Molar classification

Angle classified occlusion according to the molar relationship and this remains the most internationally recognized classification of malocclusion. When looking at ideal occlusion, Angle found that the mesiobuccal cusp of the upper first permanent molar should occlude with the sulcus between the mesial and distal buccal cusps of the lower first permanent molar (Fig. 1.2). He therefore based his classification of occlusion on this relative mesiodistal position:

Figure 1.2 The Angle molar classification.

The buccal segment occlusion can be further defined in relation to the degree of mesial or distal occlusion and this is usually measured in units of tooth space.

In clinical practice, it is common to describe molar relationships in terms of half or even a third of a tooth unit of a class II or class III relationship (Fig. 1.2). However, a basic premise of the Angle classification is that the first permanent molars hold a fixed position within the dental arch, which is not necessarily the case. Early loss of deciduous teeth can influence their position and distort the molar relationship and this classification can also be difficult to apply when there is an asymmetric molar relationship. These problems can lead to low levels of inter-examiner agreement (Gravely and Johnson, 1974).

Canine classification

The canine relationship also provides a useful anteroposterior occlusal classification:

Similarly to the molar relationship, the severity of the canine relationship can also be described in terms of tooth units and can be inappropriately influenced by local factors such as crowding (Fig. 1.2).

Incisor classification

A more clinically relevant method of classifying malocclusion is based upon the relationship of the maxillary and mandibular incisors. This represents a truer reflection of the underlying skeletal base relationship and also highlights what is often of most concern to the patient. It is essentially the Angle classification, as applied to the incisor teeth, and is defined upon the relationship of the mandibular incisor tip to the cingulum plateau of the maxillary central incisors (Fig. 1.3), being included in the British Standards Institute’s Glossary of Dental Terms:

Figure 1.3 British Standards Institute incisor classification.

Confusion can arise when the upper incisors are upright or retroclined, but with an increased overjet. This has led to the introduction of a class II intermediate classification (Williams and Stephens, 1992):

In reality, an increased overjet with retroclined upper incisors is within the descriptive range of class II division 2.

Evolutionary trends

Comparison of large population studies with archaeological records confirms that malocclusion has become more common over the past 1000 years. In fact, epidemiological data show that the increase in human occlusal variation has been rapid, taking place within a couple of generations, occasionally even from one generation to the next (Weiland et al, 1997). A rapid change such as this would imply a significant contribution from a changing environment, such as has occurred with increasingly urbanized and industrialized societies (Corruccini, 1984). It has been hypothesized that dietary changes in modern societies, with increased consumption of soft, energy-rich food, has resulted in less interproximal wear between the teeth. Research on aboriginal and stone aged populations has demonstrated this lack of attrition as a possible cause of malocclusion, particularly crowding (Begg, 1954). However, it has been shown that the amount of tooth material lost in each quadrant by interproximal wear is not more than 2 to 3-mm (Fig. 1.4).

Figure 1.4 Well-interdigitated class I dentition showing diet-related occlusal interproximal wear.

A soft diet may also result in underdevelopment of the jaws and a lack of arch space, leading to crowding. According to this hypothesis, hard diet requires vigorous mastication, stimulating the growth of facial bones, particularly in the transverse dimension of the maxilla and mandible. Tooth wear is merely a by-product, brought about by diet-related attrition and high masticatory activity, and has only a minor effect on tooth alignment. Experimental studies have shown that dietary consistency and masticatory activity affect not only the masticatory muscles, but also many aspects of bone growth, including bone size and mass, internal bone structure, and craniofacial size and morphology (Varrela, 2006).

Genetic influences

Genetically homogenous societies exhibit low levels of malocclusion compared to heterogeneous societies and a significant genetic component appears to exist for many individual dental and occlusal anomalies. Early animal experiments initially put forward a compelling argument for a genetic component to malocclusion, based upon inbreeding of dogs, culminating in gross facial deformity. It later emerged that these studies were flawed, merely segregating mutations for specific traits such as achondroplasia, which are present in many breeds of small dog, but rare in humans.

Until recently, most information on the relative contribution of genetic factors to malocclusion has been gained from family studies and the twin method. Monozygotic twins are genetically identical, whereas dizygotic twins only share 50% of their genetic makeup. Therefore, by comparing the differences in occlusal traits between pairs in both groups, some indication of the genetic influence on a particular trait is given; the larger the difference, the greater the genetic effect (Corruccini et al, 1990). This assumes that the environmental effects are similar for both groups.

