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ROOT FORMATION & ERUPTION
Jabbarifar 2009 PULP CEMENTUM DENTINE PERIODONTAL LIGAMENT/ PDL ALVEOLAR BONE
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What has to be controlled
Number of roots Shapes of root Length of root Four tissues in sequence Pulp Dentine Cementum Ligament Organize surroundings Fasten tooth to surroundings Times of eruption & coordinated Shedding of teeth e.g., cementum with PDL with bone Successional teeth
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TOOTH TISSUES: Cell Sources
DENTAL LAMINA DENTAL PAPILLA DENTAL SAC/FOLLICLE DENTAL ORGAN ALVEOLAR BONE ENAMEL Ameloblasts DENTINE Odontoblasts PULP CT cells CEMENTUM Cementoblasts PDL Fibroblasts A BONE Osteoblasts & ‘clasts Crest
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MECHANISMS OF ERUPTION
Construction & Reorganization of PDL Formation of the root Deposition of alveolar bone? Remodelling of bone overall FURTHER INFLUENCES from: tooth/teeth in occlusion; muscle actions
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TOOTH GERM: next steps Outer dental epithelium approaches inner
DENTAL LAMINA upper part degenerates lower forms 2nd bud Stellate reticulum reduces over cusp Knot cells signal to papilla Stratum intermedium DENTAL PAPILLA Inner & outer dental epithelia join to form cervical loop DENTAL SAC/FOLLICLE
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LATE CROWN FORMATION cusp enamel formed by ameloblasts
First reduction in enamel epithelium: active ameloblasts & compacted outer epithelium, stellate-reticulum cells & stratum intermedium Dentine DENTAL PAPILLA become pulp remaining Stellate reticulum Cervical loop: inner & outer epithelium DENTAL SAC still quiescent
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END OF CROWN FORMATION Ameloblasts will finish full thickness of cusp enamel & reduce in height Dentine widens DENTAL PAPILLA become pulp process proceeds downs Stellate reticulum follows Cervical loop down then stops: Crown defined Odontoblast recruitment site Cervical loop:
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ROOT FORMATION ENAMEL REDUCED DENTAL EPITHELIUM CROWN DENTINE
Where Stellate reticulum stopped, the cervical loop continued to grow down, but as PULP HERTWIG’S ROOT SHEATH & its ROOT Odontoblast recruitment site Epithelial diaphragm
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FURTHER ROOT FORMATION
REDUCED DENTAL EPITHELIUM Root sheath breaks up, allowing sac mesenchymal cells to contact root dentine ENAMEL DENTINE PULP Other sac mesenchymal cells construct PDL & some alveolar bone HERTWIG’S ROOT SHEATH grows to lengthen root Fibroblasts Odontoblast recruitment site Epithelial diaphragm
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ROOT FORMATION: Multirooted
ROOT SHEATH & ITS DIAPHRAGM widens & constricts to create two diaphragms to define two roots CROWN ENAMEL DENTINE Cross-sections PULP ROOT ROOT SHEATH Epithelial diaphragm
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ROOT FORMATION: Multirooted
Thus, one dental organ can produce two or three roots ENAMEL DENTINE PULP CROWN ROOT Similarly, one dental organ can produce two or more cusps, using multiple enamel knots Epithelial diaphragm ROOT SHEATH
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REITERATIVE SIGNALING V
REDUCED DENTAL EPITHELIUM ENAMEL DENTINE Root sheath breaks up & lifts, allowing sac mesenchymal cells to contact root dentine Dentine &/or Epithelial root sheath induces mesenchymal cells to become cementoblasts PULP Odontoblast recruitment site by root sheath: pulp signaling
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JAW & TOOTH DEVELOPMENT early arch
BONE starting BUCCAL PLATE DENTAL LAMINA BONE starting LINGUAL PLATE 10 TOOTH GERM 20 Successional TOOTH GERM WALLS OF BONY TROUGH OF DEVELOPING MANDIBLE SYMPHYSEAL CARTILAGE
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JAW & TOOTH DEVELOPMENT processes
DENTAL LAMINA will grow back to form germs for 3 permanent molars (5th e m) BONE starting BUCCAL PLATE grows up more than lingual BONE starting LINGUAL PLATE 10 TOOTH GERM 20 Successional TOOTH GERM on lingual side of 10 Interradicular septum grows between roots of multirooted teeth Bony wall grows around & encloses 20 TOOTH GERM in a crypt SYMPHYSEAL CARTILAGE will be replaced by bone Interdental septum grows across trough to separate teeth
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TOOTH & MANDIBLE DEVELOPMENT
Oral ectoderm TONGUE DENTAL SAC 10 TOOTH ALVEOLAR BONE 20 TOOTH GERM MECKEL’S CARTILAGE ALVEOLAR NERVE
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MANDIBLE DEVELOPMENT Bone added to base of alveolus for tooth eruption
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
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TOOTH & MANDIBLE DEVELOPMENT - Next
Reduced enamel epithelium fused with gingiva TONGUE DENTAL SAC Higher alveolar bone - i.e. deeper socket 10 TOOTH ALVEOLAR BONE Longer root with cementum forming 20 TOOTH GERM More advanced 2nd tooth ALVEOLAR NERVE MECKEL’S CARTILAGE Denser alveolar bone & more body-alveolus distinction Remodeling brings erupting 1o tooth over developing 2o Meckel’s cartilage gone
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TOOTH EMERGENCE ENAMEL CUTICLE will wear away GINGIVAL EPITHELIUM
still fusing with REDUCED DENTAL EPITHELIUM ENAMEL
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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
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BONE LATE ERUPTING TOOTH Epithelial diaphragm ROOT SHEATH GINGIVA
DENTINE ENAMEL BONE GINGIVA Epithelial diaphragm ROOT SHEATH CEMENTUM PDL PULP Cementum starting as sheath breaks down LATE ERUPTING TOOTH Rests of Mallassez remnants of Root sheath
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BONE LATE ERUPTING TOOTH GINGIVA CEMENTUM PDL
