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DENTAL MATERIALS MIDTERM
Has there been an ideal dental material identified? - NO What are the different classes dental materials? - -Preventive, Restorative, Auxilliary What are preventive dental materials? - -materials that prevent or inhibit the progression of tooth decay or periodontal disease What are 2 examples of preventive dental materials? - -pit and fissure sealants -therapeutic liners What are restorative dental materials? - dental materials that repair or replace tooth structure What are the different classifications of restorative dental materials (time periods)? - -temporary: short-term (months) -interim: moderate time (1-4 yrs) -permanent: 5 years or more What are direct restorative dental materials? - -dental materials placed directly into teeth What are 2 examples of direct restorative dental materials? - -dental amalgam
-composite resin What are indirect dental materials? - dental materials that require the use of models for their fabrication What are 2 examples of indirect dental materials? - -ceramics -cast metals Which material was used as a restorative dental material in ancient times? - GOLD How were toothaches treated in ancient times? - -zinc oxide-eugenol cement was often employed as an obtundent dressing for toothaches What was the earliest implant material used by the Mayans? JUST FOR FUN - seashells What were the main dental materials used in the 1700s? - -wax -plaster -ivory -porcelain -zinc phosphate cement What advancements were made in dental materials in the 1880s? - -development of amalgam by trial and error -process for constructing porcelain teeth was patented
How are standards created/ what are they based on? How many exist? - -standards are based lab tests of physical properties (strength, working time etc.), which are intended to ensure satisfactory performance -150 standards Are clinical tests included in the creation of standards? Why does this matter? - -No -lab tests fall short of accurately predicting clinical behavior for most materials What is the function of the American National Standards Institute (ANSI)? - -Has to approved standards created by the ADA -decides what tests are necessary for a material to meet the requirements of a standard -Involved in international standards (ISO) Which products is the ADA Seal of Acceptance Program applied to? - over the counter products How does the ADA Seal of Acceptance Program work? - -companies submit products voluntarily with product samples, results from lab tests and clinical studies for review -Products are reviewed and if they are accepted, the seal lasts 5 years Why would an over the counter product be provisionally accepted? How long may they display the seal?
- -provisionally accepted products lack sufficient evidence to justify classification although safety and usefulness have been established -not continued beyond 3 years Why would an over the counter product be unaccepted by the ADA Seal of Acceptance Program? -
-obsolete, markedly inferior, ineffective or dangerous products What is the FDA responsible for controlling as of 1976? - -Safety -Efficacy What are the FDA classifications of dental materials? - -Class I: general controls (registration, good manufacturing practices, proper labeling) -Class II: must meet standards- ADA, FDA, ISO -Class III: new untested products, must have pre-market clearance; biological tests (screening tests, intermediate tests, preclinical tests) & clinical trials Which FDA classification do most of the materials used in restorative dentistry fall under? - Class II Which FDA classification do all implanted and life-supporting devices fall into? - Class III How is the FDA involved in the approval of new dental materials? - -The FDA designates a panel to classify it What is the positive aspect of FDA classification? Negative? - -Positive: quality control to the dentist and public -Negative: cost (hiring a staff to deal with the FDA severely curtails the amount of money available for research of new products) What is the ISO? - -International Standards Organization is dedicated to developing international standards -80 countries involved
How do dental cements based on polyacrylic acid seal the margin? - -they chemically bond to tooth structure How do dentin bond agents seal the margin? - -they chemically and mechanically bond to dentin (initially) How does acid etching help seal the margin? - Acid etching allows mechanical bonding to occur, thereby reducing microleakage How does temperature affect microleakage? - -temp. changes increase microleakage if the restorative materials are not well bonded to tooth structure and they shrink or expand at a different rate than the tooth What is Galvanic shock? - -when two different metals are directly contacting each other in the proper electrolyte which results in a small current -ex. new amalgam contacts with previous gold crown -galvanic pain What can cause allergenicity/ toxicity to dental materials? - -breakdown of products from corrosion and degradation can be harmful to the pulp and other oral tissues NOTE: it can elicit a biological response if it is absorbed into the circulatory system What are the characteristics of an ideal restorative material? - -nontoxic and biocompatible -esthetic -strong -wear resistant -usable (avoid high labor costs)
-low material costs -bond to tooth structure and seal margins -stable properties over years (color) What are the defining features of a gas? - -free movement of molecules -low attraction -rapid diffusion What are the defining features of a liquid? - -more attraction exists between molecules which results in more internal friction -slower diffusion rates than gas What are the defining features of a solid? - -molecules are relatively fixed -molecular movement still occurs as vibration around fixed centers of location -diffusion rates are slow Name all of the primary bonds - -ionic bonds -covalent bonds -metallic bonds What is ionic bonding? - -electrostatic attraction of positive and negative charges (NaCl) -valence electrons are tightly held in place Do ionic bond have high or low electrical and thermal conductivity? - LOW AF
