DDMT FINALS QUIZ

Waxes

Are composed of high molecular weight organic molecules. Dental waxes are composed of natural and synthetic waxes, gums, fats, fatty acids, oil, natural and synthetic resins and pigments

Pattern wax

= models of a restoration or appliance a.inlay wax b.baseplate wax C.casting

Processing wax

auxiliary materials in production of casts; extension of impression trays; or in soldering

a. boxing wax

b. utility wax

c. sticky wax

d. carving wax

e. block-out wax

Impression wax

impression materials. Recently, light-cured resin pattern materials have become available.

a. corrective wax

b. bite registration wax

Type 1

medium wax for direct wax patterns in the mouth.

Type II

softer wax used in indirect technique in inlays and crowns fabrication. Generally in blue, green, or purple rods or sticks about 7.5 cm long and 6 mm in diamond

Excess residue

after melting, it is essential that no excess residue remain in the investment mold form to cause incomplete casting of the margins of the restorations. The speciation limits the nonvolatile residue of inlay waxes to a maximum of 0.10%.

Flow

highly dependent on temperature, composition of the wax, force causing deformation, and length of time that the force is applied. Greatly increases as the melting range of the wax is approached or as the load and its length of application are increased.

Thermal expansion

waxes expand when heated and contract when cooled. In general, dental waxes have the largest values of coefficient of thermal expansion of any material used in dentistry

Type 1 - The maximum allowable expansion (or shrinkage when the wax cools) between 25-30C and 25-37C is

0.20% and 0.60%

Residual stresses

Stress remaining in a wax as a result of manipulation is residual stress.

Casting Wax

for the pattern for metallic framework of RPD and other structures

Baseplate Wax

used on the baseplate tray to establish the vertical dimension, the plane of occlusion etc. for CD construction.

Boxing Wax

for forming a plaster of working cast from an impression, a wax box must be formed around the impression prior to cast construction

Utility Wax

used to reline a tray for impression; done to prevent sag and distortion of the impression material. Consists largely of beeswax, petrolatum and other soft waxes. In ortho, known as periphery wax.

Sticky Wax

used to assemble metallic resin pieces in a fixed temporary position

Bite Registration Wax

used to articulate accurately certain models of opposing quadrants. Made from 28- gauge casting wax

Steps in Inlay Construction

1.Construction of a wax pattern

2. Spruing

3. Withdraw wax pattern from cavity

4. . Washing wax pattern with wetting agent (denatured alcohol)

5. Investing

6. Place asbestos strip inside inlay ring

7. Position bur

8. Mix investment compound and pour inside the inlay ring to overfill

9. For high-fusing gold and non-precious alloys, Phosphate-bonded investments are used instead of gypsum investments

10. Expansion of the investment

11. . The investment is allowed to set in air for at least 45 minutes.

12. Wax elimination or burnout

13. Casting the alloy

14. Quenching

15. Pickling

16. Polishing after pickling

17. Fitting of the inlay inside the cavity.

18. Cementing

Spruing

forms a channel a channel for elimination of wax during burn-out & for molten alloy to enter the mold space;; a short pin known as the sprue is attached to the thickest portion of the wax pattern.

Washing wax pattern with wetting agent (denatured alcohol)

to remove oil for better adhesion of investment compound to the surface of the wax.

Investing

a. P/W 15g/ 7cc of water, construct a cherry or core using brush technique

Place asbestos strip inside inlay ring

; a cushion as the investment compound expands. Must have a clearance of 1/8 inch or 3 mm from top of ring

Position bur

(sprue pin) with cherry on the crucible former then place inside inlay ring. Must have a clearance of ¼ inch or 6mm from top of ring

Mix investment compound and pour inside the inlay ring to overll.

The investment material has a binder, calcium sulfate hemihydrate and the refractory is either quartz or cristobalite, which are forms of silica.

*For high-fusing gold and non-precious alloys,

Phosphate-bonded investments are used instead of gypsum investments.

Expansion of the investment

It is used to compensate for the shrinkage of the gold casting as it cools during the casting procedure. A total of 1.5% to 2% mold expansion is the aim in most gold castings. During the setting of the investment, an expansion of 0.25% takes place because of the gypsum crystallization process.

