25
Volume 69 December 1976
913
Section of Odontology President R D Emslie MSC FDS
Meeting 24 May 1976
Paper The Problem of the Class III Malocclusion by Professor J P Moss PhD FDS Dorth RCS (University College Hospital Dental School, Mortimer Market, London WCIE6JD) The Class III malocclusion is a problem to the general practitioner as to when to refer for treatment; to the orthodontist because he is never sure that his treatment will be successful after growth is complete; to the oral surgeon because of the infinite variety of forms of the presenting malocclusion; and to the research worker because we know relatively little about the cause. Definition and Types Angle defined a Class III malocclusion as one where there is a mesial occlusion of the mandibular teeth by more than one-half the width of a single cusp. Unfortunately, this does not take into account the skeletal pattern.
Investigations of the different types of Class III malocclusion have been undertaken by Dietrich (1970) and she showed that 28.5 % of the Class III patients fall into Group A with a maxillary and mandibular skeletal base within the normal range; 25 %, Group B, have a mandibular prognathism associated with a normal maxilla and 37.5 %, Group C, have a normal mandible and a retrusive maxilla. Thus a total of 91 % of Class III fall into these groups. These findings were comparable with the child group of Jacobsen et al. (1974) but they also showed that id the adult groups the percentages in these groups altered: Group B, mandibular prognathisms, was greatest, 48%; Group C, maxillary retrusion, was 26%, and Group A, with maxilla and mandible in the normal range, 14%.. It seems, therefore, that the
differences in the two groups are explained by the fact that with growth the potential of the Class III malocclusion is fully realized and those cases which exhibited a mandible and maxilla within the normal range in childhood develop into a more severe malocclusion in adult life. As Angle (1907) comments, 'The marring of the facial lines is more noticeable and unpleasing in advanced cases amounts to a striking deformity'. The main problem is whether it is possible to predict which malocclusion will alter during growth. St6ckli (1970) investigated Class III cases which were similar at the beginning of observation and suggested that: 'A Class III type case does not proceed along a stable growth pattern. Observations during an early phase of development are not indicative of the development at a later phase.' One of the questions that remain to be answered is: 'Can this change be predicted in other ways?' Cephalometric analysis at present does not reveal the factors in advance which lead to variations in ultimate Class III development. A further type of Class III malocclusion, the postural or pseudo Class III, is also described as being due to forward posturing of the mandible which results from an edge-to-edge incisor relationship (Schwartz 1961). In these cases the upper incisors are proclined and - the lower incisors are retroclined (Ballard 1955). There is also -an excessive inter-occlusal clearance which is eliminated once the incisor position is corrected.
Incidence The incidence of Class III was stated by Angle (1907) to be 4.2%; Goose et al. (1957) in 2956 children 7-15 years old found 2.9%; and Moss & Picton (1968) in Greek school children 3-12 years old, 5%. Seipel (1946) in 21-year-old Swedes found an incidence of 4 %, and Massler & Frankel (1951) in 2758 school children 14-18
914 Proc. roy. Soc. Med. Volume 69 December 1976 years old, 9.4%. The highest incidence - 12.2% was recorded by Huber & Reynolds (1946) in 500 students. It seems evident from these surveys that the incidence of the malocclusion increases with age.
Etiology Amongst the most notable families which exhibit an inherited prognathism, the Hapsburgs are well known. The typical protruding lower lip andI prognathic lower jaw have been demonstrated in 33 members of the family. Stiles & Luke (1953) suggested that mandibular prognathism is inherited via a dominant gene with an unknown degree of reduced penetrance. Schulze & Weise (1965) studied families and twins with a Class III malocclusion and concluded that it could be inherited as a dominant and a recessive factor. They suggested that it was a multifactorial inheritance. Whatever the means of inheritance, heredity plays an important part in the etiology of this malocclusion.
26
and the parent may seek treatment because of the appearance of the child. The child often appears rather sullen and aggressive. Later the developing Class 11.1 may present with crowding, especially of the upper arch, and an inability to eat properly, but usually the poor appearance is the dominating factor. In the adult the female tends to look aggressive and appearance predominates as the factor why patients seek treatment. Function is also important but often to a lesser degree. Timing of Treatment The difficulties of determining when treatment should start revolve around the type of malocclusion present, and whether it is possible to predict whether a Class III malocclusion will become severe with later growth.
If the soft tissues are an important factor in the etiology of this malocclusion an analysis of Others have suggested that the soft tissues are muscle activities might produce a means of important in the production of the malocclusion. monitoring its development. The position of the Angle (1907), although he admits that heredity jaw depends on the interrelationship of the plays a part, also suggests that enlarged adenoids masseter and temporal muscles. A different and a habit of protruding the mandible cause muscle pattern has been shown to be associated mesial locking of the teeth as they erupt: 'Once with normal occlusion and postural and skeletal the mesio-buccal cusp of the upper first molar Class III malocclusion (Moss & Chalmers 1974), engages the distal incline of the disto-buccal cusp in the habitual intercuspal relationship and the of the lower first permanent molar the effect is to retruded contact relationship, but in the promechanically force the lower jaw forward.' The truded contact position there was little difference muscles are thus made to exert force on the between the groups. mandible and stimulate it to abnormal growth and function. Frankel (1970) has shown that in Method of Recording Muscle Activity Class III cases treated with a functional regulator, The method of recording has been fully described which is an appliance which alters the muscle elsewhere (Moss 1976a). Briefly, a unipolar techpressures and activities on the teeth, improvement nique is used with a reference electrode placed on in the position of point 'A' is significantly the neck opposite the sixth cervical vertebra. different. These appliances work best during the Surface electrodes are placed over the superficial mixed dentition and do not respond well if used muscles bilaterally, picking up activity from the anterior and posterior parts of the temporal and at an age when growth is proceeding slowly. masseter muscles, and also from the infraMcNamara (1973), in studies on rhesus mandibular group which includes the digastric monkeys, has shown that the skeletal effects of and mylohyoid muscles; The activity is amplified, appliance therapy depend very much on the age integrated and recorded on ultraviolet-sensitive at which it is initiated, being greatest in the young. paper. The records are then particularly observed for the timing of the onset of the muscle activity Moyers et al. (1970), in 6 rhesus monkeys, and the relative amount of activity in each group experimentally produced a Class III malocclusion of muscles. by forcing the lower jaw forward on a splint. In these monkeys there was significantly more Materials growth of the condyle upwards and backwards Twenty-two adults and 21 children with a normal than in the controls. occlusion were recorded electromyographically, and also 18 children with a skeletal Class III malocclusion and 21 adults with a Class III Presenting Symptoms The general practitioner may be the first to be malocclusion. Eleven children with a postural aware of the developing Class III malocclusion Class III were also recorded. The patients were
27
Section ofOdontology
also recorded after orthodontic and/or surgical treatment and one year out of retention.
Biting on 8 sheets of paper produced a similar activity. The posterior temporal activity was often either increased or early in onset.
Patterns of Activity Normal occlusion: When the patterns of activity of a patient with normal occlusion were examined, in the habitual intercuspal relationship it was seen that there was a balance of activity between the two sides of the jaw and that the activity of the anterior masseter was greatest. The activity of the anterior temporal was next greatest, followed by the activity of the posterior fibres of temporalis and the posterior masseter.
