Temporary crowns

Question 1

Why do we need temporary restorations?

Answer 1

• There is time between the prep of the tooth and the finished crown being cemented in. This is due to time being needed for the lab to make the crown.
• Aluminium temporary crown is put on the tooth as a temporary/provisional/interim restoration/crown.
• Temporary crowns can sometimes be longer than 3 weeks.
• Sometimes the temporary crown is actually the core of our crown.
• Also need to restore aesthetics and function – need to protect the teeth that is prepared.
• Prevent dentinal sensitivity tubules affect the odontoblasts.
• Protection from re-infection
• Prevent unwanted tooth movements.
• Try-out changes to aesthetics or occlusion.

Question 2

Why do we want to prevent dentinal sensitivity?

Answer 2

we have removed a lot of tooth tissue, so we are very close to the pulp. As soon as we cut into dentine, we involve the dentine pulp complex. Deeper into the dentine we go, the more dentinal tubule density there is (per mm squared). Up to 72,000 mm squared. Fluid movement in the tubules affect the odontoblasts.

Question 3

Why do we want to prevent from re-infection?

Answer 3

Root filled molar needs protecting from bacterial recontamination. This is portal entry for bacteria. Don’t want microleakage.

Question 4

How does a temporary crown prevent unwanted tooth movements?

Answer 4

o Teeth could overerrupt, drift, crowd, and close the space after the tooth is prepared. Teeth could also tip either side.
o Crown won’t fit if the teeth move as the model doesn’t match patient’s mouth anymore.
o If the crown preparation is overerrupted, the crown will still fit, but the patient can’t bite together properly anymore as occlusion has been disrupted.
o Need to adjust the crown, but if it is too large, then you have to reject the crown, redo the preparation and impressions, and make a new crown.
o When the teeth lean in and crowd in, the space between the teeth isn’t the same, the crown can’t seat properly as adjacent teeth are in the way. You can drill the crown down and use it as a temporary crown while you get a new crown made.

Question 5

How does a temporary crown let us try changes to aesthetics or occlusion?

Answer 5

o Can use them diagnostically as well.
o Orthodontic treatment is preferred method to fix a diastem.
o Can use temporary crown to see if they like the change of preparation for aesthetics before get the real crown cemented in.

Question 6

What are the ideal properties of a temporary crown?

Answer 6

• Aesthetic
• Sufficient strength to be functional
• Restore contact points
• Accurate margins to prevent plaque accumulation.
• Retentive, but easily removed when needed.
• Biocompatible.
• If there is bleeding on probing, cannot seat the crown so there would be a delay.

Question 7

What are the 3 main methods of manufacture of temporary crowns?

Answer 7

• 1. Direct custom made:
     o I) From an impression of the patient’s teeth
     o II) From a mould taken from a wax-up (impression or splint).
• 2. Prefabricated:
     o I) Anterior Polycarbonate (Directa).
     o II) Aluminium (Ion) posterior
     o III) Stainless Steel Posterior.
• 3. Indirect Lab made (for more complex cases).

Question 8

How is a direct custom made crown made from an impression of a patient’s teeth?

Answer 8

• Make a mould of the tooth (in example UL2 and UL3 crowns are being replaced).
• Use alginate impression to make a mould of UL2, and UL3.
• You don’t need to put this into perform but need to keep it moist/damp so you wrap it up with a damp gauze.
• Then prepare the tooth for the crown.
• Use the mould to make the temporary crown.
• We use our mould to put temporary crown material into it, injected into the mould with the tip of the dispenser and back filled to avoid an air blow/bubble.
• We use bis-acryl composite – injected into mould and mould seated back on the teeth.
• When the material has set, you remove it from the mould and trim it back to remove the excess.
• Try in the new temporary crown and check that it fits well:
• Cement with temporary cement e.g. Tempbond (Kerr-Dental).
• The crown would be the same shape and size as the crown would be/patients original teeth shape.

Question 9

How do you check a temporary crown fits well?

Answer 9

o Check margins are accurate.
o Check contact points recreated.
o Check occlusal contacts recreated.
o Check shade (limited selection)

Question 10

What are bis-acryl composites?

Answer 10

• Integrity (DS) used in the LDI, Pro-Temp 4 (3M) is another example.
• Adequate strength
• Accurate fit
• No mixing required
• Granular finish but acceptable aesthetics
• Choice of accurate shades
• Can repair with composite
• Poor stain resistance.

Question 11

How are direct custom made temporary crowns from wax-ups made?

