Moist vs Dry Dentin with Etch and Rise Adhesives

Moist bonding technique

Prevents spatial alterations that occur when demineralized dentin dries.

What makes moist bonding possible?

Incorporation of acetone or ethanol in primers or adhesives.

Effect of moist bonding on bond strength

Enhances bond strength.

What does water preserve in moist dentin?

Porosity of the collagen network available for monomer interdiffusion.

How are collagen molecules arranged in wet dentin?

Wide gaps separate the collagen molecules.

What should not remain on the tooth after rinsing etching gel?

Pooled moisture.

Why should pooled moisture be removed?

Excess water can dilute the primer and render it less effective.

What happens to dentin collagen during drying?

Collagen collapses, closing micropores in exposed intertubular collagen.

Effect of collapsed collagen on resin monomers

Prevents resin monomers from penetrating.

Effect of excessive air-drying on bond strength

Bond strengths decrease substantially.

How are collagen molecules arranged in dry dentin?

Molecules are arranged more compactly.

What characteristic of collagen may be lost during drying?

Elastic characteristic.

Effect of aqueous re-wetting agents on dried etched dentin

Restore bond strength and raise collapsed collagen to a level similar to moist bonding.

What is ethanol wet bonding?

Replacing water with ethanol in the etched dentin collagen network.

Effect of 100% ethanol saturation on bond strength

Bond strengths of hydrophilic and hydrophobic resins increase significantly.

Methods of removing pooled moisture

Damp cotton pellet, high-volume suction, disposable brush, or laboratory tissue paper.

Does removing excess pooled moisture adversely affect bond strength?

No.

Why is water added to hydrophilic self-etch adhesives?

To ionize acidic methacrylate monomers and solubilize calcium and phosphate ions.

Which acidic methacrylate monomers are commonly involved?

Phosphate and carboxylic monomers.

What ions are solubilized by water?

Calcium and phosphate ions.

Solvents used in hydrophilic adhesive formulations

Ethanol, acetone, or water.

What may enhance remineralization potential of root lesions?

Partial removal of phospho-proteins.

Effect of phosphoric acid etching on dentin

Demineralizes dentin and may leave exposed collagen at the bottom of the hybrid layer.

Effect of acid etching on dentin collagen

Denaturation of collagen fibers.

What are matrix metalloproteinases (MMPs)?

Zinc- and calcium-dependent endopeptidases capable of degrading all extracellular matrix components.

What is chlorhexidine (CHX)?

A clinically relevant proteinase inhibitor.

What may happen to collagen fibrils not encapsulated by resin?

They may undergo degeneration by endogenous MMPs after acid etching.

Which endogenous MMPs are found in dentin?

Gelatinases (MMP-1 and MMP-9), collagenase (MMP-8), and enamelysin (MMP-20).

Effect of MMP inhibition on the hybrid layer

Preserves hybrid layer integrity and may reduce resin-dentin bond degeneration.

What can overcome dentin collagenolytic and gelatinolytic activities?

Protease inhibitors.

What does chlorhexidine preserve in aged resin-dentin interfaces?

Hybrid layer integrity and bond strength.

What happens without chlorhexidine?

It does not inhibit the collagenolytic activity of mineralized dentin.

What is microleakage?

Passage of bacteria and their toxins between restoration margins and tooth preparation walls.

Where can bacteria survive under composite restorations?

Within fluid-filled marginal gaps.

What is pulpal irritation more likely caused by?

Bacteria rather than chemical toxicity of restorative materials.

Can pulpal inflammation occur without bacteria?

Yes.

When may leukocytes migrate into the pulp?

Sometimes 72 hours after the pulp has been challenged.

Best way to prevent microleakage

Bonding resin to a preparation with cavosurface margins in enamel.

What happens when dentin adhesive does not adhere intimately to dentin?

An interfacial gap develops, allowing bacteria to penetrate.

What is nanoleakage?

Penetration of minuscule silver nitrate dye particles through small porosities in the hybrid layer or its transition with mineralized dentin.

What happens when ammoniacal silver nitrate is used?

Silver deposits penetrate the hybrid layer formed by etch-and-rinse or self-etch adhesives.

Two patterns of nanoleakage

Spotted pattern and reticular pattern.

What causes the spotted pattern of nanoleakage?

Possibly incomplete resin infiltration in the hybrid layer of self-etch adhesives.

What causes the reticular pattern of nanoleakage?

Areas where water was not totally removed from the bonding area.

What are water trees?

Porosities in the polymerized adhesive layer.

What may water trees contribute to?

Degradation of the bonding interface over time.

What commonly causes adverse pulpal reactions after restorative procedures?

Bacteria remaining in or penetrating the preparation.

Factors contributing to adverse pulpal reactions

Bacterial invasion, faulty restoration, pressure gradients, traumatic injuries, iatrogenic preparation, excessive pressure, heat, friction, and polymerization contraction stress.

What causes pressure gradients that may contribute to adverse pulpal reactions?

Excessive desiccation or excessive pressure during cementation.

What increases the mineral content of dentin?

Aging, dentin beneath a carious lesion, and dentin exposed to the oral cavity in non-carious cervical lesions.

What happens to dentinal tubules in these situations?

Tubules become obliterated with tricalcium phosphate crystals.

What is sclerotic dentin?

Dentin with compositional changes that make it more resistant to acid etching than normal dentin.

Effect of sclerotic dentin on bond strength

Low bond strengths.

Where has bonding to sclerotic dentin resulted in low bond strengths?

Non-carious cervical lesions.

Can some dentin adhesives perform better in sclerotic dentin?

Yes.

How does the adhesive solvent influence dentin adhesives?

It influences their clinical behavior.

Which adhesive resulted in a lower retention rate?

Acetone-based adhesive.

What does the lower retention rate of acetone-based adhesive illustrate?

Technique sensitivity associated with acetone-based adhesives.

What may influence the clinical longevity of Class V restorations?

The type of composite used.

What is the Young's modulus of microfilled composites?

Low.

Why can microfilled composites better relieve stresses?

Their low Young's modulus allows them to relieve stresses caused by polymerization or tooth flexure.

What can happen when stresses are transferred to the adhesive interface?

Debonding.

Why do materials with a higher Young's modulus not relieve stresses by flow?

They cannot compensate for stresses accumulated during polymerization.

What can improve the flow capacity of composites used in Class II preparations?

Using a flowable composite between the composite and the tooth wall.

Role of a flowable low-modulus composite

Acts as a shock absorber and protects the interface against fatigue stresses.

What theory explains dentin hypersensitivity?

Hydrodynamic theory.

Most common site of dentin hypersensitivity

Cervical area of teeth.

Purpose of dentin-desensitizing solutions

To prevent postoperative sensitivity.

What may account for the efficacy of desensitizing solutions?

Precipitation of proteins from dentinal fluid in the tubules.

What are dentin adhesives used for in desensitization?

Treating hypersensitive root surfaces.

How can dentin adhesives reduce sensitivity?

Formation of resin tags and a hybrid layer.