#5 – Crown & Bridge Procedures

#5 Crown and Bridge Procedures

A. Place Retraction Cord (if legal in your state)

Retraction cord has several functions

1. Helps control bleeding
2. Retracts tissue so margins are exposed.

Procedure

1. Measure a length of Siltrex #7 cord long enough to fit into the sulcus on the facial ½ of the tooth or completely around (up to dentist) pinkie size
2. Place the cord around the tooth gently
3. Using a small, plastic instrument or cord packer, place the cord into the sulcus beginning in the proximal where the sulcus is deepest and the cord is easiest to place. Continue around the tooth until the cord is completely placed.
4. Leave cord in for 5 minutes
5. Wet thoroughly before removal

Alternative – chemical retraction – legal

1. Isolate prepped tooth
2. Inject Retrac or Exposyl
3. Bite on cotton roll for 5 minutes
4. Remove, rinse, and dentist will immediately take impression before tissue retraction and hemostasis is lost

B. Take Lab Impression

You will need to take one (lab impression). This model will be used to check the accuracy of the lab work when the case is returned from the lab. Once this impression is in the client’s mouth, let your dentist know so the final impression can be taken quickly. If you wait longer than five minutes, the tissue will lose its retraction and we won’t get a good impression of the margins.

Place a new tip on the “gun.” Lightly air dry the teeth and cover with a 2×2 gauze. Ask the client to close gently. Load the tray. Inject around each prepared tooth three times (reduces bubbles). Seat the tray. Bring the client to an upright position. Have him/her put a fist under the chin. Hold for at least five minutes. The fist prevents the client from chewing up and down during the setting.

Polyvinyl siloxane lab impressions

Your doctor will make the impression that is used to fabricate the crown. That is the law. However, you will take a first impression. This first impression will be used to:

1. Confirm the accuracy of the fit of the crown
2. Evaluate margins on the dies
3. Clean the tooth and tissues

Currently the polyvinyl siloxanes are the best material available. Occasionally you may run into a problem using them. Here are some solutions:

1. Lack of detail

a. cause
1. material had started to set or removed before set complete
2. Sulfur in latex glove inhibits PVS set
3. exceeding manufacturers mix/set time
4. using fast set for more than 2 teeth

b. solutions
1. Double cord
2. Seat tray immediately after mixing
3. Avoid moisture contamination (speed set)
4. Seat in as straight line don’t rock the tray
5. Hold the tray steady during setting
6. Using a fast-set syringe material for more than 2 teeth at a time (must be joined to tray material in 30 seconds

2. Voids in the impressions

a. Causes
1) Impression not seated quickly enough.
2) Cotton rolls left in the month, not allow complete tray seating.
3) Blood/saliva on prep
4) Tip of syringe lifted, then put back into impression during expressing

b. Solutions
1) Keep the syringe tip near the sulcus. Ring the tooth slowly forcing the material in front of the tip. Cover the whole tooth.
2) Try surface wetting agent.

3. Short, open crown margins

a. Causes
1. not enough light body material to cover margins
2. not enough retraction
3. blood/saliva on prep
4. syringe tip not sub merged in material while syringing
5. too slow seating impression

b. Solutions
1. use 2 cord technique
2. check manufacturers mix/set times
4. Fins on teeth

a. Causes
1. client bites off to one side and slides teeth together into centric
2. tray disturbed during set
3. removed before complete set

b. Solutions
1. position tray carefully before seating and push vertically into position
2. client can rest head in palm of hand
5. Tight fitting crowns

a. Cause
1.Tray show through the impression. This could allow the tray to push out of the way, then after set when the tray is removed it could spring back into position distorting the impression.
2. Tray rocks during set
3. Weak tray that bends in the mouth and re bounds on removal
4. Tray contacts teeth
5. Adhesive not given time to set

b. Solutions
1. more rigid tray
2. makes sure tray doesn’t contact tooth

6. Inadequate margins
a. not enough retraction
b. moisture/ bleeding in sulcus
c. too much time between mixing and seating
d. tray movement after seating

Triple trays are ideal for single teeth. However, use full arch trays for bridges.You will usually take the first impression. This impression will clean blood and debris off the preparation. Let your doctor know when you plan to take the first impression. The second impression should be made no more than 8 9 minutes after the first or the retracted tissue will begin to close down over the margins. Follow these steps for accurate impressions:

1. Try in the tray for proper fit
2. Paint the tray at least 10 minutes before taking the impression so the adhesive will set and prevent the impression material from pulling away from the tray.
3. If there is bleeding, use hemodent in an Ultradent syringe or Expasil to control it. Isolate the tooth with a cotton role to keep this horrible taste away from the client.
4. Have your doctor place the retraction cord.
5. Scrub the tooth with chlorhoxidrine gluconate for 15 seconds (don’t rinse)
6. If some areas still tend to bleed, dip cotton pellets in hemodent and pack them into the bleeding areas.
7. After 2 minutes, rinse the hemodent.
8. Rinse and dry the tooth.
9. Clean the cartridge opening of set material before inserting the nozzle
10. Load the tray. Once the tray material is expressed, it begins to set, so either have someone load the tray for you, or go very quickly
11. Inject around the tooth twice pushing the material in front of the tip. Keep the syringe tip in the material at all times.
12. Leave the impression in place for 5 minutes.(Quick set 3 min)
13. Have your client place a fist under the chin and rest the elbow on the arm of the chair. This will eliminate the tendency of the client chewing on the impression during setting which can create a distortion.
14. Remove the impression rinse off all blood and spray with gluturaldehyde.
15. Examine the impression. If the tray shows through the impression, the impression may be distorted. Make a new impression.
16. After your doctor takes a second impression, show both impressions to the doctor.

C. Make temporary crowns

A temporary crown serves many functions. It is often taken for granted and made in a sloppy manner. These are the functions of a well made temporary crown.

