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WHAT IS THE PROCESS OF FORMATION OF AMELOBLASTS, DENTINOENAMEL JUNCTION, AND ENAMEL MATRIX
- the basement membrane between preameloblasts and odontoblasts disintegrates, allowing preameloblasts to come into contact with new formed predentin. This induces preambeloblasts to differentiate intoameloblasts.
- Ameloblasts begin amelogenesis or the apposition of enamel matrix on their side of the now disintegrating basement membrane.
- Dentinoenamel Junction
- Odontoblastic process
- Maturation of enamel and dentin occur later and in different processes
tapered portion of each ameloblast facing the disintegrating basement layer; secretes enamel matrix
forms as a result of the mineralization of the disintegrating basementmembrane and joining of the dentin and enamel matrixes
attached cellular extensions in the length of the predentin left by theodontoblasts; contained in a dentinal tubule
maturation of enamel and dentin
- occurs later and at different processes
- -cell bodies of odontoblasts remain within pulp tissue
- -cell bodies of ameloblasts involved in eruption and mineralization process, but lost aftereruption
when does ROOT DEVELOPMENT occur?
after crown is completely shaped and the tooth is beginning to erupt into the oral cavity.
what is the cervical root responsible for
where is the cervical loop and what does it contain
most cervical portion of enamel organ. contains the OEE (outer enamel epithelium) and IEE (inner enamel epithelium)
how does the cervical loop continue to grow?
deeper into the surrounding ectomesenchyme of the dental sac,elongating and moving away from newly completed crown, enclosing more of dental papillatissue to form Hertwig’s epithelial root sheath (HERS)
what is the function of HERS
shape the root (s) and induce dentin formation in the root so it is continouswith coronal dentin.
how does root dentin form
Root dentin forms in the same manner as crown dentin—dental papilla induced to differentiate and become odontoblasts
what is absent on the root and why is it absent
due to absence of interemediate layers (stellate reticulum andstratum intermedium) HERS induces odontoblastic differentiation, but fails to differentiate intoenamel forming ameloblasts
where does dentinogenesis begin?
Similar to crown dentin production, dentinogenesis begins in root and predentin is formed.
when root dentin formation is completed what happens?
the basement membrane and HERS sheath disintegrate
what are Epitehlial Rests of Malessez
HERS root sheath disintegrates and may become these groups ofepithelial cells located in the mature perio ligament. These may become cystic and present future problems
what are some developmental disturbances of root formation
enamel pearls-misplaced ameloblasts migrating to root area abnormally forming enamel onroot surfaces.
what are the characteristics of enamel pearls
- Small spherical enamel projections on root surface esp at CEJ or in furcation areas on molarswhere roots divide.
- May have tiny dentin and pulp core
- Appear radiopaque on radiographs
- May be confused with calc upon exploration, but cannot be removed
how is cementum and pulp formed
cementogenesis making cells become Cementoblasts which move to cover the root dentin laying down cementum matrix know as cementoid, which become cementocytes, and the cementum over dentin causes the dentinocemental junction and also at this time the central cells of the dental papilla are forming into pulp.
apposition of cementum occurs when HERS disintegrates allowingundifferentiated cells of the dental sac to come into contact with the newly formed surface ofroot dentin, inducing these cells to become immature cementoblasts
cementoblasts entrapped in cementum
matured, calcified cementoid surrounding the cementocytes
Dentinocemental Junction (DCJ):
formed as aresult of the appostion of cementum over the dentin
what is the pulp tissue surrounded by?
newly formed dentin
what are developmental disturbances of cementum and pulp formation
Concrescence: excess cementum formation; union of the root structure of two or more teeththru the cementum only
what are the characteristics of concrescence
- Usually occurs in permanent maxillary molars
- Teeth involved originally separate, but join as a result of excessive cementum deposition on oneor more teeth after eruption
- Cause may be traumatic injury or crowding of teeth during appostion and maturation stage
- May present a problem during extraction or endo tx.
- Confirmed with radiographs
how does the Periodontal Ligament and Alveolar Bone Develop
As the crown and root develop, the ecotmesenchyme from the dental sac begins to form the PDLadjacent to the newly formed cementum. It also begins to mineralize to form the alveoli of the alveolarbone surrounding the PDL.
what does the process of periodontal ligament and alveolar bone development involve?
