Growth / Tooth Development Flashcards
Average ERUPTION Time for PERMANENT TEETH 🦷 in YEARS
@YEAR ERUPTION 🌋 PERMANENT TEETH
C L Cn 1p 2p 1 2 3 Max: 7 8 11 10 10.5 6 12 17 Mand: 6 7 9 10 11 6 11 17
“MAIN” pattern
General Rules:
- Mandibular before Max (same tooth in arch)
- Females before Males
- 2-3 rule
- Teeth begin erupting when Root is 2/3 developed
- Root take 2-3 years to complete after initial eruption.
What is the FIRST STAGE of tooth development?
What happens?
I = EC➡️M
INITIATION
ECTODERM induces the MESENCHYMAL tissue in order to initiate the process.
I = EC➡️M
Calcification timing for all primary / permanent teeth.
🕙🗓🦷
🤰🦷
👼🦷
- On average PRIMARY teeth take 10 MONTHS for completion of calcification. 🕙🗓🦷
- The PRIMARY teeth BEGIN to form in UTERO at about SIX weeks.
Hard tissue formation occurs in ALL primary teeth by the 18TH week in utero. (4th fetal month)
6-18W🤰
- The PERMANENT teeth begin to develop at approximately FOUR months of age in UTERO. Maxillary and mandibular FIRST molars begin to CALCIFY at BIRTH. They are the first to begin calcification. The mandibular THIRD molars are generally the last teeth to begin calcifying. This happens at about 8-10 years of age.
👼🦷
What are the components of a tooth bud/germ?
“Bud is a pos”
TOOTH BUD - GERM - POS
These cells are derived from
- ECTODERM of the FIRST BRACHIAL ARCH
- ECTOMESENCHYME of the NEURAL CREST
- Dental Papilla
- Enamel Organ
- Dental Sac/Follicle
Where do NEURAL CREST cells originate?
What to they differentiate into?
CREST - ECTODERM - DENTIN - CARTILEDGE
Temporary group of cells that arise from the embryonic ectoderm cell layer along the LATERAL margins of the NEURAL PLATE.
Responsible for many SKELETAL and CONNECTIVE tissue.
- Bone 🦴
- Cartilage
- DENTIN
- Dermis
Not Enamal
Dental LAMINA
INITIATION
DL6 - TOOTH BUDS - CAP 🧢 - SERRES
FIRST evidence of tooth DEVELOPMENT and begins at the SIXTH week in utero = DL6
It is formed when cells of the oral ectoderm PROLIFERATE FASTER than cells of other areas.
This dividing tissue is surrounded by and stimulated by ECTOMESENCHYMAL growth.
The DL CONNECTS the developing tooth BUD to the EPITHELIUM of the oral cavity.
T (epithelium + dl)
n (tooth bud)
Responsible for the dental PAPILLA and later ODONTOBLASTS
“Papillamina”
Eventually, the DL DISINTEGRATES into small CLUSTERS of EPITHELIUM and is RESORBED.
This is responsible for the CAP 🧢 like structure of the enamel organ.
In situations when the clusters are not resorbed, (Glands/Rests of SERRES) eruption CYSTS are formed OVER the DEVELOPING TOOTH and delay its eruption into the oral cavity.
Rests of Serres?
What can develop from them?
🦴
Ok…LGg
-REMNANTS of dental LAMINA epithelium entrapped within the GINGIVA.
OK…LGG
- Odontogenic Keratocyst
- Lateral Periodontal cyst
- Gingival cyst
- Glandular Odontogenic cyst
Average ERUPTION 🌋Time for PRIMARY 👶 TEETH 🦷 in MONTHS
@MONTH ERUPTION PRIMARY TEETH
Cent - Lat - Canine - 1st M - 2nd M
Max:
8 9 16 13 26
Mand:
6 10 17 14 23
First: lower central
Last: upper 2nd
“nxi” pattern
Rests of Malassez?
What can develop from them?
EPITHELIAL cell RESTS of MALASSEZ (ERM)
Part of the PERIODONTAL LIGAMENT cells around a tooth. They are discrete clusters of RESIDUAL cells from HERTWIG’S epithelial root sheath (HERS) that didn’t completely disappear.
A specialized form of epithelium (Hertwig epithelial root sheath) directs ROOT FORMATION, and once complete, it degenerates, leaving epithelial rests of Malassez
These rests are not isolated but form vague net-like structures around root of tooth within periodontal ligament (fibrous tissue connection between tooth root and bone of jaw)
It is considered that these cell rests proliferate to form epithelial lining of various odontogenic cysts such as RADICULAR cyst under the influence of various stimuli.