1. Protect and sedate a pulp that has been injured due to the heat of preparing the tooth for the crown.

2. Keep the tooth from moving until the permanent crown can be seated.

3. Keep plaque from seeping up onto the prepared crown.

4. Keep the gums from overgrowing around the tooth.

5. Maintain the client’s appearance.

6. Help the client chew and feel comfortable.

7. Give us ideas on what the client likes for the final crown(s)

After a crown is prepared and before the impression is made, a temporary crown must be constructed.

We use 2 acrylics for temporaries:

1. Bisacrylics
a. Advantages – good for appearance, auto mix, easy to repair, ideal for anteriors.
b. Disadvantage – expensive, only strong enough for 3 unit bridge or less, limited shades
2. Polymethyl – methacrylates
a. Advantages – less costly, tear resistant, stronger, best for bridges
b. Disadvantages – heat during setting, may irritate pulp, hand mix, can mix shades to match
color.

Procedure

1. Mix/place acrylic I prepared teeth of impression
2. Seat over teeth
3. Remove after 2 minutes – if locked on tooth, tell your dentists immediately! If the acrylic sets completely, your dentist may need to cut it off and start again.
4. Remove excess carefully with a straight sleeve sandpaper disk running in reverse.
5. Seat temporary and make sure all margins covered. If areas are short, add more acrylic
6. Adjust the occlusion
7. Polish

The final shape of the crown should be:

1. Similar in shape and size to adjacent teeth
2. Straight up and down sides in the gingival 1/3
3. Good proximal contacts
4. Pontics room to run a floss threader under them and fit the threader through the proximals
5. Marginal ridges match adjacent teeth

Next, use articulating paper to check the bite. You can adjust the bite as you want until the client can close comfortably and chew in all directions without bumping the crown.

Occasionally the proximal contacts will be too light. Coat the proximal with an unfilled resin (Bonding agent). No etching is necessary. Light cure for 10 seconds. Take an old tube of off shade composite and coat the proximal. Seat the temporary. Cure for 20 seconds. Remove and cure for 20 seconds more. Smooth. This technique can also be used to repair short margins on your temporaries.

Finally, take the crown to the sterilizer soaked rag wheel and pumice to polish your crown behind op. 3 and 4. Follow this with a dry rag wheel and a polishing compound. Rinse it off. Seat it and check margins and bite. For bridges, give your client a proxibrush. Make sure the brush tip fits through the pontic proximals. Show your client. Have the doctor check the crown for you.

Temporary Crowns – Top of the line

You know how to basically construct a temporary crown. Now let’s discuss the “finer touches” to make them look like final restorations.

1. Strip off the facial surface of anterior temporaries and light care EX onto it.
2. Don’t forget that you can use color modifiers for temporary crowns to improve the match.
a. To make a tooth appear wider paint white on proximals
b. To make a tooth appear narrower paint brown on proximals
c. To make a tooth appear translucent incisal paint blue or gray on incisal

When all other steps are finished, cement with equal portions of the temporary cement. This hardens in about one minute. Carefully remove excess on facial and lingual with an exploring point. Use floss to remove excess from the proximals and show your client how to pull the floss through rather than pop out of the contact to prevent loosening the crown. Finally, use Cavidry to remove all excess. If the client will be traveling out of our area before the permanent crown is seated, tell them (or give them), that denture adhesive can be used to reseat the temporary if it comes loose.

Major Crown and Bridge Cases

Cases that involve more than 5 6 teeth in one arch require special preparations.

Your doctor will already have waxed up the final case on mounted diagnostic models so the client can see what the end result will be.

Soak this model in water for 5 minutes and make an alginate impression. This wetting keeps the alginate from sticking to the model a real mess! Coat the teeth with alginate before seating the tray for an accurate model.

Pour up the impression in quick set plaster. Make an .020 “splint” over the model. Trim the edges to the teeth, but you can make straight cuts. Don’t take the time to cut the gingival outline of all the teeth.

In the meantime, your doctor will lightly prepare the teeth on the diagnostic model.

Fit your splint onto the prepared model. Coat the model with a separating medium (such as Accufilm).

Mix a light and dark shade of Jet acrylic at the same time. Fill the incisal third and coat the facial with the light. Fill the remainder with the dark. Seat the matrix on the model. Secure it with rubber bands.

Put the model in the pressure pot for 10 minutes.

Remove, trim, use a sand blaster to clean out the inside of the crowns, and polish.

Final fitting is performed in the mouth. After the teeth are prepared and impressions made, try to seat the bridge. If it “hangs up”, grind out the inside of the crown that appears to be the problem. Be aggressive. You’re going to fill in the spaces anyway later.

If the bridge won’t eat after 3 4 adjustments, throw it away and make a new temporary bridge using your second splint.

Hopefully, the premade temporary bridge will fit. It is much stronger and polishes better than the direct method.

When your premade bridge is seated, adjust the incisal plane and occlusion.

Next, if the margins aren’t ideal, use the light activated GC acrylic around the margins. Don’t fill the crowns, only mold around and seal the margins.

When you and the client are pleased with the esthetics, take an alginate impression. One of the lab personnel should also meet the client and make notes on anything the client would like different than the temporary bridge.

D. Pick shades for esthetic dentistry

The most important function you have in crowns, bridges, partial or complete dentures is picking the right shade.

Before you start to pick shades you need to learn how professionals look at color. A color has three parts:

1. Hue what we call “color” green, yellow, red, etc.
2. Value How light the color looks
3. Chroma how deep or saturated the color is

A fourth characteristic, translucency is the depth of the value – how far you can see into the tooth.

To pick a correct shade system for a crown requires more than a “good eye for color.” The environment around you and the client must help you.
Next you must understand the 3 attributes of light:
1) Total amount of light-lumeus
2) Color temperature of light- Kelvin
3) Quality of light- CRI

A. Lighting
1. Fluorescent Recommendations
a. Color temperature (scale of warmth/redness to cool/blueness) 5500 degrees Kelvin (K)
b. Color rendition index (CRI) scale from yellow green to magenta daylight is CRI 100- bulb
must be over 90
c. Intensity of 150-200 foot candles 30 inches from floor
2. Halogen overhead lights
a. halogen lights have an average K temperature of 3,450 – way too red
3. Sunlight at noon is the ideal light.

B. The room
1. Ceilings as white as possible
2. Walls counter neutral gray or light blue
3. Uniforms ideally as neutral as possible
4. Kelvin and foot candle measures for operatories (lower temperatures look more red, proper color temperature is 4770-5500K and 95 CRI)
5. Colorimeter measurements of our rooms.

a. RM number Kelvin temp foot candles
2 6700 50
3 5100 65
4 5700 55
5 5850 30
6 5350 60
7 5750 65
8 5250 80
9 4450 80
10
11
12
13

5. Use the handheld fluorescent lites to increase the amount of light for more accurate shade selection.
6. Old fluorescent bulbs shift the Kelvin scale toward red.
7. use a light meter every 3 months to check K

C. Shade guide- Vita 3D master
1. Use same shade guide as porcelain used in the crown
2. Grind off collars
3. Shade tab should be held at same height and angle as tooth you are matching so light will reflect in the same pattern
4. Wet the tab and tooth for more equal reflectance
5. C and D shades are only A and B with different values.
a. Reddish brown
b. Reddish yellow
c. Gray
d. Reddish gray

D. The observer
1. The longer you look, the more color cones burn out, and the more shades appear to match
2. As we age, the lenses in our eyes become increasingly yellow-brown, which gives our shade choices a yellow-brown bias.
3. 10% of Americans have some degree of color blindness.
(1:13 males, 1:3000 females)

Crowns and Bridges

A. Ask ladies to remove any remaining lipstick and cover the client with the gray cover. This blocks out the view of colors from shirts, bibs, etc. that could interfere with seeing the color of the teeth. For example, a red shirt will add an orange hue to the teeth.

B. Make sure the tooth you are using to match shades is clean. Prophy this tooth if there is any stain.

C. Put the gray drape on the client’s chest. Your ability to differentiate colors is lost quickly. The color sensing rods in your eyes “burn out” in less than 15 seconds. This means that if you stare at 2 shade tabs long enough, they will begin to look the same. After you have worked on the shade for 10 15 seconds, look at the blue card for 5 10 seconds to rest your eyes.

D. Turn the lite Fantastik off. This incandescent light is too orange and too bright. Will not give you a good match. Remember the concept of “Metamerism (When you want to match a piece of cloth to a piece of clothing of yours in a store that has standard (cool white) fluorescent bulbs. It looks like a good match, but when you get outside in sunlight, the two shades don’t match at all! The problem is the wavelength of the light source. The closer the wavelength of the light source is to natural daylight, the less difference there will be in the shades. The other factor is the materials. A tooth has enamel, dentin, and pulp. A crown has layers of porcelain, gold, cement, dentin, pulp. The two objects absorb and give off light in different ways.) Our fluorescent bulbs are “color corrected”. This means they are as close to daylight as possible. They will still accentuate blues. To check your color perception, look at the shade guide. If all the tabs look the same, look at the blue paper.

E. Use the Vitapan 3D-Master shade guide. This is the most popular porcelain available. Virtually every porcelain, denture tooth, and composite is coordinated with the Vitashades. Make sure the cervical collar is removed on all tabs.
The Vita shade guide has four groups
A Dominant hue is reddish-brown (80% of natural teeth)
B Dominant hue is reddish-yellow (20% of natural teeth)
C Dominant hue is yellow gray (Not many teeth fall in this range)
D Dominant hue is reddish-gray If you look enough, you won’t be able to see the oranges in the tooth.
C and D are actually shades A and B of lower value
The main cause of mismatched crowns is not having enough light to see the shades correctly. We need 5500K. Use the hand held fluorescent light to get to this level.

F. The 3D Master System requires several steps for successful shade matching:
1. Value (light to dark) is the most important factor
i) pass back row of shade guide horizontally in front of tooth to find match while you squint
ii) write down first number 1 – 5
2. Saturation (amount or depth of color)
i) now look vertical down the row you picked to determine the correct saturation. The center tab is the shade most common in nature
3. Hue (color)
i) in the 3 centered groups, choose the correct hue L = yellowish, R = reddish
ii) complete designated: 3M2, 3L2.5, etc.

When you have a close match, turn on the Lite Fantastic just to have a second light source to match shades against.

G. Diagram the way color is distributed through the tooth on the yellow lab prescription. There is almost always a cervical and incisal separation of color. Expect to use more than 1 tab to describe these various shadings. Draw a line across the tooth to show the lab where the color changes. Sometimes this is a very distinct line. Other times it is a gradual blending that occurs over several millimeters. Use the “Doctor’s Guide to Personalized Shade Selection” to chose a close design for color distribution.

Sometimes various parts of the tooth will have different shades from more than one shade tab. Mark these tab letters and numbers on the sheet.

Look for special characteristics on the adjacent natural teeth. White spots, orange/brown discoloration, craze lines, fillings the more of these special effects you can design into the crown, the more you can miss the shade and still have a match.

H. Look at the texture of the tooth. You can diagram this texture or just note it as light, medium, or heavy. The rougher the surface, the lower the apparent value will be.

I. Look at the brightness of the tooth. Some teeth are dull. Others are very bright. Let the lab know how bright the tooth should be. The brighter the tooth, the lighter the shade will appear.

Special Notes

1. Your toughest job is to match one central incisor. Explain to your client that it is impossible to get a shade match under all light sources (remember metamerism?). If they are insistent on how important the shade is, discuss a porcelain jacket crown. By eliminating the best, liveliest as possible. However, they seldom last more than five years without breaking.

2. D4 doesn’t belong in the D group. It falls between B2 and B3.

3. Looking over a blue mask in place on your nose will give a green cast.

4. There is no such thing as a shade match only an acceptable shade range.

5. People in their 20’s have the best color vision. When you reach 30 your lens begins to yellow and crowns will look more yellow and brown than they really are.

6. Women have better color vision than men.

7. Your shade guide should be arranged in decreasing value
B1 A1 B2 D2 A2 C1 C2 D4 A3 D3 B3 A3.5 B4 C3 A4 C4
(high value brightness = low value (dull))

8. Remember the 5 characteristics of tooth esthetics
a. Color
b. Contour
c. Texture
d. Luster
e. Translucency

9. 99% of teeth don’t match shade guides

10. Beauty is natural, not perfect

11. Squint to see value (light/dark)

12. Don’t look longer than 5 seconds

13. Maxillary centrals, laterals, and first bicuspids usually the same shade.

14. Lower incisors are 1 2 shades lighter than upper centrals

15. Extrinsic stain increases chance of metamerism

16. Determine value, then chroma, then hue

17. M D contact points as far lingual as possible

18. 2 mm porcelain max.: any more = increase chance break

19. Make tooth look larger by moving ridge to D
Make tooth look smaller by moving ridge toward center of tooth
Make tooth look shorter
Make tooth look longer

20. Diastema close space and curve M to lingual

21. Esthetic verification
a. Midline
b. Arch form and contour
c. Length at width of teeth
d. Contact areas
e. Ridge contact of pontics

22. Centrals should diverge from midline slightly
Laterals should diverge from midline more
Cuspids should diverge from midline only slightly

23. Check for high or low lip line

24. The client’s canines have the highest chroma of the dominant hue of the tooth.

25. If you are deciding on the shade for 6 upper anteriors crowns, don’t make them all the same.
Follow the formula: laterals lighter than centrals lighter than canines

A. If you are not sure of a shade, always go to the lighter shade. A crown when custom shaded
always gets darker. If it’s too dark nothing can be done except start over.

Correct Tab Placement

Sending a picture to the lab of the client’s teeth with a shade tab makes the lab man’s task much easier
Follow these guidelines

1. Take a picture with the incisal edge of the shade tab near the incisal edge of the tooth adjacent to the prepared tooth.
2. Turn off the operatory light
3. Show opposing and adjacent teeth
4. Show shade tab number in picture or note on print.

Stump Shade

1. When making all porcelain crowns, the color of the tooth may show through the crown so we also color map the shade of the “stump of the tooth”
2. Use our special stump shade guide

Using X-Rite for Shade Selection

This technology is superior to using a shade tab next to the tooth. However, both have advantages. The X-rite is very accurate in determining the correct shade and the distributing of color through the tooth. At the same time, the digital picture of the shade tab next to the adjacent tooth helps our lab tech see the color and texture that must be matched.
Follow these steps to generate an X-rite print for the lab:

1. Place a disposable tip on and give it a 1/8th turn to lock in place
2. Put shade X in cradle and push read button to calibrate ( finished when button turns green)
3. Place plastic barrier over entire handpiece
4. Put tip on facial of tooth, hold steady and read button
5. Double click shade vision
6. click green button to get a patient not in list
7. type patient’s name
8. click checkmark
9. select operator
10. click green and to add
11. click green arrow (it will italicize patient)
12. wait until done
13. Remove instrument from docking station
14. Push measure with finger
15. Select a tooth with finger
16. Push target- you have 6 seconds to line up tooth
17. Push accept, put instrument down on computer

On Computer:

• Push save measurements
• Click checkmark

About tooth Picture:

 Click pull down arrow and click tooth
 Color tooth in grey
 Click incisal
 Color in incisal area with green
 Click gingival
 Color in gingival area with red
 Click green checkmark
 Click green arrow
 In work order number
 Type name
 Checkmark with tooth
 Click next green triangle
 Click finish
 Print only
 Send to lab-select H.P.
 Click checkmark
 Choose shade guide
 Printer set up-change to color
 Click ok

E. Seat Crowns

Reasons for crown remakes

Dentist says Lab says
79% Fit 78%
74% Shade 81%
52% Occlusion 66%
45% size/shape 42%
37% characterization 38%

When a case is returned from the lab, you should completely evaluate it. One of the worst experiences we have is having a client come in and trying in a crown and having a poor fit, etc. That forces us to remake the crown and our client to make another appointment. Check the fit on the die under magnification. Match the porcelain to our shade guide. Check contacts on the uncut model.

Single Crowns- Gold, PVC, Zirconia

When the client arrives, go through the seating sequence. Be sure to wear magnifying glasses.

1. Remove the temporary cap using an exploring point or a spoon excavator. Ask your client if the tooth has been comfortable. If the tooth hasn’t been comfortable, offer nitrous oxide. If this isn’t enough, then ask your doctor to numb the tooth.

2. Clean any temporary cement off the tooth with a dry 2×2 gauze or an explorer. You can rub the facial and lingual. Shoe shine carefully in the proximals. Make sure no tissue has grown up the side of the preparation. If some temporary cement won’t come off, place H202 on a cotton pellet.

If you remove your temporary crown and see overgrown tissue, bleeding gums, or smell a bad odor, then either you made a poor temporary crown or the client didn’t brush and floss adequately.

3. Seat the casting. If it won’t seat all the way, ask your client to close carefully, warning him/her that they will only be touching on the crown. Use a piece of dental floss to check the contacts. This is difficult to do by yourself. Put one finger on the casting and run the floss through the contact. You can also place the tip of an exploring point onto an occlusal groove and ask your client to hold and push while you floss. The floss won’t go through the contact that’s too heavy. Look at the model. See how much of the adjacent tooth’s proximal surface has been worn away. This will give you an idea whether the mesial or distal contact is too heavy and how much to grind. Paint White Out on the proximal. Seat the crown and remove it. The white out will rub away from the interference. Grind this area. Repeat until the floss fits correctly. Do a little at a time. Use a gray separating disk to trim the casting. The porcelain trims away much quicker than the metal.

4. When the casting seats completely on the tooth, check the proximal contacts with the floss again. Be sure to have your client bite down. Without this pressure, you may find that you still can’t get the floss through the contacts. When the floss fits through the contacts correctly (if too light, make note so the doctor can check), use an exploring point and see if you can get under the crown or catch a margin anywhere. Run the explorer from the tooth to the casting and from the casting to the tooth. Next try to rock the casting on the tooth. If there is a rock or a marginal discrepancy, look again at the die and the tooth. Is there a thin area or groove on the tooth that didn’t reproduce on the die? If so, use a high speed #4 round bur and clear out the area on the inside of the crown that corresponds to then non-reproduced area on the tooth.

Seat the crown. If there are still discrepancies, let your doctor know. While you are waiting, prepare the impression tray for a new impression (Just in case). Don’t spend more than 30 minutes in this process.

If the casting seals correctly, it’s time to check the occlusion. Remove the casting and ask your client to close together. Find an upper and lower anterior or bicuspid pair of teeth that fit together well. This is your gauge to see how the teeth fit together. Now place the casting on the tooth. Ask your client to close. Is there a space between the teeth that are supposed to touch?

If the casting is too high when your client bites down, this is called a centric interference. Look at the picture on the lab slip that shows the posterior occlusion contacts. Use a diamond (porcelain) or a #4 round bur(metal) to grind away the red contacts that show from the articulating paper. Do this holding the casting in your hand. Reseat, re-ink, and recheck the bite. If you don’t have a pair of teeth to gauge the occlusion, use the shim stock. This is a milled metal sheet (.0005 inch) that is 1/2 the thickness of a human hair. Cut off a piece that is less than the mesiodistal length of the tooth and grab it with a hemostat. Place it on the tooth behind the casting and have your client close. If s/he can’t hold the shim, then come forward and place the shim on the casting and bite again. If this holds the shim, then the casting is too high. Ink it with articulating paper and have the client tap. Stop grinding when the shim is held by the teeth in front and back of the casting. Don’t try to smooth out the occlusal surface. Just grind away the red spots.

Next, turn the articulating paper over and have the client “grind all around”. Make sure your client moves their jaw at least five mm to the left, right, and protrusive. Next, take another piece of articulating paper, red side toward the casting. Have your client tap their teeth together. Now, grind away all the black marks, but don’t touch the red. Repeat this until no black shows. This will remove all interferences and still leave your centric contacts.

Now have your client bite down again and grind around on the red articulating ribbon. Smooth and establish the occlusal anatomy, don’t remove the red contacts. These contacts support the upper tooth. Hopefully, you will have at least 2 3 contacts.

Finally, check the shade of the porcelain. Flip the client mirror down and let your client see the crown. Turn the light on and off. Don’t stare at the crown. The longer you look at it the better it will look but this is only because the color cones that sense color burn out quickly in your eyes and you won’t be able to see color differences well.

If the color match is good, call the doctor. If the match is not good, get out the shade guide take an intraoral camera picture of the crown in the mouth and a second with the crown in the mouth and the correct shade tab.

While you are waiting for the doctor, polish the crown.
1. Have you changed the anatomy during your occlusal adjustment? If you have, cut in the
anatomy again
2. Look at the margins and metal finish under the microscope.
a. Use the red rubber wheels to smooth the metal.
b. Use the Shofu porcelain polishers to smooth the porcelain.
1. White stone reshape occlusion
2. No banded mandrel first level of polish
3. Single yellow band mandrel final glaze
4. Double yellow band mandrel top polish
5. Use the Enhance kit for the final polish
3. Sandblast the inside of the crown

Now return to the client, seat the crown and check everything.
1. Margins so smooth you can hardly detect them running from tooth to crown or crown to tooth
2. Bite feels comfortable no side to side interferences
3. Looks like a real tooth in the client’s mouth
4. Floss shows tight contacts
5. Polish the porcelain where you’ve ground it with the Shofa porcelain polishers – in this order- white stone, no ring, yellow band, 2 yellow bands, and then white band

Metal crown interior that needs more retention – Tinplate (Danville kit)
1. Sandblast interior of crown, rinse, dry
2. Place the felt tip, or a small cotton pellet, into the cylindrical opening
3. Put the tip into the plating solution for 1 minute
4. Make sure the 3 batteries into the handle
5. Put the ground on the outside of the crown on metal. If this isn’t possible, put it into a dry corner inside the crown
6. Rub the felt tip over the inside of the crown
7. When plated, you’ll see a gray/white residue
8. Only place 1 coat (.2 microns)
9. Rinse, dry, and immediately cement the restoration

Zirconia Crowns- extra steps

1. Zirconia is much harder than gold or porcelain and requires some special care
2. If the occlusion must be adjusted, use a high speed diamond with water, then sandblast ,
finally polish with Dialite
3. Without a complete polish this roughened Zirconia surface will wear away the opposing
tooth.

Porcelain Crown

1. Again, porcelain requires a couple extra steps
2. Once the prepared tooth is clean, wet the inside of the crown and seat it. This allows the true color to be evaluated.
3. When the shade and fit are ok, etch with 35% phosphoric acid
4. Rinse, dry and silinate the crown( thin coat)
5. after 1 minute dry
6. paint tooth and inside of crown with SE bond
7. coat interior of crown with selected composite cement
8. seat, light cure 5 seconds
9. remove excess cement and light curing facial and lingual- 40seconds each

Bridges
1. Metal framework Try in

The occlusion is much more difficult to establish on a bridge than on a single crown. It is much more likely that the teeth may shift or the dies may not seat perfectly. Usually a combination of these facts will occur. This will result in considerable grinding on the occlusion unless the framework is tried in first.

