Blog

A frequent mishap with firing lithium disilicate is the loss of contacts. Quite a few people have reported that contacts were perfect at try-in stage, but after crystallization they were light or even open. This phenomenon is caused by a lack of support of the material while it is in the oven. The material distorts enough to render weak contacts.

Adequate support is necessary, but I like to cross the line and go against manufacturers’ recommendations when they advise using the issued pegs when placing the material in the oven – especially for larger crowns like those meant for abutments on implants, as there is a much larger surface area to address.

This photo shows how I load the internal of the crown with Quick-Peg or object fix-like material and then place the restoration on a bed of the same material, making sure that the contact areas are supported. I then place my glaze and stains on the occlusal and buccal/lingual walls. I am not concerned about the contacts areas, as these will be addressed with a quick polish on a high-speed electric handpiece.

This technique has worked well for me for more than five years, and I no longer have to contend with distorted contacts.

A common misinterpretation by dentists that do not do all-ceramic restorations – or even CEREC for that matter – is how the restorations look on bitewing X-rays.

The first image shows a white "bar" at the interproximal, which is often times interpreted as a margin that is filled in with the resin cement or an open margin. 

But taking the X-ray from varying angles reveals a completely different story.

These images are self-explanatory; however, for those who are used to metal margins, which generally hide a great deal of information due to overlap, the following concise narrative properly depicts the situation.

The ceramic material is radiolucent, while the cement is opaque. When an image is taken that bisects the margin at a 90-degree angle, the overlap of the opaque material gives the illusion that there is an open margin filled with resin material.

I'm too lazy to take impressions, pour them up, take out calipers and measure the proportions coming up for a rehab.  A quick scan and I can measure the diastema, split in half, and see if I can remove that much from the distal of the Central Incisor.  Then I measure to see if I can get to Width to Length Ratio of 75-80 % for the Central.  The only thing left is to click a button and have the virtual wax up fall into place

Everyone in the past would use a tofflemeier matrix band to seat partial restorations.  I found this difficult to do as the closed loop system would prevent it from seating all the way, hanging on the neck of the band

4 friends of mine, jumped shipped, and advised me to use a sectional band so it would keep me out of trouble.

Do yourself a favor and try this approach instead.  Works like a charm

The day goes by so much more smoothly when you think like the milling machine.  Perfect preps and good imaging leads to restorations dropping in at seat.  Here are some pointers for partial restorations with regards to fit:

1. Make sure your exit angles have a slight flare taper so that you can see all point angles in the boxes

2. Make sure the isthmus at the occlusal table is wider than the isthmus at cavosurface when you have a lingual or buccal finger / extension.  Otherwise, the bur has to mill back on itself and it can shatter the restoration

3.  At the path of draw view, make sure you see an uniterupted blue line like the image below.  If you don't. then that means there is an undercut that will be milled and you won't be able to seat the restoration.

4. The yellow shadow is a good warning also if you have undercuts.

here's a case where Cerec was used to fabricate an invislaign attachment incorporated into crown for closing a diastema. Months later the crown was replaced with a permanent crown using Cerec 

here's a quick tip!

If you place the sprue on the facial of a large crown, generally a size 14 block is required.  If you place the sprue for a crown at the interproximal, it generally takes a smaller size block to get the job done and the milling time is shorter as well.  But you have to cut the sprue off the contact area and if you are sloppy, you can remove the contact.

By moving the sprue location to the facial line angle by default you get the best of both worlds!

i took time stamps of my first procedure today for the upper right first molar:

9:34 am i captured opposing arch (so anesthesia and isolite about 5 minutes prior to this)

9:46 i captured prep arch

9:51 it was in milling machine

10:08 was in the oven

10:30 i bonded

10:44 the patient left, and that was with double hygiene running. that was a single restoration, but frequently i'm doing something else in the same arch or even the opposing arch like this: this is about the best thing about isolite, it gets you to open your mind that you can treat opposing teeth, where as a rubber dam gives you the mental block that you have to stick to one arch

One of the biggest advantages of digital impressioning is to know within seconds if you captured your margins, as opposed to waiting 4 to 5 minutes for the traditional impression to set.  But one common thing between the two is that you must make sure you have soft tissue retraction and displacement of the tissue to discern where the tooth structure ends and the tissue starts.  One big adjunct that accomplishes both those things with relative ease is a soft tissue laser.  Here you see the pre-op condition where you can tell the clinician struggled accomplishing an important task and in the immediate post op, you can appreciate how hemostasis and retraction worked to achieve the desired results

I love the idea of partial coverage restorations:  Being conservative and less invasive!  But I hate seeing some of these restorations where there now is obvious decay in the interproximal area of the wall we did not reduce.  Eventhough we made every effort to check for caries at the intial placement, there are times where they go undetected and surface years later.  This is one of the few arguments against partial coverage.  What adjuncts do you use to make sure the tooth structure you leave behind is not compromised?