1

1. The organisation of the orthodontic help to the population. A workplace of  the orthodont, equipment of an office (branch), dental laboratories. Work scheduling (clinical, preventive), conducting the medical-accounting documentation. Formation stages of the dental-jaw  device of the person in century aspect. Embriogenesis and its subsequent development in the prenatal period. Features of an oral cavity of the newborn. Possible damages during sorts and their prevention. Morphofunctional features of the temporo-mandibularis joints and chewing muscles at children. The characteristic of a time and constant bite. Features of formation of tooth arches and interocclusial parities.

2. Clinical inspection of the orthodontic patient. Value of the anamnes. Studying of hereditary diseases. Family tree drawing up. Studying of an anatomic structure of soft fabrics of an oral cavity, bridles of lips and tongue, depth of a threshold and a mouth floor, the form and position of a separate teeth, tooth alignments and their parity. Physiological and pathological forms of a bite, their obverse intraoral signs. A role of clinical tests at their definition.

3. Additional inspection methods, anthopometrical measurements on models by Pone, Korhaus, Snahina, etc.

Orthodontics relates to facial and occlusal development as well as to the supervision, interception and correction of occlusal and dentofacial anomalies. The practise of orthodontics, therefore, spans from birth into

adulthood, with current practice aiming to establish optimal and stable occlusai relationships with dentofacial harmony. An appreciation of facial and occlusal development is fundamental to understanding the possible aetiology of some orthodontic problems as well as being critical for their assessment and the planning of any likely treatment,

This chapter commences with an account of the rudiments of facial and occlusal development. It then details the elements of comprehensive clinical and cephalometric orthodontic assessment. Finally the principles of treatment planning are considered. Craniofacial growth and occlusal development

Learning objectives

You should

•   understand the pattern of growth of the catvarium, cranial base, the nasomaxillary complex and the mandible

•   be aware of what is meant by ‘growth rotations’ and their impact on the occlusion

•   know how occlusal development proceeds in the

‘average’ child.

An understanding of both craniofacial growth and occlusal development is essential to orthodontic practice as the former has a significant impact on the latter.

Craniofacial growth

Pattern of craniofacial growth

At birth the face and jaws are underdeveloped com­pared with those in the adult. More growth, therefore, occurs of the facial skeleton than of the cranial structure postnatally. Growth patterns have been established for four major body tissue systems – lymphoid, neural, gen­eral or somatic, and genital – and it is important to have an appreciation of these as some patterns are followed by tissues involved in craniofacial growth (Fig. 94). Lymphoid growth is rapid up to about 10 years but undergoes involution as the genital growth is accelerat­ing at puberty. Neural growth, however, is virtually complete by 6 to 7 years, while somatic growth increases in early childhood, then slows, before increasing dramatically at puberty.

The pattern of neural growth affects skeletal growth of the calvarium and orbit, whereas the somatic growth pattern is followed approximately by the mandible and maxilla. More precisely, the jaw growth pattern falls between that followed by the neural and general body tissues, with the mandible aligning itself more to the latter than the maxilla. The spurt in jaw growth at puberty almost coincides with the spurt in height, on average at 12 years in girls and 2 years later in boys, although considerable individual variation exists.

For both the maxilla and mandible, on average, growth in width is completed in advance of that in length, which ceases before growth in the vertical dimension. The lateral dimensions of the jaws and den­tal arches tend to alter minimally during puberty, as growth in width is largely completed before the growth spurt. Growth in length continues usually until about 14 to 15 years in girls and 17 to 18 years in boys, while ver­tical growth may extend into the late teens in females and into the twenties in males.

Growth continues into middle age, with changes in the vertical facial dimension predominating over those that occur anteroposteriorally, and least alteration tak­ing place laterally. In the early twenties, growth tends to resume slightly in females, with a backward mandibular rotation being common. Although a late resumption of growth is not witnessed in males, a forward rotating pattern of mandibular growth is usual in adulthood. Irrespective of the direction of mandibular growth rotation, compensatory adjustment occurs in the occlusal relationships. Facial growth should, therefore, be seen as a process that continues well into adult life and not as one that is complete in the late teens.

10 Age (years)

Fig. 94 Postnatal growth curves of various tissue types with superimposed maxillary and mandibular curves.

 

 

Control of facial growth

Both genetic and environmental factors impact on the regulation of craniofacial growth but the exact mech­anisms are unclear. In theory, genetic control may be expressed primarily via bone, cartilage or the soft tissue matrix. Bone is unlikely to be the primary determinant of its own growth, as sutural growth is reactive rather than inherently programmed. The nasal septum and the syn-chondroses of the cranial bones probably act as inde­pendent growth centres but the cartilage of the mandibular condyle appears to react to, rather than initiate, growth. The present concept is that bone and cartilage respond to soft tissue growth determined by functional needs (the so-called ‘functional matrix’ theory). While growth of the cranium and of the orbit in direct response to growth of the brain and of the eyes lend support to the theory, no similarly expanding structures exist within the middle and lower facial thirds. However, growth of the cranial base may be influenced by growth of the brain. The soft tissues, including the facial and masticatory muscles, are also possible contributors to downward and forward maxillary translation.

Growth prediction

At present no method is available to predict accurately the amount, direction and timing of facial growth. Instead, the assumption is usually made that for most patients whose direction and amount of facial growth are about average, the likelihood is that their growth pattern will follow the same pattern through orthodon­tic treatment.

Methods attempting to predict the pattern of facial growth to assist orthodontic treatment planning include:

•   superimposition of a template with average annual growth increments on the patient’s cephalometric tracing

•   digitisation of a cephalometric film followed by computer addition of average annual growth increments.

These data, however, are derived from children who did not receive orthodontic treatment, and as the amount and direction of growth may not be ‘average’ in an indi­vidual, the possibility of erroneous growth prediction is significant.

Growth of the craniofacial skeleton

Craniofacial growth can be considered conveniently in relation to the calvarium, the cranial base, the nasomax-illary complex and the mandible.

Calvarium

The precursors to the skull bones develop in membrane, and six open spaces (fontanelles) that exist at birth are eliminated by 18 months. Contact between the bones is at sutures. Bone apposition occurs at these periosteum-lined sites in response to brain growth and they fuse eventually in adulthood. The contour of the cranial vault also changes by periosteal remodelling at the inner and outer surfaces.

Cranial base

The cranial base forms initially in cartilage, which is transformed to bone by endochondral ossification. Sutural growth and surface remodelling occur laterally in response to brain growth. Of greater significance are primary cartilageous growth sites: sphenoethnoidal, intersphenoid and most importantly the spheno-occipital synchondrosis. The sphenooccipital synchondrosis grows until the mid-teens, having a profound impact on the anteroposterior skeletal pattern; it finally fuses at about 20 years of age. Because of its location in front of the temporomandibular joints but behind the anterior cranial base, both growth in length and in shape of the cranial base affects the maxillary-mandibular relationship. A long cranial base or large cranial base angle is associated with a class II skeletal pattern, while the converse is generally asso­ciated with a class III pattern (see Section 8.3 for definitions).

