au13_-_operative_final_exam_20141210194839 Flashcards
(224 cards)
1
Q
What is the definition of caries?
A
the demineralization and subsequent cavitation of tooth structure
2
Q
What is the goal of restorative dentistry?
A
carefully remove the diseased tissue (cavity) in a precise manner and replace the missing part with restorative material
3
Q
What are the 3 most common areas in which cavities occur?
A
- occlusal pits and fissures of posterior teeth- interproximal areas (between teeth below contact area)- smooth surfaces of facial and lingual surfaces
4
Q
Where is a Class I prep located?
A
pit and fissure preps- occlusal surfaces of premolars and molars- occlusal 2/3 of facial and lingual surfaces of molars- lingual surfaces of maxillary incisors
5
Q
Where is a Class II prep located?
A
proximal surfaces of posterior teeth
6
Q
Where is a Class III prep located?
A
proximal surfaces of anterior teeth that do not include the incisal angle
7
Q
Where is a Class IV prep located?
A
proximal surfaces of anterior teeth that include the incisal edge
8
Q
Where is a Class V prep located?
A
the gingival third of the facial or lingual surfaces of all teeth
9
Q
Where is a Class VI prep located?
A
on the incisal edges of anterior teeth or occlusal cusp tips of posterior teeth
10
Q
What are the 3 types of powered cutting equipment?
A
- rotary (routinely used since 1960s)- laser (recent FDA approval for preparing teeth)- air abrasion
11
Q
Which handpiece (high or slow speed) sprays water coolant to avoid tooth damage by heat?
A
high speed
12
Q
Is a high speed handpiece angled or straight? A low speed handpiece?
A
- high speed - angled- low speed - angled or straight
13
Q
What metal makes up a bur?
A
carbide steel (stiff, strong, and brittle)
14
Q
What are the 3 anatomical parts of a bur?
A
- head - cutting portion of bur- neck - connects head to shank- shank - part of the bur that inserts into instrument
15
Q
What are the 5 shapes of a bur head?
A
- round- inverted cone- straight fissure- tapered fissure- pear
16
Q
How many flutes are found in a standard carbide bur? How many in a finishing carbide bur?
A
- 6 flutes in a standard- 10, 12, 20, 30 in a finishing bur (more flutes = smoother finish)
17
Q
What is the purpose of the shank of the bur?
A
controls the alignment and concentricity
18
Q
What are the 3 types of shanks?
A
- friction-grip- latch-type- straight
19
Q
Of the 4 types of diamond grits for diamond burs (coarse, medium, fine, and very fine), which are the most efficient? Which are the least efficient?
A
- most efficient = coarse- least efficient = very fine
20
Q
What are the 2 cutting mechanisms of diamonds and burs?
A
- ductile fracture- brittle fracture
21
Q
Which type of fracture has deformation produced by shear forces?
A
ductile fracture
22
Q
Which type of fracture is associated with crack production from tensile loading?
A
brittle fracture
23
Q
Which type of cutting (bur or abrasive) is more efficient for cutting brittle materials like enamel?
A
abrasive cutting
24
Q
Which type of cutting (bur or abrasive) is more efficient for cutting ductile materials like dentin?
A
bladed or bur cutting
25
What speed (high or low speed) is used for abrasive cutting?
high speed
26
What speed (high or low speed) is used for bladed or bur cutting?
high and low speed
27
What is a round bur used for?
- initial enamel penetration- caries removal- retentive grooves and holes
28
What is an inverted cone bur used for?
providing an undercut in a preparation
29
What is a straight fissure bur used for?
- straight walls- flat floors
30
What is a tapered fissure bur used for?
straight but tapered walls
31
What is a pear bur used for?
similar to inverted cone undercuts but has rounded ends and a longer head
32
What are 5 precautions that need to be taken into consideration when using a high-speed handpiece?
