British Journal of Orthodontics
ISSN: 0301-228X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/yjor19
Rationale of Treatment for Class II Division 2 Malocclusion B. J. Selwyn-Barnett B.D.S., F.D.S., M.Orth. To cite this article: B. J. Selwyn-Barnett B.D.S., F.D.S., M.Orth. (1991) Rationale of Treatment for Class II Division 2 Malocclusion, British Journal of Orthodontics, 18:3, 173-181, DOI: 10.1179/ bjo.18.3.173 To link to this article: http://dx.doi.org/10.1179/bjo.18.3.173
Published online: 21 Jun 2016.
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Date: 26 September 2016, At: 07:22
Briti,·h Journal of Orthodontics/ Vol. 18/1991 I 17J-18.1
Rationale of Treatment for Class 11 Division 2 Malocclusion* B. J. SELWYN·BARNETT, B.D.S., F.D.S., M.ORTH. 33 Weymouth Street, London WIN 3FL Received for publication March 1990
Abstract. Class /I, division 2 malocclusion is a clinical entity which presents considerable difficulty in the provision of a stable treatment result. This article sets out the problems encountered, reviews teaching on the subject over a 20-year period and attempts to rationalize the current approach to treatment. The rationale presented shows the three-dimensional nature of the occlusal problem, and discusses the justification for expansion and proc/ination of lower incisors in relation to soft tissue influences and stability. The importance of correcting edge-centroid relationship and reducing inter-incisor angle is stressed. Non-extraction therapy, with some lower arch expansion and incisor advancement, is recommended and the reasoning behind this is explained with a case example to illustrate the points involved. Index words: Inter-incisor Angle, Centroid, Non-extraction, and Overbite.
Introduction Historical background
The clinical treatment of Class 11, division 2 malocclusions has always been considered difficult to carry out and of dubious prognosis, being very prone to relapse. In fact, this is a British viewpoint, the explanation for which may be found in the origins of orthodontic training in this country. The main centre for postgraduate orthodontics in the United Kingdom has been the Eastman Dental Hospital. Until 1970, Professor Clifford Ballard was still the dominant force in academic orthodontics in Britain, and teaching concentrated very largely on the influence of soft tissue factors in the aetiology of malocclusion: the limitations imposed by the soft tissues enveloping the dentition were considered of paramount importance in treatment. In relation to Class 11, division 2 cases, in which the retroclination of the upper incisor segment is attributed to the activity of a muscular, firm lower lip, the teaching stressed the inviolability of this labial curtain (Ballard, 1956). It is understandable, therefore, that senior British orthodontists of today, now consultants and teachers, who were trained during the period up to 1975, tended to be inhibited in their approach to the treatment of this particular group ofmalocclusions. A second factor is that in standard British texts over the past 20 years, descriptions of Class 11,
division 2 stated that these cases showed crowding and that this was often 'considerable' in degree. Removal of maxillary first premolars was advised and often mandibular first premolars as well (Hovell, 1966; Foster, 1975; Mills, 1982; Houston and Tulley, 1986). Thirdly, the treatment techniques current 20 years ago mainly involved removable appliances. Headgear was less widely accepted than it is today. The Begg appliance, essentially a first premolar extraction system, with its ability to produce root movement of teeth without the use of rectangular wire, was particularly good at torquing upper incisor roots and bite opening. It was well suited to Class 11, division 2 treatment, and was becoming popular at that time. These influences led to the attempted treatment of Class 11, division 2 cases being carried out by the extraction of four first premolars, the mechanics preventing advancement oflabial segments into the restraining lip muscle. It proved extremely difficult, using standard Begg appliances, to find sufficient palatal bone into which to torque the upper incisor roots while still holding the lower incisors back. It was realized that not only was the dental correction, which is grounded on the reduction of the inter-incisor angle, unattainable in moderately severe cases, but the effects on the facial profile were often disastrous with these extraction cases. However, across the Atlantic, these malocclu-
• Based on a paper delivered at the British Orthodontic Conference, Birmingham, October 1989. 0301-228X/91/000000+00S02.00
© 1991 British Society for the Study of Orthodontics
174
B. J. Selwyn-Barnett
BJO Vol. 18 No. 3
sions were treated by bringing forward the lower labial segment, and it was not accepted that all the cases 'relapsed' subsequent to this incisor advancement. Indeed, Salzmann (1966) mentions that extraction is indicated rarely in Class 11, division 2 cases. Mills (1973), in a study of sixty treated cases based on analysis of pre- and post-treatment cephalometric films, found that overbite commonly fails to be reduced or relapses. He found the most marked correlation occurred between overbite and inter-incisor angle and showed that the best treatment results combined reduction of these factors. He determined that this mainly occurred by lower incisor proclination, but stated that blind proclination of incisors is not the answer. Despite these findings, his teaching was based firmly on the principle of maintaining the presenting lower incisor position, as the stability of this position was established. This paper proposes that, by contrast, calculated proclination is the answer. A discussion of the principles and rationale followed in present-day treatment by the author is presented, and a case is described to illustrate the results achieved.
well as simply measuring the space available for alignment within the presenting arch contour. In a crowded arch, with an increased curve of Spee, space is required for alignment and levelling. In Class 11, division 2 malacclusion, this space can usually be provided by expansion in the canine/ premolar region and forward movement of the labial segment. It is necessary at this point to consider carefully the exact nature of Class 11, division 2 malocclusion and to appreciate that it is a three-dimensional discrepancy. The antero-posterior and vertical components are well known, but there is a tendency to ignore the significance of the transverse plane.
