The prevalence of Angle’s class II malocclusion varies among population groups. It is high among Caucasians and lowest among the primitive races. Class II malocclusion is noticed in a broad spectrum of presentation and severity. It is the lowest primitive race or tribals and varies from 14.6% in New Delhi children to 43.3% in Finnish children in mixed dentition age groups ( Table 61.1 ).

A distal step relationship of second deciduous molars indicates a developing class II malocclusion during mixed dentition. The occlusal traits of class II malocclusion in the deciduous dentition include a distal terminal plane at the second deciduous molars, distal canine relation, large overjet and overbite. Other findings include a narrow maxillary basal bone and reduced or lack of spacing in the deciduous dentition.

The class II children have a narrow maxillary arch, resulting in a negative transverse discrepancy (TD) between maxillary and mandibular intermolar widths in the mixed dentition (−4.1 ± 3.0 mm). The TD is nearly zero in subjects with class I occlusion (controls).

On cephalometric examination, subjects with class II malocclusion also show a significantly retruded mandible and a shorter mandibular length (Co-Pg). ^, The maxilla can also be displaced forward in class II subjects with or without a difference in the length of the mandible.

A distal step deciduous molar relationship is never a self-correcting situation. However, children with a straight terminal plane may develop into a class I molar or a class II molar relationship, with mandibular growth and adjustment of occlusion during the late mixed dentition. In a clinical sense, it infers that when we encounter a class II distal molar relation early in the mixed or permanent dentition, interceptive and corrective therapy needs to be planned. A growing class II malocclusion is unlikely to improve more so when unfavourable environmental influences continue to affect the development of face and occlusion. These adverse influences are recurrent throat infections, obstructive or adaptive mouth breathing habits, thumb sucking and lip sucking habits.

During the transition from deciduous to mixed dentition, the craniofacial skeletal pattern shows an abnormal and variable pattern of growth in class II children compared to the control group of normal occlusions. The upper jaw becomes more prominent due to larger increments of sagittal growth, leading to maxillary protrusion relative to the cranial structures.

The mandible grows at a lesser pace in class II children than in children with normal occlusion. A more backwards and downward inclination of the mandibular body leads to a worsening of the facial angle. Other variations in class II subjects consist of constriction of the maxilla at both the skeletal and dentoalveolar levels and narrowing of the base of the nose. The occlusal and skeletal characteristics of class II malocclusion during the deciduous dentition stage may either remain stable or deteriorate when transitioning to the mixed dentition stage. Favourable changes leading to the self-correction of an established class II pattern into a class I occlusion are rare.

A child with class II malocclusion presents with a protrusive midface and/or a retrusive chin. They often report complaints of superior protrusion, front teeth jutting out or showing too much. This is often accompanied by a large overjet, deep bite (open bite can be seen in some) and a class II (distal) molar, premolar and canine relationship ( Fig. 61.1 ). These children have an aberrant pattern of muscle activity in the facial musculature, such as a flaccid upper lip, hyperactive mentalis and lower lip trap under the procumbent upper incisors. The aetiology may be attributed to mouth breathing/prolonged thumb sucking, which can be elicited by carefully recording the history of the patient.

Class II malocclusion.

Note overjet and a retrognathic mandible.

Two major types of skeletal combinations in class II children have been defined by McNamara.

• 1.

  In the first group, mandibular retrusion is the single most characteristic feature contributing to the class II pattern. The skeletal maxillary protrusion is not a significant finding, but often, the maxilla is normal. This type of craniofacial pattern has been attributed to aberrant environmental factors, such as abnormal muscle function, which causes altered occlusal interdigitations.

• 2.

  In the second group, a combination of maxillary and mandibular skeletal retrusion is often found in association with an altered mode of respiration, that is, mouth breathing. These children with maxillary and mandibular retrusion show a greater vertical development of the face. Excessive labial proclination and forward position of the maxillary anterior teeth is a common finding in this type of class II division 1 malocclusion. The maxillary first molars are more mesially positioned. The anterior segment of the maxilla is more protrusive and superiorly positioned. The excessive anterior cranial base length and enlarged frontal and maxillary sinus may contribute to the development of class II division 1 malocclusion. The mandible and dentition could be identical to those of the controls in size, form and position.

