PULP

DENTINE CEMENTUM

PERIODONTAL LIGAMENT/ PDLALVEOLAR BONE

Jabbarifar 2009

ROOT FORMATION & ERUPTION

What has to be controlled

Shedding of teeth

Number of roots

Shapes of root

Times of eruption

Four tissues in sequence

Organize surroundings

Fasten tooth to surroundings

Successional teeth

Length of root

Pulp Dentine Cementum Ligament

& coordinatede.g., cementum with PDL with bone

TOOTH TISSUES: Cell Sources

DENTAL LAMINA

DENTAL PAPILLA

DENTAL SAC/FOLLICLE

DENTAL ORGAN

ALVEOLAR BONE

PULP

DENTINE

ENAMEL

CEMENTUM

PDL

A BONE

TOOTH

Crest

Ameloblasts

Odontoblasts

CT cells

Cementoblasts

Fibroblasts

Osteoblasts & ‘clasts

Deposition of alveolar bone?

MECHANISMS OF ERUPTION

Formation of the root

Construction & Reorganization of PDL

Remodelling of bone overall

FURTHER INFLUENCES from: tooth/teeth in occlusion; muscle actions

TOOTH GERM: next stepsDENTAL LAMINA upper part degenerates lower forms 2nd bud

Outer dental epithelium approaches inner

Stellate reticulum reduces over cusp

Inner & outer dental epithelia join to form cervical loop

Stratum intermedium

DENTAL PAPILLA

DENTAL SAC/FOLLICLE

Knot cells signal to papilla

First reduction in enamel epithelium: active ameloblasts & compacted outer epithelium, stellate-reticulum cells & stratum intermedium

LATE CROWN FORMATIONcusp enamel formed by ameloblasts

Dentine

Cervical loop: inner & outer epithelium

DENTAL PAPILLA become pulp

remaining Stellate reticulum

DENTAL SAC still quiescent

DENTAL PAPILLA become pulp process proceeds downs

Stellate reticulum follows Cervical loop down then stops: Crown defined

END OF CROWN FORMATION

Ameloblasts will finish full thickness of cusp enamel & reduce in height

Dentine widens

Cervical loop:

Odontoblast recruitment site

Where Stellate reticulum stopped, the cervical loop continued to grow down, but as

ENAMEL

REDUCED DENTAL EPITHELIUM

HERTWIG’S ROOT SHEATH & its

DENTINE

PULP

Epithelial diaphragm

CROWN

ROOT FORMATION

Odontoblast recruitment site

ROOT

ENAMEL

REDUCED DENTAL EPITHELIUM

HERTWIG’S ROOT SHEATH grows to lengthen root

DENTINE

PULP

Epithelial diaphragm

FURTHER ROOT FORMATION

Odontoblast recruitment site

Root sheath breaks up, allowing sac mesenchymal cells to contact root dentine

Other sac mesenchymal cells construct PDL & some alveolar bone

Fibroblasts

ROOT SHEATH & ITS DIAPHRAGM widens & constricts to create two diaphragms to define two roots

Epithelial diaphragm

ROOT FORMATION: Multirooted

ENAMEL

DENTINE

PULP

CROWN

ROOT

ROOT SHEATH

Cross-sections

Thus, one dental organ can produce two or three roots

ROOT FORMATION: Multirooted

Epithelial diaphragm ROOT SHEATH

ENAMEL

DENTINE

PULP

CROWN

ROOT

Similarly, one dental organ can produce two or more cusps, using multiple enamel knots

ENAMEL

REDUCED DENTAL EPITHELIUM

DENTINE

PULP

Odontoblast recruitment site by root sheath: pulp signaling

Root sheath breaks up & lifts, allowing sac mesenchymal cells to contact root dentine

REITERATIVE SIGNALING V

Dentine &/or Epithelial root sheath induces mesenchymal cells to become cementoblasts

JAW & TOOTH DEVELOPMENT early arch

BONE starting LINGUAL PLATE

BONE starting BUCCAL PLATE

SYMPHYSEAL CARTILAGE

10 TOOTH GERM

20 Successional TOOTH GERM

DENTAL LAMINA

WALLS OF BONY TROUGH OF DEVELOPING MANDIBLE

JAW & TOOTH DEVELOPMENT processes

BONE starting LINGUAL PLATE

BONE starting BUCCAL PLATE grows up more than lingual

SYMPHYSEAL CARTILAGE will be replaced by bone

10 TOOTH GERM

20 Successional TOOTH GERM on lingual side of 10

DENTAL LAMINA will grow back to form germs for 3 permanent molars (5th e m)