When the patient was asked to protrude the jaw into the protruded contact position the muscle activity altered, the anterior and posterior temporal activity decreased and were inhibited. A similar pattern of activity was seen when the patient was asked to bite on the incisors. When the patient was asked to move into the retruded contact position the activities of the anterior and posterior masseter were decreased, and the activity of the posterior temporal muscle increased. The patterns of activity when the patient was asked to bite on the left produced a typical pattern of activity and was exactly the opposite to that produced by a right bite. When the patient was asked to bite in the habitual intercuspal position on 8 sheets of paper (opening the bite 0.5 mm) the amount of activity increased in all muscles, but the pattern of activity did not change. The other movements investigated also produced typical patterns of activity but these will not be discussed.
915
In a patient with a postural Class III the patterns of activity were also different from those patients with a normal occlusion and those patients with a Class III mandibular prognathism or a maxillary retrusion. In the intercuspal position the activity of the masseter was increased, and the activity of the posterior temporal muscle was decreased and was very similar to the patterns of activity of a patient with a normal occlusion in the protruded contact position except that the activity was not balanced in the two sides. Biting on 8 sheets of paper altered the pattern of activity and gave a pattern which was similar to that seen in children with a normal occlusion. In patients with a maxillary retrusion the pattern of activity in the intercuspal position was similar to that of patients with a normal occlusion and the pattern was similar when the patient was asked to bite on 8 sheets of paper.
Attempted biting on the incisors in all groups of Class III malocclusion gave typical retrusive bites with increased activity of the posterior temporal muscle and decreased activity of the masseter muscle. It can be seen that each of the groups of Class III malocclusion can be differentiated on the basis of their muscle patterns. These patterns can be observed in the child, and can be used as a predictor of the type of growth that will occur.
Cases of unilateral hyperplasia of the jaw show
Class III malocclusion: As has already been shown (Moss & Chalmers 1974), the patterns of activity in the child with a Class III malocclusion and the adult with a Class III malocclusion differed from those with a normal occlusion. However, the patterns of activity in children with a Class III malocclusion were similar to those in adults with a Class III malocclusion, although the amount of activity tended to be less in the child group. The patterns of activity of the postural Class -III patients were also different, as was the pattern of activity in patients with a maxillary retrusion. Class III mandibular prognathism: The typical patterns of activity in a patient with a mandibular prognathism in the habitual intercuspal position showed the activity of the anterior masseter muscle, either bilaterally or unilaterally, to be considerably reduced, and the activity of the posterior masseter muscle was often increased.
a typical Class III pattern of activity on the side where the hyperplasia is present but a normal pattern on the normal side.
Certain types of Class III malocclusion do not fall into a distinct group and some may be complicated by a deviation of the jaw on closing, but biting on 8 sheets of paper reveals the underlying pattern of activity. Other cases may have a maxillary retrusion and a mandibular prognathism. However, electromyographic analysis can help not only to classify but also to predict what type of case the patient may develop into as these typical patterns of activity are seen in the child. Cephalometric Examination A cephalometric examination was undertaken on the postural Class III group and also on the skeletal Class III child group to see if there were any particular differences cephalometrically. The standardized lateral skull films were traced on
916 Proc. roy. Soc. Med. Volume 69 December 1976 acetate paper, and the following points identified and lines drawn: (1) Anterior nasal spine, ANS (2) Articulare, Ar (3) Gnathion, Gn (4) Gonion, Go (5) Menton, Mn (6) Nasion, N (7) Pogonion, Pg (8) Posterior nasal spine, PNS (9) Sella, S (10) Subspinale, A (11) Supramentale, B
The following planes were then-drawn: (1) Sella-nasion plane, NSL (2) Maxillary plane, MxL (3) Superior occlusal plane, OCs: A line joining the tip of the mesial cusp of the upper first permanent molar and the incisive edge of the upper incisor. (4) Medial occlusal plane, OCm: A line joining the tips of the cusps of the lower premolars and molars. (5) Inferior occlusal plane, OCi: A line joining the tip of the mesial cusp of the lower first permanent molar and the incisive edge of the lower central incisor tooth. (6) Mandible plane, MnL (7) Facial plane, FL (8) Facial height, FH: The facial height was measured in millimetres. This was the distance between the nasion and menton.
The following angles were then measured: (1) SNA (2) SNB (3) MxLMnL: The angle between the maxillary and mandibular planes. (4) MxLOCs: The angle between the maxillary plane and the superior occlusal plane. (5) MxLOCi: The angle between the maxillary plane and the inferior occlusal plane. (6) MxLOCm: The angle between the maxillary plane and the median occlusal plane.
28 (7) MxLlL: Angle between the maxillary plane and the longitudinal axis of the upper central incisors. (8) MnLIL: Angle between the mandibular plane and the longitudinal axis of the lower central incisors. (9) 1LTL: Inter incisal angle - the angle formed by the longitudinal axis of the upper and lower incisors. (10) GnL: The angle formed by the intersection of the mandibular base line and the posterior border of the ramus of the mandible. (11) NSAr: The angle between the sella-nasion plane and the articulare.
It was found (Table 1) that the reverse overbite tended to be greater in postural Class III cases in skeletal Class III patients, and that the reverseoverjet was similar. The angle SNA was also similar but the angle SNB was greater by 20 in skeletal Class III patients. The angle of the upper incisors to the maxillary plane was similar but the lower incisors were more retroclined in skeletal Class III cases. The gonial angle was greater in skeletal Class III cases a d so was the facial height from nasion to mentbn. These are the mean values, and the mean age of the skeletal Class III cases was higher than that of the postural Class III group. Although cephalometric examination is useful and has been used to predict growth, the accuracy of the prediction is not good and other means of prediction are a useful adjunct, especially in these difficult problems. Electromyography and cephalometric analysis used in conjunction with one another are a valuable aid in diagnosis of Class III cases'
Treatment The treatment of the patient with a Class III malocclusion will depend on the age at which the patient presents for treatment. Often the presence of the Class III malocclusion in a child, because it is noticeable to the lay person, drives a parent to seek orthodontic treatment for the child at an early age (Rheinwald & Becker 1962). The
Table I Skull measurements for patients with Class III malocclusion Skeletal Measurement Overbite (mm)
Overjet(mm) Maxillary/mandibular planes angle (0) Angle SNA (°) Angle SNB (°) Angle upper incisors (°) Angle lower incisors Nasion sella articulare angle (0) Gonial angle (°) Angle of upper and lower incisors (0) Nasion-menton distance (mm) Maxillary/superior occlusal planes angle (°) Maxillary/inferior occlusal planes angle (0) Age (years)
Means -2.0 -4.0 28.0 79.3 83.2 112.8 83.0 126.2 134.2 138.3
116.8 8.1 4.9 14.7
Postural s.d. 2.7 3.2
Means -4.1 -3.4
5.4
25.6
4.1 4.9 10.9 10.4 4.8 6.0 13.2 14.9
80.3 81.6 111.1
5.8 5.3 6.4
87.5 127.6 129.3
s.d. 3.3 2.1 3.9 4.6 3.6 11.3 6.1 2.9
5.7
137.2
15.3
107.0 10.9 3.6 10.1
5.1 5.8 5.1 1.7
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Section of Odontology
question of the value of early treatment has been debated for some considerable time. Poulton (1973) feels that there is little value in early treatment and that the long-term effects are not stable. Others (Graber et al. 1967, Dewell 1972), advocate early treatment and have shown that with orthopedic force using extra-oral traction considerable improvement in the occlusion and profile of the patient have been obtained.
treatment needs to be undertaken over a long period of time.