Treatment rationale The following aims of treatment should be considered in the planning of Class 11, division 2 cases:
(1) relief of crowding; (2) reduction of overbite; (3) reduction of inter-incisor angle to 125-130°; (4) bring centroid of upper incisor lingual to the lower incisor tip; (5) correct buccal segment relationship to Class I; (6) align upper labial segment, in particular (7) correct any scissor bites; (8) support the facial profile.
m;
(b)
The first four points, at least, require amplification. Relief 'of crowding
In many cases, a mild lack of space for alignment of the lower arch exists. Since the decision to treat cases by premolar extractions or a non-extraction approach is based on assessment of mandibular arch crowding, at first it is difficult to see how such crowding can be relieved without extractions. When planning space requirements, the space analysis must consider arch width change, positioning of the incisor teeth and overbite reduction, as
(c) FIG. I (a) Zone of muscular stability. (b) Class I, normal overbite. Canines appear in middle of shaded area. (c) Class 11, division 2. Deep overbite. Lower canines, premolars lingually displaced-reduced transverse width.
BJO August /99/
Treatment for Class 11 Division 2
175
The frequency of scissor bites in the first premolar region draws attention to this effect. It is fairly easy to understand that when upper and lower first premolars erupt into a relationship, where the palatal slope of the palatal cusp of the upper collides with the buccal surface of the lower, both teeth will be deflected, the upper buccally, the lower lingually. Correction of this type of scissor-bite is achieved by buccal movement of the lower premolar and palatal
FIG. 2 (a) Facial view of vertical left-right discrepancy. (b) Anterior intra-oral view shows greater canine overbite on short face side. (c) Right buccal view. (d) Left buccal view. (e) Lingual displacement of premolars and incisor crowding on deep bite side, shown occlusally.
movement of the upper, but depends on opening the bite vertically. Thus, the vertical and transverse planes are very closely inter-related. What is less obvious to the perception is the effect of this in the canine region. The typical canine relationship is one-half to two-thirds of a unit Class 11 and shows a deep vertical overlap. The product of this cusp to cusp relationship is that the thickest parts of the canine crowns bucca-lingually are in direct apposition. In the transverse plane, this can be illustrated by the cross-section through the level of the occlusal plane, seen in the diagram (Fig. la). The shaded band represents the middle of the zone of stability between muscular forces of the lip, cheek, and tongue. The cross-sections through the dental arches of a Class I normal overbite case (Fig. lb) and a Class 11, division 2 deep bite case (Fig. le) show the apposition of different thicknesses of the crown at the level of the occlusal plane. Inter-canine and inter-premolar width are both greater in the lower arch in the Class I case. In the Class 11, division 2 situation, note that the crowns of the lower canine and first premolars lie lingual to the central shaded band. The case in Fig. 2a-e illustrates the point. Note the difference in length of the right and left halves of
176 B. J. Selwyn-Barnett
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(3) extraction of teeth; (4) reduction of tooth widths. The first two points may be considered in some detail.
Transverse expansion Lateral expansion provides a realistic means of gaining space. By reducing the vertical ~>Verlap ~f the canines and premolars, some expanston of t~1s region of the arch is quite desirable and stable (Ftg. le). Several authors (Shapiro, 1974; Reidel, 1976) have stated that a slight increase in the lower intercanine width, normally inviolable, is possible in Class 11, division 2 cases, while Gardner and Chaconas (1976) showed stability of premolar expansion. FIG. 3 Diagram showing tooth movements possible (shaded) within soft tissue capsule.
this lady's face, and the associated variation in depth of canine/premolar overbite. The right side of the lower arch is well aligned, but the left side shows incisor crowding and lingual displacement of the buccal segment. There are four methods of creating space in the arch: ( l) expansion in the transverse plane; (2) anteroposterior lengthening;
Anteroposterior arch lengthening (by advancement of the lower incisors) It is generally accepted that distal movement of buccal segments en masse to provide anterior space is clinically impracticable in the lower arch. Anteroposterior arch lengthening is, therefore, confined effectively to the advancement of lower incisors. It is perfectly possible to reconcile the advancement and proclination of the lower incisors with a firm belief in the importance of the labial barrier. The lower incisors can, and indeed should, be advanced to the position limited by the original inner restraining surface of the lower lip.
/)
-~-v· . \ --
FIG. 4 Superimposition of a treated case by enlargement on SN.
FJG. 5 Dotted outline shows upper incisor beyond palatal bone and loss of lip support. C, represents the centroid.
