Quiz 1 Flashcards
1
Q
Preparation
A
The final shape (form of the tooth) produced my instrumentation, to receive a restoration
2
Q
Complete Veneer Crown Preparation
A
Extracoronal preparation involving the entire clinical crowen
3
Q
Complete Veneer Crown (CVC)
A
A cast-gold extracoronal restoration which covers the clinical crown
4
Q
Path of Withdrawal (POW)
A
The imaginary line along which a casting is moved when it is separated from its prepared tooth. For single crowns the POW should be nearly coincident with the tooth’s long axis, which can be determined clinically by bisecting the angle formed by opposing axial surfaces in the gingival third of the tooth
5
Q
Axial Wall
A
Part of a crown preparation prepared in the long axis of the tooth - can be buccal, lingual, mesial, or distal
6
Q
Convergence angle
A
The angle or taper formed by diametrically opposed axial walls
7
Q
Chamfer
A
The cervical junction of the prepared axial wall and the unprepared portion of the tooth structure. The chamfer extends around the most cervical portion of the tooth preparation
8
Q
Line Angle (general definition)
A
The lines formed by the junction of any two tooth surfaces. These should be rounded in complete crown preparations.
9
Q
Axial Wall Line Angle
A
The junction between any two axial walls
10
Q
Occlusoaxial line angle
A
The junction between the occlusal surface and an axial wall
11
Q
Cavo-surface line angle
A
The junction of prepared (cut) to unprepared (uncut) tooth structure. This is an external line angle
12
Q
Depth Orientation Grooves
A
Grooves placed on the surface of the tooth to provide a reference to determine when sufficient tooth structure has been reduced
13
Q
Functional cusp bevel
A
A wide bevel placed on the functional cusps (the buccal inclines of the mandibular buccal cusps and the lingual inclines of the maxillary lingual cusps). The thickness of the tooth structure removed when preparing this bevel ensures that correct contours of the final restoration can be re-established while providing correct convergence and adequate thickness of restorative material
14
Q
Undercut definition
A
A crown preparation where a wax pattern cannot be withdrawn from its die without distortion
15
Q
2 causes of undercuts (which can be corrected in which way, too)
A
- A depression in an axial wall caused, for example, by a carious lesion. This can often be corrected with a base material.
- Diametrically opposed axial walls that do not converge occlusally caused by imprope angulation of the cutting instrument. This type requires further reduction.
16
Q
Occlusal clearance
A
The distance between the occlusal surface of the prepared tooth and the occlusal surface of the opposing tooth. This clearance must be evaluated during excursive jaw movements, as well as intercuspal position
17
Q
Retention form
A
The characteristics of tooth preparation which tends to resist the removal of a restoration along its path of withdrawal.
18
Q
Resistance form
A
The characteristics of a tooth preparation which tends to prevent dislodgement of a seated restoration by forces directed in an apical or oblique direction. REsistance form prevents dislodgement of the restoration by occlusal forces
19
Q
4 advantages of CVC
A
- High Strength
- Longevity
- High resistance to displacement
- Ability to modify axial contours and occlusion
20
Q
4 disadvantages of CVC
A
- Display of metal
- Removal of tooth substance
- Vitality testing
- Margin close to gingival tissue
21
Q
8 indications for CVC
A
- Extensive destruction by caries or traume
- Endo treated teeth
- Large existing restorations
- Maximum retention needed
- Recountouring of axial surfaces
- Correction of malinclination
- Correction of occlusal discrepancies
- Provide contours suitable for a removable partial denture
22
Q
Contraindications for CVC
A
Wherever a tooth can be adequately restored with a more conservative restoration.
23
Q
4 Principles of tooth preparation
A
- Conservation of tooth structure
- Marginal integrity of the restoration
- Retention and resistance
- Structural durability
24
Q
Define conservation of tooth structure
A
Minimum tooth reduction compatible with adequate strength and correct contour of the restoration
25
5 causes of excess reduction
1. The tooth is prepared with excessive convergence angle (recommended 2-10 degrees)
2. The preparation does not follow the anatomical features of the tooth
3. The POW diverges from the long axis of the tooth
4. An excessively wide margin (ideal =.5mm)
5. Excessively gingival extension of the preparation (ideally no further cervically than retention form and existing resorations or defects dictate)
26
Define Marginal Integrity of a restoration
The tooth-restoration interface at the gingival margin is a potential site of failure due to cement dissolution or roughness. The preparation should be designed to enable a smooth, strong, well adapted casting to be provided.