Various reasons have been put forward to advocate the early treatment of the patient with a Class III malocclusion:
(I) To establish a normal soft-tissue environment for the developing incisors, as Graber et al. (1967) have suggested that there is an abnormal softtissue activity. (2) To prevent the locking of the mesio-buccal cusps of the upper molar on the distal incline of the distobuccal cusp of the lower molar thus forcing the lower jaw forwards into a mesial position (Angle 1907). (3) To encourage the depression of the posterior teeth and the eruption and alignment of the anterior teeth. (4) To promote the development of the upper arch to its fullest potential (Frankel 1970). (5) To restrain the forward development of the mandibular arch (Dausch-Newman 1970). (6) Changes in the morphology of the arches appear to be more marked in patients treated at an early age. McNamara (1973) showed that in monkeys the degree of maturation of experimental animals was important in determining the degree of the alterations that occurred in the craniofacial complex with appliances cemented to the occlusal surfaces of teeth. Similarly, Glass (1961) noted that the effect of the Milwaukee brace on the craniofacial complex depended on the age of the patient. In the older patient the changes were limited to the alveolar bone.
917
The main value of the chin cap is that it is easy to construct in young children, and is of value in establishing the normal soft-tissue environment for the eruption of the incisors. Fletcher (1963) has demonstrated the influence of the sqft tissues on the path of eruption of incisor teeth. There are, however, several points that should be taken into consideration when constructing the appliance. The area of the chin to be covered by the chin cap should be marked on the face with a marking pencil so that the mark is transferred to the impression. The impression should be taken in white composition impression material under pressure in the direction of the pull to be applied, as this moulds the soft tissues and gives an accurate reproduction of the soft tissues of the chin under that pressure. The direction of pull is also important and the direction should be transmitted along the mandible and pass through the condyle.
Various other forms of treatment have been shown to be of value in the early treatment of the patient with a Class III malocclusion. Various types of functional appliances and the functional corrector, or Frankel III appliance, have been used for some while for the early treatment of Class III cases, and the improvement following their use has been demonstrated by Muhlberg et al. (1968), Frankel (1970) and Dausch-Newman (1970). The sliding activator has been used for many years in the treatment of Class III cases. It consists of an upper half of the appliance joined to a lower half by means of a screw. This affords a means of forcing the mandible into a more retruded position during treatment thus promoting the activity of the muscles and tooth movement. It is important to trim the appliance to allow the correct tooth movement, especially anteriorly, otherwise a decreased overbite results.
Thilander (1965) showed that the effect of the chin cap in 45 children was to tip the lower incisors lingually and displace the mandible The functional corrector, Frankel III, is the slightly backwards. The longer the patient wore the chin cap the less the incisors tipped. The best form of early treatment as it relieves the prognosis for a favourable result depended on developing maxilla from the pressures of the lips the vertical overlap of the incisors at the end of and cheeks, and allows the pressure from the treatment, and this was related to the amount of tongue to mould the arch. Also, Frankel believes reverse overbite at the beginning of treatment. that the tension on the periosteum, caused by the The degree of the mandibular prognathism and correct positioning of the buccal and labial hereditary factors did not influence the results of shields, promotes the deposition of bone on the lateral aspects of the alveolus. The pressures treatment. from the lips and cheeks are also transmitted via Kloeppel (1970), using a chin cap in children the shields to the lower teeth causing them to be aged 4-5 years, found that 11 out of 15 relapsed forced distally. Before the appliance is constructed at the age of 6-7 years. This would indicate that a bite is taken in a retruded position slightly
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918 Proc. roy. Soc. Med. Volume 69 December 1976
opened. The models are articulated and the appliance constructed with the lower molars capped and a lower labial arch running round the lower anterior teeth; thus all the forces from the cheeks, lips and muscles of mastication are directed on to the lower dental arch, whereas the upper dental arch is free to develop. Case 1 illustrates the use of this appliance (Figs 1, 2, 3). The postural Class III cases are easily treated early as the upper incisors at that stage have not become fully retroclined and the lower incisors proclined. A simple removable appliance to guide the incisors into a correct relationship is all that is required. Once the reverse overbite is established, capping of the posterior teeth, with either springs or screws, to move the upper incisors forward, is required; an inverted labial bow is incorporated on the appliance to retrocline the lower incisors. The flat posterior capping
eliminates the incisal guidance and thus restores a normal path of closure of the mandible. Treatment During the Late Mixed and Early Permanent Dentition If patients do not present during the early phases of development often the malocclusion is well established. In such cases, a careful diagnosis and treatment planning must be undertaken. The treatment of a patient will depend on the establishment of a normal overbite and overjet that, in turn, depends on the amount of mandibular displacement, the angulation of the upper and lower incisors, the amount of reverse overbite and overjet, and the direction of growth during treatment. As has already been shown, the mandibular displacement can be demonstrated electromyographically or clinically by observing the path of
Fig 1 Case 1 A patient with a Class III malocclusion treated by a removable appliance to procline the upper incisors. Notice the proclination of the upper incisors into an unacceptable angulation. He was then given a Frankel Functional Corrector III. Notice the improvement of the apices of the upper incisors resulting in an improvement in incisor angulation using the Frankel III appliance. A, before treatment. B, after removable appliance therapy. C, at the commencement of treatment with a Frankel III appliance. D, one year later
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919
Section ofOdontology
S
Fig 2 Case 1 Profile tracing before and after removable therapy. , aged l. ----, aged 12
Fig 3 Case 1 Profile tracing before and after Frankel III therapy. -, aged 13 years 7 months. --- -, aged 14 years 7 months
closure of the mandible. If the mandible is mesially deviated the amount of reverse overjet is increased. Examination of the standardized lateral skull radiograph will reveal the angle of the upper and lower incisors and the degree of skeletal discrepancy present. Analysis of the patient and his or her radiograph will enable the orthodontist to assess whether a stable incisor relationship can be obtained.
or procline the upper incisors beyond their normal angulation. In most of these cases surgery is required to align the teeth, which may first require to be uprighted in order to achieve a satisfactory result and good interdigitation of the teeth.
During the puberty and post-puberty growth phase, a restraining appliance should be worn at night only. An activator or a Frankel III appliance is excellent for this, as these appliances restrain the forward vector of growth and translate it into a more vertical direction. This is useful even in cases where surgery is contemplated.
