eruption and shedding of teeth. mixed dentition: presence of both dentitions figure from ten...

Eruption and Shedding of Teeth Eruption and Shedding of Teeth

Mixed Dentition: Presence of both dentitionsMixed Dentition: Presence of both dentitions

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6 thth edition edition

Tooth eruption is the process by which developing teeth emergeTooth eruption is the process by which developing teeth emergethrough the soft tissue of the jaws and the overlying mucosa tothrough the soft tissue of the jaws and the overlying mucosa toenter the oral cavity, contact the teeth of the opposing arch, andenter the oral cavity, contact the teeth of the opposing arch, andfunction in mastication – function in mastication – therefore it is a continuous processtherefore it is a continuous process

Phases of tooth eruptionPhases of tooth eruptionPreeruptive phase:Preeruptive phase: All movements of primary and permanent All movements of primary and permanenttooth germs (crowns) from time of their early initiation andtooth germs (crowns) from time of their early initiation andformation to the time of crown completion (ends with early initiationformation to the time of crown completion (ends with early initiationof root formation) of root formation)

Eruptive phase:Eruptive phase: Starts with initiation of root formation and made Starts with initiation of root formation and madeby teeth to move from its position within bone of the jaw to itsby teeth to move from its position within bone of the jaw to itsfunctional position in occlusion. Has an intraosseous andfunctional position in occlusion. Has an intraosseous andextraosseous compartments. extraosseous compartments. 4 stages: root formation, movement,4 stages: root formation, movement,penetration and occlusal contact penetration and occlusal contact

Posteruptive phase:Posteruptive phase: Takes place after the teeth are functioning to Takes place after the teeth are functioning tomaintain the position of the erupted tooth in occlusion while themaintain the position of the erupted tooth in occlusion while thejaws are continuing to grow and compensate for occlusal andjaws are continuing to grow and compensate for occlusal andproximal tooth wear proximal tooth wear

Remember that during all these 3 stages is the progression thatRemember that during all these 3 stages is the progression thathappens from primary to permanent dentition which involves thehappens from primary to permanent dentition which involves theshedding (exfoliation) of primary teethshedding (exfoliation) of primary teeth

Dentition:Dentition: Diphodont: two sets of dentition in humansDiphodont: two sets of dentition in humansPrimaryPrimary vs Secondary dentition vs Secondary dentitionDeciduous vs Deciduous vs PermanentPermanent dentition dentitionMixed dentition: presence of two dentitionMixed dentition: presence of two dentition

Teeth in primary dentition are smaller and fewer in number thanTeeth in primary dentition are smaller and fewer in number thanpermanent dentition to conform to the smaller jaw sizepermanent dentition to conform to the smaller jaw size

Primary dentition: ~ 2 to 6 years of agePrimary dentition: ~ 2 to 6 years of ageMixed dentition: ~ 6 to 12 yearsMixed dentition: ~ 6 to 12 yearsPermanent dentition: > 12 yearsPermanent dentition: > 12 years

Source: http://www.columbia.edu/itc/hs/dental/d9903/lectures/lecture4.pdf

Pre-eruptive tooth movement: Why do developing crownsPre-eruptive tooth movement: Why do developing crownsmove constantly in the jaws during the preeruptive phase?move constantly in the jaws during the preeruptive phase?

To place teeth in position for eruptive tooth movementTo place teeth in position for eruptive tooth movement

1.1. To alleviate the problems of jaw growth which allows secondTo alleviate the problems of jaw growth which allows secondmolar to move backward and anterior teeth to move forwardmolar to move backward and anterior teeth to move forward

2.2. Developing crown move constantly during the preeruptive phaseDeveloping crown move constantly during the preeruptive phaseas they respond to positional changes of the neighboring crownsas they respond to positional changes of the neighboring crownsand to changes in the mandible and maxillaand to changes in the mandible and maxilla

3.3. Permanent teeth develop lingual to the incisal level of the primaryPermanent teeth develop lingual to the incisal level of the primaryanterior teeth and later as primary teeth erupt, the permanentanterior teeth and later as primary teeth erupt, the permanentcrowns are lingual to the apical 3crowns are lingual to the apical 3rdrd of primary roots of primary roots

4.4. Permanent premolars move from occlusal level of primary molarsPermanent premolars move from occlusal level of primary molarsto a position enclosed within the primary tooth rootsto a position enclosed within the primary tooth roots