Many developmental dental anomalies have been shown to occur together and have a strong familial trend. An example of this is development of a palatally impacted maxillary canine, which is more common in females and certain ethnic groups and is often associated with microdont or absent lateral incisors (Peck et al, 1994). Similarly, jaw growth appears to be mostly genetically determined. A higher correlation has been shown between patients and immediate family than in unrelated subjects for class II division 1 malocclusion, which supports a polygenetic inheritance, particularly in relation to mandibular retrognathia. However, environmental factors, such as lower lip position and digit sucking, can also play a part. Mandibular prognathism, found in class III malocclusions, seems to have a high genetic predisposition, as demonstrated by the high familial inheritance and variation amongst different ethnic groups. More robust evidence for this exists from studies of siblings and first degree relatives (Litton et al, 1970; Watanabe et al, 2005).

Dental arch size and form seems to be more subject to environmental influences (Cassidy et al, 1998). Dental crowding represents a discrepancy between the size of the teeth and the size of the dental arch. Tooth development, including the size, form and presence of teeth within a dentition, is under strong genetic influence. However, the main aetiological factor in crowding appears to be arch size as opposed to tooth size (Howe et al, 1983).

Large population studies have also investigated the influence of population admixture and inbreeding on malocclusion. Generally, the results of these epidemiological studies have shown a greater genetic influence on skeletal relations and arch size and a lower heritability of dental variables such as overbite, molar relationships and crowding, suggesting a greater environmental influence. The importance of hereditary factors also appears to increase with severity of the malocclusion. Although craniofacial form and growth may be under genetic control, the reason that siblings often present with similar malocclusions is probably related to their similar responses to environmental influences. Therefore, while malocclusion appears to be acquired, the underlying genetic control of craniofacial form will tend to divert siblings into similar physiological responses, resulting in the development of similar malocclusions (King et al, 1993).

These studies have also shown that malocclusion does not follow simple Mendelian inheritance, but rather polygenetic or epigenetic transmission, when the interaction of genes with each other and the environment during development determine the phenotypic variation of the trait. Therefore, each would have an additive effect, showing variation along a continuous scale for traits of a malocclusion, which is exactly what happens. Theoretically, in genetically isolated communities, alleles for these traits may be expressed more frequently, giving an indication which have a greater genetic component. Island studies investigating the effects of inbreeding on malocclusion support this polygenetic theory of transmission for certain traits such as overjet and overbite (Lauc et al, 2003).

Environmental factors

The developing dentition is under the influence of resting soft tissue pressure form, and function: lying in a position of muscular balance or equilibrium (Proffit, 1978). Teeth erupt under the influence of the lips and cheeks on one side and the tongue on the other. Abnormal soft tissue patterns seen in those with persistent digit-sucking habits or lip incompetence, with the lower lip trapped behind the upper incisors in function, may predispose to an increased overjet. An alteration in tooth position can also arise when there is a change in this balance of force. Possible causes may be physiological, habitual or pathological and may impact on the lips, cheeks, tongue and periodontal tissues.

Physiological factors

A physiological adaptation can take place in the presence of a skeletal base discrepancy. When teeth erupt, they do so under the influence of soft tissue pressure from the lips, cheeks and tongue. There is a tendency, most notably in the labial segments, for them to upright or procline towards teeth in the opposing arch. This is most often seen in class III skeletal cases, with proclination of the upper incisors and retroclination of the lowers (Fig. 1.5).

Figure 1.5 Class III malocclusion showing incisor dentoalveolar compensation.

The mandibular incisors have retroclined in an attempt to achieve a class I incisor relationship in the presence of a class III skeletal base.

Soft tissue envelope

The zone of balance between the lips and cheeks and tongue can in part dictate where the teeth sit. If the forces are imbalanced it can result in tooth movement. Many children have lip incompetence:

• If the lower lip rests behind the upper incisor, this may predispose to an increased overjet and is described as a lip trap (Fig. 1.6).

• In a small percentage of patients there appears to be hyperactivity of the mentalis muscle, resulting in retroclination of the lower incisors and described as a strap-like lower lip (Fig. 1.7).

• Similarly, a high lower lip position is thought to contribute to retroclination of the upper incisors in a class II division 2 relationship (Fig. 1.8).

Figure 1.6 Lip trap contributing to an increase in overjet.