BJO August 1991
Treatment for Class 11 Division 2
177
Figure 3 shows how, by intrusion and torque of the upper incisor, a space opens for the lower incisor crown within the zone of balance between the soft tissues, so that the lower incisor crown simply occupies the space vacated by the upper incisor. There is no encroachment on the lower lip space. Treatment planning
In assessing the amount ofproclination possible in a given case, a prognostic tracing, comparable with Fig. 3, should be drawn, the upper incisor being repositioned to the hatched outline. The space available to the lower incisor will then be clearly seen and the distance by which the incisor tip can be advanced is measured in millimetres. This represents half the space created in the arch, taking into account left and right quadrants. Thus, an advancement of 4 mm gives 8 mm space for relief of crowding and flattening the curve of Spee. It is difficult to be certain that planned changes have actually been achieved during treatment in a
FIG. 6 T.K. pre-treatment records, aged 12. (a) Right buccal view. (b) Anterior view. (c) Left buccal view. (d) Anterior view of overbite. (e) Occlusal view.
178
B. J. Selwyn-Bamett TABLE
BJO Vol. /8 No. 3
I
Cephalometric values A (before treatment)
SNA SNB ANB M/M 1/Max 1/Mand 1/APO SNI Inter-incisor
80 71
9 19 80 97 -5 73 164
c
B (end of treatment)
(end of retention)
D (4 years out of retention)
77 72 5 16 110 104 -I 74 130
77 72 5 16 110 105 -2 75 129
77 72 5 16 110 105 -2 75 129
growing patient. There is no direct way of visualizing the effective changes in incisor positions, in relation to the soft and hard tissues, and the facial profile, from a table of values. Superimposition of cephalometric tracings is required, and there are many alternative methods for this. The enlargement method, illustrated in Fig. 4, is an attempt to cancel out the visually confusing effect of anteroposterior growth, allowing the true mechanical change of tooth position in the plane of the soft tissues to be seen. The method is based on measuring the length of SN before and after treatment. The increase is calculated as a percentage of the post-treatment length and the pre-treatment tracing is enlarged by producing a photocopy enlargement, so that SN can be superimposed precisely. No account of vertical growth is taken, though it is realized that individuals do not grow by geometric enlargement. Nevertheless, as a visual tool, the method does have some merit as a means of showing labiodental changes more clearly in a growing child. Note in Fig. 4 the control of the upper molar and the torque of the upper incisor root together with the occupation of a planned pQSition by the lower incisor crown.
E (overall changes)
-3 +I -4
-3 +30 +8 +3 +2 -35
much as possible towards 125°, bringing the lower incisor tip anterior to the upper incisor centroid (Houston, 1989). The centroid is the mid-point of the upper central incisor root, defined by Houston, Houston and Tulley (1986). The further back the lower incisor is restrained the further back the root of the upper incisor must go to achieve this position. Unless the lower incisor is advanced, the requirement will be beyond the limit of palatal bone, as shown in Fig. 5. Goodman (1988, unpublished), in his excellent review of 50 relatively severe cases treated personally, using the Begg technique, found the most occlusally successful were those in which the interincisor angle was least and the lower incisor position more anterior when compared to the less successful results. This agrees with Mills (1973), as mentioned previously. Most of Goodman's cases were extrac-
Reduction of overbite It is a well recognized principle that proclination of
incisors leads to effective shortening of their vertical length. It is also realized that space is required for the flattening of a curve. It follows that proclination of the lower incisors can satisfy this space requirement and reduce the overbite. Overbite reduction is, therefore, achieved with ease if the lower incisors are brought forward.
Reduction of inter-incisor angle and centroid correction It is essential to reduce the inter-incisor angle as
FIG. 7 T.K. Lateral Cephalometric tracing before treatment; with the values: SNA, 80; SNB, 71; ANB, 9; MMA, 19; 1/1, 164; 1/Max, 80; 1/Mand, 91; 1/APO, -5.
Treatment for Class li Division 2
BJO August /99/
179
u
FIG. 9 T.K. treatment changes. Superimposition by enlargement on SN.
torque the roots beyond the limit of the lingual cortical plates. A deleterious effect upon lip support and facial profile can be the most serious sequel of creating excessive extraction space. It is clear that in most cases, unless the lower arch is excessively crowded, space for relief of mild to moderate crowding and the objectives of good arch form (overbite reduction, inter-incisal angle correction, centroid relationship, and support for the facial profile) are all best achieved on a nonextraction basis, following the rationale described. Case report
FIG. 8 T.K. end of active treatment. (a) Right buccal view. (b) Anterior view. (c) Left buccal view.