- damage to tooth from heat (need to use a coolant with vital teeth)- damage to soft tissue from lack of control- eye protection (safety glasses)- inhalation precautions (mask)- ear protection (plugs)
33
What is the difference between the primary and secondary cutting edge of a hand cutting instrument?
- primary cutting edge - edge that performs the most cutting (the edge of a hatchet that would scrape the pulpal floor)- secondary cutting edge - edge that also performs some cutting (the edges of the hatchet that would scrape the vertical walls of the prep)
34
In an instrument formula with 3 numbers, what does each of the numbers represent?
- 1st number - width of the blade in 10ths of a mm- 2nd number - blade length in mm- 3rd number - blade angle relative to long axis in centigrade
35
In an instrument formula with 4 numbers, what does each of the numbers represent?
- 1st number - width of the blade in 10ths of a mm- 2nd number - primary cutting edge angle in centigrade (*different than with 3 numbers)- 3rd number - blade length in mm- 4th number - blade angle relative to long axis in centigrade
36
What is the difference between a chisel and a hoe?
- chisel - used to push; less than 12.5 degrees- hoe - used to pull; greater than 12.5 degrees
37
What are the 3 characteristics that are used to categorize caries? What are the two subtypes of each characteristic?
- location - primary or secondary (recurrent) caries- extent - incipient (reversible) caries or cavitated (irreversible) caries- rate - acute (rampant) caries or chronic (slow or arrested) caries
38
What are the 3 morphologic types of caries observed clinically?
- lesions originating in enamel pits and fissures- lesions originating on enamel smooth surfaces- lesions originating on root surfaces
39
What is the definition of tooth preparation?
mechanical alteration of a defective, injured, or diseased tooth such that placement of a restorative material re-establishes normal form and function
40
What is the difference between an internal and external wall?
- internal wall - a prepared surface that does not extend to the external tooth structure- external wall - prepared surface that extends to the external tooth surface and takes the name of the surface it is adjacent to
41
Is a facial wall an internal or external wall?
external
42
Is the axial wall an internal or external wall?
internal
43
Is the mesial wall an internal or external wall?
external
44
Is the pulpal floor an internal or external wall?
internal
45
What is the definition of the cavosurface margin?
junction of a prepared wall with the uncut tooth surface
46
What is the difference between conventional preparations and modified preparations?
- conventional preparations - precise preparations resulting in uniform depths and particular wall and marginal forms- modified preparation - without specific depths, particular wall designs or retentive features
47
What type of restoration uses conventional preparations? What type uses modified preparations?
- amalgam uses conventional- composite uses modified
48
What are the 4 forms that make up the principles of cavity preparation?
- outline form- retention form- resistance form- convenience form
49
What is outline form?
- conservative preparation- margins on sound enamel- include defective enamel (pits and fissures)- depends on carious lesion or previous restoration
50
What is retention form?
features that lock or retain the amalgam in the tooth
51
What is resistance form for the tooth prep?
features that prevent the enamel from fracturing as a result of occlusal forces
52
How is retention form seen in Class I preps?
slight occlusal convergence of prepared facial and lingual walls
53
How is resistance from seen in Class I preps?
- preservation of cusps and marginal ridges- pulpal floor flat and perpendicular to occlusal forces- rounded internal preparation angles- removing unsupported tooth structure- divergence of mesial and distal prepared walls
54
What is resistance form in the amalgam?
features that help the amalgam resist fracture and wear under function
55
How thick should amalgam be in a restoration? How far into the dentin?
1.5-2 mm (adequate depth of pulpal floor) which should be 0.5 mm in dentin
56
Between what angles should the tooth prep be on the buccal and lingual walls for the resistance form of the amalgam?
80-100 degrees with an ideal angle of 90 degrees
57
What is convenience form? What are some examples?
preparation features that make the area more accessible or the procedure easier- extension of walls to provide greater access for caries removal- extension of walls to ensure the preparation is wide enough to fit the smallest condenser to ensure adequate condensation of amalgam
58
What makes up the armamentarium of tooth preparation?
