4 & 5 Principles of Tooth Preparations; Prep for Full Cov Cast & PFM

Question 1

5 PRINCIPLES THAT GOVERN THE DESIGN OF PREPARATION FOR A CAST RESTORATION

Answer 1

 1 – Preservation of tooth structure
 2 – Retention and resistance
 3 – Structural durability
 4 – Marginal integrity
 5 – Preservation of the periodontium

Question 2

• prevents removal of the restoration along the path of insertion or long axis of the tooth preparation.
• prevents dislodgment of the restoration by forces directed in an apical or oblique direction and prevents any movement of the restoration under occlusal forces.
• interrelated and often inseparable qualities.
• needed slightly to permit the restoration to seat.
• must converge occlusally
• must diverge occlusally
• 1. The relationship of one wall of a preparation to the long axis of that preparation is the ______ of that wall.
• 4. Jorgensen and Kaufman et al have demonstrated experimentally that retention _____ as taper is increased.
• • Therefore, the greater the surface area of a preparation, the ____ its retention.

Answer 2

Retention
Resistance
Retention
Resistance
TAPER
external walls
internal walls
inclination
decreases
greater

Question 3

• Maximum retention is achieved when there is ______ path.
• (a) The walls of a groove that meet the axial wall at an ___________ do not provide the necessary resistance. (b) The walls of a groove must be _____________________ to resist displacement.
• (a) The facial and lingual walls of a box will not resist rotational displacement if they form ___________ with the pulpal wall. (b) They must meet the pulpal wall at angles near _________.
• an important factor in both retention and resistance.
• • ____ preparations will have more surface area for retention.
• Preparations with _________ interferes with the tipping displacement of the restoration better than the short preparations.
• The walls of shorter preparations should have as _________ as possible to increase the resistance and even this will not help if the walls are too short.

Answer 3

only one
oblique angle
perpendicular to rotating forces
oblique angles
90 degrees
Occlusogingival length
Longer
longer walls
little taper

Question 4

• _________________ are interchangeable and can be substituted for an axial wall or for each other. _____ is important, since conditions often preclude making an ideal preparation.
• In preparing these features, the much ___________ between the walls allows the dentist to prepare them more precisely. They offer an excellent means of enhancing overall retention and resistance of an otherwise over-inclined axial wall.
• ____________ Is an imaginary line along which the restoration will be placed onto or removed from the preparation. It is determined mentally by the dentist before the prep.
• Necessary when preparing teeth for FPD since all paths of abutments must be _______ to each other
• It must be considered in two dimensions: faciolingually and mesiodistally.
  o The ______________ of the path can affect the esthetics of metal-ceramic or partial veneer crowns.
  o For metal-ceramic crowns, the path is roughly parallel with the long axis of the teeth.
• If both eyes are open when the preparation is viewed, _____ may remain.
• The path of insertion of a preparation for a metal-ceramic crown should ____ the long axis of the tooth (A). If the path is directed facially, the prominent facioincisal angle may create esthetic problems of ______ or “____________” (B). If the path is directed lingually, the facial surface will intersect the lingual surface, creating a ____ preparation. It also may encroach on the ___ (C).
• The path of insertion of a three-quarter crown on a posterior tooth parallels the long axis of the tooth (a), whereas on an anterior tooth it parallels the ______________________ of the labial surface (b).
• The path of insertion of a preparation must parallel to the adjacent proximal contacts (A) or it will be prevented from _____ (B).

Answer 4

Groove, box form, and pinhole
Substitution
shorter distance
PATH OF INSERTION
parallel
facio-lingual orientation
undercuts
parallel
ovecontouring; opaque show-through
shorter ; pulp
incisal one-half to two-thirds
seating

Question 5

• One of the most important features for providing adequate bulk of metal and strength to the restoration is _______________
  1) For gold & metal alloys, _____ of clearance on the functional cusps (lingual of maxillary molars and premolars and buccal of mandibular molars and premolars). On the nonfunctional cusp, ___ is sufficient.

2) For metal-ceramic crowns, ______ on functional cusps that will be veneered with porcelain and _______ on nonfunctional cusps to receive ceramic coverage.