tions and the mean inter-incisor angle at end of treatment was 138°, which is relatively increased compared to a norm of 130°. He stated that nonextraction treatment might have been more successful in reducing relapse. . The extraction of first bicuspids leads to retraction of the labial segments during space closure and positions the incisors too far lingually in relation to the supporting alveolar bone. It is a self-defeating approach as it becomes physically impossible to
This illustrates non-extraction treatment and lower incisor advancement. T.K. was a 12-year-old girl with a severe Class 11, division 2 malocclusion (Fig. 6a-e), on a severe skeletal 11 base (Fig. 7). The mandible was retrusive, the molar relationship was one-and-a-half units Class 11, and she was still in the mixed dentition. She had a good dentition, but generally delayed eruption, a classic Class 11, division 2 face, and typically high lip line. Radiographically, JJ was palatally displaced. The aims of treatment were initially to correct the molar relationship and open the bite to release the mandible, using headgear and removable appliances. It was felt that any skeletal improvement would be best gained by starting treatment in the inixed dentition stage, whilst some growth potential was still available. Subsequently, fixed appliances for the considerable torque required for
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BJO Vol. 18 No. 3
(e) FIG. 10 Photographs. Four years out of retention, aged 22. (a) Full face. (b) Right buccal view. (c) Anterior view. (d) Left buccal view. (e) Lateral skull tracing.
the upper central incisors and alignment of 3212 would be used on eruption of the remaining permanent teeth. The first stage lasted 12 months, the second fixed phase 16 months. An 0·022 standard Edgewise appliance was used. Figure 8a-c show the end of treatment result. Retention lasted for almost 3 years. Treatment changes are shown in Fig. 9 and Table 1; the final photographs and tracings are 4 years out of retention (Fig. lOa-e). The 4-year post-retention superimposition (Fig. 11) shows the excellent stability achieved. There has
?)
FIG. 11 Superimposition of end of retention to 4 years postretention. Ages 18-22.
BJO August 1991
Treatment for Class 11 Division 2
181
been no change in lower incisor position or interincisor angle, or overbite increase. The non-extraction approach allowed this operator to correct the overbite without difficulty, produce a good facial appearance and a completely stable result. The 28month duration of treatment in this case is not typical, being due largely to the slow eruption of the second premolars.
The Royal London Hospital Dental Institute, for which I am grateful. I would also like to thank Miss Sharon Oborn and Mrs Jean Patient for their patience in typing the manuscript.
Stability
Foster, T. {1975) A Textbook of Orthodontics, Blackwell Scientific Publications, London, 295-300.
There remains the thorny debate about stability and relapse. Relapse is a term used loosely and is often misinterpreted as being synonymous with posttreatment incisor imbrication. In the treatment of Class 11, division 2 malocclusions, it is the stability of over bite and inter-incisor angle reduction that is paramount. A small degree of lower incisor crowdIng alone does not constitute relapse and is certainly not a justification for premolar extractions, as shown by Little in a series of papers (Little et al., 1981, 1988). Conclusion This paper has attempted to show how a nonextraction method may not only enable treatment to be carried out more easily and successfully than the extraction of premolars will allow, but that this can be done without disturbing soft tissue balance. This does not mean that complete stability will be achieved in every case or that extraction can always be avoided. It is recommended that the lower arch should be retained long-term or even permanently, where any tendency to increase in the inter-incisor angle may be anticipated. No orthodontist should feel a reflection on their clinical skill when long-term retention is necessary. Indeed, lack of adequate retention should be viewed as cavalier and irresponsible, especially when occlusal trauma may be the result. Acknowledgments The concepts put forward in this paper are the views of the author. They have, however, been developed through many years of discussion with colleagues at
References Ballard, C. (1956) Morphology and Treatment of Class Il Division 2 Occlusions, Transactions European Orthodontic Society, 44-54.
Gardner, S. and Chaconas, S. {1976) Post-treatment and Post-retention changes following orthodontic therapy, Angle Orthodontist, 46, 151-161. Goodman, P. {1988) (Unpublished) Paper presented to B.S.S.O., Feb. 1988. Houston, W. {1989) Incisor edge-centroid relationship and overbite depth, European Journal of Orthodontics, 11, 139-143. Houston, W. and Tulley, J. {1986) A Textbook of Orthodontics, Wright, Bristol, 180-186, and 64, 77. Hovell, J. {1966) Current Orthodontics, John Wright and Sons Ltd., Bristol, 250-252. Little, R., Wallen, T. and Riedel, R. (1981) Stability and relapse of mandibular anterior alignment-first premolar extraction cases treated by traditional Edgewise orthodontics, American Journal of Orthodontics, 80, 349-365. Little, R., Riedel, R. and Artun, J. (1988) An evaluation of changes in mandibular anterior alignment from 10-20 years post-retention, American Journal of Orthodontics, 93, 423-428.
Mills, J. R. E. (1973) The problem of overbite in Class 11 Division 2 malocclusions, British Journal of Orthodontics, I, 34-48. Mills, J. R. E. (1982) Principles and Practice of Orthodontics, Livingston and Churchill, London, 158-172. Reidel, R. (1976) Retention and relapse, Journal of Clinical Orthodontics, 10, 454-472. Salzmann, J. {1966) Practice of Orthodontics, J. B. Lippincott Company, Philadelphia, 661. Shapiro, P. (1974) Mandibular dental arch form and dimension, American Journal of Orthodontics, 66, 58-70.
