Tooth/Periodontal Development and myth of enamel matrix derivatives (EMD) on periodontal regeneration Flashcards
Where are the Maxilla and Mandible derived from and by what process do they ossify?
Derived from the first branchial arch
Intramembranous Ossification
In which week of development does the first branchial arch from?
4th week
What is the difference between branchial (Pharyngeal) arches, clefts, and pouches?
Arches are bulges around the neck region of the embryo
Clefts separate arches externally
Pouches separate arches internally - opposing clefts
How many Branchial arches are there?
6
What structures form from the 1st Branchial Arch?
I Smelt My Many Mcdonalds Muffins.. Mm.. Smell!
Incus, Sphenomalleolar ligament, Mandible, Maxilla, Merkles cartlidge, Malleus, MUSCLES OF MASTICATION, Sphenomandibular ligament
What structures form from the 1st Branchial Groove?
External Auditory Meatus
What structures form from the 1st Branchial Pouch?
Tympanic membrane, Tympanic cavity, Mastoid antrum, Eustachian tube
What structures form from the 2nd Branchial Arch?
Styloid and facial associated things
Reichert’s cartilage: Styloid process of temporal bone, Stylohyoid ligament, Lesser horns of the hyoid, Upper part of the body of the hyoid, Stapes
STAPEDIAL ARTERY, MUSCLES OF FACIAL EXPRESSION
What structures form from the 2nd Branchial Groove?
The second groove is obliterated by the down-growth of the 2nd Arch
What structures form from the 2nd Branchial Pouch?
It’s mostly obliterated but CONTRIBUTES TO THE PALATINE TONSILS
What structures form from the 3rd Branchial Arch?
Lower part of the body of the hyoid, Greater horns of Hyoid
What structures form from the 3rd Branchial Groove?
nothing
What structures form from the 3rd Branchial Pouch?
INFERIOR PARATHYROID GLAND, Thymus
What structures form from the 4th Branchial Arch?
Cartilages of the Larynx
What structures form from the 4th Branchial Groove?
nothing
What structures form from the 4th Branchial Pouch?
SUPERIOR PARATHYROID GLAND, Ultimobranchial body, Thyroid gland
What structures are formed by the 5th and 6ths arches/clefts/pouches?
They are transient and do not form structures
How do cleft palates form?
failure of fusion between the palatine processes and the maxillary process
How do cleft lips form?
failure of fusion between the maxillary process and the median nasal process
When does the timeline of human tooth development begin? What happens on this day?
Day 26 - Primitive oral cavity formation (epithelium from ectoderm and endoderm line oral cavity)
What day of fetal development do the initial stage, bud stage, cap stage, and bell stage for deciduous teeth occur? Permanent teeth?
Deciduous:
42-48: Initial stage - Dental lamina formation (6.5 WEEKS)
55-56: Bud stage - incisors, canines, and molars
~8-14wks: Cap stage
14wks: Bell stage
18wks: Dentin and functional ameloblasts
Succedaneous teeth:
14wks: Bud stage
32wks: Dentin and functional ameloblasts
When do the following structures form?
Specialized cells of the tongue?
Oral vestibule?
Palatal shelf fusion?
7-10wks
10-14wks
8-11 wks (12 weeks complete)
What determines cell fate during tooth development?
sequential and reciprical interactions between the dental mesenchyme and oral epithelium
Note: Pax 9 is found in locations that a tooth will form - BMPs inhibit Pax9 and guide tooth location
Shh induces local cell proliferation
Why is Wnt important?
it is the most upstream signal and inducer of tooth initiation
Describe the initial stage of tooth development
Day 42-48 (6.5wks) - the Primary Epithelial Band forms in the presumed locations of the maxillary and mandibular arches in the 1st Branchial Arch
the PEB splits into 2 segments (dental and vestibular lamina)
WHAT ARE REMNANTS OF THE DENTAL LAMINA CALLED?
SERRES PEARLS
What are the 2 hypothetical models for patterning of dentition?
The Odontogenic (Homeobox Code) Model
The Clone Model
What is the Odontogenic (Homeobox) Code Model? Describe it.
A hypothetical model for dentition patterning
It postulates that tooth shape is determined by the mesenchyme - where different homeobox genes are expressed in the regions of Incisors/premolars/molars
What is the Clone Model? Describe it
A hypothetical model for dentition patterning - It postulates that each tooth class is produced by a “clone” of mesenchymal cells that were PROGRAMED BY EPITHELIAL CELLS to produce teeth of specific patterns.
Epithelium induces mesenchymal clone, clone progresses posteriorly and induces similar teeth buds.
Which model of tooth patterning could be correct?
Both!
Describe the Bud stage
Characterized by proliferation of epithelial cells and local condensation of ectomesenchymal cells
First epithelial incursion into the ectomesenchyme of the jaw
Describe the Cap Stage
Characterized by an epithelial outgrown that forms a cap of epithelium (the dental (or enamel) organ) overlying a ball of ectomesenchyme (the dental papilla) all surrounded by a condensation of ectomesenchymal cells (the dental follicle)
What structures are formed from the different parts of the dental organ?
What is Histodifferentiation and Morphodifferentiation?
When does it occur? What forms as a result?
A process by which similar epithelial cells transform themselves into morphologically and functionally distince components
Late cap - Early bell
Outer Enamel Epithelium, Stellate Reticulum, Stratum Intermedium, Inner Enamel Epithelium, Cervical loop…
How do cells of the stellate reticulum form?
During hisodifferentiation, cells within the enamel organ begin to secrete glycosaminoglycans. This attracts water into the enamel organ and their extracellular spaces, while they maintain their desmosomal contacts - forming star shaped cells.
