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Fixed Prosthodontics > Quiz 2 (Chapters 17 & 18) > Flashcards

Quiz 2 (Chapters 17 & 18) Flashcards

1
Q

The dry strength of gypsum is approximately twice that of the wet strength. True or False?

A

True

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2
Q

At what percentage of weight loss (excess water) does compressive strength of gypsum increase sharply?

A

7.5%

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3
Q

Increasng the speed of spatulation or length of time spent mixing _____ the setting time:

A

Shortens

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4
Q

What are the four characteristics of Cyanoacrylate reinforced gypsum?

A
  1. Inexpensive
  2. Easy to use
  3. Accurate
  4. Small amount of low-viscosity cyanoacrylate is applied to die and further thinned with compressed air, making die more resistant to abrasion
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5
Q

Depending upon the method of calcination, how many different forms of the hemihydrate can be obtained? And what are they?

A

3

  1. Dental plasters (produced when gypsum is heated in an open kettle at a temperature of 110-130 degrees celsius. This is known as the β-hemihydrate, and is used to produce type II Dental Stone.
  2. Hydrocal, and is used to make type III dental stone. This second form of product results when gypsum is dehydrated under pressure, and in the presence of water vapor at about 125°C. Is an α​-hemihydrate for of calcium sulfate. Type III stone is used in many laboratory procedures, as well as to fabricate diagnostic casts, and partial and complete dentures.
  3. Densite, used to make type IV and V die stones.

This third form of dental product results when gypsum mineral is boiled in a 30% calcium chloride solution. The chloride is then washed from the rock, and the remaining mineral is ground to the desired level of fineness. Type IV and V die stones are both α-hemihydrate forms of calcium sulfate as well.

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6
Q

The set time for dental plaster and stone is largely under the control of the ________:

A

Manufacturer

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7
Q

What are the two principal objectives of reflowing and refinishing the margins immediately before the investing of the wax pattern?

A
  1. Minimizing dissolution of the luting agent
  2. Facilitating plaque control
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8
Q

What are the main six die materials?

A
  1. Epoxy Resin
  2. Polyurethane
  3. Electroplated Silver or Copper Over Gypsum
  4. Flexible Silicone or Polyether
  5. Gypsum
  6. Cyanoacrylate Reinforced Gypsum
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9
Q

How can one overcome the problem of distortion or increased elasticity with their wax pattern?

A

By applying the initial layer of wax in melted increments or drops.

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10
Q

As the solidfying metal (casting, crown) cools to room temperature, it shrinks, so how is the accuracy maintained so it fits on the tooth?

A

Dimensional accuracy of the casting is achieved by balancing the shrinkage against precisly controlled expansion of the mold.

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11
Q

With gypsum, what is the definition of working time?

A

Working time is the time that elapses from the start of the mix until the mix loses it’s gloss, and the viscosity reaches a point where it will no longer flow into the impression.

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12
Q

With gypsum, increasing temperature _____ solubility of the hemihydrate relative to that of the dihydrate:

A

Lowers. At 100°C the solubility’s are equal, at which point no reaction occurs and plaster does not set.

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13
Q

With gypsum, a moderate increase in temperature will ______ set time:

A

Decrease

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14
Q

What is wet strength?

A

Wet strength is the strength measured when excess water remains in the hardened mass of stone

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15
Q

What is the name of the powder form of calcium sulfate hemihydrate?

A

Calcium sulfate anhydrite, which is the starting form of calcium sulfate used in dentistry for the production of casts and casting investments.

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16
Q

What are the six factors that increase the luting agent space?

A
  1. Increased thermal and polymerization shrinkage

of the impression material (see Chapter 14).

  1. Use of a solid cast with individual stone dies (see

Chapter 17).

  1. Use of an internal (initial) layer of soft wax in the

wax pattern.

  1. Use of die spacers.
  2. Increased expansion of the investment mold

(see Chapter 22).