- mouth mirror- pig-tail and sickle explorer- periodontal probe- small and large spoon excavator- 8-9 hatchet- cotton pliers- marginal trimmers #28 and #29- miller forceps- articulating paper- high/low-speed handpieces- burs #330, 245, 169, and 256
59
What is the appearance of a #330 bur?
pear-shaped, normal length
60
What is the appearance of a #245 bur?
pear-shaped, elongated
61
What is the appearance of a #169 bur?
tapered fissure
62
What is the appearance of a #256 bur?
straight fissure
63
What is a #245 bur generally used for?
proximal box formation in a Class II cavity preparation
64
Which bur is recommended for most conservative amalgam preparations?
#330 bur
65
What is the length and diameter of a #330 bur?
1.5 mm in length of cutting edge and 0.80 diameter at the tip
66
True or false: During a preparation of a tooth, the angle of the bur should be parallel to the long axis of the tooth.
true (mandibular teeth are lingually tilted so the bur must also be angled)
67
Should light, short strokes or long, heavy strokes be used while preping a tooth?
light, short strokes
68
When prepping a tooth, should you move mesial to distal or distal to mesial?
distal to mesial
69
In comparison to the length of a #330 bur, how deep should the pulp floor depth be? A #245 bur?
- full length of a #330 bur (1.5 mm)- half of the length of a #245 bur
70
Why should the mesial and distal walls diverge?
to maintain resistance form by conserving the ridge supporting dentin
71
True or false: The shape of a Class I prep is butterfly or dog-bone shaped.
true
72
How deep should the axial wall depth be in a buccal or lingual extension?
1.5-2.0 mm (0.2-0.5 mm into dentin)
73
How fast does a high speed handpiece rotate (in rotations per minute)?
200,000 rpm and above
74
How fast does a low speed handpiece rotate (in rotations per minute)?
12,000 rpm and below
75
Other than high, medium, and low speed handpieces, what are two alternative pieces of power equipment that can be used for removal of tooth tissue?
laser equipment and air-abrasion unit
76
How does laser equipment work? What are some of the drawbacks?
produce beams of coherent and very high intensity light- currently expensive- high amount of heat generated- inefficient at removing large amounts of tooth structure- special safety precautions required
77
How does air-abrasion work?
transfer of kinetic energy from a stream of powder particles onto tooth surface or a restoration, producing a fractured surface layer which results in roughness for bonding or disruption for cutting
78
On a bur, what is the name of the side of the blade towards which the bur is cutting?
rake face
79
On a bur, what is the name of the side of the blade away from which the bur is cutting?
clearance face
80
On a bur, what is the name of the angle between the rake face and the radius of the head diameter?
rake angle
81
What does a negative rake angle do?
minimizes fractures of the cutting edge, increasing tool life
82
What is the most important design characteristic of a bur blade?
rake angle
83
On a bur, what is the name of the angle between the rake face and the clearance face?
edge angle
84
What does increasing the edge angle do?
reinforces the cutting edge and reduces likelihood for fracture of the blade's edge
85
On a bur, what is the name of the angle between the clearance face and the tooth surface?
clearance angle
86
What type of rake angles, edge angles, and clearance angles does a carbide bur normally have?
- slightly negative rake angles- edge angles of approximately 90 degrees- low clearance angles
87
What are the 3 components of diamond burs?
- metal blank - resembles a bur without blades (head, neck, and shank)- powdered diamond abrasive- metallic bonding material
88
What are the two universal types of grasps used when holding hand instruments?
- modified pen grasp- inverted pen grasp
89
What are the goals of a rubber dam?
- moisture control- retraction and access- patient safety- increase operator efficiency
90
What are the advantages of rubber dam isolation?
- dry, clean operating field- improved access and visibility- patient protection- increased operating efficiency- improved properties of dental materials
91
What are the disadvantages of rubber dam isolation?
- time consuming- patient objection- interferes with access
92
What are the two types of rubber dam retainers/clamps?