Hyperactivity of Dental Lamina can result in what?
HYPERDONTIA
Hyperactivity or over growth of dental lamina can give rise to conditions such as Hyperdontia.
On completion of the dentition, the dental lamina is usually destroyed and reabsorbed, but when REMNANTS FAIL to RESORB. it can continue to PROLIFERATE ABNORMALLY. This abnormal proliferation can form the EXTRA tooth BUD leading to supernumerary teeth.
What Pathologies are associated with Neural Crest Cell defects?
wtf hd
FETAL ALCOHOL SYNDROME DISORDER 🍷
-impair neural crest migration
TREACHER-COLLINS SYNDROME
-mutation which causes ncc apoptosis
DiGEORGE SYNDROME
-chromosome 22 deletion disrupt ncc migration
HIRSCHSPRUNG’S DISEASE
-lack of ncc migration to gut
WAARDENBURG’S SYNDROME
-defective ncc migration: deafness piebald
WTF HD?
Enamel Organ
ENAMEL ORGAN
Periphery: low Columnar cells
Central: Polygonal cells
Composed of:
- Outer enamel epithelium
- Inner enamel epithelium
- Stellate reticulum
- Stratum intermedium.
These cells give rise to AMELOBLASTS, which produce enamel and the reduced enamel epithelium.
The location where the OUTER enamel epithelium and INNER enamel epithelium JOIN is called the CERVICAL LOOP.
n
^^ (points to cervical loop on bud)
The GROWTH of cervical loop cells into the deeper tissues forms HERTWIG’S Epithelial Root Sheath, which determines the ROOT SHAPE of the tooth.
n
⬇️
Hertwig epithelial root sheath (HERS)
IEE - OEE - 🚫- DENTIN - MALASSEZ
- is derived from the INNER and OUTER enamel epithelium of the enamel organ.
- without 🚫 Stratum intermedium and Stellate reticulum.
n
⬇️
I I
- A PROLIFERATION of EPITHELIAL cells located at the cervical loop of the enamel organ in a developing tooth.
- INITIATES the formation of DENTIN in the ROOT of a tooth by causing the differentiation of ODONTOBLASTS from the dental papilla.
Odont l l Dent Pap
^
HERS
The root sheath eventually DISINTEGRATES with the periodontal ligament, but RESIDUAL pieces that do not completely disappear are seen as epithelial cell rests of MALASSEZ (ERM).
These rests can become CYSTIC, presenting future periodontal infections.
- Radicular Cysts
- Cementicles
Dental Papilla
🧢
DENTAL PAPILLA 🧢
→ The ectomesenchymal cells which are lying deep to the enamel organ
→ will develop to become the dental PULP and the DENTIN
Formation of dental papilla occurs in the CAP 🧢 stage of Odontogenesis.
The cap stage is the third stage of tooth development and occurs during the NINTH/TENTH week of prenatal development
A section of the ECTOMESENCHYME (a group of tissue made up of neurocrest cells which are present in the initial development of an embryo) CONDENSES into a MASS within the CONCAVITY of the cap of the enamel organ. This mass is now considered the DENTAL PAPILLA.
n
^ (in middle)
dp
Meckel’s Cartilage
MECKEL’S CARTILAGE
- the cartilaginous bar of the MANDIBULAR arch is formed by what are known as Meckel’s cartilages
- above this the INCUS and MALLEUS are developed.
- Meckel’s cartilage arises from the FIRST PHARYNGEAL arch.
- Meckel’s cartilage forms in the MESODERM of the mandibular process
the cartilaginous bar of the embryonic mandibular arch of which the distal end ossifies to form the malleus and most of the rest disappears in development, with the part adjacent to the malleus being replaced by fibrous membrane comprising the sphenomandibular ligament and the connective tissue covering most of the remaining part ossifying to form much of the mandible
Stellate Reticulum
🌟💧☎️
STELLATE RETICULUM 🌟💧☎️
The stellate reticulum is a group of cells located in the CENTER of the ENAMEL ORGAN of a developing tooth.
These cells are STAR 🌟 -SHAPED and synthesize GLYCOAMINOGLYCANS
. As glycosaminoglycans are produced, WATER 💧 is drawn in from the ECTOMESENCHYME cells, stretching them apart. As they are moved further away from one another, the stellate reticular cells maintain contact with one another through DESMOSOMES ☎️ , resulting in their unique appearance.
SUPPORTS and PROTECTS AMELOBLASTS
The stellate reticulum is LOST AFTER the first layer of ENAMEL is laid down. This brings cells in the inner enamel epithelium closer to blood vessels at the periphery.
