Tips from the Technician

Helpful Hints

  • Fill major voids in the prep before impressing
  • Smooth all sharp angles and adjacent contacts before impressing.
  • Describe the type of margins prepared.
  • Ensure all preps and contacts are parallel.
  • Pour all opposing models timely and accurately to avoid soft models and distortion.
  • Provide bite registration over the prepped teeth and opposing, even when using triple tray impressions.
  • Provide preop models, especially for anteriors.
  • Share future plans for patients with the technicians.

Variables from the Lab

  • Sloppy model work
  • Voids on models and dies
  • Loose fitting dies in base
  • Mistrimmed margins
  • Dies not blocked out accurately
  • Opposing arch mismounted
  • Contacts extremely tight or too loose
  • Occlusions too heavy, or way out of occlusion

Variables from the Dentist

  • Adjacent contacts concave or convex
  • Path of insertion not parallel with preps and contacts
  • Temps made without proper contacts or occlusion
  • No bite registration
  • Margins not clear in impression
  • Voids in impression in critical areas
  • Insufficient reduction on occlusal or facial
  • Opposing poured with voids or distorted

Zirconia vs e.max

Zirconia

  • Can be milled as a substructure (Lava-type) to be layered with porcelain
  • Can be milled full-contour (Bruxzir type) which is a great alternative to gold crowns
  • Strong enough for large bridges and opaque enough to block out dark substructure; including Titanium implants

Limitations:

  • Requires 360 degree shoulder or chamfer margins for bridges, exposing margins for milling purposes to prevent open margins

e.max

  • Can be pressed as thin as .3mm for veneers
  • Can be pressed to any type of margin
  • Can be used for crowns, inlays, onlays, and Maryland Bridges

Limitations:

  • Limited to 3 unit bridges, extending to 2nd bicuspids
  • Needs adequate tooth support to be successful, otherwise a metal or Zirconia framework is advised

Taking a Shade

  • Take before beginning treatment
  • Use proper lighting
  • Best to stand the patient with a wall mirror
  • Photos with the shade tabs visible are very helpful
  • Determine the Value (grayness) or brightness first
  • Determine the Hue (color) and the Chroma (intensity)
  • Determine the Translucency (incisal edges and mammalons)
  • Take a “stump” shade for all ceramic restorations

Making a Crown Fit to an Existing Partial

Indirect Method

Use this method if the patient can’t do without the partial for a few days.

  • After prepping the tooth, place a little bite registration material or impression material over the prepped tooth.
  • Avoid using too much material because you just want an impression of the inside of the clasps and rests areas over the prepped tooth.
  • Gently seat the removable partial denture, ensuring it is completely seated.
  • The lab will make a duralay type of framework to duplicate the inside of the partial and connect it an adjacent part of the model, creating a replica of the partial.

Direct Method

This is the best method, if the patient can do without the partial for a few days. 

  • A flipper can be worn while the partial is in the lab. It’s usually a good idea to have a backup appliance anyway.
  • Take an impression with the partial in place, after prepping the tooth.
  • Be sure to use a plastic impression tray because of the metal frame on the partial.
  • A separate impression may be needed to get a good impression of the margins.
  • The lab will block out the undercuts and pour the impression, usually twice, before separating the partial from the impression.
  • The lab will need the partial while they do the model work, the metal work, and the porcelain if the partial involves the buccal or facial.

Types of Margins

Knife Edge

  Recommended Restorations:

  • e.max (Shaded)
  • Full Metal

Feather Edge

 Recommended Restorations: 

  • e.max (Shaded or Layered)
  • Full Metal
  • Porcelain to Metal w/ Metal Margins
  • Porcelain to Metal w/ Porcelain to Metal Margins

Beveled Shoulder

Recommended Restorations: 

  • e.max
  • Full Metal
  • Porcelain to Metal w/ Metal Margins
  • Porcelain to Metal w/ Porcelain to Metal Margins

Bevel

 Recommended Restorations: 

  • e.max (Shaded or Layered)
  • Milled (Zirconia, e.max, or Metal)
  • Porcelain to Metal w/ Metal Margins
  • Porcelain to Metal w/ Porcelain to Metal Margins
  • Porcelain to Metal w/ Porcelain Margins (Buccal or Facial)

Shoulder

 Recommended Restorations: 

  • e.max (Shaded or Layered)
  • Milled (Zirconia, e.max, or Metal)
  • Porcelain to Metal w/ Metal Margins
  • Porcelain to Metal w/ Porcelain to Metal Margins
  • Porcelain to Metal w/ Porcelain Margins (Buccal or Facial)

Chamfer

 Recommended Restorations: 

  • e.max (Shaded or Layered)
  • Milled (Zirconia, e.max, or Metal)
  • Porcelain to Metal w/ Metal Margins
  • Porcelain to Metal w/ Porcelain to Metal Margins
  • Porcelain to Metal w/ Porcelain Margins (Buccal or Facial)

More Hints

1. Undercut (can be blocked out)



2. Undercut margin cannot be blocked out without opening the margin.

1. Incisal one third needs reducing and sharp angles rounded.

1. Lip needs to be smoothed out.

Examples of Parallel Preps and Contacts

Examples of Nonparallel Preps and Contacts

Troubleshooting

  • Check the crown(s) on the working model and the solid model before the patient arrives.
  • Always compare the shade of the tooth to the requested shade tab, not a picture of the tooth.
  • When adjusting the crown(s) in the mouth, first check centric occlusion, then check the lateral and protrusive excursions.
  • After adjusting the crown(s) in the mouth, place it back on the model to see if there is a noticeable difference.
  • If there is a slight "rock" in a bridge, check the pontic area to see if it's blanching heavily.
  • If the tissue has shrunk from a recent extraction, put the bridge in place and squirt impression material under the pontic and over the bridge.
  • When seating bridges; after adjusting the contacts, have the patient bite on a cotton roll for a few minutes to ensure the bridge settles onto the abutments accurately.
  • When encountering an extremely high centric occlusion on a crown, take a new bite without the crown in place. If the crown is too far out of occlusion, leave it in place and take a new bite. The lab can then use the new bite to remount the crown, then adjust it as necessary and reglaze it.