Figure 1.7 Strap-like lower lip.

Figure 1.8 A high lower lip position retroclining the upper central incisors and proclining the upper lateral incisors in a class II division 2 incisor relationship (the upper lip has been retracted).

In cases with anterior open bite, an anterior oral seal on swallowing is created by the tongue coming forward to fill the gap. This is an adaptive behaviour, secondary to the malocclusion. Occasionally, a tongue thrust is the primary cause of the malocclusion: the so-called endogenous (primary) tongue thrust. Although often described, this is a rare phenomenon and is probably related to the anterior resting position of the tongue as opposed to excessive activity.

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Mouth breathing

Children with nasopharyngeal obstruction associated with enlarged adenoids have been shown to have longer faces and smaller mandibles compared to controls (Fig. 1.9) (Linder-Aronson, 1970).

Figure 1.9 Child with increased facial height and lip incompetence with a history of nasal blockage and mouth breathing.

This appearance has been described as an adenoidal face.

Neonates by necessity are nasal breathers to allow suckling but most pre-adolescent children adopt a posture with their lips habitually apart at rest. This resolves in many cases, due to greater vertical growth of the lips compared to the lower facial skeleton, particularly in boys. Total experimental obstruction of the nasal airway in primates and humans results in a change of head posture, with the neck being extended and a downward and backward growth rotation of the mandible occurring. Following adenoidectomy for children with severe nasopharyngeal obstruction, a greater horizontal rather than vertical growth pattern has been described (Linder-Aronson et al, 1986; Woodside et al, 1991). In humans, total obstruction of the nasal airway is rare and many children, even with some nasal blockage and lip incompetence, do breathe through their noses. It is therefore impossible to generalize on a normal population using data gathered from extremes. The question still remains whether partial nasal blockage is an aetiological factor in malocclusion, as the situation appears more complex than a simple form–function interaction (Vig, 1998).

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Muscular activity

Conditions associated with a loss of muscle tone, such as muscular dystrophy and certain types of cerebral palsy, result in a downward and backward rotation of the mandible, an increased lower face height and an anterior open bite (Fig. 1.10). Adults with increased anterior face height have reduced bite force and also a different composition of muscle fibres in the masseter, which implicates muscles as a primary cause of malocclusion (Hunt et al, 2006). However, in children with similar skeletal makeup, the bite force is the same as children with normal face height, implying that the loss in force may develop with, as opposed to causing, a malocclusion (Proffit & Fields, 1983).

Figure 1.10 Anterior open bite related to cerebral palsy (left) and persistent digit-sucking habit (right).

Pathology

A number of pathological conditions can contribute directly to a malocclusion, causing either skeletal discrepancies or more local effects upon the dentition.

Childhood fractures of jaws

The condyle is the commonest site of fracture in the mandible during childhood and many go undiagnosed. In severe cases with bilateral fracture and dislocation from the glenoid fossa, an anterior open bite can be one of the presenting features due to a loss in ramus height. A long-term sequelae of early trauma to the mandibular condyle can be asymmetry, with an ipsilateral decrease in ramus height and deviation of the chin point to the affected side (Fig. 1.11). The severity of outcome is in part related to the age at the time of injury. However, a high percentage of children sustaining a condylar fracture have normal mandibular growth due to the reparative capacity of the condyle, even when displaced from the glenoid fossa.

Figure 1.11 Mandibular asymmetry in an adult following fracture of the condyles as a child.

Juvenile rheumatoid arthritis

An inflammatory arthritis occurring before the age of 16 years and involving the temporomandibular joints can result in the development of a severe class II malocclusion due to restricted growth of the mandible (Fig. 1.12).

Figure 1.12 Lateral skull radiograph of patient with a history of juvenile rheumatoid arthritis.

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Excessive growth hormone

Overproduction of growth hormone from an anterior pituitary tumour causes gigantism in children and acromegaly in adults. In both circumstances, the patient presents with a worsening class III malocclusion characterized by mandibular excess (Fig. 1.13).

Figure 1.13 Lateral skull radiograph showing a class III malocclusion in an adult resulting from excessive growth hormone secondary to a pituitary tumour.

Note the indistinct and enlarged borders of the pituitary fossa.

Periodontal disease

With the loss of alveolar bone that occurs due to periodontal disease, teeth become more susceptible to influence from the soft tissue envelope that surrounds them. Any change in this balance that occurs with age can result in tooth movement. This is commonly seen when upper incisors escape control of the lower lip, resulting in an increase in the overjet and spacing (Fig. 1.14).