- Collagen fibers are formed and immediately organized into fiber bundles of the PDL.
- The ends of these fibers insert into the outer portion of the cementurm and the surroundingalveolar bone for tooth support
where do multirooted teeth originate and what causes them to be multirooted?
- Multirooted premolars and molars originate as a single root on the base of the crown called root trunk
- Differential growth of HERS causes the root trunk to divide into two or three roots.
what are some developmental disturbances during root formation?
- Accessory roots
Dilaceration: distorted roots or crown angulation in a formed tooth; results from distortion ofHERS caused by injury or pressure
Flexion: deviation or bend restricted to only the root portion of the tooth. Usually less than 90*-may be a result of trauma to the developing tooth
Accessory roots: extra roots or supernumerary roots; may be due to trauma, injury, or pressure affecting HERS.
where do accessory roots usually take place, what problems do they present.
- Mostly affects permanent third molars; rare in incisors
- Accessory roots can present problems in extractions and endo
- Pre-op radiographs essential to rule out this disturbance
actual vertical movement of the teeth
occurs as we age as gingival recedes, no actual tooth movement occur
what are the rules for tooth eruption
- Mandibular teeth usually precede maxillary teeth
- Teeth in both jaws erupt in pairs
- Permanent teeth usually erupt slightly earlier in girls than boys; not necessarily observed inprimary teeth
- Exceptions to these rules are numerous
what is the primary eruption sequence
- central incisors- 6.5 to 8 months
- lateral incisors- 7 to 9 months
- first molars- 12 to 15 months
- canines- 6-21 months
- second molars- 21 to 30 months
what is the process of tooth eruption
- -Reduced enamel epithelium (REE) covers newly formed enamel
- -Fusion of REE with oral epithelium
- -Disintegration of the central fuse tissue, leaving tunnel for tooth movement
- -Coronal fused tissues peel back from crown during eruption leaving the initial junctional epithelium near the CEJ
- -Nasmyth’s Membrane: residue formed on newly erupted tooth consisting of the fused tissue ofthe REE and oral epithelium as well as the dental cuticle placed by ameloblasts on new enamel.
what happens when the coronal fused tissues peel back from the crown during eruption leaving the initial junctionalepithelium near the CEJ?
- -creates a seal between the tissue and the tooth surface
- -this tissue is later replaced by a definitive CEJ as the root is formed
how is the nasmyth membrane removed
-easily removed with selective polishing, extrinsic stain
what is the process of exfoliation and what two types of cells help with this process, what do they do?
- Primary tooth is exfoliated as succedaneous permanent tooth develops lingual to it.
- -osteoclasts: absorb the alveolar bone between the two teeth
- -odonoclasts: cause resorption or removal of portions of the primary root of dentin andcementum, as well as small portions of the enamel crown.
how does the process of exfoliation take place
it is intermittent (on again off again)
is it important to keep the primary teeth as long as possible, if so why?
yes, to serve as a place holder for permanent teeth
what is the process of eruption of permanent dentition
same as primary dentition
what is mesial drift, give an example and tell why it matter
- tendency of the permanent molars to have an eruptive force toward the midline
- -if primary molar is missing, permanent molar will drift into that space, thus restricting eruption space for the succedaneous perm premolar
what does it mean for a tooth to be impacted, what are the two types
- teeth that do not erupt
- -can be soft tissue impaction
- -hard tissue (bony) impaction
what is congenitally missing mean
tooth that never forms because tooth bud does not develop
what is the permanent eruption sequence for all teeth (mandibular and maxillary)
- central incisors- mandibular 6-7 years maxillary 7-8 years
- lateral incisors- mandibular 7-8 years maxillary 8-9 years
- canine- mandibular 9-10 years maxillary 11-12 years
- 1st premolar- mandibular 10-12 years maxillary 10-11 years
- 2nd premolar- mandibular 11-12 years maxillary 10-12 years
- 1st molar- mandibular 6-7 years maxillary 6-7 years
- 2nd molar- mandibular 12-13 years maxillary 12-13 years
- 3rd molar- mandibular 17-22 years maxillary 17-22 years