Dental Materials Viva Voice Questions for 1st year BDS
Physical properties of Dental materials
- What is the goal of the dentistry?
The goal of the dentistry is to maintain or improve the quality of life of the dental patients. This goal can be accomplished by preventing disease, relieving pain, improving mastication efficiency, enhancing speech and improving appearance.
- What are the dental materials used in dentistry?
The four groups of materials used in dentistry today are metals, ceramics, polymers and composites.
- What are the qualities of ideal restorative material?
An ideal restorative material would be
- Be biocompatible
- Bond permanently to tooth structure or bone
- Match the natural appearance of tooth structure and other visible tissues
- Exhibit properties similar to those of tooth enamel, dentin and other tissues
- Be capable of initiating tissue repair or regeneration of missing or damaged tissues
- What is Acid-etching technique?
It is a process of roughening a solid surface by exposing it to an acid and thoroughly rinsing the residue to promote micromechanical bonding of an adhesive to the surface
- What is Adhesion?
When two substances are brought i9nto intimate contact each other, the molecules of one substance adhere or attracted to, molecules of the other substance. This force is called as adhesion. Adhesion may occur as a chemical or physical or a combination of both types
- What is Cohesion?
Force of molecular attraction between molecules or atoms of the same species.
- Define Coefficient of thermal expansion?
It is defined as the change in length per unit of the original length of a material when its temperature is raised 1 degree kelvin
- Define stress and what are the types of stresses?
Stress is defined as an internal force opposing an applied load.
Compressive stress:- internal resistance to a load that tends to compress or shorten a body
Tensile stress:– internal resistance to a load that tends to stretch or elongate a body
Shear stress:- a stress that tends to resist a twisting motion, or a sliding of one portion of a body over another is a shear or shearing stress
- What is strain?
Strain is defined as a deformation resulting from an applied load. Strain has no units to measure
- Define proportional limit?
It is defined as the maximum stress that can be induced without permanent deformation
- What is young’s modulus or modulus of elasticity?
Stress/strain ratio within the proportional limit is called elastic modulus or young’s modulus. It measures the relative rigidity or stiffness of material
- What are the different hardness tests?
Macro hardness tests:- Brinnel and Rockwell tests are classified as macro hardness tests and they are not suitable for brittle materials
Micro hardness tests:– the Knoop and Vickers tests are classified as micro hardness tests. Both of these tests employ loads less than 9.8 N
The SHORE and the BARCOL tests are used for measuring the hardness of rubbers and plastics
- What is Smear layer?
After the dentist has completed a tooth preparation for a filling, tenacious microscopic debris covers the enamel and dentin surfaces. This surface contamination, called the smear layer.
- What is Creep?
Time-dependent plastic strain of a material under a static load or constant stress
- Define Flow?
Flow is the deformation under a small static load even that associated with its own mass. Flow describes the behavior of amorphous material such as waxes.
- What is Hue?
Dominant color of an object
- What is Value?
Relative lightness of darkness of a color
- What is Chroma?
Degree of saturation of a particular hue
- Define Hardness?
The ability of a material to resist abrasion or wear
- What is Ductility?
Relative ability of a material to deform plastically under a tensile stress before it fractures
- What is Elastic modulus or Young’s modulus?
It is the ratio of elastic stress to elastic strain
- Define Plastic strain?
Deformation that is not recoverable when the externally applied force is removed
- Define Corrosion?
Chemical or electrochemical process in which a solid; usually a metal, is attacked by an environmental agent, resulting in partial or complete dissolution.
- What is Tarnish?
Surface discoloration on a metal, or as a slight loss or alteration of the surface finish or luster
- What is viscosity?
Resistance of a fluid to flow