Moyers et al. stated that while class II malocclusion cases could be clustered quite unambiguously within a population, the distinction between classes I and II is not obviously distinct. Based on advanced analytical computer-based statistical methods of cephalometric records of 697 North American children, they segregated six horizontal class II types and five vertical class II types of patterns.

• Horizontal types of class II—A, B, C, D, E, F

• Vertical types of class II—1, 2, 3, 4, 5

  • 1.

    Horizontal types class II: It is designated as A–F ( Fig. 61.2 A–F, Table 61.2 ). While types B–E have distinct craniofacial, dental and growth patterns, types A and F are loose in their description. Class II type A is more dental in nature, while type F was the largest subgroup in their sample. This group of malocclusion shows features that are not distinctly class II yet differ from class I.

    • Class II type A has a normal skeletal profile and normal position of the maxilla and mandible. The occlusal plane is normally inclined. The maxillary dentition is protracted, resulting in increased overjet and deep bite.

    • Class II type B has midface prominence due to a large maxilla and normal mandible. The anterior cranial fossa tends to be flat.

    • Class II type C has a normal or diminished midface. The profile is retrognathic due to a severe retrognathic mandible. It is a severe form of class II horizontal type with a short maxilla, shorter mandible, reduced gonial angle and flat anterior cranial base (ACB).

    • Class II type D is associated with a normal or slightly diminished midface; maxillary incisors are severely labially inclined, and the gonial angle can have extreme variations.

    • Class II type E is an extreme variation of class II with a bimaxillary protrusion type class II pattern. The prominent midface is associated with a normal or even large mandible. Both the skeleton and dentition have a forward/labial tendency.

    • Class II type F is an ambiguous type of malocclusion where class II features are not distinctly defined. It is a milder form of the B, C, D or E type of class II pattern, but the skeletal profile is in less severe forms.

    

    Diagrammatic representation of the horizontal facial types in class II.

    The large rectangles symbolise the maxilla and the mandible, and the small squares represent the first molars, incisors are represented as vertical lines when normal, angled when in labioversion. The ideal profile seen in orthognathism is depicted by a dotted line. (A) Moyers’ horizontal class II: Type A normal skeletal profile, mandibular dentition normal, maxillary dentition is protracted, greater-than-normal incisal overjet. (B) Moyers’ horizontal class II: Type B midface prominence, mandible of normal size, flat anterior cranial base (ACB). (C) Moyers’ horizontal class II: Type C maxillary and mandibular retrognathism, dental protraction and dental procumbency. (D) Moyers’ horizontal class II: Type D maxillary retrognathism, dental protraction, mandibular retrognathism. (E) Moyers’ horizontal class II: Type E prominent mid-face and normal or even prominent mandible. Bimaxillary protrusion, both dentitions have a tendency to be forward. (F) Moyers’ horizontal class II: Type F a large heterogeneous subgroup of less severity, not well-defined rigid syndromal class II type but, rather, a loose collection of cases displaying some skeletal class II characteristics.

    * Source: Reproduced with permission from Moyers RE, Riolo ML, Guire KE, Wainright RL, Bookstein FL. Differential diagnosis of class II malocclusions. Part 1. Facial types associated with class II malocclusions. Am J Orthod. 1980 Nov;78(5):477–94. PubMed PMID: 6933855. *The author has included representative cases for each type of class II malocclusion across six distinct types.

    TABLE 61.2

    Class II malocclusion: horizontal types (A–F)

    Source: Based on the concept of Moyers RE, Riolo ML, Guire E, Wainright RL, Bookstein FL. Differential diagnosis of class II malocclusions. Part 1. Facial types associated with class II malocclusions. Am J Orthod 1980 Nov;78(5):477–94.

