with spring bite-blocks were larg-ely in accordance with the annual changes inthe control sample of Riolo et al. (1974). Therewas no evidence of intrusion of the posteriorteeth or of increased mandibular growth andthus no sign of anterior rotation of the mand-ible. A slight increase of the gonial angle andan uprighting of the lower incisors were noted.The uprighting is probably an effect oftightening of the lips (or withdrawal of thetongue) due to the increased bite height causedby the wearing of the bite-blocks, similar to theeffect on incisor position of mouth-breathing(Linder-Aronson, 1970). During the year, theoverbite increased on average by 1.3 mm. Thisis more than would have been expected fromnormal development (Moyers et al., 1976,annual increase for matched controls 0.3 mm;Bergersen, 1988, annual increase for matchedcontrols 0.1 mm). This improvement of theoverbite might be due to small, but favourablecontributions from several sources, slight inhibi-tion of the eruption of the posterior teeth,


Table 5 Median and range in degrees (variables 1-7, 10-14) and in mm (variables 15-28) of the cephalometricvariables at the start of the treatment and median differences between subsequent recordings as well as annualchanges in a control sample (Riolo et al., 1974).

Variable

1 s-n-ss2 s-n-sm3 ss-n-sm4 NSL/NL5 NSL/OL6 NSL/ML7 NL/ML8 s-tgo/n-

mex 1009 n-sp'/sp'-

me x 10010 NSL/MRL11 RL/ML12 n-s-gn13 ILs/NL14 ILi/ML15 s-go16 s-tgo17 n-me18 se-pm19 gn-cd20 gn-ar21 NL-umc22 NL-is23 ML-lmc24 ML-ii25 MRL-lmc26 MRL-ii27 is-io28 ii-io

Spring bite-blocks

Recording 1

Med.

78.774.05.16.7

24.042.134.758.6

77.9

45.5131.172.6

108.892.962.563.8

111.542.5

100.393.319.827.329.338.020.531.05.0

-0.5

Range

73.1-84.067.6-78.9

-1.1-9.13.0-12.2

17.1-33.737.7-54.629.1-49.449.4-63.1

69.2-84.2

40.5-60.0124.4-144.068.7-78.097.3-116.881.0-100.453.0-70.553.5-72.099.5-120.538.5-48.594.0-108.583.5-102.015.0-25.023.0-31.526.0-33.535.0-42.516.5-22.527.5-35.0

1.0-9.0-6.0-2.0

Dif. rec3 and 1

0.20.6*

-0 .3*-0.1-0.8**

0.20.40.2

0.4

0.01.2*

-0 .3*-0.6-2.6**

1.0**1.3**2.5**1.0**3.0**2.0**0.5*

Rioloel al.

0.10.2

-0.10.1

-0.2-0.3

-0.40.10.60.4

* 1.7

• 2.4* 1.2* 2.6* 2.4

0.81.0*** 0.70.3 0.61.0*** 0.90.51.0***

-0.31.3***

Magnetic bite-blocks

Recording 1

Med.

82.176.15.26.2

20.037.131.164.4

75.3

46.0126.071.0

110.896.870.072.0

113.044.0

102.598.020.528.530.040.019.032.06.5

-2.0

Range

76.8-84.968.9-78.82.6-13.73.4-12.8

15.2-27.030.5-47.423.6-37.454.0-66.9

62.2-85.9

32.5-59.0120.7-135.064.5-77.6

101.8-116.479.6-106.559.5-77.560.5-79.0

106.5-120.039.0-51.597.0-116.590.0-109.018.5-27.022.5-30.029.0-34.034.0-41.517.0-24.025.5-35.02.0-12.0

-4.0-0.0

Dif. rec.2 and 1

-0.50.9**

-1.5**-0.4

0.0- 1 . 1 *-0.6

0.6*

0.8

-1.5*1.1*

-1.0*-3 .1**-5.3**

0.50.50.50.5*1.5**1.0*

-1.0**0.5*

-0.5*0.5**

-0.50.5*

-1.5*3.0**

Rioloet al.

0.20.4

-0.20.2

-0.5-0.7

-1.0-0.1

0.1-0.1

1.8

1.90.62.32.20.70.40.70.6

*0.01</><0.05, **0.001</><0.01, ***/»<0.001.

slightly increased eruption of the incisors andretroclination of the incisors.