ISSN: 0301-228X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/yjor19
Rationale of Treatment for Class II Division 2 Malocclusion B. J. Selwyn-Barnett B.D.S., F.D.S., M.Orth. To cite this article: B. J. Selwyn-Barnett B.D.S., F.D.S., M.Orth. (1991) Rationale of Treatment for Class II Division 2 Malocclusion, British Journal of Orthodontics, 18:3, 173-181, DOI: 10.1179/ bjo.18.3.173 To link to this article: http://dx.doi.org/10.1179/bjo.18.3.173
Published online: 21 Jun 2016.
Submit your article to this journal
Article views: 1
View related articles
Citing articles: 11 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=yjor19 Download by: [Tufts University]
Date: 26 September 2016, At: 07:22
Briti,·h Journal of Orthodontics/ Vol. 18/1991 I 17J-18.1
Rationale of Treatment for Class 11 Division 2 Malocclusion* B. J. SELWYN·BARNETT, B.D.S., F.D.S., M.ORTH. 33 Weymouth Street, London WIN 3FL Received for publication March 1990
Abstract. Class /I, division 2 malocclusion is a clinical entity which presents considerable difficulty in the provision of a stable treatment result. This article sets out the problems encountered, reviews teaching on the subject over a 20-year period and attempts to rationalize the current approach to treatment. The rationale presented shows the three-dimensional nature of the occlusal problem, and discusses the justification for expansion and proc/ination of lower incisors in relation to soft tissue influences and stability. The importance of correcting edge-centroid relationship and reducing inter-incisor angle is stressed. Non-extraction therapy, with some lower arch expansion and incisor advancement, is recommended and the reasoning behind this is explained with a case example to illustrate the points involved. Index words: Inter-incisor Angle, Centroid, Non-extraction, and Overbite.
Introduction Historical background
The clinical treatment of Class 11, division 2 malocclusions has always been considered difficult to carry out and of dubious prognosis, being very prone to relapse. In fact, this is a British viewpoint, the explanation for which may be found in the origins of orthodontic training in this country. The main centre for postgraduate orthodontics in the United Kingdom has been the Eastman Dental Hospital. Until 1970, Professor Clifford Ballard was still the dominant force in academic orthodontics in Britain, and teaching concentrated very largely on the influence of soft tissue factors in the aetiology of malocclusion: the limitations imposed by the soft tissues enveloping the dentition were considered of paramount importance in treatment. In relation to Class 11, division 2 cases, in which the retroclination of the upper incisor segment is attributed to the activity of a muscular, firm lower lip, the teaching stressed the inviolability of this labial curtain (Ballard, 1956). It is understandable, therefore, that senior British orthodontists of today, now consultants and teachers, who were trained during the period up to 1975, tended to be inhibited in their approach to the treatment of this particular group ofmalocclusions. A second factor is that in standard British texts over the past 20 years, descriptions of Class 11,
division 2 stated that these cases showed crowding and that this was often 'considerable' in degree. Removal of maxillary first premolars was advised and often mandibular first premolars as well (Hovell, 1966; Foster, 1975; Mills, 1982; Houston and Tulley, 1986). Thirdly, the treatment techniques current 20 years ago mainly involved removable appliances. Headgear was less widely accepted than it is today. The Begg appliance, essentially a first premolar extraction system, with its ability to produce root movement of teeth without the use of rectangular wire, was particularly good at torquing upper incisor roots and bite opening. It was well suited to Class 11, division 2 treatment, and was becoming popular at that time. These influences led to the attempted treatment of Class 11, division 2 cases being carried out by the extraction of four first premolars, the mechanics preventing advancement oflabial segments into the restraining lip muscle. It proved extremely difficult, using standard Begg appliances, to find sufficient palatal bone into which to torque the upper incisor roots while still holding the lower incisors back. It was realized that not only was the dental correction, which is grounded on the reduction of the inter-incisor angle, unattainable in moderately severe cases, but the effects on the facial profile were often disastrous with these extraction cases. However, across the Atlantic, these malocclu-
• Based on a paper delivered at the British Orthodontic Conference, Birmingham, October 1989. 0301-228X/91/000000+00S02.00
© 1991 British Society for the Study of Orthodontics
174
B. J. Selwyn-Barnett
BJO Vol. 18 No. 3
sions were treated by bringing forward the lower labial segment, and it was not accepted that all the cases 'relapsed' subsequent to this incisor advancement. Indeed, Salzmann (1966) mentions that extraction is indicated rarely in Class 11, division 2 cases. Mills (1973), in a study of sixty treated cases based on analysis of pre- and post-treatment cephalometric films, found that overbite commonly fails to be reduced or relapses. He found the most marked correlation occurred between overbite and inter-incisor angle and showed that the best treatment results combined reduction of these factors. He determined that this mainly occurred by lower incisor proclination, but stated that blind proclination of incisors is not the answer. Despite these findings, his teaching was based firmly on the principle of maintaining the presenting lower incisor position, as the stability of this position was established. This paper proposes that, by contrast, calculated proclination is the answer. A discussion of the principles and rationale followed in present-day treatment by the author is presented, and a case is described to illustrate the results achieved.
well as simply measuring the space available for alignment within the presenting arch contour. In a crowded arch, with an increased curve of Spee, space is required for alignment and levelling. In Class 11, division 2 malacclusion, this space can usually be provided by expansion in the canine/ premolar region and forward movement of the labial segment. It is necessary at this point to consider carefully the exact nature of Class 11, division 2 malocclusion and to appreciate that it is a three-dimensional discrepancy. The antero-posterior and vertical components are well known, but there is a tendency to ignore the significance of the transverse plane.
