Growth and Eruption in Orthodontics
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Moss Theory and 2 Examples
- Growth of face happens as response to functional needs and neurotrophic influences and is mediated via soft tissues in which jaws are embedded.
- Soft tissue growth causes both bone and cartilage to react.
- Growth of cranial vault is a direct response to growth of brain.
- Growth of eyes increases size of orbit.
- Major determinant of growth of maxilla and mandible is enlargement of nasal and oral cavities, which grow in response to functional needs. Important for orthodontic treatment with functional appliances and orthopedic treatment.
Cite and Centre of Growth Differences
Site of growth is location at which growth occurs. Center of growth is where independent growth occurs, genetically controlled growth. Center of growth is genetically programmed to grow and all centers of growth are also sites of growth but reverse isn't true.
1st Transitional Period Start and End
Starts at 6 years old, when there's exfoliation of any tooth from incisor group and eruption of any tooth from 1st molar group. Finishes when all 1st molars and all 8 incisors are present and in occlusion. Overbite varies during development during eruption of primary canines when primary dentition overbite is set, eruption of permanent 1st when overbite in mixed dentition is set, during eruption of permanent canines and premolars when overbite in permanent dentition is set.
2 Eruption Mechanisms, 2 Hypotheses
Eruptive process is a mixture of forces trying to push the tooth to the buccal surface and other opposite forces. Vascular hypothesis states that eruptive movements are maintained by pressure differentials along the periodontal ligament space and that periodontal tissue pressures are high. Root elongation hypothesis is supported by the theory of tooth movement involving root growth, as the intraosseous phase of eruption doesn't begin until root formation has begun. The root is only 2/3 formed at the time of emergency into oral cavity. Leeway space, combined mesiodistal width of permanent canines and premolars is usually less than that of the primary canine and molars, this surplus space is called leeway, 1.8mm in maxilla, 3.4mm in mandible.
Eruptive Sequences
IC 7.25, 6.25, IL, 8.25, 7.5, C, 11.5, 10.5, 1PM, 10.25, 10.5, 2PM, 11, 11.25, 1M, 6.25, 6, 2M, 12.5, 12