1. Dental materials: biological, chemical and physhical properties.

2. PROPERTIES OF THE MATERIALS
Biological
Physical
–mechanical
–thermal
–electrical
–volumetric

3. 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

4. Release of Components and Degradation Products
Figure 1: Sequence of events that may lead to biological side effects to dental materials
Dental Materials |
Release of Components and Degradation Products
Biological Effects?
Disease?

5. 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

6. 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

7. Adverse effects of tissues on materials
Material type
Polymer
Effect
Depolymerization,Crosslinking, Oxidation, Hydrolysis, Leaching of additives

8. Adverse effects of tissues on materials
Material type
Metals
Effect
Corrosion
Ion-release

9. Adverse effects of tissues on materials
Material type
Ceramics
Effect
Ageing,Dissolution

10. Adverse effects of materials on tissues
Hypersensitivity
•Toxicity
•Carcinogenicity
1, 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

11. Agents causing hypersensitivity
Metals
–Ni, Co, Cr
•Latex gloves
–thiocarbamate curing agents
•Resin monomers
- HEMA, TEGDMA

12. 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

13. 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

14. CARCINOGENICITY •Cancer:
Malignant tumors that invade neighboring tissues and which can spread to remote sites of the body.
•Rare to find biomaterials implicated.

15. Biological interaction of restorative materials
None for amalgam or composite resin fillings;|
•Glass-ionomer cements may promote remineralization.

16. MECHANICAL PROPERTIES
Restorative materials should
–be strong to be able to withstand biting forces without fracture
–be rigid to maintain their shape under load

17. 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 )

18. In materials containing
–cracks
–cuts
–fissures
–scratches
–inclusion bodies
–or having irregular dimensions
•the concentration of stress and strain can occur leading to failure

19. Maximum compressive strength
MATERIAL MPa
•zinc –polycarboxylate cements
•resins (unfilled)
•porcelane
•glass-ionomer cements –220
•DENTIN
•composites –345
•ENAMEL
amalgam

21. HARDNESS Resistance to penetration
•It allows to predict the resistans to scratching and wear

23. 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

24. 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

25. DIMENSIONAL CHANGES Can be a result of:
–chemical reaction -during setting
•eg. polymerisation shrinkage
–temperature changes in oral enviroment
•set material and tooth structures

26. 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

27. 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.

28. 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

29. ELECTRICAL PROPERTIES
Galvanic currents
Corrosion

30. 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)

31. 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

32. 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

33. SOLUBILITY AND ABSORPTION
–% 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%

34. 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