There are two interfaces that can influence the retention of glass fibre-reinforced composite resin post to dentin. The interfaces include resin to post and resin to dentin. The cohesive strength of the resin cement may influence the retention too. Conditioning the surface of root dentin removes the smear layer and widen the openings of the dentinal tubules. This will allow the impregnation of resin into the dentin and result in the formation of the hybrid layer. On the other hand, it has been reported that airborne particle abrasion of the composite post roughens the post surface and increases the luting effect of the resin cement to the post surface.
This question is interesting and has few specific answers. The over-arching concept is that posts are used to retain a core. There is usually no reason to place a post if adequate tooth structure remains to support a core. In case a post is indicated, an adhesively retained post is most conservative and superior to a cast or pre-formed metallic post system. The premise stated above is essentially correct, however the question of dentin bonding in a root canal is really nebulous. There are too many circumstances that are working against satisfactory and predictable dentin bonding. Therefore, it's the clinician's responsibility to control the variable to the best of his ability. This means using the smallest diameter post possible, controlling moisture, using a dual-cure bonding agent and a dual-cure cement, and ensuring adequate time for the chemical set of the resin cement to take place before manipulating the post/core complex. It's often most convenient to use a low viscosity dual-cure buildup material for both post cementation and core build-up. At the end, we are probably relying more on intimate adaptation of the post to the tooth rather than infiltration of resin into the dentinal tubules for post retention. Still, it's a far superior option than a conventionally cemented post/core complex.
Yes the intimate adaptation is important. In other words a snug fit of post with minimal film thickness of the luting (dual cure) cement is necessary. Also the bonding of luting resin to radicular dentin may not be relatively satisfactory in general.
This is actually a very interesting topic for discussion. With regard to fibre post cementation, there are 3 different interfaces -
1. Bonding agent -dentin interface - Dual cure bonding agents always preferred inside the root canal. 3-step Etch and rinse (4th generation) and Self Etch (6th generation) can be used. Even though the action on dentinal tubules and smear layer varies.
2. Resin cement - bonding agent interface - Use of Light cure resin cements contraindicated. Use of simplified adhesives (5th and 7th generation) has shown to have low bond strength and incompatability issues with dual cure resin cements. So that has to be taken care of.
3. Fibre post - resin cement interface - Fibre post pretreatment by air abrasion and/or using 24% H2O2 is beneficial. Silanization has also shown to enhance the bond.
There are two interfaces, dentin-luting material and luting material-post. Each one must be dealt with but preferably is a simple chairside process. The problems are differing substrates, moisture control, and clinical practicality.
Post-luting material interface
Air abrasion of the post is a possibility, but silanation is a must. A 2-component silane has the longest shelf life and the highest bond strength.
Dentin-luting material interface
Etching and rinsing the remaining dentin may open tubules to increase adhesion, but effective rinsing is questionable at the deepest portion of the post space. No etching is probably the best course.
Luting material
The best, and simplest, choices are the self-etching, self-adhesive, dual-cure resin cements.They bond well to etched or unetched denti;, they bond well to silanated posts. Generally delivered in an automix or triturated, the mixing is totally technique insensitive. Since they are moisture tolerant, the unavoidable dentinal moisture inside the post space is not a problem. And they set, with or without curing lights within 5-7 minutes.
One Step Post Cementation: no fuss, no bother, and totally predictable.
Product names include: Shofu BeautiCem and biomimetic Doxa Ceramir.
Does etching the radicular dentin with 37% phosphoric acid to open dentinal tubules when using self etching self adhesive dual cure cement lead to a weaker bond between dentin and luting cement interface than what may be achieved if no etching were to be performed. These cements have weak or mild acids in them for the self etch to take place. So is additional etching before cementation recomm Are there any studies related to this.?
A separate 37% orthophosphoric acid etching step DOES weaken the dentin bond.
If adaptation of the fiber post to the interior surface of the post space is doubtful, then a cast post might be indicated. The thickness of the luting resin has to be very thin film, otherwise the cohesive strength of the cement itself might be reduced.
Conventional three steps etching has been reported to be superior to self etching in terms of bonding resins to root dentin surface. However, it is time consuming and tedious to the operator.
Cleaning the post surface is essential before bonding and the application of silane is preferable for better bond results. Mechanical roughening methods of the post surface increases the bond strength significantly. However, one has to make sure the glass fiber content of the post matrix has to remain intact. Vigorous roughening may weaken the post structure itself.
Suggestion: using the core buildup material as the post-luting cement eliminates the fear of an overly thick cement (thickness is impossible to control within the canal and core materials are designed for use in bulk). A self-etching, self-adherent core material is an excellent choice.
Use of manufactures recommendations is necessary. Isolation techniques must be optimum and use of a suitable cement. I use relyx u200 and never had problems.
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