Bonding Agents

Applications-composites, resin-modified gIass ionomers, ceramic bonded to enamel restorations, veneers, orthodontic brackets, and desensitizing dentin by covering exposed tubules (Maryland bridges, composite and ceramic repair systems, amalgams and amalgam repair, and pinned amalgams)

Definitions;-

Smear layer - Layer of compacted debris on enamel and/or dentin from the cavity preparation process  that is weakly held to the surface (6 to 7 MPa) , and that limits bonding agent strength if not removed

Etching (or, conditioning)- smear layer removal and production of microspaces for micromechanical bonding by dissolving –minor amounts of surface hydroxyapatite crystals

Priming..- micromechanical (and chemical) bonding to the microspaces created by conditioning step.

Conditioning/priming agent-agent that accomplishes both actions

Bonding- formation of resin layer that connect  the primed surface to the overlying restoration (e.g., composite) .. –

Enamel bonding System-for bonding to enamel (although dentin bonding may be a Second step)

Dentin bonding system  for bonding  to dentin (although  enamel bonding  may have been a first step)

•        First-generation dentin bonding system for bonding to smear layer

•        New-generation dentin bonding system- for removing smear layer and etching intertubular dentin to allow  primer and/or bonding agent to diffuse into spaces between collagen and form hybrid zone

Enamel and dentin bonding system-for bonding to enamel and dentin surfaces with the same procedures

Amalgam bonding  system for bonding to enamel, dentin, and amalgam, dentin and amalgam during an amalgam placement procedure or for amalgam repair

Universal bonding system-for bonding to enamel, dentin, amalgam, porcelain , or any other substrate intraorally that may be necessary for a restorative procedure  using the  same set of procedures and materials

Types

Enamel bonding systems

Dentin bonding systems

Amalgam bonding systems

Universal bonding systems

Structure

o        Components of bonding systems

o        Conditioning agent-mineral or organic acid

Enamel only   37% phosphoric acid

Dentin only or enamel and .dentin---37% phosphoric acid, citric acid, maleic acid, or nitric acid

o        Priming agent

Hydrophobic-solvent-soluble, light cured monomer system

Hydrophilic-water-soluble, light-cured monomer system

Bonding agent

BIS-GMA-type monomer system

UDMA-type monomer system

Reaction

Bonding occurs primarily by intimate micromechanical retention with the relief created by the conditioning step

Chemical bonding is possible but is not recognized as contributing significantly to the overall bond strength

Manipulation-follow manufacturer's directions

Properties

Physical-thermal expansion and contraction may create fatigue stresses that debond the interface and permit micro leakage

Chemical-water absorption into the bonding agent may chemically alter the bonding

Mechanical-mechanical stresses may produce fatigue that debonds the interface and permits microleakage

Enamel bonding-adhesion occurs by macrotags (between enamel prisms) and microtags (into enamel prisms) to produce micromechanical retention

Dentin bonding-adhesion occurs by penetration of smear layer and formation of microtags into intertubular dentin to produce a hybrid zone (interpenetration zone or diffusion zone) that microscopically intertwines collagen bundles and bonding agent polymer

Biologic

Conditioning agents may be locally irritating if they come into contact with soft tissue

Priming agents (uncured), particularly those based on HEMA, may be skin sensitizers after several contacts with dental personnel

Protect skin on hands and face from inadvertent contact with unset materials and/ or their vapors

HEMA and other priming monomers may penetrate through rubber gloves in relatively short times (60 to 90 seconds)

Cement Bases

Applications

•    Thermal insulation below a restoration
•    Mechanical protection where there is inadequate dentin to support amalgam condensation pressures

Types

•    Zinc phosphate cement bases
•    Polycarboxylate cement bases
•    Glass ionomer cement bases (self-curing and light-curing)

Components

o    Reactive powder (chemically basic)
o    Reactive liquid (chemically acidic)

Reaction

o    Acid-base reaction that forms salts or cross linked matrix
o    Reaction may be exothermic

Manipulation-consistency for basing includes more powders, which improves all of the cement properties

