Midterm Flashcards
(174 cards)
1
Q
What is imbibition?
A
Uptake of water by hydrocolloid when immersed in water
2
Q
When are anti-sialogogues contraindicated?
A
• Prescribe with caution in older adults Many medications have a more profound affect on older patients Glaucoma incidence is higher • Should not be used in patients with heart disease • Contraindicated in patients with Glaucoma Incidence of undiagnosed glaucoma in general population in high Consider Ophthalmological evaluation prior to use of anticholinergics
3
Q
What two impression materials exhibit long-term stability?
A
Poly- ethers and addition silicones are preferable because they exhibit sufficient long-term dimensional stability; the other materials, particularly the reversible hydrocolloids, must be poured immediately.
4
Q
What are the advantages and disadvantages of displacement paste?
A
Advantages of the system include good hemostasis with less discomfort than traditional cord. However, less tissue displacement is achieved than with cord, which may make die trimming more problematic. Improved displacement may be achieved if the paste is directed into the sulcus by applying pressure with a hollow cotton roll.
5
Q
What is the difference between drying a tooth and desiccating a tooth?
A
Desiccation is losing water via evaporation, drying (not losing water)
6
Q
Does alginate reproduce fine detail?
A
No
7
Q
Why don’t you want to completely remove the smear layer when prepping a tooth for a crown? And how do hemostatic agents affect the smear layer?
A
Can cause pulpal irritation, and they are very acidic and remove more smear layer than we would like usually.
8
Q
What is the composition of alginate (irreversible hydrocolloid)?
A
! Sodium and Potassium and other salts of alginic acid react with calcium to form calcium alginate ! Calcium sulfate dihydrate is added to provide a source of Ca+2 ions to cross-link the alginic acid ! Sodium phosphate is added as a retarder and its concentration adjusted to control set time. ! Alginic acid is a naturally occurring hydrophilic colloidal polysaccharide obtained from brown seaweed
9
Q
What are the factors influencing resistance?
A
! Magnitude & Direction of Dislodging Forces ! Geometry of the Tooth Preparation ! Physical Properties of the Luting Agent
10
Q
What does Decreased Axial Wall Taper do to resistance?
A
Increases it
11
Q
What is the indirect-direct procedure for interim restorations? Advantages?
A
In this technique the indirect component produces a “custom-made preformed ESF” similar to a pre- formed polycarbonate crown. In most cases, the practitioner uses a custom ESF with an underprepared diagnostic cast as the TSF. The resulting mold forms a shell that, after tooth preparation, is lined with additional resin (the patient serving as the TSF). This last step is the direct component of the procedure. Another method of creating the shell eliminates the need for an indirect TSF. It is accomplished by painting monomer liquid into the ESF and care- fully sprinkling or blowing resin powder on it. The thickness of the resin shell is difficult to control with this technique, however, and may result in the need for time-consuming corrective grinding. The indirect-direct approach has these ad- vantages: 1. Chairside time is reduced. Most of the procedures have been completed before the patient’s visit. 2. Less heat is generated in the mouth. The volume of resin used during lining is comparatively small. 3. Contact between the resin monomer and soft tissues is minimized in comparison with the direct procedure. Because pontic ridge areas do not normally require lining, there is reduced risk of allergic reaction. However, even with the diagnostic cast method, adjustments are frequently needed to seat the shell completely on the prepared tooth. This is the chief disadvantage of the indirect-direct procedure.
12
Q
What is the best luting agent for cementation of an interim restoration?
A
Zinc oxide eugenol, doesn’t bond that strong to make it easier to get it off in the end.
13
Q
An undercut is?
A
The axial reduction near the gingival is greater than the occlusal. Answer is B.
14
Q
What is the relationship between the size of the monomer molecule and exothermic heat and physical strength? And what do fillers do?
A
In general, the greater the size of the monomer molecule, the less is the exothermic heat of reaction on setting and the lower the physical strength of the set mass. An increase in filler content reduces the relative amounts of exothermic heat and contraction while increasing the strength of the set material.
15
Q
What are the disadvantages to PFM’s?