5.5. All movements in the preruptive phase occur within the cryptsAll movements in the preruptive phase occur within the cryptsof the developing crowns of the developing crowns

Two types of tooth movement in pre-eruptive phase:Two types of tooth movement in pre-eruptive phase:

1.1. Total bodily movementTotal bodily movement

2.2. Movement where one part remains fixed while the restMovement where one part remains fixed while the restcontinues to grow leading to change in the center of thecontinues to grow leading to change in the center of thetooth germtooth germ

Essentials of Oral Histology and Embryology. James Avery, 2nd edition

Source: http://www.columbia.edu/itc/hs/dental/d9903/lectures/lecture4.pdfSource: http://www.columbia.edu/itc/hs/dental/d9903/lectures/lecture4.pdf

Eruptive Tooth MovementEruptive Tooth Movement

4 major events occur:4 major events occur:1.1. Root formation. Space is required for root formation Root formation. Space is required for root formation

Proliferation of epithelial root sheathProliferation of epithelial root sheathInitiation of root dentin and pulpInitiation of root dentin and pulpIncrease in fibrous tissue of the follicleIncrease in fibrous tissue of the follicle

2.2. Movement. Occurs incisally or occlusallyMovement. Occurs incisally or occlusallyThe main reason for movement is so that theThe main reason for movement is so that theroots can form normallyroots can form normallyReduced enamel epithelium fuses and contactsReduced enamel epithelium fuses and contactsthe oral epitheliumthe oral epithelium

3.3. Penetration of the tooth’s crown tip through the fusedPenetration of the tooth’s crown tip through the fusedepithelial layers allowing entrance of the crown into theepithelial layers allowing entrance of the crown into theoral cavityoral cavity

4.4. Intraoral incisal or occlusal movement of the erupting toothIntraoral incisal or occlusal movement of the erupting toothcontinues until clinical contact with the opposing crown occurscontinues until clinical contact with the opposing crown occurs

Essentials of Oral Histology and Embryology. James Avery, 2Essentials of Oral Histology and Embryology. James Avery, 2ndnd edition edition

Clinical crown:Clinical crown: During eruption, the exposed crown extending During eruption, the exposed crown extendingfrom the cusp tip to the area of the gingival attachmentfrom the cusp tip to the area of the gingival attachment

Anatomic crown:Anatomic crown: Entire crown, extending from cusp tip to the Entire crown, extending from cusp tip to thecementoenamel (CE) junctioncementoenamel (CE) junction

Histology – changes that occur in tissues overlyingHistology – changes that occur in tissues overlying erupting teetherupting teeth

Degeneration of connective tissue (decrease in blood vessels andDegeneration of connective tissue (decrease in blood vessels anddegeneration of nerves) immediately overlying the erupting teethdegeneration of nerves) immediately overlying the erupting teeth

Eruption pathway – altered tissue area overlying the teethEruption pathway – altered tissue area overlying the teeth

Macrophages destroy cells and fibers by secreting hydrolyticMacrophages destroy cells and fibers by secreting hydrolyticenzymesenzymes

Gubernacular cord:Gubernacular cord: The connective tissue overlying a The connective tissue overlying asuccessional tooth that connects with the lamina propria of thesuccessional tooth that connects with the lamina propria of theoral mucosa by means of a strand of fibrous connective tissue thatoral mucosa by means of a strand of fibrous connective tissue thatcontains remnants of dental laminacontains remnants of dental lamina

Gubernacular canal:Gubernacular canal: Holes noted in a dry skull noted lingual to Holes noted in a dry skull noted lingual toprimary teeth in jaws that represent openings of gubernacular cord primary teeth in jaws that represent openings of gubernacular cord

As the successional teeth erupt, gubernacular canal widensAs the successional teeth erupt, gubernacular canal widensenabling tooth to erupt enabling tooth to erupt

Essentials of Oral Histology and Embryology. James Avery,Essentials of Oral Histology and Embryology. James Avery,22ndnd edition edition

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci,Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci,66thth edition edition

Stages of tooth eruption Stages of tooth eruption


Histology – Surrounding tissuesHistology – Surrounding tissues

The surrounding fibers change from being parallel to the toothThe surrounding fibers change from being parallel to the toothsurface to bundles that are attached to the tooth surface andsurface to bundles that are attached to the tooth surface andextending towards the periodontium (bone)extending towards the periodontium (bone)

The periodontal ligament have contractile properties and changesThe periodontal ligament have contractile properties and changesdrastically during eruptiondrastically during eruption

