Understanding Bone Formation and Craniofacial Growth

Bone Formation Processes

Intramembranous Bone Formation

Bone forms via the direct secretion of bone matrix within connective tissue, without any intermediate formation of cartilage. There is no formation of cartilage in this process.

Key characteristics:

• Occurs in the periosteum (external part), endosteum, alveolar bone, and sutures.
• In the craniofacial vault complex, this type occurs specifically in the cranial vault and jaws.

Endochondral Bone Formation

In this process, cartilage is converted into bone.

Key characteristics:

• In early stages, cartilage is present from the nose to the cranial base and occipital bone.
• Prenatally, a series of synchondroses exist within and between the ethmoid, sphenoid, and occipital bones. These facilitate rapid increase in length to accommodate the growing brain.
• Synchondrosis also occurs in long bones and the cranial base.

Growth of the Nasomaxillary Complex

Growth in Width

Growth in width is generally complete before the pubertal growth spurt, with minimal changes thereafter. Intercanine width typically does not change after 12 years of age. Width increases in posterior zones due to the V-rule.

Growth in Length

• Girls: Continues during the pubertal spurt until 14-15 years of age.
• Boys: Growth rhythm decreases after 18 years of age, approximately four years after the pubertal growth spurt.

Vertical Growth

Vertical growth continues until 21-22 years of age in boys, and 1-2 years earlier in girls. This is critically important in implant therapy, as implants cannot be placed in children due to ongoing vertical growth.

Cartilage Theory and Growth Experiments

Core Principles of Cartilage Theory

Cartilage is considered the primary driver of growth; bone merely replaces it and fills the gaps.

• Condylar Cartilage: This cartilage is considered a controller of body and ramus mandibular growth.
• Growth of the maxilla is often more difficult to explain based on this theory.
• Cartilage in the nasal septum and nasomaxillary complex is believed to grow as a single unit.

Experimental Evidence

Experiments provide insights into cartilage's growth potential:

• Epiphyseal Plate Transplant: A piece of epiphyseal plate from a long bone, when transplanted, continues to grow in its new location. This demonstrates the innate growth potential of cartilages.
• Nasal Septum Cartilage: This cartilage grew nearly as well in culture as it did in its original plate.
• Mandibular Condyle Cartilage:
  • Showed little to no growth when transplanted.
  • Demonstrated less growth in culture compared to other cartilages.
  • This suggests that while other cartilages can act as growth centers, the mandibular condyle may not possess the same intrinsic growth potential.

Ricketts Facial Pattern Analysis

Ricketts analysis defines key facial measurements used for orthodontic and surgical planning:

Key Measurements:

Facial Axis

This is the angle formed behind the line Ba-Na and the Pt-Gn line.

Facial Convexity

This angle is formed by the points Na, Pg, and Ag, Me.

Mandibular Arch

The mandibular arch is formed by the lines Xi-Pm and Cd-Xi.

Lower Facial Height

This measurement is represented by the ANS-Xi-Pm angle.