Do all the steps you would go through to make sure the castings fit. Next, look at the relationship of the castings to the opposing teeth. Now remove the framework and look at the relationships of the framework to the opposing teeth on the model. A second way to do this is to place some warm, Swissdent wax on the bridge framework only and have the client close. Next, remove the bridge and seat it on the model. Does the wax force an increase in the vertical dimension (holds natural teeth out of
occlusion?)

If the framework seats in the mouth different than it does on the model, you will need a new working model. Seat the framework in the mouth. If there are teeth in front and back of the bridge you won’t need a wax bite. If there are no teeth behind the bridges, take a wax bite for an accurate mounting later. Now take an alginate impression and try to capture the bridge in the impression. If it stays on the teeth, remove it and seat it in the impression using the microscope. Make sure it seats completely in the impression. Lightly coat the inside of the crowns with Vaseline and pour the impression. When hard mount it against the original opposing model.

2. Finished bridge

If there is still a slight rock and everything looks good, seat the bridge for 24 hours with “Easy Seat” (1-888078206354, Ballard Plaza Pharmacy, 1801 NW Market ST., Seattle, WA 98107). “Easy Seat” won’t get hard, so it allows the teeth to shift slightly so the bridge will seat. If the bridge won’t stay in:

1. Seat the most retentive casting with temporary cement and the other abuttment(s) with “Easy Seat”.
2. Make a thin suck down over the whole arch.

Anterior Crowns

Again, go through the seating sequence. The occlusion (bite) is much easier to adjust on front teeth. Use the red ribbon that Dr. Smith uses for occlusal adjustments. “Your client should be able to close their back teeth together with the ribbon between the front teeth. You should be able to pull the ribbon out with only very light contact on the centrals and laterals. If the tooth hits very heavy, use the millimeter gauge calipers to gauge the thickness. Don’t grind the crown thinner than 1 1/2 mm. If you need to grind more, let your doctor take a look. Next, use the red/black articulating paper and have the client grind side to side and forward and back. Put your finger on the facial of the crown and feel for a heavy contact that loosens the crown. Again continue to grind, mark, and grind until the articulator markings are even on all the front teeth and you don’t feel any movement of the crown.

Now complete the crown as though it was a posterior crown.

Why do we go to all this trouble? The flat margin with no bulges at the gums keeps food from trapping against the gums. The tight contacts prevent food from packing between the teeth and the drifting of the teeth. A good fit protects the gums from periodontal disease and the tooth from new decay. A correct bite prevents TMJ problems. A good shade match pleases your client more than anything else!

This procedure is the ultimate dentistry. How do you complete the seating appointment with your client? I hope you will show him/her the crown in the mirror. Discuss how nice it looks. Compliment them for their choice.

Remakes

Okay, the crown didn’t fit. You can always expect that one out of every twenty crowns won’t fit. That’s acceptable human error. However, periodically in my career, I’ve gone through 1 2 months when many crowns didn’t fit. When this happens, you and I will go through the following check list to try to locate what is going wrong.
1. Preparation of the tooth undercuts, poor margins, not enough tooth reduction, not enough retention
2. Margins wiped away on die (or dentist to trimming and marking own margins)
3. Impression trays rigid so won’t give and distort
4. Is impression material pulling away from the tray
5. Did the impression material cure completely?
6. Is the die stone compatible with the impression material?
7. Are crowns mounted accurately?
8. Is the correct amount of expansion allowed for during investing/casting of the wax pattern?
9. Was the temporary crown OK?
a. Maintains occlusal contacts
b. Maintains proximal contacts
c. Fits margins of prepared tooth
10. Did we wait at least 2 hours before pouring a PolyVinyl siloxane and not more than 4 hours?
11. Was the alginate impression poured within 5 minutes?
12. Were the models mounted correctly?
13. Were the models equilibrated?

Here’s a trouble shooting outline published in Dental Practice Success

Problem: Restoration prepared on the die does not fit the preparation or is in supraocclusion.

Causes: Lack of relief in primary impression in a two step technique; The final impression with too much pressure; Triple tray distorts the impression because occlusal ribs are distorted during the bite; The stone/water ratio is incorrect when pouring the model.

Solutions: Primary impression relieved adequately to create room for final wash material; Impression held passively in mouth during curing; High durometer in material to prevent triple tray from distorting impression upon relaxation; Correct powder/water ratio in stone results in properly sized dies; Work rapidly; Cool material; Use a vinyl retarder.

Problem: Unset areas in the impression when the balance of the impression is fine.

Causes: Localized poisoning because of contact with sulfer, amine, eugenol, wax, or hemostatic agent

Solutions: Teeth or tissue should not be touched with latex gloves; Composite restorations must be in place 24 hours before crown preparation and impressions are taken; Some wax has a petroleum base and contains sulfer, therefore, such wax should not be used in or on an impression tray; Remove residue of temporary cement from the preparation before taking the impression; Change hemostatic agents or flush the sulcus thoroughly.

F. Cementing the crowns

Rely-X
1. Isolate the tooth with cotton rolls
2. Lightly dry and make sure there is no bleeding. Bleeding will displace the cement and increase the chance of recurrent decay.
3. Mix the cement.
4. Use a spatula to apply the cement to the interior of the crown and an instrument to spread an even 1mm coat over the interiors of the crown.
5. Seat the crown and doctor will check the bite. Have client bite on cotton roll (light cure 3-5 seconds). Remove the cotton roll and light cure lingual 3-5 seconds.
6. Dentist will carefully remove most excess cement.
7. Light cure facial and lingual 20 seconds each.
8. Recheck occlusion.
9. Dentist will remove any remaining excess cement.
10. Rinse, ask client if crown feels smooth/bite is ok, and walk your client to the reception desk.

Panavia F

Our best cement is Panavia F. It also costs about $10 per mix, so we only use it on crowns/bridges that might come loose with regular cement. Follow the instructions with the kit. Here are some extra tips.

1. Any gold crown should be tin plated. This triples the retention.

G. Fitting Crowns Under an Existing Partial Denture

When you have completed the lab polyvinyl siloxane impression, sent the partial denture and take an alginate. Wipe alginate all around the prepared tooth to get the most accurate impression possible.

