Functional development of dental arches and occlusion /certified fixed orthodontic courses by Indian dental academy


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Functional development of dental arches and occlusion /certified fixed orthodontic courses by Indian dental academy

  1. 1.
  2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. From birth to adulthood the dental occlusion undergoes significant changes. The term OCCLUSION refers to the manner in which the maxillary and mandibular teeth articulate
  4. 4. Easier said than done, the whole process is infact a complex series involving morphology and angulation of teeth, roles of muscles of mastication, tempromandibular joint, the skeletal components and functional jaw movements. In an earlier disscussion, the growth and development of dental arches and occlusion has already been emphasized, this presentation aims at giving an insight at the various factors that play an active role in this formation.
  5. 5. In a nutshell, the whole process can be summed as follows…. Development phases of dentition from birth to adult life…… i. Birth to complete eruption of deciduous teeth Birth – 2 ½ ii. Completion of deciduous dentition to eruption of first permanent molar 2 ½ - 6 years iii. Mixed dentition period 6 – 12 years iv. Permanent dentition period > 12years
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  8. 8. BONE RELATION…. The position, size and relationship by which the maxilla and mandible relate to one another and to other bones is governed by a variety of factors : i. Heredity ii. Congenital factors which may not be hereditary iii. Hormonal imbalance iv. Traumatic and pathological conditions
  9. 9. TOOTH RELATION…. • Some evidence suggests that tooth development is strongly linked to hereditary control • The permanent incisors develop lingual to the roots of their predecessors • Maxillary canines develop high in the maxilla close to the floor of the orbit • Mandibular canines develop near to the inferior border of the mandible • Premolar crowns develop below and between the roots of the deciduous molars
  10. 10. • The lower permanent molars develop at the root of the coronoid process, oriented with a mesial inclination which in the course of eruption takes a curved path in a upward and forward direction • The upper permanent molars swing downwards and forwards as they erupt through an arc of a circle whose center is in the region of the apex of the next tooth mesially
  11. 11. • Sometimes a defect in the development process maybe observed by the presence of an ectopic tooth or an impacted tooth. • One tooth shown to have a high degree for impaction to occur are the maxillary canines. One of the reasons postulated for this occurrence is the remoteness in the eruption pattern of this tooth. • Mandibular premolars are known for their ectopic eruption pattern, although this is a very rare occurrence. Etiology for this behavior is thought to be because of the deep position of the tooth buds between the root apices of deciduous molar that give it the freedom to ‘wander’.
  12. 12. ERUPTION…. The HOWs and WHYs about tooth eruption are satisfactorily explained by theories put forth by various authors. There is however no single theory that gives a clear definition on how tooth eruption occurs. BLOOD PRESSURE THEORY – Soft tissues at the developing end of the tooth are very vascular and increase in vascularity has been observed in cases of rapid tooth eruption ROOT GROWTH THEORY – This theory postulates that tooth eruption is accompanied by growth of root. But variations of this occur such as, a tooth may fail erupt even though root formation is over. Again, cases of tooth eruption are known to occur at birth with very little root present.
  13. 13. EPITHELIAL COIL THEORY – suggested by Warwick James. It states that epithelial remnants of tooth band and organ cause a progressive channel for tooth eruption. These epithelial coils found above the tooth determine the site of eruption. HAMMOCK LIGAMENT THEORY – suggested by Sicher. He says that the tooth in the crypt is surrounded by a a band of fibrous tissue, which is present at the open apex of the root and is attached to the bone halfway up the wall of the crypt . At this point are present many fluid droplets which act as cushion to protect the developing tooth germ.
  14. 14. INTRA – ORAL FORCES…. At the time of tooth eruption the roots are separated a considerable distance from the socket wall. This gives chance for a lot of play in the tooth. Due to this various forces may act during eruption of the tooth and cause it to be deviated in its eruption. These forces maybe from, musculature of the lips, cheeks and tongue and may also be from mesio-distal forces exerted from adjacent teeth.
  15. 15. It is to be understood that, muscles are never at a state of rest but in a state of TONICITY. This means that a small proportion of fibres even at rest are always in a state of contraction.
