Class III borderline cases pose diagnostic and therapeutic challenges for decision making, on timings and approach to treatment. Should they be treated with orthodontics alone or combined with orthognathic surgery? This is the most controversial yet crucial decision to arrive at. Often, there is a difference of opinion among peer groups in choosing a mode of therapy based on the nature and characteristics of the severity of the problem. A wide range of skeletal dysplasia can be camouflaged with tooth movement without deleterious effects on the periodontium. However, the bottom line is optimum aesthetics and stability of the treatment outcome. This chapter outlines the diagnostic and treatment considerations in the management of such borderline class III malocclusion cases.

Ethnic correlates of class III malocclusion

Class III malocclusion is more prevalent in South Asian countries, namely Korea, Japan, Taiwan, South China and Thailand, than in America, Europe and the Indian subcontinent. Therefore, in South Asian countries, a significant proportion of patients seeking orthodontic treatment belong to the class III variety compared to the class II variety in Europe and North America. Among 33% of orthodontic patients in Japan and 20% in China constitute class III malocclusion. ^,

The distribution of malocclusion among 2155 patients at youngdong Severance Hospital Korea in 10 years period was class I–27.8%, class II div 1–22.6%, class II div 2–7.9%, class III-41.6%.

The distribution of malocclusion among 9159 patients at Yonsei University Korea was class I-33.3%, class II-28.6%, class III-38.1%.

As a result, there has been an increase in clinical and research studies from countries with a high prevalence of class III malocclusion, both in English and native languages. These studies offer valuable evidence and guidance for treatment approaches, including interceptive, camouflage and surgical options for class III malocclusion ( Fig. 71.1 ).

Pattern of combination of skeletal components within class III malocclusions in two different races i.e American Caucasians and Koreans.

Source: Based on Baik HS. Limitations in orthopedic and camouflage treatment for class III malocclusion. Semin Orthod 2007;13:158–74. DOI:10.1053/j.sodo.2007.05.004 .

Class III malocclusion is defined as the supernormal class I or a frank mesial-molar relationship accompanied by an incisor edge-to-edge bite or a negative overjet. The visible abnormal sagittal relationship is only a micro-expression of the complex maxilla-mandibular deformity in sagittal, vertical and transverse dimensions. The disturbed skeletal proportions of the face are deep-seated and altered in relationship with the cranium. The abnormalities extend deep into the cranial base, particularly the anterior and middle cranial fossa and frontal sinuses. The frontal sinuses are often underdeveloped in class III malocclusions, and the frontomaxillary articulation may be located more posteriorly. There is a poor development of ‘exo-peri-face’, that is, soft tissues around the face. Poor muscle functions lead to compromised chewing, a low tongue posture and reduced airway functions.

Jean Delaire analysed a sample of 172 records of class III subjects, focusing solely on maxillary-mandibular anomalies in the sagittal plane, and categorised these into nine distinct types ( Table 71.1 ). A class III malocclusion can coexist in a normal mandible or smaller than normal.

Li et al. did a morphometric analysis using Procrustes superimposition of 472 class III patients to group according to different craniofacial morphology and relationship to treatment options. This resulted in 14 subgroups with special characters.

A class III malocclusion pattern is also contributed by other components such as protrusion and retrusion of the teeth; the orientation and height of the maxilla; the length and orientation of the ramus and body of the mandible and the mandibular angle; the cranial base flexure and vault; and the neck. ^, Studies have indicated that the relative anterior position of the glenoid fossa in class III subjects is a possible diagnostic anatomic feature of class III malocclusion associated with mandibular protrusion. Others have reported a relatively short anterior cranial base and reduced cranial base angle, an essential element of class III malocclusion. ^{, ,}

Cephalometric studies have traditionally been used to assess craniofacial morphology and the growth of such subjects. This two-dimensional (2D) radiographic tool has several limitations and fails to accurately characterise morphological variations that occur in all dimensions of space during the growth of complex structures like face and cranium.

Lately, researchers used morphometric techniques to distinguish the characterisation of morphological differences between class III and class I subjects. In an investigation employing Procrustes analysis, thin-plate spline analysis and finite element analysis, a group of 14 researchers conducted a comparative examination of the geometric configurations of children classified under class III and class I categories. The investigation revealed pronounced disparities in the morphology of the posterior cranial base region among class III individuals, characterised by horizontal compression, vertical expansion and size contraction. Additionally, the sphenoid region exhibited expansion, while the anterior regions demonstrated shearing and localised increases in size.