27
4 causes of inadequate marginal integrity
1. The chamfer is too narrow to provide sufficient bulk of restorative material without over contouring (ideal = .5mm)
2. The cavo-surface line angle cannot easily be determined during laboratory procedures
3. The chamfer is rough or uneven
4. The preparation is undercut causing distortion of wax pattern
28
Define Inadequate Retention and Resistance
Inadequate retention and resistance form may lead to displacement of the restoration during function.
29
3 causes of inadequate retention and resistance
1. Excessive convergence angle (greater than 10 degrees)
2. Inadequate height and surface area of the axial walls
3. Insufficient surface area to resist tipping of the restoration
30
Define Structural Durability of Restoration
The restoration must have sufficient bulk to desist distortion and allow for wear during service. However, an unnecessarily thick casting is indicative of excessive tooth preparation.
31
What are the recommended dimensions and acceptable ranges of a CVC to have structural stability for functional cusp, central groove, non-functional cusp, and chamfer
1. Functional cusp: 1.5 mm (1.3-1.7mm)
2. Central groove: 1 mm (0.8-1.2mm)
3. Non-functional cusp: 1 mm (0.8-1.2mm)
4. Chamfer width: 0.5 mm (0.4-0.7mm)
32
2 Advantages of using 242.6 bur for CVC
1. It is a taped bur that will create a tapered surface convergence approx. 3-4 degrees from the cervical toward the occlusal.
2. The tip is hemispherical to produce a chamfer as the bur cuts into tooth structure.
33
5 steps of tooth reduction for CVC (in order)
1. Occlusal guiding grooves
2. Occlusal reduction
3. Axial guiding grooves
4. Axial reduction
5. Finishing and evaluation
34
Indication for a crown
1. Restorative material is so large that supporting tooth structure is at risk for tooth breaking or fracture. Restoration is too large
2. Erosion of enamel and dentin is exposed resulting in increased sensitivity
3. Missing teeth need a bridge but the tooth is flat so a crown can be added to increase convexity of tooth to hold the bridge better
35
Complete veneer crown:
a cast-gold extra-coronal restoration which covers the clinical crown. Placed on top of a prep (CVC)
36
Complete veneer crown preparation:
extra - coronal preparation involving the entire clinical crown.
37
Preparation:
the final shape of the tooth produced by instrumentation to receive a restoration.
38
Step 1 Occlusal guide grooves on #30
a. 242.6m diamond bur in high speed handpiece
b. depth grooves are placed .2 mm shallower than the intended tooth reduction to allow for smoothing
c. grooves are placed at the height of each triangular ridge and in the buccal and lingual grooves
d. 1.3 mm deep on the buccal (functional cusp)
e. .8 mm deep on the lingual (non-functional cusp)
39
Step 2 Occlusal reduction on #30
a. 242.6m diamond bur to remove the tooth structure remaining between the grooves
b. tooth is reduced in planes which correspond to the anatomical features of the unprepared tooth.
c. two step reduction
d. a functional cusp bevel is added: 1. depth grooves for the bevel are 1.3 mm using a 242.6 m diamond bur held 45 degrees to the long axis of the tooth, 2. this ensures that correct contours for the final restoration can restorative materials.
e. evaluate the occlusal reduction: using the silicone putty mold and periodontal probe.
f. occlusal clearance: the distance between the occlusal surface of the prepared tooth and the occlusal surface of the opposing tooth. 1. in a patient can be evaluated by having the patient move their jaw vertically and horizontally from intercuspal position.
g. minimum tooth reduction is necessary but also must be compatible with adequate strength and correct contour of the restoration. 1. restoration must have sufficient bulk to resist distortion and allow for wear during service. 2. if casting is unnecessarily thick it indicates that there was excessive tooth preparation.
