deep bite treatment in relation to mandibular growth rotation · growth rotation and consequent...

European Journal of Orthodontics 13 (1991) 86-94

Deep bite treatment in relation to mandibulargrowth rotation

Raymond I. LevinDelft, The Netherlands

SUMMARY This paper illustrates some of the changes which occur during the treatment of Class 11division 1 malocclusions complicated by a deep bite, and reviews the significance of thesechanges in relation to concepts of deep bite treatment. Particular reference is made to mandibulargrowth rotation and consequent differential tooth eruption in assessing factors involved in initialbite opening and consolidation of the opened bite. The cases shown illustrate that although aninitial bite opening may occur by incisor intrusion and molar eruption, when viewed over a longerperiod of time rotational mandibular growth and associated differential eruption of teeth in whichmolars erupt more than incisors may be a more significant factor. Differential eruption which takesplace in response to vertical condylar growth under guidance of the appliance would appear to bea significant factor in treatment of deep bite.

Introduction

Many biomechanical systems are currently usedto correct deep bite during orthodontic treat-ment. The system of choice depends on theobjectives of treatment: incisor intrusion, incisorprotrusion and molar eruption, or extrusion.Incisor intrusion particularly of maxillary inci-sors is generally perceived to be the majorbiomechanical problem.

Incisor intrusion can convincingly be demon-strated using fixed or removable appliances(Begg, 1965; Booy, 1966; Sims, 1971; Burstone,1977; Ten Hoeve et al, 1977; van Beek, 1985;Thompson, 1985; Dermaut and Vanden Bulcke,1986; Levin, 1987). Molar extrusion or eruptioninduced by removable appliances, cervical head-gear or intra oral elastics is an established clinicalprocedure.

Molar extrusion resulting in a backward man-dibular rotation (Williams, 1965; Bijlstra, 1970)and opening of the bite is generally considered tobe contra-indicated although recovery can beanticipated (Williams, 1965; Levin, 1977; van derLinden, 1988).

Most investigations and clinical reports haveconsidered initial bite opening procedures andhave not addressed the implications of rotationalmandibular growth as described by Bjork (1969),and Bjork and Skieller (1972). Due to vertical

condylar growth in forward mandibular growthrotation the mandible rotates around a fulcrumin the incisor or premolar region. In response tothis growth, compensatory differential eruptiontakes place with molars erupting more thanincisors. Differential tooth eruption associatedwith mandibular growth, and the influence oftreatment on this growth and eruption wouldseem to be an important consideration whenassessing the factors involved in the treatment ofdeep bite. The purpose of this paper is firstly toexamine changes occurring during treatment ofindividuals with a Class II division 1 malocclu-sion complicated by a deep bite with particularreference to mandibular growth, and secondly,to review the significance of these changes inrelation to the concepts of deep bite treatment.

The cases discussed were treated with theBegg light wire technique (Levin, 1987) and inone case an activator. The cases were all consi-dered to have a forward type of mandibulargrowth rotation (Bjork, 1969). A deep bite wasdiagnosed according to a textbook definition(Moyers, 1963) which states that a deep bite ispresent when mandibular incisors impinge on thepalatal mucosa. For the purpose of analysis,tracings of lateral cephalometric radiographswere superimposed on SN and registered at S, onANS and PNS registered at ANS, and theinternal structures of the mandible (Bjork, 1969).

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DEEP BITE AND MANDIBULAR GROWTH ROTATION 87

(a

Figure 1 Treatment sequence in bite opening in a young post-adolescent female patient. (A) Pretreatment. The lower incisorsimpinge on the palatal-mucosa. (B) After bite opening. Maxillary incisors are intruded and uprighted, with apices positioneddirectly beneath the cortical plate of the nasal floor. (C) Post-retention. Overbite stable, although with slight eruption of theincisors.