Figure 1.14 Proclination and spacing of the upper labial segment resulting from periodontal bone loss.

Dentoalveolar trauma

Trauma to the primary maxillary incisors can result in displacement of the tooth into the developing tooth bud of the permanent successor. Damage to the crown or dilaceration of the root can occur, resulting in failure of eruption and impaction of the tooth. Loss of a permanent incisor due to trauma can result in space loss and shift in the dental centre line in crowded dentitions (Fig. 1.15).

Figure 1.15 Loss of UL1 through trauma with subsequent space loss and a shift in the dental centreline.

Early loss of primary teeth

Although water fluoridation and dental education has significantly reduced the incidence of caries in children, the enforced loss of primary teeth due to caries still remains a major aetiological factor in the development of a local malocclusion. In a crowded dentition, the early loss of deciduous teeth can result in space loss, increased crowding and deviations of the dental centre lines.

Resistance to caries and periodontal disease

Dental caries is endemic in most developed societies and the primary aetiological factors are the presence of cariogenic flora in dental plaque and the frequent intake of refined sugars. The disease process can be controlled with good diet and oral hygiene and is unrelated to the presence or absence of a malocclusion. There is some evidence that straight teeth and a normal overjet are easier to keep clean (Addy et al, 1986; Davies et al, 1988) and that recipients of orthodontic treatment have lower plaque scores (Davies et al, 1991), but this may be more related to the modification of behaviour during treatment rather than the actual presence of straight teeth.

The primary aetiological factor in periodontal disease is dental plaque and the principle way to avoid this condition is maintaining good oral hygiene, not orthodontic treatment. However, there are two specific areas where orthodontic treatment can help to prevent periodontal breakdown:

Improved masticatory efficiency

Evidence to suggest that having a class I occlusion improves masticatory efficiency is weak. It is perfectly possible to survive without teeth on a Western diet, as many people do, and whilst orthodontic treatment can be beneficial in correcting functional problems such as crossbites, it is unlikely to make a significant difference to masticatory efficiency. One exception is the correction of an anterior open bite when patients are unable to incise food except by biting into it with their posterior teeth.

Prevention or cure of temporomandibular joint dysfunction

The aetiology of temporomandibular joint dysfunction remains controversial, which explains in part the large variety of modalities used to treat it. At the very least, the aetiology is considered to be multifactorial. The relationship between malocclusion and temporomandibular dysfunction has been explored extensively, mostly in large epidemiological studies, and whilst some traits of a malocclusion have been shown to have a correlation with the signs and symptoms of joint dysfunction (Table 1.2), these are very weak (Egermark-Eriksson et al, 1983).

Table 1.2 Occlusal features associated with temporomandibular dysfunction

Improvement in speech

Speech patterns are established very early in life and in most cases a long time before eruption of the permanent dentition. Some speech problems are related to certain traits of a malocclusion, such as anterior open bite and a lisp, but treating the malocclusion will not guarantee resolution of the problem.

Prevention of trauma

An increased overjet is a risk factor for trauma to the upper incisors (Jarvinen, 1978). As a consequence, a high percentage of patients with a class II division 1 incisor relationship present with damaged upper incisors. Correction of the incisor relationship will theoretically reduce the vulnerability of these teeth to damage following trauma. Unfortunately most incidences of trauma occur soon after eruption of the permanent incisors and prior to the age when orthodontics is usually started.

Psychological benefits

In its original constitution the World Health Organization defined health as ‘a state of complete physical, social and mental well-being and not merely the absence of disease and infirmity’. Therefore, even though a malocclusion is not a disease state, the benefits of treating it should be considered in terms of both the social and mental well-being of an individual. Certain occlusal traits, such as an increased overjet, can lead to a reduction in self-esteem and can be a target for teasing. More severe malocclusions associated with facial disfigurement, such as those seen in cleft lip and palate, have been shown to have a profound and long-lasting psychological impact. However, longitudinal studies have demonstrated little objective evidence to support the assumption that orthodontic treatment can improve long-term psychological health of the individual (Kenealy et al, 2007).

More recently work has focused on the impact malocclusion can have on quality of life for individuals. Certain occlusal traits such as an increased overjet and spacing appear to have some negative impact in children and their families (Johal et al, 2007), whilst in adults severe skeletal problems that require surgical correction can have a profound impact on individual quality of life.