ENAMEL Rests of Mallassez remnants of Root sheath DENTINE GINGIVA PULP CEMENTUM PDL ROOT SHEATH Epithelial diaphragm Cementum starting as sheath breaks down BONE
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MANDIBULAR CENTRAL INCISORS at 2 y
Deciduous tooth Gingiva Cortical plate dense bone BODY of MANDIBLE ALVEOLAR BONE PDL Permanent tooth MANDIBULAR CENTRAL INCISORS at 2 y
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Go Gubba 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
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MANDIBULAR CENTRAL INCISORS at 2 y - Bone
Deciduous tooth MANDIBULAR CENTRAL INCISORS at 2 y - Bone Resorption of bone & deciduous root will start here Permanent tooth Spongy/ cancellous bone Cortical plate dense bone
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Close to EXFOLIATION of Deciduous/10 Tooth
Odontoclasts have resorbed most of deciduous root PDL attachment is surprising persistent Pulp is left alive Bone remodellling has brought 20 tooth under 10 20 tooth Bone trabeculae added by layers at base of alveolus 20 tooth would be LARGER than shown
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BONE LATE ERUPTING TOOTH: Origins Epithelial diaphragm
ROOT SHEATH Dental organ GINGIVA Oral Ectoderm CEMENTUM Dental sac PDL DENTINE ENAMEL PULP Rests of Mallassez remnants of Root sheath BONE PDL Dental sac BONE Arch Mesenchyme & Dental sac
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APEX INCOMPLETE WHY STILL ERUPTING BONE PDL DENTINE ENAMEL PULP
Cementum not to apex Epithelial diaphragm present Pulp chamber wide (no apical taper) Immature connective tissue & Bone forming in base of alveolus
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STARTING EXFOLIATION of DECIDUOUS MOLAR I
ENAMEL DENTINE ALVEOLAR BONE PULP PDL Root resorption by osteoclasts Inter-radicular septum of bone also houses 2nd tooth germ & is its crypt Permanent Tooth under deciduous molar, & between its roots
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EXFOLIATION of DECIDUOUS MOLAR II
Crypt bone eroded here ENAMEL DENTINE ALVEOLAR BONE PDL Resorbed dentine partly repaired by new cementum Focal erosion along this line leaves a ROOT FRAGMENT which may be retained PDL is disrupted in regions of root resorption & repair
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EXFOLIATION of DECIDUOUS MOLAR III
DENTINE ENAMEL 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
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FUNCTIONAL ERUPTION & TOOTH MOVEMENT
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
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Tooth drifts mesially by combined actions of osteoclasts & osteoblasts moving bone, taking tooth with it TOOTH MOVEMENT Osteoblasts laying down bundle bone Osteoclasts resorbing bone Basil
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TOOTH MOVEMENT Tooth drifts mesially by combined actions of osteoclasts & osteoblasts moving bone, taking tooth with it Basil Earlier bone position
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Intra-oral phase TOOTH ERUPTION Pre-oral phase
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TOOTH ERUPTION Once the teeth meet in occlusion, their further eruption separates the jaws Once the teeth meet in occlusion, they influence each other mechanically
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PERIODONTITIS GINGIVA Periodontal ligament TOOTH
EPITHELIAL ATTACHMENT- unstable, loosens & migrates down, & allows bacteria into CONNECTIVE TISSUE resulting in chronic infection & inflammation & systemic spread of bacteria & loss of teeth GINGIVA Periodontal ligament Alveolar bone
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PASSIVE ERUPTION Gingival recession onto & down the cementum with loss of alveolar-crest bone Raising the banana, then peeling the banana
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Fate of exposed cementum & dentinal consequences & reactions
PULP Cementum readily abraded & eaten by oral acids DEAD TRACT in Dentine wide, empty dentinal tubules easily colonized by bacteria REPARATIVE DENTINE - response to caries/erosion
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TOOTH MOVEMENTS Occurring in eruption & use
By root growth & bone remodelling AXIAL - in long axis of the tooth DRIFTING e.g., mesially, laterally TILTING By bone remodelling & PDL reorganization ROTATORY Combinations of these four movements frequently occur Basil
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TILTING TOOTH MOVEMENT 2
Basil Earlier bone position TILTING Tooth tilts by combined actions of both osteoclasts & osteoblasts on bone of each side of socket
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3rd MOLAR’S TILTING ERUPTION
2nd 2nd 3rd 3rd 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
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YOUNG CHILD’S ERUPTION SEQUENCE
YEARS 1 2 3 4 5 6 7 KEY Time of emergence Crown forming Root forming 10 2nd Molar Deciduous Permanent 20 Incisor 20 Cuspid 20 2nd PreMolar
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YOUNG CHILD’S ERUPTION SEQUENCE
YEARS 1 2 3 4 5 6 7 10 Incisor 10 Cuspid 10 2nd Molar 20 Incisor 20 Cuspid 20 2nd PreMolar
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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
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5-yr CHILD’S DENTITION: 0ne arch
Oral Pre-oral These 12 “teeth” require a very coordinated remodelling of the bone (& PDL) supporting & enclosing them
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ERUPTION: Problems Delayed eruption Early eruption Missing tooth
Impaction - failure to erupt e.g., from too little gap after premature loss of deciduous tooth Retained root fragment Malocclusion Infra-occlusion (not high enough) Excessive drift Tilting (can occur early from germ rotation)
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