Nasomaxillary complex

The frontal process and a mesenchymal condensation in the maxillary processes of the first pharyngeal arch form the maxilla’ which then ossifies intramem-braneously starting in the lateral aspects of the car­tilagenous nasal capsule. Growth of the maxilla occurs via boneapposition at the circum-maxillary suture system passive displacement from its articulation with the cranial base

•   surface remodelling.

Growth at the maxillary sutures assumes a greater role after age 7, when neural growth is complete and growth at the cranial base synchondroses lessens. As the maxilla moves downwards and forwards in response to growth of the surrounding soft tissues, the space opened at the superior and posterior sutures is obliterat­ed by bone deposition on either side of the suture. Resorption of the anterior maxillary surface occurs simultaneously. Displacement of the maxilla inf eriorly is accompanied by bone resorption from the nasal floor and deposition on the palate, while the alveolar process also develops vertically with tooth eruption. Bone is deposited also at the midline suture in response to later­al displacement of the maxillary halves, leading to an increase in midfacial width. Growth is complete by about 17 years in males and on average 2 years earlier in females.

Mandible

Like the maxilla, the mandible is derived from the first pharyngeal arch. It begins development as a mesenchy­mal condensation just lateral to Meckel’s cartilage. Bone formation proceeds intramembraneously, spreading posteriorly along Meckel’s cartilage without directly replacing it by newly formed bone. Condylar cartilages are formed distant to the mandibular body but fuse with it at about 4 months. These secondary cartilages are not primary instigators of mandibular growth but respond to other controlling influences. Endochondral ossifica­tion at the condyles accounts, in part, for mandibular growth. Elsewhere, bone apposition and remodelling are responsible for an increase in size and shape. As the mandible is translated downwards and forwards, largely in response to muscular forces, contact with the base of the skull is maintained by cartilagenous growth at the condylar heads, which increases ramal height. The alveolar processes also increase in height with tooth eruption.

Mandibular length is increased by periosteal appo­sition along the posterior border and simultaneous bone removal from the anterior aspect of the ramus. Increase in mandibular width occurs principally by remodelling posteriorly. The chin is almost passive as a growth area but by the late teenage years it has become more prominent in response to forward mandibular translation. On average, mandibular growth is complete by about 17 years in females and 2 years later in males, but it can proceed for longer.

Growth rotations

The trend is for the facial skeleton to grow downwards and forwards away from the cranial base, although implant studies have indicated that rotations of both the maxilla and mandible occur during growth. These have more marked effects on the mandible than on the maxilla, where remodelling disguises their true impact. Mandibular growth rotations represent a growth imbalance in anterior and posterior facial heights. The direction of condylar growth and the vertical magnitude of growth at the spheno-occipital synchondrosis influence posterior face height. Growth of the masticatory and suprahyoid musculature, including associated fascia and influenced partly by the vertical growth changes in the spinal column, affects the anterior face height together with the eruption of teeth.

While mandibular growth rotations occur in all individuals, these are particularly different where the vertical facial proportions are markedly reduced or increased. A forward rotation, characterised by greater growth in posterior than in anterior facial height, is more common than a posterior growth rotation, where the change in facial height ratio is opposite to that observed in forward rotation (Fig. 95). Where forward rotation of the mandible is extreme

•   the lower border is convex with a reduced mandibular plane angle

•   the lower anterior face height is reduced

•   the overbite is deep

Soft tissue growth

At birth, the orofacial musculature is well developed to allow suckling and breathing, and it soon responds to other functional demands of mastication, speech, facial expression and changes to the swallowing pattern. The light pressures from the lingual and buccolabial muscu­lature affect tooth position, guiding the teeth towards a functional relationship and compensating, where pos­sible, for any skeletal discrepancy. However, where a severe skeletal discrepancy or abnormal soft tissue behaviour exists, for example a lip trap with a class II division 1 malocclusion, the dentoalveolar compensa­tory mechanism will be insufficient.

Facial musculature lengthens with facial growth, and these soft tissue influences may be inherently respon­sible for the skeletal growth processes. The likelihood of lip competence increases during the late stages of facial growth, but soft tissue changes continue into middle age with the chin and nose assuming relatively greater prominence as the lips tend to flatten.

Occlusal development

What follows is an account of normal occlusal develop­ment: the changes one would expect to see in the ‘average’ child. It is important to appreciate the range that exists withiormal boundaries, so that developing problems may be recognised early and appropriate orthodonticb intervention planned, if required. A thorough knowledge of the calcification and eruption dates of the 20 primary and 32 permanent teeth is essential (see Tables 11 and 12, p. 170). As well as allowing comparison of dental and chronological age, this information also helps to identify the timing of any insult that has led to alterations in the enamel or dentin mineralisation and indicates if a tooth that is absent radiographically is likely to develop.

Development of the deciduous dentition

The gum pads, containing the deciduous teeth, enlarge and widen following birth, with the lower lying slightly behind the upper by the time the first deciduous teeth (lower incisors) start to erupt at about 6 months of age. These are followed closely by the other incisors. The first deciduous molars erupt 3 to 4 months later, followed by the deciduous canines and the eruption of the second deciduous molars at about 3 years. The incisors tend to be upright, and anterior spacing is normal. Spacing is most common mesial to the upper canine and distal to the lower canine – the anthropoid or primate spaces. With 1-2 mm increase in the intercanine distance, spac­ing between the incisors often increases as the child grows. In the absence of generalised spacing of the deciduous teeth, crowding of the permanent teeth is likely. The overbite, which is often initially ‘deep’ in terms of lower incisor crown coverage, reduces and by 5 years of age an edge-to-edge occlusion with incisor attri­tion is common.

Development of the permanent dentition

At about 6 years, the eruption of the first permanent molars, followed by the permanent incisors, signifies the transition from the primary to the permanent dentition,commonly referred to as the ‘mixed dentition phase’. The permanent successors are slightly larger than the primary teeth and the first permanent molars need to be accommodated. Existing space is present between the deciduous teeth. Additional space is provided by minor modifications in arch length, arch width and intercanine distance (Table 26). Once the primary dentition is fully erupted, however, the dental arch size remains more or less constant anteriorly apart from a modest change in shape with some growth in the intercanine distance. In addition, growth at the back of the arches is necessary to accommodate the permanent molars and to maintain the arch relationship while the face grows vertically.

The permanent lower incisors develop lingual to their predecessors and are frequently misaligned on eruption, but this usually resolves with intercanine growth. The upper anterior teeth develop palatal to their deciduous predecessors and are accommodated

•   by the existing spacing in the arch

•   by erupting downwards and slightly forward so that they are placed on a wider arc

•   by a small increase in intercanine distance (Table 26).

The upper permanent lateral incisors usually move distally and labially with eruption of the central inci­sors, but they may be trapped palatally in crowded arches. The upper central incisors are often distally inclined when they first appear. An associated diastema tends to reduce as the lateral incisors erupt. At this time, the upper central and, to a greater extent, the lateral incisors are divergent, the latter because of pressure on their roots from the unerupted canines; this is often referred to as ‘the ugly duckling’ phase of dental development.

