COMPOSITE RESINS

Types

• Amount of filler-25% to 65% volume, 45% to 85% weight
• Filler particle size (diameter in microns)
  • Macrofill 10 to 100 µm (traditional composites)
  • Midi fill- 1 to 10 µm(small particle composites)
  • Minifill— 0.l to 1 µm
  • Microfill-: 0.01 to  0.1 µm (fine particle composites)
  • Hybrid--blend (usually or  microfill and midifill or minifill and microfill)
• Polymerization method
  • Auto-cured (self-cured)
  • Visible light cured
  • Dual cured
  • Staged cure
• Matrix chemistry
  • BIS-GMA type
  • Urethane dimethacrylate (UDM or UDMA) type
  • TEGDMA-diluent monomer to reduce  viscosity

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

Classification of Dental amalgam

1. By powder particle shape .

• Irregular (comminuted, filing, or lathecut)
• Spherical (spherodized)
• Blends (e.g., irregular-irregular, irregularspherical, or spherical-spherical)

2. By total amount of copper

• Low-copper alloys (e.g., conventional, traditional); <5% copper
• High-copper alloys (e,g.  corrosion resistant); 12% to 28% copper

3.By presence of zinc

Examples

• Low-copper, irregular-particle alloy-silver (70%)-tin (26%)-copper (4%)
• High-copper, blended-particles alloy-irregular particles, silver (70%) –tin (26%) -Copper (4%); spherical particles, silver (72%)-copper (28%)
• High-copper, spherical-particles alloy-silver (60%) - tin (27%)-copper (13%)

Mercury hygiene

• Do not contact mercury with skin
• Clean up spills to minimize mercury vaporization
• Store mercury or precapsulated products in tight containers
• Only triturate amalgam components-in tightly- sealed capsules
• Use amalgam with covers
• Store spent amalgam under water or fixer in a tightly sealed jar
• Use high vacuum suction during amalgam alloy placement, setting, or removal when mercury may be vaporized
• Polishing amalgams generally causes localized melting of silver-mercury phase with release of mercury vapor, so water cooling and evacuation must be used

Applications

a. Dentulous impressions for casts for prosthodontics

b. Dentulous impressions for pedodontic appliances

c. Dentulous impressions for study models for orthodontics

d. Edentulous impressions for casts for denture construction

CASTING DEFECTS

Classification :

1) Distortion.
2) Surface roughness .
3) Porosity .
4)Incomplete casting .
5) Oxidation .
6) Sulfur contamination .

Distortion
It is usually due to the distortion of wax pattern.

To avoid this :
Manipulation of the wax at its softening temp
Invest the pattern at the earliest .
If storage is necessary store it in a refrigerator .
Surface roughness

May be due to :
Air bubbles on the wax pattern .
Cracks due to rapid heating of the investment .
High W/P ratio .
Prolonged heating of the mold cavity .
Overheating of the gold alloy .
Too high or too low casting pressure .
Composition of the investment .
Foreign body inclusion.

POROSITY
May be internal or external .
External porosity causes discolouration .
Internal porosity weakens the restoration .

Classification of porosity .
I .Those caused by solidification shrinkage :
a) Localised shrinkage porosity .
b) Suck back porosity .
c) Microporosity .

They are usually irregular in shape .

II ) Those caused by gas :

a) Pin hole porosity .
b) Gas inclusions .
c) Subsurface porosity .

Usually they are spherical in shape .

III ) Those caused by air trapped in the mold :

Back pressure porosity .

Localised shrinkage porosity

Large irregular voids found near sprue casting junction.
Occurs when cooling sequence is incorrect .
If the sprue solidifies before the rest of the casting , no more molten metal is supplied from the sprue which can cause voids or pits (shrink pot porosity )

This can be avoided by -
- using asprue of correct thickness .
- Attach the sprue to the thickest portion of the pattern .
-Flaring of the sprue at the point of atttachment .
-Placing a reservoir close to the pattern .

Suck back porosity

It is an external void seen in the inside of a crown opposite the sprue .
Hot spot is created which freezes last .
It is avoided by :
Reducing the temp difference between the mold & molten alloy .

Microporosity :

Fine irregular voids within the casting .
Occurs when casting freezes rapidly .
Also when mold or casting temp is too low .

Pin hole porosity :
Upon solidification the dissolved gases are expelled from the metal causing tiny voids .
Pt & Pd absorb Hydrogen .
Cu & Ag absorb oxygen .

Gas inclusion porosities

Larger than pin hole porosities .
May be due to dissolved gases or due to gases Carried in or trapped by molten metal .
Apoorly adjusted blow torech can also occlude gases .

Back pressure porosity

This is caused by inadequate venting of the mold .The sprue pattern length should be adjusted so that there is not more than ¼” thickness of the investmentbetween the bottom of the casting .
This can be prevented by :
- using adequate casting force .
-use investment of adequate porosity .
-place the pattern not more than 6-8 mm away from tne end of the casting .
Casting with gas blow holes
This is due to any wax residue in the mold .
To eliminate this the burnout should be done with the sprue hol facing downwards for the wax pattern to run down.

Incomplete casting

This is due to :
- insufficient alloy .
-Alloy not able to enter thin parts of the mold .
-When the mold is not heated to the casting temp .
-Premature solidification of the alloy .
-sprues blocked with foreign bodies .
-Back pressure of gases .
-low casting pressure .
-Alloy not sufficiently molten .

Too bright & shiny casting with short & rounded margins :
occurs when wax is eliminated completely ,it combines with oxygen or air to form carbon monoxide .

Small casting :

occurs when proper expansion is not obtained & due to the shrinkage of the impression .

Contamination of the casting
1) Due to overheating there is oxidation of metal .
2) Use of oxidising zone of the flame .
3) Failure to use a flux .
4) Due to formation sulfur compounds .

Black casting

It is due to :
1) Overheating of the investment .
2) Incomplete elimination of the wax .