- winged clamp- anterior clamp
93
What are the 4 parts of a rubber dam retainer/clamp?
- bow- hole- jaw- prong
94
True or false: Rubber dam should be passed between interproximal contacts.
true
95
True or false: The rubber dam should not go into the gingival sulcus on the facial and lingual surface of teeth.
FALSE. The rubber dam should be inverted into the gingival sulcus around the teeth.
96
Describe the steps of the removal of a rubber dam.
- cut the septa- remove the retainer/clamp- remove the rubber dam/frame- examine the rubber dam for any missing pieces- remove any torn pieces from the patient's mouth
97
True or false: Sharp angles should be made in occlusal outline of a Class II tooth prep.
FALSE. Sharp angles should be avoided in the occlusal outline.
98
Why is it bad to have a wide isthmus?
the triangular ridges of the cusps would be removed and the cusps would be weaker
99
How deep should the occlusal prep of a Class II tooth prep be?
1.5-2.0 mm
100
The occlusal prep of a Class II tooth prep should be perpendicular to the long axis of the tooth in every mandibular posterior tooth except which tooth?
mandibular 1st premolar (because the non-functional cusp makes the crown tilt severely to the lingual)
101
How wide should the isthmus of an occlusal prep be?
1.0 mm
102
What should the bur orientation be parallel to? What should it be perpendicular to?
- parallel to the long axis of the tooth- perpendicular to the occlusal table
103
What does the location of the proximal box depend on?
the location of the interproximal contacts
104
How deep should the proximal box extend?
2.5-3.0 mm
105
How high should the axial wall be?
1.0 mm
106
What instrument should remove "crab claws" from a proximal box so as not to damage the adjacent tooth?
large spoon
107
What instruments are used to refine proximal box walls?
- 10-7-14 (#8-9 hatchet)- #169 bur
108
What is used to bevel the enamel portion of the gingival wall?
enamel margin trimmer
109
What is used to bevel the axiopulpal line angle?
gingival margin trimmer
110
How much space should be between the buccal and lingual edges of the proximal box and the adjacent tooth?
0.2-0.3 mm
111
How much space should be between the gingival edge of the proximal box and the adjacent tooth?
0.5 mm
112
Does the proximal box converge or diverge occlusally?
converges occlusally as a retentive feature
113
What two burs are used to place retention grooves?
- #169 bur- 1/4 round bur
114
When prepping an occlusal outline, should it be done meisal to distal or distal to mesial?
distal to mesial
115
With what bur is the occlusal outline usually prepped?
#330 bur
116
With what bur is the proximal box usually formed?
#245 bur
117
With what bur is the proximal box usually refined?
#169 bur
118
True or false: The final clearance of the proximal box should be checked with the wedge in place.
FALSE. The wedge should be removed prior to checking the final clearance.
119
With what burs is a slow-speed used to refine the occlusal outline?
#256 or #245 bur
120
List the 9 steps of tooth preparation.
1. outline form and initial depth2. primary resistance form3. primary retention form4. convenience form5. remove any remaining defective tooth or materials6. pulp protection7. secondary resistance and retention form8. finish external walls9. cleaning and sealing the preparation
121
Explain what is done during the 1st step in tooth preparation: outline form and initial depth.
- margins are placed where they will be in the final prep (preop visualization)- ideal placement- extend for decay
122
In order to gauge buccal and lingual clearance of the proximal box, what 4 instruments may be used? Which is closest to the correct measurement of 0.5 mm?
- perioprobe = 0.5 mm- shepard hook explorer = 0.76 mm- #8/9 hatchet = 0.6 mm- pig tail explorer = 0.5 mm
123
Explain the purpose of the primary resistance form (step 2 of tooth preparation). How is this achieved in tooth preparation?
a shape that enables tooth and restorative materials to resist vertical forces in long axis of tooth- flat floor- flat walls- rounded internal line angles- thickness of material- cap weak cusps
124
Explain the purpose of primary retention form (step 3 of tooth preparation). How is this achieved?
resistance to tipping or lifting forces- converging walls of box and isthmus
125
Explain the purpose of convenience form (step 4 of tooth preparation). How is this achieved?
shape or form that provides for adequate observation and accessibility- proximal extensions or clearance
126
At what angle should the cavosurface margin be with the external walls of the prep at the edge of the box? In the occlusal outline? At the gingival edge of the proximal box?