Risks from appliances

The principle risks arise from the use of fixed appliances and these can affect the teeth, periodontium and soft tissues.

Enamel decalcification

The incidence of demineralization during fixed appliance therapy is high and can result in the development of enamel opacities on the labial surfaces of the teeth. Incidences of up to 50% of patients undergoing fixed appliance therapy have been reported (Gorelick et al, 1982). The main aetiological factors are poor oral hygiene and a diet high in refined sugars. In combination and over the long-term, these factors will inevitably result in demineralization and permanent marking of the teeth (Fig. 1.16). Excellent oral hygiene and a non-cariogenic diet are therefore a prerequisite to orthodontic treatment involving fixed appliances. During treatment, the chances of developing enamel opacities can be reduced by the regular use of topical fluoride supplements. The use of a 0.05% sodium fluoride mouthwash on a daily basis will significantly reduce the incidence of white spot lesions (Benson et al, 2005) and fluoride-releasing bonding agents such as glass ionomer will reduce caries levels experienced during treatment (Derks et al, 2004).

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Figure 1.16 Generalized demineralization following orthodontic treatment with fixed appliances.

Root resorption

External root resorption is an almost universal finding following orthodontic treatment, but this is usually not clinically significant and has no influence on long-term health of the teeth. Severe root resorption, when more than a quarter of the root length is lost, has been reported to occur in less than 3% of orthodontic patients (Fig. 1.17) (Sameshima and Sinclair, 2004). The greatest amount and severity of root resorption is seen in the anterior maxillary region, especially the maxillary lateral incisors. There is a genetic tendency and ethnic susceptibility, with Asian patients having a lower incidence. The greatest association with root resorption appears to be the duration of treatment and the distance the teeth must move (Linge and Linge, 1991; Segal et al, 2004). Other risk factors associated with a higher incidence of root resorption include:

• Unusually shaped roots, including blunted, pipette-shaped and short roots;

• History of dentoalveolar trauma;

• Excessive orthodontic force;

• Movement of teeth without occlusal contact;

• Intrusive forces;

• Reduction of large overjets by distal movement of anterior teeth; and

• Pushing apices of teeth into cortical bone.

Figure 1.17 Severe root resorption during orthodontic treatment.

Gingivitis

Gingival irritation is inevitable with the use of fixed appliances, especially the placement of bands and this is exacerbated by poor oral hygiene, which can result in gingival hyperplasia. Gingival health improves significantly following the removal of appliances, with a reduction in probing depths mainly due to shrinkage of hyperplastic tissues (Fig. 1.18). Certain medications such as antiepileptic drugs and immunosuppressants in combination with poor oral hygiene can result in extensive gingival hyperplasia that can require gingival surgery following appliance removal.

Figure 1.18 Gingival hyperplasia during orthodontic treatment and subsequent improvement on removal of the appliance.

Oral ulceration

Aphthous ulceration in susceptible individuals is common with fixed appliances, particularly during the early stages of treatment. This can be exacerbated if archwires are not cut or bent back and left protruding from molar tubes (Fig. 1.19).

Figure 1.19 Oral ulceration from a fixed appliance.

Generalized risks associated with orthodontic treatment

A number of more general risks have been proposed with regard to orthodontic treatment, in particular causing damage to the facial profile or temporomandibular joints. A great deal of controversy surrounds these claims and currently there is little robust evidence in the literature to support them. In contrast, it is well recognized that the final tooth positions achieved following orthodontic treatment can relapse and it is important for any orthodontic patient to understand that absolute stability cannot be guaranteed without permanent retention.

Index of Treatment Need (IOTN)

The IOTN was developed within the UK (Brook and Shaw, 1989) where the majority of orthodontic treatment has been provided within a state-funded health service and this has proved to be the most widely used and recognized index. Based on the Swedish National Board for Welfare Index (Linder-Aronson, 1974), it defines need for treatment, both in terms of dental health benefits and aesthetic handicapping and has been shown to be reproducible and reliable over time (Cooper et al, 2000). The IOTN is split into Dental Health and Aesthetic components.

Dental Health Component (DHC)

The DHC has five categories, defining treatment need from none (Grade 1) to a great need (Grade 5). The following characteristics are scored for each individual:

• Missing teeth;

• Overjet;

• Crossbites;

• Displacement of contact points (crowding); and

• Overbite.

