Dental Materials

Strain Hardening (Work hardening)

Increase in strength and hardness and corresponding decrease in ductility of a metal that is caused by plastic deformation.

Plastic Strain

Irreversible deformation that remains when the externally applied force is removed.

Proportional Limit

Magnitude of elastic stress above which plastic deformation occurs.

Percent Elongation

Maximum amount of plastic strain, expressed as a percent of original length, which tensile test specimen can sustain at it fractures .

Shear Strength

Maximum shear stress at the point of fracture of a test specimen.

Strength

Maximum stress that a structure can withstand without sustaining a specific amount of plastic strain (yield strength) or stress at the point of fracture (Ultimate strength).

Biointegration

Process in which bone or other living tissue becomes integrated with an implanted material with no intervening space.

Osseointegration

Process of forming a direct structural and functional interface between live bone and an artificial implant surface without any intervening fibrous connective tissue.

Sensitization

Process that produces an allergy antibody is produced, which reacts specifically to the causative foreign substance.

True Stress

Ratio of applied force to the actual cross-sectional area; however for convenience stress is often calculated as the ratio of applied force to the initial cross-sectional area.

Shear stress

Ratio of force to the original cross-sectional area parallel to the direction of the force applied to a test specimen.

Tensile Stress

Ratio of tensile force to the original cross-sectional area perpendicular to direction of applied force.

Ductility

Relative ability of a material to deform plastically under a tensile stress before it fractures. This property is reported quantitatively as percent elongation.

Brittleness

Relative inability of a material to deform plastically before it fractures.

Stress Intensity (Stress Intensity factor)

Relative increase in stress at the tip of a crack of given shape and size when the crack surfaces are displaced in the opening mode.

Tensile Strength (Ultimate Tensile Strength)

Tensile stress (in a tensile test specimen) at the point of fracture.

Safety

The absence (freedom) from unacceptable risks.

Resilience

The amount of elastic energy per unit volume that is sustained on loading and released on unloading of a test specimen.

Lethal dose 50 (LD 50)

The calculated dose of a substance that is expected to cause the death of 50% of the entire population of specific experimental animals.

Risk

The combined probability of a harmful effect and the severity of the effect.

Chronic Exposure

The contact with a substance that occurs over a long time (more than 1 year)

Fracture toughness

The critical stress intensity factor at the beginning of rapid crack propagation in a solid containing a crack of known shape and size.

No-observed-adverse-effect Level (NOAEL)

The highest tested dose of a substance that has been reported to have no harmful (adverse) effects on people or animals.

Toxic dose low (TD Lo)

The lowest does of a substance introduced by any route except inhalation over any given period that has been reported to produce any toxic effect in humans or carcinogenic, neoplastigenic, or teratogenic effects in humans or animals.

Lowest-observed-adverse-effect level (LOAEL)

The lowest level tested dose of a substance that has been reported to cause harmful health effects in people or animals.

Toxicity

The relative ability (Dose-related potential)of a material to cause injury to biological tissues, ranging from improper biochemical function, organ damage, and cell destruction, or death.

Yield Strength

The stress at which a test specimen exhibits a specific amount of plastic strain.

Adverse Reaction

any unintended, unepxected,a dn harmful response of an individual to a dental treatment or biomaterial.

Immediate duration exposure

the contact with a substance that occurs for more than 14 days and less than 1 year

Hardness

Resistance of a material to plastic deformation typically measured under an indentation load.

Elastic modulus (Modulus of elasticity or Young's Modulus)

Stiffness of a material; ratio of elastic stress to elastic strain.

Hyper sensitvity

(1) The objectively reproducible symptoms or signs initiated by an exposure to a defined stimulus at a dose tolerated by normal persons; (2) abnormal clinical reaction or exaggerated immune response to a foreign substance that is manifested by one or more signs or symptoms, such as breathing difficulty, erythema, itching, sneezing, swelling and vesicles.

All of the following would be expected to significantly increase the mechanical properties of a polymer EXCEPT (This question was thrown out) A. Increasing the amount of branching B. increasing the material's average molecular weight C. Increasing the number of multi-functional monomers D. increasing the amount of cross-linking.

A

Characteristics of light-activated polymerization include all of the following EXCEPT: A: light-activated dental resin-composites must be supplied in 2 pastes that are mixed together. B. light-activated dental resin-composite are activated using light in the 400-500nm wavelength range. C. light-activated dental resin-composite require a minimum threshold of proper activation.

A

Composite materials are often engineered to obtain new properties, better property combinations, or higher levels of properties. The principle of "judiciously combining two or more distinct materials' to guide the development of these composite systems is called: A. principle of combined action B. principle of deceptive interaction C. Principle of summative properties D. Principle of additive indices

A

If a resin composite has a linear coefficient of thermal expansion that is 4.0 times that of enamel, what is its expected volumetric coefficient of thermal expansion relative to enamel? A. 12 times B. 20 times C. 16 times D. 8 times

A

Resin-modified glass ionomer cement utilizes all of the following activation mechanisms EXCEPT: A. heat B. light C. chemical

A

The fundamental monomer used in the polymer matrix of glass ionomer cement is: A. acrylic acid B. methacrylic acid C. Bis-GMA D. UDMA

A

The nature of ceramics is that they: A. are strong in compression B. are very active chemically C. have low melting points D. have low moduli of elasticity

A

Which of the following concerning the degree of conversion and degree of polymerization in dental direct restorative resin composite is correct? A. Commonly the degree of conversion is less that the degree of polymerization. B. The degree of conversion is the number of monomer molecules that become part of the polymer. C. Commonly 99% of all reactive sites react in the polymerization reaction. D.. The degree of polymerization is the number of potential reactive sites that actually react in a polymerization reaction.

A

Which of the following is CORRECT about metals A. The electron cloud in the metal makes metal a good electrical and thermal conductor. B. Metals conduct electricity because of the presence of ionic bonds C. Metals usually form ionic bonds with other metals D. Only metals form crystalline solids. Nonmetals always form amorphous solids.

A

Which of the following linkages within a polymer backbone is representative of a chain polymer? A. -CH2-CH2- B. -CO-O- C. -NH-CO- D. -Si-O-

A

crystalline solids differ from amorphous solids in that crystalline solids have____? A. a long-range repeating pattern of atoms, molecules, or ions. B. appreciable intermolecular attractive forces. C. no ordered structure D. only short-range repeating pattern of atoms, molecules, or ions.

A

Xenoestrogen

A chemical, not indigenous to the body, that acts in the body in a manner similar to that of estrogen.

Estrogenicity

Ability of a chemical to act in the body in a manner similar to that of estrogen, the female sex hormone

Toughness

Ability of a material to absorb elastic energy and to deform plastically before fracturing; measured as the total area under a plot of tensile stress vs tensile strain.

Biocompatibility

Ability of a material to elicit an appropriate biological response in a given application in the body.

Malleability

Ability to be hammered or compressed plastically into thin sheets without fracture.

Acute Toxicity

Adverse response to a substance that causes ill effects relativlty soon after a single exposure or after multiple exposures over a relatively short time (usually less than 2 weeks)

Reference dose (RfD)

An Environmental Protection Agency (EPA) estimate, with uncertainty or safety factors built in, of the daily lifetime dose of a substance that is unlikely to cause harm in humans.

Stress Concentration

Area or point of significantly higher stress associated with a structural discontinuity such as a crack or pore or a marked change in dimension of a structure.

