Class III Malocclusions

1. Introduction

So-called “class III” malocclusions include a certain number of varied clinical expressions which affect a significant number of patients with high orthodontic demands and which sometimes make it difficult for the practitioner to make a precise diagnosis and start the appropriate treatment. 

This is especially true since the confusion between the terms “class III” and “mandibular prognathism”, long considered synonymous, is no longer acceptable today with the development of knowledge on the growth of craniofacial structures, and the advent of increasingly precise cephalometric analyses which should help the orthodontist to make a precise positive and etiopathogenic diagnosis.

2. Definitions 

ANGLE (1907) was the first to propose a classification of dysmorphoses into three classes I, II, and III; he defined the latter as: ” mesial occlusion of the lower jaw and arch, as indicated by the occlusion of the first mandibular molars at the time of their eruption .”

Class III Malocclusions

This concept will be spread by various authors and various analyses including BASSIGNY  : “Class III malocclusions correspond to a heterogeneous group whose common characteristics are a more or less pronounced mesioclusion of the first lower molars, a concave profile and, in general, an inverted occlusion in the incisal sector. The associated skeletal dysmorphoses affect either the mandible, or the maxilla, or both maxillae at the same time. These morphological anomalies may be accompanied by kinetic anomalies, progression, or more rarely laterodeviation.  “

Jean DELAIRE, faced with the “multiplicity of Class III”, uses the name of syndrome which according to him: ”  best combines all the clinical and para-clinical manifestations of class III dysmorphoses ” 

3. Frequency and Multiplicity of Classes III

Frequency: low, 2-8% of the orthodontic population 

Associated with other pathologies (transverse, vertical, DDM, dento-alveolar compensations, dental pathologies). 

It is noted that the number of varieties increases with the number of factors taken into account (maxillary retrusion, mandibular protrusion, laterodeviation of the mandible or maxilla, excess or insufficiency of height of the lower level of the face, incisor infraclusion or supraclusion, etc.)

4. Etiopathogenesis of Class III

5.1. Primary Causes: (hereditary, genetic)

Like BASSIGNY who states that class III anomalies are most of the time of hereditary origin, various authors have carried out studies in order to establish a theory of its transmission.  

RUBRECHT (1930) who followed the Habsburg family and established an interesting genealogical tree, and he advanced that this “prognathism” could not be due to acquired causes but to heredity.

Similarly, SUZUKI carried out its study on 243 Japanese families presenting this anomaly.

IWAGAKI suggests that in the case where the mother is prognathous: 18% of children will be prognathous, on the other hand if it is the father who is prognathous: the percentage will be 31%.

The results of these studies demonstrate that this transmission is of a “complex mechanism” and that it is of “variable heredity”.

5.2. Secondary causes:

1. General:

Hormonal causes: hypersecretion of somatomedin leads to hyperdevelopment of the condyles, macroglossia, progressive mandibular prognathism (Acromegaly)

Psychological causes: facial expressions, imitation of parents themselves in class III, sulking child… 

2. Local:

• During the passage D ^ture temp🡪 perm.
• Agenesis of the lateral incisors.
• Premature loss of first molars.
• Hyperactivity of the thrusters (CHATEAU)
• Upper lip hypertonicity
• Short lingual frenulum 🡪 low tongue position.
• RICKETTS obstruction syndrome.

5.2.3. Functional disorders

In the presence of oral ventilation, this completely destroys the functions (chewing, swallowing, phonation, facial expressions), they cannot then be normal and lead to a dysmorphofunctional spiral.

Disorders of cervical, velopharyngeal, mandibulolingual, nasolabial and labiomental postures cannot be dissociated. They coexist and associate their deforming effects.

5.2.4. Congenital

• Cleft lip and palate
• Various malformation syndromes:
  • CROUZON, APERT
  • BINDER
  • PIERRE MARIE and SAINTON
  • DOWNS (trisomy 21)
  • Uni- or bilateral HYPERCONDYLIA

5. Clinical forms

5.1. Pseudo Class III with mandibular progression:

• This is not a skeletal class III, but a skeletal class I with an abnormality of the closure path 
• In resting position: the position of the mandible is +/- balanced
• In occlusion (in ICM) Class III relationships appear.
• May be associated with inferior or superior retroalveolar prolapse.
• The closing path can be diverted to the right or left.
• The Denevrezé Maneuver is positive.