In cases where the incisors can be aligned and the crowding, if present, relieved, either removable or fixed appliances may be used to undertake the tooth alignment, depending on the type of tooth movement and the motivation of the Once growth has ceased and the patient patient. At the end of treatment the patient should have a normal pattern of activity of the requests further treatment to improve either muscles. Evidence of a Class III pattern of esthetics or function, he should be carefully activity at the end of treatment indicates that the examined and assessed, in collaboration with the oral surgeon, and a cephalometric analysis and case may deteriorate when out ofretention. electromyographic analysis of jaw movements Cases which show a normal pattern of activity should be undertaken. The details have already at the end of treatment remain within normal been reported in detail elsewhere (Moss 1976a). Briefly, the soft tissues of the nose, lips, tongue growth patterns. and pharynx are assessed. The relationship of the Patients who have no or minimal crowding in teeth to the basal bone, basal bone to base of the arches may be treated with functional skull, the face height and the proportion of upper appliances, -and a successful result may be face height to lower height, and the size of the obtained. However, the persistence of a skeletal chin are carefully assessed. The study models are Class III muscle pattern of activity usually carefully examined and the postoperative occluindicates a deterioration during the late stages of sion and the resultant improvement in the profile calculated. Case 2 illustrates mandibular progrowth. gnathism with an anterior open bite (Figs 4, 5, 6, 7). In cases where there is no possibility of obtainCases exhibiting a maxillary retrusion often ing a stable relationship, the teeth should be aligned and crowding relieved but no attempt exhibit a concave face with narrow nares. The should be made to retrocline the lower incisors mandible is often of normal size but the maxilla
920 Proc. roy. Soc. Med. Volume 69 December 1976
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1Fig 4 Case 2 A patient with a Class III malocclusion and an anterior open bite. Analysis showed that the tongue was large andfilled the oral cavity. .dA tongue reduction was undertaken prior to a mandibular osteotomy (Professor R O'Neil) and the case was held in retention following the ssurgery using an Andresen appliance. A, before treatment. B, after surgery. c, out of retention after treatment with an Andresen appliance 4
/ /
~~~~~~~~~~~~~~~~~~~~~~R. L A T
A
PTM
|
R
L
A T P T PM
B
Fig 5 Case 2 Before and after treatment. aged 21 months aged 23 years 11 months ,
years 11
AM
Fig 6 Case 2 A, thepattern ofactivity of the muscles in the habitual bite position; notice the lower anterior masseter activity on the right and the increased posterior temporal activity on the left. B, the pattern of activity of the muscles in the habitual bite position with the jaws separated by 8 sheets ofpaper raising the bite 0.5 mm. Notice that the pattern on the right has not changed but the posterior temporal muscle has increased on the left. A, anterior. P, posterior. L, left. R, right. M, masseter muscle. T, temporal muscle
Section of Odontology
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921
Fig 7... Case2Profleadlaeralview.A,B,. c at -"_ treatment
Fig 7 Case 2 Profile and lateral views. A, B, before treatment. c, D, after treatment exhibits a narrow palate with a bilateral crossbite and crowding of the teeth anteriorly. Usually there is a low tongue position and the tongue spreads over the occlusal surfaces of the lower teeth during swallowing. The most valuable form of treatment for this type of malocclusion at the puberty growth phase is rapid expansion of the upper arch. At this age there is not only considerable growth of the bone but also of the soft tissues, and if adaptation of the tongue is to occur to the new position of the teeth following rapid expansion it is most likely to occur during a normal phase of development when there is rapid adaptation and change of the soft tissues.
The method employed in the treatment of this type of Class III varies, but the best is a silver cap joined with an acrylic baseplate split in the centre, and a large Fischer screw connecting the two halves of the appliance. The screw is turned three times a day (morning, noon and night), and the arch is expanded until it has been over-expanded by 4-5 mm because, as Krebs (1964) showed, the suture does not open as much as the arch widens. The arch width always shows some relapse.
Fifteen patients with a Class III malocclusion treated by rapid expansion of the upper arch were compared with 9 Class III cases without
922 Proc. roy. Soc. Med. Volume 69 December 1976 rapid expansion. Two to three years postretention the molar width was 3.55 mm wider on average. The worst relapse was equal to the best expansion in the control group. Also, the upper incisors were, on average, 2 mm further forward than in the control group (Moss 1976b). Once the patient enters the late teens the rapid expansion of the upper arch becomes more painful, and it is better to wait until growth has ceased and then consider surgery to the upper arch, -either a labial set forward with a bone graft, or maxillary osteotomy moving the whole maxilla forward into its correct position. The treatment of a maxillary retrusion by moving the premaxilla forwards produces space in the premolar region which can be utilized to relieve the crowding anteriorly by means of orthodontic appliances.
Summary The etiology and treatment of Class III malocclusion has been discussed. The value of electromyographic assessment in the assessment and prediction of Class III malocclusion has been shown. I should like to record my. indebtedness to my colleague Professor R O'Neil who operated on Case 2, and to Mr C Day for photographic assistance.
Acknowledgments:
RIFERENCES
Angle E H (1907) Treatment of Malocclusion of the Teeth. 7th edn. S S White Dental Manufacturing Company, Philadelphia Ballard C F (1955) Transactions of the British Society of Orthodontia pp 117-127
Dausch-Newuman D (1970) Transactions ofthe European Orthodontic Society pp 213-224
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Dewell B F (1972) American Journal ofOrthodontics 62, 530-532 Dietrich V C (1970) Transactions ofthe European Orthodontic Society pp 131-143 Fletcher G G T (1963) Transactions ofthe British Society of Orthodontia pp 124-153 Frankel R (1970) Transactions ofthe European Orthodontic Society pp 249-259 GlassDF (1961) Transactions ofthe European Orthodontic Society pp 302-310 Goose D H, Thomson D G & Winter F C (1957) British Dental Journal 102, 174-178 Graber T M, Chung D D B & Aoba J T (1967) Journal of the American Dental Association 75, 1145-1166 Huber R E & Reynolds J W (1946) American Journal ofOrthodontics 32, 1-21 Jacobsen A, Evans W G, Preston C B & Sadowsky P L(1974) American Journal ofOrthodontics 66, 140-171 Kloeppel J G (1970) Transactions of the European Orthodontic Society pp 225-237 Krebs A (1964) XL European Congress of the European Orthodontic Society pp 131-142 McNamara J A (1973) American Journal of Orthodontics 64, 578-606 Massler M & Frankel J M (1951) American Journal ofOrthodontics 37, 751-768 MossJP (I 976a) Transactions of the European Orthodontic Society (in press) (1976b) International Journal of Orthodontics (in press) Moss J P & Chalmers C (1974) American Journal ofOrthodontics 66, 538-556 Moss J P & Picton D C A (1968) Dental Practitioner and Dental Record 18, 442-448 Moyers R E, Elgoyhen J C, Riolo H L, McNamara J A & Kuroda T (1970) Transactions of the European Orthodontic Society pp 61-75 MUhlberg G, SchrOter U & Zill G (1968) Fortschritte der Kieferorthopddie 29, 393-405 Poulton P R. (1973) American Journal of Orthodontics p 311 Rheinwald U & Becker R (1962),Fortschritte der Kieferorthopddie 23, 5-21 Schulze C & Weise W (1965) Fortschritte der Kieferorthopadie 26, 213-229 Schwartz A M (1961) Lehrgang der Gebissregelung. Urban & Schwarzenberg, Innsbruck Seipel C M (1946) Variations of Tooth Position: A Metric Study of Variation and Adaptation in the Deciduous and Permanent Dentitions. Hakun Ohissons Boktryckeri, Lund Stiles K A & Luke J E (1953) Journal of Heredity 44, 241-245 St6ckli P W (1970) Transactions of the European Orthodontic Society pp 145-153 Thilander B (1965) Transactions of the European Orthodontic Society pp 311-327
Volume 69 December 1976
913
Section of Odontology President R D Emslie MSC FDS
Meeting 24 May 1976
Paper The Problem of the Class III Malocclusion by Professor J P Moss PhD FDS Dorth RCS (University College Hospital Dental School, Mortimer Market, London WCIE6JD) The Class III malocclusion is a problem to the general practitioner as to when to refer for treatment; to the orthodontist because he is never sure that his treatment will be successful after growth is complete; to the oral surgeon because of the infinite variety of forms of the presenting malocclusion; and to the research worker because we know relatively little about the cause. Definition and Types Angle defined a Class III malocclusion as one where there is a mesial occlusion of the mandibular teeth by more than one-half the width of a single cusp. Unfortunately, this does not take into account the skeletal pattern.