Initial bite opening

Initial bite opening during treatment with thelight wire technique has been shown to resultfrom incisor intrusion, molar eruption or acombination of these factors (Williams, 1965;Bijlstra, 1970; Thompson, 1985; Levin, 1987).

In non-growing individuals or dolichofacialtypes with a backward mandibular growthrotation tendency, incisor intrusion is the pri-mary treatment objective. Initial incisor intru-sion is illustrated in the first case report (Fig. 1B).

In growing individuals with deep bite andforward mandibular growth rotation both inci-

-sor-intrusion-and.molar_eniptiqn^an initially bedemonstrated (Fig. 2). An initial backward man-"dibular rotation may also occur when the rate ofmolar eruption exceeds the rate of verticalcondylar growth resulting in bite opening causedby molar eruption. Excessive eruption is trans-lated into a backward mandibular rotation (Fig.2). However, molar eruption is not necessarilyassociated with backward mandibular rotation(Fig. 3). Provided that the rate of molar eruptiondoes not exceed the relative rate of verticalcondylar growth no backward rotation willoccur.

It is clear on examination of treated cases thatit is difficult to apportion the significance ofincisor intrusion as opposed to molar eruption inopening the bite and the stability of the opened

Figure 2 Treatment of a Class II division I malocclusion byextraction of second premolars and light wire technique. Theoverall superimpositions illustrate an initial backward man-dibular rotation followed by a forward rotation.


88 RAYMOND I. LEVIN

Figure 3 Treatment of a Class II division 1 malocclusion by extraction of four first premolars and light wire technique. (A) Theoverall superimposition shows considerable mandibular growth with no rotational effect during or after bite opening. (B)Maxillary superimposition shows initial incisor intrusion followed by eruption. (C) The mandibular superimposition showsmolars erupting more than incisors, both during and following bite opening. Considerable condylar growth is evident.

bite. This is particularly so in growing indi-viduals in whom both incisor intrusion andmolar eruption are significant initially (Fig. 3).However, subsequent vertical facial growth maymask the initial incisor intrusion and furthercompensatory molar eruption takes place inresponse to condylar growth. Differential tootheruption is evident in the period after biteopening with molars erupting more than incisors(Fig. 3). The absolute incisor intrusion is ofminor importance when compared to the con-siderable vertical eruption of mandibular molarsassociated with condylar growth occurring bothduring and following treatment (Fig. 3).

Management of differential tooth eruption

Traditionally, mandibular molar elevation dur-ing treatment was found to cause bite openingand backward mandibular rotation. Backwardrotation occurred around a fulcrum in the molarregion and an axis near the condylar fossa. Thisconcept of bite opening was based on cephalo-metric observations and a belief in linear facial

growth. It had been developed prior to the Bjorkstudy on rotational facial growth (Bjork, 1969)which results in differential tooth eruption andconsequently the finding that molar eruptionduring growth was greater than had previouslybeen believed (Bjork and Skieller, 1972). It wouldseem likely that the management of this tootheruption which occurs in response to verticalcondylar growth would be a factor in the treat-ment of deep bite without causing inadvertentbackward mandibular rotation. This conceptcan be illustrated by Fig. 4 and the following casereports.

The first case illustrates treatment using pri-marily an activator. The salient features of thisabnormality are a deep bite, a so-called 'gummysmile', and maxillary prognathism. During treat-ment considerable mandibular growth asso-ciated with differential tooth eruption took place(Fig. 5). Maxillary prognathism and deep bitehas been reduced. No active intrusion of incisorstook place. The malocclusion has apparentlybeen corrected as a result of mandibular growthand differential tooth eruption, molars erupting



Figure 4 Diagram indicating (a) growth occurring awayfrom the condylar fossa, with three different amounts ofmolar eruption (b), and their influence (a + b) on incisorposition (c) and chin position (d). With excessive eruptionbackward rotation of the mandible would accompany biteopening. With non-eruption of the molars the mandible isadvanced with forward rotation and deepening of the bite.Eruption and condylar growth are illustrated occurring awayfrom condylar fossa and maxilla.

more than incisors. The result of this treated casebrings into question the necessity to treat themaxillary prognathism by incisor intrusion. Byimproving the incisor inclination and altering theratio of anterior maxillary height to anterior

mandibular height by a mandibular height in-crease, the 'gummy smile' problem has beenresolved.