A
Significanttoothreductionisnecessarytoprovide
sufficientspacefortherestorative materials
-Asub-gingivalmarginisoftenrequiredonthefacialaspectwhichhasthepotentialto increase the risk of periodontal disease Increasedriskforcontactdermatitis(gingivitis)withsomemetals(Thesemetalsmust have a melting point higher than the fusing point of the porcelain. Many are not high noble and some are base metal.) -Moredifficulttoachievepremiumestheticsthanwithallporcelainrestorations -Porcelainfracturerisk -Feldspathicporcelaincanbeabrasivetoopposingtoothstructure -Laborintensivenatureoftherestorationcanleadtohigherlaboratoryexpenses
16
Q
Nerve impulses from the periodontal ligament form part of the mechanism that regulates saliva flow. What can help stop saliva production and flow?
A
Profound anesthesia
17
Q
Why is the lingual concavity important in an anterior PFM preparation, following the anatomy of the tooth?
A
Allows you to mimic the anatomy that was there and recreate marginal ridges, contributes to anti-deformation strength of the crown as well.
18
Q
The recommended convergence angle for something is……
A
6 degrees
19
Q
What does shortening proximal projections of the impression material do?
A
Shortening proximal projections of the impression material facilitates complete reseating of the ESF
20
Q
What is the only thing that changes between a gold crown or zirconia crown prep for a maxillary bicuspid?
A
The non-functional cusp bevel
21
Q
When are PFM’s contraindicated?
A
Largely whenever maximum esthetics is indicated and feasible, with young patients with large pulp chambers, when a more conservative approach would suffice, with patient with caries.
22
Q
When doing an anterior PFM in two planes, what are the gingival and incisal 1/3rd’s parallel to?
A
! Gingival 1/3 is parallel to the path of insertion or line of draw ! Incisal 2/3 is parallel to the facial surface of the tooth
23
Q
What is the ideal margin adaptation with Gold, PFM’s, and PCC?
A
10, 50, and 50-200 microns
24
Q
Which impression material is affected by latex gloves?
A
Addition silicones (PVS)
25
What are some disadvantages to polyether?
The stiffness of the set material is one such disad- vantage, which causes problems when a stone cast is separated from the impression. Thin and single teeth, in particular, are liable to break unless the practitioner uses great care. Polyether is stable only if stored dry, because it absorbs moisture and under- goes significant dimensional change.
26
What is a colloid?
A colloid is composed of two substances, one dispersed within another, and can exist in two distinct phases.
27
Which two components are elastomeres supplied in?
Catalyst paste and Base paste
28
What is a solution?
A solution, on the other hand, exists only in a single phase.
29
Which provisional material is the most deficient in contours and marginal fit and cannot be used for bridges?
Aluminum and tin-silver
30
Which of the following can be indications for a full coverage restoration?
F, all of the above
31
What is polycarbonate mainly used for?
It is lined with light cured PMMA to be helpful when no matrix is available.
32
The preparation for a tooth for a zirconia crown can be the same as for.......
All of the above, although the ideal would be like the full metal preparation.
33
What are the main indications for PFM's?
-Teeth that require complete coverage, and that... -Require considerable attention to esthetics -Teeth requiring more durability than all ceramic restorations -Excellent choice for bridge retainers -The incorporation of occlusal or cingulum rests and proximal and reciprocal guide planes in metal make it an excellent choice for removable partial denture abutments in the esthetic zone -The indications for Porcelain Fused to Metal (PFM) Crowns are similar to those for the FGC, when esthetics are also important
34
What is the ideal clearance of the area of the lingual cavity where you're putting porcelain over the metal?
1.5 mm
35
Electrosurgery facts:
7. The electrode should be passed rapidly through the tissue with a single light stroke and kept moving at all times. 8. If the tip drags, the instrument is at too low a setting, and the current should be increased. 9. If sparking is visible in the tissue, the instrument is at too high a setting, and the current should be decreased. 10. A cutting stroke should not be repeated within 5 seconds. 11. The electrode must remain free of tissue fragments. 12. The electrode must not touch any metallic restoration. Contact lasting just 0.4 second has been shown to lead to irreversible pulpal damage in dogs.23 13. The sulcus should be irrigated with hydrogen peroxide before the displacement cord is placed.
36
Where on teeth do you not build?
Posterior excursive interferences
37
What are the names of the two surface forms involved in making interim restorations?
External surface form and Tissue surface form
38
What is the main drawback to reversible hydrocolloid materials?