- 90 degrees at the edges of the box (no "crab claws")- 100 degrees or greater at the occlusal margins- sloped gingival margin
127
Describe the shape of the occlusal outline form of a maxillary molar when performing a DO or MO tooth prep. Does the occlusal prep go through the oblique ridge?
the prep only extends up until the oblique ridge (it does NOT cross the oblique ridge!)
128
Describe the shape of the occlusal outline form of a maxillary molar when performing a MOD tooth prep. Does the occlusal prep go through the oblique ridge?
the prep only extends up until the oblique ridge on either side so it preserves the oblique ridge
129
Describe the shape of the occlusal outline form of a maxillary molar when performing a OL extension tooth prep.
the extension into the lingual groove leaves the distolingual cusp weak so the cusp is usually taken out too and capped, hooded, overlayed, or onlayed with restorative material
130
If the mouth was divided into a sextant, how many sections would there be and name their location.
- 6 sections- maxillary left, right, and anterior- mandibular left, right, and anterior
131
What is quadrant dentistry?
treating all of the affected teeth in 1 quadrant/sextant during the same visit as opposed to 1 tooth at a time
132
What are the advantages of quadrant dentistry?
- less number of appointments for patient- less discomfort for patient- more efficient and productive for dentist
133
What are the disadvantages of quadrant dentistry?
- increased chairside time- does not follow the ideal treatment sequence (3 phases: get the patient out of pain, remove caries, and then restorative care)
134
What are some reasons to perform (indications) quadrant dentistry?
- adjacent interproximal caries ("kissing caries)- multiple faulty restorations- pediatric dentistry- medically compromised patients
135
What are some reasons not to perform (contraindications) quadrant dentistry?
- lack of dental experience- patient who have TMJ dysfunction syndrome- patients who cannot stay in a reclined position for a long time
136
What is the formula of a low-copper amalgam?
Ag3Sn (gamma) + Hg --> Ag2Hg3(gamma1) + Sn7-8Hg(gamma2) + Ag3Sn (unreacted gamma)
137
What is the weakest phase of low-copper amalgam?
gamma2
138
What is the most corrosion-prone phase in low-copper amalgam?
gamma2
139
Which type of amalgam (high or low copper) has high creep? Why?
low-copper because gamma2 doesn't prevent gamma1 from sliding
140
What is creep?
the tendency of a solid material to flow or permanently deform under constant cyclic loading over time
141
What percentage of copper is considered a low-copper amalgam? A high-copper amalgam?
- low-copper amalgam = 6% Cu
142
What is the difference in phases between high-copper and low-copper amalgams?
high-copper amalgam has a n' phase of Cu6Sn5 so there is no gamma2
143
What is the composition of gamma?
Ag3Sn
144
What is the composition of gamma1?
Ag2Hg3
145
What is the composition of gamma2?
Sn7-8Hg
146
What is the composition of n'?
Cu6Sn5
147
What are the two types of high-copper amalgams?
- admixed alloy (lathe-cut and spherical)- unicompositional (spherical)
148
What is the difference in the reaction formula of admixed alloy and unicompositional high-copper amalgams?
- admixed alloy has two steps: first step in which gamma2 forms and then second step in which n' forms so no gamma2 is left- unicompositional is only one step in which n' forms (in addition to gamma1)
149
How is creep minimized in high-copper amalgam?
the n' phase prevents the sliding of gamma1 to minimize creep and marginal breakdown
150
Which amalgam particle shape (lathe-cut or spherical) requires less condensation forces since it has looser contact?
spherical
151
Which amalgam particle shape (lathe-cut or spherical) has a low packing density with more spaces?
lathe-cut
152
Which amalgam particle shape (lathe-cut or spherical) has a higher surface area so more Hg and more expansion?
lathe-cut
153
Which amalgam particle shape (lathe-cut or spherical) packs more efficiently and slides easier to make less voids and higher strength?
spherical
154
Which amalgam particle shape (lathe-cut or spherical) is difficult to achieve proximal contact?
spherical
155
Which amalgam particle shape (lathe-cut or spherical) requires a large diameter condenser for proper condensation?
spherical
156
What type of amalgam is used at OSU? Describe it.
- Permite C- high-copper amalgam- admix type (spherical and lathe-cut)- zinc-containing (0.2%)
157
What is the problem with zinc-containing amalgams?
if moisture contaminates, it will cause delayed expansion
158
What is the difference between direct and indirect restorations?
- direct restorations are placed directly in the oral cavity as a soft plastic material to build lost structure before they set hard- indirect restorations are fabricated outside the oral cavity (like crowns)
159
True or false: A rubber dam is not necessary in quadrant dentistry.
FALSE. A rubber dam is a prerequisite of quadrant dentistry.
160
What should you do if you have multiple adjacent Class II preps when performing quadrant dentistry?
restore two non-adjacent teeth first and then do the teeth in between
161
When doing a back-to-back Class II amalgam restoration in quadrant dentistry, what are the two methods you could use? Which is recommended?
- Method 1: band and restore the Class II preps simultaneously- Method 2: band and restore each tooth separately, one preparation at a time starting with the most posterior tooth- Method 2 is recommended.
162
What is flash?
when excess amalgam is covering the cavosurface margin
163
What is the definition of submarginal in amalgam restorations?
the amalgam doesn't reach the cavosurface margin
164
What is the definition of an open margin in amalgam restorations?
the amalgam is at the right height with the cavosurface margin except right at the edge of the restoration where a chunk is missing
165
What are the steps of an amalgam restoration?
- activation- trituration- placement- condensation- carving- finishing- polishing
166
What are the characteristics of under triturated amalgam?
- incomplete amalgamation- poor working quality- granular and crumbly- decreases final strength
167
What are some characteristics of over triturated amalgam?
- decreases final strength- overly warm and shiny- decreases working time
168
True or false: Deep occlusal grooves should be avoided when carving.
true because this thins the amalgam at the margins
169
A faint marking is left on the opposing tooth after an amalgam restoration was completed. Should the amalgam be carved down?
No. You don't want to take the amalgam completely out of occlusion. You carve down if a patient says that they can feel it or if there is a heavy marking like a bullseye/halo/doughnut.
170
What are the two types of matrix bands? What is the difference between the two?
- No. 1 - normal (like we use in lab)- No. 2 - has gingival extensions for preps that are extended occlusogingivally
171
What are the purposes of a matrix band?
- provides a wall against which one can condense amalgam- re-establish proximal contact of restoration with adjacent tooth- aids in isolation of preparation during the fill- provides containment of the amalgam- aides in prevention of voids- helps to shape the proximal contacts
172
What are the two types of Tofflemire retainers?
- contra-angle- straight
173
Which Tofflemire retainer is usually used on the buccal side of a tooth? Which on the lingual side?
- contra-angle on the lingual- straight on the buccal
174
What are the functions of a wedge?
- adapts the gingival edge of the matrix band against the gingival cavosurface of the preparation to prevent flash from squeezing out gingivally- spearates the teeth slightly to compensate for the thickness of the band- helps stabilize the band
175
What is the purpose of trituration?
to remove the oxide coating and wet each particle of alloy with mercury
176
How much pressure is necessary to place amalgam?
5-10 lbs
177
What does burnishing amalgam do?
- a form of final condensation- removes mercury-rich excess at surface- begins development of occlusal grooves and fossae
178
How is amalgam carved: from tooth to amalgam or amalgam to tooth?
tooth to amalgam
179
What are the 3 routes of mercury exposure?
