Malocclusion refers to any deviation from normal occlusion, ranging from slight tooth position variations to significant abnormal position of a group of teeth within arches or in relation to each other, including dentofacial structures ( Fig. 5.1 ).

Class I molar and canine relation, normal overjet, and overbite.

When referring to occlusion, the norm is a range, but the quantum of deviation that encompasses the category of normal occlusion needs to be clearly defined. The evaluation and definition of occlusion are determined by the intra-arch dental alignment and arch forms, the inter-arch relationship of each dental unit and arch and the harmony of the underlying skeleton bases (i.e. maxilla, mandible and cranium). Normal occlusion comprises a normal overjet and overbite, buccal occlusion, arch forms and compensating curves besides alignment along the line of occlusion ( Figs 5.2 and 5.3 ).

Overjet: labial/buccal overlap; overbite: vertical overlap.

Buccal overjet, crossbite and a scissors bite.

(A) Normal buccolingual relationship of the posterior teeth showing buccal overjet. (B) Bilateral buccal crossbite, (C) Unilateral scissors bite.

The face’s soft tissue, in harmony with the craniofacial skeleton, dentition and occlusion, creates a pleasing profile. The muscles, jaw joints and functional spaces harmonise to create optimum facial aesthetics and function. The norm, therefore, includes preserving the health and functional integrity of the stomatognathic system. The primary functions of the stomatognathic system include mastication, speech, respiration and deglutition.

The concept of malocclusion is primarily influenced by the definition of the ‘norm’ and its ‘range’. There could be innumerable deviations within the range, and those beyond it would be termed malocclusion. Malocclusion deviations may be limited to within the arch (intra arch) and as a single or a group of teeth with those in the opposite arch (inter arch) in the sagittal (anteroposterior), transverse (lateral) and superoinferior (vertical) planes of space.

The aesthetics and beauty of the face and dentition vary globally in people of different ethnicities and races. A median diastema could be generally unacceptable, but it is considered a sign of beauty in African races. The concept of beauty has evolved with evolution and civilisation and changed with time.

Classification and grouping of clinical conditions are needed to facilitate accessible communication among professionals and understand disorders’ type, severity, or management. Terminologies have been coined to categorise malocclusion. A classification is often developed specific to aim(s), which includes documentation and, to great, an approach to a treatment plan.

Strang (1938) suggested that the classification of malocclusion should also include a direction to a systematic treatment plan.

Strang said, ‘I would define classification as a process of analysing cases of malocclusion for the purpose of segregating them into a small number of groups, which are characterised by certain specific and fundamental variations from normal occlusion of the teeth, which variations become influential and deciding factors in providing the fundamental data for the preparation of a systematic and correlated plan of treatment’.

Georg Carabelli, in 1842, developed a system to describe abnormal relationships between the upper and lower dental arches. He is credited with creating the terms ‘Edge-to-edge Bite’ and ‘Overbite’. Carabelli’s classification system, which is based on the positions of incisors and canines, is illustrated in Table 5.1 .

In 1880, Norman Kingsley, an eminent orthodontist, classified malocclusion into two categories: According to him, all malocclusion falls into one of the two categories.

• 1.

  Malocclusion of developmental origin and

• 2.

  Accidental malocclusion.

Edward H. Angle (1899, 1900, 1906 and 1907) provided a comprehensive explanation of malocclusion, which he divided into three classes. According to his theory, the maxillary first molar and canine positions are stable in the maxilla, while the corresponding lower teeth and jaw show deviations in their anteroposterior positions.

He classified all types of malocclusions into three classes, namely class I, II and III. In his later works, Angle also described the normal occlusion, the line of occlusion and the severity or quantification of each class based on full-cusp deviation or half-cusp deviation in the inter-arch molar relationship.

Dr Angle used the following nomenclature to describe deviations from normal tooth positions ( Table 5.2 ).

Traits of malocclusion.

Crowding of teeth.

Spaced anterior dentition in the maxillary arch.

Traits of malocclusion.

(A) Proclination of maxillary incisor teeth. (B) Retroclination of maxillary incisor teeth.

Different types of inter-arch malocclusions can occur, described in planes like sagittal, vertical, transverse or a combination. However, it is usually done in the sagittal plane when describing malocclusion. Malocclusion conditions in the vertical and transverse planes are as follows:

Transverse plane malocclusions

These include crossbites and scissor bites.

Crossbite: Crossbite refers to an abnormal bite where either the upper or the lower teeth are positioned improperly or both and can be labiolingual or transverse. Crossbite may affect a single tooth, a group of teeth or an entire arch. It may affect anterior ( Fig. 5.10 A, B) or posterior teeth or in combination. Posterior crossbite can be unilateral or bilateral ( Fig. 5.10 C).