Check the impression to make sure the partial denture is still completed seated. Use the microscope to be sure.

Pour this impression quickly if the client won’t leave the partial denture with us. It will take 15 30 minutes for the stone to harden. Have the lab carefully remove the partial denture from the model. Clean the partial denture and return it to the client.

Find out from the lab when they will be ready to fit the partial denture around the crown.

H. Pour Models (currently done by commercial lab)

Learn lab duties pour models using Whipmix Vacu Vestor trim, mount, using facebow

When you know the alginate impressions will be made, set up early. Get out the stone and shake it up. The rubber bowls, spatulas, and lay down two paper towels in front of the vibrator. After the impression is made:
1. Rinse impression to remove all blood and saliva
2. Spray it with Biocide at the sink where you rinsed the model
3. Wrap a wet towel around the model
4. Take the impression to the lab
5. Rinse and pour the model

Pour it as quickly as possible. Alginate impressions begin to dry out and distort within 5 7 minutes. If you are going to be more than a couple minutes, cover the impression with a paper towel. Use Play Dough to fill in the tongue space of a lower impression.
When you are ready to pour the impression use these steps:
1. Using a spatula, feed stone into one end of the impression. The vibrator on the counter should be set at a medium speed and the handle of the impression tray should be held against the vibrator. This prevents you from over vibrating which would cause air bubbles to form in the stone.
2. Move the stone around the impression so slowly that you can see the stone drop in one side of the impression of a tooth, fill the tooth, and then flow over into the depression of the next tooth. This will clear out any remaining saliva.
3. When the base of the impression is filled, allow stone to run out the opposite side to make sure all saliva and air bubbles are eliminated. If you pour the stone too quickly from tooth to tooth, you may trap air and end up with many bubbles.
4. Next remove the handle from the vibrator and take a bulk of stone and scrape it into the sides of the tray to fill it to the rim. When this is finished, again briefly put the handle on the vibrator to fuse all this stone. Remember, over vibrating traps air bubbles.
5. Finally, overfill the tray to a height of about 3/4″. Hold your spatula vertically against the side of the tray and scrape away the excess. This will save you a great deal of grinding later.
6. Place the handle of the impression in the wooden slot in the plastic humidor with a wet paper towel and close the lid. This high humidity keeps the alginate from drying out as the stone hardens avoiding more distortion.
7. Quickly rinse the plastic bowl. If the stone sets in the bowl it is difficult to remove.
8. Now turn off the Vacuvestor. It needs to run about one minute after the vacuum seal is broken to relubricate itself. Surfactant spray first before pouring.

9. Pour Models using Whip mix vacuum investor
a. Model is removed from client’s mouth
b. Spray model with Biocide, rinse

c. Mix stone in Whip mix vacuvestor
1. Type of stone
a. Pink Vel Mix used to parallel models except crown and bridge
b. blue die stone use for crown and bridge

2. Fill vial to top blue line and pour in to round plastic container (wet container first)
3. Use a spatula to mix the stone in the container use enough stone to make a “cake like” batter
4. Turn on Vacuvestor
5. Fit top on Vacuvestor and insert vacuum hose in small opening on top
6. Insert drive shaft in top of plastic container into receptacle on unit
7. Run for 20 seconds
8. Remove from drive shaft
9. Sit bottom of plastic container on rubber vibrator rotate around to vibrate stone down sides and off the metal blades
10. Pull plastic vacuum line out of lid and let vacuum run for 1 more minute to automatically re-oil machine
11. Remove lid and immediately rinse off in the sink
12. Use a spatula to lift the stone from the container and feed into the molar end of the impression
13. Put the impression tray handle on the round vibrator on the table, the vibrator should be turned on a medium setting and the impression only vibrated enough to move the plaster over the impression. If you vibrate too hard you’ll force air bubbles into the plaster.
14. Pour only a small amount of plaster around the teeth in the impression and pour it out the other side. This will remove saliva, etc. from the impression.
15. Next, fill each tooth impression, one tooth at a time with plaster. Go slow. You should be able to see the plaster fall into one side, fill the tooth space and roll over to the next tooth
16. When all the teeth spaces are filled, take a large amount of stone and fill the rest of the tray. Mound this material up about 3/8″ above tray. Using your spatula scrape the excess plaster off the sides. If the plaster is too runny, it will keep falling over the sides. With practice, you will learn how stiff to make your plaster mix.
When the impression is poured, place it in the humidor with a wet paper towel. This will give us the most dense plaster model possible. Fit the tray handle into the wood block. This keeps the tray off the floor of the container where it could be warped.

I. Trim models

1. The plaster will usually harden in 15 minutes. If your finger can’t scratch into the plaster with light pressure, you can break the model out of the tray.
a. Be careful! If you twist the model too much you could break the teeth off the model!
b. Use a “buffalo knife” to wedge between the model and the impression. Twist only enough to lift the model slightly. Do this on the front and each side. Now go back to the first side and separate the model about 1/2″. Do the same on the other sides. Now use your hands to separate the models the rest of the way.

2. Clean the impression material out of the trays and place them in the tray cleaning solution under the sink. Clean up any plaster mess.

3. Take the models into the lab and trim off the excess plaster:
a. Wear safety glasses
b. Turn the model trimmer on and turn the cold side water on. This will run water through the cast grinder and prevent the plaster from clogging the grinder. Too much water will allow it to run out the front of the grinder. Too little will allow plaster to clog the grinding wheel.
c. Begin by flattening the bottom of the model. This will make all your other cuts easier. It should be about 3/8″ thick. This will give the model strength, but still be thin enough to mount on an articulator. Cut the base parallel to the occlusal (biting surface) plane.
d. Place the flat side of the lower model down and trim the back don’t trim any of the sides. If you are trimming upper and lower models for display to a client and they aren’t going to be mounted, fit them together using the bite registration and carefully grind both backs at the same time.
e. Next, trim the sides and the front. Be careful not to cut the teeth. Trim until you are about 1/2″ from the teeth. The lower model has a rounded front. The upper model comes to a point at the center.
f. If you are trimming a model that will be used for an appliance complete, partial denture, or TMJ splint, have someone show you how far to cut. You could destroy this model if you’re not careful.
g. If your models are to be used for client demonstration, follow these steps:
1. Using the microscope, remove all bubbles with a sharp knife.
2. Using magnification, fill in all voids with a mix of stone and water.
3. Make sure the lingual area of the lower model is smooth and neat.

