Operative, 11/7/11

Front 1

Best way to remove an undercut?

Back 1

1. eliminate what's in the way of your line of sight.
2. Block it out with a glass ionomer material.

Undercuts are barriers to smooth path of insertion.

Front 2

Occlusal and axial reduction.

3 disadvantages to underreduction for gold, ceramic, and PFM

Back 2

All indirect materials must have certain amount of thickness to meet properties of the material.
-Give lab tech enough space to work with.
-dependent on the floor depths.
-can get a hole in your restoration if not adequately reduced; wear through if its gold, breakage if its ceramic, and also esthetics for PFM.

Front 3

How to check occlusal reduction?

Back 3

Fast setting bite registration material - ramotec and blue moose..
-Designed to register the bite. 2ndary use is to check occlusal clearance.
-squirt it out over prepared tooth, bite down and don't open. 15 sec for fast set. Open quickly, and look at cross section. Look at how much space you have between crown prep and upper tooth.
1. could take iwanson gauge
2. make slices across the bite registration with a scalpel blade.

Front 4

How much space do you allow depends on what?

Back 4

1. depends on material.
2. resistance form - min thickness.
3. fracture + wear resistance
4. conservation of healthy tooth structure
5. keep technician happy
6. very common error

Front 5

What may inadequate axial reduction lead to?

Back 5

Esthetics will be poor because the outer surface may be too bright. Not enough translucency.

Front 6

Describe retention form for indirect restorations

Back 6

-can't be too retentive or else you'll have poor path of insertion.
Need some degree of taper for all and divergence for inlays.
-Many ceramics will be etched on internal surface. Veneers only retained by micromechinical retention.

Most are retained through micro and macro mechanical retention. Metallics: macromechanical. 5 to 10 degrees of divergence or convergence.
Ceramic: micro and macro retention. Macro isn't that important.

Front 7

Retention rules

Back 7

1. Preparation height. more vertical height, teh more retention you have.
2. degree of taper - should be between 5 and 10 for metal. 10 to 20 for ceramic. for long crown, don't need a lot of parallel walls (can get away with lot of taper)
3. boxes, grooves, and shoulders. accessory to previous preps to increase surface area of vertical walls.
5. sets of vertical walls

Front 8

Resistance form

Back 8

1. always important no matter what material.
best way to get flat gingival floors for inlay.
gold can bend or flex a little, breaking the cement seal. rocking may ocur.
2. resist rocking, gold flexion, tooth flexion/cement breakdown and cracking.
3. resist wear through of gold

-can adequate thickness
-flat floors: occlusal, gingival
-no sharp angles
-minimally invasive preps

Front 9

What's the best cavo surface angle?

Back 9

-Readable, proper finish line

Front 10

Definitions
1. seating
2. sealing
3. bevel

Back 10

1. how small the space is going to be that is occupied by cement. 5 to 7 microns is ideal.
2. how big is the space at the margin. esp on internal surface of inlay
3. bevel: 2 planes come together at something other than 90 degrees.

Front 11

Margins for cast gold

Back 11

Beveled gingival margin is always better than butt joint or 90 degree margin. Always will have a little gap .

Butt joint = sapce will equal the amt of non seating. If you put bevel on it, smaller sapce between gold and tooth at teh margin. The more acute the margin is, the smaller the space will be. If its too acute, (more than 20 degree) it becomes unworkable in wax and gold.
-makes it harder to push down the crown.
-finishing and polishing restoration is tough.
Ideal gingival margin is between 30 and 45 degrees.

Front 12

What about burnishing?

Back 12

gold can be burnished due to ductitlity. teh mroe acute the bevel is, up to 20 degrees, its easier to burnish.
30 to 45 is still ideal.

Front 13

for ceramic margins..
What are the rules?

Back 13

1. no bevels (poor edge strength)
2. etchble enamel - little bit more acute than 90 degrees.
3. no "j" margins (very common problem - small lip of unsupported enamel. will chip or breakdown. lab tech can't give you a good result
4. forget burnishing!

Front 14

Regardless of material, what must the margins and finish line be?

Back 14

1. flowing and continuous
2. right cavo surface angle
3. supragingival if possible. root surface margins are never as good as enamel margins. be above the CEJ or above the tissue. Only go below the gum if you need to.
4. clear, distinct, and readable. lab tech needs to see exactly where it is.

Front 15

Inlay 2 surface preparation steps

Back 15

1. diamonds that are tapered with flat end and rounded corners. Line up burr and handpiece above the tooth, near path of insertion. parallel to long axis of tooth. will end up with divergent walls.
2. Deep? Depends on material. cast gold - 1.5 mm min on working cusps. nonworking 1 mm.
lithium disilicate - 1 mm.
3. axial wall tapers inward so you have smooth path of insertion. MOD inlay - M and D must slightly converge towards each other. All other walls should diverge.