Lec. 3 Pedodontics د.حسن الوطيفي Eruption of the teeth
Definition: The process of eruption involves the movement or change of position of the tooth from the deeper portion of the jaws into the oral cavity until it achieves occlusal contact with adjacent and apposing teeth.
Although many theories have been advanced, the factors responsible for the eruption of the teeth are not fully understood.
The factors that have been related to the eruption of teeth include:
Elongation of the root.
Forces exerted by the vascular tissues around and beneath the root.
Growth of the alveolar bone.
Growth of dentin.
Growth and pull of the periodontal membrane.
Presence of a viable dental follicle.
Pressure from the muscular action.
Resorption of the alveolar crest.
Factors influencing the timing of eruption
Genetic factors: lower teeth erupted before upper teeth.
Gender: girls precede boys.
Hormonal factors: pituitary growth hormones and thyroid hormones.
The researchers state that tooth eruption is a complex and tightly regulated process that involves cells of the tooth organ and the surrounding alveolus. Mononuclear cells (osteoclast precursors) must be recruited into the dental follicle prior to the onset of eruption. These cells, in turn, fuse to form osteoclasts that resorb alveolar bone, creating an eruption pathway for the tooth to exit its bony crypt. In recent years, knowledge of the biology of tooth eruption has greatly increased. What has emerged is the realization that interactions of osteoblasts, osteoclasts, and dental follicles involve a complex interplay of regulatory genes that encode various transcription factors, proto-oncogene, and soluble factors.
Phases of tooth eruption:
1. Presumptive phase (pre-eruptive phase):
All movements of primary and permanent tooth germs (crowns) from time of their early initiation and formation to the time of crown completion (ends with early initiation of root formation).
2. Eruptive phase: Starts with initiation of root formation and made by teeth to move from its position with in bone of the jaw to its functional position in occlusions. Has an intraosseous and extra osseous compartment. It includes 4 stages: Root formation, movement, penetration and oclussal contact.
3. Post eruptive phase: Takes place after the teeth are functioning to maintain the position of the erupted tooth in occlusion while the jaws are continuing to grow and compensate for colossal and proximal tooth wear.
Why do developing crowns move constantly in the jaws during the presumptive phase?
1. To place the teeth in position for eruptive tooth movement.
2. To alleviate the problems of jaw growth, this allows second molar to move backward and anterior teeth to move forward
2 Developing crown move constantly during the presumptive phase as they respond to positional changes of the neighboring crowns and to changes in the mandible and maxilla.
3. Permanent teeth develop lingual to the incise level of the primary anterior teeth and later as primary teeth erupt, the permanent crowns are lingual to the apical 3rd of primary roots.
4. Permanent prernolars move from colossal level of primary molars to a position enclosed within the primary tooth roots.
5. All movements in the presumptive phase occur within the crypts of the developing crowns.
Type of tooth movement in pre-eruptive phase:
Total bodily movement.
Movement where one part remains fixed while the rest continues to grow leading to change in the center of the tooth germ.
Eruptive tooth movement: 4 major events occur:
1. Root formation: Include:
Space is required for root formation.
Proliferation of epithelial root sheath.
Initiation of root dentin and pulp.
Increase in fibrous tissue of the follicle
Occurs finically or colossally.
The main reason for movement is so that the roots can form normally.
Reduced enamel epithelium fuses and contacts the oral epithelium.
3. Penetration of the tooth's crown tip through the fused epithelial layers allowing entrance of the crown into the oral cavity.
4. Intraoral incisal or colossal movement of the erupting tooth continues until clinical contact with the opposing crown occurs.
Clinical crown:During eruption, the exposed crown extending from the cusp tip to the area of the gingival attachment.
Anatomic crown: Entire crown, extending from cusp tip to the cementoenamel (CEJ.) junction
Pos- eruptive tooth movement:
1. Movements to accommodate the growing jaws. Mostly occurs between 14 and 18
years by formation of new bone at the alveolar crest and base of socket to keep pace wit increasing height of jaws.