 

J. Mount Casts Using Facebow (used to relate the upper model to the TMJ)

1, Pick the correct Whip mix. The one marked “A” never leaves the office all diagnostic cases go on this one. All others go on any other instruments.
2. Clean all excess plaster off articulator
3. Place mounting plates on the upper and lower members of the articulator
4. Remove the vertical dowel pin from the front of the Whipmix articulator
5. Attach the sides of the facebow to the small dowels sticking out on the sides of the articulator and tighten the 3 facebow screws.
6. Take upper and lower models to the microscope and remove all bubbles on the sides of the teeth and the biting surfaces.
7. Place the model in the red wax of the fork. Make sure the teeth fit all the way down. sometimes the untrimmed back or sides will prevent the model from seating completely. Trim the model until it seats properly.
8. Close the top member of the articulator down to make sure the front projection touches the facebow. If the model prevents this trim enough off the bottom of the model so that the contact is made.
9. Mix white plaster in a rubber bowl and mound some on top of the model. Lower the top of the articulator down until is flattens the plaster between the mounting plate and the model and the articulator top rests on the facebow.
10. Use extra plaster to fill in the sides between the mounting plate and the model.
11. Scrape out the bowl with your spatula and throw the excess plaster into the trash. Never wash it down the sink. It can clog the pipes.
12. Run water in the plaster bowl and, using your fingers, smooth the plaster while holding the articulator with your left hand.
13. Wait about 3 minutes for the plaster to harden. Then remove the facebow by unscrewing the 3 screws.
14. Replace the vertical dowel and turn the articulator upside down. There are markings on the dowel. The round end should be against the plate of the lower member. The one line that goes all the way around the dowel should be at the top of the ring of the lower member.
15. Fit the lower model against the upper. Usually, they will fit right together. If you aren’t sure that the teeth mesh well, check with one of the doctors. Make sure that no tissue areas interfere and hold the teeth apart.
16. Set the lower model on the upper and, while supporting it, place a mound of white plaster on the middle of the lower model.
17. Close the lower member of the articulator down onto the vertical dowel. Set at the “0” mm mark.
18. Complete same as top model.
19. When finished, spray facebow and wrench used to tighten sections to sink, spray with Biocide, and scrub.
Return to numbered bin.

K. Sectioning

Once the C&B model is hard (allow at least 20 minutes a good test is to try to scratch the back of the model If you can cut easily into it, it’s too soon to pull it apart you might break a die by pulling it apart too soon. Don’t wait until the model is no longer warm this is longer than necessary) separate the impression from the model. The flat end of a Buffalo knife wedged between the model and impression and carefully twisted will help separate them. Be sure not to wedge where the teeth are prepared.

When you are beginning, hold the model up and look at it. Take a pencil and draw a vertical line that parallels the dowelpin (for hydrocolloid) or the prepped tooth and adjacent teeth (laminar technique). Place the model on the gray putty to support it and prevent it from twisting in your hands.

Determine the angle of the cut for hydrocolloid. If the cuts are wider at the bottom than at the top, you won’t be able to remove the die. With only slight pressure run the blade along the spot you want to cut. Don’t touch the margin of the die! This light pulling movement of the blade gives you great control and avoids the blade skipping and cutting your die. Next, saw carefully back and forth once to make sure the blade will stay in the groove. If it won’t; score it again. If it will, check your lines on the side of the cast and then make your saw cuts follow these lines. In the laminar technique, cut completely through the model. In the hydrocolloid technique, only cut through the first stone pour. Then turn the model over and hit the dowel with the handle of the silver spatula.

Gross Trim

Now that the die is separated, gross trim it. Turn the lathe on high, turn on the light, and turn on the vacuum. In the hydrocolloid technique trim the entire die smooth, top to bottom, within 1 mm of the finish line of the prepped tooth. Wear a pair of loops to do this. As you do more intricate technique work with your hands, you will need them more and more. In the laminar technique, only gross trim the top 1/2 of the die. The bottom 1/2 is needed to lock into the tray. Trim the top 1/2 as you would a hydrocolloid die.

L. Lab infection control

Our lab is in a separate room to make it easier to maintain ideal infection control procedures. All labwork should be performed in the lab. All clients and their lab generated materials must be treated as though they are infections.

Receiving area
1. Every case that comes into the lab from a client must be decontaminated.
2. Cover area with a paper towel.
3. Disposable trays, impression material, and other waste should be disposed of in normal trash unless designated as medical waste.
a. Sharps into sharps container.
b. Reusable items sterilized before reuse.
4. Alginate impression spray with Glutaraldehyde
5. Vinyl polysiloxane – spray with glutaraldehyde
6. Prosthetic appliance scrub with soap/water

Shipping area

1. Receiving area should be separate from the shipping area.
2. Make sure all items properly disinfected before packing.
3. Never pack lab cases in packages containing disinfectant.

Lab equipment/supplies

1. Articulators, lab pans, face bows, etc. should be cleaned, sprayed with Glutaraldehyde, wiped down, rinsed, and dried.
2. Change lab pumice daily.
3. Lathe should be cleaned daily.
4. Change rag wheels daily.
5. Pressure pot should be cleaned daily
6. Contaminated bench tops should be cleaned daily.

General Rules

1. No eating or drinking in the lab