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

Manipulation

Selection

o    Microfilled composites or hybrids for anterior class III, IV, V
o    Hybrids or midifills for posterior class I, II, III, V

Conditioning of enamel and / or dentin

Do not apply fluorides before etching.-->Acid-etch --> Rinse for 20 seconds with water --> Air-dry etched area for 20 seconds but do not desiccate or dehydrate --> Apply bonding agent and polymerize

Mixing (if required)--> mix two pastes for 20 to 30 seconds

o    Self-cured composite-working time is 60 to 120 seconds after mixing
o    Light-cured composite-working time is unlimited (used for most anterior and some posterior composite restorations)
o    Dual-cured composite-working time is > 10 minutes
o    Two-stage cured composite-working time is >5 minutes

Placement

use plastic instrument or syringe --> Light curing --> Cure incrementally in <2 mm thick layers. Use matrix strip where possible to produce smooth surface and contour composite .Postcure to improve hardness
 

Casting Alloys

Applications-inlay, onlay,  crowns, and bridges

Terms

a. Precious-based on valuable elements
b. Noble or immune-corrosion-resistant element or alloy
c. Base or active-corrosion-prone alloy
d. Passive -corrosion resistant because of surface oxide film
e. Karat (24 karat is 100% gold; 18 karat is 75% gold)
f. Fineness (1000 fineness is I00% gold; 500 fineness is 50% gold)

Classification

High-gold alloys are > 75% gold or other noble metals

Type 1-    83% noble metals (e.g., in simple inlays)
Type II-≥78% noble metals (e.g.,in inlays and onlays)
Type IlI-≥75% noble metals (e.g., in crowns and bridges)
Type IV-≥75% noble metals (e.g., in partial dentures)

Medium-gold alloys are 25% to 75% gold or other noble metals

Low-gold alloys are <25% gold or other noble metals

Gold-substitute alloys arc alloys not containing gold

(1) Palladium-silver alloys-passive .because of mixed oxide film
(2) Cobalt-chromium alloys-passive because of Cr203 oxide film
(3) Iron-chromium alloys-passive because of Cr203 oxide film

Titanium alloys are based on 90% to 100% titanium ; passive because of TiO2 oxide film

Components of gold alloys

-    Gold contributes to corrosion resistance
-    Copper contributes to hardness and strength
-    Silver counteracts orange color of copper
-   Palladium increases melting point and hardness
-    Platinum increases melting point
-    Zinc acts as oxygen scavenger during casting

Manipulation

-    Heated to just beyond melting temperature for casting
o    Cooling shrinkage causes substantial contraction

Properties

Physical

-    Electrical and thermal conductors
-   Relatively low coefficient of thermal expansion

Chemical

-    Silver  content affects susceptibility to tarnish
-   Corrosion resistance  is attributable to nobility or passivation

Mechanical

-   High tensile and compressive strengths but relatively weak in thin sections, such as margins, and can be deformed relatively easily
-    Good wear resistance except in contact with Porcelain
 

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

Denture Teeth

Use-complete or partial dentures

Type

a. Porcelain teeth
b. Acrylic resin teeth
c. Abrasion-resistant teeth (microfilled composite)

Structure and properties

1. Porcelain teeth (high-fusing porcelain)
Only bonded into denture base mechanically. Harder than natural teeth or other restorations and abrades those surfaces. Good aesthetics.Used when patients have good ridge support and sufficient room between the arches

2. Acrylic resin teeth (PMMA  [polymethyl methacrylate])

Bonded pseudochemically into the denture base. Soft and easily worn by abrasive foods . Good initial aesthetics
Used with patients with poor ridges and in cases where they oppose natural teeth

3. Abrasion-resistant teeth (microfilled resins)
Bonded pseudochemically into the denture base.Better abrasion resistance then  acrylic resin teeth
 

COMPOSITE RESINS

Reaction

• Free radical polymerization

Monomers + initiator. + accelerators-+ polymer molecules

• Initiators-start polymerization by decomposing and reacting with monomer
• Accelerators-speed up initiator decomposition

• Amines used  for accelerating self –curing  systems
•  Light  used for accelerating light-curing systems

Retarders or inhibitors-prevent premature polymerization