40
Step# 3: Axial guide grooves on #30
a. prepared in the long axis of the tooth which is determined clinically by bisecting the angle formed by opposing axial surfaces in the gingival third of the tooth.
b. POW= imaginary line along which a casting is moved when it is separated from its prepared tooth. should be nearly coincident with the tooth's long axis.
c. want a little taper so use tapered burs: 1. when moved parallel to the long axis of the tooth will ceate a tapered surface converging 3-4 degrees from the cervical towards the occlusal. 2. 242.6 m and 243.6 m diamonds as well as 170L carbide
d. shank of diamond bur must be held parallel to the proposed POW
e. place 3 shallow grooves on buccal and lingual axial walls with 242.6m diamond bur
1. one should be in the center and one at each mesio-buccal and disto-buccal line angle
2. these grooves determine the POW of the restoration and should be in the long axis of the tooth.
f. evaluate guide grooves and assess alignment
41
Step #4: Axial reduction on #30
a. mark gingival extent with pencil line (.5 mm above plastic gingival)
b. use 242.6m diamond bur to remove remaining tooth structure between grooves
c. hold diamond parallel to POW
d. tip of the diamond bur creates chamfer slightly short of the pencil mark.
e. chamfer: cervical junction of prepared axial wall and unprepared portion of the tooth structure. 1. extends around the most cervical portion of the tooth preparation.
f. extend buccal and lingual reduction into the interproximal area. but be careful not to damage adjacent tooth.
g. prepare the interproximal area when only narrow islands of tooth remain. 1. first use 169 carbide to reduce size of islands. 2. followed by 747.6 m diamond. 3. refine to smooth chamfer with 242.6 m diamond
h. want axial walls to have a convergence/taper formed from tapered burs: 2-10 degree taper is ideal.
42
Step #5: finishing and evaluation on #30
a. line angles should all be rounded
b. preparation should exhibit overall smothness but a polished surface is unacceptable
c. check for undercuts: 1. an undercut is present if a wax pattern can't be withdrawn from its die without distortion. 2. a depression in the axial wall can cause this. 3. opposing axial walls will have undercut if they don't converge occlusally.
43
Recommended dimensions: MEMORIZE ON EXAM
- Central Grove: 1.0mm
- Functional Cusp: 1.5mm
- Non-Functional Cusp: 1.0mm
- Chamfer Width: .5mm
- POW +/- 5 degrees
- Convergence: 6 degrees
- Linguo-occlusal line angle reduction: 8mm
44
Silicone Reduction Guide
for tooth number 30 reduction guide should be made from tooth number 28 to 32.
45
Line Angles: The lines formed by the junction of any two tooth surfaces should be rounded in preparations types:
- axial wall line angle
- occlusoaxial line angle
- cavo-surface line angle
46
Retention Form:
characteristics of the tooth preparation which tend to resist the removal of the restoration along its POW Vs.
47
Resistance Form:
characteristics of a tooth preparation which tend to prevent dislodgement by forces directed in an oblique or apical direction.
- inadequate retention and resistance may lead to displacement of the restoration during function
- causes of inadequate retention and resistance:
- excessive convergence angle (greater than ten degrees)
- inadequate height of axial walls
- insufficient surface area to resist tipping
48
Excess Reduction of the prep will occur if:
- excessive convergence angles
- preparation doesn't follow the tooth anatomy
- POW diverges from the long axis of the tooth
- excessively wide margins (greater than .5mm)
- excessive gingival extension of preparation
49
Occlusal Guide Grooves:
- place guide grooves in the following places:
- Lingual:
- lingual groove
- distolingual triangular ridge
- distal cusp (treat like a marginal ridge)
- mesiolingual triangular ridge --- this ridge is heavily angulated to the mesial so you don't make the guide groove exactly with the tooth's anatomy but more parallel with the other grooves.
- Mesiolingual supplemental groove
- Buccal same as lingual
- Use a 242 bur and lay it on the tooth's original anatomy to maintain correct angulation.