During eruption, collagen fiber formation and turnover are rapidDuring eruption, collagen fiber formation and turnover are rapidenabling fibers to attach and release and attach in rapid succession.enabling fibers to attach and release and attach in rapid succession.Some fibers may attach and reattach later while the tooth movesSome fibers may attach and reattach later while the tooth movesocclusally as new bone forms around it and the fibers will organizeocclusally as new bone forms around it and the fibers will organizeand increase in number and density as the tooth erupts and increase in number and density as the tooth erupts

Histology – Underlying tissuesHistology – Underlying tissues

As the tooth moves occlusally it creates space underneath theAs the tooth moves occlusally it creates space underneath thetooth to accommodate root formationtooth to accommodate root formation

Fibroblasts around the root apex form collagen that attach toFibroblasts around the root apex form collagen that attach tothe newly formed cementumthe newly formed cementum

Bone trabeculae fill in the space left behind as the tooth eruptsBone trabeculae fill in the space left behind as the tooth eruptsin the pattern of a ladder which gets denser as the tooth eruptsin the pattern of a ladder which gets denser as the tooth erupts

After tooth reaches functional occlusion periodontal fibers attachAfter tooth reaches functional occlusion periodontal fibers attachto the apical cementum and extend into the adjacent alveolar boneto the apical cementum and extend into the adjacent alveolar bone

The rate of tooth eruption depends on the phase of movementThe rate of tooth eruption depends on the phase of movement

Intraosseous phase: 1 to 10 Intraosseous phase: 1 to 10 µm/dayµm/day

Extraosseous phase: 75 Extraosseous phase: 75 μμm/daym/day

Environmental factors affecting the final position of the tooth:Environmental factors affecting the final position of the tooth:Muscular forcesMuscular forcesThumb-suckingThumb-sucking

Mechanisms of Eruptive Tooth MovementMechanisms of Eruptive Tooth Movement

Eruption is a multifactorial processEruption is a multifactorial process

The accepted theories of tooth eruption are:The accepted theories of tooth eruption are:1.1. Root Formation.Root Formation. Should be an obvious cause of tooth eruption. Should be an obvious cause of tooth eruption.

But studies have not provided evidence for this. If a tooth thatBut studies have not provided evidence for this. If a tooth thatis continuously erupting (rodent incisor and guinea pig molar) isis continuously erupting (rodent incisor and guinea pig molar) isprevented the root still forms by causing bone resorption.prevented the root still forms by causing bone resorption.Rootless tooth still erupt, some teeth erupt more than the totalRootless tooth still erupt, some teeth erupt more than the totallength of the roots and the teeth still erupt after completion oflength of the roots and the teeth still erupt after completion ofroot formation. Therefore root formation is accommodatedroot formation. Therefore root formation is accommodatedduring eruption and may not be the cause of tooth eruption. during eruption and may not be the cause of tooth eruption.

One point of importance is that, the tissue beneath the growingOne point of importance is that, the tissue beneath the growingroot resists the apical movement of the developing root. Thisroot resists the apical movement of the developing root. Thisresistance results in the occlusal movement of the tooth crownresistance results in the occlusal movement of the tooth crownas the root lengthens.as the root lengthens.

2.2. Bone Remodeling.Bone Remodeling. Major proof is when a mand PM is Major proof is when a mand PM is removed without disturbing its follicle or you wire down theremoved without disturbing its follicle or you wire down the tooth germ, an eruptive pathway still forms within bone astooth germ, an eruptive pathway still forms within bone as osteoclasts widen the gubernacular canal. If the dental follicleosteoclasts widen the gubernacular canal. If the dental follicle is also removed no eruption path develops. So not sure if boneis also removed no eruption path develops. So not sure if bone remodeling plays a significant role but is involved.remodeling plays a significant role but is involved.

One point to remember: Bone formation also occurs apical to theOne point to remember: Bone formation also occurs apical to thedeveloping toothdeveloping tooth

• Dental Follicle.Dental Follicle. Studies have shown that the reduced dental Studies have shown that the reduced dentalepithelium initiates a cascade of intercellular signals that recruitepithelium initiates a cascade of intercellular signals that recruitosteoclasts to the follicle. By providing a signal andosteoclasts to the follicle. By providing a signal andchemoattractant for osteoclasts, it is possible that the dentalchemoattractant for osteoclasts, it is possible that the dentalfollicle can initiate bone remodeling which goes with toothfollicle can initiate bone remodeling which goes with tootheruption. Teeth eruption is delayed or absent in animal modelseruption. Teeth eruption is delayed or absent in animal modelsand human diseases that cause a defect in osteoclastand human diseases that cause a defect in osteoclastdifferentiation.differentiation.