Investigations of the different types of Class III malocclusion have been undertaken by Dietrich (1970) and she showed that 28.5 % of the Class III patients fall into Group A with a maxillary and mandibular skeletal base within the normal range; 25 %, Group B, have a mandibular prognathism associated with a normal maxilla and 37.5 %, Group C, have a normal mandible and a retrusive maxilla. Thus a total of 91 % of Class III fall into these groups. These findings were comparable with the child group of Jacobsen et al. (1974) but they also showed that id the adult groups the percentages in these groups altered: Group B, mandibular prognathisms, was greatest, 48%; Group C, maxillary retrusion, was 26%, and Group A, with maxilla and mandible in the normal range, 14%.. It seems, therefore, that the
differences in the two groups are explained by the fact that with growth the potential of the Class III malocclusion is fully realized and those cases which exhibited a mandible and maxilla within the normal range in childhood develop into a more severe malocclusion in adult life. As Angle (1907) comments, 'The marring of the facial lines is more noticeable and unpleasing in advanced cases amounts to a striking deformity'. The main problem is whether it is possible to predict which malocclusion will alter during growth. St6ckli (1970) investigated Class III cases which were similar at the beginning of observation and suggested that: 'A Class III type case does not proceed along a stable growth pattern. Observations during an early phase of development are not indicative of the development at a later phase.' One of the questions that remain to be answered is: 'Can this change be predicted in other ways?' Cephalometric analysis at present does not reveal the factors in advance which lead to variations in ultimate Class III development. A further type of Class III malocclusion, the postural or pseudo Class III, is also described as being due to forward posturing of the mandible which results from an edge-to-edge incisor relationship (Schwartz 1961). In these cases the upper incisors are proclined and - the lower incisors are retroclined (Ballard 1955). There is also -an excessive inter-occlusal clearance which is eliminated once the incisor position is corrected.
Incidence The incidence of Class III was stated by Angle (1907) to be 4.2%; Goose et al. (1957) in 2956 children 7-15 years old found 2.9%; and Moss & Picton (1968) in Greek school children 3-12 years old, 5%. Seipel (1946) in 21-year-old Swedes found an incidence of 4 %, and Massler & Frankel (1951) in 2758 school children 14-18
914 Proc. roy. Soc. Med. Volume 69 December 1976 years old, 9.4%. The highest incidence - 12.2% was recorded by Huber & Reynolds (1946) in 500 students. It seems evident from these surveys that the incidence of the malocclusion increases with age.
Etiology Amongst the most notable families which exhibit an inherited prognathism, the Hapsburgs are well known. The typical protruding lower lip andI prognathic lower jaw have been demonstrated in 33 members of the family. Stiles & Luke (1953) suggested that mandibular prognathism is inherited via a dominant gene with an unknown degree of reduced penetrance. Schulze & Weise (1965) studied families and twins with a Class III malocclusion and concluded that it could be inherited as a dominant and a recessive factor. They suggested that it was a multifactorial inheritance. Whatever the means of inheritance, heredity plays an important part in the etiology of this malocclusion.
26
and the parent may seek treatment because of the appearance of the child. The child often appears rather sullen and aggressive. Later the developing Class 11.1 may present with crowding, especially of the upper arch, and an inability to eat properly, but usually the poor appearance is the dominating factor. In the adult the female tends to look aggressive and appearance predominates as the factor why patients seek treatment. Function is also important but often to a lesser degree. Timing of Treatment The difficulties of determining when treatment should start revolve around the type of malocclusion present, and whether it is possible to predict whether a Class III malocclusion will become severe with later growth.
If the soft tissues are an important factor in the etiology of this malocclusion an analysis of Others have suggested that the soft tissues are muscle activities might produce a means of important in the production of the malocclusion. monitoring its development. The position of the Angle (1907), although he admits that heredity jaw depends on the interrelationship of the plays a part, also suggests that enlarged adenoids masseter and temporal muscles. A different and a habit of protruding the mandible cause muscle pattern has been shown to be associated mesial locking of the teeth as they erupt: 'Once with normal occlusion and postural and skeletal the mesio-buccal cusp of the upper first molar Class III malocclusion (Moss & Chalmers 1974), engages the distal incline of the disto-buccal cusp in the habitual intercuspal relationship and the of the lower first permanent molar the effect is to retruded contact relationship, but in the promechanically force the lower jaw forward.' The truded contact position there was little difference muscles are thus made to exert force on the between the groups. mandible and stimulate it to abnormal growth and function. Frankel (1970) has shown that in Method of Recording Muscle Activity Class III cases treated with a functional regulator, The method of recording has been fully described which is an appliance which alters the muscle elsewhere (Moss 1976a). Briefly, a unipolar techpressures and activities on the teeth, improvement nique is used with a reference electrode placed on in the position of point 'A' is significantly the neck opposite the sixth cervical vertebra. different. These appliances work best during the Surface electrodes are placed over the superficial mixed dentition and do not respond well if used muscles bilaterally, picking up activity from the anterior and posterior parts of the temporal and at an age when growth is proceeding slowly. masseter muscles, and also from the infraMcNamara (1973), in studies on rhesus mandibular group which includes the digastric monkeys, has shown that the skeletal effects of and mylohyoid muscles; The activity is amplified, appliance therapy depend very much on the age integrated and recorded on ultraviolet-sensitive at which it is initiated, being greatest in the young. paper. The records are then particularly observed for the timing of the onset of the muscle activity Moyers et al. (1970), in 6 rhesus monkeys, and the relative amount of activity in each group experimentally produced a Class III malocclusion of muscles. by forcing the lower jaw forward on a splint. In these monkeys there was significantly more Materials growth of the condyle upwards and backwards Twenty-two adults and 21 children with a normal than in the controls. occlusion were recorded electromyographically, and also 18 children with a skeletal Class III malocclusion and 21 adults with a Class III Presenting Symptoms The general practitioner may be the first to be malocclusion. Eleven children with a postural aware of the developing Class III malocclusion Class III were also recorded. The patients were
27
Section ofOdontology
also recorded after orthodontic and/or surgical treatment and one year out of retention.
Biting on 8 sheets of paper produced a similar activity. The posterior temporal activity was often either increased or early in onset.
Patterns of Activity Normal occlusion: When the patterns of activity of a patient with normal occlusion were examined, in the habitual intercuspal relationship it was seen that there was a balance of activity between the two sides of the jaw and that the activity of the anterior masseter was greatest. The activity of the anterior temporal was next greatest, followed by the activity of the posterior fibres of temporalis and the posterior masseter.
