An Introduction to Orthodontics, 2nd Edition

20. Orthodontics and orthognathic surgery


Orthognathic surgery is concerned with the correction of dento-facial deformity. In the vast majority of cases a combined surgical and orthodontic approach is required to achieve an optimum result.


Patients with a craniofacial deformity, for example cleft lip and palate, may require orthognathic surgery to correct or mask their underlying abnormality.

Orthognathic surgery may be necessary for those cases with a skeletal discrepancy outside the limits of orthodontic treatment either because of their severity or a lack of growth. Examples include the following:

·     severe Class II malocclusions

·     severe Class III malocclusions

·     vertical discrepancies

·     anterior open bite

·     markedly increased overbite

·     skeletal asymmetry.


An integrated team approach is essential as this allows the surgeon and orthodontist to produce a coordinated treatment plan tailored to an individual patient's needs. This is best achieved by holding joint clinics where treatment can be discussed with the prospective patient. In some centres a psychologist is also a member of the team, helping to identify those patients with unrealistic expectations of treatment. There should also be access to speech and language therapy.

20.2.1. The patient's perception of the problem

Patients seek orthognathic surgery for a number of reasons. The most common are the following:

·     appearance

·     masticatory difficulties

·     speech

·     traumatic overbite

·     temporomandibular joint dysfunction.

Treatment should always attempt to address the patient's concerns. However, it is important to assess whether an individual's perception of the problem is realistic.

A small number of patients project their difficulties in forming relationships or friendships onto a particular facial feature. Their expectations are unrealistic, as they expect surgery to provide an instant solution to their problems and they may react unfavourably post-operatively.

20.2.2. Clinical examination

A systematic approach is required which should include the whole of the patient's face including the forehead and neck. The data given in Table 20.1 can be used as a guide.

Fig. 20.1. Patient with mild facial asymmetry: (a) extra-oral; (b) intra-oral.



Table 20.1 Useful measurements for dentofacial assessment

Mid-facial third

Males 66 mm

Females 60 mm

Lower facial third

Males 66 mm

Females 60 mm

Subnasale to vermilion lower lip

Males 33 mm

Females 30 mm

Vermilion lower lip to menton (ST)

Males 33 mm

Females 30 mm

Intercanthal width

34 ą 4 mm

Alar base width

34 ą 4 mm

Interpupillary width

65 ą 4 mm

Width of mouth

65 ą 4 mm

Length of upper lip

Males 22 mm

Females 20 mm

Exposure of upper incisor at rest

Males 0 mm

Females 3 mm

Exposure of upper incisor smiling

7–10 mm

Projection of supra-orbital ridge:

5–10 mm

Nasolabial angle

110° ą 9°

Labiomental angle

124° ą 10°

Neck–chin angle


Full face

This should include an assessment of the symmetry and balance of the face from the frontal view. Although no face is completely symmetrical, obvious deviations from normal between left and right should be noted. This examination should include the level of the orbits and also the contour of the maxilla and mandible, particularly any deviation of the chin point (Fig. 20.1). In an aesthetically pleasing face the upper, middle, and lower facial thirds are nearly equal in height (Figs. 20.2 and Fig. 20.3), and the face also divides into fifths vertically.

Fig. 20.2. An aesthetic face will divide into thirds vertically. The distance from stomion to menton is two-thirds of the lower facial third.

Fig. 20.3. A patient with a long lower third of the face, with a proportionately increased distance between stomion and menton.


The upper, middle, and lower facial thirds should be considered in turn, so that the forehead and the neck–throat angle are assessed as well as the relationship of the maxilla to the mandible. Maxillary retrognathia is more easily diagnosed from this perspective, as the profile appears concave. The shape of the nose and the nasolabial angle are also important, as retraction of the upper incisors will lead to an increase in obliquity of the nasolabial angle, making the nose more prominent (Fig. 20.4). Conversely, proclination of the upper incisors or forward movement of the maxilla will make the angle formed between the nose and the upper lip more acute.

Fig. 20.4. A patient with a Class II division 1 incisor relationship on a Class II skeletal pattern and a good nasolabial angle. Retraction of the upper incisors would lead to a flattening of the upper lip and make the nose appear more prominent.

The effect on the profile of surgery to advance the mandible can be judged by asking the patient to posture forwards the desired amount. Advancement of the maxilla can also be evaluated by placing cotton wool rolls under the patient's upper lip.