    Type A	Normal skeletal profile Normal occlusal plane Normal maxilla/mandible Normal mandibular dentition Maxillary dentition placed forward in class II molar, increased overjet and bite	Orthognathic maxilla/orthognathic mandible
    Type B	Class II skeletal profile Midface prominence Normal mandible Flat anterior cranial base	Prognathic maxilla/orthognathic mandible
    Type C	Smaller facial dimensions than other class II types Maxilla and mandible retrognathic Lower incisors tipped labially Upper incisors upright/tipped labially Squarish gonial angle Flat anterior cranial base	Retrognathic maxilla/retrognathic mandible
    Type D	Normal midface Small mandible Mandibular incisors upright/lingually inclined Maxillary incisors tipped labially	Orthognathic maxilla/retrognathic mandible
    Type E	Prominent midface Normal or even prominent mandible Maxillary/mandibular incisors proclined	Bimaxillary protrusions
    Type F	No specific features are well defined, but it has a loose collection of cases with some class II characteristics

• Vertical types class II: Five vertical types are segregated, which are not as clearly distinguished as the four horizontal types (B–E) of class II. In each horizontal type of class II, only some of the vertical patterns are visible. Certain vertical patterns tend to be more commonly associated with specific horizontal types. For instance, in horizontal types A and F, the vertical measurements are either normal or nearly normal ( Fig. 61.3 ).

  • • Class II vertical type 1 suggests a ‘long face syndrome’ or ‘steep mandibular plane angle’ type of class II. The functional occlusal plane is also steep and associated with a tipped-down palatal plane.

    • Class II vertical type 2 is associated with a squarish face. The anterior cranial fossa is more horizontal than normal, as are the mandibular, functional occlusal and palatal planes. The incisors tend to be upright in a deep bite, and the gonial angle is squarish.

    • Class II vertical type 3 is a distinct class II associated with skeletal anterior open bite and increased anterior face height. The palatal plane is tipped anteriorly upward, and the mandibular plane is steep.

    • Class II vertical type 4 is a rare and severe anomalous vertical class II type. The mandibular plane, functional occlusal plane and palatal plane are markedly tipped downward, leaving the lip line high on the alveolar process of the maxilla. The gonial angle is obtuse.

    • Class II vertical type 5 is somewhat seen in bimaxillary protrusion horizontal class II, where the face is squarish. The mandibular and functional occlusion planes are small and associated with a small gonial angle, resulting in a deep skeletal bite.

  

  Moyers’ five vertical types of class II malocclusion.

  Solid red lines represent the normal position of the cranial base, palatal plane, occlusal and mandibular planes. Broken purple lines represent the variation from normal for each vertical types.

  Source: Based on Moyers RE, Riolo ML, Guire KE, Wainright RL, Bookstein FL. Differential diagnosis of class II malocclusions. Part 1. Facial types associated with class II malocclusions. Am J Orthod. 1980 Nov;78(5):477–94. PubMed PMID: 6933855.

In brief, each case of class II malocclusion cannot be placed in a single category or type, and it may have a combination of sagittal, vertical and transverse deviations of varying severity.

Research on the phenotype and genetic identification of class II malocclusion is ongoing at the University of Iowa. A cephalometric study by Howe S on 309 class II Caucasian adult patients of both sexes analysed 63 cephalometric variables. These were reduced to seven principal components (PC) that explained 81% of the variation of the class II sample. Each PC represents a specific phenotype or trait of the malocclusion. Furthermore, five distinct clusters have been identified that divide this malocclusion into homogeneous phenotypic groups. The seven PCs are:

• 1.

  Vertical trends/mandibular plane angle-cranial base: PC1 explained most of the variation. The first component describes the vertical dimension in regard to the angulation of the mandibular plane to the cranial base. The verticality of the craniofacial component plays a significant role in determining the treatment approach, and treatment response may differ in patients with a flat plane versus a steeper plane.

• 2.

  Maxillary incisor angulation: PC2 refers to maxillary incisor inclination. Maxillary incisor proclination is a significant feature distinguishing class II subdivision.

• 3.

  Mandible horizontal and vertical lengths: PC3 differentiates the range of mandibular lengths present in class II patients. Subjects with class II malocclusion may exhibit smaller mandibles. However, some subjects may have normal-sized mandibles and be class II skeletal due to a malpositioned maxilla. For each patient, the affected jaw size and position will govern the treatment approach.