The maxillary canines migrate from their palatal developmental position to lie labially and distally

Table 26 Dental arch development
Characteristic	Measurement	Developmental changes
Arch length	Perpendicular distance from 1Д contact point to a	Maxilla:    slight increase 6-10 years; followed by
	line contacting the distal surfaces of e/e or 5/5	a 1-2 mm decrease Mandible: no increase 6-10 years; at 10-17 years 1-2 mm decrease
Arch circumference	Line drawn through the buccal cusps and incisal	Maxilla:    -1 mm increase in male: -0.5 mm
	edges of the teeth from the distal surface of e/e or	increase in female
	5/5	Mandible: -3.5 mm decrease in male: -4 mm decrease in female
Intercanine width	Distance between the cusp tips ot c/c or 3/3	Maxilla:     -1-2 mm from 3-6 years: -3.5 mm from 6-12 years Mandible: -1-2 mm from 3-6 years: -3 mm from 6-10 years
Arch width	Distance from the palatal/lingual cusps of second	Maxilla:    -2-3 mm increase from 3-18 years:
	molars or 5	greater in males than females Mandible: -3.6 mm increase from 3-18 years in both mates and females

above the roots of the lateral incisors, leading to approximation of the incisor crowns as they erupt.

The combined mesiodistal widths of the deciduous canines and molars in each quadrant are slightly greater than those of the permanent canines and premolars. This difference in dimension is known as the ‘leeway space’ and is about 1 mm in the upper arch and 2.5 mm in the lower arch. The larger leeway space in the lower arch, probably in combination with mandibular growth, allows greater forward movement of the lower first permanent molar, converting a ‘flush terminal plane’ relationship of the deciduous molars to a class I occlu­sion (see below).

The static occlusal and functional relations of the normal permanent dentition are:

•   the mesiobuccal cusp of the upper first permanent molar lies in the buccal groove of the lower first permanent molar (class I occlusion)

•   upper and lower incisors are slightly proclined, with the lower incisors occluding on the cingulae of the upper incisors with an average overjet and overbite of 7.-Л mm

•   there is no spacing or rotations, and marginal ridges are level

•   the occlusal plane is flat or with a slight curve of Spee

•   each tooth, with the exception of the lower incisors, is slightly mesially inclined

•   the canines through to the molars are inclined lingually

•   centric relation should coincide with centric occlusion

•   a working side canine rise or group function should be present on lateral excursions with no occlusal contact on the non-working side; the incisors should only contact in protrusion.

Table 27 Factors implicated in late lower incisor crowding³

Factors

Effects/affected tissues

Increase in mandibular prognathism Mandibular growth rotations Minimal forward maxillary growth

Increase in soft tissue tone of lips and cheeks Transseptai fibre contraction

Lack of approxima! attrition Dentoalveolar disproportion Tooth size Mesial drift secondary to anterior

component of occlusal force, eruptive

force of posterior teeth Uprighting of posterior teeth in response

to increase in lower facial height

^aTends to be greater in females than males.

Malocclusion: classification and aetiology

Learning objectives

You should

•   be able to classify the first molar and incisor relationship

•   know how to apply and categorise malocclusion according to the Index of Orthodontic Treatment Need (IOTN)

•   be aware of how the outcome of orthodontic treatment may be assessed.

Maturational changes in the occlusion

The occlusion of any child must be seen as dynamic and responding to changes in the facial skeleton. As the face continues to grow throughout the late teens and into adulthood, changes in the dentition and occlusion follow.

•   There is an increase in lower incisor crowding. This has been observed even in children with previously well aligned, spaced arches and can be regarded as normal. Factors implicated in its aetiology are listed in Table 27.

•   There is an increase in the interincisal angle, with uprighting of the incisors.

•   A tendency for the overbite to reduce is seen.

•   A slight increase occurs in mandibular prognathism in males and in mandibular retrusion in females.Malocclusion is an unacceptable deviation either aes­thetically and/or functionally from the ideal occlusion. Prevalence of malocclusion varies with age and racial origin as well as according to the assessment methods, but not all malocclusion requires treatment.

Classification of malocclusion

Classification for diagnosis

Angle’s classification

Angle’s classification is based on the molar relationship (Fig. 96).

Class I (also referred to as normal occlusion or neutrocclusion). The mesiobuccal cusp of the upper first permanent molar occludes in the buccal groove of the lower first permanent molar. Discrepancies no greater than half a cusp width were also regarded as class I by Angle.o

 

Class

Class II

Class III

Class

Class II division 1

Class II

division 2

Class III

Fig. 96 Angle’s classification based on first molar relationships.

Fig. 97 British Standard Institute classification based on incisor relationship.

Class II (also referred to as postnormal occlusion or distocclusion). The mesiobuccal cusp of the upper first permanent molar occludes anterior to the buccal groove of the lower first permanent molar.

Class III (also referred to as prenormal occlusion or mesiocclusion). The mesiobuccal cusp of the upper first permanent molar occludes posterior to the buccal groove of the lower first permanent molar.

Angle believed that the anteroposterior dental base rela­tionship could be assessed reliably from the first perman­ent molar relationship, as its position, he maintained, remained constant following eruption. As this tenet is incorrect and difficulties arise in classification where mesial drift or loss of a first permanent molar has occurred, other classification systems are now used to categorise the anteroposterior dental base relationship.

British Standard Institute classification

The British Standard Institute classification relates to the incisor relationship (Fig. 97).

Class I. The lower incisor edges occlude with, or lie immediately below, the cingulum plateau (middle third of the palatal surface) of the upper incisors.

Class II. The lower incisor edges lie posterior to the cingulum plateau of the upper incisors.

Division 1. There is an increase in overjet and the upper incisors are proclined or of average inclination.

Division 2. The upper central incisors are retroclined; the overjet is usually minimal but may be increased.

Class III. The lower incisor edges lie anterior to the cingulum plateau of the upper incisors. The overjet is reduced or reversed.

Index of Orthodontic Treatment Need (IOTN)

The IOTN was developed to help to identify those mal-occlusions most likely to benefit in dental health and appearance from orthodontic treatment. It comprises two components.