Not stable, doesn't last long, subject to imbibition and syneresis.
39
What is one of the biggest drawbacks of porcelain fused to zirconia?
You don't have a real good bond, better with PFM's
40
When should polysulfide impressions be poured up?
Immediately
41
What are the main consequences of an inadequate axial reduction?
Overer-contoured Crown ! Ledging at Margin ! Poor Esthetics ! Plaque Retention ! Gingival Margin Inflammation ! Periodontal Disease ! Furcation Involvement ! Recurrent Caries
42
What does a surfactant do when pouring up silicone in stone?
Helps prevent bubbles
43
Is alginate accurate?
Yes
44
What is the preferred design of an anterior PFM?
Wingless is the preferred design • Better esthetics • Slightly less retentive • Easier
45
Which of the following numbers best describes the clinically acceptable range for fixed prosthodontics overall taper?
5-22 degrees
46
In taking an impression with polysulfide or silicone materials, if the heavy bodied tray material begins to set before seating, the resulting dye will be........ Or if you are using the technique of a silicone putty in a tray with a spacer, you will get.........
Overall smaller. Distortion, and it will also be smaller.
47
What is syneresis?
Exuding liquid if left standing
48
What are the Perfect Provisional material requirements?
Biocompatible No mal odor or taste No exotherm on polymerization No polymerization shrinkage Good compressive and tensile strength Easy to manipulate Easy to add to and or repair Wide range of shades, including translucent Color stable over time
49
What is the strain in compression a measurement of?
The rigidity of a material. In general, polyethers are the stiffest impression material, followed by the addition silicones. Excellent for implant impressions.
50
What are the advantages and disadvantages of reversible hydrocolloid?
! Advantages: Few ! Hydrophilic – “Likes water” ! Injected material stays on tooth, in sulcus, etc... ! Easily poured up ! Once equipment is purchased, cost per impression is low ! Disadvantages: Many ! Expensive start-up costs ! Difficult to read accuracy of impression ! Can’t double-pour impression ! Impression must be poured immediately ! Impression material distorts when it cools to room temperature ! If left in water, the impression will imbibe (absorb) water, thereby distorting and losing accuracy ! If left standing, the impression will undergo syneresis (exuding liquid) thereby contracting and dimensionally distorting ! Temperamental at higher altitudes
51
What are the four types of elastomeric impression materials?
! Addition silicone ! Polyether ! Polysulfide Rubber Base ! Condensation silicone
52
Refrigerating addition silicone material can add up to two minutes of working time, if needed. True or False?
True
53
Should the non-functional cusp bevel be smooth or sharp and why?
Making the non-functional cusp bevel smooth instead of sharp so you don’t catch as many air bubbles when taking impressions.
54
What does PMMA in a light cured formulation help overcome?
Both polymerization shrinkage and exothermic deficiencies
55
What do you do with cementing if the provisional is overly retentive?
Only place cement around marginal area.
56
What does decreased crown height do to resistance?
Decreases it
57
Which acrylic material is the easiest to add to?
PMMA. Poly-methylmethacrylate. They shrink a lot when they cure, and they give off heat. (Bite splints). It is easy to add to, that is a test question, if you break it or need to repair it you can add some, the liquid is called monomer.
58
The gingival margin for a preparation for a full coverage crown should be placed......
At least 1 mm supra-gingivally, ideally with a gold crown keep your margins as high as you can.
59
Noble metals do not form chemical bond. True or False?
True
60
What are the disadvantages to PVS?
Hydrophobic (Relative to Hydrocolloid) - Sulfur contamination from latex gloves can inhibit set - Typically only a problem when working with a putty PVS - Sulfur compounds interfere with platinum catalyst, resulting in retarded or no polymerization at the site of contamination - Vinyl and nitrile gloves do not have this effect
61
When is electrosurgery for tissue preparation for impressions contraindicated?
1. It is contraindicated on or near patients with any electronic medical device (e.g., a cardiac pace- maker, transcutaneous electrical nerve stimula- tion [TENS] unit, insulin pump)22 or patients with delayed healing as a result of debilitating disease or radiation therapy. 2. It is not suitable on thin attached gingivae (e.g., the labial tissue of maxillary canines). 3. It should not be used with metal instruments, because contact could cause electric shock. (Plastic mirrors and evacuation tubes are available.)