  1. Removal of metal from the fitting surface by

grinding, airborne-particle abrasion, etching with aqua regia, or electrochemical milling.

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17
Q

What is the lost wax technique?

A
  • This technique consists of obtaining an accurate impression of the prepared tooth and making a cast from the impression on which a wax pattern that resembles the shape of the final restoration is shaped. A mold is then made around the wax pattern with a refractory investment material. When the investment has set, the wax is vaporized in an electric furnace. The hollow mold is then filled with molten casting alloy, reproducing every detail of the wax pattern. The metal casting is retrieved, excess metal is removed, and after polishing, the cast restoration is ready for clinical evaluation.
  • As the solidifying metal (casting) cools to room temperature, it shrinks. Dimensional accuracy of the casting is achieved by balancing this shrinkage against precisely controlled expansion of the mold. Wax is used to make the patterns because it can be conveniently manipulated and precisely shaped. By heating, it can be completely elimminated from the mold after investing.
  • The lost-wax technique is widely used in industrial and jewelry manufacturing. The first bronze castings reportedly were made in the third millennium B.C.E. with beeswax and clay refractory materials. Ancient lost-wax castings such as Chinese bronzes, Egyptian deities, and Greek statues have withstood the centuries, yielding information about ancient societies and cultures. The lost-wax method may have been used in Sumer as early as the Second Early Dynastic Period for figurines and even larger body parts.
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18
Q

What are the six steps in order for waxing a tooth to anatomic form?

A
    1. The die is modified as necessary and lubricated
    1. An initial coping is waxed, forming the internal surface
    1. The proximal surfaces are developed, with correctly located contact areas.
    1. The axial surfaces are waxed. Overcontouring near the gingival margin must be avoided.
    1. The occlusal surfaces are developed with a wax addition technique, which makes it easier to determine the best location of cusps and occlusal contacts.
    1. The margins are reflowed, and the wax pattern is finished.
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19
Q

The maxillary cusps become shorter, farther distally. True or False?

A

True. The mandibular cusps become taller, farther distally.

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20
Q

What is another name for the curve of Spee?

A

The anteroposterior curve. The wax cones (if used) should line up with the curve of Spee.

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21
Q

In what third of the crown are most posterior contact areas located? Any exceptions?

A

Occlusal third of the crown. However, contact between the maxillary first and second molar occurs in the middle third.

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22
Q

What are the four main characteristics of regular gypsum?

A
  1. Inexpensive
  2. Easy to use
  3. Accurate
  4. Easily abraided
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23
Q

What happens during spatulation with gypsum product powder?

A

Newly formed dihydrate crystals are broken into smaller crystals, which serve as nucleation sites for further growth. Slurry water sets faster because of this. Because increased spatulation causes more nuclei centers to be formed, conversion from hemihydrate to dihydrate is accelerated.

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24
Q

Type IV die stone is ___ strength and ___ expansion?

A

High, Low

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25
Q

The surface of set gypsum is porous on a microscopic level. True or False?

A

True

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26
Q

What is the definition of a die?

A

Positive reproduction of the prepared tooth.

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27
Q

Do most adults with a class I occlusion and unworn teeth have a cusp-fossa scheme or a cusp-marginal ridge scheme?

A

Cusp-marginal ridge. Cusp-fossa is only with slight class II. But the cusp-fossa arrangement is recommended for the casting to prevent food impaction, help with centric relation, and improve stability.

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28
Q

What type of hydrate are stone II and III?

A

Hemihydrate

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29
Q

When set, about 50% of gypsum products show a measurable linear expansion. True or False?

A

False, they all do.

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30
Q

What happens when the luting agent space is too narrow?

A

The casting does not seat properly during cementation because of hydraulic pressure that develops when the viscous mass of luting agent cannot escape through the narrow gap between the crown and preparation as the restoration is seated.

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31
Q

What are the three main characteristics of Polyurethane?

A
  1. More abrasion resistant than gypsum
  2. More expensive than gypsum
  3. Must use PVS or Polyether impression material (Incompatible with hydrocolloid and polysulfide rubber base).
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32
Q

What is centrum?

