DENTIN PRIMING

DEEP DENTIN AND PULPAL CONSIDERATIONS

Postoperative comfort requires that dentin  tubules are well occluded in the bonding protocol. See Standard Bonding Protocol.

Deep restorations and many crown procedures need reduction into deep dentin. In direct dentistry, heavy reduction follows caries and fracture. In crowns, heavy buccal reduction – 1.5 to 2mm- is often required to create the thickness necessary for realistic aesthetics in porcelain and for strength of the crown itself. In many maxillary teeth, especially in smaller teeth, this axial reduction cuts into deep dentin.

Deep dentin is completely different from shallow dentin:

Deep dentin has:

  • 58,000 tubules per square mm, rather than 20,000 per square mm in shallow dentin, three times the number.
  • An average area of 40% to 88% tubules while superficial dentin contains 4% to 10% tubules- ten times more intertubular dentin than
  • Tubules are 3 microns in diameter rather than 1 micron- 3  times bigger
  • These tubules contain more odontoblast cell bodies than superficial dentin.

Cutting larger, more open and more cellular tubules invites histological damage-pulpal injury during procedures, from:

  • dentin dessication
  • heat from burs
  • ionic stress from water spray
  • negative effects from astringents, medications, temporary and permanent cements
  • between prep and cementation appointments, microleakage of fluids and exposure to organisms

Direct procedures usually require less  axial penetration to establish a clean, restorable finish line than crowns. Single visits reduce the metabolic drain on the pulp between appointments. This allows the direct restoration to potentially  be the more comfortable and biocompatible of the two options.

But in all bonded restorations, proper priming of the dentin  increases the odds of maintaining long term vitality.

DOUBLE PRIMING TO ENSURE POST-OPERATIVE COMFORT

METHOD:

To ensure that dentin is always well-primed, to assure post- op comfort, to inactivate MMPs, and to close tubules to resin leachates, a dentin primer can be added to any Generation IV or V bonding system. These systems have a dentin primer in their formulation but a separate dentin primer increases the effectiveness, amounting to “double-priming”

Clinician’s Report in August 2002 reviewed “universal primers”. They noted a likelihood of tissue burns in glutaraldehyde formulations.

Soppy technique, such as allowing primer to pool 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 from this article to replace gluteraldehye formulations is Microprime B, by  Zest Dental Products. There are alternative  products from other manufacturers based on chlorhexidine, glutaraldehyde, benzalkonium chloride, or, in this case, benzethonium chloride. These share the capacity to act as mild disinfectants, and protein fixatives.

They state: MicroPrime™ B is a desensitizing agent containing benzethonium chloride and HEMA. The benzethonium chloride and HEMA combination present in MicroPrime B acts as both – a flocculating constituent that strengthens the collagen framework, and a facilitating agent that helps create tubular occlusion with minimal or no sensitivity. Indispensable prior to the luting or cementation of indirect restorations, MicroPrime B limits the movement of fluids without affecting the strength of adhesive systems while offering reliable antimicrobial protection.”

I have used it for the last 22 years with excellent results.

It is not sold in Canada because our national market is  not profitably large enough. It can be imported by direct mail from Shasta Dental Supply. 

What is Microprime B? It is formulated as follows: 59% water, NaF 1%, HEMA 35%, and 5% Benzethonium chloride. It is available in the USA, but in Canada, due to low volume of sales, no supplier has taken out a device license with Health Canada to import it. It is perfectly legal to use, however. Call Shasta at1-800-554-6394.

Why is it a good choice? It is far less cytotoxic than glutaraldehyde products but just as effective.  I have virtually no post-operative pain, no debond, and long adhesive perforamncein restorations-often over 25 years. When removing a restoration of this age it is still bonded to dentiin,

Other clinical uses of Microprime B

  •  desensitization of exposed roots.  a single application of Microprime B followed by fluoride paste and a home routine of desensitizing toothpaste are often enough to eliminate painful cervical areas.
  •  desensitization of crown preps. Before cementation of a temporary, it is applied to dentin. Several weeks later,   no anesthesia is needed at  the crown insertion appointment when the prep has been so treated. This is much appreciated by dentist and patient alike. Proprioception of occlusion is better, leading to more exact occlusal harmony. In some cases, such as older patients being recrowned, no  temporary crown is necessary between appointments  for comfort. It is a truism in dentistry that tissue often is healthiest after a period without any temporary because access of the toothbrush is better, and the inexact fit of a temporary is not there to irritate tissues. In locations where there is no esthetic need, and the interim period between prep and cement is short, so that we do not   worry  about tooth drift, it is expedient.

HOW TO APPLY MICROPRIME B WHEN BONDING:

In above applications  there is no etch prior to application. It saturates though the smear layer.

Bonded restorations go as follows:

  • etch
  • rinse
  • dry the prep to the point that no visible standing water remains in the prep. It is no longer shiny.
  • Apply Microprime B using a Voco #1Pele Tim foam pledglet. Smaller preps require a brush, such as the Centrix Bendabrush, regular size.
  • 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.
  • Proceed to apply the bonding agent Generation IV or V. These have their own primer in the formulation and so the prep ahs been “Double-Primed” with this method. Post operative sensitivity has been absent in my clinic for over 30 years with this approach. The tubules are effectively closed and the pulp does not “see” that anything has happened  over top of  the contiguous dentin in this method.
  • Unfortunately, Microprime  B is not suitable for use with any SE protocol, such as Generation VI and VII products, or “single bottle bonds”, because it  prevents access of the bonding agent to dentin for etching. Unfortunately this limits use with bonding products that have a separate etching step, Generation IV or V.