62
What are the two best impression materials for implants?
-The two best impression materials for implants are addition silicones and polyethers, and polyethers might have the edge.
63
Which acrylic exhibits the greatest polymerization shrinkage?
PMMA
64
What are the effect of luting agents on resistance?
Complete Seating of Restoration (Decreased Cement thickness) = Increased Resistance ! Luting Agents with Increased Compressive Strength = Increased Resistance ! Luting Agents with Increased Modulus of Elasticity = Increased Resistance ! Chemically Bonded Restoration = Increased Resistance ! Micro-Mechanically Bonded Restoration = Increased Resistance 
65
For a PFM crown on tooth 8, the ideal facial reduction is?
1.2-1.7 mm
66
What is syneresis?
! With time, relaxation of internal stresses within the hydrocolloid expresses fluid onto the surface of the impression, resulting in dimensional change and distortion ! This expression of fluid from the hydrocolloid impression material is called syneresis
67
How do you measure wettability?
Assessed by measuring the advancing contact angle of water on the surface of the set impression material. Only the hydrocolloids are considered truly hydrophilic. Surfactants reduce the contact angle, improve wettability and simplify the pouring of elastomeric impressions. Also, simply using caution and pouring slowly can yield bubble-free casts with any impression material.
68
What is urethane dimethacrylate DMA?
Putty, light cure
69
What does decreased taper of axial walls to to retention?
It increases it
70
What does resistance mean?
Prevents dislodgement of restoration along a path other than path of insertion.
71
Which two acrylics are the softest?
PEMA and PIMA
72
What is the elastic recovery of alginate?
! Alginate is typically compressed about 10% when removed from undercut areas of the mouth ! Elastic recovery is both time and degree of compression dependent, as shown to the right ! Percent compression set (permanent deformation) is a function of ! Percent compression (10, 20, or 30% strain) ! Time under compression (5 or 10 seconds) ! Time after removal of the compressive load (5-15 minutes)
73
What are the three most common deficiencies of provisionals?
1. Exothermic 2. Polymerization shrinkage 3. Color degradation over time
74
What is the degree of a sloped shoulder margin of a PFM facial aspect of an anterior tooth?
120 degrees, with a 1.2mm reduction.
75
Why don't you completely desiccate the tooth when placing a retraction cord?
Induces post-operative sensitivity
76
What does increased axial surface area do to retention?
It increases it
77
How does reversible hydrocolloid differ from elastomeric impression material when it comes to accuracy and bulk?
The accuracy of a reversible hydrocolloid impression is improved if the material has as much bulk as possible (low surface area/volume ratio). This contrasts with the elastomeric impression materials, whose accuracy is improved by minimizing bulk (e.g., polysulfide and condensation silicone), because stresses produced during removal are reduced. Therefore, an additional advantage of reversible hydrocolloid is that a custom impression tray is not required.
78
What are the reduction dimensions for the facial chamfer, lingual concavity, and lingual chamfer on an anterior PFM?
• Facial Chamfer 1.2 mm • Lingual Concavity 1.0 mm (metal lingual) 1.5 mm (porcelain lingual) • Lingual Chamfer 0.5 – 1.0 mm
79
What are the five blueprints for excellent impressions?
Adequate Moisture Control • Maintain Visibility & Accessibility • Good Soft Tissue Management • Proper Use of Appropriate Impression Material • Proper Care of the Impression
80
What is the advantage of polyether over polysulfide base?
Polyether is very accurate and stable while polysulfide is only accurate
81
What is the ideal clearance for a posterior PFM with porcelain covering the occlusal, both non and functional cusp?
2 mm at least, everywhere
82
What is the most hydrophillic elastomeric impression material?
The ether-dominated polymer backbones make Polyethers the most hydrophilic of the elastomeric impression materials -Has low, medium, and high viscosities.
83
What is cellulose acetate?
It is for interim restorations and it is a clear preformed shell used.
84
When does the colloid phase change occur with reversible hydrocolloids?
Colloid phase change occurs with temperature change. These are made of Agar-agar 12-15% (Brown seaweed extract, also in many ice creams) Water: 85% ! Modifiers:
85
What are the characteristics of PIMA?
Poly-isobutylmethacrolate. This is a thicker material that is a putty, great for porcelain veneer temporaries.