The dental health component Malocclusion is cat­egorised into five grades (Table 28) based on the severity of occlusal characteristics that could increase the mor­bidity of the dentition and impair function. Grading, in relation to treatment need, is according to the worst fea­ture of a malocclusion, as follows:

To facilitate the grading process, a ruler (Fig. 98) has been developed. Occlusal features are assessed in the following order:

•   missing teeth (M)

•   overjet (O)

•   crossbite (C)

•   displacement of contact points, i.e. crowding (D)

•   overbite (O)4 -ms—55 Defect of CLP

5 Non eruption of teeth

5 Extensive hypodontia

4 Less extensive hypodontia

4 Crossbite >2 mm discrepancy

4 Scissors bite

4 O.B. with G + P trauma

3 O.B. with NO G + P trauma

3 Crossbite 1-2 mm discrepancy

2 OB. >      —

2 Dev. from full interdig

2 Crossbite < 1 mm discrepancy

DISPLACEMENT OPEN BITE V

4   3   2   1Fig. 98 The IOTN ruler. Occlusal features are assessed in the order given by the acronym ‘MOCDO’. M = missing teeth; О = overjet; С = crossbite; D = displacement of contact point (i.e. crowding); О = overbite.O

Table 28 The Index of Orthodontic Treatment Need: dental health component

Grade CharacteristicsNone       Extremely minor malocclusions including displacements <1 mm

1Little       a.  Increased overjet >3.5 mm but <6 mm with competent lips

b. Reverse overjet >Q mm but <1 mm

с   Anterior or posterior crossbite with <1 mm discrepancy between retruded contact position and intercuspal
position

d. Displacement ot teeth >1 mm but <2 mm

e. Anterior or posterior open bite >1 mm but <2 mm

f. Increased overbite >3.5 mm without gingival contact

g. Prenormal or postnormal occlusions with no other anomalies; includes up to half a unit discrepancy.

a. Increased overjet >3.5 mm but <6 mm with incompetent lips

b. Reverse overjet >1 mm but <3.5 mm
с  Anterior or posterior crossbites with >1 mm but <2 mm discrepancy between retruded contact position

and intercuspal position

d. Displacement of teeth >2 mm but <4 mm

e. Lateral or anterior open bite >2 mm but <4 mm

f. Increased and complete overbite without gingival or palatal trauma

a. Increased overjet >6 mm but <9 mm

b. Reverse overjet >3.5 mm with no masticatory or speech difficulties
с   Anterior or posterior crossbites with >2 mm discrepancy between retruded contact position and

intercuspal position

d. Severe displacements of teeth >4 mm

e. Extreme lateral or anterior open bites >4 mm

f. Increased and complete overbite with gingival or palatal trauma
h.  Less extensive hypodontia. requiring prerestorative orthodontics or orthodontic space closure to obviate the need for a prosthesis I.    Posterior lingual crossbite with no functional occlusal contact in one or both buccal segments m. Reverse overjet >1 mm but <3.5 mm, with recorded masticatory and speech difficulties t.   Partially erupted teeth, tipped and impacted against adjacent teeth x.   Supplemental teeth

a.  Increased overjet >9 mm

h.  Extensive hypodontia with restorative implications (more than one tooth missing in any quadrant requiring prerestorative orthodontics i.    Impeded eruption of teeth (with the exception of third molars) owing to crowding, displacement, the presence of supernumerary teeth, retained deciduous teeth and any pathological cause m. Reverse overjet >3.5 mm with reported masticatory and speech difficulties p.  Defects of cleft lip and palate s.  Submerged deciduous teeth giving the acronym MOCDO. With practice it is possible to ascribe reliably and easily the treatment need category to a given malocclusion.

The aesthetic component The aesthetic component of the IOTN (Fig. 99) uses a set of 10 photographs of anteri­or teeth in occlusion with increasing aesthetic impair­ment to grade the dental attractiveness of an individual malocclusion. Colour or black and white photographs can be used to apply a grade to the malocclusion clinical­ly or from study models. The assessment is made by selecting the photograph thought to match the aesthetic handicap of the patient, but judgement is very subjec­tive. The need for treatment is categorised, by score (Fig. 99). Because of the lack of objectivity in assessing the aes­thetic component, treatment need is based primarily on the dental health component of IOTN.

To assess treatment outcome Assessment can be car­ried out objectively by applying the dental health com-ponent of IOTN and subjectively by application of the aesthetic component. In addition, the Peer Assessment Rating (PAR) may be recorded. A score is given to the pre- and post-treatment occlusion from the study mod­els. Six aspects are assessed and a weighting given to each, in accordance with their perceived importance as judged by current UK opinion. The components and their weightings (by which the score is multiplied) are: buccal segment alignment (xO), upper/lower anterior segment alignment (xl), buccal occlusion (xl), overjet (x6), overbite (x2) and centreline (x4). Measurement is facilitated by use of a specially designed ruler.

The percentage change in PAR score, obtained from the difference in pre- and post-treatment scores, is a measure of treatment success. A reduction of greater than 70% indicates a ‘greatly improved’ occlusion while a ‘worse/no different’ assignment is indicated by less than or equal to 20%.

Malocclusion

A general overview of the aetiology of malocclusion is presented here while specific aspects related to the aetiol­ogy of each malocclusion type are considered in Chapter 9.

The aetiology of malocclusion is often the result of several interacting factors. These are principally genetic and environmental, although the precise role of inher­ited factors is not fully understood. Whereas the cranio-facial dimensions and both size and number of teeth are largely determined genetically, the dental arch dimen­sions are influenced more by environmental factors.

Specific congenital defects with a genetic basis, which involve the maxilla or mandible, are rare, as is malocclu­sion caused primarily by trauma or pathology.

Skeletal problems

The majority of anteroposterior skeletal problems are caused by inherited jaw proportions, which are strongly genetically determined. Inherited characteristics, forexample mandibular deficiency, account for almost all of moderate class II malocclusion, while the added insult of environmental soft tissue influences is likely in more severe cases. Both maxillary deficiency and mandibular prognathism appear to contribute equally to the aetiology of marked class III malocclusion. In addition, a strong racial and familial tendency to mandibular prognathism exists, although mandibular posturing, possibly caused by tongue size, may stimu­late growth and influence jaw size secondarily.

Vertical jaw proportions are also inherited, but soft tissue postural effects, for example anterior tongue position or mandibular postural changes induced by partial nasal obstruction, may contribute in particular to anterior open bite. Other environmental influences such as a high lower lip line may contribute to deep overbite.

Crowding

Crowding is the most common orthodontic problem, and is caused in part by a reduction in jaw andtooth size over the centuries. Also implicated is interpopulation breeding, with independent inheritance of jaw and tooth characteristics. This facilitates the development of crowding as arch width is influenced by jaw size, which is under tight genetic control.

Environmental influences must also be instrumental in the aetiology of crowding, perhaps because a softer diet requires less powerful jaw function, precipitating a reduction in jaw size. Early loss of primary teeth may also increase or create crowding. In particular, soft tissue pressure of sufficient duration in combination with the developmental tooth position may be responsible for a localised crossbite or malalignment. A unilateral cross-bite with displacement is often caused by a functional alteration, but it is usual for a skeletal crossbite to have an additional genetic input.

 

Patient assessment in orthodontics

Learning objectives

You should

•   know what to ask about in the orthodontic history and how to conduct an orthodontic assessment

•   be confident in basic cephalometric analysis and interpretation.

Orthodontic diagnosis consists of a list of all aspects that deviate from normal in relation to a particular occlusion. It is a prelude to treatment planning as it allows the relationship between the various factors and their likely impact on treatment and prognosis to be considered. Diagnosis is based on the accurate gather­ing of information about the patient from a logical case assessment.

