"Good Things We Learned From the Kois Center"
Q: Does alumina oxide particle abrasion affect the bond strength of self-adhesive luting cement for final restorations?
A: No. Our study reveals that alumina oxide particle abrasion does not have an adverse effect on the bond strength of the self-adhesive cement (e.g. RelyX
Unicem, Maxcem, Multilink) but, to the contrary, helps increase it. It is clear from Scanning Electron Microscope (SEM) pictures and Energy Dispersive Analysis (EDS) that most of the particles were gone after being sprayed with water and an irregular, rough surface appeared on the tooth surface after particle abrasion. The roughness on the surface increased the bonding area, which consequently increased the bond strength. When applying the mechanical cleaning protocol before final cementation, it is advisable to use small nozzle tips (0.015), small alumina oxide particles (27 um), low parameters (e.g. nozzle tip diameter, nozzle tipdistance, air pressure, particle size and type of air abrasive) could affect the bond strength.
Q. Why is RelyX Unicem cement occasionally too thick and viscous?
A. Mostly, excessive cement viscosity and film thickness result from improper mixing. It is important that the capsules be securely placed in the activator and the lever arm firmly pressed down to activate the liquid for an adequate time period. If the capsule is activated for too short a time, some of the liquid will not be injected into the powder and a "thick" mix will be observed. We tested various mixing protocols to find the most efficient. Our data revealed that a long liquid activating time (5 seconds) and a longer mixing time (15 seconds) for both a centrifugal mixing machine (e.g. Rotomix) or a high frequency mixing machine (eg. Capmix/Amalgamator) yielded the best results. If possible, light-curing the restoration for about 20 seconds for indirect
restoration is also suggested. Recently, a new RelyX unicem paste named "Clicker" was introduced into the market, which we also included in our study. It was found that this
type of cement's shear bond strength was comparable to the capsule-mixed cements. Unfortunately, with the paste system you may need to use a hand-mixed protocol, which might cause the mixing to be technique sensitive again.
As part of the Kois Center program, we benefit from the knowledge and experience of doctors who support the Center. In the premier issue of our newsletter "Excellence", we found an informative monthly Q&A from Dr. Yada Chaiyabutr (DDS, MSD, DSc). - Eric P. & Tony L.