86
What is the concept of centrum?
Cusp tip touching on flat receiving area
87
We talked about tissue management and cords and stuff, what to do with them?
Leave them in when we do an impression
88
What is the scientific term for stiffness?
Modulus of elasticity
89
What are the numbers needed for custom trays?
Resin thicknesses of 2 to 3 mm are needed for adequate rigidity. Clearance between the tray and the teeth should also be 2 to 3 mm; however, greater clearance is necessary for the more rigid polyether materials. The completed custom tray (Fig. 14-18O) needs to be rigid, with a consistent thickness of 2 to 3 mm. It should extend about 3 to 5 mm cervical to the gingival margins and should be shaped to allow muscle attachments. It should be stable on the cast with stops that can maintain an impression thickness of 2 or 3 mm. The tray must be smooth, with no sharp edges. Finally, the handle should be sturdy and shaped to fit between the patient’s lips (Fig. 14-26). To avoid distortion from continued polymeriza-ion of the resin,56 the tray should be made at least 9 hours before its use. When a tray is needed more urgently, it can be placed in boiling water for 5 minutes and allowed to cool to room temperature. A light-polymerized tray can also be made.
90
What is the main function of interim luting agent?
The primary function of the interim luting agent is to provide a seal, preventing marginal leakage and hence pulp irritation. Unintentional displacement of an interim restoration is frequently caused by a nonretentive tooth preparation or excessive cement space rather than the choice of luting agent.
91
What are the numbers for gold reductions?
1.5 functional cusp reduction and bevel, non-functional is 1, bevel on non-functional is 0.3-0.7 mm
92
Why is an irregular crown margin not desirable?
You have a longer margin, harder to read it, basically it.
93
What is Urethane DMA mainly used for?
Good for all-ceramic provisionals (Triad)
94
What are the main six contraindications to occlusal adjustment?
1. A bruxer whose habit cannot be controlled. 2. A diagnostic correction that indicates that too much tooth structure will be removed. 3. A complex spatial relationship (e.g., an Angle Class II and a skeletal Class III). 4. Maxillary lingual cusps contacting mandibular buccal cusps. 5. An open anterior occlusal relationship. 6. Excessive wear. (((He doesn't agree with 3-6))))))))!!!!!!!! 7. Before orthodontic or orthognathic treatment. 8. Before physical or occlusal appliance therapy. 9. A patient with temporomandibular joint pain. 10. A patient whose jaw movements cannot be manipulated easily.
95
The ideal depth for a lingual axial chamfer for an anterior pfm is?
0.5-1 mm
96
What is the name of the flapship polyether that some people love, including his brother?
Impregum
97
The prime advantage of vacuum firing porcelain is?
To increase strength
98
What are the three acrylic materials?
PMMA, PEMA, PIMA
99
What does sodium phosphate do in impression material?
It is a retarder, controls set time
100
What is a by-product of the condensation setting reaction of condensation silicone?
Ethyl alcohol is a by-product of this condensation setting reaction.
101
An decrease in temperature accelerates the setting time for all elastomeric impression materials. True or False?
False, opposite, an increase in temp accelerates.
102
What is agar-agar primarily composed of?
Alginic acid
103
What is the ideal minimum thickness of metal for a PFM?
0.3 mm
104
Where is the best place to start around the tooth when placing a retraction cord?
It is best to start in the interproximal area (Fig. 14-6D), because the cord can be placed more easily there than facially or lingually.
105
What is working time?
Working time begins when mixing is started, and ends immediately before elastic properties develop
106
What should the minimal incisal reduction of an anterior PFM be?
2.0-2.5 mm. ALLOWS FOR PROPER PORCELAIN TRANSLUCENCY. 1.7 – 2.2 MM FOR PORCELAIN AND 0.3 – 0.5 MM FOR METAL. PARALLEL TO INCISAL EDGE. PERPENDICULAR TO THE DIRECTION OF LOADING OF THE MANDIBULAR ANTERIOR TEETH.
107
How many appointments does an amalgam build-up take?
2, unless using high copper alloy
108
What are stock impression trays NOT used for?
Not for conventional multi-unit fixed, implant, or removable final impressions. Custom trays are more ideal for these ones.
109
How much weaker is a provisional restoration made of PMMA from a full crown?