- Place grooves .2mm shallower than intended final depth to allow for refinement
- A 242.6m bur is tapered 8 degrees at the tip and is .8mm at the tip. At the proximal end it is 1.2 to 1.3mm
- on the lingual don't fully bury the proximal end.
- on the buccal fully bury the proximal end
- Reduction: first lingual then buccal
- See previous lecture
- Be sure to re-angulate bur with triangular cusp ridge orientation groove and head down towards supplemental groove.
- Only go back into supplemental grooves with running bur
- Make sure the tip of the bur is matched with the central groove when doing occlusal reduction.
50
Functional Cusp bevel:
go full depth of proximal end of bur to get a 1.3mm groove
51
Axial reduction:
- make sharp pencil line .5mm above the gingiva
- guide grooves should be placed .5mm above this line
- 3 guide grooves: central, just mesial of mesial line angle and just distal of distal line angle.
- must be parallel to POW and long axis of tooth
- sink bur 1/2 diameter tip of 242 bur (.4 mm)
- pick POW by combing the BL and MD planes in the middle
- slow handpiece to smooth chamfer
52
Interproximal reduction requirement
must obtain .5mm clearance interproximally
53
Refining includes what two steps?
- round all sharp transitional line angles
| - add nun functional cusp bevel to get to a 1.0 mm reduction (bevel should be only .5-.6mm)
54
Bonds will break with stress:
schematic movement of edge dislocation = mechanism for permanent defraction of metals
-must have regular crystal structure to get 1/2 dislocation
55
Stress-stain curve for metal: see slides
- strain plotted vs. stress
- first linear part=elastic range (elastic modulus)
- metal deforms until yield strength is reached
- yield strength is the amount of stress needed for a small PERMANENT deformation.
- want to stay below yield strength to prevent deformation
56
Properties of Gold:
- Most noble and corrosion -resistant metal
- Most ductile and mealleable metal
- Too weak for dental restorations unless other alloying elements are used.
57
Noble Metals
- can not form stable oxides are room temp-dental
- lowest tendency to lose electrons and become positive ions-chemistry
- seven noble metals
- silver is not noble metal in oral environment
58
Precious Metals
- classification is based upon unit metal price and not electrochemistry
- relatively common and inexpensive metals become precious when very high purity is required
59
Classification of Gold based on unit metal price - Carat and fineness for gold purity (TEST QUESTION)
- carat (k) - arts in 24 with pure gold=24k. Provides no information about other elements
- fineness-parts in 1000 with pure gold= 1000
60
Avoirdupois and troy weight systems
1 dwt=1.555 gm
noble alloys are typically packaged in 1 dwt or 2 dwt pieces
1 oz gold=20 dwt (penny weight)
61
Current approximate unit metal prices
-gold=$1,360 per oz. *on test: what does 1 dwt cost? 1360/20
62
Dental gold casting alloys
- coining gold and 22k gold formerly used for dental restorations
- type 1 to 5 increase in hardness from 1 to 5
63
Functional uses of gold casting alloys - Which type of Gold is Used for what type of restorations
-type 1: rarely used. Very low stress bearing inlays.
-type 2: Inlays and onlays subject to moderate stress
-type 3: three-quarter crowns, full cast crowns, and short span fixed partial dentures
--Type 2 and 3 are the most commonly used in
dentistry
-type 4: cast restorations subject to highest stress: thin veneer crowns, long span fixed partial dentures, and removable partial denture frameworks
-type 3 and 4 alloys termed **heat-hardenable** because have sufficient copper for ordering reaction.
-type 1 and 2 contain insufficient copper and can't be hardened by heat treatment
64
Roles of Major Elements in Gold Casting Alloys
- Gold-provides *ductility, tarnish and corrosion resistance Copper - principal element for *hardening and strengthening
- Silver-counteracts effect of copper on color and substitutes economically for gold without degrading mechanical properties
- Platinum and palladium-also provide tarnish and corrosion resistance as well as strengthening
- Zinc-oxygen scavenger during melting to minimize oxidation of other elements, and considered to improve castability or fluidity of molten alloy (picks up oxygen so prevents silver from oxidizing)
65
Substitution solid solution vs interstitial solid solution
- substitution solid solution: solvent atoms substitute for solute atoms
- interstitial solid solution: solvent atoms go between solute atoms
66
Gold-copper phase diagram:
- composition vs. tem
- below the curve=solid
- see slides
- in high temperatures gold and copper atoms are randomly distributed. When it cools gold and copper atoms go to specific planes=ordered.