The following case (Fig. 6) illustrates treat-ment of excessive overbite and overjet compli-cated by the premature loss of four first molars.The Begg light wire appliance was used. Con-siderable vertical height increase in the molarand premolar regions is evident. Despite active

jncisor intrusion-the overbite appears to havebeen treated by molar eruption (Fig. 6f) asso-ciated with vertical condylar growth. The resultis stable 7 years after retention.

Orthodontic treatment appears to have util-ized inherent growth to establish Class I anteriorocclusion. By correcting the anterior occlusion,forward mandibular growth rotation can occuraround a fulcrum in the incisor region (Bjork,1969). Figure 6 illustrates forward mandibularrotation occurring subsequent to correction ofthe anterior occlusion (SN2-SN3).

The significance of vertical condylar growthand corresponding compensatory molar erup-tion during treatment is that it appears that themanagement of the mechanism of differential

a

Figure 5 Treatment with an activator. Note deep bite and maxillary prognathism. No intrusion of incisors. Correction seems tobe the result of considerable mandibular growth, (a) Overall superimposition shows mandibular growth and relative rotationalstability, (b) Maxillary and (c) Mandibular superimposition on internal structures illustrate considerable differential eruptionand condylar growth. Molar eruption considerably greater than incisor eruption.


90 RAYMOND I. LEVIN

Figure 6 Class II division I malocclusion complicated by deep bite. Four first molars had been extracted prior to start oftreatment. (6c) Overall tracings superimposed on SN. Slight backward rotation in first phase of treatment, followed by recoverywith considerable mandibular growth. (6f) Superimposition on internal structures of the mandible. Growth rotation measuredby change in inclination of SN. Between SN1 and SN2 ho discernible rotation. From SN2 to SN3 indicative of forwardmandibular rotation (Bjork, 1969). Intra-oral views before treatment (above) and 6 years post-retention (below).


DEEP BITE AND MANDIBULAR GROWTH ROTATION

tooth eruption in response to condylar growthhas the potential to be a significant factor in deepbite treatment. The differential eruption occur-ring during active guidance of fixed appliancesand Class II elastics or the passive guidanceof the activator appliance. Vertical condylargrowth is also translated into mandibular growthreducing the sagittal jaw discrepancy.

Orthopaedic-effects - -

In light wire treatment initial reduction of over-bite and overjet may be considered a functionalstage of treatment. During this phase of treat-ment a functional improvement of the occlusionand perioral musculature may occur (Fig. 7).

This case also illustrates a reduction in theskeletal discrepancy as a result of mandibulargrowth (Fig. 7). Bite opening is associated withincisor intrusion, molar eruption, and consider-able condylar growth. No inadvertent backwardmandibular rotation is evident.

The following cases illustrates a functionalimprovement of occlusion and perioral muscu-lature. The result is stable 7 years after retentionand the initial skeletal discrepancy has beenresolved as a result of mandibular growth (Fig.8). In assessing treatment changes it wouldappear that deep bite was resolved mainly as aresult of mandibular growth occurring at thecondyle and a consequent molar eruption greaterthan that of incisors. Maxillary molar eruption isobviously also important.

(d

Figure 7 Functiona] improvement of perioral musculature during initial phase of treatment of Qass II division 1 malocclusion(7c) Superimposition on SN. A reduction of skeletal Class II is evident with absence of backward mandibular rotation. (7f)Superimpositions on maxillary and mandibular structures showing incisor intrusion, some molar eruption and considerablecondylar growth. Photographs of patient before (above) and after (below) treatment.