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The DHC is hierarchical, for each individual the highest score is found and recorded, irrespective of any other features within the malocclusion. The five categories are further subdivided using letters, which describe the feature of the malocclusion that has been scored (Table 1.3).

Table 1.3 Dental health component of the IOTN

Grade 1—No treatment required
1.	Extremely minor malocclusions, including displacements less than 1 mm
Grade 2—Little need for treatment
2.a	Increased overjet > 3.5 mm but ≤ 6 mm (with competent lips)
2.b	Reverse overjet greater than 0 mm but ≤ 1 mm
2.c	Anterior or posterior crossbite with ≤ 1 mm discrepancy between RCP and ICP
2.d	Displacement of teeth > 1 mm but ≤ 2 mm
2.e	Anterior or posterior open bite > 1 mm but ≤ 2 mm
2.f	Increased overbite ≥ 3.5 mm (without gingival contact)
2.g	Prenormal or postnormal occlusions with no other anomalies (up to a unit of discrepancy)
Grade 3—Borderline need for treatment
3.a	Increased overjet > 3.5 mm but ≤ 6 mm (incompetent lips)
3.b	Reverse overjet greater than 1 mm but ≤ 3.5 mm
3.c	Anterior or posterior crossbites with > 1 mm but ≤ 2 mm discrepancy between RCP and ICP
3.d	Displacement of teeth > 2 mm but ≤ 4 mm
3.e	Lateral or anterior open bite > 2 mm but ≤ 4 mm
3.f	Increased and incomplete overbite without gingival or palatal trauma
Grade 4—Treatment required
4.a	Increased overjet > 6 mm but ≤ 9 mm
4.b	Reverse overjet > 3.5 mm with no masticatory or speech difficulties
4.c	Anterior or posterior crossbites with > 2 mm discrepancy between RCP and ICP
4.d	Severe displacements of teeth > 4 mm
4.e	Extreme lateral or anterior open bites > 4 mm
4.f	Increased and complete overbite with gingival or palatal trauma
4.h	Less extensive hypodontia requiring pre-restorative orthodontics or orthodontic space closure to obviate the need for a prosthesis
4.l	Posterior lingual crossbite with no functional occlusal contact in one or more buccal segments
4.m	Reverse overjet > 1 mm but < 3.5 mm with recorded masticatory and speech difficulties
4.t	Partially erupted teeth, tipped and impacted against adjacent teeth
4.x	Existing supernumerary teeth
Grade 5—Treatment required
5.a	Increased overjet > 9 mm
5.h	Extensive hypodontia with restorative implications (more than one tooth missing in any quadrant requiring pre-restorative orthodontics)
5.i	Impeded eruption of teeth (apart from 3rd molars) due to crowding, displacement, the presence of supernumerary teeth, retained deciduous teeth and any pathological cause
5.m	Reverse overjet > 3.5 mm with reported masticatory and speech difficulties
5.p	Defects of cleft lip and palate
5.s	Submerged deciduous teeth

Aesthetic Component

This records the aesthetic handicapping of the malocclusion and is based on a series of ten photographs, which show a graduated decrease in dental aesthetics (Fig. 1.20). A score is given from 0 to 10 based upon the perceived aesthetic impairment of an individual’s malocclusion, not morphological similarities with the photographs. A high-level agreement has been found between scores given by professionals and those given by patients.

Figure 1.20 The aesthetic component of the IOTN. The SCAN scale was first published in 1987 by the European Orthodontic Society (Evans R and Shaw W, Preliminary evaluation of an illustrated scale for dental attractiveness. Eur J Orthod 9: 314–318). IOTN aesthetic and dental health components reproduced courtesy of Orthocare.

Index of Complexity and Orthodontic Need (ICON)

Based on the IOTN and PAR indices a single index, the Index of Complexity and Need (ICON), has been developed to measure both treatment need and outcome of treatment (Daniels and Richmond, 2000). By combining five occlusal traits (IOTN Aesthetic Component, crossbite, upper arch crowding and spacing, buccal segment anteroposterior relationships, and anterior vertical relationship) with different weightings, a numeric score is given that can be used to ascertain need for treatment, the complexity of the treatment and the improvement resulting from treatment. This has been shown to be reproducible for treatment need and complexity but less so for outcome, due to low levels of agreement between examiners as to what constitutes acceptable treatment (Richmond and Daniels, 1998a, b).