- other important elements:
- small amounts of indium and gallium may be present to provide hardening and strengthening
- very small amounts (less than 100 ppm) of iridium or ruthenium are generally incorporated by manufacturers to provide grain refinement, hardening gold casting alloys is done by adding copper, platinum, palladium, silver and zinc
67
What are the 5 general properties of metals?
1. 3D repeating pattern formed during solidification
2. High electrical and thermal conductivity (due to free electrons)
3. Permanent deformation (caused by anatomic defects
4. Ductility
5. Malleability
68
What is the difference between ductility and malleability?
Ductility is when the metal stretches while malleability is due to metal being compresed
69
In metallic bonding, what phase are the free valance electrons in?
Gas phase
70
In what arrangement are ionic cores during metallic bonding?
Crystalline arrangement
71
Give 5 properties of Grains in metallic bonding
1. Microscopic single crystals
2. Last region to solidify
3. Greater atomic disorder
4. High concentration of impurity atoms
5. Attached by chemical etchants
72
What 7 elements have a schematic face-centered cubic (FCC) structure? TEST QUESTION
1. Gold
2. Silver
3. Copper
4. Palladium
5. Platinum
6. Nickel
7. Iron at HIGH temeratures
73
What two elements have a schematic body centered cubic (BCC) structure?
1. Iron at LOW temp
| 2. Titanium at HIGH temp
74
Define polymorphic/allotropic forms
Different crystal structures of same atoms
75
What is a unit cell?
Smallest repeating portion of 3D crystal structure
76
What are dislocations?
In metallic bonding, dislocations allow for permanent deformation of metals as there is movement along slip planes under shear stress. Blocked at grain boundaries.
77
When do dislocations NOT exist?
In crystalline structures
78
Describe the function of an Extensometer
An extensometer measures change in specimen length over a central gauge section as increasing force is applied by a mechanical testing machine
79
What is Strain due to during tension testing?
Length change
80
What is Stress due to during tension testing?
Applied force/cross-sectional area
81
What are the 2 major deformation points on a stress-strain curve?
1. Elastic deformation
| 2. Permanent deformation
82
What causes permanent deformation>
Movement of dislocations
83
In what 5 ways can you strengthen metal materials as to impede dislocations? (#4&5 are TEST QUESTIONS - think of a penis!)
1. Decrease grain size
2. Form alloys
3. Ordered structure
4. Increasing in hardness
5. Decrease in ductility
84
Describe the effect of air, water, acid, and aqua regia on gold (TEST QUESTION)
Air and Water = Do NOT tarnish
Acid = Will NOT dissolve
Auqa Regia = can be used to etch gold
85
What is the minimum off-set yield strentgth of dental gold casting alloys? TEST QUESTION
0.2%
86
What are the 4 selection factors when deciding which dental gold allow to use?
1. Cost
2. Burnishability
3. Solderability
4. Experience of the lab
87
Describe ordering transformation due to:
1. Slow cooling
2. Quenching
3. Bench cooling
4. Ordered phase
1. Slow cooling = allows for ordering to occur
2. Quenching = softened condition
3. Bench cooling = hardened condition
4. Ordered phase = AuCu for high gold alloys
88
Dentin and Pulp tissue are the physiological system for a tooth that maintains ______
Internal stability
89
Dentin and Pulp tissue have a coordinated response to _______ that disrupts the tooth's ______
Stimulus; Condition/Function
90
_____ makes up the bulk of the tooth and completely covers the pulp
Dentin
91
Dentin and Pulp tissue provided awareness of _____&_____ of tissues and their ______&______ phenomenon
Structure&Function; Physical&Chemical
