TOOTH ERUPTION AND SHEDDING

DR. BHARTI SACHDEVAM.D.S. 1ST YR

CONTENTS Introduction Dental lamina Vestibular lamina Developmental stages Tooth eruption Pre eruption phase Eruption phase Theories of eruption Post eruption phase Chronology of human dentition Shedding of teeth Clinical considerations Bibliography

During the development of embryo, there is formation of three germ layers – a)Ectoderm

b)Endoderm c)Mesoderm At 6th week of I.U.L. – horseshoe shape – primary

epithelial band At 7th week of I.U.L. – dental lamina & vestibular

lamina

All deciduous teeth arises from dental lamina , later permanent successors arise from its lingual extension & permanent molars from its distal extension.

It serves as primordium for ectodermal portion of deciduous teeth.

Later during development of jaws , permanent molars arise directly from distal extension of dental lamina.

The successors of deciduous teeth develop from lingual extension of free end of dental lamina opposite to enamel organ of each deciduous teeth.

The lingual extension of dental lamina is named successional lamina & develops from 5th month in utero (permanent central incisor )to 10th month of age (second premolar).

EARLY BELL STAGE

ERUPTIONERUPTION

ERUPTION / EMERGENCE OF TEETH

Maurya Massler & Schour (1941) – eruption as process whereby forming tooth migrates from its intraosseous location in the jaw to its functional position within the oral cavity.

“eruption” denote tooth emerging through the gingiva

PRE-ERUPTIVE PHASE Includes movement of developing tooth germs

within alveolar process Growing tooth moves in two directions to maintain

its position in expanding jaws viz. bodily movement & eccentric movement

Bodily movement –which occurs continuously as jaw grows ,is a movement of entire tooth germ.

This causes bone resorption indirection of tooth movement

and bone apposition behind it

Ecentric growth- growth in one part of tooth while rest of remains constant .

For example- root elongates ,yet crown does not increase in size the crown maintains a constant relationship to surrounding alveolar bone while increase in alveolar height compensates for root growth.

Successional permanent teeth develop lingual & near to occlusal level of their primary predecessor.

But at the end of this phase , teeth positioned lingually & near apical third of primary teeth.

Tooth germs grow rapidly

crowding

relieved by lengthing of jaw

tooth germ move outward & upward

This change occurs mainly due to eruption of primary teeth & increase in height of supporting tissues.

Anatomic Stages of tooth eruption – NOYES & SCHOUR

Roots begin their formation as a result of proliferation of both epithelial root sheath & mesenchymal tissue of dental pappila & dental follicle

The erupting tooth moves through bone of crypt & connective tissue of oral mucosa

REE of crown proliferates & forms a thin attachment with oral epithelium

Crown erupts further & lateral border of oral mucosa now becomes DEJ

Tip of crown enters oral cavity by degenerating membrane & breaking through center of double–layered epithelium

REE now surrounding like a cuff , becomes known as junctionl or attachment epithelium

Erupting tooth continues to move occlusally as result of active eruption , exposing more of clinical crown

Separation of attachment epithelium from crown & resulting apical shift of attachment epithelium

Alteration of connective tissue of dental follicle to form pathway initiates by root formation & ends by occlusal contact.

Eruption pathway appears as a decreased & degenerated connective tissue fibers, cells, blood vessels & terminal nerves . These changes are due to loss of blood supply & release of enzymes that aid in degradation of these tissues.

Eruptive phase / pre-functional eruptive phase- Initiates by root formation & ends by occlusal contact.

POST ERUPTIVE PHASE Movements made by the tooth after it has reached its functional position in the occlusal plane.They may be divided in three categories:

Accomodation for growth

Compensation for occlusal wear

Accomodation for interproximal wear

ACCOMMODATION FOR GROWTH - 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. COMPENSATION FOR OCCLUSAL WEAR - Compensation primarily occurs by continuous deposition of cementum around the apex of the tooth. However, this deposition occurs only after tooth moves.

ACCOMMODATION FOR INTERPROXIMAL WEAR - Compensated by mesial or approximal drift.