The shape differences of the cranial base in subjects with class III malocclusion compared to those with class I configuration are in part contributed by deficient ortho-cephalisation or failure of the cranial base to flatten during development. Additionally, they demonstrated that a reduction in size or a change in the shape of the anterior cranial base (ACB) could influence and reveal a retrognathic midfacial profile associated with class III malocclusions ^, ( Fig. 71.4 ).

Cranial base morphology of skeletal class III assessed on Procrustes, thin-plate spline and FEM analysis.

Thirteen craniofacial landmarks (A) used in this study superimposed on a cephalographic tracing of a class I profile. The geometry used for the Procrustes, thin-plate spline and FEM analyses, (B) as well as the linear, (C) and angular, (D) measurements used in the bivariate and multivariate analysis are superimposed on tracings of class III subjects..

Source: Reproduced with permission from Singh GD, McNamara Jr JA, Lozanoff S. Morphometry of the cranial base in subjects with Class III malocclusion. J Dent Res 1 997; 76 (2): 694–703; PubMed PMID: 9062564. DOI:10.1177/00220345970760021101

Our face, virtually without exception, is the composite of a great many regional ‘imbalances’. Individuals with class III malocclusion are brachycephalic; they have a more upright basicranial floor and a closed flexure angle, which decreases the effective anteroposterior dimension of the middle cranial fossa. The result is a more posterior placement of the maxilla and a shorter horizontal length of the nasomaxillary complex. Because the basicranium is wider but less elongated, the middle and anterior cranial fossa are correspondingly foreshortened. The composite result is relative retrusion of the nasomaxillary complex and more forward mandible placement. This leads to a prognathic mandible and class III molar relationship.

The class III skeletal pattern is apparent much early in the postnatal life by age 6–8 years or before. The excessive lower anterior facial height, dentoalveolar compensations, maxillary retrusion and mandibular prognathism were evident in the class III sample as early as 5 years of age. Several growth studies have indicated that the class III pattern worsens with age. ^, It is essential to know that:

• 1.

  Growing class III individuals show increased amounts of growth of the lower jaw and deficient development of the upper jaw, including zygoma and nasomaxillary complex.

• 2.

  There is a sexual dimorphism in the growth of class III subjects. ^,

• 3.

  In females, maximum changes for facial characteristics occur between average ages of 11 and 12 years but continue after 15 years and beyond 17 years in contrast to class I subjects when growth is essentially ceased. The peak mandibular growth corresponded with stage CS3 through CS4 in cervical vertebral maturation.

• 4.

  In male subjects, peak mandibular growth occurred between 12.8 and 14 years, corresponding to CS3-CS4 of cervical vertebrae maturation. The increase in mandibular length continues at a significant rate from CS4-CS5 and CS5-CS6, which is the age beyond normal maturation.

• 5.

  The peak interval of growth duration is longer by 6 months in both male and female class III subjects than in individuals with normal occlusion who present with an average CS3-CS4 interval of 1 year.

The findings mentioned above have a direct bearing on treatment planning, considerations of camouflage orthodontic treatment, the timing of the evaluation of the stability of treatment protocols and the surgical age of the patient ( Fig. 71.5 ).

Average differences between cervical vertebral maturation (CVM) stages for mandibular length in class III females and males.

Cross-sectional study.

Source: Reproduced with permission from Baccetti T, Franchi L, McNamara JA. Growth in the untreated class III subject. Semin Orthod 2007;13:130–42. doi:10.1053/j.sodo.2007.05.006 .

Cassidy et al. described borderline patients as ‘those patients who were similar in the characteristics on which the orthodontic/surgical decision appeared to have been based on the observation from the study of class II division 1 cases. In day-to-day clinical practice, we often encounter patients who make it challenging to make a treatment decision for orthognathic surgery. Also, sometimes, there is a difference of opinion among a peer group about choosing a therapy based on the mild nature of the problem.

Cephalometric findings in borderline class III malocclusion

Cephalometric features of borderline class III vary significantly according to type, nature, the severity of the malocclusion and the patient’s age.

A lateral cephalogram helps evaluate the severity of the relationship and existing dental compensations in the maxilla and mandible. The postero-anterior (PA) view is beneficial in assessing coexisting facial asymmetry. The PA view cephalogram helps measure the site and extent of maxillary arch constriction, the width of the large mandible and transverse discrepancy, including midline shift and deviations. It also provides a valuable supplement to clinical examination on the buccal/lingual compensation of maxillary and mandibular posterior teeth, which should help to outline possible limits of orthodontic tooth movements.

