Lab Manual Quiz Flashcards
questions taken from Chapters 1-7 of the lab manual
Define preparation.
the final shape (form of the tooth) produced by instrumentation, to receive a restoration
Define complete veneer crown preparation.
extracoronal preparation involving the entire clinical crown
Define complete veneer crown (CVC).
a cast-gold extracoronal restoration which covers the clinical crown
Define path of withdrawal (POW).
imaginary line along which a casting is moved when it is separated from its prepared tooth; for single crowns, it should correspond with the long axis of the tooth
Define axial wall.
part of a crown preparation prepared in the long axis of the tooth (buccal, lingual, mesial, or distal)
Define convergence angle.
the angle or taper formed by diametrically opposed axial walls
Define chamfer.
the cervical junction of the prepared axial wall and the unprepared portion of the tooth structure; it extends around the most cervical portion of the tooth preparation
Define axial wall line angle.
the junction between any two axial walls
Define occlusoaxial line angle.
the junction between the occlusal surface and an axial wall
Define cavo-surface line angle.
the junction of prepared to unprepared tooth structure; external line angle
Define depth orientation grooves.
grooves placed on the surface of the tooth to provide a reference to determine when sufficient tooth structure has been reduced
Define functional cusp bevel.
a wide bevel placed on the functional cusps
What is the purpose of a functional cusp bevel?
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
Which cusps are the functional cusps?
- mandibular - buccal cusps
- maxillary - lingual cusps
Define undercut.
a crown preparation is undercut if a wax pattern cannot be withdrawn from its die without distortion
What are the 2 causes of an undercut? How can each be fixed?
- a depression in an axial wall, caused, for example, by a carious lesion; can be corrected with a base material
- diametrically opposed axial walls that do not converge occlusally caused by improper angulation of the cutting instrument; requires further tooth reduction to fix
Define occlusal clearance.
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 in intercuspal position
Define retention form.
the characteristics of the tooth preparation which tends to resist the removal of a restoration along its path of withdrawal
Define resistance form.
the characteristics of a tooth preparation which tends to prevent dislodgement of a seated restoration by forces directed in an apical or oblique direction; prevents dislodgement of the restoration by occlusal forces
What are the advantages of a complete veneer crowns?
- high strength
- longevity
- high resistance to displacement
- ability to modify axial contours and occlusion
What are the disadvantages of complete veneer crowns?
- display of metal
- removal of tooth substance
- vitality testing
- margin close to gingival tissue
What are some indications for complete veneer crowns?
- extensive destruction by caries or trauma
- endodontically treated teeth
- large existing restoration
- maximum retention needed (ex. long span fixed partial denture abutment)
- recontouring of axial surfaces
- correction of malinclination
- correction of occlusal discrepancies
- to provide contours suitable for a removable partial denture
What is the contraindication for complete veneer crowns?
wherever a tooth can be adequately restored with a more conservative restoration
What are the principles of tooth preparation for CVCs?
- conservation of tooth structure
- marginal integrity of the restoration
- retention and resistance
- structural durability
What are 4 ways inadequate marginal integrity can occur in a CVC prep?
- chamfer is too narrow to provide sufficient bulk of restorative material without over-contouring
- the cavo-surface line angle cannot easily be determined during laboratory procedures
- the chamfer is rough or uneven
- the preparation is undercut causing distortion of the wax pattern
What are 3 ways inadequate retention and resistance form may occur in a CVC prep?
- excessive convergence angle
- inadequate height and surface area of the axial walls
- insufficient surface area to resist tipping of the restoration
What is the recommended depth of a functional cusp reduction?
1.5 mm
What is the recommended depth of a central groove reduction?
1.0 mm
What is the recommended depth of a non-functional cusp reduction?
1.0 mm
What is the recommended width of the chamfer?
0.5 mm
What convergence angle is formed by the taper of a 242.6M bur?
3-4 degrees from cervical to occlusal
What is the sequence of steps of tooth reduction that will be used in the complete veneer crown preparation?
1) occlusal guiding grooves
2) occlusal reduction
3) axial guiding grooves
4) axial reduction
5) finishing and evaluation
If you are prepping tooth #30 for a CVC, which teeth should be included in the silicone reduction guide?
28 - #31
Where is a silicone reduction guide cut?
from mid-buccal to mid-lingual of the tooth being prepped
What is the dimension of the interproximal chamfer placement (margin clearance interproximally) for a CVC prep of tooth #30?
0.5 mm
In a CVC prep of tooth #29, how many guide grooves are placed in the axial wall of the buccal and linual sides?
- 3 guide grooves on the buccal axial wall
- 3 guide grooves on the lingual axial wall
What bur is used to remove the last few milimeters of tooth structure interproximally in a CVC prep of tooth #29?
an extra thin 747.6M diamond bur
With what bur is the chamfer (including interproximally) refined?