FACTORS CONTROLLING MESIAL DRIFT:

(a) Contraction of the transseptal fibers: As the proximal tooth

surfaces of adjacent teeth become worn from functional tooth movement, the transseptal fibers of the periodontal ligament become shorter (due to contraction) and thereby maintain tooth contact .

(b) Adaptability of bone tissue: The side of pressure on PDL fibers causes bone resorption, whereas pull on the fibers causes bone apposition. Therefore, as the contact areas of the crowns wear, the teeth tend to move mesially, thereby maintaining the contact.

(c) Anterior compartment of occlusal force: An anteriorly directed force is generated when teeth are clenched, due to the mesial inclination of most teeth and the forward-directed force generated from inter-cuspal forces. Eliminating opposing teeth results in elimination of biting forces, causing a slowing down of the mesial migration

(d) Pressure from soft tissues: Buccal mucosa and tongue push teeth mesially

THEORIES OF TOOTH ERUPTIONRoot elongation theory ( hammock ligament theory )(TOMES 1872)Bone remodelling theory(BRASH 1928)Periodontal ligament contraction theory (THOMAS 1967)Vascular pressure theory Pulp constriction theory(V.KORFF 1935)Dental follicle theory (MARKS & CAHILL 1984)Growth of periodontal tissues Pressure from muscular actionResorption of alveolar crest Hormonal theoryCellular proliferation theory

PTHrp osteoblast activation

RANKL (ODF)

RANK

Osteoclast formation signal transduction

Alveolar bone growth: HERMAN believed that the growth of the alveolar bone might push or squeeze the tooth out of its alveolar and into the oral cavity. However, X-ray and histological section show that the bone does not actually touch the tooth, In addition, this mechanism can operate only upon single conical roots but not on multi rooted teeth.

Pressure from muscular action

Berten suggested that action of musculature of cheeks & lips upon alveolar process might serve to squeeze crown of tooth out into oral cavity like a pumpkin seed from between fingers.

This process continuous until the teeth is in occlusion.

Resorption of alveolar crest – serve to expose crown of tooth into oral cavity. This theory is not tenable since histological examination shows that alveolar crest is the site of most rapid & continous growth of bone.

Hormonal theory – Arthur Keith suggested that hormones secreted by thyroids & pituitary glands might govern eruption of teeth .

This theory does not explain mechanism of eruption of teeth & only points out fact that hormones may affect eruption of teeth.

Foreign body theory – states that calcified body such as tooth tends to be exfoliated by tissue just as does any foreign body.

Cellular proliferation theory – Noyes point out that tremendous pressure ,which is evolved from cellular proliferation, provides growing plant with sufficient force to break through hard obstacles. Similarly ,osmotic pressure & forces resulting from cellular proliferation in pulp & surrounding tissues may account for eruption of teeth.

In 1944 Carlson published a comprehensive radiographic analysis of eruption of different types of permanent teeth. He showed that for human permanent premolars:1) eruption begins only after crown formation is complete,2) root formation occurs initially at expense of basal bone without movement of crown,3) Most of root growth occurs during stage of rapid preocclusal eruption to occlusal plane,4) completion of root, like its initial growth, is at expense of basal bone, &5) teeth continue to erupt slowly or move with growth of alveolar process throughout life.

The Intraosseous Stage of Eruption

All teeth develop within the alveolar bone of jaws. Challenge of intra osseous stage of tooth eruption is to escape from bone surrounding crown and to redirect growth of alveolar bone proper to surround & support a developing root. Former involves bone resorption & latter bone formation on opposite sides of erupting tooth. These activities have been shown to depend upon the adjacent parts of the true dental follicle.

Studies in nonhuman primates have shown that rootless teeth can erupt & that follicle is important in eruption. Damage to follicle was most reliable predictor of failed eruption in transplantation studies.In periods of rapid root growth, bone formation occurs primarily in furcation areas

. Bone growth in apical region occurs only if root growth is not fast enough to keep up with eruption. Rate of eruption is rate of formation of eruption pathway and its coordination with bone formation in selected areas of crypt & alveolar crest. Since rootless teeth can erupt, root formation is not considered prime mover in tooth eruption.