2. Movements to compensate for continued occlusal wears. Compensation primarily occurs by continuous deposition of cernentum around the apex of the tooth. However, this deposition occurs only after tooth moves. Similar to eruptive tooth movement.
3. Movements to accommodate interproximal wear. Compensated by mesial or proximal drift. Mesial drift is the lateral bodily movement of teeth on both sides of the mouth. Very important in orthodontics.
Active eruption: to compensate incisal arid occlusal wear.
Passive eruption: gradual recession of the gingiva and the underlying alveolar bone.
Both active and passive eruption leads to lengthening of clinical crown.
Variation in the sequence of eruption:
1- The mandibular first permanent molars are often the first permanent teeth to erupt. They are quickly followed by the mandibular central incisors.
2- Moyers stated that the most common sequence of eruption of permanent teeth in the mandible is first molar, central incisor, lateral incisor, canine, first premolar, second premolar, and second molar.'' The most common sequence for the eruption of the maxillary permanent teeth is first molar, central incisor, lateral incisor, first premolar, second premolar, canine, and second molar (Fig. 1).
3- These common sequences in each arch to be favorable for maintaining the length of the arches during the transitional dentition.
4- The mandibular canine erupted before the maxillary and mandibular first premolars in girls. In boys the eruption order was reversed, the maxillary and mandibular first premolars erupted before the mandibular canine.
5- The mandibular canine erupts before the first and second premolars because of:
This sequence aids in maintaining adequate arch length.
Prevent lingual tipping of the incisors. Lingual tipping of the incisors not only causes a loss of arch length but also allows the development of an increased overbite.
An abnormal lip musculature or an oral habit that causes a greater force on the lower incisors than can be compensated by the tongue allows a collapse of the anterior segment. For this reason use of a passive lingual arch appliance is often indicated when the primary canines have been lost prematurely or when the sequence of eruption is undesirable.
6- A deficiency in arch length can occur if the mandibular second permanent molar develops and erupts before the second premolar.
7- Eruption of the second permanent molar first encourages mesial migration or tipping of the first permanent molar and encroachment on the space needed for the second premolar.
8- In the maxillary arch the first premolar ideally should erupt before the second premolar, and they should be followed by the canine.
9- The untimely loss of primary molars in the maxillary arch, which allows the first permanent molar to drift and tip mesially, results in the permanent canines being blocked out of the arch, usually to the labial side.
10- The position of the developing second permanent molar in the maxillary arch and its relationship to the first permanent molar should be given special attention. Its eruption before the premolars and canine can cause a loss of arch length, just as in the mandibular arch.
11- The eruption of the maxillary canine is often delayed because of an abnormal position or devious eruption path. This delayed eruption should be considered along with its possible effect on the alignment of the maxillary teeth.
LINGUAL ERUPTION OF MANDIBULAR PERMANENT INCISORS
The eruption of mandibular permanent incisors lingual to retained primary incisors is often a source of concern for parents. The primary teeth may have undergone extensive root resorption and may be held only by soft tissues. In other instances the roots may not have undergone normal resorption and the teeth remain solidly in place. It is common for mandibular permanent incisors to erupt lingually, and this pattern should be considered
essentially normal. It is seen both in patients with an obvious arch length inadequacy and in those with a desirable amount of spacing of the primary incisors.
1. In either case the tongue and continued alveolar growth seem to play an important role in influencing the permanent incisors into a more normal position with time. Although there may be insufficient room in the arch for the newly erupted permanent tooth, its position will improve over several months.
2. In some cases there is justification for removal of the corresponding primary tooth. Extraction of other primary teeth in the area is not recommended, however, because it will only temporarily relieve the crowding and may even contribute to the development of a more severe arch length inadequacy.
Influence of premature loss of primary teeth on the eruption time of their successors
1- Eruption of the premolar teeth is delayed in children who lose primary molars at 4 or 5 years of age and before.
2- If extraction of the primary molars occurs after the age of 5 years, there is a decrease in the delay of premolar eruption.
3- At 8, 9, and 10 years of age, premolar eruption resulting from premature loss of primary teeth is greatly accelerated.
Teeth reach occlusion before the root development is complete.