Bony wall grows around & encloses 20 TOOTH GERM in a crypt

Interdental septum grows across trough to separate teeth

Interradicular septum grows between roots of multirooted teeth

TOOTH & MANDIBLE DEVELOPMENT

10 TOOTH

20 TOOTH GERM

MECKEL’S CARTILAGE

TONGUE

ALVEOLAR BONE

DENTAL SAC

ALVEOLAR NERVE

Oral ectoderm

Bone added to base of alveolus for tooth eruption

10 TOOTH

20 TOOTH GERM

MECKEL’S CARTILAGE

Alveolar crest grows up

regresses & not used to form mandible

Bony plate grows up to enclose 2nd tooth germ in a CRYPT

Bone grows over alveolar nerve & vessels

Alveolus becomes distinct from BODY

DENTAL SAC contributes also to alveolar bone

MANDIBLE DEVELOPMENT

Remodeling will bring erupting 1o tooth over developing 2o

10 TOOTH

20 TOOTH GERM

MECKEL’S CARTILAGE

TONGUE

ALVEOLAR BONE

DENTAL SAC

ALVEOLAR NERVE

Reduced enamel epithelium fused with gingiva

Higher alveolar bone - i.e. deeper socket

Longer root with cementum forming

More advanced 2nd tooth

Denser alveolar bone & more body-alveolus distinction

Meckel’s cartilage gone

TOOTH & MANDIBLE DEVELOPMENT - Next

Remodeling brings erupting 1o tooth over developing 2o

ENAMEL

REDUCED DENTAL EPITHELIUM

TOOTH EMERGENCE

GINGIVAL EPITHELIUM

still fusing with

CUTICLE will wear away

ORGANIC ENAMEL SURFACES

CUTICLE will wear away

PELLICLE of glycoproteins etc is acquired later from saliva

PLAQUE the biofilm of many kinds of bacteria then attaches to the pellicle, & later mineralizes - tartar

DENTINE

ENAMEL

BONE

GINGIVA

Epithelial diaphragmROOT SHEATH

CEMENTUMPDL

PULP

Cementum starting as sheath breaks down

LATE ERUPTING TOOTH

Rests of Mallassez remnants of Root sheath

Epithelial diaphragm

ROOT SHEATH

LATE ERUPTING TOOTH

DENTINE

ENAMEL

BONE

GINGIVA

CEMENTUMPDL

PULP

Rests of Mallassez remnants of Root sheath

Cementum starting as sheath breaks down

Deciduous tooth

Gingiva

Cortical plate dense bone

BODY of MANDIBLE

ALVEOLAR BONE

PDLPermanent tooth

MANDIBULAR CENTRAL INCISORS at 2 y

Gubernacular cord of fibrous tissue Gubernacular cord

runs through a canal left in the bony crypt, where the dental lamina extended down to establish the germ for the 2nd tooth

Permanent tooth

Go Gubba

Deciduous tooth

Cortical plate dense bone

Permanent tooth

MANDIBULAR CENTRAL INCISORS at 2 y - Bone

Spongy/ cancellous bone

Resorption of bone & deciduous root will start here

10/Deciduous tooth

PDL attachment is surprising persistent

Close to EXFOLIATION of Deciduous/10 Tooth

Bone trabeculae added by layers at base of alveolus

Odontoclasts have resorbed most of deciduous root

Pulp is left alive

Bone remodellling has brought 20 tooth under 10

20 tooth would be LARGER than shown

20 tooth

DENTINE

ENAMEL

BONE

GINGIVA Oral Ectoderm

Epithelial diaphragmROOT SHEATH Dental organ

CEMENTUM Dental sacPDL

PULP

PDL Dental sac

LATE ERUPTING TOOTH: Origins

Rests of Mallassez remnants of Root sheath

BONE Arch Mesenchyme & Dental sac

WHY STILL ERUPTING

DENTINE

ENAMEL

BONE PDL

PULP

APEX INCOMPLETE

Pulp chamber wide (no apical taper)