Soft tissues

The form and tone of the soft tissues should be recorded. The fullness of the lips and the amount of tooth show, particularly the upper incisors, at rest and during function should be assessed (Fig. 20.5). Liposuction and/or platysma plication can sometimes be used to improve the neck–throat angle.

Fig. 20.5. (a) A patient with a Class II division 1 malocclusion with an excessive amount of upper incisor show; (a) the same patient following segmental surgery in the upper arch and a mandibular advancement. The lips are now competent.



Temporomandibular joints

The presence of any signs or symptoms of temporomandibular joint dysfunction should be included in the examination of a patient for orthognathic surgery. The role of the occlusion in the aetiology of temporomandibular dysfunction is discussed in more detail in Chapter 1. Ideally, any symptoms should be treated conservatively prior to treatment. However, in patients with grossly deranged occlusions and/or multiple non-working side interferences, it may be necessary to commence treatment which will address these occlusal problems.

Dental health

Good dental health is a prerequisite to a successful outcome. The long-term prognosis of all restored teeth should be taken into consideration when extractions are planned. On occasion this can compromise the treatment plan (Fig. 20.6).

Fig. 20.6. The DPT radiograph of a patient for whom it was decided to avoid presurgical orthodontic alignment in the lower arch.

Occlusal assessment

A thorough examination of the occlusion should be carried out by an orthodontist (see Chapter 5). It is important to check whether the centrelines of the upper and lower arches are coincident with each other and the centre of the face, and to note the direction and nature of any discrepancies.

20.2.3. Radiographic examination

This usually includes those radiographs taken as part of the routine orthodontic assessment of a patient with a skeletal discrepancy, namely a panoramic dental view (DPT), a lateral cephalometric radiograph, and, if indicated, a view of the upper incisors. On occasion, other views may be indicated, for example a posteroanterior skull for asymmetry or a submentovertex to assess mandibular flare prior to a mandibular setback.

20.2.4. Cephalometric assessment

In addition to a routine cephalometric analysis (Chapter 6), many surgeons and orthodontists will carry out more specialized analyses to help determine the underlying aetiology of a particular problem. Many such analyses exist, and for details of these the reader is referred to the section on further reading. One commonly used approach is to compare the patient's cephalometric values with the norm by means of a ‘standard’ tracing. Perhaps the most widely used of these is the Bolton standard (Fig. 20.7). The Bolton standard is a composite tracing derived from the lateral cephalometric radiographs taken every year for a group of individuals followed from birth to maturity. An ‘average’ tracing is available for each year of age, which can be compared against a patient's tracing to help determine areas of discrepancy. However, care is required, as the discrepancies will alter depending on which structures the tracings are superimposed upon. Also, the Bolton tracings are determined from a relatively small group of individuals of both sexes, and therefore should only be used as a guide and not a treatment goal.

Fig. 20.7. Computer print-out to show superimposition of a Bolton composite for an 18-year-old (bold outline) upon the tracing of a patient with a severe Class III malocclusion on the sella–nasion line at sella.

20.2.5. Planning

The following are essential for the purposes of planning and audit:

1. Study models In addition to ‘angled’ study models, it is often helpful to have at least one set of duplicate models for model surgery, usually mounted on a plane line articulator (Fig. 20.8). However, if it is thought that treatment is likely to involve bimaxillary surgery and/or autorotation of the mandible, a set of models should be mounted on a semi-adjustable articulator.

2. Photographs Most orthodontists have a routine set of extra-oral and intraoral views taken before orthodontic treatment. In addition to these, some surgeons find it helpful to have a negative of the patient's profile enlarged to fit 1:1 to their lateral cephalometric radiograph so that the two are superim-posed allowing both soft and bony tissues to be seen. This can then be cut up to help determine the effects of different surgical options upon the patient's profile and can be used to give the patient an idea of his appearance post-surgery. However, care is required not to instill unrealistic expectations, as although some allowance can be made for the responses of the soft tissues to different surgical procedures, there is wide individual variation.

Fig. 20.8. Model surgery.

