The most ideal connection of a definitive restoration to an implant is with a metal connection, rather than a ceramic one. If there is a direct connection of zirconia to a titanium implant, there is a significant risk of the internal aspect of the implant connection wearing, due to the fact zirconia is harder than titanium.
Micromovements of the restoration during function will cause the titanium to wear. This also poses a higher risk of the zirconia restoration breaking at the head of the connection, which inserts into the implant.
Titanium bases, which are cemented inside the restoration, have eliminated these two problems. The zirconia, e.max or polymer infiltrated ceramic network is bonded to the titanium base. There are unique designs to every manufacturer's titanium bases, with varying surface retention features. The height of the titanium base, which extends inside the restoration, is the most important factor when considering resistance and retention of the components.
Many manufacturers have recognized this and have introduced height options. The taller the titanium base that fits inside the restoration, the better the retention. Manufacturers also recommend different protocols for cementing the titanium base to the restorative material.
In June at the Quintessence Publishing 13th International Symposium on Periodontal and Restorative Dentistry in Boston, Dr. Irena Sailer spoke on one of her soon-to-be published articles. The goal of the research was to determine if sandblasting the titanium base improved the bonding stability of a hybrid crown.
The materials evaluated were e.max, zirconia and Enamic, the cements Multilink Hybrid Abutment with Monobond Plus, Panavia VS with primer, and RelyX Ultimate with RelyX Universal. The results for pull-off forces varied depending on the cement and the restorative material. The best result for e.max was Multilink Hybrid Abutment. The best result for zirconia was 3M's RelyX Ultimate. The best result for Enamic was with Panavia VS and RelyX Ultimate. MultiLink Hybrid Abutment was slightly lower. There is more covered in her research, but I am waiting for the article to be published before reporting any other information.
Dr. Tomas Linkevicius recently published an article in the Journal of Prosthetic Dentistry that shows abrading the titanium base with 50 µm of aluminum oxide significantly decreases the dislodging force. The materials he tested were G-CEM LinkAcc (GC), RelyX U200 (3M ESPE) and Ceka Site (CEKA PRECI-LINE).
So, what is the bottom line? We cannot rely on a standard protocol for all materials. It is critical to follow the manufacturers recommendations and be aware of independent research. Remember, the research outcomes are technique and material specific. It is also important to maintain clear lines of communication with your laboratory or lab technician, because they are the ones typically cementing the components together.
Robert Winter, D.D.S., is a member of Spear Resident Faculty.