Treatment rationale The following aims of treatment should be considered in the planning of Class 11, division 2 cases:
(1) relief of crowding; (2) reduction of overbite; (3) reduction of inter-incisor angle to 125-130°; (4) bring centroid of upper incisor lingual to the lower incisor tip; (5) correct buccal segment relationship to Class I; (6) align upper labial segment, in particular (7) correct any scissor bites; (8) support the facial profile.
m;
(b)
The first four points, at least, require amplification. Relief 'of crowding
In many cases, a mild lack of space for alignment of the lower arch exists. Since the decision to treat cases by premolar extractions or a non-extraction approach is based on assessment of mandibular arch crowding, at first it is difficult to see how such crowding can be relieved without extractions. When planning space requirements, the space analysis must consider arch width change, positioning of the incisor teeth and overbite reduction, as
(c) FIG. I (a) Zone of muscular stability. (b) Class I, normal overbite. Canines appear in middle of shaded area. (c) Class 11, division 2. Deep overbite. Lower canines, premolars lingually displaced-reduced transverse width.
BJO August /99/
Treatment for Class 11 Division 2
175
The frequency of scissor bites in the first premolar region draws attention to this effect. It is fairly easy to understand that when upper and lower first premolars erupt into a relationship, where the palatal slope of the palatal cusp of the upper collides with the buccal surface of the lower, both teeth will be deflected, the upper buccally, the lower lingually. Correction of this type of scissor-bite is achieved by buccal movement of the lower premolar and palatal
FIG. 2 (a) Facial view of vertical left-right discrepancy. (b) Anterior intra-oral view shows greater canine overbite on short face side. (c) Right buccal view. (d) Left buccal view. (e) Lingual displacement of premolars and incisor crowding on deep bite side, shown occlusally.
movement of the upper, but depends on opening the bite vertically. Thus, the vertical and transverse planes are very closely inter-related. What is less obvious to the perception is the effect of this in the canine region. The typical canine relationship is one-half to two-thirds of a unit Class 11 and shows a deep vertical overlap. The product of this cusp to cusp relationship is that the thickest parts of the canine crowns bucca-lingually are in direct apposition. In the transverse plane, this can be illustrated by the cross-section through the level of the occlusal plane, seen in the diagram (Fig. la). The shaded band represents the middle of the zone of stability between muscular forces of the lip, cheek, and tongue. The cross-sections through the dental arches of a Class I normal overbite case (Fig. lb) and a Class 11, division 2 deep bite case (Fig. le) show the apposition of different thicknesses of the crown at the level of the occlusal plane. Inter-canine and inter-premolar width are both greater in the lower arch in the Class I case. In the Class 11, division 2 situation, note that the crowns of the lower canine and first premolars lie lingual to the central shaded band. The case in Fig. 2a-e illustrates the point. Note the difference in length of the right and left halves of
176 B. J. Selwyn-Barnett
BJO Vol. /8 No. 3
(3) extraction of teeth; (4) reduction of tooth widths. The first two points may be considered in some detail.
Transverse expansion Lateral expansion provides a realistic means of gaining space. By reducing the vertical ~>Verlap ~f the canines and premolars, some expanston of t~1s region of the arch is quite desirable and stable (Ftg. le). Several authors (Shapiro, 1974; Reidel, 1976) have stated that a slight increase in the lower intercanine width, normally inviolable, is possible in Class 11, division 2 cases, while Gardner and Chaconas (1976) showed stability of premolar expansion. FIG. 3 Diagram showing tooth movements possible (shaded) within soft tissue capsule.
this lady's face, and the associated variation in depth of canine/premolar overbite. The right side of the lower arch is well aligned, but the left side shows incisor crowding and lingual displacement of the buccal segment. There are four methods of creating space in the arch: ( l) expansion in the transverse plane; (2) anteroposterior lengthening;
Anteroposterior arch lengthening (by advancement of the lower incisors) It is generally accepted that distal movement of buccal segments en masse to provide anterior space is clinically impracticable in the lower arch. Anteroposterior arch lengthening is, therefore, confined effectively to the advancement of lower incisors. It is perfectly possible to reconcile the advancement and proclination of the lower incisors with a firm belief in the importance of the labial barrier. The lower incisors can, and indeed should, be advanced to the position limited by the original inner restraining surface of the lower lip.
