All Ceramic Restorations Quiz

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Questions and Answers

What is the primary purpose of using a separating medium after plaster sets?

To improve the color quality of the resin

To ensure proper adhesion of the wax

To enhance the strength of the plaster

To facilitate the easier removal of acrylic resin (correct)

What is the first step in the wax elimination process?

Opening the flask

Flushing with cold water

Removing the acrylic resin

Immersing the flask in hot water (correct)

In the wet pack technique, how is the gingival color resin treated during the packing process?

It is applied dry and then saturated

It is mixed last with the other shades

It is packed after reaching the dough stage (correct)

It is packed and the flask is closed immediately without paper

Which of the following is a characteristic of the dry pack technique compared to the wet pack technique?

It allows for better detail reproduction Signup and view all the answers

What is done immediately after deflasking the acrylic resin?

Plaster is cleaned away Signup and view all the answers

During acrylic resin processing, how is the temperature treated after the flask is closed and pressed?

It is gradually brought to boiling over 30 minutes Signup and view all the answers

What material is used for polishing the crown after processing?

A felt wheel Signup and view all the answers

Which resin type is mentioned as being heat cured?

Bis-GMA Signup and view all the answers

What factor contributes to the risk of fracture in short clinical crowns?

Inadequate tooth preparation Signup and view all the answers

Which of the following is a contraindication for using full-crown restorations?

Presence of parafunctional habits like clenching Signup and view all the answers

What is the primary material composition of the aluminous core in porcelain buildup?

50% by weight alumina Signup and view all the answers

What is a primary advantage of full-crown restorations?

Excellent aesthetics and natural translucency Signup and view all the answers

What is the purpose of the binder used in porcelain mixing?

To form a creamy paste for application Signup and view all the answers

What is a disadvantage of full-crown restorations?

Susceptibility to recurrent caries Signup and view all the answers

What is the preferred reduction for the lingual half of the tooth during preparation?

1 mm Signup and view all the answers

During which stage of porcelain firing does maximum cohesion occur?

High Bisque Stage Signup and view all the answers

Which preparation parameter is NOT mentioned in the content?

Chemical Signup and view all the answers

What is one key advantage of the condensation process in porcelain preparation?

Decreases shrinkage during firing Signup and view all the answers

What happens during the sintering process in porcelain manufacturing?

Glass bridges form between unfused particles Signup and view all the answers

Which tool is referred for creating depth orientation grooves during crown preparation?

Flat end diamond stone Signup and view all the answers

Patients at high risk of fractures should avoid full-crown restorations due to what reason?

Higher fracture susceptibility in relation to physical activities Signup and view all the answers

What is the consequence of the 30% volumetric shrinkage after firing?

Reduction in size of the final product Signup and view all the answers

Which binder is most commonly used for dentin and enamel powders in porcelain mixing?

Distilled water Signup and view all the answers

What is one effect of increasing density during the porcelain preparation process?

Improved strength of porcelain Signup and view all the answers

What is a disadvantage of long span fixed bridges regarding tooth reduction?

Excessive tooth reduction is required. Signup and view all the answers

Which of the following is required to prepare the lingual half of an anterior tooth for metal casting?

A reduction of 1 mm with a chamfer finish line. Signup and view all the answers

For a full veneered restoration, what is the minimum incisal reduction required for translucency?

1.5 mm. Signup and view all the answers

Which armamentarium is used for bulk reduction during tooth preparation?

Round-ended rotary diamonds. Signup and view all the answers

What happens to porcelain in long span fixed bridges?

It may fracture. Signup and view all the answers

What is the appropriate taper for all axial opposing walls in tooth preparation?

5-10°. Signup and view all the answers

What can complicate the detection of caries under a fixed restoration?

Caries cannot be detected clinically or radiographically. Signup and view all the answers

What is a primary reason for incorporating rests in metal copings for removable prostheses?

To provide additional support. Signup and view all the answers

What is the purpose of creating a controlled oxide layer on the metal surface?

To establish a chemical bond with porcelain Signup and view all the answers

Which property is NOT a requirement for dental porcelain used as a veneering material?

Chemical and optical instability Signup and view all the answers

What is the consequence of the porcelain having a coefficient of thermal expansion higher than that of the metal?

Crack formation in the porcelain Signup and view all the answers

What type of angles should be avoided in the design of a metal substructure?

Acute angles Signup and view all the answers

Why is adequate support important for porcelain in a metal-ceramic restoration?

To prevent fracturing of the brittle porcelain Signup and view all the answers

How much should the firing temperature of dental porcelain be lower than the melting range of the cast metal substrate?