The strength of polymethyl methacrylate resin is about one-twentieth that of metal-ceramic alloys,5 which makes fracture of the interim fixed restoration much more likely.
110
What is anti-deformation form?
Prevents dislodgement of restoration due to permanent deformation (bending) of restoration during function.
111
When would you use a cast metal interim restoration?
A long-span posterior partial fixed dental prosthesis Prolonged treatment time Patient’s inability to avoid excessive forces on the prosthesis Above-average masticatory muscle strength History of frequent breakage
112
How close or tight with the best techniques can you bring a margin of the casting to the tooth?
10 microns
113
What various methods are marketed to maintain the stability of hydrocolloid impressions?
For this reason, various media such as 2% potassium chloride solutions or humidors are marketed to maintain the stability of hydrocolloid impressions ! Best method is to either wrap in moist towel or disinfect in plastic bag for 8 – 10 minutes, then pour immediately
114
What is the only best use for condensation silicone?
For silicone matrices.
115
When would you do an onlay vs inlay?
-If your preparation is more than a third of the distance between the buccal and lingual cusp tips, then you would do an onlay.
116
Which third of the facial axial wall is the lingual axial wall lined up with on an anterior PFM?
With the gingival 1/3rd
117
What are thermoplastic sheets (bleach tray material) for interim restorations made out of?
Polypropylene
118
Which provisional material exhibits the least polymerization shrinkage?
Microfilled Bis-GMA and Urethane DMA
119
What do definitive axial angles (not rounded) do to resistance?
Increases it
120
What are the factors influencing retention?
! Magnitude of the Dislodging Forces ! Geometry of the Tooth Preparation ! Roughness of Intaglio Surface of Fixed Restoration ! Material being Cemented or Bonded
121
When do dental casts reach their maximum strength?
At around 24 hours
122
Several byproducts are given off with the polyether polymerization reaction?
False, none are, which is an advantage
123
When is a sub-gingival margin placement necessary?
Occluso-gingival height of preparation (less than 3 mm) Caries extending sub-gingivally Existing restoration extending sub-gingivally Necessary for esthetics (only if anterior porcelain, not gold)
124
What is the phase change that occurs as the reversible hydrocolloid is cooled?
Sol to gel. ! Impression tray is inserted into the mouth during the sol phase. The gel phase is the elastic, set phase of the material.
125
Which provisional material is most expensive?
Cast metal
126
What do proximal grooves and boxes do to resistance?
Increases it
127
When is an electrosurgery unit used?
An electrosurgery unit15—18 (Fig. 14-9A) may be used for minor tissue removal before impression making. -In one technique,19 the inner epithelial lining of the gingival sulcus is removed, thus improving access for a subgingival crown margin (see Fig. 14-9B to F) and effectively controlling postsurgical hemorrhage20 (provided that the tissues are not inflamed). Unfor- tunately, there is the potential for gingival tissue recession after treatment.21 An electrosurgery unit works by passage of a high-frequency current (1 to 4 million Hz\*) through the tissue from a large electrode to a small one. At the small electrode, the current induces rapid localized polarity changes that cause cell breakdown (“cutting”). For restorative procedures, an unmodulated alternating current is recommended, because it minimizes damage to deeper tissues.
128
What does silicone and polysulfide give off from their polymerization reactions?
Silicone and polysulfide have a dimensional instability that results from their mode of polymerization. Both are condensation polymers, which, as a byproduct of their polymerization reactions, give off alcohol and water, respectively.
129
An impression material with a higher elastic limit should exhibit more permanent deformation. True or False?
False. An impression material with a higher elastic limit should exhibit less permanent deformation. A permanent deformation of 1% has an elastic recovery of 99%.
130
What are the main three PMMA characteristics?
PMMA exhibits greatest polymerization shrinkage Exhibits highest exotherm light cured formulation helps overcome both shrinkage and exothermic deficiency
131
What are the main temporary cements?
-Zinc Oxide and eugenol -Non-zinc oxide and eugenol -Bis-GMA resin -Polycarboxylate
132
What is composed of potassium salts of alginic acid?
Alginate
133
What does increased Preparation Diameter do to resistance?
Decreases it
134
How much space is there between the tray and teeth during alginate impression?