/)
-~-v· . \ --
FIG. 4 Superimposition of a treated case by enlargement on SN.
FJG. 5 Dotted outline shows upper incisor beyond palatal bone and loss of lip support. C, represents the centroid.
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Figure 3 shows how, by intrusion and torque of the upper incisor, a space opens for the lower incisor crown within the zone of balance between the soft tissues, so that the lower incisor crown simply occupies the space vacated by the upper incisor. There is no encroachment on the lower lip space. Treatment planning
In assessing the amount ofproclination possible in a given case, a prognostic tracing, comparable with Fig. 3, should be drawn, the upper incisor being repositioned to the hatched outline. The space available to the lower incisor will then be clearly seen and the distance by which the incisor tip can be advanced is measured in millimetres. This represents half the space created in the arch, taking into account left and right quadrants. Thus, an advancement of 4 mm gives 8 mm space for relief of crowding and flattening the curve of Spee. It is difficult to be certain that planned changes have actually been achieved during treatment in a
FIG. 6 T.K. pre-treatment records, aged 12. (a) Right buccal view. (b) Anterior view. (c) Left buccal view. (d) Anterior view of overbite. (e) Occlusal view.
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I
Cephalometric values A (before treatment)
SNA SNB ANB M/M 1/Max 1/Mand 1/APO SNI Inter-incisor
80 71
9 19 80 97 -5 73 164
c
B (end of treatment)
(end of retention)
D (4 years out of retention)
77 72 5 16 110 104 -I 74 130
77 72 5 16 110 105 -2 75 129
77 72 5 16 110 105 -2 75 129
growing patient. There is no direct way of visualizing the effective changes in incisor positions, in relation to the soft and hard tissues, and the facial profile, from a table of values. Superimposition of cephalometric tracings is required, and there are many alternative methods for this. The enlargement method, illustrated in Fig. 4, is an attempt to cancel out the visually confusing effect of anteroposterior growth, allowing the true mechanical change of tooth position in the plane of the soft tissues to be seen. The method is based on measuring the length of SN before and after treatment. The increase is calculated as a percentage of the post-treatment length and the pre-treatment tracing is enlarged by producing a photocopy enlargement, so that SN can be superimposed precisely. No account of vertical growth is taken, though it is realized that individuals do not grow by geometric enlargement. Nevertheless, as a visual tool, the method does have some merit as a means of showing labiodental changes more clearly in a growing child. Note in Fig. 4 the control of the upper molar and the torque of the upper incisor root together with the occupation of a planned pQSition by the lower incisor crown.
E (overall changes)
-3 +I -4
-3 +30 +8 +3 +2 -35
much as possible towards 125°, bringing the lower incisor tip anterior to the upper incisor centroid (Houston, 1989). The centroid is the mid-point of the upper central incisor root, defined by Houston, Houston and Tulley (1986). The further back the lower incisor is restrained the further back the root of the upper incisor must go to achieve this position. Unless the lower incisor is advanced, the requirement will be beyond the limit of palatal bone, as shown in Fig. 5. Goodman (1988, unpublished), in his excellent review of 50 relatively severe cases treated personally, using the Begg technique, found the most occlusally successful were those in which the interincisor angle was least and the lower incisor position more anterior when compared to the less successful results. This agrees with Mills (1973), as mentioned previously. Most of Goodman's cases were extrac-
Reduction of overbite It is a well recognized principle that proclination of
incisors leads to effective shortening of their vertical length. It is also realized that space is required for the flattening of a curve. It follows that proclination of the lower incisors can satisfy this space requirement and reduce the overbite. Overbite reduction is, therefore, achieved with ease if the lower incisors are brought forward.
Reduction of inter-incisor angle and centroid correction It is essential to reduce the inter-incisor angle as
FIG. 7 T.K. Lateral Cephalometric tracing before treatment; with the values: SNA, 80; SNB, 71; ANB, 9; MMA, 19; 1/1, 164; 1/Max, 80; 1/Mand, 91; 1/APO, -5.
Treatment for Class li Division 2
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u
FIG. 9 T.K. treatment changes. Superimposition by enlargement on SN.
torque the roots beyond the limit of the lingual cortical plates. A deleterious effect upon lip support and facial profile can be the most serious sequel of creating excessive extraction space. It is clear that in most cases, unless the lower arch is excessively crowded, space for relief of mild to moderate crowding and the objectives of good arch form (overbite reduction, inter-incisal angle correction, centroid relationship, and support for the facial profile) are all best achieved on a nonextraction basis, following the rationale described. Case report
FIG. 8 T.K. end of active treatment. (a) Right buccal view. (b) Anterior view. (c) Left buccal view.