A

Occlusal contacting scheme or pattern for posterior teeth. Cusp tip to flat receiving area, no contacts on inclines, 2 to 4 per tooth. Receiving area can be a marginal ridge, or any artificially created area in a fossa (make it flat!)

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33
Q

What happens when gypsum product powder is place in water?

A

The reaction starts and calcium sulfate dihydrate is formed.

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34
Q

What are the characteristics of type IV dental stone?

A
  • High-strength low-expansion
  • α-hemihydrate
  • Uses
    • Cast inlays and onlays
    • Implant prostheses
    • Removable partial denture frameworks
    • Milled restorations
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35
Q

Overtimming the die directly beneath the margin will result in?

A

Overcontoured restorations.

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36
Q

What are the five types of gypsum products established by the ADA?

A
  1. Type I - Plaster, impression
  2. Type II - Plaster, model
  3. Type III - Dental stone
  4. Type IV - Dental stone, high strength
  5. Type V - Dental stone, high strength, high expansion
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37
Q

What is the hottest point on the bunsen burner?

A

The meniscus

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38
Q

What is the definition of abrasion?

A
  • It is the removal of material that occurs when surfaces slide across or against each other. There is two-body abrasion and three-body abrasion.
  • Poor abrasion resistance is a disadvantage of gypsum materials
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39
Q

How can one increase the expansion of the investment mold?

A

Heat the mold to a slightly higher temperature during the wax elimination phase.

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40
Q

Gypsum dies usually provides better surface detail than electroplated or epoxy dies. True or False?

A

False, it is the opposite.

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41
Q

What are the four characteristics of Flexible Silicone or Polyether?

A
  1. Die can be fabricated in a matter of minutes
  2. Used primarily for chairside indirect composite resin inlays or onlays
  3. Can also be used for interim restorations
  4. Restoration is easily separated from die
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42
Q

Natural teeth are rarely more than 1 mm wider at their height of contour than at the CEJ. True or False?

A

True

43
Q

What is dry strength?

A

The dry strength of gypsum products is the strength with all of the excess water driven out.

44
Q

Where do bubbles form?

A

Where two masses of material meet

45
Q

The time required for the reacitno to go to completeion is called the ______:

A

Final set time

46
Q

Type V die stone is ___ strength and ___ expansion:

A

High, High

47
Q

What is the color, type, and use of Mounting Stone?

A
  • Color = white
  • Type I stone
  • Mounting casts
48
Q

What are the four die requirements?

A
  1. Must accurately reproduce the prepared tooth or teeth
  2. All marginal areas must be accessible
  3. The unprepared tooth structure immediately cervical to the margins should be easily discernible (0.5 to 1.0 mm beyond prepared margin if possible). This enables the correct cervical contours to be determined.
  4. Must be of a durable material that is not easily abraded
49
Q

What happens when either α or β-hemihydrate is mixed with water?

A

The calcination reaction is reversed

50
Q

What is the name of the set form of dental stone?

A

Calcium sulfate dihydrate

51
Q

What are the main seven different compositions of Inlay Casting Wax?

A
  1. Paraffin (40-60%)
  2. Dammar Resin
  3. Carnuba
  4. Ceresin
  5. Candelilla Wax
  6. Beeswax
  7. Dyes
52
Q

What is another name for the curve of Wilson?

A

The mediolateral curve. This is when the mandibular cusps become taller farther distally, and the opposite for the maxillary cusps.

53
Q

Which type is the hardest type of stone?

A

Type V

54
Q

What is the emergence profile?

A

It is the tooth surface gingival to its height of contour immediately adjacent to the gingival soft tissues. it is usually flat or concave

55
Q

Why is it helpful to use an entire anterior bite tray when waxing up #6?

A

Because then it can also give you an impression of #11, and they can use that tooth to match their wax, and the canines are extremely important because of guidance and such.

