Craniofacial Development and Malocclusion Etiology

Cranial Synchondroses and Closure Times

Synchondroses are temporary cartilaginous joints crucial for craniofacial growth:

1. Spheno-occipital: Located between the occipital and sphenoidal base. Closes at 18–20 years old.
2. Inter-sphenoidal: Located between the anterior and posterior sphenoid. Closes before birth (prenatally).
3. Spheno-ethmoidal: Located between the sphenoidal and ethmoidal bones. Closes at 5–7 years old.
4. Intra-occipital: Located inside the occipital bone. Closes at 3–5 years old.

Etiology of Local Malocclusion

Local factors contributing to malocclusion are categorized as Hereditary, Acquired, or Other:

• Hereditary Manifestations:
  • Skeletal manifestation
  • Soft tissue manifestation
  • Dental manifestations
• Acquired Factors:
  • Trauma (Macro trauma, Micro trauma [oral habits])
  • Dental diseases (Caries, Gingival and periodontal diseases)
• Other Local Factors:
  • Abnormal labial frenum
  • Ectopic eruption
  • Impacted teeth

Systemic Conditions Related to Craniofacial Development

Diseases Associated with Class III Malocclusion

• Achondroplasia
• Craniofacial dysostosis
• Cleidocranial dysostosis
• Cleft lip and palate
• Hyperpituitarism (Acromegaly)

Diseases Affecting Skull Sutures

• Achondroplasia
• Cleidocranial dysostosis
• Craniofacial dysostosis (Crouzon syndrome)
• Mandibulofacial dysostosis (Treacher Collins syndrome)
• Teratogens (Vitamin D excess)

Conditions Leading to Mouth Breathing

• Cleft lip and palate
• Respiratory diseases (obstructive, habitual, anatomical)
• Microtrauma (oral habits)
• Class II Division 1 Malocclusion

Factors Influencing the Neutral Zone

The Neutral Zone is the space where the forces exerted by the tongue are balanced by the forces exerted by the lips and cheeks. Key influencing factors include:

• Lip and cheek forces acting lingually, balanced by tongue force acting buccally.
• Intraoral pressure induced by mandibular position and movements.
• Occlusal contacts.
• Periodontal ligaments.

Malocclusion Patterns: Deep Bite and Open Bite

Causes of Deep Bite (Excessive Overbite)

• Failure of posterior teeth to reach proper eruptive height.
• Anterior teeth show over-eruption.

Causes of Anterior Open Bite

• Thumb sucking
• Tongue thrust
• Skeletal manifestation

Causes of Posterior Open Bite

• Lateral tongue thrust keeping posterior teeth apart.

Features of Thumb Sucking

• Injured thumb
• Proclination and protrusion of maxillary anterior teeth
• Increased overjet
• Mandibular teeth retrocline
• Mandible retruded
• Anterior open bite
• Maxillary constriction
• Posterior crossbite

Tongue Thrusting Patterns

Adaptive Tongue Thrust (Retained Visceral Swallow Pattern)

This pattern is often associated with general features:

• Proclination of maxillary and mandibular teeth
• Reverse curve of Spee
• General spacing
• Decreased overjet
• Anterior open bite
• Interdental lisp
• Scalloping of the tongue

Adaptive patterns are further classified based on posterior contact:

• Posterior Teeth Together (Remain in Contact): Features include posterior teeth in contact, proclined maxillary and mandibular teeth, and anterior open bite.
• Posterior Teeth Apart (Not in Contact): Features include lateral open bite, anterior teeth over-eruption (deep bite), constriction of the maxilla (posterior crossbite), and anterior lisp.

Endogenous Tongue Thrust

This involves a neuromuscular swallow pattern that is not an acquired habit.

Features:

• Anterior open bite
• Anterior lisp