Where a skeletal discrepancy exists, the action of the soft tissues can lead to tilting of the teeth which compensates for the underlying skeletal problem to varying degrees. This is known as dento-alveolar compensation. It is most commonly seen in Class III malocclusions where proclination of the upper incisors and retroclination of the lower incisors occurs owing to the action of the lips and tongue striving to form an anterior oral seal (Fig. 20.9). If an orthodontics-only approach is to be undertaken for a skeletal discrepancy, this usually involves a degree of dento-alveolar compensation, whereas if orthognathic surgery is to be carried out, ideally any dento-alveolar compensation needs to be eliminated prior to surgery in order that a full correction of the underlying skeletal discrepancy can be carried out. Obviously, in patients with a marked skeletal discrepancy, consideration should be given to the need for surgery before embarking on orthodontic treatment alone as the tooth movements required are in the opposite direction.

Fig. 20.9. Dento-alveolar compensation.

Occasionally it is not feasible or desirable to correct the incisor angulations to their ideal values, for example a narrow mandibular symphysis and/or thin labial periodontal tissues may preclude complete decompensation of retroclined lower incisors in a Class III malocclusion. Therefore it is imperative that the surgeon and orthodontist work closely together at the planning stage to ensure that a co-ordinated approach is employed and the desired skeletal changes can be correlated with the planned occlusion.

A number of methods are used to determine the effect of different treatment plans upon the patient's face and occlusion. There are several manual methods where a ‘guesstimate’ of the effect of orthodontics and surgery is constructed from the lateral cephalometric tracing. The method described previously, which utilizes a 1:1 photograph superimposed upon a lateral cephalometric radiograph is a variation on this theme. Increasingly, specially designed computer programs (Fig. 20.10) can be utilized to evaluate the effects of different orthodontic and surgical approaches on a particular malocclusion. Use of these sophisticated programs saves considerable time over the manual method, allows the investigation of an almost endless range of treatment permutations, and also provides a data-base for the subsequent analysis of the results of treatment. However, a degree of caution is required when using these programs so that only those approaches that are technically feasible for a particular patient are selected for further consideration.

Fig. 20.10. Print-out of the treatment planned (dashed line) for a patient with a Class III malocclusion using a computer planning program (COGsoft).

Fig. 20.11. A patient in her early twenties with a Class III malocclusion who refused to wear orthodontic appliances. She was treated by a maxillary advancement alone, and whilst there is an obvious aesthetic improvement the resulting buccal occlusion is not ideal: (a), (b) pre-operatively; (c), (d) post-operatively.










Following this process it should be possible to determine where the discrepancy lies and whether, and to what degree, it can be corrected. Often, more than one option can be presented to the patient showing varying levels of complexity and final result. Patients often find it helpful to meet a previous (successful!) candidate to discuss the effects of treatment.

A proportion of patients will refuse to consider wearing orthodontic appliances. Rarely, a reasonable occlusion may be possible with surgery alone and perhaps a little judicious occlusal grinding (Fig. 20.11). In the majority a very poor occlusion will result following surgery without orthodontic preparation and if dentoalveolar compensation is not reduced then the facial result may also be prejudiced. In these cases it may be advisable not to proceed unless the patient accepts orthodontic appliances.


Except for some of the craniofacial anomalies, orthognathic surgery is usually carried out when the patient has finished growing so that a good result is not spoiled by further growth. However, the presurgical orthodontic preparation can be commenced earlier, so that its conclusion is timed to coincide with the completion of growth.

20.3.1. Extractions

Extractions may be necessary to relieve crowding and to provide space in order to align the teeth over their skeletal bases (i.e. reduce any dento-alveolar decompensation). In addition, it is important for the surgeon to decide whether any impacted third molars should be removed prior to the start of treatment or during surgery itself, particularly if mandibular ramus surgery is planned.

20.3.2. Presurgical orthodontics

A phase of presurgical orthodontics is usually necessary to establish the desired anteroposterior and vertical position of the incisors, and to align and coordinate the arches so that the teeth do not interfere with placing the jaws in their planned relationship. If a segmental procedure is to be carried out, space will need to be created interdentally for the surgical cuts. However, it is inefficient to carry out tooth movements that can be accomplished more readily at or after surgery, for example levelling of the lower arch in a Class II division 2 malocclusion. As with any orthodontic or surgical procedure, some relapse can be anticipated. Therefore it is helpful if the orthodontics can be planned so that the orthodontic relapse is in the opposite direction to the expected surgical relapse, so that they tend to cancel each other out. It is important to forewarn the patient that the presurgical orthodontic phase may make their appearance worse as any dento-alveolar compensation is reduced (Fig. 20.12).

