Presentation on theme: "Tooth Eruption Tooth eruption is the process by which a tooth moves from its site of development within the jaws to its final functional position in the."— Presentation transcript:
1Tooth EruptionTooth eruption is the process by which a tooth moves from its site of development within the jaws to its final functional position in the oral cavity.it is a continuous process
2Phases of tooth eruption Pre-eruptive phasePre-functional eruptive phaseFunctional eruptive phase
3Pre-eruptive phaseAll movements of primary and permanent tooth germs (crowns)fromtime of their early initiation and formation to the time of crown completionends with early initiation of root formation
4Pre-Eruptive PhaseEarly in the stage, the permanent anterior teeth begin developing lingual to the incisal level of the primary teeth. Later, as the primary teeth erupt, the secondary teeth are positioned lingual to the apical third of their roots.Permanent premolars shift from a location near the occlusal area of the primary molars to a location enclosed within the roots of the primary molars
7Permanent molars have no predecessors Maxillary molars develop within the maxillary tuberosity with their occlusal surfaces slanted distallyMandibular molars develop in the ramus with the occlusal surfaces slanting mesially
8Pre-Functional Eruptive Starts with the initiation of root formation and ends when the teeth reach occlusal contactFour major events occur during this phase:Root formationMovement occurs incisally or occlusally through the bony crept to reach the oral mucosaPenetration of the tooth crown tip into the oral cavityIntraoral movement occlusally and incisally until clinical contact with the opposing crown occurs.
9The rate of tooth eruption depends on the phase of movement Intraosseous phase: 1 to 10 μm/dayExtraosseous phase (soft tissue): 75 μm/day
10Functional Eruptive Phase Takes place after the teeth are functioning and continues as long as the teeth are present in the mouth
11Post 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 with increasing height of jaws.
122. Movements to compensate for continued occlusal wear. Compensation primarily occurs by continuous deposition of cementum around the apex of the tooth.However, this deposition occurs only after tooth moves. Similar to eruptive tooth movement.
133. Movements to accommodate interproximal wear. Compensated by mesial or approximal drift.Mesial drift is the lateral bodily movement of teeth on both sides of the mouth.Very important in orthodontics.
19Mechanisms of Eruptive Tooth Movement Root formationBone remodelingDental folliclePeriodontal ligamentRole of hydrostatic pressure
20Root formationShould be an obvious cause of tooth eruption. But studies have not provided evidence for this.If a tooth that is continuously erupting is prevented the root still forms by causing bone resorption.
21Rootless tooth still erupt, some teeth erupt more than the total length of the roots and the teeth still erupt after completion of root formation.Therefore root formation is accommodated during eruption and may not be the cause of tooth eruption.Root formation produces a force which causes bone resorption by osteoclast.
22Root growth theory suggested the presence of the cushion hammock ligament at the base of the socket that transmits the force to cause eruption but the ligament was never found histologicallyOne point of importance is that, the tissue beneath the growing root resists the apical movement of the developing root.This resistance results in the occlusal movement of the tooth crown as the root lengthens
23Bone RemodelingAn inherent growth pattern of the maxilla and mandible supposedly moves teeth by selective deposition and resorption of bonenot sure if bone remodeling plays a significant role but is involved
24Dental follicleInvestigators indicate a pattern of cellular activity involving the reduced enamel epithelium (REE) and the follicles associated with tooth eruption.Studies have shown that the reduced dental epithelium initiates a cascade of intercellular signals that recruit osteoclasts to the follicle.
25By providing a signal and chemo-attractant for osteoclasts, it is possible that the dental follicle can initiate bone remodeling which goes with tooth eruption.RDE also secretes proteases, which assist in breakdown of connective tissue to produce a path of least resistance.Teeth eruption is delayed or absent in animal models and human diseases that cause a defect in osteoclast differentiation
26Periodontal ligamentPeriodontal Ligament Traction theory Formation and renewal of the PDL has been considered a factor in tooth eruption because of the traction power of the fibroblasts.Most accepted theory Due to contraction of the FB situated in the PDL, a pressure is created which favors eruption
27Hydrostatic PressureA number of studies exist to demonstrate that there is a hydrostatic pressure difference between the tissue around the erupting crown and its apical extentThe hydrostatic theory was investigated by Hassel and McMinn (1972) who demonstrated that the tissue pressure apically was greater than occlusally theoretically generating an eruptive force.No association was found between the rate of eruption and the pressure gradient.Modification of the pressure changed the rate of eruption in rabbits which somewhat supported the theory
28Shedding of Primary Teeth Shedding is the loss of the primary dentition caused by the physiologic resorption of the roots, the loss of the bony supporting structure and therefore the inability of these teeth to withstand the masticatory forces.Resorption of anterior teeth occurs on the lingual surface and these teeth are shed with their pulp chamber intactResorption of primary molars occurs in interradicular dentine with some resorption of the pulp chamber, coronal dentine and sometimes enamel
31Pressure plays an important role in the exfoliation of primary teeth Resorption of dental hard tissues is achieved by cells with a histological nature similar to that of osteoclasts called OdontoclastsPressure plays an important role in the exfoliation of primary teethStem cells ????These cells are derived from monocytes migrating from blood vessels where they fuse to form multinucleated odontoclasts with clear attachment zone and ruffled border. Little is known on the resorption of the periodontal ligament. Changes in PDL organization and the ability to withstand occlusal forces
32Hormonal Control Mechanisms Eruption occurs only during a critical period between 8pm and midnight or 1am.During the morning, tooth eruption ceases or even the tooth intrudes a bit.This reflects Circadian Rhythm reflecting the possible involvement and control of growth hormone and thyroid hormone.
33Logan and Kronfeld’s chronology of human dentition (1933)
35The time of eruption for primary and permanent teeth varies greatly. A variation of 6 months on either side of the usual eruption date may be considered normal for a given child.Girls eruption of their permanent teeth are 5 months earlier than the boys
36Tooth eruption has three stages Deciduous dentitionMixed dentitionPermanent dentition
37Primary dentitionstarts on the arrival of the mandibular central incisors, typically from around six months,lasts until the first permanent molars appear in the mouth, usually at six years. The primary teeth typically erupt in the following order: (1) central incisor, (2) lateral incisor, (3) first molar, (4) canine, and (5) second molar
38Mixed dentitionstarts when the first permanent molar appears in the mouth, usually at five or six years,lasts until the last primary tooth is lost, usually at ten, eleven, or twelve years.
39Sequence of eruptionThe sequence of calcification is not a sure clue to the sequence of emergence in the mouthWide variabilityMax ( / )Mand ( / )Most common sequenceMax ( ) & Mand ( )
46Primary dentition occlusion Types of molar relationship1- Flush terminal plane:distal surface of opposing E are at the same level37% of primary molar relationship75% of them result in ideal class Ipermanent molar relationship25% will shift to class II
482- mesial step: Distal surface of lower E mesial to distal of upper 49% of primary of molar relationship (most common)mesial step will result in ideal class I molar relationship
493- Distal step : Distal surface of lower E distal to distal of upper 14% of primary molar relationshipResult in class II molar relationship
50Permanent dentition occlusion Molar classification :Class I mesiobuccal cusp of upper 1st molar in buccal groove of lower 1st molar 55%Class II mesiobuccal cusp of upper 1st molar mesial to opposing one 19%Class III mesiobuccal cusp of upper 1st molar distal to opposing oneEnd-on relation ship : mesiobuccal cusp of both molars at the same level 25%
51Criteria for ideal occlusion: Class I molar relationshipOver jet & overbite = 2 mmTight proximal contactsCoincidental dental midlinesFlat occlusal plane