Traits of malocclusion.

(A) Anterior crossbite of one tooth. (B) Anterior crossbite involving a group of anterior teeth. (C) Bilateral buccal crossbite. (D) Scissors bite involving left deciduous molars.

Scissors bite. The term ‘scissors bite’ is commonly used in dentistry to describe a specific condition wherein the mandibular buccal arch teeth are so inclined lingually so that their buccal cusps are lingual to the palatal cusps of the maxillary teeth ( Fig. 5.10 D).

Rotation and torsiversion. A tooth may be so rotated along its long axis. An extreme rotation that leads to its lingual surface almost appearing to be labial is called torsiversion ( Fig. 5.11 ).

Severe rotation and torsiversion of the right maxillary incisor.

Edward H. Angle considered the first permanent molar’s position as a reference point to judge normality and very lucidly described it as follows:

‘In normal occlusion, the mesiobuccal cusp of the upper first molar is received in the sulcus between the mesial and distal buccal cusps of the lower, the slight overhanging of the upper teeth bringing the buccal cusps of the bicuspids and molars of the lower jaw into the mesiodistal sulci of their antagonists, while the upper central incisors, lateral incisors and cuspids teeth overlap the lower anterior teeth about one-third the length of their crowns. The mesial and distal inclines of the mesiobuccal cusp of the upper first molar are received between the mesial and distal buccal cusps of the lower first molar, and the inclines of the distobuccal cusp are received between the distobuccal cusp of the first lower molar and the mesiobuccal cusp of the second lower molar’. ( Fig. 5.12 ).

Region of “key ridge” and class I molar relation.

Later, Angle (1906) published his classic article in Dental Items of Interest entitled ‘The upper first molars as a basis of diagnosis in orthodontics’, where he espoused the virtues of the maxillary first molars. He believed the upper first molars were the key to occlusion for the following merits.

The upper first molars are:

• 1.

  Largest in dimensions among all teeth.

• 2.

  They are the firmest in their attachment to the maxilla.

• 3.

  Have a crucial location in the dental arches.

• 4.

  Influence the dental and skeletal vertical proportions due to the height of their crowns.

• 5.

  The maxillary first molars occupy a normal position in the arches far more often than any other teeth because they are first among the permanent teeth to erupt in the mouth and are less restrained in taking their normal position in the dental arch.

• 6.

  The maxillary first molars also guide the positions of other permanent teeth erupting in the arch.

• 7.

  Have the most consistent timing of eruption.

• 8.

  Determine the inter-arch relationship of all teeth upon eruption and locking with the mandibular first molars.

Angle’s conviction that the first molar position in the maxillary arch was constant was also supported by Atkinson, who suggested the relative constancy of the maxillary first molar and its association with a bone buttress of the zygomatic process under its maxillary process, which he called the ‘key ridge’. Atkinson has shown that maxillary first molars bear the most significant stresses of occlusion and mastication; they are in the key ridge of the maxilla area, which has condensed bone. In deciduous dentition, the key ridge is located in the second deciduous molar region. After the permanent dentition develops, the position of the key ridge relocates more distally in the maxilla to the permanent first molar with growth as an adjustment of function.

For comparison with the normal, two reference norms are of particular importance: (1) the line of occlusion of the dentition and (2) the harmony line of the face.

Angle wrote:

• 1.

  The line of occlusion. ‘When the teeth are in normal occlusion, the line of greatest occlusal contact will be found to pass over the mesial and distal inclined planes of the buccal cusps of the molars and bicuspids and the cutting edges of the cuspids and incisors of the lower arch, and along the sulcus between the buccal and lingual cusps of the upper molars and bicuspids, henceforward, crossing the lingual ridge of the cuspids and the marginal ridges of the incisors at a point about one-third the length of their crowns from their cutting edges. This we shall call the line of occlusion’.

  • Angle continued, ‘This line describes more or less of a parabolic curve, and varies somewhat within the limits of the normal, according to the race, type, temperament, etc. of the individual’ ( Fig. 5.13 ).

    

    Line of occlusion.

    According to Edward Angle’s (1899) description, the line of occlusion is a parabolic curve that runs smoothly through the central fossa of each upper molar and across the buccal cusps and incisal edges of the lower teeth. This curve determines the occlusal relationship and the inter-arch relationship once the position of the molars has been established.

• 2.

  The harmony line. Angle gave immense importance to the soft-tissue profile and believed that malocclusion destroyed the profile. He considered the profile of Apollo, the Greek mythological God, as so faultless in the form that to change it in the least would be to mar the wonderful harmony of proportions. As Fuseli puts it, ‘Shorten the nose by, but a tenth of an inch and the God would be destroyed’ ( Fig. 5.14 ).

