In which direction do the principal (oblique) periodontal fibres lie, relative to the alveolar bone and cementum?
The principal PDL fibres run obliquely from the alveolar bone to the cementum. The bone attachment of a given fibre bundle is more cervically placed than the cementum attachment, which is more apical.
What is the advantage of the orientation of the principal (oblique) periodontal fibre
Only with this arrangement can the biting forces be transmitted and dissipated to bone.
What is the main protein in the principal fibres
collagen - types 1 and 3
What types of cementum can you see on the root of the tooth? Where are they located?
Acellular cementum is found on all parts of the root. Cellular cementum is usually found in the apical half of the root and in furcation regions (not seen in this slide).
in which part of the root is the cementum layer thickest
apex
what structures pass through gaps in the inner cortical plate of alveolar bone
Blood vessels pass through nutrient canals (Volkmann’s canals). These can be seen in a dried skull penetrating the bone lining the tooth socket.
How does cementum differ from bone?
Cementum is avascular and has no innervation. It is also less readily resorbed. All these aspects are relevant during orthodontic tooth movement, when bone must be remodelled without damaging cementum.
What is the usual relationship between cellular and acellular cementum? What type of variations from this relationship can occur?
Usually, cellular cementum overlies acellular cementum. However, the reverse can occur. An also common feature is to have a sequence of various alternating layers of cellular and acellular cementum. This is especially true at the apex.
The periodontal space is frequently described as of an hourglass shape. Can you explain why?
Lateral occlusal forces are transmitted and dissipated by a lever mechanism where the fulcrum or hinge is located at the mid third of the root. Therefore, the periodontal space is wider at the force source (cervical region of the root) and the dissipation area (apex) while being narrower at the fulcrum (the median portion).
are collagen fibres straight or wavy and why
wavy
This allows a small amount of tooth movement before the tissue is placed under tension (in association to crimping).
In view of Sharpey’s fibres contribution to the cementum, what other name is used for these embedded fibres?
Extrinsic fibres of cementum.
What cells lie on the cementum surface, and what is their function?
Cementoblasts. These form cementum. Some cementoblasts become trapped in the cementum; they are then called cementocytes. They are equivalent to osteocytes in bone.
In the centre of the periodontal ligament, what is the main cell type?
Fibroblasts.
what is the main function of the fibroblasts
Fibroblasts are involved in formation and degradation of collagen fibres and in forming ground substance of the PDL.
On which side of the PDL are the fibre bundles larger/thicker?
They are larger/thicker on the bone side.
On which side of the PDL are the fibre bundles closer together?
They are closer together on the cementum side.
What is the advantage of this fibre bundle arrangement?
Forces from the tooth are spread and dissipated into a larger bone area. 12.
Describe collagen crimping and what the proposed function of it is.
Collagen fibres have an alternate wavy pattern under polarised light. This is further to the already mentioned wavy pattern of the periodontal fibres. Crimping is involved on the early dissipation of tooth movement before the tissues are placed under stress.
fibre groups pass from cementum to bone in different directions in a vertical plane but also in a horizontal plane - what is the advantage of this arrangement
Allows the tooth to resist rotational forces.
Which group of fibres can be seen in the interdental region that isn’t present on the labial and lingual aspects of the periodontium?
Transseptal fibres
Which group of fibres can be seen on the labial and lingual aspects of the periodontium that isn’t present in the interdental region?
Alveolar crest fibres.
Which fibres are not attached to bone?
Transseptal fibres and gingival fibres.
Which fibres are not attached to bone or tooth?
Circular free gingival fibres.
what is the dental gingival function
The dento-gingival junction is clinically a very important area. It is the boundary between the oral cavity and the underlying connective tissue of the tooth-supporting tissues
what type of epithelium is the oral gingival epithelium
It is a stratified squamous, keratinised epithelium
What are the major differences between the oral gingival epithelium and the sulcular epithelium?
The sulcular epithelium is thinner and has no keratinised layer. In addition, the rete ridges are fewer, or absent, and project less deeply into the connective tissue.
On the root surface, what tissue lies apical to the junctional epithelium?
Cementum. You should be able to see the alveolar crest fibres of the periodontal ligament attached to it.
What influence might periodontal disease have on the position of the junctional epithelium?
The junctional epithelium attachment will move apically, creating an enlarged (deepened) gingival sulcus. This enlarged space is now called a true periodontal pocket, which patients can find difficult to clean. (How does this differ from a ‘false pocket’?)
Of what type(s) of epithelium(a) are the junctional and sulcular epithelia?
junctional epithelium consists of a single layer of cuboidal cells overlying several layers of flattened cells.
What is the major structural difference between the two epithelia?
Junctional epithelium is considerably thinner than sulcular epithelium and in life was attached to enamel.
What unusual feature does the junctional epithelium exhibit?
The junctional epithelium has two basal laminae – one which joins with the underlying connective tissue, and the other on the superficial aspect which joins to enamel. The latter junction involves hemidesmosomes.
What shape is the interface between the junctional epithelium and the underlying connective tissue?
There are no rete ridges present and, therefore, the junction between the two tissues is smooth. 5.
In health, the interface between the sulcular epithelium and the connective tissue should exhibit considerably fewer rete ridges than the oral gingival epithelium. In this section, however, as in most sections of this area, chronic inflammation has modified the structure. In the connective tissue immediately below the epithelium there is an inflammatory cell infiltrate. The sulcular epithelium shows some hyperplasia in response to this irritation.
how does the oral gingival epithelium compare in thickness with the sulcular epithelium
The oral gingival epithelium is thicker.
What shape is its (oral gingival epithelium) junction with the underlying connective tissue
Similar to oral gingival epithelium elsewhere, there are numerous rete ridges.
what is the free gingival groove
demarcates the free gingiva and the attached gingivae
The majority of the tooth tissue present is an unerupted permanent tooth below a portion of interdental gingivae (of a primary tooth) that extends from the buccal to the lingual aspects. Also present are the resorbing roots of the primary molar. Look at the layer of cells on the outer aspect of the enamel space around the crown of the permanent tooth. what is this layer and what cells contribute to it
Reduced enamel epithelium, formed from amelolasts, stratum intermedium and outer enamel epithelium.
What name is given to the area between the approximal (interproximal) surfaces of teeth where these peaks lie?
The embrasure 4
In life, what lies coronal to the col?
The contact point between the teeth.
What shape is its (col) junction with the lamina propria?
It is smooth centrally and irregular at the periphery due to the inflammatory reaction. 7.
Deep to the interdental gingival tissues are fibres of the periodontal ligament.
what group of fibres do the interdental gingival fibres belong to
transeptal group
what tissue lies deep to the transeptal fibres
Alveolar bone (crest).The main venous plexuses are in the apical region.
