54. Class III malocclusion. Prevention and treatment Flashcards
(13 cards)
Class III malocclusion
- Buccal groove of mandibular first permanent molar occludes mesial to mesiobuccal cusp of maxillary first permanent molar
Types of Class III malocclusions
- Mandibular Prognathism=>forward positioning of mandible
- Maxillary Retrognathia=>backward positioning or underdevelopment of maxilla
- Pseudo Class III(Anterior Crossbite)=>
- Normal mandible
- Underdeveloped maxilla
Etiological factors of Class III malocclusion
- Heredity
- Compulsive habits like protruding mandible
- Enlarged Tonsils and Naso-Respiratory Diseases=>anterior tongue posturing
- Premature Loss of Deciduous Molars
- Tongue Thrusting Habit
- Maxillary Hypodontia
- Mandibular Hyperdontia
- Hormonal Disorders=>acromegaly
Vertical components of Class III malocclusion
- Vertical deficiency
- Vertical normal
- Vertical excess
Sagittal components of Class III malocclusion
- Maxillary deficiency
- Mandibular excess
- Combination of both
Extraoral features observed in Class III malocclusion
- Well-formed nasolabial angle
- Thickness of soft tissues of chin
- Gingival recession or dehiscence
- Increased lower facial third
- Concave profile
- Increased gonial angle and positive lip step
Intraoral features observed in Class III malocclusion
- Anterior crossbite
- Posterior crossbite (discrepancy in relative width of arches)
- Relative crowding within arches(upper arch commonly more crowded)
- Dentoalveolar compensation (upper incisors proclined, lower incisors retroclined)
- Anterior open/overbite
Cephalometric analysis in Class III malocclusion
- Dentoalveolar Class III=>
- Normal ANB angle=>no apparent sagittal skeletal discrepancy
- Tipping of incisors (upper lingually, lower labially)
- Skeletal Class III=>
- Maxillary retrusion, mandibular prognathism, or combination
- Pseudoclass III=>
- Intermediate cephalometric values between Class I and Class III
- Functional positioning of mandible due to premature contacts
Functional analysis in Class III malocclusion patients
- Clinician manually retrudes mandible to distal position=>
- If edge-to-edge bite is obtained=>anterior crossbite
- If distal movement impossible=>prognathism requiring further evaluation
-Path of closure from postural rest position to occlusion studied=>
-Anterior displacement due to premature contact and tooth guidance=>favorable prognosis.
-Problems from anterior rest position w/ habitual occlusion may require orthognathic surgery
TMJ and tongue assessments in Class III malocclusion
- Assessment of condyle position in temporal fossa=>
- Note increased likelihood of clicking and lateral crepitus if in most posterior position
- Abnormal tongue=>
- Function, size, posture
- Low positioning and macroglossia
Lip function and morphological assessments in Class III malocclusion
- Presence of short, hypotonic, retrusive upper lip
- Appearance of long, lower lip due to closed lip position over Class III molar relationship
- Verification of lower lip length w/ lower incisor tip to soft tissue menton
- Upper lip retrusion associated w/ maxillary retrusion and straight maxillary sulcus curve
Diagnostic characteristics of an unfavorable Class III growth
- Increased gonial angle
- Antegonial notching
- Backward direction of condylar growth
- Thin mandibular symphysis
- Compensation in position of upper and lower incisors due to disproportionate jaw growth
- Retroclined mandibular incisors and flared maxillary incisors as child ages
How differential diagnosis between true Class III and pseudo Class III malocclusion made
- Mandible guided to centric relationship
- Pseudo Class III=>
- Normal overjet or edge-to-edge incisor relation
- Normal SNA and slightly increased SNB
- True Class III cases=>
- Large SNB angle or small SNA angle=>underdeveloped maxilla or long mandibular base
- Strong hereditary component
