Science of Dental Materials Flow chart indicating a

Science of Dental Materials

Flow chart indicating a logical method of material selection

Analysis: The analysis of the situation requiring selection of a material may seem obvious but it is of paramount importance in some circumstances. An incorrect decision may cause failure of the restoration or appliance. For example, when considering the selection of a filling material it is important to decide whether the restoration is to be placed in an area of high stress. Will it be visible when the patient smiles? Is the cavity deep or shallow? These factors and many more must be evaluated before attempting materials’ selection.

Requirements: Having completed a thorough analysis of the situation it is possible to develop a list of requirements for a material to meet the needs of that situation. For the example mentioned in the previous section, it may be decided that a filling material which matches tooth color and is able to withstand moderately high stresses without fracture is required. Some tooth cavities are caused by toothbrush/toothpaste abrasion. In this special case the restorative material used should naturally possess adequate resistance to dentifrice abrasion. Hence, it is possible to build a profile of the ideal properties required for the application being considered

Available materials: The consideration of available materials, their properties and how these compare with the requirements is carried out at two levels. The dentist, faced with the immediate problem of restoring the tooth of a patient in his surgery, must choose from those materials on hand at the time. Previous experience with materials in similar circumstances will be a major factor which influences selection. On a wider scale, the practitioner is able to consider the use of alternative materials or newly developed products where these appear to offer a solution to cases which have proved difficult with his existing armoury of products. It is of paramount importance that the practitioner keeps up to date with developments in materials whilst taking a conservative approach towards adopting new products for regular use in his surgery until they are properly tested.

Choice of material Having compared the properties of the available materials with the requirement, it is possible to narrow the choice to a given generic group of products. The final choice of material brand is often a matter of personal preference on the part of the dentist. Factors such as ease of handling, availability and cost may play a part at this stage of the selection process.

Evaluation of materials As the number of available materials increases, it becomes more and more important for the dentist to be protected from unsuitable products or materials which have not been thoroughly evaluated. It should be emphasized, however, that most manufacturers of dental materials operate an extensive quality assurance programme and materials are thoroughly tested before being released to the general practitioner.

Standard specifications ﺍﻟﻤﻮﺍﺻﻔﺎﺕ ﺍﻟﻘﻴﺎﺳﻴﺔ Many standard specification tests, of both national and international standards organizations, are now available which effectively maintain quality levels for some dental materials. Such specifications normally give details for the testing of certain products, the method of calculating the results of the minimum permissible result which is acceptable. Although such specifications play a useful part they should not be seen as indicating total suitability since the tests carried out often do not cover critical aspects of the use of a material. For example, many materials fail by a fatigue mechanism in practice, but few specifications involve fatigue testing.

ﻣﺆﺴﺴﺎﺕ ﺗﺤﺪﻳﺪ ﺍﻟﻤﻮﺍﺻﻔﺎﺕ ﺍﻟﻘﻴﺎﺳﻴﺔ ﻭ ﻣﺮﺍﻗﺒﺔ ﺍﻟﺠﻮﺩﺓ q. American Dental Association (ADA) q. Food and Drug Administration (FDA) q. International Standard Organization (ISO) q. Association for the Advancement of Medical Instrumentation (AAMI)

Laboratory evaluations ﺍﻟﺘﻘﻴﻴﻢ ﺍﻟﻤﺨﺒﺮﻱ Laboratory tests, some of which are used in standard specifications, can be used to indicate the suitability of certain materials. For example, a simple solubility test can indicate the stability of a material in aqueous media – a very important property for filling materials. It is important that methods used to evaluate materials in the laboratory give results which can be correlated with clinical experience. For example, when upper dentures fracture along the midline they do so through bending. Hence a bending or transverse strength test is far more meaningful for denture base materials than a compression test.

Clinical trials ﺍﻻﺳﺘﻌﻤﺎﻝ ﺍﻟﺴﺮﻳﺮﻱ ﺗﺠﺎﺭﺏ Although laboratory tests can provide important and useful data on materials the ultimate test is the randomized controlled clinical trial and the verdict of practitioners after a period of use in general practice. Many materials produce good results in the laboratory, only to be found lacking when subjected to clinical use. The majority of manufacturers carry out extensive clinical trials of new materials, normally in co-operation with a university or hospital department prior to releasing a product for use by general practitioners.

Rheological properties ﺍﻻﻧﺴﻴﺎﺑﻴﺔ ﺧﺼﺎﺋﺺ

Models involving the use of springs and dashpots can be used to explain the elastic and viscoelastic behavior of materials When a spring, which represents an elastic material, is fixed at one end a load applied at the other it becomes instantaneously extended. When the load is removed it immediately recovers its original length.

This behavior is analogous to that of a perfectly elastic material. The two things that characterize the material are firstly the perfect recovery after removal of the force and secondly the lack of any time dependency of either the deformation under load or the recovery after removal of the applied force.

When a load is applied to a dashpot, which represents a viscous material, it opens slowly, strain being a function of the time for which the load is applied

When the load is removed the dashpot remains open and no recovery occurs. This is in distinct contrast to the behavior of an elastic material. The time-dependent opening of the dashpot is akin to the way in which the flow of a viscous or plastic material is controlled by its viscosity.