3) There should be ____ of occlusal clearance on preparations for all-ceramic crowns.

4) Malposed teeth may have occlusal surfaces that are not parallel with the occlusal table. Therefore, it may __________ to reduce the occlusal surface by 1.0 mm to achieve 1.0 mm of clearance.

• Occlusal reduction should reproduce __________________ rather than being cut as one flat plane.

Answer 5

occlusal clearance/ reduction
1.5 mm; 1.0 mm
1.5 to 2.0mm; 1.0 to 1.5 mm
2.0mm
not be necessary
basic inclined planes

Question 6

1. _______________ An integral part of the occlusal reduction.
2. A ___________ on the lingual inclines of the maxillary lingual cusps and the buccal inclines of mandibular buccal cusps provides space for an adequate bulk of metal in an area of heavy occlusal contact.
3. Without this bevel, several problems may occur. If the crown is waxed and cast to normal contour, the casting will be extremely ____ in the area overlying the junction between the occlusal and axial reduction.

• ___________ of the buccal surface will destroy excessive tooth structure while lessening retention.

1. _____________ also plays an important role in securing space for an adequate thickness of restorative material.
2. If restorations are made with normal contours over preparations with ________________________, they will have thin walls that will be subject to distortion.
3. Frequently laboratory technicians attempt to compensate for this by overcontouring the axial surfaces. While this “solution” to the problem strengthens the restoration, it can have a disastrous effect on the ________.

• There are other features that serve to provide space for metal that will improve the rigidity and durability of the restoration: (5)
• The _______ connects the boxes, and the _________ ties the grooves together to enhance the reinforcing “________.”

Answer 6

FUNCTIONAL CUSP BEVEL
wide bevel
thin
Overinclination
Axial reduction
inadequate axial reduction
periodontium

(1) Offset
(2) Occlusal shoulder
(3) Isthmus
(4) Proximal groove
(5) Box.

isthmus
offset
truss effect

Question 7

• ____ have been advocated as means of diminishing marginal discrepancy.
• Studies show that the presence of cement changes the scenario completely. The ________________________ will prevent the complete seating of a casting with bevels that are nearly parallel with the path of insertion of the restoration.
• The more nearly the bevel ________ the path of insertion, the greater the distance by which the restoration _________.
• _______________ It dictates the shape and bulk of restoration and it can help in both marginal adaptation and the degree of seating of the restoration.
• Wide, shallow bevels that are nearly parallel with the outer surface of the tooth should be avoided They are likely to lead to ____________. Even if the axial surfaces of the overlying crown are not overcontoured, the resultant thin, unsupported wax at the margin potentially will break or distort when the wax pattern is withdrawn from the die and invested. The optimum margin for a gold alloy casting is an acute edge with a nearby bulk of metal.
• __________ has been shown experimentally to exhibit the least stress, so that the cement underlying it will have less likelihood of failure.
• A ________________ is used to provide a 90-degree cavo-surface angle with a large-radius rounded internal angle.
• It provides better support for a ceramic crown than does a conventional chamfer, but it is not as good as a _______. A bevel can be added to the heavy chamfer for use with a metal restoration.

Answer 7

Bevels
film thickness of the cement
parallels
fails to seat
FINISH LINE CONFIGURATIONS
overcontouring
Chamfer
heavy chamfer
shoulder

Question 8

• The ____________________ has long been the finish line of choice for the all-ceramic crown.
• The ___________ provides resistance to occlusal forces and minimizes stresses that might lead to fracture of the porcelain. It produces the space for healthy restoration contours and maximum esthetics. However, it does require the destruction of ___________________ than any other finish line. The shoulder generally is not used as a finish line for cast metal restorations.
• A ___________ on an all-ceramic crown preparation combines maximum support of the ceramic with a stress-reducing rounded gingivoaxial angle.
• The ___________________ is a finish line in a variety of situations. It is used as the gingival finish line on the proximal box of inlays and onlays, and for the occlusal shoulder of onlays and mandibular 3⁄4 crowns. It can also be used for the facial finish line of PFM restorations where gingival esthetics are not critical. Also used in situations where a shoulder is already present, either because of destruction by caries or the presence of previous restorations. It is also a good finish line for preparations with extremely short walls, since it facilitates axial walls that are nearly parallel.
• The ultimate in finish lines that permit an acute margin of metal is the ___________. Unfortunately, its use can create problems. Unless it is carefully cut, the axial reduction may fade out instead of terminating in a definite finish line. The thin margin of the restoration that fits this finish line may be difficult to accurately wax and cast. It is also more susceptible to distortion in the mouth when the casting is subjected to occlusal forces.
• The use of the knife edge can result in overcontoured restorations when an attempt is made to obtain adequate bulk by adding to the external axial contours of the restoration. In spite of its drawbacks, it is sometimes necessary to use the knife edge. It may have to be used on the ______ surface of mandibular posterior teeth, on teeth with very _________________, and on the surface toward which a tooth may have ______.