In the group treated with magnetic bite-blocks, in contrast, definite therapeutic effectswere seen. Thus, during the 3 months the man-dibular prognathism increased twice as muchas during one year in the control sample (var.2, Table 5). There was also clear evidence ofanterior mandibular rotation. Thus, the angleNSL/ML decreased by twice the annualdecrease in the control sample in three months.The anterior mandibular rotation of 1.5 degrees(change in the angle NSL/MRL) during threemonths is large in comparison with the normalannual anterior rotation of 1 degree found byBjork and Skieller (1983). With the use of themagnetic bite-blocks, both the upper and the

lower molars intruded, and there was possiblyalso an increased rate of eruption of the incisors(large changes of the variables 22 and 24 com-pared to the annual changes in the controlsample). The molar intrusion and possiblyincreased mandibular growth (comparativelylarge three-month changes of variables 19 and20) led to an anterior rotation of the mandible.This, together with a marked eruption of theincisors, resulted in a favourable medianincrease of the overbite of 3 mm in 3 months.In the group with magnetic bite-blocks, therewas a more marked uprighting of the incisors(which also tends to increase the overbite) thanin the group with spring bite-blocks. This isprobably due to the fact that the magnetic bite-blocks were worn day and night.


Several of the effects of the bite-blocks foundin this study agree with the results of otherinvestigations. There was thus no effect of eitherof the two bite-blocks on the maxilla. This isin agreement with the results of other studiesin humans (Kalra et al., 1989; Barbre andSinclair, 1991), but in contrast to the experi-ments in monkeys mentioned in the introduc-tion. In all the animal experiments, a markedmaxillary displacement was found. The anteriormandibular rotation found by us in the groupwith magnetic bite-blocks agrees very well withthe results of Kalra et al. (1989), but wassomewhat greater than that found by Barbreand Sinclair (1991) in their studies of the effectsof magnetic bite-blocks. Kalra et al. (1989)found an increased mandibular growth with theuse of their cemented magnetic splints. Themandibular length increment in our study (vars.19 and 20) was less than in the study of Kalraet al., but still large compared to the controlsample of Riolo et al. No definite conclusionscan be drawn, however, because of the lack ofa specific control group in our study. Theoverbite correction found by us after the use ofmagnetic bite-blocks was of the same magnitudeas reported by Kalra et al. (1989), and Barbreand Sinclair (1991). Like the latter authors, wefound an increased eruption and uprighting ofthe incisors. An uprighting of the incisors wasalso noted by Dellinger (1986), and by Woodsideand Linder-Aronson (1986).

In 9 of the 11 patients treated with magneticbite-blocks, cephalograms were taken one yearafter the removal of the bite-blocks. During thisinterval, three patients had been treated withmulti-band appliances. Two patients had hadno appliances and four had worn an appliancefor retention. Thus, in one case an activatorwas used and the three other patients wore anupper removable plate with bite platforms overthe posterior teeth for 6-8 months. The sixpatients with no treatment or retention onlyunderwent the following development: increaseof the overbite by 3 mm during active treatmentfollowed by a decrease by 1.5 mm after treat-ment, i.e. a 50 per cent relapse. Decrease of theangles NSL/ML and NL/ML by 1.1 degreesand 0.3 degree, respectively, during treatment,increase by 1.2 degrees and 0.4 degree, respect-ively, after treatment, i.e. a complete relapse.An anterior rotation of the mandible of 1.5degrees (angle NSL/MRL) during treatment

followed by 0.5 degree posterior rotation aftertreatment. It is thus clear that the resultsachieved by treatment with magnetic bite-blockstend to relapse. It therefore seems to be neces-sary to continue the treatment with so-calledactive retention for a long period. A combina-tion of cemented magnetic bite-blocks for theactive treatment followed by a longer period ofwearing of removable bite-blocks for part ofthe day and night might be successful in thecorrection of skeletal open bite.

It should be noted that the same effect onmandibular rotation as in the present study wasfound after training of the masticatory musclesin long-face children (Ingervall and Bitsanis,1987). The increase in bite-force found duringthe first phase of the treatment with bite-blocksmight thus be a positive factor to stabilize thetreatment result. Further studies should be per-formed to determine whether it would be ofadvantage to increase the height of removablebite-blocks (without magnets) from time to timeto achieve a greater increase in muscle strength.