Assessment

Timing

At 7 to 8 years, a careful assessment of the developing occlusion should be undertaken to note, in particular, the form, position and presence of the permanent inci­sors and to plan appropriate intervention should an abnormality be detected that is likely to interfere with the normal eruption sequence. The prognosis of the first permanent molars should be assessed routinely from age 8, and palpation of the maxillary permanent canines is carried out on a regular basis from about 10 years. Early detection of a skeletal discrepancy will allow also for optimal timing of treatment to maximise growth potential, but in most children assessment is delayed until the permanent dentition has erupted.All general dentists should be able to carry out a basic orthodontic assessment for their patients and recognise when referral to a specialist is appropriate. When dental and/or occlusal development deviates from normal, or when significant discrepancies in established dentofacial or occlusal relationships con­cern the patient and may compromise dental health long term, referral is indicated.

Apart from basic personal details, the referral letter should include specific reference to:

•   the patient’s perception of the problem

•   their attendance record

•   their level of dental awareness including that of their parents (if appropriate)

•   the oral hygiene status

•   the likely prognosis of restored or traumatised teeth.

Recent radiographs and a set of trimmed current study models registered with the patient in centric occlusion should be forwarded with the referral. Study models are essential for diagnosis; if none are available, two appointments will be necessary to allow collation of the information required to make an accurate assessment of the case. At a first visit, impressions should be taken of the dental arches and the occlusion recorded with a wax registration so that study casts can be available for inspection at the second visit. Orthodontic assessment comprises three stages:

•   a complete history

•   a thorough and systematic clinical examination

•   collating relevant information from appropriate special investigations.

Demand for treatment

The demand for orthodontic treatment is influenced by two main factors:

•   patient/parent factors, which include patient gender, age, level of self-esteem, self- and peer-perception of any occlusal or skeletal discrepancy, social class and parental desires

•   awareness by dental professionals and the health care system.

In general, demand for treatment is greatest when the orthodontistpopulation and orthodontist:general dentist ratios are small. Overall demand is increasing in adults, is higher in females, in those from better socioeconomic backgrounds and when a lower orthodontist:population ratio exists, as appliances become more common and their acceptance increases.

History

Initially the dentist must identify:the patient’s reason for attendance

•   who raised the question of treatment

•   the attitude to treatment.

It is important to document if the patient is unconcerned with the appearance of their teeth, particularly in the presence of obvious malocclusion, as any attempt to persuade the patient to undertake treatment is likely to be met with indifference. Attitude to treatment is best assessed from response to enquiries about their percep­tion of orthodontic treatment for their peers, and by observing carefully their reaction when shown photo­graphs or examples of appliances.

Medical history

A health questionnaire should be completed by each patient or their parent, and the findings verified by a clinical interview. A number of conditions may impact on orthodontic treatment.

Rheumatic fever/congenital cardiac defects

Antibiotic cover will be required prior to band place­ment and extractions in patients with a history of rheumatic fever. For all congenital cardiac defects, it is wise to consult the patient’s cardiologist to ascertain the need for antibiotic prophylaxis.

Recurrent oral ulceration

Appliance therapy should be avoided until this condi­tion has been investigated thoroughly. Depending on the frequency and nature of ulceration, limited appli­ance treatment may be possible.

Epilepsy

Because of the risk of airway obstruction from appliance parts fractured during an epileptic attack and the diffi­culty with tooth movement in the presence of gingival hyperplasia, no orthodontic appliance should be fitted until the epilepsy is well controlled and the gingival condition healthy.

Diabetes

Diabetic patients are more prone to periodontal break­down, and active appliance therapy should be withheld until the periodontal condition is sound and the diabetes is stabilised.

Hay fever

Hay fever may interfere with the wearing of functional appliances over the summer months. An alternative approach to treating the malocclusion may be sought.

Nickel allergies

Although rare, patients sensitised to nickel are at risk of developing a severe allergic reaction to appliance com­ponents that contaiickel and these must be avoided.

Bleeding diatheses

If extractions are necessary, special medical arrange­ments will need to be in place.

Severe physical/mental handicap

In selected patients, extractions only may produce an improvement in dental aesthetics and facilitate tooth-cleaning measures. Appliance therapy is invariably not a viable option.

Dental history

The nature, extent and frequency of previous dental treatment together with the level of patient co­operation should be recorded, along with details of daily oral hygiene practices. A history of early loss of primary teeth or of incisor trauma should be noted. If orthodontic treatment has been carried out previously, details relating to extractions and appliance type should be recorded. If treatment was abandoned, the patient must be questioned carefully for the reasons. For the child patient, enquiries about orthodontic treat­ment for other siblings, and their co-operation with appliances, may be helpful in indicating the level of family dental awareness and likely support if treatment is offered. It is also wise to ask at this stage if there is any history of temporomandibular joint symptoms including pain, muscle tenderness or difficulty with mouth opening and to record if the patient is aware of any bruxing habit.

Social history

The distance at which the family live and an estimate of travelling time to and from potential appointments should be noted. Access to transport, the ease with which a responsible adult can accompany the child patient, together with information relating to forthcom­ing events that may influence attendance, are impor­tant.

Clinical examination

Before the child patient takes a seat in the dental chair it is often worthwhile to attempt to estimate their chrono­logical age from their height and general level of phys­ical maturity. This may give some indication of future growth potential. If the patient is accompanied by a par­ent, obvious familial occlusal traits (e.g. upper median diastema) may be observed also. The purpose of the examination is to record and assess facial, occlusal and functional aspects of a patient in order to request appro­priate diagnostic aids. An extraoral followed by an intraoral examination should be performed.

 Extraoral examination

The skeletal pattern, soft tissues of the lips and tongue, speech, temporomandibular joints and mandibular path of closure should be assessed and the presence of any habits noted.

The relationship of the mandible to the maxilla should be assessed in all three planes of space: antero-posteriorly, vertically and laterally. Before proceeding it is important to ensure that

•   the patient is seated upright with the head in the natural postural position or with the Frankfort plane (a line joining the upper border of the external auditory meatus to the inferior aspect of the bony orbit) horizontal. Natural head posture may be obtained by asking the patient to look straight ahead focusing on the horizon

•   the lips are in repose

•   the teeth are in centric occlusion.

Anteroposterior plane

The relationship of the mandible to the maxilla in the anteroposterior plane is assessed by observing the patient in profile. In most cases, an indication of the skeletal pattern in this dimension may be gained from the soft tissue facial profile allowing the following classification to be made (Fig. 100):

Class I: the mandible lies 2-3 mm behind the maxilla

Class II: the mandible is retruded in relation to the

maxilla

Class III: the mandible is protruded in relation to the

maxilla.

No indication, however, is given as to where a skeletal discrepancy may lie as the classification reflects solely the position of the mandible and the maxilla relative to each other.

This method is not always reliable because of varia­tion in lip thickness, and palpation of the alveolar bases over the apices of the upper and lower incisors in the midline has been claimed to give a better estimate of skeletal pattern. In essence, any significant discrepancy in the anteroposterior dental base relationship should be investigated more thoroughly by taking and analysing a lateral cephalometric film (see below).

Vertical plane

Two assessments of the vertical relationship of the face should be made (Fig. 101).

Assessment of lower face height In a well-balanced face, the upper face height (distance from the mid-eyebrow level to the base of the nose) should be equal to that of the lower face height (base of the nose to the inferior aspect of the chin). The lower face height may, therefore, be assessed as average (when these

measure­ments are equal), reduced (when lower face height is less than upper face height) or increased (when lower face height is greater than upper face height).