-skin contact-inhalation of vapor-airborne droplets
180
At how many nanograms of mercury per mL blood are symptoms of mercury poisoning observed?
100 ng/mL blood
181
How should mercury be disposed of in a dental practice?
-use single-use capsules-use a no-touch technique and clean up any spilled mercury-store/discard dental amalgam scrap in cool space in capped, unbreakable jar holding water with finely divided sulfur
182
What does the ADA recommend for operators using mercury in their practices?
-single-use capsules-no-touch technique to clean any spills-discard old or damaged mixing capsules-store any scraps in a cool space in a capped, unbreakable jar holding water with finely divided sulfur-avoid baseboard heating in operatories where dental amalgam is used-use face mask and water spray with high vacuum evacuation when finishing new dental amalgam restorations or removing old restorations-do not use ultrasonic condensers-check mercury vapor levels frequently-office personal should have mercury levels monitored periodically through urinalysis
183
What type of reaction may some patients experience with exposure to dental amalgams?
allergic skin reaction; other options other than amalgam are available for restorations
184
Is it better to have high-copper or low-copper materials? Why?
high-copper-greater clinical longevity of restorations-much lower creep values measured in laboratory
185
What are the consequences of placing zinc in a material?
-facilitates machining lathe-cut particles (makes it more brittle)-improves corrosion resistance-less plastic amalgam mix
186
What are the consequences of having a zinc-free alloy?
no concerns about moisture contamination during trituration or condensation
187
If there is a higher mercury-alloy ratio, would the setting time increase or decrease?
setting time would increase (slower setting time)
188
What is the composition of gamma 1?
Ag2Hg3
189
What is the composition of gamma 2?
Sn8Hg
190
In low-copper dental amalgams, what is the setting reaction equation?
alloy (gamma) + Hg --> (gamma)1 + (gamma)2 + unreacted alloy particles
191
In high-copper dental amalgams, what is the setting reaction equation?
alloy (gamma) + Hg --> (gamma)1 + n' + unreacted alloy particles*NOTE: (gamma)2 does not form
192
What are the three metal elements that are reacted with mercury in high- and low-copper amalgams?
silver (Ag), tin (Sn), and copper (Cu)
193
What is the composition of n' that is produced in the high-copper amalgam setting reaction?
Cu6Sn5
194
For dispersalloy-type dental amalgams (low-Cu lathe-cut and spherical Ag-Cu particles of eutectic composition), what is the setting reaction equation?
Two steps:1. (gamma)1 + (gamma)2 form2. (gamma)2 disappears; n' phase appears
195
Which sets faster: high-copper spherical particles of single composition (HCSS) or dispersalloy-type dental amalgams?
HCSS is faster because it is only 1 step as opposed to 2
196
When amalgams set, do they expand or contract?
slightly contract; clinical problems would occur with excessive setting expansion (loss of anatomy and postoperative pain) or excessive setting contraction (microleakage)
197
Describe the steps of the setting process of amalgams.
Setting process is combination of solution and crystallization (precipitation).1. initial contraction from absorption of mercury (diffusion) by amalgam alloy particles.2. can be subsequent expansion from formation and growth of (gamma)1 and (gamma)2 or Cu-Sn (n') phases (matrix)3. final absorption of mercury by remaining amalgam alloy particles causes contraction*no free mercury in final set dental amalgam!*
198
What is the strongest phase of dental amalgams?
gamma phase (incompletely consumed starting alloy particles)
199
What is the weakest phase of dental amalgams?
(gamma)2 phase (in low-copper amalgams
200
What are the 6 types of corrosion in dental amalgams?