The space between the tray and the teeth allows for 4 – 5 mm of alginate material
135
What are the steps of a direct technique for provisionals?
-Create Matrix -Insert matrix containing un-polymerized material onto prepared tooth -Cure material, but do not lock polymerized material into proximal undercuts -Trim, adjust, polish
136
What is the double-cord technique for gingival displacement?
With this technique, a thin cord is placed without overlap at the bottom of the gingival crevice. A second cord is placed on top to achieve lateral tissue displacement. The latter is removed immediately before impression making, whereas the initial cord is left in place to help minimize seepage.
137
How does a custom tray improve the accuracy of an elastomeric impression?
A custom tray improves the accuracy50 of an elas- tomeric impression by limiting the volume of the material, thus reducing two sources of error: stresses during removal and thermal contraction. Although reducing the bulk of an elastomeric impression material increases its accuracy, the opposite is true for reversible hydrocolloid impressions. In hydrocol- loid impressions, dimensional change is caused by water loss (or gain) from the surface of the impres- sion. A bulky hydrocolloid impression has a lower surface area/volume ratio and is therefore less subject to dimensional change.
138
What is Microfilled Bisphenol A diglycidylether resin?
Bis-GMA resin, paste-paste, dual cure
139
Which acrylic exhibits the highest exotherm?
PMMA
140
What two things are often used to help separate provisional material to a tooth?
Petrolatum and Mineral Oil
141
What are the main advantages to indirect interim restorations over direct?
1. There is no contact of free monomer with the pre- pared tooth or gingiva, which might cause tissue damage11 and an allergic reaction or sensitiza- tion. 2. The procedure avoids subjecting a prepared tooth to the heat evolved from polymerizing resin. 3. The marginal fit of interim restorations that have been polymerized undisturbed on stone casts is significantly better than that of interim restora- tions that have been removed from the mouth before becoming rigid. 4. When a dimensionally stable elastomer impres- sion is made to form the TSF,10 it can be retained for possible reuse with the ESF. This allows replacement restorations to be made without having the patient present. 5. The technique gives the patient a chance to rest, and it frees the dentist to perform other tasks, pro- vided that an auxiliary is trained to carry out the laboratory procedures.
142
What are the steps of an indirect technique for provisionals?
-Create matrix -Insert matrix containing un-polymerized material onto prepared tooth -Allow material to completely polymerize under pressure in warm water -Separate from cast -Trim, adjust, polish
143
What does retention form mean?
Prevents dislodgement of restoration parallel to path of insertion.
144
What are stainless steel crowns made of?
Nickel-Chromium
145
What is the cheapest elastomer?
Polysulfide, but it stinks, takes 10 min to set in mouth, can stain because of a metal.
146
How much space should be left between cord and tooth when taking impression with double-cord technique?
The thin first cord remains during impression making. In order to be successful, this technique requires that about 1 mm of intact tooth structure remains between the top of the initial cord and the preparation margin.
147
What are the two best methods for removing carious dentin?
A large round bur and a slow speed hand-piece and hand excavation.
148
A patient is unhappy with the esthetics of an anterior metal-ceramic crown, complaining that it looks too opaque in the incisal third. The reason for this is most likely...?
A. Using the incorrect opaque porcelain shade B. Inadequate vacuum during porcelain firing C. Not masking the metal well enough with the opaque D. The tooth was prepared in a single facial plane D is the answer.
149
What is the most retentive near-term cement?
Adhesive resin, the least is zinc-oxide eugenol. Same applies for resistance
150
What is the occlusal reduction dimensions for a posterior PFM? Axial reduction?
2 mm for everything. 1.2-1.7 mm for axial reduction.
151
What are the three main noble metals, and what is silver?
-Gold, platinum, palladium are noble, and silver is a precious
152
One of the ways grooves and boxes improves resistance is by?
Subjecting additional luting agent areas to compression forces on cement. If you increase tension forces on cement, it will decrease resistance. You want to increase compression forces, that is the answer.
153
What are the advantages to PFM's?
! Similar to “Indications” list, plus... ! Retention and resistance qualities can be excellent because all axial walls are included in the preparation ! Permits easy correction of axial form ! Also can be useful in making alterations to occlusal form ! Preparation is often less demanding on the operator than partial coverage options
154
What is the silicone technique involving putty material used to customize a stock impression tray?