Assessment of the Frankfort-mandibular planes angle (FMPA) With a finger along the inferior aspect of the mandible and a ruler placed along the Frankfort plane, these two lines can be projected backward in the imagination to give an estimate of the FMPA. Where the vertical dimensions of the face are normal, both lines should meet at the back of the skull (occiput) and the FMPA is regarded as average. If the FMPA is reduced the lines will meet beyond occiput and if the FMPA is increased they will meet anterior to it.

Transverse plane

Obvious facial asymmetry may be observed by standing directly behind the patient and looking down across the face, checking the coincidence of the midlines of the nose, upper and lower lips and midpoint of the chin. Alternatively, the face may be assessed from in front.

Class IClass II

Fig. 101  Assessment of the vertical facial relationships: lower facial height (LFH) compared with upper facial height (UFH) and Frankfort-mandibular planes angle (FMPA).most people, some degree of facial asymmetry is present and may be regarded as normal. Marked asymmetries, however, require further investigation. The location and extent of any marked asymmetry, e.g. upper, middle or lower facial third, should be recorded

Soft tissues of the lips and tongue

Seven aspects should be assessed in relation to the lips and tongue:

•   lip form and fullness: form may be described as vertical, average or everted, and fullness in terms of whether the lips are full or thin

•   lower lip position in relation to the upper incisors: the upper incisors may lie behind, on, or in front of the lower lip

•   lower lip coverage in relation to the upper incisors: at rest, on average, the lower lip should cover at least one third to one half of the upper incisor teeth

•   upper lip level in relation to the upper incisors: the length of the upper lip and amount of exposure of the upper incisors at rest should be assessed; in males 1-2 mm display of the incisors is average, with slightly more in females

•   whether the lips are together (competent) or apart (incompetent) at rest: if lips are apart, it should be noted if they are slightly or wide apart, and if the patient makes any habitual effort to hold them together; markedly incompetent lips confer a poor prospect for stability of a corrected overjet in patients with class II division 1 malocclusion

•   tongue position at rest: should be assessed throughout the examination and particular note made if it lies in contact with the lower lip as this is likely to contribute to an incomplete overbite

• lip and tongue behaviour during swallowing, speech
and facial expression: abnormal tongue activity on
swallowing, or marked hyperactivity of the lower lip
on smiling, should be noted, as should the presence
of a marked ‘gummy’ smile.

Speech

Obvious defects such as a lisp will be noticed during general questioning of the patient, and specific assess­ment by a speech therapist is rarely indicated in patients referred for orthodontic advice.

Habits

The tell-tale signs of finger- or thumb-sucking habits are generally easy to ascertain:

•   proclination of maxillary incisors

•   retroclination of mandibular incisors

•   incomplete overbite or open bite, often asymmetric

•   increase in overjet

•   tendency to bilateral buccal segment crossbite, often resulting in a unilateral crossbite with displacement.

Effects vary depending on whether the finger or thumb is placed in a median or paramedian position and on whether one or more digits are sucked. An adaptive tongue thrust is common. Inspection of the hands will usually identify the offender. The patient and their par­ent should be made aware of the effects of the habit on the dentition and occlusion. Note also if the patient is a nailbiter or bruxist.eatm

Temporomandibular joints

Opening and lateral mandibular movements should be assessed by first observing the patient from in front and second by palpation of the condylar heads while listen­ing for the presence of crepitus, or a joint click. Normal findings should be recorded as a baseline for future ref­erence. Palpation of the masticatory muscles is not required unless symptoms are present.

Mandibular path of closure

The path of closure from rest position to maximum interdigitation should be assessed, noting any anterior or lateral mandibular displacement. This may be diffi­cult to detect in a young and anxious patient where a habitual posture has developed to avoid a premature contact, often from an instanding incisor. Applying gentle backward and upward pressure to the chin while instructing the patient to touch the back of the mouth with the tip of the tongue usually gets around this problem.

Intraoral examination

The soft tissues of the buccal mucosa, floor of the mouth, tongue and the attachment of the maxillary labi­al frenum should be observed and any abnor­mality noted. A general dental examination should be carried out prior to assessing the individual arches of teeth and the occlusal relationships. The following should be charted.

•   Standard of oral hygiene and caries rate.

•   Gingival condition, paying particular attention to any area of gingival recession or attachment loss.

•   All erupted teeth, noting those with abnormal shape or size. A quick way to assess if an anterior tooth-size discrepancy exists is to compare the mesiodistal widths of the upper and lower lateral incisors. The upper laterals should be larger than the lower incisors, but only discrepancies of greater than

1.5 mm should be recorded as these are likely to affect treatment planning.

•   Teeth with untreated caries, large restorations or previous trauma. The condition of the first permanent molars should be examined, in particular, and a record made of any cervical decalcification (buccally on the uppers or lingually on the lowers), which may indicate a poor prognosis.

•   The presence of erosion on the palatal surfaces of the upper incisors. In these cases, the patient should be questioned about frequency of dietary intake of acidic or carbonated drinks.

•   Marked attrition of the dentition. This is likely to be present in individuals with a bruxing habit.The lower arch followed by the upper arch should then be assessed independently. It is very helpful to refer to the study models during this part of the examination.

Assessment of the upper and lower arches

Angulation of the lower labial segment to the mandibular plane. By placing the index finger of the right hand along the mandibular body and gently everting the lower lip, the angulation of the lower incisors may be assessed as average (if they appear to make almost a 90° angle with the mandibular plane), retroclined or pro-clined.

Angulation of the upper incisors relative to the Frankfort plane. With the patient sitting upright and a finger or ruler placed along the Frankfort plane, the inclination of the upper incisors may be assessed as retroclined, aver­age or proclined.

Presence and site of spacing or crowding including the magnitude of each. The degree of spacing/crowding may be assessed by performing a space analysis on the study models. This only takes account of any space dis­crepancy anterior to the first permanent molars and is usually carried out as follows:

For each quadrant. Measure with dividers the distance from the mesial surface of the first permanent molar to the distal surface of the permanent lateral incisor, and from there to the midline. Add these measurements for each arch to give the space available.

Measure the mesiodistal width of each tooth and add these together to calculate the space required where the canines and premolars have not erupted, on aver­age 21 mm or 22 mm per quadrant in the lower or upper arch respectively is an estimate of their space requirements.

Quantify any surplus deficit. Subtract the space avail­able from the space required. Individual arches may then be classified as uncrowded, mildly crowded (0-4 mm), moderately crowded (>4 but <7mm) or severely crowded (>7 mm).

General alignment of the teeth. Include here the pres­ence of rotations (classified by the surface furthest from the line of the arch).

Inclination of the canines. These may be described as upright, mesially inclined or distally inclined.

Assessments with the teeth in occlusion With the teeth in maximum intercuspation, the remaining aspects should be recorded.

Incisor relationship. This may be categorised accord­ing to the British Standards Institute classification (see Section 8.2).