Movement of tooth through bone requires a coordinated resorption & formation of bone, that this process can be plastic, & asymmetrical to accommodate root growth and tooth drift,& that these metabolic events likely begin in enamel epithelia & are continued and coordinated by dental follicle.

Speed of Tooth Eruption

Erupting tooth move at different speeds at different times. Initially, eruption is slow in bone. If there are prolonged delays, ankylosis of tooth to bone can result. The rate of eruption increases as tooth is released from bone, penetrates mucosa, & becomes very slow as it approaches occlusal plane. These shifts in speed are also seen in root formation.

 Basic Principles in Tooth EruptionActive tooth eruption begins in an interaosseous environment. Bone resorption, necessary for eruption, is regulated by dental follicle. Like bone resorption, alveolar bone formation associated with tooth eruption depends upon dental follicle & is associated with high cell proliferation.

(1) Any region of a dental follicle has the potential for initiating and regulating bone resorption and bone formation or for not influencing bone metabolism.(2) Movement of teeth during eruption consists of preparing a path through bone or soft tissues and moving them along this path. There is a failure of eruption when an eruption pathway has not been formed.

(3) Root formation is accomodated during tooth eruption & is a consequence, not a cause of the process.

(4) Bone formation & root formation move an erupting tooth through oral epithelium & into its position within dental arch at occlusal plane. It is unlikely that periodontal ligament contributes substantially to eruption, but may have a role late in process. Bone formation & possibly formation of apical cementum maintain a slow eruptive movement throughout life of tooth.

SEQUENCE OF EMERGENCE OF PRIMARY TEETH Predominant sequence of eruption of primary

teeth in individual jaw is – Central incisor Lateral incisor

First molar Canine

Second molar

TIME LINE FOR HUMAN TOOTH DEVELOPMENT Age developmental characterisitics42-48 days bud stage : deciduous incisors , canines & molars55-56 days bell stage for deciduous teeth , bud stage for permanent 14 weeks bell stage for deciduous teeth ;bud stage for permanent teeth 18 weeks dentin & functional ameloblats in deciduous teeth32 weeks dentin & functional ameloblasts in permanent first molars

SHEDDING OF TEETH Physiologic process resulting in complete elimination of

deciduous dentition. Pattern of sheddingResult of progressive resorption of roots of deciduous teeth and its supporting tissues.Pressure generated by erupting permanent tooth guides pattern of deciduous tooth resorption.Initially , pressure is against root surface of deciduous tooth and resorption occurs on lingual surface.

Later these developing tooth germs occupy a position directly apical to the deciduous tooth.

In mandibular incisors the apical positioning of the tooth germs does not occur thus permanent tooth erupts lingually.

RESORPTION OF DECIDUOUS MOLARS Resorption of roots of deciduous molars first begin on

their inner surfaces because early developing bicuspids are found between them.

With continued growth of jaws & occlusal movement of deciduous molars, successional tooth germs lie apical to deciduous molars.

When bicuspids begin to erupt , resorption of deciduous molars is again initiated and continues until roots are completely lost & tooth is shed.

Occurs on surface of cementum and dentine .

  Involves a loss of the organic as well as

mineral constituent of the matrix .

During resorption process of disorganization relative to mineral & organic components occurs more or less concomitantly.

Resorption of cementum & dentine of

deciduous teeth is characterized by the presence of osteoclasts.

PRIMARY ROOT RESORPTION WITH PERMANENT SUCCESSOR Root resorption of primary teeth starts at site of

root that is closest to permanent successor. E.g in anterior teeth completed crown of permanent successor is found lingual to apical third of root of primary predecessor:

Resorption of lingual surface of apical third of primary tooth root.

Resorption proceeds horizontally in incisal direction until primary tooth sheds & permanent tooth erupts.