Presurgical orthodontics is carried out using fixed appliances, which are left in place during surgery. The pre-adjusted appliances (see Chapter 17) make this phase of treatment much easier. Rigid rectangular archwires are usually required to complete presurgical alignment. However, it is important that these are passive before surgery is carried out, particularly if inter-occlusal wafers are to be used during surgery. In most cases the rigid archwires are left in situ and hooks are added for intermaxillary fixation during surgery. Some orthodontists choose a fixed appliance system with a hook on each bracket for orthognathic cases to save having to place hooks onto the archwire — which can be a fiddly and time-consuming exercise (Fig. 20.13).

Presurgical orthodontics usually takes between 12 and 18 months depending upon the complexity of the case. At this stage new study models, radiographs, and photographs are recorded to check what has been achieved during this phase so that the surgical plan can be modified or confirmed as indicated. Model surgery is often carried out to determine the amount and site of bone removal and to fabricate inter-occlusal wafers (or splints) used to locate the bony segments to the planned position during surgery, prior to fixation.

20.3.3. Surgery

A brief description of the common surgical procedures is given in Section 20.4.

In the past, wires were used to locate and fix the bony segments in their corrected position. This necessitated the use of intermaxillary fixation (i.e. the upper and lower teeth were wired together) for about 6 weeks until bony union had occurred. Apart from being unpleasant for the patient, there was a greater morbidity in the immediate post-operative period, often necessitating admittance to an intensive-care bed for the first 24 hours.

The introduction of small bone plates to fix the position of bony segments semirigidly in the maxilla and the use of plates and/or screws in the mandible has completely revolutionized orthognathic surgery. This means that it is not necessary to rely only on intermaxillary fixation following surgery. This approach, together with advances in the use of steroids to reduce swelling and modern antibiotic regimens, means that patients can often be released from hospital within 2 or 3 days of their operation. More recently, resorbable plates and screws have been introduced.

Fig. 20.12. Patient aged 16 years with a Class III malocclusion: SNA = 84°, SNB = 91.5°, ANB = -7.5°, UInc to MxPl = 123°, LInc to MnPl = 76°, MMPA = 21° and FP = 55 per cent. Following the extraction of all four second premolars and presurgical orthodontics, the patient had bimaxillary surgery; (a), (b) pretreatment; (c), (d) at the end of presurgical alignment; (e), (f) at the end of treatment.













Fig. 20.13. (a) Ball hooks crimped onto archwire for the application of intermaxillary fixation during surgery. (b) Bracket system with hook incorporated into each bracket.



20.3.4. Post-surgical orthodontics

Although intermaxillary elastic traction can be started immediately post-operatively to help guide the arches into the desired position, active tooth movement is not usually commenced until approximately 4 weeks after surgery. Lighter round wires, and elastic traction are utilized to detail the occlusion into a good interdigitation. This phase of orthodontics should last for about 6 months.

If the bony segments are not correctly positioned during surgery, a limited amount of movement towards the desired position is possible using intermaxillary elastics in the immediate post-operative period. This problem occurs most commonly when the condyles have been displaced from the glenoid fossa during surgery, with the result that when they return to their correct articulation post-operatively the occlusion is wrong.

20.3.5. Retention

This is usually along similar lines as for conventional fixed appliance therapy (see Chapter 17), namely an upper removable retainer and either a lower removable or bonded (lingual to the lower incisors) retainer as indicated.


Only a brief overview of some of the more popular surgical techniques is included here. Additional information is available in the literature cited in the section on further reading.

As aesthetics are of major importance, where possible an intra-oral approach should be used to avoid unsightly scars. Segmental procedures have an increased morbidity, as damage to the teeth or disruption of the blood supply to a segment is more likely.

20.4.1. Maxillary procedures

Segmental procedures

One or more teeth and their supporting bone can be moved as a segmental procedure. The Wassmund technique involves movement of the upper premaxillary segment of incisors and canines as a block, either distally to reduce an increased overjet or upwards to reduce excessive upper incisor show. Nowadays a Le Fort I procedure is more frequently carried out and the maxilla divided from above into segments.