4.4. Periodontal ligament.Periodontal ligament. Formation and renewal of PDL can Formation and renewal of PDL can be a factor in tooth eruption because of the traction powerbe a factor in tooth eruption because of the traction power of the fibroblasts. However, presence of PDL does not alwaysof the fibroblasts. However, presence of PDL does not always correlate with tooth eruption. Other factors involved arecorrelate with tooth eruption. Other factors involved are vascular pressures within the PDL. Examples of PDL beingvascular pressures within the PDL. Examples of PDL being present but tooth not erupting and rootless teeth eruptingpresent but tooth not erupting and rootless teeth erupting have been reported. have been reported.


Post Eruptive Tooth MovementPost Eruptive Tooth Movement

1.1. Movements to accommodate the growing jaws. Mostly occursMovements to accommodate the growing jaws. Mostly occursbetween 14 and 18 years by formation of new bone at thebetween 14 and 18 years by formation of new bone at thealveolar crest and base of socket to keep pace wit increasingalveolar crest and base of socket to keep pace wit increasingheight of jaws. height of jaws.

2.2. Movements to compensate for continued occlusal wear.Movements to compensate for continued occlusal wear.

Compensation primarily occurs by continuous deposition ofCompensation primarily occurs by continuous deposition ofcementum around the apex of the tooth. However, thiscementum around the apex of the tooth. However, thisdeposition occurs only after tooth moves. Similar to eruptivedeposition occurs only after tooth moves. Similar to eruptivetooth movement.tooth movement.

3.3. Movements to accommodate interproximal wear. CompensatedMovements to accommodate interproximal wear. Compensated

by mesial or approximal drift. by mesial or approximal drift. Mesial drift is the lateralMesial drift is the lateralbodily movement of teeth on both sides of the mouth.bodily movement of teeth on both sides of the mouth.Very important in orthodontics.Very important in orthodontics.

Several factors control mesial drift:Several factors control mesial drift:(a) Contraction of the transseptal fibers: As the proximal tooth(a) Contraction of the transseptal fibers: As the proximal tooth surfaces of adjacent teeth become worn from functional toothsurfaces of adjacent teeth become worn from functional tooth movement, the transseptal fibers of the periodontal ligamentmovement, the transseptal fibers of the periodontal ligament become shorter (due to contraction) and thereby maintainbecome shorter (due to contraction) and thereby maintain tooth contact tooth contact

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

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

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

Active eruptionActive eruption: to compensate incisal and occlusal wear : to compensate incisal and occlusal wear

Passive eruptionPassive eruption: gradual recession of the gingiva and the: gradual recession of the gingiva and theunderlying alveolar boneunderlying alveolar bone

Both active and passive eruption leads to lengthening ofBoth active and passive eruption leads to lengthening ofclinical crownclinical crown

Shedding of TeethShedding of Teeth

1.1. Osteoclast/bone remodelingOsteoclast/bone remodeling2.2. Odontoclast (cementoclast; dentinoclast)Odontoclast (cementoclast; dentinoclast)3.3. Resorption of soft tissuesResorption of soft tissues

Pressure from successional teethPressure from successional teeth

OdontoclastOdontoclast

Figure Source: Dr. Sandra MeyersFigure Source: Dr. Sandra Meyers

OsteoclastsOsteoclasts are bone resorbing cells derived form monocyte- are bone resorbing cells derived form monocyte-macrophage lineagemacrophage lineage

Giant multinuclear cells with 4-20 nucleiGiant multinuclear cells with 4-20 nuclei

Osteoclasts resorb hard tissue by separating mineral from theOsteoclasts resorb hard tissue by separating mineral from thecollagen matrix through the action of hydrolytic enzymescollagen matrix through the action of hydrolytic enzymes

Resorption occurs at the ruffled border which greatly increasesResorption occurs at the ruffled border which greatly increasesthe surface area of the osteoclast in contact with bone the surface area of the osteoclast in contact with bone

Hard Tissue resorption: Hard Tissue resorption: 1. Extracellular phase1. Extracellular phase2. Intracellular phase2. Intracellular phase

