Biomaterials- Chapter 3

physical properties

• can be measured & observed w/o having to change the composition of material & they describe it

• ex. color, thermal conductivity, and solubility

mechanical properties

• define the materials ability to perform in the oral environment and resist stresses and strains

• ex. elasticity, ductility, durability, & ultimate strength

necessary to categorize materials by classification:

• physical structure

• application

• composition

• reaction

• manipulation

2 categories of bonds:

• strong bonds- primary bonds

• weaker bonds- secondary bonds

primary bonds

• “chemical bonds”

• strongest bonds

primary bonds: 3 types

• ionic bonds

• covalent bonds

• metallic bonds

covalent bonds

• a type of bond that occurs when 2 nonmetal share electrons in their outer shells, creating full shells for both

ionic bonds

• when atoms gain or lose electrons they become electrically charged and are called ions

metallic bonding

• instead of electron sharing between 2 atoms, electrons in the outer shells are shared among all the atoms in a lattice, with all the same positively charged

secondary bonds

• “physical bonds”

• much weaker than primary bonds

• ex. hydrogen bond

3 states of matter: three basic forms

• solid

• liquid

• gas

3 states of matter

• most materials are mixtures of more than one state of matter

  • plaster- both solid and a liquid

  • fluoride forms- both liquid and gas (air)

solids have:

• both shape and volume

solids: are described by

• density

• hardness

• elasticity

• stiffness

• ductility

• malleability

• brittleness

solids

• amorphous:

  • if molecules are arranged in a random form with no regular pattern; the solid is less stable

density:

• measure of the weight a material has compared with its volume

• measure of the compactness of matter, or how much mass is squeezed into a given space

• enamel- densest of the tooth structures

  • gold is a dense restorative material

hardness:

• resistance of a solid to penetration

• used to define a materials resistance to wear and abrasion

• hardness of dental structure/porcelain determines the extent to which it is scratched by an abrasive material

• enamel & porcelain are more resistant to being scratched than are cementum/dentin, composite, or gold crowns

  • important the restorative material or tooth surface be determined prior to procedure

ultimate strength:

• maximal amount of stress a material can withstand without breaking

• ability of material to recover its shape completely after deformation from an applied force is elastically

• ex. stiffness of a material, lack of elasticity, means that it resists being deformed and is measured by young’s modules

  • restorative materials should have modules that is compatible w tooth structure

proportional limit:

• greatest stress a structure can withstand without permanent deformation

• when enough force is applied to a structure, it may not be able to recover, and the structure may become permanently deformed

• resilience is the amount of energy a material can absorb without permanent deformation

• impression materials and ortho wire must be resilient to be successful

  • “an appliance is only as good as the impression”

toughness:

• ability of a material to absorb energy without failure

• restorative materials (porcelain vs. gold)

  • pulling or stretching of ortho wire under tensile stress is a measure of its ductility; amount of dimensional change it can withstand without breaking

• materials w poor ductility=brittle=weaker

• much weaker w tensile forces than compressive forces

durability:

• ability of a material to withstand damage due to pressure or wear

  • porcelain/metal- very durable, resilient, tough, & can absorb stress w/o breaking

  • porcelain- brittle & cannot withstand shearing stresses as well as metal

  • all ceramic crowns- r replaced w porcelain; excellent mechanical properties & esthetic

  • amalgam- durable, longevity, cost effective, but lacks esthetics and has mercury

  • composites- durable where esthetics are important, but can stain & don’t resist abrasion when compared to others

liquids have:

• has volume but no definite shape

liquids: viscosity

• blank of a liquid is its resistance to flow

  • thin fluids- low viscosity

  • thicker fluids- high viscosity

  • viscosity of liquids- usually decreases as the temp increases

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thixotropic fluids

• liquids that flow more easily under mechanical force

• ex. fluoride gel

application: materials are classified by

• application

• how used or fabricated

• expected longevity

application: may be

• preventative

• therapeutic

• restorative

materials can be further classified as:

• direct restorative materials

• indirect restorative materials

preventative materials:

• directed toward preventing the occurrence of oral disease and promoting oral health

therapeutic materials:

• used in treatments of disease and include materials such as medicated bases or topical treatments for perio disease

restorative materials:

• largest classification

• short/long term use

direct restorative materials:

• fabricated directly in the mouth

indirect restorative:

• materials are fabricated outside the mouth

longevity

• how long they are expected to hold up in the oral cavity

• all materials will degrade, wear, or fracture over time

permanent restorations:

• expected to be long lasting replacement for missing, damaged, or discolored teeth

temporary restorations:

• “provisional”

• used for short periods of time (several days to weeks)

  • function in the place of the permanent restoration to protect teeth, prevent sensitivity and unwanted tooth movements, maintain the health and contours of the periodontal tissues, enable the patient to function normally, and provide temporary esthetics

intermediate restorations:

• like provisional, are placed for a limited time

• several weeks to months

• used when there is other ongoing treatment such as ortho or implant therapy that is needed before a permanent restoration is required

many materials require the combination of 2 components to form resulting final material

• water and powder

• liquid and powder

• paste and liquid

• paste and paste

• paste and indicator (blue light)

components: are classified as catalyst and base

• catalyst is responsible for the speed at which the reaction occurs and is often the liquid components

reaction: occurs when

• when components are mixed together

reactions can be:

• physical

• chemical

manipulation and reaction stage:

• both are defined in units of time

manipulation stage:

• includes mixing time and working time

reaction stage:

• includes the initial set and final set times

mixing time:

• length of time the dental auxiliary has to bring the components together into a homogeneous mix

working time:

• time permitted to manipulate the materials in the mouth

initial set time:

• begins when the material no longer can be manipulated in the mouth

final set time:

• time occurs when the material has reached its ultimate state

reaction*

• mixing slowly

• cool water

• pedo patients and unlimited opening

chemical set materials:

• they set through the timed chemical reaction of the catalyst and base

• once 2 components contact w each other, the chemical reaction begins and continues through the reaction stage

• the clinician has little or no control over the time

light activated:

• use a light source in the blue light range to initiate the reaction stage

• both components are present in the material but do not react until the material comes in contact with the blue light source, thus

• giving the clinician unlimited working time

dual set materials:

• have a slow chemical set that is activated when components are mixed but the set can be accelerated by light curing

• more control over the working time

• assurance of complete setting in deeper or more difficult to access areas of the mouth or prep

setting times, initial, final are important:

• material must not be disturbed through the end of the initial set

• moisture and pressure controls are frequently important during- initial set

• continued firm pressure essential for materials needing intimate contact with the tooth

• final set- may occur while the patient is in the office or several hours later

• appropriate post op instructions are needed to avoid fracture

manipulation

• final characteristic of the material are achieved

• some materials are:

  • offer some variation in the manipulation

  • others are very technique sensitive and even the slightest variation will have a detrimental effect on the final product

manipulation: variables begin with the ratio of components

• measured & dispensed according to manufacturer’s recommendations

• predosed units- standardizing the ratios

manipulation: variables

• ratios of components

• external variables

• shelf life

manipulation: external variables

• temp of the material/room temp and humidity can effect the manipulation

  • high temps/humidity- will accelerate the reaction

  • low temps/humidity- will retard the reaction

• how components are mixed

  • quick or slow

  • paper pad or glass slab

  • hand mixing or using auto mix dispensers

  • will affect consistency

shelf life

• refers to the deterioration and change in quality of a material over time

• date or expiration is important for consistency of the characteristic of a product

conditions of storage:

• temp, humidity, storage container, require fridge, and protected from direct light

  • refer to manufacturer’s directions to determine conditions of storage and expiration