Over jet (the horizontal overlap of the upper over the lower incisors). This is usually measured (in millimetres) from the central incisor teeth. If there is a marked difference in the overjet for each maxillary central incisor, both meas­urements should be noted.

erbite (vertical overlap of the upper over the lower inci­sors). This is measured (in millimetres) – an indication should be given as to whether it is complete, incomplete or if there is an anterior open bite or traumatic overbite. The overbite is complete when the lower incisors occlude with the opposing maxillary teeth or with the palatal mucosa; it is incomplete if there is no contact with the opposing surfaces. The extent (in millimetres) of an anterior open bite should be noted and the site of mucosal ulceration recorded (either palatal to the upper incisors, labial to the lower incisors or in both locations) in the presence of a traumatic overbite.

Centrelines. Upper and lower centrelines should be coincident with the midline of the face, and any centre­line shift should be recorded (in millimetres) with a note to indicate the direction of the shift.

Molar relationship. Providing a corresponding molar is present in the opposing arch, the molar relationship may be categorised according to Angle’s classification (see Section 8.2).

Where the first permanent molar is missing in either arch, the premolar or canine relationship may be assessed.

Canine relationship. This should be recorded in add­ition to the molar relationship, as although they are often the same, on occasion discrepancies are present.

The presence of anterior or posterior crossbite (bucco-lingual discrepancy in arch relationship). Is the crossbite buccal or lingual, bilateral or unilateral (Fig. 102)? For the premolar and/or molar teeth, a buccal crossbite exists when the buccal cusps of the lower tooth occlude buccally to the buccal cusps of the upper teeth. A lingual crossbite exists when the buccal cusps of the lower tooth occlude lingually to the palatal cusps of the upper teeth. A unilateral crossbite affects teeth on one side of the arch while teeth on both sides of the arch are affected with a bilateral crossbite. Often a unilateral crossbite is associated with a mandibular displacement (Fig. 103).

Special investigations

Vitality tests

Traumatised incisors or other teeth with suspect vitality should be electric pulp tested and their status recorded.

Radiography

All radiographs should be justified on clinical grounds. Radiographs forwarded by a referring practitioner may provide sufficient information to supplement the clinical findings but often the following views are needed.

A dental orthopantogram (DPT) or right and left lateral oblique views. These are good screening radiographs. The bony architecture of the maxillary and mandibular bases as well as that of the mandibular condyles (if included) should be checked first to exclude any dentally related, or other, pathology. All teeth should be identified and counted. It is a good routine to start in one area, e.g.

Fig. 102 Bucco-lingual discrepancies, (a) bilateral buccal crossbite. (b) bilateral lingual crossbite

Fig. 103 Unilateral buccal crossbite with mandibular displacement and associated lower centreline shift, (a) Cusp-to-cusp molar contact, (b) Maximum intercuspal position.

per right third molar area, and follow systematically through the upper left, lower left and finally lower right quadrants to ensure that nothing is missed. Finally, the condition of each tooth should be checked for caries, hypoplasia, or resorption. All unerupted teeth should be charted, noting their developmental stage and position. Teeth previously extracted, those congenitally absent and any pathology should be recorded. Although large carious lesions will be obvious on a panoramic film, a more thorough assessment should be made from bite-wing or periapical films if required.

A maxillary anterior occlusal view. This provides a good view of the upper anterior teeth and is useful to check root lengths of the incisor teeth and to exclude the presence of a supernumerary or other pathology.

A lateral cephalometric radiograph. This film is indicated in the presence of anteroposterior and/or vertical skeletal discrepancies, particularly when incisor movement anteroposteriorly is planned, and prior to implant placement.

Cephalometric analysis

Cephalometric analysis involves the evaluation and subsequent interpretation of both lateral and postero-anterior views of the skull, although in practice it is usually confined to the former because of difficulty in interpreting the posteroanterior view.

To allow comparison of measurements recorded for the same patient at different times, or between patients, attempts have been made to standardise the radio-graphic technique. Originally developed by Broadbent and Hofrath independently in 1931, the radiograph is taken with the Frankfort plane horizontal, the ear posts positioned in the external auditory meati and the teeth in centric occlusion. The central ray should pass through the ear posts. Importantly, the X-ray source to midsagit-tal plane distance and the midsagittal plane-to-film distance should be standardised to facilitate repro-ducibility and to minimise magnification. To allow accu­rate calculation of magnification, a steel rule of known length should be placed at the midsagittal plane and recorded on each film.

It is now common practice to collimate the X-ray beam, thereby avoiding radiation exposure to areas of the head not required for lateral cephalometric analysis. To enhance the soft tissue profile, the beam intensity can be reduced by placing an aluminium filter between the X-ray source and the patient.

Uses of lateral cephalometric analysis

Lateral cephalometric analysis is used • as a diagnostic aid

•   to check treatment progress

•   to assess treatment and growth changes.

A diagnostic aid

Lateral cephalometric analysis sheds light on the dental and skeletal characteristics of a malocclusion, thereby allowing its aetiology to be determined and focusing attention on the aspects that require correction. It also serves as a useful reference of pretreatment incisor posi­tion, particularly if anteroposterior movement is inten­ded. In some patients, particularly those with class III skeletal bases, growth may be checked from serial radio­graphs and treatment commenced at the appropriate time. Unerupted teeth may also be located accurately, soft or hard tissue pathology identified and upper incisor root resorption observed.

A means of checking treatment progress

During treatment with fixed or functional appliances, it is customary to check incisor inclinations and anchorage considerations. Any change in the position of unerupted teeth may be checked also.

A means of assessing treatment and growth changes

If films are to be compared, they must be superimposed on some stable area or points. As orthodontic treatment is generally carried out during the growth period, no natural fixed points or planes exist. The following, however, are reasonably stable areas and are used com­monly for superimposition:

•   cranial base: after 7 years of age, the anterior cranial base is found to be relatively stable. The S-N (sella-nasion) line is a close approximation to the anterior cranial base (N is not on the anterior cranial base), and holding at sella allows the general pattern of facial growth to be assessed; superimposition on de Coster’s line (the anatomical outline of the anterior cranial base) reflects more accurately changes in facial pattern but requires greater skill to carry out

•   maxilla: superimposition on the anterior vault of the palate shows changes in maxillary tooth position

•   mandible: changes in mandibular tooth position may be assessed by superimposition on Bjork’s structures, the most useful of which are the inner cortex of the inferior and lingual aspect of the symphysis and the mandibular canal outline.

Aim and objective of cephalometric analysis

The aim of cephalometric analysis is to assess the anteroposterior and vertical relationships of the upper and lower teeth with supporting alveolar bone to their respective maxillary and mandibular bases, and to the cranial base. The objective is to compare the patient with normal population standards appropriate for his/her

racial group, identifying any differences between the two. The technique used is outlined in Box 40.