56
Q

What five things influce abrasion resistance or wear resistance?

A
  1. Material Strength
  2. Material Surface hardness and roughness
  3. Material Third-body wear particle size
  4. Material Mode of fracture (ductile vs. brittle material) (-More ductile means might have great compressive strength, means the ability to move rather than break under pressure)
  5. Material Applied force
57
Q

What is the four proper steps of calcination?

A
  1. Calcium sulfate dihydrate
  2. Plaster or stone (calcium sulfate hemihydrate
  3. Hexagonal anhydrite
  4. Orthorhombic anhydrite

And in between all of these steps we are heating and gradually getting hotter, and in between steps 3 and 4, we are at 200 to 1000 degrees Celsius.

58
Q

Should water or powder be added to the mixing bowl first?

A

Water

59
Q

The compressive strength of dental stone is also slightly improved with vacuum mixing. True or False?

A

True

60
Q

Which stone has the fewest voids and the highest compressive strength?

A

Dense stone

61
Q

What is the Wax Cut-Back for a ceramic veneer?

A
  • If a ceramic veneer is to be used, once the final contour of the wax pattern has been completed, the pattern is cut back over an even thickness—usually about 1 mm—to provide room for the porcelain fused onto the cast metal substructure.
62
Q

What are the characteristics of Type I dental stone?

A
  • Impression plaster
  • Composed of plaster of Paris (β-hemihydrate)
  • Modifiers have been added to regulate the setting time and expansion
  • Historically, it was used to make impressions of intra-oral structures, but has been replaced by hydrocolloid and elastomeric impression materials
63
Q

Which type is the most commonly used type of stone?

A

Type III

64
Q

What type of stone do you use to mount, and why?

A

Mounting stone, type I, because of its low expansion, otherwise you will get inaccuracies.

65
Q

What are the four main reasons why we use the triple-tray technique despite its limitations?

A
  1. Can provide an extremely accurate bite record when done correctly
  2. Error is an inherent aspect of any copy
  3. Fewer interactive surfaces can increase accuracy
  4. Reasonable quality with minimal time investment.
66
Q

What are the effets of water content on compressive strength involving the crystal details?

A
  • When the last trace of water is lost, fine crystals of gypsum precipitate, which serve as anchors between the larger crystals
  • Similarly, if excess water is reconstituted by immersion or absorption, these small crystals are the first to dissolve
67
Q

What is the name of the form of gypsum that is used in dentistry?

A

Calcium Sulfate Hemihydrate, which is produced by heating ground gypsum. After mixing a dental gypsum product with water, it reverts back to gypsum.

68
Q

After how many hours of mixing and pouring gypsum, does hardened gypsum product appear to have reached maximum strength?

A

1-2 hours. However at room temperature, about 7 days are needed for an average denture flask filled with gypsum product to lose excess water

69
Q

What are the four characteristics of Epoxy Resin?

A
  1. More abrasion resistant than gypsum
  2. More expensive than gypsum
  3. Some formulations undergo slight shrinkage upon polymerization
  4. Must use PVS or Polyether impression material (Incompatible with hydrocolloid and polysulfide rubber base).
70
Q

What are the two limitations of the partial arch articulation system?

A
  1. No contralateral guidance in excursions
  2. No condylar reference
71
Q

What has the greatest quantity of excess water and what contains the least excess water, when referring to gypsum products?

A

Plaster has most, high strength dental stone has least.

72
Q

What is the proper name for mined gypsum?

A

Calcium sulfate dihydrate. It is a mineral mined in many parts of the world.

73
Q

Why are gypsum products popular in dentistry?

A

When set, they show relatively high values of compressive strength

74
Q

Burnishing is more effective than carving from removing wax. True or False?

A

False. Carving is easier, but harder to control than burnishing.

75
Q
A
76
Q

When dental stone and high strength dental stone is mixed with the same water/powder ratio as model plaster, the compressive strength is doubled. True or False?

