Lecture 2 Flashcards
- Looks good
- Functions properly
- Longevity
Patient satisfaction
-goal of dental material
Do models have limitations?
Yes
contact angle
used to measure how liquid
interacts with solid
Measure
Cannot Know Everything About a Given Material
or System
Models
- Unfilled diluted resins
- Self or light cured
- Clear or opaque
- Radiopaque
Sealants
Anticipated on the basis of the Hydrophobicity (water-hating) and hydrophilicity (water loving) of materials
Wetting
Allow penetration into areas with water
Hydrophilic primers
Solvent that hydrophllic primers are mixed with
Alcohol or acetone
Viscosity of hydrophilic primers
Low
Allows for attatchment to composite
Hydrophilic primers
Will wet hydrophlic surfaces
Hydrophlic chemicals
Important anytime two different materials come into contact
Surface wetting
Important in impression materials, adhesives and bacterial adhesions
Surface wetting
involve changes in the primary and secondary
bonding of the material
Chemical properties
generally affected by chemical and
electro chemical reactions
Primary bonding
generally affected by processes
such as adsorption (onto) and absorption (into)
Secondary bonding
The spontaneous destructive oxidation of metals
Corrosion
Do all metals corrode?
Yes
Copper roofs turn
green
What color do amalgam filling turn over time?
black
Designed to minimize corrosion
Gold alloys
recently deemed a noble metal ADA
Titanium
Desirable for ceramic to metal bonding
Metal oxides (ceramics)
Metal corrosion that leads to destruction
Active
Gamma 2
Metal corrosion that produces corrosion film that prevents further corrosion
Passive
Titanium implants
Metal corrosion of noble metals
Immune
gold
Electrochemical corrosion
Active
Corroding metal
anode
Different metal
-Passive-supplied electrons to solution
Cathode
A conducting environment for ionic movement
electrolyte
An electrical connection
between the anode and cathode for the flow of
Electron current
Two phases in amalgam
Anode and cathode
normally occurs through
dissolution of oxides created by hydrogen bonding effects of water in local areas of high acidity.
Chemical dissolution
How are ceramics affected by dissolution
Chemical dissolution
- Absorption of water into polymers
- Hydrolytic degradation and release of components
How polymers are affected by dissolution
Absorption of water into polymers
Dimensional changes
Hydrolytic degradation and release of components
Contribute to wear problems with composites
Metal ion interation
Hg, Ni
Biological properties are interrelated with
- Degradation properties
- Polymerization process or processing
Biological properties are
dynamic
Describe how a material responds to loads
forces
Mechanical properties
Single dimension of force
- Compression
- Tension
- Shear
Combinations of forces
- Torsion (twisting)
- Flexsion (tensile)
- Diametral compression (tensile)
Measures of
absorbed energy by
material
Resilience and toughness
Before deformation occurs
Resilience
Before failure or fracture occurs
toughness
Time and temperature dependent
Mechanical events
Measures of
absorbed energy by
material
Hardness
Indent with a load
and measure size of
indentation
Hardness
Measures a Materials Resistance to Crack Propagation
Fracture toughness
Has High Clinical Correlation to Clinical Wear Data
Composits- fracture toughness
Deformation over time in response to low constant
stress
Creep (strain relaxation)
Deformation over time in response to low constant
strain
Stress relaxation
Multiple cycles of low stress
Fatigue
Effects of forces on the
motion of biomaterials
and biologic structures
Biomechanics
Teeth and restorations (and therefore restorative materials) must withstand forces in service during
Mastication and fabrication
Are teeth rigid?
No
When teeth are
subject to chewing
forces (stresses)
they undergo
Subclinical movements (Strains)
usually associated with
heavy wear facets
Abfractions
Cyclic tension and
compression of
enamel rods lead to
Microfractures
transfers stress from
enamel to dentin
DEJ
B-L rigidity of teeth
Cuspal independence
How do teeth fail or fracture?
- Single cycle overload
- Fatigue
“unexpectedly bit on cherry pit or bone” (rare)
Single cycle overload
- cyclic loads well below
breaking load
Fatigue
- “I was eating something soft” (more common)
-Slow crack propagation over
time
Fatigue
- Restorative material
- Tooth structure
- Interface (stress transferred)
Biomechanical unit