170-280 °C Signup and view all the answers

What happens to porcelain if fired multiple times without proper precautions?

It becomes milky and difficult to glaze Signup and view all the answers

Which of the following metals is primarily used to harden the alloy and provide oxides for ceramic bonding?

Indium Signup and view all the answers

Study Notes

Contraindications for All Ceramic Restorations

Short clinical crowns, either naturally or due to attrition, can lead to stress concentration and fracture.
Young patients with large pulps may be at risk for pulp exposure.
A more conservative restoration should be considered when possible.
Patients with high risk of fractures, such as contact sport athletes, are not ideal candidates.
Patients with parafunctional habits, such as clenching and bruxism, can put extra stress on restorations.
Periodontally compromised teeth with root exposure may lack adequate margin support.
Thin teeth labio-lingually can be problematic due to aggressive shoulder preparation.

Advantages of All Ceramic Restorations

Excellent aesthetics due to the ability to reproduce natural color and translucency.
Good resistance and retention thanks to full coverage.
Biocompatibility: good tissue response even with subgingival margins.
Reduction facially is more conservative than veneered restorations because there is no need to mask the metal and create translucency.
Low thermal conductivity.

Disadvantages of All Ceramic Restorations

Brittle restorations can be prone to fracture.
Pulp vitality cannot be tested.
Recurrent caries under the restoration cannot be detected.

Biological, Mechanical, and Esthetical Preparation Parameters

These parameters must be considered during preparation for all ceramic restorations.

Armamentarium for All Ceramic Restorations

End cutting bur
Finishing stone

Anterior All Ceramic Index Fabrication

Facial Index
Mid-sagittal index

Preparation Aim

Labially, two sets of depth orientation grooves are made cervically and incisally in a two-plane reduction using a tapered with flat end diamond stone instrument.
Tooth structure between the grooves is removed.
The labial surface is reduced uniformly in two planes to correspond to the geometric planes of a natural tooth.
The lingual half of the tooth is reduced 1 mm with a shoulder finish line, 1 mm in width.

Porcelain Build Up

An aluminous core (50% by weight alumina) is built up incrementally using powder and liquid, creating an opaque core.
Veneer porcelain, with matching thermal expansion to the core, is used to build dentine and enamel parts, after which the restoration is fired and glazed.

Porcelain Firing

Porcelain is fired in special furnaces with controlled temperatures and environments.
Most thermo-chemical reactions between porcelain components are completed during manufacturing.
Sintering: a process where glass bridges form between unfused particles to produce a continuous mass, accompanied by a 30% volumetric shrinkage after firing.
Causes of shrinkage:
- Loss of water.
- Densification through sintering.

Stages of Porcelain Firing

Low Bisque Stage: Glass bridges flow between particles.
Medium Bisque Stage: More glass bridges flow, resulting in increased cohesion and shrinkage.
High Bisque Stage: Maximum cohesion, resulting in a dense, closely packed mass with no more shrinkage.

Porcelain Handling

Mixing: Dental porcelain powder is mixed with a binder to form a creamy paste.
- Distilled water or a water-based glycerine containing liquid is commonly used for dentin and enamel powders.
- Propylene glycol is used with the powder of aluminous core build-up..
Application: The porcelain paste is applied to the Pt foil, refractory die or coping, using a brush or spatula, in incremental layers.
Condensation: Removes excess water from the porcelain working mass to:
- Decrease firing shrinkage.
- Adapt the paste to the required form.
- Increase strength of porcelain by closely packing particles.
- Decrease porosity.

Condensation Advantages

Less porosity
Increased density and adaptation
Less shrinkage during firing
Better surface texture

Flask Preparation

When the plaster sets, lubricate the plaster with separating medium.
The upper part of the flask is filled with plaster, and after closing the flask parts together, it is kept under a press while the plaster hardens.

Wax Elimination

Wax is eliminated by immersing the flask in hot water for 5 minutes.
The flask is then opened and flushed with hot water to eliminate wax.
After the flask cools, cold water is applied as a separating medium for the acrylic resin.

Acrylic Resin Packing

Wet Pack Technique:
- 3 shades of acrylic resin (gingival, body, and incisal) are mixed in 3 dappen dishes.
- When the resin reaches the dough stage, gingival color resin is packed, and the flask is closed after putting a wet cellophane paper over it and pressed.
- The flask is then opened, excess is removed, and the step is repeated for body and incisal color.
- The cellophane paper is removed, and the flask is closed for processing.
Dry Pack Technique:
- Gingival resin powder is applied cervically, then saturated with monomer, and the flask is bench tapped.
- Wet cellophane paper is applied, excess is removed, and body and incisal resin are applied and adapted.
- The flask is then closed for processing.

Acrylic Resin Packing Technique Comparison

Wet Pack Technique:
- Waste material
- Harder technique
- Fine details are not reproduced
- Better P:L (powder: liquid) proportioning
Dry Pack Technique:
- No waste material
- Easier technique
- Reproduces fine details and color shades.

Acrylic Resin Processing

The flask is closed and pressed, then placed in a hot water bath.
The temperature is gradually brought to boiling in 30 minutes.
The flask is left for 30 minutes, then bench cooled to room temperature.

Deflasking, Finishing, and Polishing

The flask is opened, and the crown is retrieved.
A sharp instrument is used to clean away the plaster.
A tweezer is used to remove the tin foil.
Resin flashes are trimmed with a small acrylic stone, a sandpaper disc, pumice, and a rubber cup.
Polishing is done using a felt wheel.
Store the jacket crown in water.

Types of Resin

Heat-cured resin
Bis-Gma: Protemp & Systemp

Causes of Cracks and Flaws in Ceramics

Indium (In), Tin (Sn), Gallium (Ga), and Iron (Fe) harden the alloy and provide oxides for ceramic bonding.

Cleaning Procedures

Air-abrasion of the veneering area, with margins protected by soft wax.
The completed substructure is ready for oxidizing.

Oxidizing

A controlled oxide layer must be created on the metal surface to establish a chemical bond between metal and porcelain.
This oxide layer is obtained by placing the substructure on a firing tray and inserting it into a porcelain furnace, raising the temperature to a specified level.

Basic Requirements for Dental Porcelain

Low fusing temperatures: less than the melting range of the cast metal substrate by about 170-280 °C.
High viscosity and high resistance to slumping to maintain basic shapes during firing
Chemically and optically stable over multiple firing cycles
Should resist devitrification (porcelain becoming milky and difficult to glaze after multiple firings)
Coefficient of thermal expansion should be lower than that of the metal by 1 × 10-6 °C to enhance bond strength and avoid crack formation.

Principles of Metal Substructure Design

No sharp or acute angles: Rounded convex metal surface with no sharp angles eliminates areas of stress concentration, distributes occlusal forces evenly, and facilitates wetting of the metal with porcelain, enhancing bonding.
Adequate support to porcelain: Lack of adequate support can lead to fracture of porcelain, thick porcelain layers under tension, and subsurface porosity.
A distinct margin for finishing the veneer: Rounded angles are necessary to accommodate the veneer.

Advantages of Metal Ceramic Restorations

Good biocompatibility, durability, and resistance to wear. - Long span fixed bridges maybe done.
May correct the occlusal plane. - Rests maybe incorporated in the metal coping to accommodate support for removable prosthesis.

Disadvantages of Metal Ceramic Restorations

Excessive tooth reduction is required.
Pulp vitality cannot be detected.
Caries under the restoration cannot be detected clinically or radiographically.
Porcelain may fracture and resin may undergo discoloration.
All ceramic restorations provide superior aesthetics.
Expensive restoration.
Difficult shade match.

Armamentarium for Anterior Veneered Preparations

Round-ended rotary diamonds
Football- or wheel-shaped diamond
Flat-ended, tapered diamond
Finishing stones
Explorer and periodontal probe

Anterior Veneered Preparation

Labially, the labial half has greater reduction to provide enough space for metal and veneering material (1.2 mm for base metal & 1.5 mm for noble metal), extending proximally and ending lingual to the contact area.
The finishing line is shoulder.
The labial surface is reduced uniformly in two planes to correspond to the two geometric planes of a natural tooth.
The lingual half of the tooth is reduced 1 mm to receive a metal casting only, with a chamfer finish line that is 0.5 mm wide.
In case of full veneered more reduction is needed.
The meeting of both reductions results in a half groove (wing) proximally due to the abrupt meeting of different depths of reductions.
This wing extends inciso-gingivally and adds resistance to the preparation.
All axial opposing walls should have a taper of approximately (5-10°).
In anterior teeth, the palatal fossa is prepared with 1 mm clearance if the centric contacts are located on the metal. Full veneered restorations require additional clearance.
Incisal reduction should be 1.5-2 mm at least for adequate translucency of the final restoration.

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Description

Explore the contraindications and advantages of all ceramic restorations in dentistry. This quiz will test your understanding of the factors affecting restoration success and the aesthetic benefits that these materials offer. Perfect for dental students and professionals seeking to enhance their knowledge.