2. Maxillary retrognathia and maxillary brachygnathia:

Basal dysmorphosis in the sagittal direction characterized by a maxilla in a posterior position relative to the mandible and the base of the skull.

It can be positional ( retrognathia ) or anatomical ( brachygnathia ).

1. Etiopathogenic diagnosis:

• Hereditary 
• Post-operative consequence in a cleft lip and palate patient. 
• Positional retrognathia: is due to insufficient development of the anterior part of the base of the skull.
• Anatomical anomaly: is due to insufficient development of the upper jaw in the antero-posterior direction.

2. Positive diagnosis:

Facial signs: the aesthetic impact is important.

From the front: 

• Thin upper lip and impression of lower prochelia
• Lower floor reduced or normal.

In profile:

• cheekbones appear receding, without relief. 
• The nasolabial fold is very marked. 
• The retrusion of the upper lip is clear, it is thin, while the lower lip, red, is everted and prominent.
• The nasolabial angle, more open than normal
• Concave profile according to Ricketts.

Occlusal signs

Occlusion arches:

Incisors in end-to-end or reverse bite.

Class III canine and molar.

Separate arches: upper dental crowding

Ogival palatine vault

Functional signs

• Disturbed chewing especially in severe cases (no incision due to lack of contact at the incisal level)
• Atypical swallowing
• Disturbed phonation

Straight closing path (when retrognathia is not associated with a sliding with deviation)

Teleradiographic signs:

• TWEED : SNA < 82°; ANB < 2°; AOBO decreased
• W. WYLIE:   FPM – ENA Diminu

S – FPM

AT de Château normal: retrognathia (positional)

AT of Château diminished: brachygnathia (anatomical)

3. True Undershot Prognathism and Mandibular Dolichognathia:

It means a mandible that is too far forward in relation to the maxilla and in relation to the base of the skull.

It can be a positional anomaly (mandibular prognathism) or a volume anomaly (mandibular dolichognathism).

1. Etiopathogenic diagnosis

• Hereditary causes: are the most incriminated in these two clinical forms
• Skeletal causes: closure of the angle of the base of the skull (which advances the glenoid cavity downward and forward); mandibular hypertrophy.
• Muscular and functional causes:
  • Break in balance between lowering and lifting gears
  • Upper airway obstruction (ventilation disorders)
  • Deviated closing path leading to a slide which will become anatomized.

Dental causes: absence of abutment (leads to sliding and excessive growth of the mandible)

2. Positive diagnosis

Facial Signs: 

• Significant aesthetic impact
•  Concave profile, long face, lower prochelia, progeny
• The mandible appears very long and the gonial angle very obtuse.

Occlusal signs

Very pronounced class III ratio

Class III canine and molar

Incisors in abutting or reverse articulated form

The lower arch appears larger than the upper one and circumscribes it

ICM and RC coincide (Negative Denevrézé maneuver with straight closing path

Teleradiographic signs

Glenoid cavity located ant/base of the skull.

SASSOUNI: Pog ahead of arc 1 bis.

W.WYLIE:   Xi-Pm         

Long mdb

STEINER:   SND > 76° Increased

ANB< 2°

 SE – SL

5.4. Mixed forms

Combination of the 2 previous forms

• Associated dysmorphoses of the maxilla and mdb.
• Most severe form.
• The entire face (including the base of the skull) is affected.

5.5. Alveolar Class III

• Supra retroalveolus
• Inferior proalveolus 
• Associated or not with a progression

6. Consequences without treatment of Classes III

6.1. Occlusal consequences:

o No previous guide;

o No use of propulsion ;

o Occlusal trauma due to reverse bite

o No dog protection.

6.2. Periodontal consequences:

o Gingival recessions and denudations ;

o Dental mobility;

6.3. Psychological consequences:

o Aesthetic damage, poorly accepted especially among girls.

Class III Malocclusions

 Conclusion

Class III malocclusions constitute a syndrome with multiple expressions often associated with transverse and vertical dysmorphoses, to which the orthodontist must provide an immediate response.

The diagnosis of class III is first clinical, refined by teleradiography which allows the location and clinical form to be specified in order to provide the therapy adapted to the clinical form.

Class III Malocclusions

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Class III Malocclusions