  

  Harmony line of Apollo on described by Edward H Angle

  Source : Belvedere Apollo Pio-Clementino Inv1015 n5– Apollo Belvedere– Wikipedia.

Angle also described other parts of the face, ‘Ideal facial beauty consists in a short, finely curved and prominent upper lip; a full, round, but less prominent lower lip, and a strongly marked depression at the base of the lower lip giving roundness and character to the chin’. Angle gave particular importance to the lower part of the face, so much so that he found that a beautiful outline is a constant feature in handsome profiles, while the upper half of the face may show variations.

The harmony line in such profiles is a straight line extending from the most prominent points of the frontal (glabella) and mental (chin) prominences and the middle of the ala of the nose.

Angle used Roman numerals I, II and III to classify the anteroposterior arch into three main classes. Class I is also known as normal, class II is distal and class III is mesial relationship. The reference points are the buccal grove of the mandibular first molars to the mesiobuccal cusp of the maxillary first molars. He further divided each class into two Arabic numbered subdivisions, 1 and 2. Additionally, Angle referred to unilateral deviations as subdivisions.

This condition requires special mention because the treatment of this class of malocclusion is entirely different from the true class III situation. The differentiating feature of this condition is that dental occlusion is class III in maximum intercuspation or habitual occlusion, while it is class I in centric occlusion. Here, the disturbance is functional, where the mandible is postured anteriorly in a crossbite because of dental interference to achieve a ‘bite of convenience’. While a static evaluation will give a class III reading, a diligent functional examination at the postural rest position of the mandible and on the closure to first dental contact, the mandible is positioned in a normal relationship (class I) ( Fig. 5.18 ).

Functional component in class III malocclusion.

(A) Initial contact during closure. (B) Incisor in full cross-bite in occlusion.

Critical diagnostic features for this condition can be better recognised in study models, such as apparent occlusal interference in the form of crossbite of a single or more tooth and a severely constricted maxillary arch both anteroposteriorly and transversely.

Angle also recognised the existence of cases in which one side is a class II molar relationship, and the contralateral side is a class III molar relationship. However, he discounted these as being exceedingly rare.

Despite several shortcomings, Angle’s classification system has been significantly used in clinical settings and orthodontic research.

The virtues and limitations of Angle’s classification are compiled in Table 5.3 .

TABLE 5.3

Virtues and drawbacks of Angle’s classification

Virtues	Drawbacks of Angle’s classification
1. Simplicity in use	1. Angle’s classification is inadequate to describe all clinical conditions of malocclusion and has many shortcomings.
2. It is practical, easy to understand and can be applied in day-to-day clinical practice.	2. Angle classified all types of malocclusions into three categories based on their anteroposterior deviations. Initially, the classification was based on the full-cusp width of the maxillary first molar, with class I being normal, class II (disto) being a posterior deviation and class III (mesio) being an anterior deviation. Later, in 1904 and 1907, the classification was revised to use half-cusp width instead.
3. Three anteroposterior classes can also be applied to denote underlying skeletal types seen on a cephalogram (i.e., class I, class II, and class III skeletal relations). However, the dental relationship may or may not confirm underlying skeletal malocclusion or vice versa.	3. During his early works (1899), Angle assessed all teeth at the harmony line and used the maxillary first molars and canines as reference points. However, he later realised that the maxillary first molar was a more stable landmark and modified his method (1904, 1907) to lay greater emphasis on it. His conviction was found to only sometimes be consistently true as there can be variations in the location of the maxillary first molar within the maxillary arch and the jaw bones.
4. Angle had a brilliant eye for normality and, in the pre-cephalometric era, could identify dental or skeletal abnormal situations.	4. Angle classified malocclusions based solely on sagittal deviations, overlooking vertical and transverse variations.
5. The classification has stood the test of time and is the most widely used system in day-to-day practice.	5. Angle’s classification system is solely based on dental relationships and does not take into account the underlying craniofacial relationship.
	6. This classification system does not provide information about the severity and complexity of malocclusion, which is necessary to identify the need for treatment.
	7. The Angle’s classification system for malocclusion does not consider the condition’s underlying causes.
	8. It does not apply to deciduous teeth and requires significant expertise to evaluate correctly during the transition and deciduous dentition stages.
	9. Additionally, it is not suitable for measuring orthodontic treatment needs.
	10. Angle’s classification can pose challenges when discrepancies between sides or tooth movements occur due to crowding or premature loss of deciduous teeth.
	11. Furthermore, there are relatively high inter-examiner and intra-examiner errors in categorising Angle’s class II and division 2 malocclusions.
	12. Angle’s classification does not consider bimaxillary/bidental malocclusions.

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