Hi, I have started the preparation for NBDE part2. I am doing operative these days. I want to know the exact meanings of the following:
1) microleakage and marginal leakage
microleakage is leakage of the restoration material due to its internal material structure failure. This can happen because of aging resin that degraded over time, remember there are no eternal materials in this worlds!
Marginal leakages is a leakage at a margin area between the filling material -tooth interfaces, it can happend because of different in coef thermal expansion or aging restoration.
2) micromechanical retention.
From the meaning of mechanical retention - means retention is gained by preparing the cavity wall to such a shape that when the material is apply to the cavity, it will stay properly and can resist the forces. Example a dove-tail class II Amalgam restoration and convergence buccal-lingual wall preparation to oclussal surfaces in clas I Amalgam prep.
If we visual mechanical retention in micro-aspect, it name micromechanical retention. We can see so many materials used in dentistry are bonded by this mechanism, such as acid-etch the surfaces of the enamel or dentin to creates an micro-irregularity on the tooth surfaces that can increases the bonding strength. Beside of etching, sand blasting and laser methods have been used to create micro irregularities.
3) The mesial and distal walls of class 1 amalgam preparation should diverge slightly towards the occlusal surfaceto prevent undermining the marginal ridges of their dentine support.
Yes, for class I restoration, the M-D wall should diverge and the B-L wall converge to oculsal, the reasons for the M-D should diverge is to removed unsupported enamel rod - look at Dental anatomy of the enamel rods angulation on ocusal surface!
I wish this will help!
