DEEP DENTIN AND PULPAL CONSIDERATIONS
It is possible to ensue postoperative comfort if dentin tubules are well occluded in the bonding protocol. See Standard Bonding Protocol.
Deep restorations and many crown procedures involve reduction into deep dentin. In direct dentistry, reduction follows caries and fracture. In crowns, heavy reduction is necessary but elective. Heavy buccal reduction – 1.5 to 2mm- is often required to create the thickness necessary for realistic aesthetics in porcelain. In many maxillary teeth, especially in smaller teeth, this axial reduction cuts into deep dentin. Deep dentin is completely different from shallow dentin:
- The surface is 40% to 88% tubules rather than superficial dentin containing 4% to 10% tubules
- Tubules are 3 microns in diameter rather than 1 micron
- Deep dentin has 58,000 tubules per square mm, rather than 20,000 per square mm in shallow dentin
- These tubules contain more odontoblast cell bodies than superficial dentin. Deep preparation entails histological damage.
Cutting larger, more open and more cellular tubules invites pulpal injury during procedures: dentin dessication, heat from burs, ionic stress from water spray, negative effects from astringents, medications, temporary and permanent cements. In crown preparation, relative to direct dentistry, microleakage of fluids and exposure to organisms occur demonstrably between prep and cementation appointments.
Preparation for a composite restoration does not require a great deal of increased axial penetration to establish a clean, restorable finish line. A single visit excludes the metabolic drain on the pulp between appointments. This allows the direct restoration to potentially be the more comfortable of the two options. Proper priming of the dentin can ensure long term vitality.
DOUBLE PRIMING AS A METHOD TO ENSURE POST-OPERATIVE COMFORT
To ensure that dentin is always well-primed, to assure post- op comfort, to inactivate MMPs, and to close tubules to resin leachates, a universal primer can be added to any Generation IV or V bonding system.
Universal primers were reviewed by Clinician’s Report in August 2002. They noted a lessened likelihood of tissue burns in non-glutaraldehyde formulations.
However, sloppy technique, for example, primer pooling under cotton rolls, will cause a soft tissue burn that is painful for 24 hours. Not a practice builder, my friends. Safety of materials is not absolute, we have tools which can hurt people when misapplied.
The product chosen for this Handbook is Microprime B, by Danville Dental Products. It is similar products based on either chlorhexidine, glutaraldehyde, benzalkonium chloride, or, in this case, benzethonium chloride. These are all mild disinfectants, and protein fixatives.
Microprime B is formulated as follows: 59% water, NaF 1%, HEMA 35%, and Benzethonium chloride. It is available in the USA, but in Canada, due to low volume of sales, no supplier has taken out a device licence with Health Canada to import it. It is perfectly legal to use, however. Now it must be ordered direct from Tin Man Dental, California, 1-800-554-6394.
Why is it a good choice? It is much less cytotoxic than glutaraldehyde products. There are other clinical uses,
- desensitization of exposed roots
- desensitization of crown preps after preparation.
The latter is a worthwhile benefit, because often no anesthesia is needed at a crown insertion appointment when the prep has been so treated. This is much appreciated by dentist and patient alike, and proprioception of occlusion is better, leading to more exact occlusal harmony.
HOW TO APPLY MICROPRIME B:
Once etch and rinse are complete, dry the prep to the point that no visible standing water remains in the prep. Apply Microprime B with a Voco #1 foam pledglet and immediately air-blow off the tooth until a consistent low gloss finish is seen on the tooth surface and there are no visible droplets or standing moisture. Smaller preps require a brush, such as the Centrix Bendabrush, regular size.