Clinicians and researchers have tried to work out cephalometric guidelines to decide the treatment modalities for class III patients to know if the patient is suitable for camouflage or orthognathic surgery. Rabie et al. suggested that the Holdaway’s angle can be a reliable guide in determining the treatment modality for patients who represent borderline class III surgical cases. Rabie et al. used several variables and discriminant analysis to conclude that for the measurement of the profile, the Holdaway’s angle was the most crucial variable to classify patients. The threshold value was 12 degrees, which meant that if one patient had a Holdaway’s angle greater than 12 degrees, he/she would most likely be treated successfully by orthodontics ( Fig. 71.6 ).

Holdaway’s H-line

angle is formed by the intersection of soft tissue nasion–soft tissue pogonion line (N’-Pog’) and a line tangent to the chin point (Pog’) and the upper lip (Ls). Holdaway’s angle can be a reliable guide in determining the treatment modality for patients who represent borderline class III surgical cases. If a patient had a Holdaway’s angle of greater than 12 degree, he/she would most likely be successfully treated by orthodontics.

Ricketts described eight significant characteristics of surgical class III ( Table 71.2 ). According to him, the first three are weighed heavily in early prognosis for surgical cases.

TABLE 71.2

Ricketts’ eight significant characteristics of surgical class III

1. An open (large) angle formed by Basion-Nasion plane and Frankfort horizontal (FH) plane. Average 27 degrees 2. Closed Xi axis angle—average 15 degrees 3. Obtuse central mandibular core-corpus condyle axis 4. Long condyle neck 5. Long corpus 6. Short porion distance from pterygoid vertical 7. Short anterior cranial length on Basion-Nasion 8. A concave profile

The extreme diversity of craniofacial patterns seen with class III patients offers diagnostic and therapeutic dilemmas. The growth of the mandible is often prolonged beyond adolescence, the amount and intensity of which cannot be predicted with any accuracy.

The above considerations further contribute to the clinician’s dilemma, for the unpredictable response, often with uncertainty of outcome and sustainability of the treatment results achieved. The relapse of orthodontic/orthopaedic treatment in class III malocclusion is frequent, up to 50%.

There have been two philosophical approaches to therapeutic inventions to class III malocclusion. First, wait for most skeletal growth to be completed and intervene according to the severity of deformity; or second, intervene early with dentofacial orthopaedics followed by aggressive orthodontic compensations in selective cases. Philosophy of institution, choice and experience of operator and patient’s cooperation has often influenced treatment decisions.

Orthodontic treatment can correct class III cases with mild to moderate skeletal deformity and minimal impact on facial soft tissue. Such a treatment approach where the underlying bony deformity is left untreated, but teeth are moved to such positions to create an acceptable occlusion without violating the aesthetics and stability of treatment results is categorised as ‘camouflage treatment’.

Patients suited for camouflage class III malocclusion have often passed their pubertal growth spurt, having completed the major growth component and exhibit more of a horizontal rather than vertical face type. Such camouflage treatment has also been instituted in cases with mild open bite. ^,

Rationale of class III camouflage

Growth

Due to the complexity of genetic variation in the growth, the morphology of the face and the lack of absolute precision of research tools on growth forecast, uncertainty persists in accurately predicting treatment responses of the craniofacial complex. Each class III patient may have unique features and a unique growth pattern. Therefore, two similar looking cases of similar ages may respond differently to the same treatment approach. Class III skeletal discrepancies in the growing period cannot be resolved in toto with growth modification approaches. After significant growth, they require a second phase of treatment using non-surgical orthodontic approaches in the permanent dentition stage.

Limitation of tooth movement

In class III malocclusion, dental compensations mask the severity of the underlying skeletal dysplasia. While planning the treatment by camouflage approach, the pre-treatment dental compensations need to be enhanced, which might result in unfavourable sequelae such as the labio-gingival recession in mandibular incisors and root resorption of maxillary incisors. Extensive labial movement of maxillary incisors would move roots in proximity to the palatal cortical plate. Retraction and lingual tipping of lower incisors may reduce lip prominence, which could enhance chin prominence, affecting the profile adversely. Excessive proclination of maxillary incisor and lingual tipping of mandibular incisors could result in roots too close to the palatal and labial alveolus, compromising periodontal health ( Fig. 71.7 A and B).

(A) Consequences of proclined maxillary incisors beyond the alveolar limits leading to maxillary incisor root resorption. (B) Excessive mandibular incisor retroclination leading to root prominence and resorption of labial cortical plate.

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