Introduction to DMS Flashcards
What are the stages of a clinical episode affected by dental material behaviour? 5
Selection, preparation of cavity design and tooth surface, placement of material, performance of material and patients expectations
How is safety of materials insured?
CE mark
Does a CE mark guarantee the material is the best available?
No
What do impressions record? 2
Negative replica of the teeth and a valuable record of space and shape of patient’s teeth
What is gypsum used for?
Creates positive replica of the impression and can be used to create prostheses to fit patient and identify shape of teeth.
What can stainless steel be used for?
Orthodontic appliances or denture base
What is CoCr used for?
Partial denture
What are mechanical properties?
Force applied to material
What can forces applied to materials do?
Stretch/compress, deform or fracture
How is force calculated? What is the units?
mass in kg x gravitational acceleration, units is N
What are the different types of forces?
Compressive, tensile (stretch) and shear (pushing along contact area)
How is stress calculated? What is the units?
Force / area, units is Pascals
How is strain calculated?
change of length of material / original length of material for ratio, x100 for percentage
On a stress strain curve, when is the material at maximum stress?
At maximum stress when stress and strain are proportional.
On a stress strain curve, when will the material fracture?
After the proportional limit when the curve falls off.
What is young’s modulus?
Stress/ strain, Measure of rigidity ( higher YM, more rigidity)
When biting, which teeth is withstanding forces and which type?
Upper teeth- compressive force
What is the typical biting force?
50-70 N
When grinding/chewing, what type of force is applied and how?
Tooth slides along the surface of the other, frictional forces experienced
Which has a greater YM, enamel or dentine?
Enamel
What is the difference in cavity design between amalgam and composite?
Amalgam flares out from the tooth, requiring an undercut design whereas composite resin has a much smaller, minimal design
Which material is held by mechanical retention and which material is bonded with adhesion?
Amalgam- mechanical retention
Composite- adhesion
How should a material be transformed to fill a cavity?
Material must be pliable to fit shape of interest, and must set to form hard strong material
What are some failure mechanisms that the likeliness needs to be assessed when working with dental materials?
Fracture, hardness, abrasion, abrasion resistance, fatigue, creep, deformation, de-bond and impact
What is abrasion?
Tooth grinds/slides along the opposing tooth/material surface and the tooth/material surface is abraded, resulting in loss of surface layer and roughened surface
What is fatigue?
Repeated loads applied causes small cracks in a material grow, allowing fracture when only a relatively small force is applied.
What is creep?
Repetitive forces causes dimensional change
If stress is over the elastic limit, what happens?
Permanent deformation
What is debonding?
To apply shear stress, causing material to pull away from the tooth
What is ductility?
Quality of being pliable and flexible.
What is tear strength?
Material’s ability to resist failure perpendicular to the stress being applied.
What are the chemical properties you have to consider when choosing a dental material? 3
Setting mechanism, setting time and corrosive potential
What are the physical properties you have to consider when choosing a dental material? 5
Viscosity, thermal conduction and expansion, density and radiodensity
What do we have to consider in the oral environment when choosing a dental material? 4
Saliva, temperature variations, pH variations and oral bacteria