Cap Stage
🧢🧢🧢
Proliferation
Morphodifferentiation
Histodifferation
CAP STAGE 🧢🧢🧢
9 weeks in utero
Placodes proliferate into ENAMEL ORGAN
3 CELL types of EO:
- OUTER enamel epithelium (CUBOIDAL ▪️▪️)
- INNER enamel epithelium (LOW ➿ Columnar)
- STELLATE reticulum (STAR 🌟 shaped)
UNEQUAL proliferation of cells, RAPIDLY dividing at the LATERAL area of the tooth BUD, giving rise to a CAP shape, pushing the lateral ends more into the ectomesenchyme leading to a CONCAVITY or infolding creating the INNER epithelium area.
(n - iee, inside border)
Stellate reticulum: - layer between the IEE and the OEE
Condensed MESENCHYME becomes dental PAPILLA.
The Papilla essentially is wearing the Enamel Organ as a “cap”
Dental FOLLICLE is the surrounding SAC that surrounds the entire Papilla + Enamel Organ
Defects during Cap Stage:
(Cyst, Odontoma, Gemination, Fusion, Dens in Dente)
What are Placodes?
PLACODES
The term placode refers to ECTODERM THICKENINGS in the cranial region that have important roles in development of special sensory and other systems.
Dental placode is the main EPITHELIAL structure participating in tooth formation. The dentla placode FORMS ALONG the dental LAMINA, rapidly INVADES the underlying MESENCHYME and gives rise to enamel-producing ameloblasts.
DENTAL LAMINA ⬇️ DENTAL PLACODES (20 in #, primary teeth) ⬇️ MESENCHYME
***PERMANENT teeth 🦷 FORM from a LINGUAL EXTENSION of the dental lamina called SUCCESSIONAL LAMINA.
***Except Permanent MOLARS, which are from the LAMINA itself.
Bell Stage 🛎 🔔
Proliferation
Morphodifferentiation
Histodifferation
BELL STAGE 🛎🔔
11 weeks in Utero
Marked by BOTH happening simultaneously:
- MORPHODIFFERENTIATION
- establishment of the SHAPE of the CROWN - HISTODIFFERENTIATION
- Dental Papilla cells ➡️ Odontoblasts
- Inner Enamel Epithelium cells ➡️ Ameloblasts
The junction where Odontoblasts and Ameloblasts meet becomes the DEJ
Ameloblast Cells = TALL ➰➰columnar
iee ➿ ➡️ ➰ a
- EARLY BELL 🛎 STAGE
FRAGMENTATION of the Dental LAMINA.
-separating the tooth germ from the oral epithelium
STRATUM INTERMEDIUM (straddles)
-cells BETWEEN iee and stellate reticulum
-SPINDLE shaped
➿l l🌟
^
SI
- speculated to work in TANDOM with the IEE to form ENAMEL
- CUSP TIP begins to form FIRST making its way sloping down to the CERVICAL region by differing rates of CELL DIVISION giving it its SHAPE.
- ADVANCED BELL STAGE 🔔
Marked by MINERALIZATION of ENAMEL and DENTIN
- Stellate Reticulum collapses
- AMELOBLASTS finally FUSE with OUTER enamel epithelium forming REDUCED enamel epithelium surrounding the entire crown.
- once ENTIRE crown is formed, the CERVICAL LOOP gives rise to HERTWIGS
- Hertwig’s bends in towards the pulp at 45 DEGREES constricting the cervical opening creating the EPITHELIAL DIAPHRAGM.
DEFECTS IN BELL STAGE:
Histo: (Amelogenesis-Dentogenesis Imperfecta)
Morpho: (size and sharp anomalies, peg laterals, example)
Odontoblasts
ODONTOBLASTS
- derived from the DENTAL PAPILLA cells
- DIFFERENTIATE under the INFLUENCE of the INNER enamel epithelium
- starting at CUSP TIP simultaneously with the ameloblasts forming the enamel.
List the Morphological Tooth Stages in Order.
MORPHOLOGIC TOOTH STAGES
- Dental Lamina
- Bud Stage
- Cap Stage
- Early Bell Stage
- Advanced Bell Stage
Initiation Development Phase
“Downloading”
Morphological Stage?
Deficient Development?
Excessive Development.
INITIATION PHASE
-Dental Lamina morphological phase
DL (DownLoading
6 weeks in utero
Effects # of Teeth (Downloading issues)
DEFICIENT Development
- Anodontia
- Hypodontia
- Oligodontia
EXCESSIVE Development
-Hyperdontia
