Biological Properties Of Dental Materials Question And Answers

Biological Properties Of Dental Materials

Question 1. Describe the biological consideration that is associated with the selection and uses of dental material designed for the oral cavity.
Answer:

The science of dental materials must include a knowledge and appreciation of certain biological considerations that are associated with the selection and use of materials designed for the oral cavity.

Biological Requirement of Dental Materials:

• They should be non-toxic to the body.
• They should be non-irritating to the oral and other tissues.
• They should be non-mutagenic or carcinogenic.
• They should not produce allergic reactions.
• They should be biologically inactive

Read And Learn More: Dental Materials Question And Answers

Classification of Dental Material from a Biological Perspective:

• Those that contact the soft tissues within the mouth.
• Those which could affect the health of the dental pulp.
• Those that are used as root canal filling materials.
• Those that affect the hard tissues of the teeth.
• Those used in the dental laboratory though not used in the mouth are handled and may be accidentally ingested or inhaled.

Hazards of Dental Materials: There are two types:

1. Chemical hazard.
2. Physical hazard.

Chemical Hazards of Dental Materials :

• Dental cement which is acidic in nature can cause pulp irritation.
• An unreacted monomer can irritate the pulp.
• Phosphoric acid which is used as an etchant can harm the surrounding tissue of the tooth.
• Eugenol can cause irritation and a burning sensation.
• Beryllium use in casting alloys can cause “Berylliosis”.
• Some dental products contain nickel and some patients are allergic to nickel.
• Lead used in elastomeric material causes a hazard.
• Alginate dust while mixing precipitates asthma.
• Mercury is used in dental amalgam, mercury vapor is toxic.

Physical Hazards of Dental Materials: Physical hazards are classified as:

1. Dimensional hazard
2. Thermal hazard
3. Electrical hazard.

1. Dimensional hazard:

• Microleakage: A microscopic space between the restoration and the prepared cavity is called microleakage.
• Microleakage can result in:
  • Secondary caries: The seepage of acids and microorganisms could initiate caries around the margins of the restorations.
  • Stains or discoloration can also develop.
  • Sensitivity: Sometimes, because of microleakage the tooth remains sensitive even after placement of the filling, bacterial growth occurs in between restoration and cavity. Toxic products liberated by microorganisms produce irritation to the pulp.

2. Thermal change: Tooth structure and dental restorations are continually exposed to hot and cold beverages and foods. Instantaneous temperature fluctuation during the course of an average meal may be as great as 85 °C.

• The temperature fluctuation can crack the restorative materials or produce undesirable dimensional changes in them because of thermal expansion and contraction.
• Many restorative materials are composed of metals. Metals conduct heat and cold, patient complaint of sensitivity in the tooth.

3. Electric hazards: Galvanism Another cause for sensitivity is the small currents created whenever two different metals are present in the oral cavity.

• The presence of metallic restoration in the mouth can cause a phenomenon called galvanic action, or galvanism.
• This results from a difference in potential between dissimilar filings in opposing or adjacent teeth.
• These filings in conjunction with saliva as an electrolyte, make up an electric cell.
• When two opposing filings contact each other the cell is short-circuited and the patient experiences pain.

Question 2. Write a short note on the biocompatibility test.
Or
Write in brief on biocompatibility tests for dental materials.
Answer:

Evaluation of biocompatibility of dental materials is a complex and comprehensive area due to unwanted tissue reactions that occur in many types.

• Individual test methods are usually adequate only to describe a single aspect of certain types of unwanted reactions.
• Following are the biocompatibility tests: These tests are carried out at three levels one after another. If the material is successful in the first test then only the second test is carried out and likewise. If successful in the second test then the subsequent tests are carried out.

Group I: Initial or Primary Tests:

• Genotoxicity test: In this test, the effect of the material on the genes is carried out.
• Cytotoxic assays: By these tests, the effect of the material or its leachable products is studied on the metabolic functions of the test cell system.
• Cell plating and growth tests: These tests are done to determine if the material interferes with cell functions by releasing some component of the material into the medium. In this a small piece of sterile material is placed in the cells of tissue culture dishes then the cells are plated at a particular density within the cells in tissue culture medium for l to 3 days. Biologically inert materials like siloxane polymer or Teflon are used as negative controls.
• Mutagenesis assays: These assays are done in vitro to identify materials and chemicals that are capable of producing cancer.

Group II: Intermediate or Secondary Tests: After screening by initial tests of the materials developed for a specific use, the successful materials are tested generally on experimental animals, i.e. guinea pigs, rodents, and hamsters.

• Systemic toxicity test: In this, the product is evaluated for its potency to create systemic toxicity.  For this oral median lethal dose (LD50) test is done in which a test sample is daily administered to rats for l4 days. If half or more than half of the animals survive it is considered that the product has passed the test.
• Inhalation toxicity test: This test is done on guinea pigs, rats, rabbits, or hamsters in exposure to aerosol preparations and the material is sprayed for l0 times around the head and chest of the animals for 30 seconds at half an hour intervals.
• If any animal dies within 3 minutes the product is considered very toxic. If none of the animals dies in four days the product is considered safe.
• Mucous membrane irritation test: In this, the product is applied directly to the oral mucous membrane or abraded skin continuously for several weeks in 10 animals. The histological examinations are done along with controls, if there is no irritation or histological changes the product is considered safe.
• Skin irritation toxicity and sensitization tests (maximization test).
• Implantation tests: Done for the materials that will contact subcutaneous tissues and bone.

Group III: Human Trials: If the material has passed primary and secondary tests, it is ready for trial in humans where: Reactions and performance under clinical conditions are studied.

Question 3. Write a short note on cytotoxicity.
Answer:

Cytotoxicity is defined as the cascade of molecular events that interfere with macromolecular synthesis, causing unequivocal cellular, functional, and structural damage. Cytotoxic screening can be done in vivo or in vitro.

In vitro, tests are conducted on cultured cells like mouse L–929 fibroblasts and human Hela cells. There are many in vitro tests. For example, Agar overlay technique; Agar is spread over a layer of culture cells in a culture plate. The test material is then placed on it and incubated. A toxic material will show a clear zone of dead cells.

Advantages of Cytotoxicity:

• Screening a large number of samples quickly and inexpensively
• Quantifying results
• Greater sensitivity to toxic material than usage tests
• Testing for specific functions of cell metabolism.

Disadvantages of Cytotoxicity:

• Limitation of testing to only one cell type at a time
• Dissimilarity of test cells and host cells
• Lack of inflammatory and other tissue protective mechanisms in tissue culture.