PRIMARY ROOT RESORPTION WITHOUT PERMANENT SUCCESSOR Root is protected from resorption by

presence of narrow PDL cell layers which are composed of-

Collagen fibers Fibroblasts Cementoblasts Degrdation of PDL proceed root resorption &

root removal of collagen fibres of PDL is considered main step in initiation of this process.

As face grows & muscles of mastication enlarge ,forces that are applied on deciduous tooth become heavier than primary tooth periodontal ligament can withstand.

HISTOLOGY OF SHEDDING Odontoclasts are resorbing cells derived from

monocytes & migrate from blood vessels to resorption site , wthere they form multinucleated odontoclast with a clear attachment zone & ruffled border.

Giant multinuclear cells with 4-20 nuclei Resorption occurs at ruffled border which greatly

increses surface area of odontoclast in contact with bone.

Distribution of odontoclast during tooth resorption- found on surface of roots in relation to advancing permanent tooth.

Single rooted tooth shed before root resorption is completed.

Odontoclasts are not found in pulp chamber of these teeth.

In molars, roots are completely resorbed & crown is partially resorbed.

Odontoblasts layer is replaced by odontoclasts.

Sometimes all dentine is removed & vascular tissue is seen beneath translucent cap of enamel.

CLINICAL CONSIDERATIONS Natal or neonatal teeth (Massler & Savara 1950) Eruption of teeth at birth called natal teeth or during first 30 days of life called neonatal

teeth

They may be well formed & normal or represent hornified epithelial structures without roots.

Found on gingivae over crest of ridge & arise either from an accessory bud of dental

lamina ahead of deciduous bud or from bud of an accesssory dental lamina

Macknin et al (2000) identified symptoms like general irritability ,disturbed sleep, gum inflammation ,drooling , loss of appetite, diarrhea, circumoral rash ,intraoral ulcers, sucking ,wakefullness & ear rubbing temporailly related to teething.

•Baby is teething when his or her first set of teeth, called primary teeth , break through the gums.•Begins at around 6 months of age.

TEETHING

•Carpenter (1978) found that in 120 subjects ,during eruption of anterior teeth only 39% exhibited several symptoms ( fever , vomiting, diarrhea, drooling irritability ,rashes) & 78% exihibited symptoms in case of eruption of posterior teeth .Also observed that symptoms disappeared on either day of or day after eruption of tooth.

270 children aged between 8 and 36 months were selected & divided into 5 groups with 54 children initially enrolled in each group. Children were seen during an 8-day period during tooth eruption. Five methods used as remedies to reduce teething symptoms were: 1) cuddle therapy, 2) ice, 3) rubbing the gums, 4) teething rings and 5) food for chewing. Teething symptoms, type of erupted tooth, symptoms of recovery & mother’s satisfaction with treatment were evaluated.Results:250 children (mean age 16 ± 7.2 months) completed study. Most frequent teething symptoms were drooling (92 %), sleep disturbances (82.3 %) and irritability (75.6 %). These symptoms were more pronounced in low birth weight children (p > 0.05). Canine eruption led to more loss of appetite than incisor (p = 0.033) or molars eruption (p = 0.014).

The most favorable results for time to recovery & mother’s satisfaction were seen when teething rings were used, followed by cuddle therapy and rubbing the gums.

By: Memarpour, Mahtab; Soltanimehr, Elham; Eskandarian, Taherh. BMC Oral Health. Jul2015, Vol. 15 Issue 1, p1-8. 8p

Develops from third tooth bud arising from dental lamina near permanent tooth bud or possibly from splitting of permanent bud itself.

BIBLIOGRAPHY

Orbans oral histology & embryology (12th edition) (22- 45) (281 – 303)

Memarpour, Mahtab; Soltanimehr, Elham;Eskandarian, Taherh. BMC Oral Health. Jul2015, Vol. 15 Issue 1, p1-8. 8p

Wise GE, Frazier- Bowers S ,D’Souza RN:Crit Rev Oral Biol Med 2002; 13-323

Ten’s cate of oral histology 8th edition(70 – 94)

Oral development of histology by James k. Avery 3RD edition (92 – 105)Shafer’s textbook of oral pathology 6th edition (38- 79)