Frequently Asked Questions

Prep design/Tooth reduction

What is your recommendation for prep design and tooth reduction?

In general, we recommend using at least a chamfer or a shoulder prep design. The reason for this is twofold; First, it allows for more reduction in the gingival 1/3 providing more depth of material, increasing the esthetics of the restoration. Second, most dentists have a much easier time capturing the margin in the impression, and the technician has an easier time reading the margin when ditching the die versus a featheredge prep design. We realize there are certain cases that don’t allow for that amount of reduction in that area, but as a general rule, that is what we recommend.

As far as tooth reduction is concerned, for optimal esthetics, we recommend 1.5mm axially, and 2.0mm occlusally. Of course, with full contour zirconia you can get away with as little as .6mm axially, and .8mm-1.0mm occlusally, but, if at all possible, we recommend the former.

For E-Max restorations, please see the prep chart on our resources page.

Impressions

What is your recommendation for capturing the most accurate impressions?

1. Analog impressions: The most important thing in capturing the margin and providing an accurate impression is adequate retraction. That is the biggest issue we run into when trying to ditch the dies. Especially when a featheredge prep design is used, and there is little or no retraction, it is very difficult for the technician to tell where the margin is with certainty. We have found over the years that the dentists we work for that have the least number of remakes or short margins are the ones who routinely employ retraction cord, and even double-packing cord, and then syringing light body into the sulcus and around the prep followed by the over impression.

Of course, it is also imperative that the field is dry, and there is no blood or saliva in or around the sulcus, no movement of the tray during setting, or premature removal.

2. Intraoral Scans: The biggest issues we run into with intraoral scans are inadequate retraction, and saliva or blood in and around the sulcus, or anywhere on the preparation. In the case of inadequate retraction, it shows up as marginal obscurations when the gingival tissue lays on the margin, but even when it is allowed to rest against the margin. In the case of blood or saliva being present, that shows up as bumps, lumps, pockets, and abnormalities. Just as with an analog impression, full retraction and a dry field will yield the most consistent results, and better fitting restorations.

Implants

Do you prefer closed tray or open tray implant transfer impressions?

We prefer closed tray impressions if at all possible. While we have success with both methods, when employing an open tray technique, there is always a slight possibility that the transfer coping can rotate slightly in the impression when screwing on the analog. Another potential issue is that the transfer could move slightly up or down out of position. In our opinion, it’s better to be on the safe side, and eliminate any potential issues by using a closed tray technique.

What information is needed when we send an implant case?

You should always write on the prescription the name of the implant, and the platform size. Ex: Nobel 4.3 RP Conical connection, Biohorizon 3.5, Zimmer 4.5 etc. In addition, to be on the safe side, you could always include a copy of the surgeon's report.

Nobel Angulated Screw Channel (ASC)

Why does the Ti base separate from the implant abutment?

The Ti base for ASC restorations is a friction fit and can separate from the abutment before it is torqued down in the mouth. It is for this reason why we send a notice with every ASC case that you should not place the restoration on the model before insertion as it may separate. Once the restoration is torqued, it cannot separate.

Is ASC available for the 3.0 platform?

No, and the 3.0 platform is only available in Titanium due to its small size.

What driver do I use for ASC?

Nobel Omnigrip driver.

Fit Issues

Why are the contacts too tight/too loose on the crown?

When we adjust the contacts of the restoration in the lab, we always make them full but passive on the working model. Additionally, we pour a secondary solid model to do our final checks on the contacts. Every dentist is a little bit different when it comes to adjusting the contacts of the temporary. If the contacts of the temp are slightly loose, then the contacts of the restoration will be slightly tight. Conversely, if the contacts of the temp are slightly tight, then the contacts of the restoration will be slightly loose or open. The time between the final impression and the insertion of the restoration is more than enough time to have slight movement in the adjacent contacting teeth. Even slight movement will result in a lot of adjustment. It is for this reason that it is imperative that you communicate with us what you are experiencing upon insertion. It is one of the advantages of being a small, quality-oriented lab that we can make these individualized adjustments for each dentist that we work for.

Why are the bites high on the restoration?

If you are having to make consistent occlusal adjustments on the final restoration, the first thing you want to check is that the articulation is accurate. Our normal protocol in the lab is to take our restorations slightly out of occlusion if the space is there for us to do so. If it is verified that the articulation is correct, and the restoration is slightly out of occlusion on the mounted model work, then other issues could be:

The restoration is not fully seated

Contacts are too tight

The original impression had a dimensional distortion or a marginal inaccuracy

The prep erupted due to slight over adjustment of the temporary

If all of these potential issues are determined to be non-existent, then it is imperative that you communicate this anomaly with us in order that we can start to employ over compensation, and relieve the occlusion a bit more on the restoration.

Why am I getting short or open margins?

The most common reasons for open margins are pulls, dimensional distortions, or marginal obscurations in the impression. When we see these issues in the impression, and we are able to scrape the die to remove them we do so. If we feel the distortions are too significant to do that accurately, we will send the model back to you for your inspection so you can determine if you want to retake the impression. As far as short margins are concerned, the most common reasons are inadequate retraction, or excessive bleeding or saliva in and around the sulcus.

Other FAQ’s

Can I use an E-Max veneer or crown over a very dark prep, or a prep with a metal post and core?

No. E-Max restorations are too translucent to use for this type of application. The final restoration will look grey, and there is nothing we can do about that to remove it or compensate for it in the lab.

Can I use a full contour anterior zirconia crown over a very dark prep, or a prep with a metal post and core?

In most cases no. The degree of translucency in this type of restoration is usually still too high to offset the grey bleed through. In case like these, we would recommend either a layered zirconia or a porcelain fused to metal restoration.