Properties

Physical-excellent thermal and electrical insulation

Chemical-much more resistant to dissolution than cement liners

    Polycarboxylate and glass ionomer cements are mechanically and chemically adhesive to tooth structure

    Solubility of all cement bases is lower than cement liners if they are mixed at higher powder- to-liquid ratios

Mechanical- much higher compressive strengths (12,000 to 30,000 psi)
    Light-cured hybrid glass ionomer cements are the strongest
    Zinc oxide-eugenol cements are the weakest

Biologic (see section on luting cements for details)

    Zinc oxide-eugenol cements are obtundent to the pulp
    Polycarboxylate and glass ionomer cements are kind to the pulp
 

Temporary Filling Materials

Applications / Use

While waiting for lab fabrication of cast restoration
While observing reaction of pulp tissues

Objectives

Provide pulpal protection
Provide medication to reduce pulpal inflammation
Maintain the tooth position with an aesthetic restoration

Classification

Temporary filling cements
Temporary filling resins

Components

Temporary filling cements

1. Zinc oxide-eugenol cement with cotton fibers added
2. Polyme r powder-reinforced zinc oxide eugenol cement

Temporary filling resins

•    MMA / PMMA filling materials
•    Polyamide filling materials
•    BIS-GMA filling materials
 

RINGLESS INVESTMENT TECHNIQUE
Used for phosphate bonded investments .
This method uses paper or plastic casting ring .
It is designed to allow urestricted expansion .
Useful for high melting alloys .

Model. Cast. and Die Materials

Applications
- Gold casting, porcelain and porcelain-fused–to metal fabrication procedures
- Orthodontic and pedodontic appliance construction
- Study models for occlusal records

Terms
a. Models-replicas of hard and soft tissues for study of dental symmetry
b. Casts-working replicas of hard and soft tissues for use in the fabrication of appliances or restorations
c. Dies :-  working replicas of one tooth (or a few teeth) used for the fabrication of a restoration
d. Duplicates-second casts prepared from original  casts

Classification by materials

a Models :- (model plaster or orthodontic stone; gypsum product)
b. Stone casts (regular stone; gypsum product)
c. Stone dies (diestone; gypsum product)-may electroplated
d. Epoxy dies (epoxy polymer)-abrasion-resistant dies

POLYCARBOXYLATE CEMENT 

Use:. The primary use of polycarboxylate cement is as a cementing medium of cast alloy and porcelain restorations. In addition, it can be used as a cavity liner, as a base under metallic restorations, or as a temporary restorative material. 

Clinical Uses

Polycarboxylate cement is used in the same way as zinc phosphate cement, both as an intermediate base and as a cementing medium. 

c. Chemical Composition. 

(1) Powder:. It generally contains zinc oxide, 1 to 5 percent magnesium oxide, and 10 to 40 percent aluminum oxide or other reinforcing fillers. A small percentage of fluoride may be included. 
(2) Liquid. Polycarboxylate cement liquid is approximately a 40 percent aqueous solution of polyacrylic acid copolymer with other organic acids such as itaconic acid. Due to its high molecular weight, the solution is rather thick (viscous). 

d. Properties. 

The properties of polycarboxylate cement are identical to those of zinc phosphate cement with one exception. Polycarboxylate cement has lower compressive strength. 

e. Setting Reactions: 

The setting reaction of polycarboxylate cement produces little heat. This has made it a material of choice. Manipulation is simpler, and trauma due to thermal shock to the pulp is reduced. The rate of setting is affected by the powder-liquid ratio, the reactivity of the zinc oxide, the particle size, the presence of additives, and the molecular weight and concentration of the polyacrylic acid. The strength can be increased by additives such as alumina and fluoride. The zinc oxide reacts with the polyacrylic acid forming a cross-linked structure of zinc polyacrylate. The set cement consists of residual zinc oxide bonded together by a gel-like matrix. 

Precautions. 
The following precautions should be observed. 
o    The interior of restorations and tooth surfaces must be free of saliva. 
o    The mix should be used while it is still glossy, before the onset of cobwebbing. 
o    The powder and liquid should be stored in stoppered containers under cool conditions. Loss of moisture from the liquid will lead to thickening.