L-242.6M diamond bur
True or false: When finishing a CVC prep, the prep should have a polished surface.
FALSE. A polished surface is unacceptable; there should be light striations in the finish.
When doing a CVC prep for tooth #20, what teeth should be covered by the silicone reduction guide?
18 - #22
Which cusps are the functional cusps on a maxillary molar?
lingual cusps
What is Aluwax used to measure?
occlusal clearance after completing the occlusal reduction
How many planes of reduction does the buccal surface of a maxillary posterior tooth have?
2
Describe the planes of reduction of the buccal surface of a maxillary posterior tooth.
- first plane - from the gingival crest to about the junction of the middle and occlusal third of the tooth
- second plane - from the junction of the middle and occlusal third of the tooth to the occlusal edge
Which plane of reduction on the buccal surface of a maxillary posterior tooth establishes the path of withdrawal?
buccal first plane of reduction
Which plane of reduction on the buccal surface of a maxillary posterior tooth is reduced to provide sufficient space for the restoration metal?
both the first and second planes of reduction
Which plane of reduction on the buccal surface of a maxillary posterior tooth is reduced to restore the tooth to its original contour?
buccal second plane of reduction
True or false: The buccal second plane reduction on a maxillary posterior tooth is carried interproximally.
FALSE. It is not carried interproximally because it would overconverge the occlusal 1/3 of the mesial and distal proximal axial walls.
What is the ideal dimensions of a buccal second plane reduction on a posterior maxillary tooth?
1.0 mm
“Each provisional restoration should be made with the idea that _____________________.”
it can adequately protect the patient for an extended time period (of the order of months anyway).
What are the 5 biologic provisional restoration requirements?
- protect pulp
- maintain periodontal health
- provide occlusal compatibility
- maintain tooth position
- protect against fracture
What are the 3 mechanical provisional restoration requirements?
- resist functional loads
- resist removal forces
- maintain interabutment alignment
What are the 4 esthetic provisional restoration requirements?
- easily contourable
- color compatibility
- translucence
- color stability
What two forms are assembled to make a mold cavity when making provisional restorations?
- tissue surface form
- external surface form
What are the 3 categories for a tissue surface form?
- indirect
- indirect-direct
- direct
Which type of tissue surface form is preferred when making a provisional restoration?
indirect
How is the external surface form normally developed?
diagnostic waxing procedure
True or false: In the clinic, the external surface form should be made during the patient’s appointment.
FALSE. The external surface form should be made prior to the patient’s appointment.
Describe the steps for producing an external surface form in lab for tooth #3.
- use a typodont with unprepared teeth
- make an alginate impression of the whole arch
- pour fast-setting plaster into the impression
- after 20 min, trim it for use as a vacuum-form mold
- vacuum-form a polypropylene sheet on this “diagnostic cast”
- trim to the distal of tooth #2 and mesial of tooth #6; the buccal and lingual extension should be trimmed with scissors 3 mm from the gingival margin in order to form an adequate seal around #2-6
Describe the steps for producing an internal surface form for tooth #3.
- choose an impression tray for an irreversitble hydrocolloid impression (needs to extend 2 teeth beyond the tooth)
- place prepared tooth #3 into typodont
- if necessary, use cord to displace rubber gingival tissue to expose the cavosurface margins
- make an irreversible hydrocolloid impression
- pour impression in fast-setting plaster and wait 20 minutes
Describe the procedure for fabricating an indirect provisional crown for tooth #3.
- remove the cast of the prepared tooth #3 and trim it to provide proper indexing with the external surface form; check that the two forms fit together!
- paint the cast with one layer of separating medium (Al-Cote)
- when dry, lightly mark the cavosurface margins of the preparations with a soft lead pencil (repaint margins with separator if you have removed the previously applied coat with the pencil)
- mix Jet autopolymerizing resin (a methyl-methacrylate) and use a 8A or cement spatula to carry the resin to the polypropylene external surface form
- fill the external surface form methodically, starting at one end of the restoration and working to the other (to avoid air bubbles, add only to existing resin); resin should reach the level of the gingiva
- seat the cast of the prepared tooth in the filled external surface form (hold together with rubber band, not over tooth #3)
- place the assembly in warm water in pressure vessel; apply air at about 0.15 Mpa (pressure curing reduces resin porosity)
- remove assembly after 15 min
- separate the external surface form from the cured resin; the bulk of the stone can be removed on a cast trimmer and with a Carborunum disk
- remove resin flash with an acrylic-trimming bur and fine-grit garnet paper disk
- polish the restoration with wet pumice and acrylic resin-polishing compond
What is evaluated about the proximal contacts in the evaluation of a provisional restoration?
- presence
- contour
- location
What is evaluated about the axial contours in the evaluation of a provisional restoration?