-temporary partial charges which change -very weak What are permanent dipole bonds? Which type of molecules result from this? - -partial charges which aries from differences in electronegativity -polar molecules Why are permanent dipole bonds important in polymers? - -the breakage of these bonds permit molecular sliding which ultimately causes rupture of the material to occur Explain how hydrogen bonding works. - -strong permanent dipole -since there is only one electron in the hydrogen atom, it requires substantial force to pull the electron toward the bond and away from the nucleus, leaving it partially unshielded Which type of bond is the strongest type of secondary bond? - HYDROGEN Name the physical properties of ceramic materials. (bonding, optical, electric/thermal, mechanical) - -bonding: ionic and covalent -optical: translucent -electric & thermal: insulators -mechanical: very strong and brittle Name the physical properties of polymers. (bonding, optical, electric/thermal, mechanical) - -bonding: covalent & secondary -optical: translucent -electric/thermal: insulators
-mechanical: weak & stretch Name the physical properties of metals. (bonding, optical, electric/thermal, mechanical) - -bonding: metallic -optical: very opaque -electric/thermal: conductors -mechanical: strong and tough What determines the physical and electronic properties of materials? - valence electrons What is the coulombic attraction equation? When are attractive forces the greatest? - -Fa= +k/a^ -as ions approach one another attractive forces increase first What is the coulombic repulsion equation? When are repulsive forces the greates? - -Fr= -b/a^ -As the distances between atoms further decreases, repulsive forces increase faster Is the coulombic attractive force or the coulombic repulsive force more dependent on atomic separation? - repulsive force What is the equation for the total force on an ion as it is approaching another ion? - -Ft= Fa +Fr Which coulombic force is greatest at equilibrium? attractive? repulsive? neither? - -at equilibrium the two forces are equal
-the material with the deep energy well -stronger atomic bonding= less atomic movement LOOK AT ENERGY GRAPH WHEN ANSWERING: When comparing a material with a deep energy well to a material with a shallow energy well, which material has a higher melting/boiling point? - -the material with the deep energy well has a higher melting/boiling point due to stronger atomic bonding -melting/boiling occurs when atomic bonds are broken, therefore it takes more energy to break the bonds of this material What are the two arrangements of atoms in solids? - crystalline & non-crystalline What does a crystalline configuration of solids look like? - -a regular configuration of atoms -space lattice or crystal What type of lattice to most metals metals used in dentistry have? - cubic systems What does a non-crystalline configuration of solids look like? What type of ordering is seen? - -when atoms or molecules are distributed at random -amorphous -short range ordering What is the glass transition temperature of non-crystalline materials? - -the temperature at which these materials first become "rubbery" What are 3 examples of non-crystalline dental materials? - -waxes
-glasses (porcelain glazes) -most dental resins What is stress? - -the force measured across a given area What is strain? - -the change in dimension of the material in response to stress When does fracture occur in a material? - -when the stresses pulling atoms apart exceed the attractive forces which hold them together Which factors does diffusion rate depend on? - -temperature -atomic size -interatomic bonding -lattice imperfections -D, the coefficient of diffusion What is the kinetic vibration of atoms in a sold dependent on? - temperature What is mechanical bonding? what are several dental materials that exhibit this type of bonding? - -the interlocking of two objects (nut&bolt) -amalgam, some cements, acid etching What is cohesion? - -molecular attraction of two like materials
What factors affect the wetability of a surface? - -cleanliness of the surface -inherent surface energy available (need electrons available for bonding) -surface roughness What is the contact angle? - -the angle formed between the adhesive and the adherend at their interface Do you want a low contact angle or high contact angle for better adhesion? WHY THO - -low contact angle -if the atoms of the adhesive are more strongly attracted to those of the adherend than they are to each other, the adhesive will readily wet the surface of the adherend which is gucci How does surface roughness affect wettability? - -the surface must be rough (but not too rough) to allow the liquid bonding agent to wet the surface effectively (liquid flows into all the crevices and creates low contact angle) How does fluoride reduce the adhesion of plaque to teeth? - -fluoride reduces the surface energy available for plaque attachment, attack by acids, etc. What characterizes poor adhesion? - -failure which occurs at the interface between materials Where will a material fracture when a STRONG adhesive joint is present? - -it will fracture cohesively or within one of the materials and not at the interface Why does debris accumulate at the margins? - -more free energy is available at the surface of a dental restoration, therefore debris is more likely to accumulate at the margins
-NOTE: this may also cause recurrent decay How does poor adhesion affect tooth sensitivity? - -deterioration at the restoration margins reflect a lack of adhesion between the material and the tooth, which causes tooth sensitivity
