PFM Alloys

Applications-substructures for porcelain-fused-to-metal crowns and bridges
 
Classification
o    High-gold alloys
o    Palladium-silver alloys
o    Nickel-chromium alloys

Structure

Composition
o    High-gold alloys are 98% gold. platinum. And palladium
o    Palladium-silver alloys are 50% to 60% palladium and 30 to 40% silver
o    Nickel-chromium alloys are 70% to 80% nickel and 15% chromium with other metals

Manipulation
o    Must have melting temperatures above that of porcelains to be bonded to their surface
o    More difficult to cast (see section on chromium alloys)

Properties - Physical

Except for high-gold alloys, others are less dense alloys
Alloys are designed to have low thermal expansion coefficients that must be matched to the overlying porcelain

Chemical-high-gold alloys are immune, but others passivate

Mechanical-high modulus and hardness
 

Dental Implants

Applications/Use
 
Single-tooth implants
Abutments for bridges (freestanding, attached to natural teeth)
Abutments for over dentures

Terms

Subperiosteal- below the periosteum -but above the bone (second most frequently used types)
Intramucosal-within the mucosa
Endosseous into the bone  (80%of all current types)
Endodontics-through the root canal space and into the periapical bone
Transosteal-through the bone
Bone substitutes -replace. Long bone

Classification by geometric form

Blades
Root forms
Screws
Cylinders
Staples
Circumferential
Others

Classification by materials type

Metallic-titanium, stainless steel, and .chromium cobalt
Polymeric-PMMA
Ceramic hydroxyapatite, carbon, and sapphire

Classification by attachment design

Bioactive surface retention by osseointegration
Nonative porous surfaces for micromechanical retention by osseointegration
Nonactive, nonporous surface for ankylosis. By osseointegration 
Gross mechanical retention designs (e.g.. threads, screws, channels, or transverse holes)
Fibrointegration by formation of fibrous tissue capsule
Combinations of the above

Components

a. Root (for. osseointegration)
b. Neck (for epithelial attachment and percutancaus sealing)
c. Intramobile elements (for shock absorption)
d. Prosthesis (for dental form and function)

Manipulation

a. Selection-based on remaining bone architecture and dimensions
b. Sterilization-radiofrequency glow discharge leaves biomaterial surface uncontaminated and sterile; autoclaving or chemical sterilization is contraindicated for some designs

Properties

1. Physical-should have low thermal and electrical conductivity

2. Chemical

a. Should be resistant to electrochemical corrosion
b. Do not expose surfaces to acids (e.g.. APF fluorides).
c. Keep in mind the effects of adjunctive therapies (e.g., Peridex)

3. Mechanical
a. Should be abrasion resistant and have a high modulus
b. Do not abrade during scaling operations (e.g.with metal scalers or air-power abrasion systems like  Prophy iet)

4. Biologic-depend on osseointegration and epithelial attachment

Finishing and Polishing

Remove oxygen-inhibited layer .Use stones or carbide burs for gross reduction.Use highly fluted carbide burs or special diamonds for fine reduction.Use aluminum oxide strips or disks for finishing. Use fine aluminum oxide finishing pastes. Microfills develop smoothest finish because of small size of filler particles
 

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)

Components 

a. Fillers added to most to control shrinkage
b. Matrix

Investment Techniques 

Single step investing technique:
The investing procedure is carried out in one step either by brush technique or by vacuum technique.

a). Brush technique:
The accurate water-powder ratio is mixed under vacuum. A brush is then used to paint the wax pattern with mix then the casting ring is applied over the crucible former and the ring is filled under vibration until it is completely filled.

b). vacuum technique:
• The mix in first hand spatulated, and then with the crucible former and pattern is place, then ring is attached to the mixing bowl.
• The vacuum hose is then attached to the assembly. The bowel is inverted and the ring is filled under vacuum and vibration

Two-step investing technique:

The investing procedure is carried out in two steps:

• First, the wax pattern is painted with a thick mix andis left till complete setting, the set investment block(first cost) is immersed in water for about tenminutes . the casting ring is then applied over the crucible former and filled with the properly mixedinvestment (second coat) till the ring is completely filled and the mix is left to set.The two-step investing technique is recommendedwhenever greater amount of expansion is required. Thistechnique also minimizes the distortion of the waxpattern and provides castings with smoother surfaces.

• The investment is allowed to set for the recommendedtime (usually one-hour) then the crucible former is removed. If a metal sprue former is used, it is removedby heating over a flame to loosen it from the wax pattern. Any loose particles of investment should beblown off with compressed air should be placed in a humidor if stored overnight.