First check the radiograph to ensure that the teeth are in occlusion and that the patient is not postured forward. It may be necessary to refer to clinical measurements to verify the overjet. !t is advisable to scan the film for any pathology including resorption of the upper incisor roots, enlarged adenoids or degenerative changes in the cervical spine In a darkened room attach tracing paper or tracing acetate to the X-ray film and secure both to an illuminated viewer ensuring that the Frankfort plane is horizontal and parallel to the edge of the viewing screen

Witha4H pencil identify the points (Fig. 104) and planes, the definitions of which are listed in Table 29. By convention, the most prominent incisor is traced and for structures with two shadows (e.g. the mandibular outline), the average is selected for analyses. Alternatively, landmarks may be digitised using a cursor linked to a computer program that allocates x and у coordinates to each point. Angular and linear measurements are calculated automatically. A piece of cardboard with a cut-out area of about 5 cm x 5 cm is helpful in blocking out background light and aiding landmark identification. Record the values for the measurements listed in Table 30.

It is important, however, to remember that irrespec­tive of whether cephalometric measurements are made directly from a digitiser or indirectly from a tracing, the cephalometric technique and its subsequent analysis are open to error. The technique relies on reducing the three-dimensional facial skeleton to a two-dimensional X-ray film. Bilateral landmarks, therefore, are superim­posed. The validity of the analysis depends upon the ability of the operator to identify points accurately and reproducibly which in turn is dependent on the film quality and operator experience.

Table 29 Definition of commonly used cephalometric points and planes (see Fig. 104)

Definition

Planes S-N line Frankfort plane Maxillary plane Mandibular plane Functional occlusal planesella: midpoint of seila turcicanasion: most anterior point of the frontonasal suture (may use trie deepest point at thejunction of the frontal and nasal bones instead) porion: uppermost, outermost point on the bony external auditory meatus (upper border ofthe condylar head is at the same level, which helps location) orbitale: most inferior anterior point on the margin of the orbit (use average of the left and  right orbital shadows) tip of the anterior nasal spine tip of the posterior nasal spine (pterygomaxillary fissure is directly above, which helpslocation) A point: most posterior point of the concavity on the anterior surface of the premaxilla in themidline below ANS В point: most posterior point of the concavity on the anterior surface of the mandible in themidline above pogonion pogonion: most anterior point on the bony chin menton: lowermost point on mandibular symphysis in the midline gonion: most poster-inferior point at the angle of the mandible (bisect the angle betweentangent to the posterior ramus and inferior body of the mandible to locate) line drawn through S and N line connecting porion and orbitale line joining PNS and ANS line joining Go to Me line drawn between the cusp tips of the first permanent molars and premolars/deciduousmolarsO

rtCephalometric interpretation

The following aspects may be assessed from the cephalometric analysis.

Skeletal relationships

Maxillary prognathism (SNA). This value is much affected by the cant of the S-N line and the position of nasion. Mandibular prognathism (SNB).

Skeletal pattern (ANB). The skeletal pattern may be clas­sified broadly according to the ANB value:

Class I skeletal pattern: 2° < ANB < 4° Class II skeletal pattern: ANB > 4° Class III skeletal pattern: ANB < 2°.

The ANB value should be considered along with the measurement for SNA, as ANB is affected by variation in both the vertical and anteroposterior position of nasion. In cases where the SNA value is above or below the average value of 81° and provided the S-N/maxil-lary plane angle is within 8 ± 3°, a correction may be employed to the ANB value as follows: for every degree SNA is greater than 81°, substract 0.5° from the ANB value, and vice versa.

The Wits analysis. This is an alternative means of assessing the skeletal pattern in which the distance (in millimetres) is measured between perpendiculars from

A and В point to the functional occlusal plane (a line joining the cusp tips of the permanent molars and pre-molars or deciduous molars). The average values for males and females are 1 ± 1.9 mm and 0 ±1.77 mm, respectively. No indication is given, however, of the rela­tion of the dental bases to the cranial base. The function­al occlusal plane is also difficult to locate, which casts doubts on any claims made about the skeletal assess­ment using this method. In some cases, however, it may be a useful check to complement that made from the ANB value alone.

Vertical skeletal relationship (MMPA and facial proportion) (Fig. 105)

The mandibular-maxillary planes angle (MMPA) is often correlated with the amount of overbite and the pattern of mandibular growth – a low MMPA being associated with an increased overbite and a forward pat­tern of mandibular growth while the converse is often true for those with a high MMPA. The facial proportion should lend support to the value obtained for the MMPA; a reduced facial proportion is usually consistent with a low MMPA and vice versa. Where there is dis­agreement between these two assessments, the tracing should be checked to identify the cause.

Tooth position

Angle of the upper incisor to the maxillary plane. The incli­nation of the upper incisors may be assessed as average (109° ± 6°), retroclined (<103°) or proclined (>115°). In class II division 1, it is often helpful to carry out a ‘prog­nosis tracing’ to indicate if correction of the incisor rela­tionship may be undertaken by tipping or bodily movement (Fig. 106). An alternative method is to apply the following rule of thumb: for every 1 mm of overjet reduction subtract 2.5° from the upper incisor to maxil­lary plane angle. Provided the final upper incisor inclina­tion is not likely to be less than 95° to the maxillary plane, tipping rather than bodily movement will be possible.

Angle of the lower incisor to the mandibular plane. This must be looked at in conjunction with the ANB and MMPA angles as the lower incisor inclination may com­pensate for discrepancies in the anteroposterior and ver­tical skeletal pattern. Under the influence of the soft tissues, the lower incisors may procline in class II maloc-clusion while in class III cases they may retrocline. There is also an inverse relation between the lower incisor angulation (LIA) and the MMPA: for every degree the LIA is greater than the average (93°), the MMPA is I^е less than the average (27°); the opposite holds true when the LIA is less than the average.

Inter-incisal angle. Provided the incisors contact, overbite depth is associated with the inter-incisal angle -the greater the angle, the deeper the overbite.

 

Although measurement of FMPA is favoured by some analyses, MMPA is preferable due to easier and more accurate location of the maxillary plane.

Facial proportion =(y= perpendicular distance from maxillary plane to Me x= perpendicular distance from maxillary plane to N)Fig. 106 Prognosis tracing to assess if correction of the incisor relationship can be achieved by tipping or bodily movement, a = presenting angle of 1 to maxillary plane; b = inclination of 1 to maxillary plane following rotation around the centroid to simulate tipping movement.Lower incisor position to A-Pogonion line. This has been used as an aesthetic reference line for lower incisor posi­tioning (average 0-2 mm) but it is unwise to lend too much credence to this measurement for treatment planning pur­poses. Both point A and Pogonion may shift with treat­ment or growth, and orienting the lower incisors correctly with respect to the A-Pog line does not improve the prospect of a stable result.

Analysis of soft tissues

Various reference lines, regarded as indicators of pleas­ing facial appearance, have been suggested to assess the relationship of the soft tissues of the nose, lips and chin. These lines are more helpful in orthognathic surgical planning than in planning conventional orthodontic treatment. Two lines are shown in Figure 107.

 

•   Holdaway line: joins the upper lip and chin; for optimal facial aesthetics the lower lip should lie ± 1 mm to this line

•   Rickett’s E-line: joins the nasal tip to the chin such that the lower lip is positioned 2 mm (± 2 mm) in front of the E-line, the upper lip lying slightly further behind.