- galvanic corrosion - at interproximal contacts with gold alloys- electrochemical corrosion - because multiple phases- crevice corrosion - at margins- corrosion at unpolished scratches or secondary anatomy - lower pH and oxygen concentration of saliva- corrosion under retained plaque - because of lower oxygen concentration- chemical corrosion - from reaction with sulfide ions at occlusal surface
201
Limited corrosion is beneficial. Why?
because it reduces microleakage ((gamma)2 in low-copper amalgams and n' in high-copper amalgams)
202
How can corrosion be minimized?
by polishing amalgam restorations (scratches and pits trap debris, enhancing corrosion because lower oxygen concentration under deposit)
203
What metal may reduce corrosion in amalgam?
zinc
204
Does amalgam have low or high tensile strength?
low tensile strength; allows fracture of edges easily
205
Does amalgam have low or high compressive strength?
high compressive strength; strength increases as the amalgam sets until it reaches maximum strength at approximately 1 week
206
What is creep? How does it occur?
- metals may become elongated or deformed as a result of a load being applied for a long period of time- grain boundary sliding of (gamma)1 phase
207
Do high-copper amalgams have high or low creep?
low creep; the n' phase blocks sliding of the (gamma)1 phase in high-copper amalgams
208
Do low-copper amalgams have a high or low creep?
high creep; creep is the only mechanical property correlated with clinical marginal fracture of low-copper amalgam restorations
209
Why is it important to have adequate trituration time?
so that all alloy particles are coated with mercury and optimum mechanical properties are obtained
210
With what type of amalgam is moisture contamination a problem? What will moisture contamination cause?
- zinc-containing dental amalgam- causes delayed setting, excessive increase in setting expansion and decreased strength (H2 is released from Zn reduction of water)
211
What will happen if amalgam is overtriturated?
makes the material hot, reduces working time, and increases creep
212
What 3 things were considered historically when placing amalgam?
- adapt amalgam to cavity walls- minimize porosity in restoration- control final mercury content of resotration
213
What elements make up the alloy in amalgam?
silver, tin, copper, zinc, indium, mercury, and/or noble metals, gold, platinum, and palladium
214
What are the two methods of making amalgam particles?
- filing or lathe-cut (machined from cast ingot)- spherical (molten alloy blown through nozzle)
215
Which type of amalgam particles (lathe-cut or spherical) are wetted with a lower mercury:alloy ratio?
spherical particles
216
Which type of amalgam particles (lathe-cut or spherical) are able to resist forces of condensation more?
lathe-cut particles
217
What is enameloplasty?
when you modify the enamel of a tooth's surface to make it easier to clean and remain caries-free; this could occur if there is a deep fissure/pit, etc.*NOTE: it does not extend the outline form of a prep, it is just carves away no more than 1/3 of the enamel at the surface
218
What are the principles of outline form and initial depth?
- all unsupported or weakened enamel should usually be removed- all faults should be included- all margins should be placed in a position to allow finishing of the margins of restoration
219
What are the features of establishing proper outline form and initial depth?
- preserving cuspal strength- preserving marginal ridge strength- minimizing faciolingual extensions- connecting two close (<0.5 mm) defects or tooth preparations- restricting the depth of the preparation into dentin
220
What are the principles in obtaining primary resistance form?
- using a box shape with a relatively horizontal floor which helps the tooth resist occlusal loading- restricting the extension of the external walls to allow strong cusp and ridge areas- slight rounding of internal line angles to reduce stress- reducing and covering weak cusps- providing enough thickness of restorative material to prevent fracture- bonding the material to tooth structure when appropriate
221
What are the features of primary resistance form?
- relatively horizontal floor- box-like shape- inclusion of weakened tooth structure- preservation of cusps and marginal ridges- rounded internal line angles- adequate thickness of restorative material- reduction of cusps for capping, when indicated
222
What is a feature of primary retention form for an amalgam restoration?
external tooth walls that converge occlusally
223
What are the two types of secondary retention and resistance forms?
- mechanical preparation features- treatments of the preparation walls with etching, priming, and adhesive materials
224
What are the 3 prerequisites for amalgam success?
- 90 degree junctions of amalgam with tooth structure- mechanical retention form- adequate thickness for the amalgam material
