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.

Very interesting I had put this down to the density of the material and length of time to mill compared to feldspathic blocks , and always added additional strength to the contact to overcome this issue during the design phase . This works well for me and overcomes the issue you describe , sometimes the error in addition needs a little further adjustment with rubber wheels though .