Dental materials: biological, chemical and physhical properties

Dental materials: biological, Dental materials: biological, chemical and physhical chemical and physhical

properties. properties.

PROPERTIES OF THE MATERIALS

Biological Physical –mechanical –thermal –electrical –volumetric

BIOLOGICAL PROPERTIES

Dental materials should be biocompatibile, that means

–non toxic for patient, dentist and staff

–non irritating to oral cavity and tooth tissues

–non allergenic

–non mutagenic or cancerogenic

Figure 1: Sequence of events that may lead to biological side Figure 1: Sequence of events that may lead to biological side effects to dental materials effects to dental materials

Dental Materials Dental Materials

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Release of Components and Release of Components and Degradation Products Degradation Products

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Biological Effects? Biological Effects?

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Disease?Disease?

BIOCOMPATIBILITY

The ability to perform with an appropriate host response in a specific application

Features of biocompatibility •Not only a property of a material, but

also of the location used •Not a single property, but a collection of

attributes •Acknowledges that no material is truly

inert •States that functionis critical

BIOMATERIAL A substance which –is not a drug –can be used for some period of time as

a part of a system used for •treatment •enlargement •replacement of tissue, organ or body

function

Adverse effects of tissues on materials

Material type

Polymer Effect

Depolymerization,Crosslinking, Oxidation, Hydrolysis, Leaching of additives

Adverse effects of tissues on materials

Material type

Metals Effect

Corrosion

Ion-release

Adverse effects of tissues on materials

Material type

Ceramics Effect

Ageing,Dissolution

Adverse effects of materials on tissues

Hypersensitivity •Toxicity •Carcinogenicity1, HYPERSENSITIVITY Adverse reactions caused by exposure to a particular

substance. •May present as: –local effects •egeczema •itchiness and/or •redness of skin –or systemic effects •egasthma •Can be immediate or delayed

Agents causing hypersensitivity

Metals

–Ni, Co, Cr •Latex gloves

–thiocarbamate curing agents •Resin monomers

- HEMA, TEGDMA

TOXICITY May cause death or injury to the cells •Depends on a dose •May be acute or chronic Types of toxicity Acute •Arises soon after administration •Results either in death or in complete recovery

•Chronic •Takes time to develop •Needs prolonged exposure or repeated doses •Results in prolonged ill-health •Most likely type for biomaterials

Target organs

Usually a toxic agent affects a particular organ of the body

•For dental materials it is

–dental pulp

–gingiva

–periodontium and periaplcal bone

CARCINOGENICITY

•Cancer:

Malignant tumors that invade neighboring tissues and which can spread to remote sites of the body.

•Rare to find biomaterials implicated.

Biological interaction of restorative materials

None for amalgam or composite resin fillings;|

•Glass-ionomer cements may promote remineralization.

MECHANICAL PROPERTIES

Restorative materials should

–be strong to be able to withstand biting forces without fracture

–be rigid to maintain their shape under load

STRESS

When an external force is applied on a test specimen an internal force, equal in magnitude but opposite in direction is set up in the body

•STRESS= FORCE/AREA,UNITS= Pascal (Pa)

–Tensile(a)

–Compressive(b)

–Shear(c )

In materials containing –cracks –cuts –fissures –scratches –inclusion bodies –or having irregular dimensions •the concentration of stress and strain

can occur leading to failure

Maximum compressive strength

MATERIAL MPa •zinc –polycarboxylate cements 90 •resins (unfilled) 97 •porcelane 150 •glass-ionomer cements 180 –220 •DENTIN 297 •composites 200–345 •ENAMEL 400 amalgam 310-483

HARDNESS

Resistance to penetration

•It allows to predict the resistans to scratching and wear

Abrasion resistance Wear can occur by one or more

mechanism

-due to abrasive forces

-intermittent stresses

-chemical degradation •The rate of wear of dental materials are

difficult to measure since they are complex and laboratory assessments often give misleading results

FATIGUE Materials when subjected to cyclical or

intermittent loading over a period of time can lead to failure

•Small microcracks may occur caused by stress concentration and the crack is likely to propagate leading to fracture

DIMENSIONAL CHANGES

Can be a result of:

–chemical reaction -during setting

•eg. polymerisation shrinkage

–temperature changes in oral enviroment

•set material and tooth structures

Thermal expansion Is most often different for a material and

for tooth structures

•that leads to formation of microfissure between filling and tooth

•that leads to microleakage

When the coefficient of thermal expansion of a restorative material does not match that of the tooth structure, uneven expansion and contraction occur. In turn, gaps and leakage occur at the interface of the restoration and the tooth.

Thermal conductivity

Describes an amount of conducted thermal energy

•Is different for various materials and tooth structures

–dentine, enamel, cements, composites and ceramics are good thermal insulators

–gold, casts, amalgam and other metals are good thermal conductors

ELECTRICAL PROPERTIES

Galvanic currents Corrosion

GALVANISM IN DENTISTRY

Phenomenon of electric cell and flow of electrons in oral cavity which is perceived by patient as pain or discomfort and metalic taste

•Requires presence of two metals of different electric potential and an electrolyte (saliva)

Example Electric potential of aluminium +1.33V •Electric potential of gold -1.36V •in case of contact of these two metals in

oral cavity the potential difference will be 2.69V and a mild current will be conducted

•patient will complain of discomfort and metalic taste

CORROSION Metals and amalgams in oral cavity can

undergo corrosion - roughening of the surface due to ion exchange

•Corrosion is a result of

–galvanic currents

–chemical interaction with oral fluids and food

SOLUBILITY AND ABSORPTION

Solubility –% of mass of dissolved material –bigest for cements •Absorption –describes absorption of a liquid by a

solid –bigest for resins –for unfilled resins absorption of water is

2%

PROCESS OF MATERIAL SELECTION

Analysis of the problem -Direct filling material: Is the restoration in a high stress bearing

area? Is it visible when smiling? Is it a deep or a shallow cavity? •Based on the analysis identify a set of

requirements and make an informed choice from the available materials