Describe in detail and in the correct sequential order, the various stages that are required to complete a bonded porcelain crown with a palatal collar and porcelain margin, starting from the divesting of a successful alloy casting.

Flowchart nodes

• Describe in detail and in the correct sequential order, the various stages that are required to complete a bonded porcelain crown with a palatal collar and porcelain margin, starting from the divesting of a successful alloy casting.

•      Metal casting is desprued, using a high-speed circular drill head to remove the metal sprue

•      Any irregularities that may cause the coping to not seat down fully on the model are removed

• 3.  Using a tungsten burr, lightly trim the surface of the casting in one direction. This prevents any microscopic hooks occurring that could prevent the porcelain successful bonding to the metal.

• 4.  Gritblast lightly to remove any residues

• 5.  With the use of gloves protecting the casting from being contaminated, place on firing stand and put in furnace for de-gas or oxidation firing (960⁰C in air for NP alloy) is not recommended for all alloys,(check manufacturers instructions) and may require a 2nd grit blasting stage before opaque application

• 6. Blast coping with Aluminium Oxide to remove the excess green oxide layer prior to opaque application

• 7. The Wash Opaque powder (also available as paste) is mixed with Opaque Fluid and applied to the clean coping. This dries quickly, place near (but not in) the open furnace for a few minutes before commencing the firing cycle. (fired at 940- 950⁰C or 50⁰C lower for precious alloys)

• 8. The Wash Opaque when fired is quite glossy and patchy and cannot be used on its own. Repeat opaque application once or twice, and firings, to hide the dark oxide colour

•    9. A conventional opaque layer is applied to cover the Wash Opaque (WO) and fired at 920-930ºC for NP alloys, under vacuum (30º lower for Precious alloy)

• 10. A thin, almost dry coat of ceramic separating agent is applied to the shoulders of the pre-sealed die prior to building the margin with the Shoulder Porcelains

• 11. Place tiny blobs of shoulder porcelain along the anterior periphery and pat down so that it is flush with the margin

• 12.  To remove the copings from the dies, push the coping gently down towards the shoulder with thumb and forefinger while gently twisting the coping and lifting off

•     13. The ‘Margin‘ or shoulder porcelain is fired at 890-900⁰C or 10⁰C higher than the recommended 1st Dentine firing

• 14.  The Basic Layered Crown consists of Opaque, Base Dentine, ENL Enamel with Shoulder or Margin material in the Cervical neck area and should follow the emergence profile of the natural tooth relative to the gingival tissue

•  15.  Place the model in a bowl of water to soak. Meanwhile mix a small amount of shade Base Dentine with Dentine Liquid using a glass or agate spatula, never use a metal spatulas this could contaminate the porcelain mixture.

• 16. Dentine and Enamel Modelling or Build Up liquids consist of colloids (suspension of particles in a solution) which help to control the wetness of the porcelain mix throughout the building up process. Their use can aid the way in which the porcelain ‘stacks’  and holds together through changes to the positive and negative charged ions within the mixture. Tap water should not be used as a substitute either, it contains many minerals which may not fully ‘burn out’ during firing particularly with ceramics that fire below 800⁰C, causing inclusions or a grey appearance in the ceramic after firing.

• 17. Apply the Base Dentine around the cervical neck and labial face quite quickly, keeping the ceramic moist

•    18. Apply Base Dentine to the palatal aspect, while the ceramic is all still moist it will flow together easily

• 19. The Base Dentine is built to roughly the same length and width as the adjacent tooth

• 20.  Build up the porcelain in order to mimic the corresponding tooth. For an incisor create a palatal concavity to begin the shaping of the cingulum and lobes. For molars cusps must be designed in order to function.

•     21.  ‘cut back’ an incisal wedge on incisors to allow for the enamel porcelain to act as a translucent layer.

• 22. Mix enamel porcelain with the modelling liquid and apply the wet paste across the labial/incisal face starting from one of the corners and working across to the other

•   23.   The enamel layer is completed leaving the crown 1.5-2mm longer than the corresponding tooth to allow for the 15-20% shrinkage during firing, check the palatal occlusion

•  24. The crown is carefully pushed or lifted from the model, this exposes voids on the mesial and distal sides which need to be filled with enamel to increase the overall width, 2mm

• 25. After filling the proximal voids, check for additions around the shoulders, remove any remaining moisture with tissue paper and carefully remove the crown and place on a firing stand

• 26.  After the crown has fully cooled, examine the inside to check for interferences caused by small pieces of ceramic that may affect the fit. Carefully remove these interferences with a fine diamond bur until the crown fits down passively on the die.

•   27.  Place the crown and die gently into the model, taking care not to force the die to fully seat down, this could damage the stone contact areas. If the crown is very tight, remove one of the adjacent sections of the model.

• 28. The basic layered crown after 1st Dentine firing is slightly oversized which will need adjusting before attempting to seat the crown within the model

• 29. Using a strip of single-sided red articulating foil, place it between the oversize crown and the contact with the adjacent tooth, gently pulling it through the contact to mark the widest area of the crown

• 30. Using a medium abrasive Heatless Wheel, gently reduce the area on and just above the red mark towards the incisal tip

• 31. After easing this area, repeat the process until there is no heavy red mark and the foil can ‘just ‘be pulled through, indicating a passive fit

• 32. Using a diamond bur blend the ceramic/metal interface on the palatal surface and create a concave surface on the palatal aspect while checking the occlusion

• 33. Begin to shape the labial surfaces using a heatless wheel or Green stone. Wet the surface with water to enable the dentine/enamel depth to be determined and show where the light is being reflected

•   34.  Apply Base Dentine or Enamel to the crown if required to improve the shape, contact areas, or to improve the marginal fit

•     35.  The Basic Layered crown with added enamel is placed on a firing stand to dry briefly then fired on 2nd Dentine firing cycle, 10⁰C below the 1st Dentine Firing temperature

•    36.  The labial face is lightly ground with a flame shape diamond to produce a slight concavity which will enhance the mesial facial lobe

•      37. The crown and die are removed from the model and a very small amount of Clear porcelain is added to the contact areas to compensate for any slight firing shrinkage on the 2nd dentine firing

•   38. Draw lines to follow the Lobes and Supra- Bulge, this will show where the crown needs altering to make a matching pair of Central Incisors

• 39.  A Cerapol rubber wheel can be used to accurately blend the ceramic into the margin of the die removing any remaining overhanging edges

• 40. Once the final shaping is complete and there are no ledges around the crown/tooth margins, the crowns may be glazed. Glazing can be done using an Overglaze powder mixed with Stain and Glaze Fluid and fired at the same temperature as the 1st dentine firing (880⁰C) in air rather than firing in a vacuum, for 1 minute.

•    41.  Alternatively glazing may also be completed without using an Overglaze, by firing the crowns in air for 2 minutes at 880⁰C. This may cause the crowns to change shape and be slightly rounded if kept at this temperature for too long.

• 42. After glazing, remove the dark oxide layer from the palatal metal collar with a fine or worn diamond bur prior to polishing with a rubber wheel, then gloss with polishing compound using a felt wheel or soft bristle brush

•      43. The polished metal collar should blend perfectly with the ceramic at the interface to prevent plaque adhering.