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
 

Cement liners

Applications (if remaining dentin thickness is <0.5 mm)

o    Used for thermal insulation where cavity preparation is close to the pulp
o    Used for delivering medicaments to the pulp

•    Calcium hydroxide stimulates reparative dentin or
•    Eugenol relieves pain by desensitizing nerves
•    Used to deliver F ion to enamel and dentin

Components

o    Paste of calcium hydroxide reactant powder, ethyl toluene sulfonamide dispersant, zinc oxide filler, and zinc stearate radiopacifier
o    Paste of glycol salicylate reactant liquid, titanium dioxide filler powder, and calcium tungstenate radiopacifier

Reaction

Chemical reaction of calcium ions with salicylate to form methylsalicylate salts Moisture absorbed to allow calcium hydroxide to dissociate into ions to react with salicylate Mixture sets from outside surface to inside as water diffuses

Manipulation

Dentin should not be dehydrated or material will not setMix drop of each paste together for 5 secondsApply material to dentin and allow I to 2 minutes to set

Properties

o    Physical-good thermal and electrical insulator
o    Chemical-poor resistance to water solubility and may dissolve
o    Mechanical-low compressive strength (100 to 500 psi)
o    Biologic-releases calcium hydroxide constituents, which diffuse toward the pulp and stimulate
o    reparative dentin formation

The Sprue :

Its a channel through which molten alloy can reach the mold in an invested ring after the wax has been eliminated. Role of a Sprue: Create a channel to allow the molten wax to escape from the mold. Enable the molten alloy to flow into the mold which was previously occupied by the wax pattern.

FUNCTIONS OF SPRUE

1 . Forms a mount for the wax pattern .
2 . Creates a channel for elimination of wax .
3 .Forms a channel for entry of molten metal
4 . Provides a reservoir of molten metal to compensate for the alloy shrinkage .

SELECTION OF SPRUE

Sprue former gauge selection is often empirical, is yet based on the following five general principles:
1.   Select the gauge sprue former with a diameter that is approximately the same size as the thickest area of the wax pattern. If the pattern is small, the sprue former must also be small because a large sprue former attached to a thin delicate pattern could cause distortion. However if the sprue former diameter is too small this area will solidify before the casting itself and localized shrinkage porosity may result.
2.   If possible the sprue former should be attached to the portion of the pattern with the largest cross-sectional area. It is best for the molten alloy to flow from the thick section to the surrounding thin areas. This design minimizes the risk of turbulence.
3.   The length of the sprue former should be long enough to properly position the pattern in the casting ring within 6mm of the trailing end and yet short enough so the molten alloy does not solidify before it fills the mold.
4.   The type of sprue former selected influences the burnout technique used. It is advisable to use a two-stage burnout technique whenever plastic sprue formers or patterns are involved to ensure complete carbon elimination, because plastic sprues soften at temperatures above the melting point of the inlay waxes.
5.   Patterns may be sprued directly or indirectly. For direct sprueing the sprue former provides the direct connection between the pattern area and the sprue base or crucible former area. With indirect spruing a connector or reservoir bar is positioned between the pattern and the crucible former. It is common to use indirect spruing for multiple stage units and fixed partial dentures.

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

Root canal sealers

Applications

Cementation of silver cone gutta-percha point
Paste filling material

Types

Zinc oxide-eugenol cement types
Noneugenol cement types
Therapeutic cement types

properties

Physical-radiopacity
Chemical-insolubility
Mechanical-flow; tensile strength
Biologic-inertness

Gingival tissue packs

Application-provide temporary displacement of gingival tissues
Composition-slow setting zinc oxide-eugenol cement mixed with cotton twills for texture and strength

Surgical dressings
1.Application-gingival covering after periodontal surgery
2. Composition-modified zinc oxide-eugenol cement (containing tannic, acid. rosin, and various oils)

Orthodontic cements

Application-cementation of orthodontic bands
Composition-zinc phosphate cement 

Manipulation

Zinc phosphate types are routinely mixed with cold or frozen mixing slab to extend the working time
Enamel bonding agent types use acid etching for improved bonding
Band, bracket, or cement removal requires special care
 

I . Procedure for single casting :

A 2.5 mm sprue former is recommended
for molar crowns 2.0 mm for premolars & partial coverage crowns .

II . Procedure for multiple casting :

Each unit is joined to a runner bar .

A single sprue feeds the runner bar

4 . SPRUE FORMER DIRECTION
Sprue Should be directed away from the delicate parts of the pattern
It should not be at right angles to a flat surface .(leads to turbulance  porosity .)
Ideal angulation is 45 degrees .

5 . SPRUE FORMER LENGTH

Depends on the length of casting ring .. Length of the Sprue former should be such that it keeps the wax pattern about 6 to 8 mm away from the casting ring. Sprue former should be no longer than 2 cm. The pattern should be placed as close to the centre of the ring as possible.

Significance

Short Sprue Length:

The gases cannot be adequately vented to permit the molten alloy to fill the ring completelyleading to Back Pressure Porosity.

Long Sprue Length:

Fracture of investment, as mold will not withstand the impact force of the entering molten alloy.

Top of wax should be adjusted for :

6 mm for gypsum bonded investments .

3 -4 mm for phosphate bonded investments .
TYPES OF SPRUES

I . - Wax . II . Solid

- Plastic . Hollow
- Metal .