  16. 16. Forces generated by the muscles maybe active or passive. Active muscle forces exert forces that are of greater force and frequency and the pressure exerted is only intermittent. One example of such a force system is that of deglutition. The others include speech, mastication, and expression. Passive muscle forces are continuous but light, and mainly due to muscle tonus. Examples of such muscle systems include the Buccinator mechanism, tension from the Orbicularis Oris.
  17. 17. Lip and cheek pressures lost due to tropical disease. The teeth have moved out buccally because of pressure from the tongue and no balancing force from buccinator and orbicularis oris.
  18. 18. OCCLUSAL FORCES…. It is a well know fact that in adult dentition the teeth are held in close approximation with each other because of the tendency of the posterior teeth to move forward. As a result, at the time of eruption there is a chance for crowding in the dentition to occur. Upper and lower alveolar borders grow in a direction that is outwards and forwards as pointed out by Brash. He also suggested that evidence for this was the curvature of the roots.
  19. 19. This forward movement of the dentition may however prove detrimental in cases where a tooth becomes lost because of some pathology. During this time, the tooth just distal has a tendency to tilt into that space. This can result in loss of contact with the opponent result in malocclusion. Thus, a pressure is transmitted mesially from tooth to tooth. The upper incisors are thus prevented from moving mesially by lip pressure and the lower incisors are prevented by overbite of the upper incisors
  20. 20. Trajectorial theory of forces (Wolff’s Law)
  21. 21. Bone is the hardest material in the body and yet the most plastic. It is this resilient feature of the bone that is taken advantage of in meeting the various demands of functional forces. From a historical perspective, the first studies on function of the bone were done on the femur. 1867 - von Meyer and Culmann occurrence on stress lines on long bones like femur 1870 - Julius Wolff proposition of the trajectorial theory of forces (Wolff’s law) 1881 - Wilhelm Roux biological basis for bone formation 1925 - Benninghoff beam hypothesis
  22. 22. The story unfolded … … In 1867, anatomist von Meyer in Zurich, while drawing the pattern of trabecular architecture in long bone of femur, realized with the help of Culmann who was an engineer visiting Zurich, that the trabeculae followed certain patterns similar to internal stress patterns seen in the Fairbairn crane that he was designing.
  23. 23. However it was only 2 years later that, anatomist and orthopedic surgeon von Meyer while doing his dissertation on the normal and abnormal bone formation in animals brought to light that the patterns which Meyer and Culmann saw were infact stress patterns produced as a result of bone adaptation to functional forces. He brought out a law based on these trajectories of stress patterns he observed which came to be known as ‘Wolff’s law’. The law states as follows: “ Every change in the form and the function of a bone or of their function alone is followed by certain definite changes in their internal architecture, and equally definite secondary alterations in their external confirmation, in accordance with mathematical laws ”
  24. 24. In truth, Wolff's law laid the mathematical formulae for the development of such internal stresses and it was around the same time that Roux in 1881 propounded that bone formation occurred as a result of stresses of tension or pressure on the bone. He hypothesized that apposition and resorption by cells determines change in bone structure and that this change is brought about by action of local forces. He infact gave an insight to the biological phenomenon behind this occurrence.
  25. 25. In 1925, Benninghoff, suggested the beam hypothesis after studying lines of stresses in skull. He postulated that these lines were trajectories corresponding to functional stresses. The trajectories in the maxilla can be broadly classified as horizontal and vertical trajectories. Horizontal trajectories : a. Hard palate b. Orbital ridges c. Zygomatic arches d. Palatal bones e. Lesser wings of sphenoid
  26. 26. Vertical trajectories include: a) Fronto-nasal buttress b) Malar-zygomatic buttress c) Ptearygoid buttress
  27. 27. One of the deficiencies of the beam hypothesis is that only mechanical stresses resulting from bite forces on the dentition are considered. In many instances, mechanical stresses resulting from muscle contraction produce large bending moments and therefore large bone strain adjacent to several cranial and zygomaticotemporal facial and sutures reaction temporomandibular joint. such forces as the from the
  28. 28. CONCLUSION: This presentation has aimed at reavealing information on the functional factors that affect the developing dentition. “An orthodontist can establish a perfect occlusal relationship, but unless he takes into consideration the effects of the use of these teeth, unless he makes allowances for the manifold environmental functional influences, the delicately responsive bony structures are apt to change, and the tooth positions will change with them.” GRABER
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