When the patient was asked to protrude the jaw into the protruded contact position the muscle activity altered, the anterior and posterior temporal activity decreased and were inhibited. A similar pattern of activity was seen when the patient was asked to bite on the incisors. When the patient was asked to move into the retruded contact position the activities of the anterior and posterior masseter were decreased, and the activity of the posterior temporal muscle increased. The patterns of activity when the patient was asked to bite on the left produced a typical pattern of activity and was exactly the opposite to that produced by a right bite. When the patient was asked to bite in the habitual intercuspal position on 8 sheets of paper (opening the bite 0.5 mm) the amount of activity increased in all muscles, but the pattern of activity did not change. The other movements investigated also produced typical patterns of activity but these will not be discussed.
915
In a patient with a postural Class III the patterns of activity were also different from those patients with a normal occlusion and those patients with a Class III mandibular prognathism or a maxillary retrusion. In the intercuspal position the activity of the masseter was increased, and the activity of the posterior temporal muscle was decreased and was very similar to the patterns of activity of a patient with a normal occlusion in the protruded contact position except that the activity was not balanced in the two sides. Biting on 8 sheets of paper altered the pattern of activity and gave a pattern which was similar to that seen in children with a normal occlusion. In patients with a maxillary retrusion the pattern of activity in the intercuspal position was similar to that of patients with a normal occlusion and the pattern was similar when the patient was asked to bite on 8 sheets of paper.
Attempted biting on the incisors in all groups of Class III malocclusion gave typical retrusive bites with increased activity of the posterior temporal muscle and decreased activity of the masseter muscle. It can be seen that each of the groups of Class III malocclusion can be differentiated on the basis of their muscle patterns. These patterns can be observed in the child, and can be used as a predictor of the type of growth that will occur.
Cases of unilateral hyperplasia of the jaw show
Class III malocclusion: As has already been shown (Moss & Chalmers 1974), the patterns of activity in the child with a Class III malocclusion and the adult with a Class III malocclusion differed from those with a normal occlusion. However, the patterns of activity in children with a Class III malocclusion were similar to those in adults with a Class III malocclusion, although the amount of activity tended to be less in the child group. The patterns of activity of the postural Class -III patients were also different, as was the pattern of activity in patients with a maxillary retrusion. Class III mandibular prognathism: The typical patterns of activity in a patient with a mandibular prognathism in the habitual intercuspal position showed the activity of the anterior masseter muscle, either bilaterally or unilaterally, to be considerably reduced, and the activity of the posterior masseter muscle was often increased.
a typical Class III pattern of activity on the side where the hyperplasia is present but a normal pattern on the normal side.
Certain types of Class III malocclusion do not fall into a distinct group and some may be complicated by a deviation of the jaw on closing, but biting on 8 sheets of paper reveals the underlying pattern of activity. Other cases may have a maxillary retrusion and a mandibular prognathism. However, electromyographic analysis can help not only to classify but also to predict what type of case the patient may develop into as these typical patterns of activity are seen in the child. Cephalometric Examination A cephalometric examination was undertaken on the postural Class III group and also on the skeletal Class III child group to see if there were any particular differences cephalometrically. The standardized lateral skull films were traced on
916 Proc. roy. Soc. Med. Volume 69 December 1976 acetate paper, and the following points identified and lines drawn: (1) Anterior nasal spine, ANS (2) Articulare, Ar (3) Gnathion, Gn (4) Gonion, Go (5) Menton, Mn (6) Nasion, N (7) Pogonion, Pg (8) Posterior nasal spine, PNS (9) Sella, S (10) Subspinale, A (11) Supramentale, B
The following planes were then-drawn: (1) Sella-nasion plane, NSL (2) Maxillary plane, MxL (3) Superior occlusal plane, OCs: A line joining the tip of the mesial cusp of the upper first permanent molar and the incisive edge of the upper incisor. (4) Medial occlusal plane, OCm: A line joining the tips of the cusps of the lower premolars and molars. (5) Inferior occlusal plane, OCi: A line joining the tip of the mesial cusp of the lower first permanent molar and the incisive edge of the lower central incisor tooth. (6) Mandible plane, MnL (7) Facial plane, FL (8) Facial height, FH: The facial height was measured in millimetres. This was the distance between the nasion and menton.
The following angles were then measured: (1) SNA (2) SNB (3) MxLMnL: The angle between the maxillary and mandibular planes. (4) MxLOCs: The angle between the maxillary plane and the superior occlusal plane. (5) MxLOCi: The angle between the maxillary plane and the inferior occlusal plane. (6) MxLOCm: The angle between the maxillary plane and the median occlusal plane.
28 (7) MxLlL: Angle between the maxillary plane and the longitudinal axis of the upper central incisors. (8) MnLIL: Angle between the mandibular plane and the longitudinal axis of the lower central incisors. (9) 1LTL: Inter incisal angle - the angle formed by the longitudinal axis of the upper and lower incisors. (10) GnL: The angle formed by the intersection of the mandibular base line and the posterior border of the ramus of the mandible. (11) NSAr: The angle between the sella-nasion plane and the articulare.
It was found (Table 1) that the reverse overbite tended to be greater in postural Class III cases in skeletal Class III patients, and that the reverseoverjet was similar. The angle SNA was also similar but the angle SNB was greater by 20 in skeletal Class III patients. The angle of the upper incisors to the maxillary plane was similar but the lower incisors were more retroclined in skeletal Class III cases. The gonial angle was greater in skeletal Class III cases a d so was the facial height from nasion to mentbn. These are the mean values, and the mean age of the skeletal Class III cases was higher than that of the postural Class III group. Although cephalometric examination is useful and has been used to predict growth, the accuracy of the prediction is not good and other means of prediction are a useful adjunct, especially in these difficult problems. Electromyography and cephalometric analysis used in conjunction with one another are a valuable aid in diagnosis of Class III cases'
Treatment The treatment of the patient with a Class III malocclusion will depend on the age at which the patient presents for treatment. Often the presence of the Class III malocclusion in a child, because it is noticeable to the lay person, drives a parent to seek orthodontic treatment for the child at an early age (Rheinwald & Becker 1962). The
Table I Skull measurements for patients with Class III malocclusion Skeletal Measurement Overbite (mm)
Overjet(mm) Maxillary/mandibular planes angle (0) Angle SNA (°) Angle SNB (°) Angle upper incisors (°) Angle lower incisors Nasion sella articulare angle (0) Gonial angle (°) Angle of upper and lower incisors (0) Nasion-menton distance (mm) Maxillary/superior occlusal planes angle (°) Maxillary/inferior occlusal planes angle (0) Age (years)
Means -2.0 -4.0 28.0 79.3 83.2 112.8 83.0 126.2 134.2 138.3
116.8 8.1 4.9 14.7
Postural s.d. 2.7 3.2
Means -4.1 -3.4
5.4
25.6
4.1 4.9 10.9 10.4 4.8 6.0 13.2 14.9
80.3 81.6 111.1
5.8 5.3 6.4
87.5 127.6 129.3
s.d. 3.3 2.1 3.9 4.6 3.6 11.3 6.1 2.9
5.7
137.2
15.3
107.0 10.9 3.6 10.1
5.1 5.8 5.1 1.7
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Section of Odontology
question of the value of early treatment has been debated for some considerable time. Poulton (1973) feels that there is little value in early treatment and that the long-term effects are not stable. Others (Graber et al. 1967, Dewell 1972), advocate early treatment and have shown that with orthopedic force using extra-oral traction considerable improvement in the occlusion and profile of the patient have been obtained.
treatment needs to be undertaken over a long period of time.
