Contentious issue #4: Thermoplastic versus room temperature obturation

For a change of pace, let’s consider the pros and cons of thermoplastic and room temperature obturation. We’ll start with thermoplastic oburation.

My understanding of thermoplastic obturation is its supposed superior adaption of gutta percha to the walls of the canal maximizing the presence of gutta percha and minimizing the thickness of the cement interface, an interface that has been considered a weak link due to its potential to dissolve in the presence of oral fluids. If the cement interface is thin to begin with, what is potentially washed out will leave a smaller gap less likely to lead to leakage and failure of treatment.

Thermoplastic obturation requires greater tapered preparations to produce resistance to overextension of the obturation material when a vertical force is applied. In effect, we are removing dentin for reasons other than cleansing the canals that are necessary to add predictability to the obturation procedure. The sacrifice of dentin can only be justified if the results attained are superior to what would be accomplished with less aggressive steps in preparation for obturation. The advocates of thermoplastic obturation emphasize the adaptation to the canal walls when gutta percha is temporarily liquefied increasing its flowability markedly, and displacing any cement present to the thinnest interface possible. This strategy makes sense as long as the cements used are subject to dissolution and washout. These cements include zinc oxide and eugenol, calcium hydroxide and glass ionomers all of which are particulates that are subject to hydrolytic degradation. They do not include polymeric cements such as methacrylates and epoxies that are not subject to dissolution and washout.

Once polymeric cements are introduced, the need for the thinnest cement interface is eliminated. Whether thick or thin along the length of the canal they are not subject to breakdown. With dissolution no longer a concern, thermoplastic adaptation of gutta percha to the canal walls is no longer necessary.  A disadvantage of thermoplastic obturation is gutta percha’s subsequent contraction as it cools to body temperature. With the cement already displaced by the flowable gutta percha, shrinkage results in a gap between the canal walls and the contracted gutta percha. Taking an extended viewpoint, the introduction of polymeric cements has done away with the need for greater tapered shaping leaving the safety of the instruments as its only justification. With the increasing awareness of the dentinal defects produced with greater tapered rotary preparations, both greater tapers and rotary instrumentation are undergoing increasing amounts of critical review.

The justification of room temperature obturation is based on polymeric cements. Prefitted so it fits snugly at the apex, the gutta percha is a carrier and a driver of the cement that first floods the canal space. The gutta percha in this procedure is the equivalent of the thermoplastic metal spreader or the internal support in carrier based systems. It drives the cement that is significantly more flowable than thermoplasticized gutta percha laterally with excess cement escaping coronally. The entire system has the advantage of being room temperature. Nothing shrinks and, in fact, both the cement and gutta percha expand slightly as they warm from room to body temperature.  This type of system requires little more than gutta percha sized to the space created for it. If the canal is cleansed via 30º reciprocation, a taper no greater than 04 and often no greater than 02 is generally coupled to an apical preparation of 30-40 depending upon the original canal dimensions. Small amplitudes of motion preclude the need for greater tapered crown-down preparations. Yet the apical third of the canal where most pulpal branching occurs is prepared to a greater degree providing improved irrigation where it matters most.

My preference in room temperature obturation is the use of epoxy resin cements for the following reasons.
1. They are dimensionally stable during the polymerization process.
2. They are highy antibacterial
3. They bond to both gutta percha and the canal walls
4. They penetrate the dentinal tubules
5. Cement beyond the apex, is digested by the macrophage
6. Most studies demonstrate a superior seal apically and along length
7. They are well tolerated by the periapical tissues.
8. They have over 70 years of positive research supporting their use-no surprises.

My bias to room temperature obturation is supported by its simplicity and predictability. It’s elimination of the need for greater tapered preparations. It’s elimination of shrinkage as an undesirable side effect and its dramatic savings in costs.           Dr.BARRY