45

The investment is allowed to set in air for at least ?? minutes.

Wax elimination or burnout

The mold is placed in a burnout oven with the sprue hole facing downward to facilitate outward ow of the molten wax for 30 minutes, temperature of 482 C – 650 C

Casting the alloy

gold alloys may be melted for casting by the use of a gas-air blow torch or in an electric casting machine.

Quenching

After the casting machine stops rotating, the mold is removed and quenched in water and casting is recovered by breaking away the investment mold.

Pickling

The casting is pickled in acid after casting to remove the surface oxidation that gives it a dark appearance.

Polishing after pickling

is done with the use of abrasive wheels, rubber wheels, pumice, Tripoli and finally, rouge.

Dental Porcelain

a mixture of FELDSPAR (main constituent), QUARTZ, & metallic oxides

The compressive strength of a porcelain restoration is _______ than it's tensile or shear strengths.

Greater

Brittle

Dental porcelain restorations are _______ and are not capable of much plastic deformation.

Quartz

a strengthener.

Aluminous Porcelain

uses alumina instead of quartz as a strengthener. This porcelain is considerably stronger than conventional porcelains.

Kaolin

a clay and sticky material that binds the particles together when the porcelain is "green" or unfired.

Silicone Dioxide (64-6(%)

Aluminum Oxide (8-19%)

Potassium oxide (8%)

Sodium oxide (2-5%).

Constituents of Dental Porcelain

a. Be low-fusing temperature.

b. High viscosity

c. Resistance to devitrification (crystallization)

Dental porcelain used in fabricating restorations MUST have these properties

1. High Fusing Porcelains

2. Medium Fusing

3. Low Fusing

3 classes of dental porcelain

High fusing porcelains

used to manufacture DENTURE TEETH.

Medium fusing

used for all-ceramic and porcelain jacket crowns. § Components: oxides of lithium, magnesium, and phosphate (in addition to silicone dioxide, aluminum oxide, potassium oxide, and sodium oxide).

Low fusing

used for metal-ceramic (PFM) crowns.

Aluminum oxide

increase its resistance to "slumping down" during firing.

Calcium oxide

- also added to low-fusing porcelains.

DEGASSING (HEAT TREATMENT)

the process by which a casting is heated in a porcelain furnace to a temperature of 980°C to burn off any remaining impurities prior to adding porcelain.

1. Composition

2. Fabrication Method

WAYS TO CLASSIFY ALL-CERAMIC CROWNS

Feldspathic porcelain

used for conventional porcelain-jacket crowns.

Aluminous porcelain

- found in Vitadur, Hyceram, Cerestore, & Inceram systems.

Alumina

is used to reinforce glass. Porcelain strength is determined by the amount of alumina reinforcement

1. Low Bisque Firing

2. Medium Bisque Firing

3. High Bisque Firing

3 stages involved in firing dental porcelain

Low bisque firing

Particles lack complete adhesion; low amount of shrinkage occurs and very porous

Medium bisque firing

: Water evaporates with better cohesion to powder particles and some porosity.

High bisque firing

Fusion of particles to form a continuous mass, complete cohesion and no more shrinkage.

GLAZED PORCELAIN

It is non-porous, resists abrasion, possesses esthetic ability, and is well tolerated by the gingiva.

OVER GLAZES (APPLIED GLAZES)

It is a ceramic powder that may be added to a porcelain restoration after it has been fired.

0.7 mm

(Metal Ceramic Restorations) The absolute minimum required thickness of the porcelain is

0.3 - 0.5 mm for high noble gold alloys, 0.2 for base metal alloys

Metal coping thickness can vary from

.5mm, 1.0mm

For metal ceramic crown, it is required to create space for ____ mm of metal + ____ of porcelain

inadequate condensation of the porcelain

The most common cause of porosity in the porcelain is

green discoloration

Porcelain baked onto a high-fusing gold alloy may exhibit a

High-gold noble alloy

Palladium-Silver alloys

Nickel-Chromium alloys (base metal alloys):

PFM ALLOYS: