Dentistry 019: Crown & Bridge

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Questions and Answers

What is the primary reason for using electroplating in die fabrication?

To modify the chemical composition of die materials

To decrease the setting time of die materials

To enhance the aesthetic properties of the die

To improve the abrasion resistance of gypsum dies (correct)

Which material is commonly used as a base for electroplated dies?

Type 4 stone (correct)

Type 3 gypsum

Resin

Pure Gold

In conventional die fabrication for crowns or bridges, which material is most frequently utilized?

Acrylic resin

Pure Silver

Type 4 stone

Type 3 Gypsum (correct)

What is the primary purpose of creating a die in the fabrication process of a crown or bridge?

To provide an isolated replica of the prepared tooth Signup and view all the answers

Why is the accurate replication of margins a key consideration when creating a die?

To ensure the precise fit and adaptation of the final crown or bridge Signup and view all the answers

What is the primary reason for blocking out undercuts on a die?

To allow for easy removal of the final restoration from the die. Signup and view all the answers

If a defect on the die extends 0.5mm from the cavity margin, what should be done?

The undercut should be blocked out with wax. Signup and view all the answers

What does the term 'die spacer' refer to?

The space between the casting and prepared tooth surface for luting agent Signup and view all the answers

Where should space for the luting agent NOT be present?

Immediately adjacent to the margin. Signup and view all the answers

What does the lab technician do when an undercut is present?

They block out the undercut with wax, if not too close to the margin. Signup and view all the answers

Why is it important that the unprepared tooth structure cervical to the finish line is discernible on the die?

To accurately establish the cervical contour of the restoration. Signup and view all the answers

What is the primary purpose of using a retraction cord during the impression process?

To open the gingival sulcus and retract soft tissue to expose the finish line and tooth structure below it. Signup and view all the answers

What is a 'cuff' on a dental impression?

The area of the impression below the finish line that captures the tooth structure. Signup and view all the answers

What is the consequence of not having a cuff on an impression?

The die will lack the area below the finish line, leading to an inaccurate restoration. Signup and view all the answers

Why is adequate access to the margins imperative during impression taking?

To accurately capture the detail of the finish line and the surrounding tooth structure. Signup and view all the answers

Which type of gold alloy is typically used with gypsum-bonded investment?

ADA Type IV gold alloys Signup and view all the answers

What is a significant limitation of gypsum-bonded investments?

Low melting temperature tolerance Signup and view all the answers

For what purpose are gypsum-bonded investments primarily used?

Casting dental gold alloys Signup and view all the answers

Which of the following is NOT a typical type of gold alloy used with gypsum-bonded investments?

Type VI Signup and view all the answers

What is the main characteristic that would exclude a metal from being used with a gypsum-bonded investement?

High melting temperature Signup and view all the answers

For which type of restoration would a framework be cast instead of a full contour?

A crown that will be veneered with porcelain Signup and view all the answers

What is the primary reason for ensuring good occlusal contact on a wax pattern?

To accurately reproduce the contact on the final restoration Signup and view all the answers

What does the term "cut back technique" refer to in the context of dental restorations?

The process of reducing a full anatomical wax up to allow for layering of porcelain Signup and view all the answers

Which material is typically used to veneer a framework made using the cut back technique?

Feldspathic porcelain Signup and view all the answers

Why is the occlusal contact of the wax pattern so important for the final restoration?

It directly influences the occlusal contact of the final restoration Signup and view all the answers

What is the primary purpose of the sprue in the casting process?

To serve as a channel for the molten metal to reach the investment cavity. Signup and view all the answers

What is the function of the rotational arm in a casting machine?

To help introduce the molten metal into the investment cavity. Signup and view all the answers

Why is it important to have a smooth fitting surface on the final casting?

It reduces the requirement for further adjustments and provides an accurate fit. Signup and view all the answers

What does a generalized casting roughness typically suggest?

A breakdown of the investment material from excessive burnout temperature. Signup and view all the answers

How does the process of pressing ceramic differ from traditional metal casting?

Ceramic is pressed directly, rather than metal being cast into the investment. Signup and view all the answers

What happens to the wax pattern in the investment material after it is placed in the oven?

It melts and is removed, and the space remains in the investment. Signup and view all the answers

After the casting process, what action is taken regarding the sprue?

It is cut off using burs and discs to separate the final casting from the sprue channel. Signup and view all the answers

What is a key advantage of using gold in the casting process, as mentioned in the content?

Gold can be remelted and reused after the casting. Signup and view all the answers

Study Notes

Crown & Bridge

Presented by Dana ballout, corrected by Islam abd alraheam
Course: Dentistry 019, University of Jordan
Subject matter: Communication with the dental laboratory and procedures for fixed prosthodontics
Importance of clear communication and understanding between clinicians and laboratory personnel is essential for high-quality prostheses

Communication with the Dental Laboratory

Clinicians need in-depth understanding of lab work, technical, and materials science for informed clinical decisions
Communication is critical between dentists and lab technicians for success
Detailed prescription is necessary to guide the lab, including materials, occlusion, shade, shape, pontic and substructure designs, and any additional info
The dentist and the lab technician need to be on the same page in terms of material science and the restorations being planned
Accuracy for the prepared teeth needs to be accurate and precise, with no voids
Communication with the lab includes the necessary information about design and the restoration planning

Definitive Casts and Dies

The lab's first task after receiving an impression is to produce a definitive cast
The definitive cast must meet specific requirements, including accurate reproduction of prepared and unprepared tooth surfaces, absence of voids, and precise representation of occlusal surfaces for articulation
Diagnostics are created to ensure the diagnostic cast and the die accurately represent the prepared tooth
The die should accurately duplicate all surfaces of the prepared tooth, including cervical areas.
Smooth surfaces are essential for articulating dental models

Material Science

Gypsum is the most common material for creating casts and dies (types 3, 4, and 5 are used for fabrication
Other materials, like resin, are sometimes used, are generally tighter fitting when made on resin when compared to those made using gypsum
Important characteristics for these materials are dimensional accuracy and resistance to wear
Different types of gypsum have different expansions, and technicians must be aware of these differences to avoid problems with the fit of the restoration

Separating and Returning Dies in Model

Methods like dowel pins (Pindex / Whalerent) create precise placements for separating and returning dies to the original position
Di-Lok (DentiFax/Di-Equi), involves a plastic base that ensures accurate positioning of the dies
Additional techniques like the Zeiser (Girrbach) system use a wide plastic base

Ditching the Dies

Dies must be prepared by cutting away areas below the finish line. This is important for precise placement in the mold.
Proper marking of the finish line is extremely important

Mounting Casts on Articulator

Accurate bite recording is key for precisely mounting casts on an articulator.
The cast's bite records the relationship between the upper and lower teeth
Avoiding adjustments during mounting ensures precise reproduction of the patient’s occlusion.

Before Starting Waxing Procedure

Correcting defects in the die(undercuts) is crucial before waxing
Provision of adequate space for cement or luting agent is essential
The space between the internal casting surface and the tooth must be enough for the cement to fill nicely
Space measurements should be 20-40 µm between the restoration and the tooth's surface
It should be noted that too little or too much space can affect the longevity of the restoration

Metal Casting

The correct metal is selected according to the needed alloy temperatures, and a mold is created from the investment material
The molten metal is introduced into the space, and after cooling, the casting is removed from the mold.
The finished casting will need additional machining
The proper procedure for using these different methods, along with any specific requirements, is critical to producing a high quality restoration
Pressing ceramic techniques are similar, but the ceramic material is pressed into the investment mold.
The castings are tested, and any defects noted

Evaluation of the Casting

Casting defects can occur due to investment errors and temperature issues.
Identifying roughness, nodules, fins, incompleteness, voids, and dimensional inaccuracies can require corrections and adjustments.
Evaluating the casting involves checking both the quality of the mold and the casting procedure.

Porcelain Layering over Metal Core/Restoration Finishing

Layering porcelain over the casting is a crucial step in fixed prosthodontics.
Proper layering technique is critical for a good-looking, fit restoration. Different materials such as Zirconia may replace metals
A specific material is used for porcelain firing(crystallization)

Vacuum Mixing

Proper mixing of investment materials is important to avoid gas/bubble formation

Lost Wax Technique

Lost wax method is a common technique in casting metal prosthetics
The process involves making a mold from refractory material that will be heated during casting.
The wax pattern is enclosed in a mold and after solidifying the refractory material, the wax is melted, leaving a cavity where metal can be inserted

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Description

This quiz explores the vital role of communication between dentists and dental laboratories in the field of fixed prosthodontics. It emphasizes the importance of detailed prescriptions and a solid understanding of materials and techniques to ensure high-quality prostheses. Test your knowledge on the processes and practices essential for success in dental restorations.