Monthly Archive April 2016

Dental Materials Viva Voice Questions for 1st year BDS

Physical properties of Dental materials

dental viva

  1. 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.

  1. What are the dental materials used in dentistry?

The four groups of materials used in dentistry today are metals, ceramics, polymers and composites.

  1. 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

 

  1. 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

  1. 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

  1. What is Cohesion?

Force of molecular attraction between molecules or atoms of the same species.

  1. 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

  1. 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

  1. What is strain?

Strain is defined as a deformation resulting from an applied load. Strain has no units to measure

  1. Define proportional limit?

It is defined as the maximum stress that can be induced without permanent deformation

  1. 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

  1. 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

  1. 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.

  1. What is Creep?

Time-dependent plastic strain of a material under a static load or constant stress

  1. 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.

  1. What is Hue?

Dominant color of an object

  1. What is Value?

Relative lightness of darkness of a color

  1. What is Chroma?

Degree of saturation of a particular hue

  1. Define Hardness?

The ability of a material to resist abrasion or wear

  1. What is Ductility?

Relative ability of a material to deform plastically under a tensile stress before it fractures

  1. What is Elastic modulus or Young’s modulus?

It is the ratio of elastic stress to elastic strain

  1. Define Plastic strain?

Deformation that is not recoverable when the externally applied force is removed

  1. 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.

  1. What is Tarnish?

Surface discoloration on a metal, or as a slight loss or alteration of the surface finish or luster

  1. What is viscosity?

Resistance of a fluid to flow

 

 

 

 

 

Lasers in Conservative Dentistry and Endodontic

Laser technology has been developed rapidly in the last decade. New lasers with a wide range of characteristics are available now which are being used in various branches of dentistry. The application of these new technologies in endodontics has always been challenging. Today more experience and knowledge in applying lasers in operative dentistry and endodontics is available.

The interest in endodontic use of dental laser systems is increasing. There are several studies performed which prove the benefits of using a dental laser for cavity preparation over conventional rotary abrasives. Dental lasers are now set to perform almost every dental procedure which is to be carried out in the field of conservative dentistry and endodontics.

Conservative Dentistry:-

lasers in conservative dentistry

Cavity preparation:-

The science of conservative dentistry aims at saving natural teeth that have defects due to dental caries, trauma, abrasion or attrition and esthetic disharmony including developmental anomalies or tooth discoloration, as well as pulpal and or periapical diseases to maintain their inherent masticatory, phonetic and esthetic function and the physiologic integrity in harmonious relationship with the adjacent hard and soft tissues through diagnosis, treatment, post op evaluation and prevention.

One of the most commonly performed procedures in conservative dentistry is cavity preparation which done so that the diseased tooth is rid of all its infection and can receive a suitable restorative material. Cavity preparation is done conventionally by using a rotary abrasive. This results in a cavity form, which is irregular, and it damages the natural morphology of the dental hard tissues. The enamel prisms are destroyed and the dentinal tubules are packed with debris and dentinal muds.

Using a dental laser for this procedure has obvious advantages. The hard tissue dental laser such as the Er:YAG would retain the natural morphology of the dental hard tissues during cavity preparation. The Er:YAG laser radiation appears to be a promising alternative in treating dental hard tissues due to its thermo mechanical ablation properties and the lack o thermal side effects.. The laser cavity preparation results in clean, open and patent dentinal tubules and hence the step of acid-etch which is used in the conventional procedures can be skipped while using a dental laser. As there is absence of smear layer and debris in a laser cavity preparation, it can also be called a sterile cavity preparation as there is almost a 0% possibility of infections.

Tooth etching:-

Acid etching is widely used in clinical dentistry to facilitate the mechanical retention of resin based materials to teeth, in particular enamel surfaces. Several laser systems have been developed with the aim of modifying dental hard tissues and the Er:YAG laser may offer possible alternative to the acid etching technique. Even cementation of resin bonded partial dentures can be facilitated by the use of laser for etching the tooth surface.

Endodontic therapy:-

The endodontic therapy lasers have been used as treatment coadjuvant with refrence to0 both, low intensity laser therapy and high intensity laser treatment to increase the success rate of the clinical procedure. Low intensity laser therapy has the ability to produce analgesic, anti-inflammatory and biomodulation effects on the irradiated soft tissue thereby improving the wound healing process and giving the patient a better condition of the postoperative experience. High intensity laser irradiation on a soft tissue in a defocused mode could have similar effects to low intensity laser therapy. Depending on the wavelength, high intensity laser irradiation may be used on hard dental tissues such as on the root canal dentin cut surface after apicoectomy to produce structrural morphological changes, to remove the smear layer, to melt and recrystallize dentine or to expose dentinal tubules.

Disinfection of the root canal system:-

While the mechanical and manual challenges of root canal debridement and obturation remain, it has become increasingly clear that the largest proportion of endodontic disease, both pulpal and periradicular, is due to the presence of microorganisms. Therefore, treatment success is related very closely to the ability to remove these irritants and to prevent reinfection.

Application of Er:YAG laser radiation through a flexible waveguide helps to attain antibacterial effect, not only in the root canal walls, but also in the surrounding tissues. Therapeutic doses of laser radiation guarantee one-step disinfection, including of anaerobic microorganisms.