- faciolingual profile
- line angle location
- embrasure form
What is evaluated about the pontic in the evaluation of a provisional restoration?
- height
- gingival surface contour
- facial contour
- lingual contour
What is evaluated about the occlusion in the evaluation of a provisional restoration?
- maximum intercuspation
- protrusive
- lateral
What is evaluated about the margins in the evaluation of a provisional restoration?
- fit
- contour
What is evaluated about the finish in the evaluation of a provisional restoration?
- porosity
- smoothness
When making a provisional restoration, why is the resin cured under pressure?
pressure curing reduces resin porosity
What portion of a metal-ceramic crown is metal and what is porcelain?
- facial and occluso-buccal surface are porcelain
- the remainder of the crown is metal
How far should the shoulder margin extend interproximally in a MCC prep?
from a point approximately 1 mm lingual to the mesiobuccal line angle, around the buccal surface, to a point approximately 1 mm lingual to the distobuccal line angle
Why is the shoulder of a MCC prep extended past the mesio- and distobuccal line angles?
allows the porcelain veneer far enough interproximally to mask the metal contact area
True or false: The shoulder recess should maintain a uniform width around its entire circumference.
true
True or false: In mandibular posterior teeth, the proximal extent of the shoulder in a MCC prep can often stop just lingual to the proximal contact area.
FALSE. It stops just buccal to the proximal contact area because the esthetic demands for mandibular teeth are not as high as maxillary teeth.
If the occlusal surface of a mandibular posterior tooth is covered with porcelain, how is the occlusal reduction changed?
the occlusal surface must be reduced at least another 0.5 mm
What are the 3 major disadvantages to covering the occlusal surface in porcelain?
- it has the potential to abrade opposing natural dentition
- the potential for failure due to fracture under heavy occlusal loads is increased
- more removal of tooth structure is required
For MCC preps, what is the purpose of the buccal first plane?
- establishes the path of withdrawal for the crown
- provides space for the veneering medium
For MCC preps, what is the purpose of the buccal second plane?
reduced to provide for a uniform thickness of porcelain
The typodont buccal second plane of a MCC prep is usually what fraction of the occlusal-cervical height of the buccal surface after occlusal reduction?
1/3 - 1/2
What determines the angle of the buccal second plane of a MCC prep?
the depth orientation grooves which are the same as the original facial surface
What 2 problems will over-convergence cause?
- loss of retention form
- loss of resistance form
For a mandibular posterior MCC restoration, what is the final reduction of the buccal (functional) cusp?
1.5 mm
For a mandibular posterior MCC restoration, what is the final reduction of the lingual (non-functional) cusp?
1.0 mm
For a maxillary posterior MCC restoration, what is the final reduction of the buccal (non-functional) cusp?
1.5 mm (although non-functional cusp, need to allow room for porcelain and metal substructure)
For a maxillary posterior MCC restoration, what is the final reduction of the lingual (functional) cusp?
1.5 mm
For a maxillary or mandibular posterior MCC restoration, what is the final reduction of the central groove?
1.0 mm
What diamond bur is only used for MCC preps and what is it used for?
- 702.8M diamond bur
- designed to prepare the shoulder through its flat end
On the buccal and occlusal surfaces of a finished MCC restoration, what is the thickness of porcelain and metal substructure?
- 1.0 mm thickness of porcelain
- 0.5 mm thickness of metal substructure
What is the sequence of tooth reduction for a MCC prep?
- occlusal reduction
- buccal reduction
- buccal first plane
- buccal second plane
- lingual reduction
- proximal reduction
- shoulder finish line (1.2 mm wide)
- finishing and rounding of line angles
What bur is used to make the axial reduction guide grooves of the buccal first plane? Where are these guide grooves placed?
- 702.8M diamond bur
- 3 grooves: one in the mesio-distal center of the tooth, one as close to the mesial proximal contact as possible, and one as close to the distal proximal contact as possible
How far cervically should the axial reduction guide grooves be placed for the buccal first plane?
0.75 mm coronal to the pencil line
Where should the buccal second plane depth orientation grooves be placed in an MCC prep?
between the first plane grooves, angled with the occlusal half of the buccal surface
True or false: During the MCC axial reduction, the shoulder is prepared no wider than the diameter of the bur.
true
What bur is used for the buccal axial reduction of a MCC prep? What bur is used for the lingual axial reduction of a MCC prep?
- 702.8M diamond bur
- 242.6M diamond bur
True or false: The prepared mesial and distal walls of a MCC prep should not be parallel.
FALSE. The mesial and distal walls should be parallel.
What instruments can be used to refine the sloped shoulder margin?
7-8 or #9-10 off-angle hatchet
What is the ideal cavosurface angle of the shoulder in a MCC prep?
120 degrees
What is the ideal width of the shoulder in a MCC prep?
1.2 mm
What is the ideal facial reduction in a MCC prep?
1.5 mm