Answer 11

• We do this technique if the tooth that needs the crown has a poor shape to start with or if we want to change the shape of the teeth.
• We ask the lab to make a wax-up of the shape of the final crown, and take a mould from that, usually with putty.
• Need a wax-up to show the patient.
• Lab produces an ideal shape of the crowns, to make a mould with.
• Vinyl mould:
  o Can make the final mould into a splint in order to make the crowns as well.
  o It is harder to do this one as it would be one big crown, rather than individual crowns as the temporary material would spill to other tooth grooves in the splint.
  o Can use integrity, as an aesthetic preview of the crown, to show the patient the final preview of what it would look like. We wouldn’t use bond so it wouldn’t stick and can be removed very quickly.

Question 12

What are pre-fabricated temporary crowns and how are they used?

Answer 12

• Crown prep –> select crown from range of sizes –> customise to fit the tooth accurately.
• Use soflex discs to adjust the anterior prefabricated temporary crowns.
• I) Anterior Polycarbonate (Directa).
• II) Aluminium (Ion) Posterior.
• III) Stainless Steel Posterior
• Mostly use aluminium for posterior teeth. Aluminium works well for posterior teeth when you haven’t got much space.
• First, we need to choose the material we are going to use.
• These are made in the factory so are a good hard outer shell which we fill with integrity and bond to cement to the patient’s crown preparation.

Question 13

How are anterior polycarbonate (Directa) prefabricated crowns used?

Answer 13

• Select the nearest size.
• Trim and line:
  o Trimmed to create a neat margin so it can be seated onto the crown preparation and adjust the margins.
  o Line the crown with integrity material (bis-acrylate composite) to create a close fit as the crown is hollow and fit into preparation.
  o Once it sets, it can lock into the embrasure spaces and it’s hard to remove, so remove while rubbery – to avoid locking into undercuts.
• Finished and cemented with a temporary cement (e.g. TempBond) – refined margin with integrity there, is customised to fit onto the tooth.

Question 14

How are Posterior Aluminium preformed crowns (prefabricated crowns) used?

Answer 14

• Readily adapted to the occlusion.
• Margins can be sharp and irritant – need to be trimmed correctly
• Poor contact points – need to burnish them
• Poor aesthetics
• Metallic taste.
• Margins trimmed to shape – use sheers/scissors to cut them.
• Patient bites onto the crown to deform it slightly to allow you to adapt the occlusion/adjust it.
• The crown is then relined with integrity.
• Then it is cemented with temporary cement e.g. TempBond.
• This crown doesn’t look good, but these are function, has proximal contact and fits all the margin.

Question 15

How are indirect laboratory made technique prefabricated crowns made?

Answer 15

• Used if we want a longer lasting temporary crown or temporary bridge (>3 to 4 weeks).
• Made in laboratory on a model.
• Made by a lab technician using acrylic materials usually Polymethylmethacrylate (PMMA).
• Acrylic materials are stronger and more aesthetic than direct chairside materials.
• PMMA has a lot of shrinkage and is a highly exothermic reaction so is not suitable for direct use in the mouth.
• We do the impression for the lab.
• 1. Technician starts with a pre-operative plaster model of the tooth.
• 2. A minimal crown preparation is carried out on the model and the crown made with heat-cured PMMA. They create a shell crown for us, to allow us to do our crown preparation, and then line with the crown made by the lab and integrity.
• 3. Return to clinician who prepares the tooth and then modifies the lab made temporary to make it fit using a chairside material such as Bis-acryl composite (E.g. Integrity).

Question 16

What are the advantages of indirect laboratory made technique crowns?

Answer 16

o Good marginal fit
o Good strength can also be used for temporary bridges.
o Can be polished
o Durable
o Lab does all this work for us.

Question 17

What are the requirements of a temporary cement?

Answer 17

o Strong enough to retain the crown for the period of temporisation.
o Allows easy removal when required.
o Does not adhere to the tooth.
o Don’t want it to be like resin cement.

Question 18

What are some examples of temporary cementation used?

Answer 18

• Fine particle zinc oxide eugenol cement e.g. Tempbond (Kerr Dental USA).
• Non-eugenol temporary cements available for use if using cements for permanent crown e.g. Tempbond NE (Kerr Dental USA).
• If we were planning to do a resin cement for our permanent crown, we want to use a non-eugenol version of Tempbond as we don’t want eugenol on our tooth when we cement the permanent crown with resin cements.