Class III malocclusion Copyright (c) Department of Orthodontics University of Dental Medicine, Yangon

1. CLASS III MALOCCLUSION
DdYEEDr Hla Hla Yee

2. INCISOR RELATIONSHIP
 Class III incisor relationship (The lower incisor edges lie anterior to
the cingulum plateau of the upper central incisors)
 In mild cases , the incisors meet in an edge to edge relationship , when
there may be an anterior mandibular displacement to obtain a
posterior occlusion .This exaggerates the class III incisor relationship.
( or )
 In very mild cases , there is compensatory proclination of upper incisors
and compensatory retroclination of lower incisors resulting in class I
incisor relationship.
 In more severe cases , there is an appreciable reverse overjet with
normal path of closure.

3. BSI ---Class III
Anterior and posterior crossbite

4. Premature contact Anterior
displacement

5. Premature contact Anterior displacement

7. CANINE RELATIONSHIP
 The upper canine occludes a whole tooth width further
posterior than normal and occludes in the embrasure
between lower first premolar and second premolar.
Buccal segment relationship
 Angle’s class III molar relationship.
 May be class I in mild to moderate class III cases , if
molar position has not been changed due to mesial drift.

8. BSI -- CLASS III
CANINE -- CLASS III
MOLAR – CLASS III

10. TRANSVERSE OCCLUSION
 The upper arch is often narrow and short. Therefore , the upper
arch is frequently crowded.
 The lower arch is broad , therefore , the lower arch may be
spaced.
 In case with slight narrowing of the upper arch leading to equal
width between upper and lower arches , there may be
unilateral displacement leading to unilateral cross bite.
 There may be bilateral crossbite in severe discrepancy cases.

11. NARROW UPPER ARCH LARGER
LOWER ARCH

12. OVERBITE
 No overbite in edge to edge occlusion.
 May be increase in moderately severe cases, in which
the intermaxillary height is reduced and the lower
incisors lie anterior to the upper.
 The skeletal openbite may be seen in increased anterior
intermaxillary height cases.

13. SKELETAL RELATIONSHIPS
Antero-posterior relationship
 The skeletal pattern is usually classIII
 The skeletal discrepancy may be exaggerated due to
forward displacement of mandible.
Vertical relationship
 Normal or increase or decreased.

14. SKELETAL---CLASS III

15. TRANSVERSE RELATIONSHIP
 As the mandible is occluding with the narrow part of the maxilla
due to antero- posterior discrepancy , there is obvious
transverse discrepancy in the occlusion.
 There may be true transverse deficiency of the maxilla .
 When the maxillary basal bone is slightly narrower than the
mandible , the buccal teeth may meet tip to tip resulting in
lateral mandibular displacement to obtain maximum
intercuspation.
 If the discrepancy is severe , the transverse discrepancy will be
visible in the occlusion as bilateral buccal crossbite.

16. BILATERAL POSTERIOR CROSSBITE

17. LATERAL DISPLACEMENT OF MAMDIBLE (TO RIGHT SIDE )
LOWER ARCH – CENTRE LINE SHIFT TO RIGHT SIDE
LATERAL DISPLACEMENT LEADING TO UNILATERAL CROSSBITE
ON RIGHT SIDE

18. FACIAL GROWTH
 Is usually unfavourable.
 The prognathism of the mandible relative to the maxilla will
increase with further growth.
 In mild case , the occlusion may be maintained with
dentoalveolar adaptation and compensation.
 In cases with posterior mandibular rotation , further growth may
increase the tendency to develop anterior openbite as the
vertical growth of the mandible may exceed the growth potential
of the alveolar bone.

19. PROGNATHIC MANDIBLE

23. SOFT TISSUE
 Do not play any role in the development of the malocclusion.
 Tend to encourage dentoalveolar compensations to reduce the
severity of malocclusion.
 Lips maintain in competent in cases with anteroposterior and
vertical discrepancy.
 There will be an adaptive tongue thrust with tongue to upper
lips contact to obtain anterior oral seal , in cases with gross lip
incompetence due to skeletal discrepancy.

24.  The lower lip may be full and pendulous. Therefore
, the lower incisors may be proclined and
exaggerating the reverse overjet.
 If the volume of the oral cavity is reduced , the
tongue may have to be postured forward to avoid
encroachment on the airway and therefore dental
relapse may occur.

25. MANDIBULAR PATH OF CLOSURE
 If the anteroposterior discrepancy is mild , there will
be an anterior crossbite with anterior mandibular
displacement.
 In cases with transverse discrepancy , there will be
lateral mandibular displacement with unilateral
crossbite.
 If the path of closure is not corrected , it may ever
lead to mandibular dysfunction.