A

False. The compressive strength is almost the same. With a water/powder ratio of 0.50, the compressive strength for all three is 10.5-11 MPa.

77
Q

What is the theoretical lowest required volume of water needed to hydrate 100 g of hemihydrate in either the α or β form?

A

18.6 ml. However none of the dental products currently in use can be mixed with this volume of water and still develop a mass that can be manipulated. The reason for differences among the recommended volumes of mixing water for plaster, dental stone and die stone is due to shape and size of the different forms of calcium sulfate hemihydrate particles.

78
Q

In regards to set time, what are five factors that are under the control of the operator?

A
  1. Changing the temperature of the water to accelerate or retard the set
  2. Increasing or decreasing spatulation (mix) time can accelerate or retard the set
  3. Substituting 2% K2SO4 for water will accelerate the set time
  4. If you grind a small amount of set dental stone and create a slurry in the water used to mix with the gypsum product, it will accelerate the set
  5. Adding more water to the mix slows the set time
79
Q

What is the color, type, and use of Die-Keen?

A
  • Color = green, blue, pink, ivory
  • Type V stone
  • Optimum expansion for crown and bridge, porcelain
80
Q

What are the four factors that reduce the luting agent space?

A
  1. Reduced thermal and polymerization shrinkage

of the impression material.

  1. Use of resin or electroplated dies.
  2. Use of alloys with a higher melting range.
  3. Reduced expansion of the investment.
81
Q

What is the process of gypsum from ground gypsum to dental stone? And what is the name of this process?

A
  1. Commercially, gypsum (dihydrate) is ground and subject to temperatures of 110°C-130°C in open containers to drive off water
  2. The resulting hemihydrate is a fibrous, porous crystalline aggregate known as plaster of Paris, or dental plaster
  3. As the product is heated further, it becomes an anhydrite known as dental stone

The Process is called Calcination = increasing calcium concentration by reducing water to make it into a gypsum product

82
Q

What type of stone are ortho plasters, lab plasters, and model plasters?

A

Type II

83
Q

What are the five characteristics of electroplated die materials?

A
  1. Difficult process
  2. Easily distorted
  3. When done properly, can be very accurate and durable
  4. Incompatible with polyether and Polysulfide rubber base
  5. Silver plating requires a cyanide solution which introduces toxicity and disposal challenges
84
Q

What is the color, type, and use of Denstone?

A
  • Color = Golden, white, pink
  • Type III stone
  • Full and partial dentures, cast partials
85
Q

Opposing incisors should contact evenly during lateral excursions but not during protrusive movements. True or False?

A

False, it is just the opposite. Opposing incisors should contact evenly during protrusive movements but not during lateral excur- sions. This is achieved by making a concavity in the lingual surface of maxillary incisors. The ability to make this concavity smooth is very important. As a result, the patient is given a smooth envelope of motion, and potential neuromuscular disturbances are avoided. In maximum intercuspation, anterior teeth ideally should be just out of contact.

86
Q

Water in excess of 18.6 ml/100 grams of product is excess water. True or False?

A

True

87
Q

What are the four main differences between the α and β hemihydrates?

A
  1. Crystal size, surface area, and lattice perfection.
  2. β-hemihydrate crystals require the most water because they are more irregular in shape and porous. (More water is needed to wet the particles when mixing.)
  3. The powder particles of α-Hemihydrate used for dental stone are smaller, more prismatic, and more regular in shape then those for plaster.
  4. The α-hemihydrate produces a much stronger, harder and denser structure than the β-hemihydrate because it is mixed with less water.
88
Q

What happens when the luting agent space is too wide?

A

The casting is loose on the tooth, resistance form is reduced, and the position of the casting is difficult to maintain accurately during evaluation and occlusal adjustment.

89
Q

What happens when set stone dries with excess water in it?

A

The water evaporates and voids are left in the remaining stone.

90
Q

What are the six master cast requirements?