RAYMOND I. LEVIN

Figure 8 Mandibular growth resulting in an orthopaedic effect. Result stable 6 years after retention. Considerable molareruption with only slight incisor intrusion. Skeletal discrepancy reduced as a result of mandibular growth, (c) Tracingssuperimposed on SN. Considerable mandibular growth during treatment period. Slight horizontal growth after end of retention,(f) Mandibular superimposition showing molar eruption and considerable condylar growth. Intra-oral photographs beforetreatment and 6 years after retention.



Discussion and conclusions

Definite conclusions cannot be drawn from anumber of selected cases. Nevertheless, certainobservations may be made. These observationsare based on individual cases and the likelihoodthat they are not unique. Similar cases whentreated under similar circumstances may beexpected to respond in an analogous fashion.Changes observed during treatment whenviewed in the light of the Bjork description ofrotational facial growth and consequent differ-ential tooth eruption may serve as a model forunderstanding some of the factors which may beinvolved in the treatment of deep bite.

Deep bite treatment is fundamentally a prob-lem that should be resolved in relation to indi-vidual facial type and anticipated mandibulargrowth. Dolichofacial types tend to have rela-tively less mandibular molar eruption than bra-chyfacial types and greater incisor eruption(Bjork and Skieller, 1972). Consequently, theresolution of a deep bite in growing individualswould appear to be a biomechanical problemrequiring not only an emphasis on incisor intru-sion or molar eruption, but also the evaluationand management of rotational facial growth andresulting differential tooth eruption.

The case reports in this presentation illustratethe use of Class II elastics and in one case anactivator appliance in bite opening during treat-ment. The judicious use of Class II elastics in thelight wire technique provides a means of manag-ing the differential tooth eruption which occursduring treatment. Similarly, the passive imposi-tion of an activator on the occlusal developmentcan be shown to reduce deep bite during treat-ment presumably by altering the differential ratesof tooth eruption.

Initially, bite opening in the light wire tech-. nique can be shown to occur by incisor intrusion,molar eruption and in some case by inadvertentbackward mandibular rotation induced bymolar elevation (Williams, 1965; Bijlstra, 1970;Thompson, 1985; Levin, 1987). Rotational stabil-ity of the mandible is influenced by the rate ofmolar eruption and the concomitant verticalcondylar growth. Thereafter, it can be shown(Figs 3 and 6) as a result of vertical facial growthand vertical growth at the condyle that the initialincisor intrusion appears insignificant whencompared to the considerable differential erup-tion of incisors and molars. Although initialincisor intrusion is important in establishing a

normal anterior occlusion early in treatment theintrusion of incisors may be a relatively minoraspect of deep bite treatment when compared tothe potential vertical eruption of molars occur-ring in response to rotational mandibulargrowth. After initial bite opening, differentialtooth eruption, in which molars erupt more thanincisors in forward mandibular growth rotation,may contribute to a consolidation of the openedbite and a long-term stability thereof.

Despite the complexity of fixed appliances, fewpublications have dealt with the orthopaediceffects of these appliances. Although Thompson(1985) found that mandibular growth was im-portant in bite opening when using the light wiretechnique, and Petrovic (1984) stated that ClassII elastics can significantly increase cellular acti-vity in the mandibular condyle. This wouldenhance vertical growth. Gianelli et al. (1984)found that most treatment modalities influencethe face in a similar manner, while Edwards(1983) and Mollenhauer (1987) reported onorthopaedic effects resulting from fixed appliancetreatment. Several cases shown in this reportillustrate a reduction in sagittal jaw discrepancyas a result of mandibular growth. This reductionin sagittal jaw discrepancy may be considered tobe an orthopaedic effect occurring in associationwith bite opening.

Address for correspondence

Dr R. I. LevinKoningsplein 102611 XD DelftThe Netherlands

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deep bite treatment in relation to mandibular growth rotation · growth rotation and consequent...

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