Various reasons have been put forward to advocate the early treatment of the patient with a Class III malocclusion:
(I) To establish a normal soft-tissue environment for the developing incisors, as Graber et al. (1967) have suggested that there is an abnormal softtissue activity. (2) To prevent the locking of the mesio-buccal cusps of the upper molar on the distal incline of the distobuccal cusp of the lower molar thus forcing the lower jaw forwards into a mesial position (Angle 1907). (3) To encourage the depression of the posterior teeth and the eruption and alignment of the anterior teeth. (4) To promote the development of the upper arch to its fullest potential (Frankel 1970). (5) To restrain the forward development of the mandibular arch (Dausch-Newman 1970). (6) Changes in the morphology of the arches appear to be more marked in patients treated at an early age. McNamara (1973) showed that in monkeys the degree of maturation of experimental animals was important in determining the degree of the alterations that occurred in the craniofacial complex with appliances cemented to the occlusal surfaces of teeth. Similarly, Glass (1961) noted that the effect of the Milwaukee brace on the craniofacial complex depended on the age of the patient. In the older patient the changes were limited to the alveolar bone.
917
The main value of the chin cap is that it is easy to construct in young children, and is of value in establishing the normal soft-tissue environment for the eruption of the incisors. Fletcher (1963) has demonstrated the influence of the sqft tissues on the path of eruption of incisor teeth. There are, however, several points that should be taken into consideration when constructing the appliance. The area of the chin to be covered by the chin cap should be marked on the face with a marking pencil so that the mark is transferred to the impression. The impression should be taken in white composition impression material under pressure in the direction of the pull to be applied, as this moulds the soft tissues and gives an accurate reproduction of the soft tissues of the chin under that pressure. The direction of pull is also important and the direction should be transmitted along the mandible and pass through the condyle.
Various other forms of treatment have been shown to be of value in the early treatment of the patient with a Class III malocclusion. Various types of functional appliances and the functional corrector, or Frankel III appliance, have been used for some while for the early treatment of Class III cases, and the improvement following their use has been demonstrated by Muhlberg et al. (1968), Frankel (1970) and Dausch-Newman (1970). The sliding activator has been used for many years in the treatment of Class III cases. It consists of an upper half of the appliance joined to a lower half by means of a screw. This affords a means of forcing the mandible into a more retruded position during treatment thus promoting the activity of the muscles and tooth movement. It is important to trim the appliance to allow the correct tooth movement, especially anteriorly, otherwise a decreased overbite results.
Thilander (1965) showed that the effect of the chin cap in 45 children was to tip the lower incisors lingually and displace the mandible The functional corrector, Frankel III, is the slightly backwards. The longer the patient wore the chin cap the less the incisors tipped. The best form of early treatment as it relieves the prognosis for a favourable result depended on developing maxilla from the pressures of the lips the vertical overlap of the incisors at the end of and cheeks, and allows the pressure from the treatment, and this was related to the amount of tongue to mould the arch. Also, Frankel believes reverse overbite at the beginning of treatment. that the tension on the periosteum, caused by the The degree of the mandibular prognathism and correct positioning of the buccal and labial hereditary factors did not influence the results of shields, promotes the deposition of bone on the lateral aspects of the alveolus. The pressures treatment. from the lips and cheeks are also transmitted via Kloeppel (1970), using a chin cap in children the shields to the lower teeth causing them to be aged 4-5 years, found that 11 out of 15 relapsed forced distally. Before the appliance is constructed at the age of 6-7 years. This would indicate that a bite is taken in a retruded position slightly
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918 Proc. roy. Soc. Med. Volume 69 December 1976
opened. The models are articulated and the appliance constructed with the lower molars capped and a lower labial arch running round the lower anterior teeth; thus all the forces from the cheeks, lips and muscles of mastication are directed on to the lower dental arch, whereas the upper dental arch is free to develop. Case 1 illustrates the use of this appliance (Figs 1, 2, 3). The postural Class III cases are easily treated early as the upper incisors at that stage have not become fully retroclined and the lower incisors proclined. A simple removable appliance to guide the incisors into a correct relationship is all that is required. Once the reverse overbite is established, capping of the posterior teeth, with either springs or screws, to move the upper incisors forward, is required; an inverted labial bow is incorporated on the appliance to retrocline the lower incisors. The flat posterior capping
eliminates the incisal guidance and thus restores a normal path of closure of the mandible. Treatment During the Late Mixed and Early Permanent Dentition If patients do not present during the early phases of development often the malocclusion is well established. In such cases, a careful diagnosis and treatment planning must be undertaken. The treatment of a patient will depend on the establishment of a normal overbite and overjet that, in turn, depends on the amount of mandibular displacement, the angulation of the upper and lower incisors, the amount of reverse overbite and overjet, and the direction of growth during treatment. As has already been shown, the mandibular displacement can be demonstrated electromyographically or clinically by observing the path of
Fig 1 Case 1 A patient with a Class III malocclusion treated by a removable appliance to procline the upper incisors. Notice the proclination of the upper incisors into an unacceptable angulation. He was then given a Frankel Functional Corrector III. Notice the improvement of the apices of the upper incisors resulting in an improvement in incisor angulation using the Frankel III appliance. A, before treatment. B, after removable appliance therapy. C, at the commencement of treatment with a Frankel III appliance. D, one year later
31
919
Section ofOdontology
S
Fig 2 Case 1 Profile tracing before and after removable therapy. , aged l. ----, aged 12
Fig 3 Case 1 Profile tracing before and after Frankel III therapy. -, aged 13 years 7 months. --- -, aged 14 years 7 months
closure of the mandible. If the mandible is mesially deviated the amount of reverse overjet is increased. Examination of the standardized lateral skull radiograph will reveal the angle of the upper and lower incisors and the degree of skeletal discrepancy present. Analysis of the patient and his or her radiograph will enable the orthodontist to assess whether a stable incisor relationship can be obtained.
or procline the upper incisors beyond their normal angulation. In most of these cases surgery is required to align the teeth, which may first require to be uprighted in order to achieve a satisfactory result and good interdigitation of the teeth.
During the puberty and post-puberty growth phase, a restraining appliance should be worn at night only. An activator or a Frankel III appliance is excellent for this, as these appliances restrain the forward vector of growth and translate it into a more vertical direction. This is useful even in cases where surgery is contemplated.
