(2a) Principles of crown preparation

What are the objectives that full coverage restorations should fulfill

Function

Esthetics

Preservation of periodontium

Marginal integrity

Preservation of tooth structure

T/F We should only do full coverage restorations when necessary and you should not over prepare the tooth

True

When preparing a tooth for a crown there should always be at least _____ planes of reduction

2 planes

What are the two things that you can use as a guide in order to preserve as much tooth structure as possible when doing a crown preparation

- matrix (putty)

- depth cuts

When do you fabricate the matrix for the crown preparation

Before you prep the tooth

How do we use depth cuts as a guide for tooth preparation reduction

You can use the crown gauge or the dental caliper in order to measure the diameter of the bur which will allow you to know how deep you are drilling into the tooth. Which can serve as a guide.

T/F Depth cuts can be done are different surfaces depending on what tooth you are preparing

True

If you under reduce the prep you might not have enough space for the _____ and if you over reduce that can affect the _____ of the crown

Material, retention

When making sure the crown is going to provide the correct function what should you look at

Marginal adaptation

Occlusal Harmony

Patient satisfaction

What is marginal adaptation

A seamless meeting of the restoration and the tooth

When the crown is in function the patient should not feels and ________

Pain or sensitivity

What are the esthetics of the crown determined by

The shade and contours of the restoration blending in with adjacent dentition

The shade of the crown is influenced by the _____ used and the thickness of the crown is determined by he amount of _______

Material, reduction

T/F The materials used should have the strength to hold up the oral environment without complication

True

What could be some complications of a crown

Fracture

Early cement failure

Shade stability

Marginal decay

T/F Even if a crown fits a tooth, if certain principles are not followed the crown may not be sufficiently retentive and will eventually fail

True

Principles of crown preparation are based on the ______ used to fabricate the prosthesis and different _______ have different tooth reduction requirements

Materials, materials

T/F A porecelain fused to metal crown has different requirements than an all ceramic crown

True

What is a crown that has a core of a metal coping with a bonded layer of porcelain that provides the esthetics

Porcelain fused to metal (PFM)

Or

Ceramic-metal crown

Metal ceramic crown

For a PFM crown the metal must have sufficient thickness to resist ______ and the porcelain requires a certain thickness to provide an ______ result and resist _______

Flexure, esthetic, fracture

(These requirements is where the amount of tooth reduction for a PFM comes from)

What is the difference between PFM and all ceramic crowns

The ACC does not have metal underneath the porcelain.

T/F Ceramics are brittle so the material will affect the amount of reduction and the preparation and finish line geometry

True

What requires more tooth reduction and PFM or a ACC

PFM generally requires more facial reduction because it needs room for the metal and porcelain layers.

What is the strength of the crown material measured by

It's ability to resist the forces that are applied to it

What is the most common property of a crown that is measured

Stiffness

What is tensile stress

The stress state leading to expansion that is the length of a material tends to increase in the tensile direction

What is the main difference between tensile stress and shear stress

The forces causing tensile stress are at right angles to the surface but in shear stress it is parallel

____ is the resistance of an elastic body to deflection or deformation by an applied force

Stiffness

A _____ graph is used to determine the stiffness of a material

Stress/strain

As stress is _____ the material strains until fracture occurs

Increased

What is the slope of the stress strain curve referred to as

Modulus of elasticity

The higher the MOE the higher the ______ of a material

Stiffness

A high MOE (stiff object) will withstand a high amount of _____ but not ______ to a high degree before fractures

Stress, strain

Materials with a high MOE are said to be _____

Brittle

_____ have a low MOE so they are ductile and _____ have a high MOE so they are brittle

Metals, porcelain

Porcelain has a higher MOE which means it is very brittle. If an object is brittle it was have more resistance to ______ than _____

Compression, tension

Metals has a lower MOE which means it is very ductile. If an object is ductile it will ______ prior to fracture

Deform

What needs to be in order for a PFM crown to be strong and durable

The ductile metal and brittle porcelain must be of sufficient thickness to withstand the forces applied

What will happen to the PFM crown if it has the ideal porcelain thickness but the metal is too thin

It will fracture because the thin metal can not cope with the resistance to flexure the brittle porcelain will fracture when the thin metal flexes

What is the minimal thickness for the metal of a PFM crown

0.5mm

T/F The ideal thickness of the metal may vary depending on what metal it is

True

What is the ideal thickness of the porcelain for a PFM crown

1.5mm

If the porcelain is too thin this can be a problem with _____

Esthetics

What must there be a balance between when placing a crown

A balance between the amount of reduction required by the materials with the amount of reduction a tooth can tolerate

T/F Every crown material requires a minimal thickness

True

What is the minimal amount of occlusal tooth reduction for a PFM crown preparation

2mm

What are some factors to consider for tooth reduction of a crown preparation

- Preservation of pulp vitality

- Optimum thickness of materials for function and longevity

- Optimum thickness of materials for esthetics

- Tooth fracture

T/FPulp chambers are variable sizes in different teeth

True

What is significant to consider when doing a crown preparation

The age of the patient because young pulp chambers are larger than more advanced pulp chambers