• 4.

  Position of the maxilla, especially in regard to the maxillary incisor angulation: PC4 signifies the position of the maxilla, especially in regard to the maxillary incisor angulation.

• 5.

  Facial taper and mandibular incisors: PC5 deals with mandibular incisors’ proclination, which is variable.

• 6.

  Position of the maxilla and cranial base inclination: PC6 deals with the position of the maxilla and is seen by the distance from A-point to nasion perpendicular, where the low extreme has an A-point set back from N perpendicular, and the high extreme has an A-point much more forward of that line, depicting a more protrusive maxilla. The inclination of the anterior cranial base can create variation in the measurements based on these landmarks. Below normal values of angles, SNA and SNB angles can be a reflection of maxillo-mandibular retrusion or can be an outcome of a low Sella or high nasion point, creating a steeper cranial base.

• 7.

  Overjet and WITS values (University of the Witwatersrand, Johannesburg): PC7 describes the overjet as a reflection of the differences in the underlying skeletal discrepancy. It is obvious that the patient on the high end is a more severe class II, while the low end has normal overjet and may have only mild class II skeletal tendencies.

In view of the above findings, studies are in progress to explore the characterisation of the class II malocclusion integrating measurements on lateral cephalograms, photographs, 3D dental models and cone beam computed tomography (CBCT). Further studies correlating the above data with DNA and environmental data will be researched to identify the causative gene for developing a class II malocclusion. The ultimate objective is to decide on an individualised plan of treatment.

In a recent study, Qiang Dong et al. used the CBCT Fixed-Point Measurement Method to compare skeletal class I and class II skeletal patterns. The study found statistically significant differences between skeletal class I and class II patients in the three-dimensional morphology of the mandible. The results showed that the mandibular ramus height, mandibular body length and condylar width in skeletal class II patients were smaller than in skeletal class I patients. The study also found that the mandibular shape was more extended in skeletal class II patients.

With access to CBCT technology, current trends in research on craniofacial morphology are focused on 3D evaluation of skeletal soft tissue with tongue posture and volumetric data on retropalatal, retroglossal and oropharyngeal airway. ^,

Only limited orthodontic interventions are possible during the deciduous dentition stage for the interception of developing class II malocclusion.

An essential approach to the interception of class II malocclusion involves redirecting the growth to a favourable pattern and eliminating aberrant muscle behaviour and/or deleterious habits, thereby allowing the face, jaws and occlusion to grow in abnormal occlusion.

Cases requiring treatment of maxillary excess and short mandible would need a more aggressive approach, which involves dentofacial orthopaedic treatment.

More severe forms of class II dysplasia, such as an extreme vertical type of pattern and those with open bite, may benefit partially or not benefit at all from interceptive procedures alone. These cases would require a surgical approach at an appropriate stage of their occlusal and skeletal development.

• 1.

  Kloehn’s facebow can act upon maxillary molars to achieve dental or orthopaedic effects on maxillary dentoalveolar segments.

• 2.

  It can be used to distalise maxillary molar(s), which have mesially migrated due to the premature loss of the deciduous molars.

• 3.

  The Kloehn’s facebow has also been used to reinforce anchorage in the maxillary arch.

• 4.

  It is combined with a maxillary splint appliance to achieve orthopaedic effects on the maxillary skeleton through a removable appliance:- activator headgear approach.

Kloehn’s facebow is made from a rigid stainless steel wire framework. It has a horseshoe shape/dental arch form of an inner bow of 0.045 in. diameter and an outer bow of 0.071 in. diameter. The inner bow follows the curves/arch form of the maxillary arch while the long arms of the outer bow lie on either side of the face, extending close to the tragus of the ear. Both bows are laser welded or soldered in the incisor region and strong enough to withstand orthopaedic forces applied to the inner bow through an extraoral traction system either from a cervical neck strap or a high-pull headgear. Cervical facebows are commercially available in different sizes to suit variable arch lengths ( Fig. 61.5 ).

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