Describe the Bell Stage
Histo and Morphodifferentiation continue - form the OEE, Stellate R, Stratum I, IEE, CL… Form the shape of a bell
Dental lamina degenerates and separates the developing tooth from the oral epithelium
What process forms the hard tissues of the tooth?
Reciprocal Induction
What is Reciprocal Induction?
At the site of future cusp tips, mitotic activity ceases
Local IEE is induced to differentiate (reverse their polarity so nuclei are adjacent to stratum and Golgi face dental papilla - and elongate) into Pre-Ameloblasts
Pre-ameloblasts secrete enamel matrix proteins that induce outer ectomesenchyme to differentiate into Pre-Odontoblasts
Pre-Odontoblasts secrete Mantle Dentin
Mantle Dentin causes Pre-Ameloblasts to differentiate into Ameloblasts
Ameloblasts secrete organic matrix that immediately mineralizes to enamel
Which comes first - amelogenesis, or dentinogenesis?
Dentinogenesis
What is HERS and when/how does it form?
Hertwig’s Epithelial Root Sheath
Once the crown formation is complete, the IEE and OEE proliferate at the cercical loop and form a double cell layer (HERS)
What is the rim of HERS called? What does it enclose?
the Epithelial Diaphram
The primary apical foramen
How does the root form?
As HERS encloses the dental papilla, it induces peripheral cells of the papilla to differentiate into odontoblasts. HERS disintegrates except at the advanceing epithelial diaphram. Exposed dentin that contacts the Dental Follicle cells induce differentiation into Cementoblasts
How does root separation occur during multi root formation?
The epithelial cells of the epithelial diaphram grown towards each other and divide a single apical foramen into 2-3 apical foramina corresponding to the number of roots.
What structurs/pathology can HERS contribute to?
What are remnants of HERS referred to as?
Failure of HERS to detach can lead to Enamel Pearls or Cervical Enamel Projections
Invagination of HERS forms Palatogingival Grooves
Remnants of HERS = Epithelial Rests of Malassez - can form Dental Cysts
What is the origen of Masicatory Mucosa?
Ectoderm
How does Junctional Epithelium form?
JE forms during tooth eruption when oral epithelium and reduced enamel epithelium fuse
What is the origen of the PDL? What cell type forms the PDL?
Ectomesenchymal cells of the Dental Follicle differentiating into Fibroblasts
What is the average width of the PDL? What happens to it as we age?
0.15 - 0.38mm
It decreases in width
What is the origen of the Cementum?
Ectomesenchymal cells of the Dental Follicle induced by Enamel Matrix Proteins secreted by HERS differentiate into cementoblasts
or
HERS differentiate into Cementoblasts
What is the origen of the Alveolar Bone
Ectomesenchymal cells of the Dental Follicle differentiating into Osteoblasts
What is Bundle Bone?
The alveolar bone lining the socket that has Sharpey’s Fibers embedded in it
What are Sharpey’s Fibers?
The terminal portion of PDL fibers that are embedded in Bundle Bone and Cementum
What are the Principal Fiber Groups of the PDL
Transseptal Fibers
Alveolar Crest Fibers
Horizontal Fibers
Oblique Fibers
Apical Fibers
Interradicular Fibers
What are Transseptal Fibers? Location? Response to perio?
Fibers that connect two adjacent teeth
located above the alveolar crest
Always present, even after destruction from periodontal disease
What are Alveolar Crest Fibers responsible for? Location? Orientation?
Responsible for resisting tooth extrusion and lateral movement.
Located below the JE and running obliquely from cementum to alveolar crest
What are Horizotal Fibers responsible for? Location? Orientation?
Responsible for resisting lateral tooth movement.
Located in the Cervical Third
Oriented perpendicular from cementum to bone
What are Oblique Fibers responsible for? Location? Orientation?
Responsible for resisting occlusal forces/shock absorption.
Located in the Middle Third (most abundant fiber) Oriented obliquely from bone to cementum
What are Apical Fibers responsible for? Location? Orientation
Oriented in an irregular pattern around the apex
Where are Interradicular fibers located?
Fan out from the fcementum of the tooth at furcation areas of multirooted teeth.
What is EMD? When is it expressed? What is it composed of?
Enamel Matrix Derivatives
Expressed transiently during early root formation (by HERS)
Induces cementoblast or odontoblast formation
Composed of: 90% Amelogenin 10% proline rich non-amelogenins, tuftelin, tuft protein, serum protein, etc.
What is EMD developed from?
Porcine unerupted tooth-buds
Sculean et al. 2006
Aim: to determine the effect of root conditioning on the healing of intrabony defects treated with EMD
Results: NSSD in groups treated with or without PrefGel (24% EDTA)
How is PrefGel supposed to be used
Applied to the root surface for 2min, after the bleeding from the pocket has stopped, followed by copious irrigation with saline.
How does EMD help with Non-Surgical therapy?
No additional benefit to SRP alone for pocket depth reduction and CAL gain. However, may enhance early soft tissue healing (lower GI, less BOP, less post-op discomfort)
Wennstrom and Lindhe 2002
How does EMD help with Intrabony defects?
Systematic review and meta analysis comparing flap alone vs GTR, EMD, GTR+EMD found that no regenerative procedure was significantly better than the others in either CAL or PD reduction.
Tsai et al. 2020
How does EMD help with Class II furcation defects?
RCT
EMD vs Membrane
45pts with 90 defects
EMD>Membrane in Horizontal depth reduction, less pain/swellling, recession reduction, resorption
Jepsen 2004
How do minimally invasive therapies compare when using EMD?
Entire Papilla Preservation technique showed equal gain in patients with EPP+EMD+DBBS vs EPP alone
Aslan et al. 2020
How does EMD help with root coverage procedures?
Mixed reviews
Clinically insignifiant differences
Histologically significant
