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Dispersalloy® Dental Amalgam
- 50% Powder (Alloy of Ag-Sn and Ag-Cu) + 50% Liquid (Mercury (about 4% excess Hg))
- mix in amalgamator
- Mixture (amalgam paste)
- place in cavity preparation
- Solid Amalgam Restoration (initial state):
- Ag-Sn + Ag-Hg + Sn-Hg + Ag-Cu
- γ γ1 γ2 eutectic
- After 1 - 24 hours
- Solid Amalgam Restoration (final state):
- Ag-Sn + Ag-Hg + Cu-Sn
- γ γ1 η
Improperly Mixed Amalgam
- Undermixed: Dry, crumbly texture, Sets very slowly
- Overmixed: Wet texture, Sets very quickly, Feels hot
- In both cases, the final restoration will contain excess mercury which results in restoration that is weak and more corrosion prone.
Do not use the paste mixture beyond __ minutes after you have mixed it; otherwise ___________.
- the excess mercury will have begun to react with the alloy, and it will NOT rise to the surface
Acid etch the enamel for __ seconds, and the dentin for __ seconds, wash the preparation with water for __ seconds. Applying bonding agent for __ seconds and light curing it for __ seconds.
The dentinal tubules show increased __________ when closer to the pulp.
permeability, diameter, and density
Calcium hydroxide has following qualities when used as a liner:
- stimulates the formation of reparative dentin
- has antibacterial qualities
- is highly soluble - may increase marginal leakage
Actions of acid on enamel allows _________.
micromechanical retention of resin by etched enamel
___________ bonding agents can enter etched interprismatic spaces in dry cow dentin, but has poor clinical performance due to ________.
- Low viscosity hydrophobic
- very low permeability in freshly cut dentin due to smear layer
- acid etching can remove smear layer, but increases dentin fluid flow, resulting in adhesive failure of the hydrophobic bonding agents
_______: penetration of resin into tubules.
Adhesive failure vs cohesive failure
- detachment at the interface
- dentin fracture; break within the supporting material, adhesive comes off together with some supporting material, indicating strong bonding.
Without acid etching, hydrophobic bonding agents bond with _________ and low strength, leading to _________.
- smear layer
- gap formation and microleakage
________ agent is necessary in order to bond to wet dentin, involving ________ in ______ solvents such as ________.
- hydrophilic monomer
- water miscible
- EtOH and acetone
In moist dentin, bonding agent diffuses into collagen fibers forming __________. In over dried dentin, collagen ____ resulting in _________.
- the “hybrid layer”
- poor hybridization
- Etching removes smear layer, exposes collagen fibers, and removes hydroxyapatite within the intertubular dentin.
- Primers penetrate collagen network.
- Resin microtags formed by adhesive resins and primers
Acid etch remove the smear layer and smear plugs from the dentin and peritubular dentin, increasing the diameter of the tubules. The dilute methacrylates in a volatile solvent expands and coat the matrix. Solvent free adhesive diffuses into the primed surface and down into the tubules while polymerizing with the primer.
- Deep > shallow
- axial > occlusal
- healthy >> below caries
- pulp horn > under fissure
Self-etching primer adhesive system
- directly applied to dry, smear layer covered enamel and dentin. less acidic than phosphoric acid (pH=2).
- after agitating for 20 sec, the solvent is evapaorated.
- no rinsing.
- primer dissolves or disperses the smear layer without removing all smear plugs.
- primed dentin is then sealed w/ a layer of adhesive that is then light cured.
One step systems
- All in one systems have low pH, hydrophilic primer and bonding agents.
- Ideal pH for self etching systems is about 2, partly remove smear layer w/o removing smear plugs.
- Incomplete polymerization can lead to the formation of water channels in the bonded layer.
- Deep areas of hybrid layer may be incompletely infiltrated by monomer. This can lead to hydrolytic breakdown of both the monomers and the collagen.
Limitations of self etch primers
- Weaker acid, poor adhesion to un-cut enamel.
- Self etch pit and fissure sealants are no good.
Early stages in the caries process - When enamel is exposed to caries acids an enamel white spot forms. Can partial remineralize and become less white and smoother. Can also progress to probeable caries.
Acid alone will demineralize dentin, leaving collagen.
Acid plus colagenase enzyme demineralize and remove surface.
Remineralization requires mineral, collagen, and tubules abailable.
Soft dentine, leathery dentine, firm dentine, hard dentine
Necrotic zone + contaminated zone + demineralized zone = soft dentine
- Demineralized dentin = leathery dentine
- Translucent zone = firm dentine
- Sound dentine = hard dentine
Soft dentine will deform when a hard instrument is pressed onto it and can be easily scooped up (little force required)
Although the leathery dentine does not deform when an instrument is pressed onto it, it can still be easily lifted without much force being required. There may be little difference between leathery and firm dentine, with leathery being a transition on the spectrum between soft and firm dentine
physically resistant to hand excavation, and some pressure needs to be exerted through an instrument to lift it.
For hard dentine
- a pushing force needs to be used with a hard instrument to engage the dentine, and only a sharp cutting edge or a bur will lift it.
- A scratchy sound or “cri dentinaire” can be heard when a straight probe is taken across the dentine.
Decision to end excavation:
- Tactile- Hard glassy (hypermineralized) dentin
- Color-some discoloration may be present
Treatment of circumpulpal decay
- Stepwise excavation:
- Visit 1 remove bulk of decay taking care to remove peripheral decay without exposing pulp.
- Visit 2 (6 weeks later) assure symptom status and vitality complete excavation restore.