tions and the mean inter-incisor angle at end of treatment was 138°, which is relatively increased compared to a norm of 130°. He stated that nonextraction treatment might have been more successful in reducing relapse. . The extraction of first bicuspids leads to retraction of the labial segments during space closure and positions the incisors too far lingually in relation to the supporting alveolar bone. It is a self-defeating approach as it becomes physically impossible to
This illustrates non-extraction treatment and lower incisor advancement. T.K. was a 12-year-old girl with a severe Class 11, division 2 malocclusion (Fig. 6a-e), on a severe skeletal 11 base (Fig. 7). The mandible was retrusive, the molar relationship was one-and-a-half units Class 11, and she was still in the mixed dentition. She had a good dentition, but generally delayed eruption, a classic Class 11, division 2 face, and typically high lip line. Radiographically, JJ was palatally displaced. The aims of treatment were initially to correct the molar relationship and open the bite to release the mandible, using headgear and removable appliances. It was felt that any skeletal improvement would be best gained by starting treatment in the inixed dentition stage, whilst some growth potential was still available. Subsequently, fixed appliances for the considerable torque required for
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(e) FIG. 10 Photographs. Four years out of retention, aged 22. (a) Full face. (b) Right buccal view. (c) Anterior view. (d) Left buccal view. (e) Lateral skull tracing.
the upper central incisors and alignment of 3212 would be used on eruption of the remaining permanent teeth. The first stage lasted 12 months, the second fixed phase 16 months. An 0·022 standard Edgewise appliance was used. Figure 8a-c show the end of treatment result. Retention lasted for almost 3 years. Treatment changes are shown in Fig. 9 and Table 1; the final photographs and tracings are 4 years out of retention (Fig. lOa-e). The 4-year post-retention superimposition (Fig. 11) shows the excellent stability achieved. There has
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FIG. 11 Superimposition of end of retention to 4 years postretention. Ages 18-22.
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been no change in lower incisor position or interincisor angle, or overbite increase. The non-extraction approach allowed this operator to correct the overbite without difficulty, produce a good facial appearance and a completely stable result. The 28month duration of treatment in this case is not typical, being due largely to the slow eruption of the second premolars.
The Royal London Hospital Dental Institute, for which I am grateful. I would also like to thank Miss Sharon Oborn and Mrs Jean Patient for their patience in typing the manuscript.
Stability
Foster, T. {1975) A Textbook of Orthodontics, Blackwell Scientific Publications, London, 295-300.
There remains the thorny debate about stability and relapse. Relapse is a term used loosely and is often misinterpreted as being synonymous with posttreatment incisor imbrication. In the treatment of Class 11, division 2 malocclusions, it is the stability of over bite and inter-incisor angle reduction that is paramount. A small degree of lower incisor crowdIng alone does not constitute relapse and is certainly not a justification for premolar extractions, as shown by Little in a series of papers (Little et al., 1981, 1988). Conclusion This paper has attempted to show how a nonextraction method may not only enable treatment to be carried out more easily and successfully than the extraction of premolars will allow, but that this can be done without disturbing soft tissue balance. This does not mean that complete stability will be achieved in every case or that extraction can always be avoided. It is recommended that the lower arch should be retained long-term or even permanently, where any tendency to increase in the inter-incisor angle may be anticipated. No orthodontist should feel a reflection on their clinical skill when long-term retention is necessary. Indeed, lack of adequate retention should be viewed as cavalier and irresponsible, especially when occlusal trauma may be the result. Acknowledgments The concepts put forward in this paper are the views of the author. They have, however, been developed through many years of discussion with colleagues at
References Ballard, C. (1956) Morphology and Treatment of Class Il Division 2 Occlusions, Transactions European Orthodontic Society, 44-54.
Gardner, S. and Chaconas, S. {1976) Post-treatment and Post-retention changes following orthodontic therapy, Angle Orthodontist, 46, 151-161. Goodman, P. {1988) (Unpublished) Paper presented to B.S.S.O., Feb. 1988. Houston, W. {1989) Incisor edge-centroid relationship and overbite depth, European Journal of Orthodontics, 11, 139-143. Houston, W. and Tulley, J. {1986) A Textbook of Orthodontics, Wright, Bristol, 180-186, and 64, 77. Hovell, J. {1966) Current Orthodontics, John Wright and Sons Ltd., Bristol, 250-252. Little, R., Wallen, T. and Riedel, R. (1981) Stability and relapse of mandibular anterior alignment-first premolar extraction cases treated by traditional Edgewise orthodontics, American Journal of Orthodontics, 80, 349-365. Little, R., Riedel, R. and Artun, J. (1988) An evaluation of changes in mandibular anterior alignment from 10-20 years post-retention, American Journal of Orthodontics, 93, 423-428.
Mills, J. R. E. (1973) The problem of overbite in Class 11 Division 2 malocclusions, British Journal of Orthodontics, I, 34-48. Mills, J. R. E. (1982) Principles and Practice of Orthodontics, Livingston and Churchill, London, 158-172. Reidel, R. (1976) Retention and relapse, Journal of Clinical Orthodontics, 10, 454-472. Salzmann, J. {1966) Practice of Orthodontics, J. B. Lippincott Company, Philadelphia, 661. Shapiro, P. (1974) Mandibular dental arch form and dimension, American Journal of Orthodontics, 66, 58-70.