Answer 8

shoulder finish line
wide ledge
more tooth structure
radial shoulder
shoulder with a bevel
knife edge
lingual; convex axial surfaces; tilted

Question 9

• The best results can be expected from margins that are as smooth as possible and are fully exposed to cleansing.
• Whenever possible, the finish line should be placed in an area where the margins of the restoration can be finished by the dentist and kept clean by the patient.
• In addition, finish lines must be placed so that they can be duplicated by the impression, without tearing or deforming the impression when it is removed past them.

Answer 9

PRESERVATION OF THE PERIODONTIUM

Question 10

• Controlled laboratory studies have shown that when compared with partial coverage designs, the ____________ exhibits superior retention and resistance.
• Full coverage in the right circumstances can be excellent treatment, but it is ______. More conservative dentistry has become easier, and the preservation of tooth structure is important.
• Less destructive than metal-ceramic or all ceramic crowns ?
• Occlusal reduction: ________________________
• Function cusp bevel ____________
• Buccal and lingual axial reduction: _______________
• Proximal axial reduction: __________________
• Chamfer and axial finishing: _______________
• Placing of a seating groove: ____________
• On preparations for long-span fixed partial dentures, there should be a __________________ to increase the resistance to mesiodistal movement.

Answer 10

full coverage crown
overused
FULL METAL CROWN PREPARATION
Round- end tapered diamond and no. 171L bur
Round- end tapered diamond and no. 171L bur
Torpedo diamond
Short needle and torpedo diamonds
Torpedo carbide bur
No. 171L bur
buccal and a lingual groove

Question 11

• Friedlander et al found the metal-ceramic restoration to be ___ times as strong.
• If the facial surface is reduced in one plane that is an extension of the gingival plane, the incisal edge will protrude, resulting in a bad shade match or an ____________“block.”
• If the facial surface is prepared in one plane that has adequate facial reduction in the incisal aspect, the facial surface will be ____________ and too __________.
• Incisal reduction: ______________________-
• Labial reduction_____________________
• Lingual reduction: ________________________
• proximal reduction: __________________
• Lingual axial reduction: _________________
• Axial finishing:_________________
• Axial and shoulder finishing: _________________
• A ____________________ (Suter Dental Mfg, Chico, CA), is recommended to avoid this problem. This instrument has a hoe (pull stroke) blade at both ends.
• A ___________________________ has a hoe (pull stroke) blade at one end and a chisel (push stroke) blade at the other.

Answer 11

2.8
overcontoured; overtapered; close to the pulp
flat-end tapered diamond bur.
flat-end tapered diamond bur.
Small wheel diamond bur
long needle diamond bur
Torpedo diamond bur
Torpedo carbide bur
Radial fissure bur
modified 15-8-8 binangle chisel, the RS-1
conventional 15-8-8 binangle chisel

Question 12

• Planar occlusal reduction _______________________
• Functional cusp bevel ___________
• Depth-orientation grooves_______________
• Facial reduction__________________
• Proximal axial reduction ___________
• Lingual axial reduction and finishing ____________________________
• Facial axial and radial shoulder finishing _________________________
• Gingival bevel _________________________

Answer 12

round ended tapered diamond and no. 171L bur
round ended tapered diamond and no. 171L bur
flat-end tapered diamond
flat end tapered diamond.
short needle diamond.
torpedo diamond and carbide burs.
radial fissure bur.
flame diamond and carbide finishing bur.