5 months5 monthsAt birthAt birth 1 year1 year

2 years2 years 3.5 years3.5 years 4.5 years4.5 years

Shedding of mandibular incisorShedding of mandibular incisor


Deciduous 1Deciduous 1stst molar molar


Shed element following “shedding of primary incisorShed element following “shedding of primary incisor

Complete resorption of rootsComplete resorption of roots

Resorption lacunae seen (arrow)Resorption lacunae seen (arrow)

Most of coronal pulp is intactMost of coronal pulp is intact


7 years-functional occlusion attained7 years-functional occlusion attainedbut root apex is still not fully formedbut root apex is still not fully formed

15 years – incisal wear15 years – incisal wearFigure Source: Dr. Sandra MeyersFigure Source: Dr. Sandra Meyers

Sequence of Tooth EruptionSequence of Tooth Eruption

PrimaryPrimary

CICI LILI 1M1M CuspidCuspid 2M 2MLL UU UU UU L L

UU LL LL LL U U

PermanentPermanent

U1MU1M LCILCI ULUL LCULCU U1PMU1PM U2PMU2PM UCUUCU L2ML2M L3ML3M

L1ML1M UCIUCI LLLL L1PML1PM L2PML2PM U2MU2M U3MU3M


Sequence and chronology of tooth eruptionSequence and chronology of tooth eruption


The six/four rule for primary tooth emergenceThe six/four rule for primary tooth emergenceFour teeth emerge for each 6 months of ageFour teeth emerge for each 6 months of age

1.1. 6 months: 4 teeth (lower centrals & upper centrals)6 months: 4 teeth (lower centrals & upper centrals)2.2. 12 months: 8 teeth (1. + upper laterals & lower laterals)12 months: 8 teeth (1. + upper laterals & lower laterals)3.3. 18 months: 12 teeth (2. + upper 118 months: 12 teeth (2. + upper 1stst molars & loer 1 molars & loer 1stst molars) molars)4.4. 24 months: 16 teeth (3. + upper canines & lower canines)24 months: 16 teeth (3. + upper canines & lower canines)5.5. 30 months: 20 teeth (4. + lower 230 months: 20 teeth (4. + lower 2ndnd molars & upper 2 molars & upper 2ndnd molars) molars)

SummarySummary

1.1. By 5 months in utero, all crowns started calcificationBy 5 months in utero, all crowns started calcification2.2. By 1 year old, all crowns completed formationBy 1 year old, all crowns completed formation3.3. By 2.5 years, all primary teeth eruptedBy 2.5 years, all primary teeth erupted4.4. By 4 years old, all primary teeth completed root formationBy 4 years old, all primary teeth completed root formation


Chronology of Human Permanent DentitionChronology of Human Permanent Dentition


The rules of “Fours” for permanent toothThe rules of “Fours” for permanent tooth development (3development (3rdrd molars not included) molars not included)

At birth, four 1At birth, four 1stst molars have initiated calcification molars have initiated calcificationAt 4 years of age, all crowns have initiated calcificationAt 4 years of age, all crowns have initiated calcificationAt 8 years, all crowns are completedAt 8 years, all crowns are completedAt 12 years, all crowns emergeAt 12 years, all crowns emergeAt 16 years, all roots are completeAt 16 years, all roots are complete


Rules of “sixes” in dental developmentRules of “sixes” in dental development

6 weeks old in utero: beginning of dental development6 weeks old in utero: beginning of dental development6 months old: emergence of the first primary tooth6 months old: emergence of the first primary tooth6 years old: emergence of first permanent tooth6 years old: emergence of first permanent tooth


Problems of Primary Tooth EruptionProblems of Primary Tooth Eruption

Natal and Neonatal TeethNatal and Neonatal Teeth

Retained Primary teethRetained Primary teeth

Submerged primary teethSubmerged primary teeth

Hyper or supra eruptionHyper or supra eruption

AnkylosisAnkylosis

Source: Color atlas of clinical oral pathology. Neville, Damm and White. 2Source: Color atlas of clinical oral pathology. Neville, Damm and White. 2ndnd edition edition

Congenitally Missing Congenitally Missing TeethTeeth

Cleidocranial DysplasiaCleidocranial Dysplasia

Osteopetrosis – Defect in OsteoclastsOsteopetrosis – Defect in Osteoclasts

eruption and shedding of teeth. mixed dentition: presence of both dentitions figure from ten...

Documents

dentition teeth

permanent teeth

shedding of teeth slide

primary anterior teeth

years permanent dentition

primary tooth roots

tooth germ slide

eruptive tooth movement