Le Fort I (Fig. 20.14)

This is the most widely used technique. The standard approach is a horseshoe incision of the buccal mucosa and underlying bone, which results in the maxilla being pedicled on the palatal soft tissues and blood supply. The maxilla can then be moved upwards (after removal of the intervening bone), downwards (with interpositional bone graft), or forwards. Movement of the maxilla backwards is not feasible in practice. Where there is concern regarding the blood supply provided by the palatal vessels, the buccal approach can be made via small vertical incisions and tunnelling of the mucosa, but this makes plating difficult and may increase the likelihood of relapse.

A transpalatal approach is favoured in a small number of centres.

Le Fort II

This is employed to achieve mid-face advancement.

Le Fort III

This usually necessitates raising of a bicoronal flap for access and is commonly used in the management of craniofacial anomalies.

20.4.2. Mandibular procedures

Ramus procedures

The most commonly used ramus techniques are the following.

Vertical subsigmoid osteotomy

This is used for mandibular prognathism and involves a bone cut from the sigmoid notch to the lower border. This can be performed intra-orally using special instruments or extra-orally using standard instruments at the expense of a scar.

Fig. 20.14. Diagram to show the position of the surgical cuts (dashed lines) for a Le Fort 1 procedure.

Sagittal split osteotomy (Fig. 20.15)

This procedure can be used to advance or push back the mandible or to correct mild asymmetry. The bony cut extends obliquely from above the lingula, across the retromolar region, and vertically down the buccal plate to the lower border. The main complication is damage to the inferior alveolar nerve.

Body osteotomy

This operation is useful if there is a natural gap in the lower arch anterior to the mental foramen in a patient with mandibular prognathism. Now rarely used.

Genioplasty (Fig. 20.16)

The tip of the chin can be moved in almost any direction, limited by sliding bony contact and the muscle pedicle. This technique can sometimes be usefully employed as a masking procedure, thus avoiding more complex treatment (for example, mild asymmetry).

Post-condylar cartilage graft

This technique differs from those discussed previously, as it is usually utilized for the correction of severe mandibular retrognathia in growing children. Insertion of a block of cadaveric or autologous cartilage behind the condylar head can produce results analogous to instantaneous functional appliance treatment in Class II division 1 malocclusions, with remodelling of the condylar fossa and surprisingly few adverse reactions. However, this approach may require multiple interventions to achieve an adequate result and definitive orthognathic surgery may still be required.

20.4.3 Bimaxillary surgery

Many patients require surgery to both jaws to correct the underlying skeletal discrepancy (Fig. 20.17).

20.4.4 Distraction Osteogenesis

One of the difficulties posed by the treatment of congenital craniofacial deformities, is the limitations placed by the soft tissues on the amount of movement that is achievable. Although this problem has been addressed to an extent by the use of tissue expanders, the introduction of ‘slow’ distraction osteogenesis in the management of limb deformity has opened up a wealth of opportunity for the management of craniofacial anomalies. Basically this process involves the application of incremental traction to osteotomized bone ends. As a result tension arises in the healing callus and new bone is stimulated in the direction of the traction. Thus this technique avoids the problems of harvesting and maintaining a viable bone graft in the treatment of deficiencies and, in addition, the forces also act upon the surrounding soft tissues leading to adaptive changes termed distraction histogenesis. Distraction osteogenesis is useful for the correction of severe deformity in the growing child and it is hoped will help to reduce the number of surgical procedures previously required to treat these children.

Fig. 20.15. Diagram to show the position of the surgical cuts (dashed/dotted lines) for a sagittal split osteotomy.

Fig. 20.16. (a) A genioplasty being carried out; (b) a lateral cephalometric radiograph of a patient who had a genioplasty carried out in addition to a sagittal split ramus procedure (note the plates securing the genioplasty).



Fig. 20.17. A 16-year-old patient with a Class III malocclusion: SNA = 72.5°, SNB = 79°, ANB = -7.5°, UInc to MxPl = 112.5°, LInc to MnPl = 81°, MMPA = 26.5° and FP = 59 per cent.
Following presurgical orthodontics, the patient had a maxillary advancement and a mandibular set-back: (a), (b) pretreatment; (c) during orthodontic preparation; (d), (e) at the end of treatment.







