Intro to DMS Flashcards
steps in dental procedure
- examination
- diagnosis
- treatment plan - need knowledge of DMS to select and explain to patient material used
- surgical procedure
what does the behaviour of dental materials affect? (5)
- choice
- preparation
- application
- performance
- patient’s expectation
how is choice of dental material effected by the dental material’s behaviour?
adequate/best type
select the best option for the patient/circumstances based on knowing what available materials offer
how is preparation effected by the dental material’s behaviour?
cavity design and tooth surface depends on the material
many different procedures depending on the material
how is application effected by the dental material’s behaviour?
technique of placing (increments/curing)
placement of materials, working time, setting time vary with materials - don’t want to repeat applications due to lack of knowledge
how is performance effected by the dental material’s behaviour?
quality of fit, longevity
need to know what you can reasonably expect of a material; how well it fits, how long till the material sets fully/ when can patient eat/drink; how smooth the surface is etc.
how can patient’s expectations be effected by the dental material’s behaviour?
aesthetics, durability
can be very high, need to explain what the material offers in terms of performance e.g. longevity, appearance
CE mark
mark of safety
- essential requirement
material is safe if used appropriately
2 challenges in choosing dental materials
- the number of types of materials
- constant refinements of products and changes in product names
examples of restorative materials
- amalgam
- composites
- glass ionomer cements
- compomers
- porcelain
examples of impression materials
- impression compound
- impression paste (hydrocolloids)
- alginate
- elastomers (polysulphides, polyethers, silicones)
alginates, polyethers, silicones are most commonly used
examples of metals/alloys
- amalgam
- cobalt chromium
- titanium
- gold
- stainless steel
what do impression materials record?
record the dentition
negative replica
what does gypsum (dental stone) reocrd?
positive replica of dentition
allows to study dentition (survey models) and make appliances e.g. partial denture framework
what is PMMA used for?
typically full dentures have acrylic teeth and PMMA denture bases
- aesthetically high quality
- accurate fit
- lightweight
stainless steel alloys can also be used
what does PMMA stand for?
Poly (methyl methacrylate)
what is the use of stainless steel orthodontic appliances?
complex structure to re-align many teeth
- wire under tension to produce force on teeth and so move them
strong to withstand masticatory forces
adjustable to shape
not aesthetic
what is the use of cobalt chromium partial denture?
complex framework to hold artificial tooth/teeth in place
- easy to place and remove
- lightweight
why study DMS?
- will use many different materials with range of characteristics and modes of use
- must use materials appropriately
- must be independent (not constantly asking colleagues or dental nurse for help!)
- communicate with other dental professionals (dentist/nurse/technician)
- provides a framework for understanding materials
- be able to address Health & Safety issues of materials used clinically (risks, allergic components)
- manage patient expectations (aesthetics, longevity of restoration)
3 property categories for dental materials
- mechanical
- chemical
- physical
3 consequences of a force being applied to a material
- stretch/compress (depending on how force applied)
- deform (temporary or permanent)
- fracture (failure)
force is…..
a mass on a tooth
gravity pulls the mass downwards - so exerting a downward force on the tooth
3 types of force dental materials can experience
compressive
tensile
shear
what is compressive force?
squeeze
what is tensile force?
stretch
what is shear force?
object bounded to another surface and apply a force, apply force along same parallel as object can leave a cavity)
stress is…..
= force / unit area = F/A
unites Pascal - Pa=N/m2
squeeze cylinder, stress on cross sectional area
strain is….
When a STRESS is applied to an object/dental material it will change shape slightly.
The material is said to undergo STRAIN
- change in dimensions
proportional limit on a stress-strain diagram
up until this point stress and strain are linearly related
i.e. double stress = double strain
Elastic (Young’s) Modulus measures
rigidity (stiffness)
YM = stress/strain
unites: MPa
higher YM means more rigid
opposite of hard
soft
opposite of strong
weak
opposite of rigid
flexble
opposite of brittle
ductile
3 distinct properties of enamel
- hard surface
- strong
- rigid
- brittle
what is the ideal behaviour of a dental material?
same as enamel or dentine
action of biting
compressive force applied to upper tooth when biting
typical biting force= 500 to 700N
action of grinding/chewing
tooth slides along the surface of the other
- frictional forces experiences
- everyday repeated episodes
can loose enamel surface integrity
- abrasion
action of removal
material needs to adhere to enamel or it will be removed by masticatory forces
enamel properties V dentine properties
enamel is stronger (higher fracture stress)
enamel is more rigid (higher YM and proportional limit)
what type of cavity design is needed for amalgam?
undercut
- splays outwards as carry downwards towards base of cavity
- helps keep material in place
what type of cavity design is needed for composite?
minimal
- no unsupported enamel
what type of retention is used for amalgam?
mechanical
what type of retention is used for composite?
adhesive
what are the stages in material transformation for filling a cavity?
must be pliable, to fit shape of interest;
must set to form hard, strong material
fracture failure mechanism
large force causes catastrophic destruction of material’s structure
hardness failure mechanism
ability of surface to resist indentation (KHN)
abrasion failure mechanism
material surface removal due to grinding
abrasion resistance failure mechanism
ability to withstand surface layers being removes, so compromising surface integrity
fatigue failure mechanism
repetitive ‘small’ stresses causes material failure
small flaws (cracks) in a material grow (propagate), allowing fracture when only a relatively small force is applied
creep failure mechanism
gradual dimensional change due to repetitive small forces
deformation failure mechanism
an applied force may cause permanent change in material’s dimensions (but not fracture it)
de-bond failure mechanism
applied forces sufficient to break material-tooth bond
impact failure mechanism
large, sudden force causes fracture
hardness test
a weight pushes an indenter
- which has a distinctively shaped end into the material surface, causing a notch to form. The bigger the dimensions of the notch the softer the material
hardness different to other mechanical properties involving stress - to do with surface
abrasion
tooth grinds/slides along the opposing tooth surface (or restorative material)
loss of material surface layers causing a roughened surface
how is a surface roughness colour map made?
profilometer
- stylus running along the material surface
permanent deformation
stress exerted is greater than the Elastic Limit
- Material cannot return to normal shape
- bigger
- permanently deformed
elasticity example - impression material
tooth surrounded by impression material and then impression tray
to remove impression tray from mouth the material needs to overcome the bulbosity of the teeth
- needs to change shape and splay outwards
ideally return to original shape when removed
when is de- bonding needed in a material?
to remove orthodontic appliance,
shear force is applied to separate bracket/bonding material from tooth surface
- Interested in how well the bracket adheres to the tooth - will it crack
3 chemical characteristics of dental materials
- setting mechanisms
- setting time
- corrosive potential
5 physical characteristics of dental materials
- viscosity
- thermal conductivity
- thermal expansion
- density
- radiodensity
what do we need to know about each dental material?
it’s ‘ideal’ properties
so we can try and predict how it will behave and manage patient expectations
conditions to consider in the oral environment
variable environment
- saliva
- temperature
- pH
- oral bacteria
retrospective clinical evidence
uses real clinical data from range of GDPs, but with no control over the exact method used
prospective clinical evidence
uses defined protocol, motivated clinicians, unrealistic for actual practice use
issues with gathering clinical evidence
- time-consuming
- costly
- limited in scope: retrospective/prospective
Means there is less robust evidence for the performance of dental materials in vivo than we’d like