A
  1. Must accurately represent both prepared and unprepared tooth surfaces
  2. Unprepared teeth immediately adjacent to the prepared teeth must be free of voids, defects or other irregularities
  3. All contacting surfaces of opposing teeth in MI and any tooth surfaces involved in anterior guidance must be free of defects and allow for precise articulation
  4. All relevant soft tissues must be accurately reproduced, especially edentulous ridges that will be involved in a fixed prosthesis
  5. Overall cast shape and form must be an accurate representation of the relevant anatomical structures
  6. Must be neatly trimmed and de-bubbleized
91
Q

What is the definition of surface hardness?

A
  • Hardness is a surface measurement of the resistance of one material to be deformed by indenting or scratching another material
  • Scratch test: First hardness scale proposed by Fredrich Mohs
  • Indentation test: Knoop and Vickers
  • Depth of surface penetration is reported in units of force/area
  • Hardness has been correlated with wear resistance
  • Surface hardness has been shown to be a poor predictor of material wear
92
Q

What’s the ideal dimension for the luting agent space for each wall of the wax-up and future crown?

A

Has been suggested at 20 to 40 microns for each wall, which implies that a complete crown should have an internal diameter between 40 and 80 microns larger than the diameter of the prepared tooth.

93
Q

What type of stone is used most commonly for fixed prosthodontics or restorations?

A

Types IV and V.

94
Q

What is the definition of a Master Cast?

A

Same as definitive cast, working cast. They are replicas of the prepared tooth or teeth, ridge, areas, and other parts of the dental arch. Also called models.

95
Q

What is the color, type, and use of Die-Stone?

A
  • Color = Peach
  • Type IV stone
  • Crown and bridge porcelain, partials
96
Q

The percentage of setting expansion varies from one gypsum product to another. True or False?

A

True. Typically, over 75% of the expansion observed at 24 hours occurs in the first hour of setting

97
Q

A wax that solidifies at a lower temperature shrinks more and therefore requires more compensation to control fit than does a wax that solidifies at a higher temprature. True or False?

A

False, a wax that solidifies at a HIGHER temp shrinks more and requires more compensation.

98
Q

What is the color, type, and use of Labstone?

A
  • Color = Green, Blue
  • Type III stone
  • Articulating, master models, flasking
99
Q

What are the characteristics of type III dental stone?

A
  • α-hemihydrate
  • Wide range of uses, where strength in excess of plaster is needed, but not to the level provided by the high-strength die stones
  • Diagnostic casts
  • Working casts for removable complete dentures
  • Altered cast segments for removable partial dentures
  • uasts for general utility purposes including
    • Bleachingtrays
    • Athleticmouthguards
    • Nightguards
    • Duplicatecasts
    • etc…
100
Q

What are the characteristics of type II dental stone?

A
  • Laboratory plaster
  • Composed of plaster of Paris (β-hemihydrate)
  • Used commonly in the laboratory in removable denture construction
  • Commonly used to articulate casts (but should not be due to significant expansion!)
  • Usually marketed in a white color so that it can easily be distinguished from other types of stone, which are usually colored
101
Q

What are the characteristics of type V dental stone?

A
  • High-strength & high-expansion
  • α-hemihydrate
  • Used with cast full-coverage restorations to compensate for casting shrinkage
  • Uses
    • Full coverage cast crowns, inlays and onlays
    • Fixed partial dentures with full coverage cast retainers
102
Q

What are the two different types of casting wax, and their characteristics?

A
  1. Type I - Medium to hard in consistency, generally used with the direct technique for making patterns in the oral cavity. Solid at 37 degrees C. Shrinks more than type II Inlay Wax.
  2. Type II - Softer. More commonly used in the indirect technique. Solid at 25 degrees C.
103
Q

Why have epoxy resins and light-cured dimethacrylate resins been embedded in gypsum?

A

To help increase hardness and scratch resistance. However differences in abrasion resistance between conventional and resin impregnated type IV gypsum at 24 hours and 7 days has not been established.

Fixed Prosthodontics (8 decks)

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