Whilst this system is still in the process of being developed up to 20 mm of additional mandibular length has been gained by some workers and the technique can also be used for the correction of midface and cranial deformities. Most workers have utilized external fixators, which are manually controlled; however, this approach often leads to significant scarring. Intra-oral mechanisms are now commercially available and future possibilities include implanted telemetrically controlled devices.


With biological systems there is always a tendency for any changes to regress. Therefore the potential for relapse should be assessed at the treatment planning stage and if necessary steps should be taken to limit or compensate for it. A number of factors can lead to relapse and these are broadly classified as follows:

1. Surgical factors

·     Poor planning.

·     The size of the movement required. Movement of the maxilla by more than 5–6 mm in any direction is more susceptible to relapse, as is movement of the mandible by more than 8 mm.

·     Direction of movement required (see Table 20.2)

·     Distraction of the condylar heads out of the glenoid fossa during surgery.

·     Inadequate fixation.

2. Orthodontic factors

·     Poor planning.

·     Movement of the teeth into zones of soft tissue pressure will lead to relapse when appliances are removed. Therefore treatment should be planned to ensure that the teeth will be in a zone of soft tissue balance post-operatively and that the lips will be competent.

·     Extrusion of the teeth during alignment tends to relapse post-treatment.

·     Soft tissue habits, for example a tongue thrust, may persist, leading to a recurrence of an anterior open bite.

3. Patient factors

·     The nature of the problem; for example, anterior open bites associated with abnormal soft tissue behaviour are notoriously difficult to treat successfully and have a marked potential to relapse, and patients should be warned of this prior to treatment.

·     Movements which put the soft tissues under tension, as in the correction of deficiencies, are more susceptible to relapse.

·     In patients with cleft lip and palate advancement of the maxilla is difficult and prone to relapse because of the scar tissue of the primary repair.

·     Failure to comply with treatment; for example, patient does not wear intermaxillary elastic traction as instructed.

Table 20.2 Stability of orthognathic surgery

Most stable
Maxillary impaction
Mandibular advancement
Genioplasty (any direction)
Maxillary advancement
Correction of maxillary asymmetry
Maxillary impaction with mandibular advancement
Maxillary advancement with mandibular setback
Correction of mandibular asymmetry
Mandibular setback
Movement of maxilla downwards
Surgical expansion of maxilla
Least stable
Based on the article by Proffit et al. (1996).


Barnard, D. and Birnie, D. (1990). Scope and limitations of orthognathic surgery. Dental Update17, 63–9.

A well-illustrated easy-to-read article introducing the reader to orthognathic surgery.

Cope, J. B., Samchukov, M. D., and Cherkashin, A. M. (1999). Mandibular distraction osteogenesis: A historic perspective and future directions. American Journal of Orthodontics and Dentofacial Orthopedics115, 448–60.

Cunningham, S. J. and Feinmann, C. (1998). Psychological assessment of patients requiring orthognathic surgery and the relevance of body dysmorphic disorder. British Journal of Orthodontics25, 293–8.

Epker, B. N. and Fish, L. C. (1986). Dentofacial deformities integrated orthodontic and surgical correction. Mosby, St Louis, MO.

A standard text of its time.

Harris, M. and Reynolds, I. R. (1991). Fundamentals of orthognathic surgery. Saunders, London.

A concise but complete account of the subject for those with little background in the field.

Hunt, N. P. and Rudge, S. J. (1984). Facial profile and orthognathic surgery. British Journal of Orthodontics11, 126–36.

A detailed account of assessment of a patient for orthognathic surgery.

Lee, R. T. (1994). The benefits of post-surgical orthodontic treatment. British Journal of Orthodontics21, 265–74.

Proffit, W. R., Turvey, T. A., and Phillips, C. (1996). Orthognathic surgery: a hierarchy of stability. International Journal of Adult Orthodontics and Orthognathic Surgery11, 191–204.

Proffit, W. R. and White, R. R. (1991). Surgicalorthodontic treatment. Mosby Year Book, St Louis, MO.

A comprehensive well-written text which is highly recommended.

Tuinzing, D. B., Greebe, R. B., Dorenbos, J., and van der Kwast, W. A. M. (1993). Surgical orthodontics diagnosis and treatment. VU University Press, Amsterdam.

This book provides a interesting insight into an ingenious method of planning orthognathic management. It also contains a useful section on areas requiring further investigation for those looking for ideas for research projects.

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