Address for correspondence

Dr Robert KusterKlinik fur KieferorthopadieFreiburgstrasse 7CH-3010 BernSwitzerland

Acknowledgement

This study was supported by SchweizerischerNationalfonds zur Forderung der wissen-schaftlichen Forschung, Grant No. 3.905-0.85

References

Altuna A, Woodside D G 1985 Response of the midfaceto treatment with increased vertical occlusal forces. AngleOrthodontist 55: 251-263

Bakke M, Siersbaek-Nielsen S 1990 Training of mandibularelevator muscles in subjects with anterior open bite.European Journal of Orthodontics 12: 502 (Abstract)

Barbre R E, Sinclair P M 1991 A cephalometric evaluationof anterior open bite correction with magnetic activevertical corrector. Angle Orthodontist 61: 93-102

Bergersen E O 1988 A longitudinal study of anterior verticaloverbite from eight to twenty years of age. Angle Ortho-dontist 58: 237-256

Bjork A, Skieller V 1983 Normal and abnormal growth ofthe mandible. A synthesis of longitudinal cephalometricimplant studies over a period of 25 years. EuropeanJournal of Orthodontics 5: 1-46


Carlson D S, Schneiderman E D 1983 Cephalometric ana-lysis of adaptations after lengthening of the massetermuscle in adult rhesus monkeys Macacca mulatta.Archives of Oral Biology 28: 627-637

Dellinger E L 1986 A clinical assessment of the activevertical corrector—A nonsurgical alternative for skeletalopen bite treatment. American Journal of Orthodontics89: 428-436

Dine S, Kober M 1985 Bisskraftmessungen an 9-bis 11-jahrigen Kindern. Medical Dissertation, University ofBerne

Ellis E, McNamara J A, Jr, Lawrence T M 1985 Compon-ents of adult Class II open-bite malocclusion. Journal ofOral and Maxillofacial Surgery 43: 92-105

Fields H W, Promt W R, Nixon W L, Phillips C, Stanek E1984 Facial pattern differences in long-faced children andadults. American Journal of Orthodontics 85: 217-223

Floystrand F, Kleven E, Oeilo G 1982 A novel miniaturebite force recorder and its clinical application. ActaOdontologica Scandinavica 40: 209-214

Ingervall B, Bitsanis E 1987 A pilot study of the effect ofmasticatory muscle training on facial growth in long-facechildren. European Journal of Orthodontics 9: 15-23

Ingervall B, Helkimo E 1978 Masticatory muscle force andfacial morphology in man. Archives of Oral Biology 23:203-206

Ingervall B, Egermark-Eriksson I 1979 Function of tem-poral and masseter muscles in individuals with dual bite.Angle Orthodontist 49: 131-140

Ingervall B, Thuer U, Kuster R 1989 Lack of correlationbetween mouth-breathing and bite force. EuropeanJournal of Orthodontics 11: 43-46

Kalra V, Burstone C J, Nanda R 1989 Effects of a fixedmagnetic appliance on the dentofacial complex. AmericanJournal of Orthodontics and Dentofacial Orthopedics 95:467-478

Kiliaridis S, Egermark I, Thilander B 1990 Anterior openbite treatment with magnets. European Journal ofOrthodontics 13: 447-457

Linder-Aronson S 1970 Adenoids Their effect on mode ofbreathing and nasal air flow and their relationship tocharacteristics of the facial skeleton and the dentition.Acta Oto-Laryngologica Suppl 265

McNamara J A Jr 1977 An experimental study of increasedvertical dimension in the growing face. American Journalof Orthodontics 71: 382-395

Moyers R E, van der Linden F P G, Riolo M L, McNamaraJ A Jr 1976 Standards of human occlusal development.Monograph Number 5, Craniofacial Growth Series,Center for Human Growth and Development, Universityof Michigan, Ann Arbor, Michigan

Proffit W R, Fields H W, Nixon W L 1983 Occlusal forcesin normal and long-face adults. Journal of DentalResearch 62: 566-571

Ringqvist M 1973 Isometric bite force and its relation todimensions of the facial skeleton. Acta OdontologicaScandinavica 31: 35-42

Riolo M L, Moyers R E, McNamara J A Jr, Hunter W S1974 An atlas of craniofacial growth. Cephalometricstandards from the University School Growth Study,Monograph Number 2, Craniofacial Growth Series,Center for Human Growth and Development, Universityof Michigan, Ann Arbor, Michigan

Woods M G, Nanda R S 1988 Intrusion of posterior teethwith magnets. An experiment in growing Baboons. AngleOrthodontist 58: 136-150

Woodside D G, Linder-Aronson S 1986 Progressive increasein lower anterior face height and the use of posteriorocclusal bite-block in its management. In: Graber L W(ed.) Orthodontics; state of the art, essence of the science.The CV Mosby Company, St Louis

Documents

The effect of treatment of skeletal open bite with two