Denture Liners

Use - patients with soft tissue irritation

Types

Long-term liners (soft liners)-used over a period of months for patients with severe undercuts or continually sore residual ridges

Short-term liners (tissue conditioners)-used to facilitate tissue healing over several days

Structure

Soft liners-plasticized acrylic copolymers or silicone rubber

Tissue conditioners-PEMA plasticized with ethanol and aromatic esters

Properties

Liners flow under low pressure, allowing adaptation to soft tissues, but are elastic during chewing forces. 
Low initial hardness, but liner becomes  harder as plasticizers are leached out during intraoral use 
Some silicone rubber liners support growth of yeasts
 

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
 

Properties of Acrylic Resins.

• They have a low thermal conductivity. These resins are not easily washed out by the acids of the oral cavity (low solubility). Acrylic resins are also resilient, which allows them to be used in stress-bearing areas.
• Acrylic resins exhibit a moderate shrinkage of from 3 to 8 percent. This shrinkage and low marginal strength can lead to marginal leakage. Acrylic resins have a low resistance to wear. Acrylic resins cannot be used over a zinc oxide and eugenol-type base because eugenol interferes with the acrylic curing process.
• Mixing. Insufficient mixing will cause an uneven color or streaks in the mixture. Overmixing will cause the material to harden before it can be placed
• Poor distortion resistance at higher temperatures, therefore dentures should not be cleaned in hot water
• Good resistance to color change
• Absorbs water and must be kept hydrated  (stored in water when not in mouth) to prevent dehydration cycling and changes in dimensions
• Not resistant to strong oxidizing agents
• Low strength; however, flexible, with good fatigue resistance
• Poor scratch resistance; clean tissue-bearing surfaces of denture with soft brush and do not use abrasive cleaners

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

Manipulation

Mixing

o    P/L types mixed in bowl (plaster and alginate)
o    Thermoplastic materials not mixed (compound and agar-agar)
o    Paste/paste types hand mixed on pad (zinc oxide-eugenol, polysulfide rubber, silicone rubber, polyether rubber. and poly-vinylsiloxane)
o    Paste/paste mixed through a nozzle on an auto-mixing gun (poly-vinylsiloxane)

Placement

o    Mixed material carried in tray to mouth (full arch tray, quadrant tray. or triple tray)
o    Materials set in mouth more quickly because of higher temperature

Removal - rapid removal of impression encourages deformation to take place elastically rather than permanently (elastic deformation requires about 20 minutes)

Cleaning and disinfection of impressions 

Classification

Rigid impression materials

(1) Plaster
(2) Compound
(3) Zinc oxide-eugenol

Flexible hydrocolloid impression materials

(I) Agar-agar (reversible hydrocolloid)
(2) Alginate (irreversible hydrocolloid)

Flexible, elastomeric, or rubber impression materials

(1) Polysulfide rubber (mercaptan rubber)
(2) Silicone rubber (condensation silicone)
(3) Polyether rubber
(4) Polyvinyl siloxane (addition silicone)