Eruption of teeth

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tooth eruption


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Eruption of teeth :

Eruption of teeth ERUPTION – Breaking of the teeth through the gums Latin word – “Erumpere” ------means ‘breaking out’

Tooth Eruption:

Tooth Eruption Eruption is the axial movement of the tooth from its developmental position within the jaws to the functional position in the occlusion plane. Tooth movement - includes variety of complex movement

Tooth Eruption Phases:

Tooth Eruption Phases Pre-eruptive phase Pre-functional/ eruptive phase Post eruptive / Functional phase Avery & Steel. Essentials Of Oral Histology And Embryology: A Clinical Approach. 2 nd Edition

Pre-Eruptive Phase :

Pre-Eruptive Phase All movements of primary and permanent tooth crowns from the time of their early initiation and formation to the time of crown completion. Eccentric growth is accompanied with bone resorption altering the shape of the crypt The phase is finished with early initiation of root formation.

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For Decidious dentition – jaw is small, to provide space jaw increases in their size – Increases in length – ant. Toothe germs are carried anteriorly and post tooth germs are carried posteriorly . Mesiodistal growth of tooth germs Increases in their height – to accommodate root growthal growth Increases in width – buccolingual growth of the tooth germs.

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Early 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

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Permanent molars have no predecessors Maxillary molars develop within the maxillary tuberosity with their occlusal surfaces slanted distally Mandibular molars develop in the ramus with the occlusal surfaces slanting mesially

Pre-Functional Eruptive :

Pre-Functional Eruptive Starts with the initiation of root formation and ends when the teeth reach occlusal contact Four major events occur during this phase: Root formation Movement occurs incisally or occlusally through the bony crept to reach the oral mucosa Penetration of the tooth crown tip into the oral cavity Intraoral movement occlusally and incisally until clinical contact with the opposing crown occurs.

Functional Eruptive Phase:

Functional Eruptive Phase Takes place after the teeth are functioning and continues as long as the teeth are present in the mouth Compensate for jaw growth at the condylar area which takes place approx. Upto 18-20 yrs. Compensate for the masticatory wear.

Histology of Tooth Eruption:

Histology of Tooth Eruption Pre eruptive phase – 2 types of movement BODILY MOVEMENT – tooth germ moves from one from one place to other as a whole. EXCENTRIC MOVEMENT – one part of the tooth germ is fixed while the other region keeps proliferating.

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Eruptive phase – 3 main events Development of root Development of periodontal ligament Development of dentogingival junction

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Root – proliferation of HERS in the apical direction Later – proliferation occurs in occlusion direction. 2/3 rd root is complete – eruption begins Initially bone resorption occurs apically but later bone formation occurs apically and resorption occlusally . PDL – all supporting tissue of tooth are formed. Important changes that takes place in the cells of DF – Fibroblasts develop contact with other FB and other cells of DF.

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Appearance of microfilaments within the FB – favour tooth eruption Formation of fibronexus – morphological relationship b/w the intracellular microfilaments and extracellular fibers through transmembrane proteins called fibronectin . Plays a major role in eruption. Dual function of FB – resorption of fibers and ground substance on one side and synthesis or deposition on other side.

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Formation of DGJ - The globernacular cord: The fibrocellular follicle surrounding a successional tooth retains its connection with the lamina propria of the oral mucous membrane by means of a strand of fibrous tissue containing remnants of the dental lamina In a dried skull it is called globernacular canal During eruption the canal is widened rapidly by local osteoclastic activity, delineating the eruptive pathway for the tooth

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Rate of eruption depends on the phase of movement. In the intraosseous phase the rate is 1-10µm per day. In soft tissues it is 75µm per day. As the tooth is erupting into the oral cavity fusion between the reduced enamel epithelium and the oral epithelium occurs to allow the emergence of the tooth into the oral cavity

Theories of Tooth Eruption:

Theories of Tooth Eruption Mechanism of tooth eruption is not fully understood yet, most reviews on the subject concluded that eruption is a multifactorial process in which cause and effect are difficult to separate. Theories of tooth eruption include: Role of root formation Role of bone remodeling Role of dental follicle Role of periodontal ligament Role of hydrostatic pressure

Root Formation:

Root Formation It was believed that root formation is an obvious cause of tooth eruption because it causes an overall increase in length of the tooth that must be accommodated by the growth of the root into the bone, an increase in jaw height or by the occlusal movement of the crown (eruption). Root 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 histologically

Root formation:

Root formation Clinical observation, experimental studies and histological analysis argue strongly against this theory: In animal studies, if a continuously erupting tooth is pinned to bone, root formation continues Rootless teeth erupt Some teeth erupt a greater distance more than the length of their roots Teeth still erupt even following root completion Removal of tissues forming the root are excised surgically teeth continue to erupt

Bone Remodeling :

Bone Remodeling An inherent growth pattern of the maxilla and mandible supposedly moves teeth by selective deposition and resorption of bone. Theory – not accepted Bone resorption and formation is as a result of eruptive forces applied by tooth over the bone.

Hydrostatic Pressure:

Hydrostatic Pressure A number of studies exist to demonstrate that there is a hydrostatic pressure difference between the tissue around the erupting crown and its apical extent The 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.

Periodontal Ligament Traction theory:

Periodontal 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 presure is createwd which favors eruption. Fibronexus – favors eruption – contraction of all FB together and contraction of PDL fibers .

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Studies favouring the theory – rodents study Certain drugs which prevents CF formation – no eruption. Becoz , CF of PDL is not formed. Tooth placed in a medium of collage gel and FB – root is moved from one place to other.

Dental Follicle :

Dental Follicle Marks and Cahill (1980, 1984) demonstrated in animal studies the role of the dental follicle in tooth eruption. Investigators indicate a pattern of cellular activity involving the reduced enamel epithelium (REE) and the follicles associated with tooth eruption. Intercellular signals that recruit osteoclasts to the follicles thus allowing remodeling of bone that occurs with tooth movement EO and DP were removed and replaced by silica – eruption of the silica replica was observed. DF plays a vital role in eruption.

Control of Eruption:

Control of Eruption 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. Hormonal Control Mechanisms

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A study by Leache et al (1988) of children with growth deficit concluded that children with delayed growth due to growth hormone deficiency or low genetically determined height had delayed tooth eruption. However those with delayed growth for other reasons show normal dental development. This was a large study of children who were shorter than average for their chronological age, although the numbers of children in each group studies were relatively small.

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Logan and Kronfeld’s chronology of human dentition (1933)

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The 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.

Teething and teething difficulties:

Teething and teething difficulties According to Macknin et al the teething period was defined as the 8-day period beginning 4 days before a tooth emergence and extending 3 days after the event. Over half of babies have one or more problems during teething. In a prospective study by Seward, mothers of 224 infants reported 74% and 100% to suffer at least one local disturbance during the eruption of the front and back teeth, respectively.

Extraoral & Intraoral symptoms:

Extraoral & Intraoral symptoms Finger chewing Lip biting Object biting Irritability/restlessness Night crying Drooling Circumoral rash and inflammation Appetite loss Flushed cheeks Mild temperature elevation Ear rubbing Gum rubbing Inflammation/gingival redness over erupting tooth Tender swollen gums Tooth erupting

Myths and Realities:

Myths and Realities Although many studies have suggested associations between teething and a range of signs and symptoms; both local and systemic, the level of evidence remains poor for any cause-effect relationship. Historically, teething has often been blamed when diagnostic ability has failed . Since the eruption of teeth is a normal physiologic process, the association with fever and systemic disturbances is not justified. A fever or respiratory tract infection during this time should be considered coincidental to the eruption process rather than related to it.

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High temperature (higher than 39°C) should not be attributed to teething, and should be investigated Since eruption takes place over a period of two and a half years, it is not surprising that these coincidental factors emerge. If attention is given to these symptoms, it is often recognized that some other coincidental mild infection is present, usually gastro-intestinal or upper respiratory. An undiagnosed primary herpetic infection (primary herpetic gingivo-stomatitis) could be responsible for the symptoms of fever, irritability and appetite loss

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Reassurance of the parents regarding teething signs and symptoms by the pediatrician, dentist or auxiliary staff is necessary. Steward recommended a sequential approach to the management of teething ranging from giving the child objects to bite on through topical and systemic medications.

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