A beam of dental composite (A) with width, depth, and length of 2mm x 2mm x 25 mm is tested under 3-point bending. The distance between the supports was 15 mm. The beam failed at 48N. A beam of dental composite (B) with a width, depth, and length of 1mm x 1mm x 25mm is tested under 3-point bending. The distance between the support was 15mm. The beam failed at 48N. Which of the 2 materials has the greater flexural strength? O=3FL/2bd(squared) A. Dental composite (A) B. Dental composite (B)

B

A significant caution that should be exercised when using a Light Emitting Diode curing unit is that some of these units may not activate: A. benzoyl peroxide B. lucerin TPO C. camphorquinone

B

Chain-growth polymers differ from step-growth polymers in that: A. chain-growth usually form small molecular weight by-products. B. chain-growth polymers are widely used as dental restorative resins. C. chain-growth polymers slowly form high molecular weight molecules. D. All of the chain-growth monomers are simultaneously available for polymerization.

B

Chemical- or dual-activate resins are needed in dentistry because: A. photo-initiation begins closest to the light. B. adequate photo-initiation does not occur beneath opaque materials. C. Polymerization shrinkage tends to pull material away from preparation walls.

B

Dental restorative composites can be classified into categories such as microfill, hybrid, nanofill. This type of classification is based on: A. filler composition B. filler size C. matrix composition D. matrix size

B

Energy density is calculated using all of the following EXCEPT: A. time B. spectral emission C. irradiance

B

Engineering Stress is greater than true stress because engineering stress takes into account the reduction in cross-sectional area of a specimen during tension. A. True B. False

B

Malleability of a metal is the: A. ability to withstand deformation under shear. B.. property by which a material can be hammered into a sheet. C. property by which a material can be drawn into a wire D. ability to withstand compressive stresses.

B

Occlusal Force of Molars A. 400-500 N B. 400-800 N C. 200-500 N D. 100-300 N

B

The addition of high amounts of crystalline materials in dental ceramics will ________. A. increase the ceramic aesthetics B. increase the ceramic resistance to crack propagation C. decrease the ceramic fracture toughness D. decrease the ceramic strength

B

The polymerization mechanism found in most dental restorative resins used today includes: A. step-growth polymerization B. free-radical chain polymerization C. condensation polymerization

B

The risk of fracture in all-ceramic restorations can be reduced by proper preparation design. This design includes: A. uneven axial reduction B. rounding of all angles. C. providing sharp retentive points D. parallel axial walls.

B

What is a common chemical component used in dental resin composites to enhance bonding between polymer matrix/ceramic particles? A. a tertiary amine B. a coupling agent C. Camphorquinone D. ethylene glycol dimethacryalate

B

When evaluating the properties of the composite systems, an increased percentage of the ______ is usually found to increase mechanical properties. A. Matrix B. Filler

B

Which of the following is NOT correct concerning water absorption in dental restorative resins? A. It requires at least 7 days to reach equilibrium B. It is a surface phenomenon C. It is a diffusion controlled process D. It results in swelling of the material.

B

Which of the following methods of activation is NOT commonly used when placing direct resin composite restorations? A. chemical activation B. heat activation C. dual activation D. light activation

B

According to Hooke's Law: A. In the plastic range, strain is proportional to stress B. In both elastic and plastic range, strain is proportional to stress C. In the elastic range, strain is proportional to stress.

C

Diametral tensile testing is characterized by all of the following EXCEPT: A: It is valid if fracture results in 2 half-cylinders B. It is indicated for use with brittle materials C. It is indicated for use with ductile materials. D. It is valid if significant plastic deformation of the material does not occur.

C

In free-radical chain polymerization, the molecules that generate the free-radicals are the A: propagators B. activators C. initiators D. inhibitors

C

Occlusal force of premolars A. 400-500N B. 400-800N C. 200-500N D. 100-300N

C

Resin composites used as core materials typically A. are used for long term direct occlusal restorations. B. required no mechanical retention to keep them in place long-term. C. are tinted to provide contrast with tooth structure. D. require a delay of 1-2 weeks before preparation to allow for full polymerization.