Silicone impression material is available in a variety of viscosities. One technique involves a heavily filled putty material that is used to customize a stock impression tray in the mouth, generally with a polyethylene spacer. The spacer allows room for a thin wash of light-bodied material, which makes the impression. The tech- nique requires considerable care in seating, however, to prevent strain in the set putty. If this happens, the impression rebounds when removed from the mouth, which results in dies that are too small.
155
What is light cured PMMA mainly used for?
Routine use in single and small (2-3) multiple unit situations
156
Which material has the most natural look out of all of them for interim restorations?
Polycarbonate
157
What does decreased preparation height due to retention?
It decreases it
158
What happens to the non-functional cusp bevel as you go more anterior with teeth on maxillary teeth, and on mandibular?
-The non-functional cusp bevel as you go more anterior teeth, gets longer and more in line with the long axis of the tooth, on maxillary, and on mandibular, it is the functional cusp bevel.
159
What are the steps of an indirect-direct technique for provisionals?
-Create matrix -Insert matrix containing un-polymerized material onto prepared tooth -Allow material to completely polymerize under pressure in warm water -Separate from cast -Trim, adjust -Reline with more of the same material intraorally -Trim, adjust, polish
160
What is the difference between dimensional accuracy and dimensional stability?
DIMENSIONAL ACCURACY: Lack of dimensional change during setting, and shortly after removal from the mouth DIMENSIONAL STABILITY: Lack of dimensional change over time
161
How is irreversible hydrocolloid material best removed?
By snapping
162
How long to wait after taking impression of alginate before pouring up?
10 minutes, to allow for elastic recovery.
163
What are the three forms of mechanical considerations?
1. Retention, 2. Resistance 3. Anti-deformation
164
Irreversible hydrocolloid is not sufficiently accurate for cast restorations. True or False?
True. But can be used for diagnostic casts, just not definitive.
165
Which provisional material is the most brittle and difficult to repair?
Microfilled Bis-GMA
166
What is the sol to gel reaction with alginate?
! Forms Sol when powder is first added to water ! As the alginic acid becomes cross- linked via the calcium ions, the gel is formed (This is the set material.)
167
What percent of tooth fractures overall involve the pulp?
5-10 %
168
Profound anesthesia is mandatory for electrosurgery techniques. True or False?
True
169
What is set time?
Set time is defined as the time from the beginning of mixing until the impression can be removed from the mouth with no distortion
170
What are the three principles of tooth preparation?
Biologic, Mechanical, Esthetic
171
What is the name for addition silicones and what are they made up of?
PVS, or VPS, Polyvinylsiloxane. - The base paste consists of polymethylhydrosiloxane, divinylpolysiloxane and a filler - The accelerator paste contains divinylpolysiloxane and a platinum salt catalyst - The setting reaction is based upon the addition polymerization between divinylpolysiloxane and polymethylhydrosiloxane - Historically, some addition silicone products were found to release H2 gas as a by-product ! Most now employ a scavenger such as palladium which absorbs H2 gas - H2 gas can create bubbles in stone if impression is poured too soon - Best to simply avoid addition silicones that realease H2 gas - Can be used with implants
172
What is the biologic width?
Biologic width is the distance established by "the junctional epithelium and connective tissue attachment to the root surface" of a tooth.[1] In other words, it is the height between the deepest point of the gingival sulcus and the alveolar bone crest. This distance is important to consider when fabricating dental restorations, because they must respect the natural architecture of the gingival attachment if harmful consequences are to be avoided. The biologic width is patient specific and may vary anywhere from 0.75-4.3 mm. Should be about 1:2 ratio
173
How can addition silicones become more hydrophillic?
Some formulations contain surfactants, which give them hydrophilic properties,45 imparting wettability similar to that of the poly- ethers.46 However, these products also expand like polyether when in contact with moisture.47 Addition silicone is generally used as a two-viscosity system, although monophase formulations are also available. It is easier to trap bubbles when the monophase formulation is used.
174
Diagnostic tooth preparation, if you re doing one, they are done before the final impression, they can be helpful when contemplating making changes in axial inclination, occlusion, and used in conjunction with diagnostic wax up. What is the only wrong option for this question?
The only wrong one is that they are not done after the preparation on the actual tooth.