Cementum not to apex

& Bone forming in base of alveolus

Epithelial diaphragm presentImmature connective tissue

STARTING EXFOLIATION of DECIDUOUS MOLAR I

ALVEOLAR BONE

DENTINE

ENAMEL

Permanent Tooth under deciduous molar, & between its roots

Inter-radicular septum of bone also houses 2nd tooth germ & is its crypt

Root resorption by osteoclasts

PDL

PULP

EXFOLIATION of DECIDUOUS MOLAR II

ALVEOLAR BONE

DENTINE

ENAMEL

Focal erosion along this line leaves a ROOT FRAGMENT which may be retained

Resorbed dentine partly repaired by new cementum

Crypt bone eroded here

PDL

PDL is disrupted in regions of root resorption & repair

EXFOLIATION of DECIDUOUS MOLAR III

Erosion of bone and the deciduous root is not steady & continuous, but may cease briefly, when some repair of eroded cementum & dentine can occur (by cementum).

Bone remodelling also goes on, and the alveolus and crypt are changing all the time - repeated all along the jaw

DENTINE

ENAMEL

Osteoclasts resorbing bone

PDL fibers incorporated in bone as Sharpey’s fibers

FUNCTIONAL ERUPTION & TOOTH MOVEMENT

Osteoblasts laying down bundle bone

Cellular cementum added to apex Compensates for occlusal wear?

Occlusal wear

Bony interdental septum

Basil

TOOTH MOVEMENT

Osteoblasts laying down bundle bone

Tooth drifts mesially by combined actions of osteoclasts & osteoblasts moving bone, taking tooth with it

Basil

Osteoclasts resorbing bone

TOOTH MOVEMENT

Tooth drifts mesially by combined actions of osteoclasts & osteoblasts moving bone, taking tooth with it

Basil

Earlier bone position

Intra-oral phase

TOOTH ERUPTION

Pre-oral phase

Once the teeth meet in occlusion, their further eruption separates the jaws

TOOTH ERUPTION

Once the teeth meet in occlusion, they influence each other mechanically

PERIODONTITIS

Periodontal ligament

TOOTH

Alveolar bone

GINGIVA

EPITHELIAL ATTACHMENT- unstable, loosens & migrates down, & allows bacteria into

CONNECTIVE TISSUE resulting in chronic infection &

inflammation &

systemic spread of bacteria &

loss of teeth

Gingival recession onto & down the cementum with loss of alveolar-crest bone

PASSIVE ERUPTION

Raising the banana, then peeling the banana

PULP

Fate of exposed cementum & dentinal consequences & reactions

Cementum readily abraded & eaten by oral acids

REPARATIVE DENTINE - response to caries/erosion

DEAD TRACT in Dentine - wide, empty dentinal tubules easily colonized by bacteria

TOOTH MOVEMENTS

DRIFTING e.g., mesially, laterally

AXIAL - in long axis of the tooth

Basil

Occurring in eruption & use

ROTATORY

TILTING

By root growth & bone remodelling

By bone remodelling & PDL reorganization

Combinations of these four movements frequently occur

TOOTH MOVEMENT 2

Basil

Earlier bone position

TILTING Tooth tilts by combined actions of both osteoclasts & osteoblasts on bone of each side of socket

3rd MOLAR’S TILTING ERUPTION

TILTING mechanism may be useful, e.g., in bringing upright the third molar that starts tilted

Failure can lead to an impacted molar still within the bone

2nd2nd

3rd

3rd

1 32 54 760YEARS

YOUNG CHILD’S ERUPTION SEQUENCE

Time of emergence

Root formingCrown forming

KEY

10 2nd Molar

20 Incisor

20 Cuspid

20 2nd PreMolar

Deciduous

Permanent

10 Incisor

10 Cuspid

1 32 54 760YEARS

YOUNG CHILD’S ERUPTION SEQUENCE

10 2nd Molar

20 Incisor

20 Cuspid

20 2nd PreMolar

5-yr CHILD’S DENTITION: 0ne arch

5 deciduous teeth working, but 1o incisor root is being resorbed

7 successional/succedaneous teeth developing pre-orally

dental lamina for 3rd molar

Oral

Pre-oral

5-yr CHILD’S DENTITION: 0ne arch

These 12 “teeth” require a very coordinated remodelling of the bone (& PDL) supporting & enclosing them

Oral

Pre-oral

ERUPTION: Problems

Early eruption

Missing tooth

Impaction - failure to erupt e.g., from too little gap after premature loss of deciduous tooth

Delayed eruption

Malocclusion

Tilting (can occur early from germ rotation)

Infra-occlusion (not high enough)

Retained root fragment

Excessive drift