C

Step-growth polymers have been used extensively in dentistry as: A. direct resin composite restorative materials B. indirect resin composite restorative materials. C. impression materials D. denture-base resin materials.

C

The deformation in a material due to stress is called A. Poisson's ratio B. load C. strain D. elastic modulus

C

The fundamental element providing structure to the glass used in glass ionomer cement is: A. oxygen B. hydgrogen C. silica D. fluoride

C

When performing a 3-poiint bend test on a brittle material, the material failure will begin where the material experiences the most ________ stress. A. compressive B. shear C. tensile

C

Which of the following dental ceramics present the lowest mechanical strength? A. alumina B. lithium disilicate C. feldspathic D. zirconia

C

Which of the following is NOT one of the four major components of a dental resin-matrix composite restorative material? A. organic polymer matrix B. initiator-accelerator system C. elastomer D. inorganic filler particles E. coupling agent

C

Toxic

Capable of causing injury or death, typically by a chemical agent.

Strain

Change in dimension per unit initial dimension. For tensile and compression strain, a change in length is measured relative to the initial reference length.

Strain Rate

Change in strain per unit time during loading of a structure

Compressive Stress

Compressive force peer unit area perpendicular to the direction of an applied force.

Compressive Strength

Compressive stress within a compression test speciman at the point of fracture.

A manufacturer modifies a resin composite by increasing the amount of filler. It would be expected that doing this would do all of the following EXCEPT: A. increase the compressive modulus. B. increase the flexural modulus. C. decrease the polymerization shrinkage D. decrease the viscosity

D

Advantages of using glass ionomer cement as a restorative material include all of the following EXCEPT A. high levels of fluoride release B. a potential to be "recharged" with fluoride. C. good adhesion to tooth structure D. high ability to resist fracture.

D

In terms of flexural strength, the strongest ceramic is: A. Glass-infiltrated alumina B. Feldspathic porcelain C. aluminous porcelain D. Zirconia

D

Occlusal Force of Incisors A. 400-500N B.. 400-800N C. 200-500N D.. 100-300N

D

Tensile or compressive stress experienced in a material is described as: A. Load per unit volume B. The cross sectional area divided by the force C. Force per unit volume D. The force divided by the cross sectional area.

D

The color of an object as sensed by a human observer is impacted by all of the following EXCEPT: A. The properties of the object B. the properties of illumination C.. the properties of the observer D. the properties of elongation.

D

Which ONE of the following properties is NOT associated with the presence of a glassy phase in dental ceramics? A. increased translucency B. decreased strength C. act as the matrix phase of the composite system D. increased toughness

D

Which of the following general properties is NOT characteristic of polymers? A. Formability B. Low density C. Low hardness D. High electrical/thermal properties

D

Which of the following is the predominant interatomic bonding in dental ceramics? A.. Hydrogen B. Metallic C. Van der Waals D. Ionic E. Covalent

D

Which of the followingn is NOT a desirable quality of an impression material? A. able to flow, wet and adapt to oral structures B. short setting time C. readily disinfected D. able to form a solid with low elastic recovery capability

D

Elastic Strain

Deformation that is recovered instantaneously upon removal of an externally applied force or pressure.

Which of the following best describes a thermoplastic polymer? A. Insoluble B. Soften when heated C. Can be recycled D. Do not soften when heated E. B and C only

E

Pressure

Force per unit area acting on the external surface of a material.

Flexural strength (Bending strength or Modulus of rupture)

Force per unit area at the point of fracture of a test specimen subjected to flexural loading

Flexural Stress (Bending stress)

Force per unit area of a material subjected to flexural loading.

Stress

Force per unit area within a structure subjected to an external force or pressure

Allergy

(1) A hypersensitivity reaction initiated by specific immunological mechanisms. (2) Abnormal antigen-antibody reaction to a substance that is harmless to most individuals. (3) antigen-inducing an allergic reaction