In cases where the incisors can be aligned and the crowding, if present, relieved, either removable or fixed appliances may be used to undertake the tooth alignment, depending on the type of tooth movement and the motivation of the Once growth has ceased and the patient patient. At the end of treatment the patient should have a normal pattern of activity of the requests further treatment to improve either muscles. Evidence of a Class III pattern of esthetics or function, he should be carefully activity at the end of treatment indicates that the examined and assessed, in collaboration with the oral surgeon, and a cephalometric analysis and case may deteriorate when out ofretention. electromyographic analysis of jaw movements Cases which show a normal pattern of activity should be undertaken. The details have already at the end of treatment remain within normal been reported in detail elsewhere (Moss 1976a). Briefly, the soft tissues of the nose, lips, tongue growth patterns. and pharynx are assessed. The relationship of the Patients who have no or minimal crowding in teeth to the basal bone, basal bone to base of the arches may be treated with functional skull, the face height and the proportion of upper appliances, -and a successful result may be face height to lower height, and the size of the obtained. However, the persistence of a skeletal chin are carefully assessed. The study models are Class III muscle pattern of activity usually carefully examined and the postoperative occluindicates a deterioration during the late stages of sion and the resultant improvement in the profile calculated. Case 2 illustrates mandibular progrowth. gnathism with an anterior open bite (Figs 4, 5, 6, 7). In cases where there is no possibility of obtainCases exhibiting a maxillary retrusion often ing a stable relationship, the teeth should be aligned and crowding relieved but no attempt exhibit a concave face with narrow nares. The should be made to retrocline the lower incisors mandible is often of normal size but the maxilla
920 Proc. roy. Soc. Med. Volume 69 December 1976
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1Fig 4 Case 2 A patient with a Class III malocclusion and an anterior open bite. Analysis showed that the tongue was large andfilled the oral cavity. .dA tongue reduction was undertaken prior to a mandibular osteotomy (Professor R O'Neil) and the case was held in retention following the ssurgery using an Andresen appliance. A, before treatment. B, after surgery. c, out of retention after treatment with an Andresen appliance 4
/ /
~~~~~~~~~~~~~~~~~~~~~~R. L A T
A
PTM
|
R
L
A T P T PM
B
Fig 5 Case 2 Before and after treatment. aged 21 months aged 23 years 11 months ,
years 11
AM
Fig 6 Case 2 A, thepattern ofactivity of the muscles in the habitual bite position; notice the lower anterior masseter activity on the right and the increased posterior temporal activity on the left. B, the pattern of activity of the muscles in the habitual bite position with the jaws separated by 8 sheets ofpaper raising the bite 0.5 mm. Notice that the pattern on the right has not changed but the posterior temporal muscle has increased on the left. A, anterior. P, posterior. L, left. R, right. M, masseter muscle. T, temporal muscle
Section of Odontology
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921
Fig 7... Case2Profleadlaeralview.A,B,. c at -"_ treatment
Fig 7 Case 2 Profile and lateral views. A, B, before treatment. c, D, after treatment exhibits a narrow palate with a bilateral crossbite and crowding of the teeth anteriorly. Usually there is a low tongue position and the tongue spreads over the occlusal surfaces of the lower teeth during swallowing. The most valuable form of treatment for this type of malocclusion at the puberty growth phase is rapid expansion of the upper arch. At this age there is not only considerable growth of the bone but also of the soft tissues, and if adaptation of the tongue is to occur to the new position of the teeth following rapid expansion it is most likely to occur during a normal phase of development when there is rapid adaptation and change of the soft tissues.
The method employed in the treatment of this type of Class III varies, but the best is a silver cap joined with an acrylic baseplate split in the centre, and a large Fischer screw connecting the two halves of the appliance. The screw is turned three times a day (morning, noon and night), and the arch is expanded until it has been over-expanded by 4-5 mm because, as Krebs (1964) showed, the suture does not open as much as the arch widens. The arch width always shows some relapse.
Fifteen patients with a Class III malocclusion treated by rapid expansion of the upper arch were compared with 9 Class III cases without
922 Proc. roy. Soc. Med. Volume 69 December 1976 rapid expansion. Two to three years postretention the molar width was 3.55 mm wider on average. The worst relapse was equal to the best expansion in the control group. Also, the upper incisors were, on average, 2 mm further forward than in the control group (Moss 1976b). Once the patient enters the late teens the rapid expansion of the upper arch becomes more painful, and it is better to wait until growth has ceased and then consider surgery to the upper arch, -either a labial set forward with a bone graft, or maxillary osteotomy moving the whole maxilla forward into its correct position. The treatment of a maxillary retrusion by moving the premaxilla forwards produces space in the premolar region which can be utilized to relieve the crowding anteriorly by means of orthodontic appliances.
Summary The etiology and treatment of Class III malocclusion has been discussed. The value of electromyographic assessment in the assessment and prediction of Class III malocclusion has been shown. I should like to record my. indebtedness to my colleague Professor R O'Neil who operated on Case 2, and to Mr C Day for photographic assistance.
Acknowledgments:
RIFERENCES
Angle E H (1907) Treatment of Malocclusion of the Teeth. 7th edn. S S White Dental Manufacturing Company, Philadelphia Ballard C F (1955) Transactions of the British Society of Orthodontia pp 117-127
Dausch-Newuman D (1970) Transactions ofthe European Orthodontic Society pp 213-224
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Dewell B F (1972) American Journal ofOrthodontics 62, 530-532 Dietrich V C (1970) Transactions ofthe European Orthodontic Society pp 131-143 Fletcher G G T (1963) Transactions ofthe British Society of Orthodontia pp 124-153 Frankel R (1970) Transactions ofthe European Orthodontic Society pp 249-259 GlassDF (1961) Transactions ofthe European Orthodontic Society pp 302-310 Goose D H, Thomson D G & Winter F C (1957) British Dental Journal 102, 174-178 Graber T M, Chung D D B & Aoba J T (1967) Journal of the American Dental Association 75, 1145-1166 Huber R E & Reynolds J W (1946) American Journal ofOrthodontics 32, 1-21 Jacobsen A, Evans W G, Preston C B & Sadowsky P L(1974) American Journal ofOrthodontics 66, 140-171 Kloeppel J G (1970) Transactions of the European Orthodontic Society pp 225-237 Krebs A (1964) XL European Congress of the European Orthodontic Society pp 131-142 McNamara J A (1973) American Journal of Orthodontics 64, 578-606 Massler M & Frankel J M (1951) American Journal ofOrthodontics 37, 751-768 MossJP (I 976a) Transactions of the European Orthodontic Society (in press) (1976b) International Journal of Orthodontics (in press) Moss J P & Chalmers C (1974) American Journal ofOrthodontics 66, 538-556 Moss J P & Picton D C A (1968) Dental Practitioner and Dental Record 18, 442-448 Moyers R E, Elgoyhen J C, Riolo H L, McNamara J A & Kuroda T (1970) Transactions of the European Orthodontic Society pp 61-75 MUhlberg G, SchrOter U & Zill G (1968) Fortschritte der Kieferorthopddie 29, 393-405 Poulton P R. (1973) American Journal of Orthodontics p 311 Rheinwald U & Becker R (1962),Fortschritte der Kieferorthopddie 23, 5-21 Schulze C & Weise W (1965) Fortschritte der Kieferorthopadie 26, 213-229 Schwartz A M (1961) Lehrgang der Gebissregelung. Urban & Schwarzenberg, Innsbruck Seipel C M (1946) Variations of Tooth Position: A Metric Study of Variation and Adaptation in the Deciduous and Permanent Dentitions. Hakun Ohissons Boktryckeri, Lund Stiles K A & Luke J E (1953) Journal of Heredity 44, 241-245 St6ckli P W (1970) Transactions of the European Orthodontic Society pp 145-153 Thilander B (1965) Transactions of the European Orthodontic Society pp 311-327
