1. Biologic consideration of dentin & its clinical significance in operative dentistry

2. Dentin
Function.
Support.
Morphology.

3. During tooth preparation, dentin is distinguished from enamel by:
Color dentin.
Reflectance.
Hardness.
Sound.

4. Two main type of D. are present:
Intertubular dentin.
Peritubular dentin.
Depth of dentin:
Outer dentin.
Inner dentin.
Permeability of dentin.
Sensitivity of dentin.

5. Theories of thermal sensitivity:
Theory of thermal shock.
A hydrodynamic theory.
Physiologic & tertiary dentin:
Physiologic dentin:
Primary dentin: formed relatively quickly until root formation is completed by odontoblasts.
Secondary dentin: this is slowly formed dentin that continues to constrict the dimensions of the pulp chamber.

6. Sclerotic dentin (transparent or peritubular dentin)
Results from aging or mild irritation (such as slow caries) & causes a change in the composition of the primary dentin.
Sclerosis resulting from aging is (physiological dentin sclerosis) and that resulting from mild irritation called (reactive dentine sclerosis).

7. Reparative dentin (tertiary dentin)
Intense traumatic insult (injury) to the tooth, whether caused by bacterial penetration associated with caries, or heat & trauma from a dental bur, may be severe enough to destroy the supporting odontoblasts in the affected location. Within 3 weeks, fibroblasts or mesenchymal cells of the pulp are converted or differentiated to stimulate the activates of original odontoblasts, & form irregularly organized tubules.

8. Dentin bonding:
Dentin is an intrinsically hydrated tissue, penetrated by fluid—filled dentin tubules. Movement of fluid from the pulp to DEJ is a result of a slight, constant pulpal pressure.
Adhesion can be affected by the remaining dentin thickness after tooth preparation, bond strength are generally less in deep dentin than in superficial dentin.
The presence of smear layer of debris on the surface of the tooth after tooth preparation may affect the adhesion.(smear layer is a semi permeable film of organic and inorganic debris on the prepared dentinal surface, the smear layer fills the orifices of dentin tubules, forming smear plugs).
Several additional factors affect dentin permeability, the use of vasoconstrictors in local anesthetics, which decreases pulpal pressure and fluid flow in tubules, factors such as the radius and the length of the tubules. All of these variables make dentin a dynamic substrate and consequently a difficult substrate for bonding.

9. Current strategies for adhesion of resin to dentin
Total etch adhesive:
Three step total etch adhesive: Etchant (E )+primer (P)+ bonding agent (B).
Etchant (E ): removes the smear layer.
Exposes the intertubular and peritubular collagen.
Opens the tubules.
Decreases the surface free energy.
Primer (P): includes bifunctional molecules (hydrophilic and hydrophobic).
Envelops the external surface of collagen fibrils.
Re-establishes surface free energy to levels compatible with more hydrophobic restorative materials.
Bonding agent(B): includes monomers that are mostly hydrophobic such as Bis-GMA.
Copolymerizes with the primer molecules penetrates and polymerizes into interfibriller spaces to serve as a structural backbone to hybrid layer.
B. one-bottle total-etch (two step total-etch adhesive):
Etchant (E )+ Primer and bonding agent (PB).

10. II: Self-etch adhesive:
Two-bottle self-etch: Etchant and Primer (EP)+Bonding (B). Self- etch adhesive does not remove the smear layer, but fixes it, the smear plug is impregnated with acidic monomers, but it is not removed and prepares the pathway for the penetration of fluid resin into micro channels that permeate the smear plug.
All-in-one self-etch (EPB) we call it single application:
It demineralizes and penetrates dentin simultaneously leaving a precipitate on the hybrid layer.
Forms a thin layer of adhesive.
A multi-coat approach is recommended.

11. Expanded clinical indications for dentin adhesives:
Desensitization: hypersensitivity is a major problem for periodontal patients, with gingival recession and exposed root. Dentin adhesives have been suggested to treat hypersensitivity by occlusion of the dentinal tubules.
Adhesive amalgam restorations: to overcome the marginal micro leakage and postoperative sensitivity, the use of dentin adhesive systems has been proposed for amalgam restorations.
Indirect adhesive restorations: such as indirect ceramic and resin-based restorations(crowns, inlays, onlays, veneers and indirect composite restorations).