Immediate Dentin Sealing

Augusto Robles, DDS, MS, DMD (AR): The purpose of immediate dentin sealing is to seal the dentinal tubules from contamination and allow the time necessary for the formation of a stronger and more developed bond to the dentin than can be achieved using other methods. Every bond to dentin will eventually deteriorate via one of several mechanisms. The insides will degrade the bond area (ie, proteolysis), and water circulating through will degrade the collagen (ie, hydrolysis). In a case involving an onlay, for example, this will happen regardless of whether you cement it onto a preparation or if you perform immediate dentin sealing and then bond the onlay to that. Both restorations will deteriorate, but the one that will deteriorate less and last longer will be the one with the bond that was allowed to mature properly with no stress, no pressures, and no effort over the tooth.

ID: How does the use of fiber meshes or fiber composites improve bond strength?

AR: This works in conjunction with immediate dentin sealing. Immediate dentin sealing is about closing the tubules and the dentin, but how can you further improve the strength of the bond and its ability to resist the stresses placed on it? This depends on the amount of material that you put on top, the method used to place it, and the overall configuration or shape of the preparation. A newer method of accomplishing this is to incorporate a fiber material, especially those manufactured in a leno weave, which is more like a fabric with fibers intertwined in several different directions. The incorporation of fiber permits deformation, which absorbs any shrinkage stress and alleviates other problems associated with polymerizing composites. In addition, embedding fiber into your resin makes it more rigid and fracture resistant. The fiber inside the composite acts like a deflector. When a fracture occurs, instead of going through the whole tooth, it hits the fiber mesh and  gets deflected sideways. These are the benefits of using fiber materials.

ID: Could you explain the clinical advantages of using stress-reduction protocols when bonding?

AR: In 1987, Feilzer and colleagues presented research about the configuration factor,¹ which refers to the ratio of bonded to unbonded surfaces in a restoration. Their findings indicated that the specific geometry of a preparation can result in more or less relief from stress. Composites will shrink as they polymerize, and the more that they are bound to the walls of the preparation, the more stress that will develop as they shrink. This stress can result in a multitude of failure modes, including debonding and fracture of the enamel. For composite restorations, configuration factor is one of the most important topics of discussion today. In the immediate dentin sealing protocol, because the tooth is fully open and the dentin is simply being coated without connecting the walls, a very favorable configuration factor is created that does not allow pooling from any side. With no connection to the other walls to constrain the composite and develop stress, it will only shrink toward the dentin. This is what allows the bond created by immediate dentin sealing to become more mature, stronger, and better preserved than one created following provisionalization or by just cementing something directly to the dentin.

ID: How did the concept of immediate dentin sealing evolve and what research supports its benefits?

AR: This idea originated in 1992, and the process is very interesting. Around the time when the first really stable, effective bonding agent was developed, the highly regarded researcher David Pashley, DMD, PhD, posed the question of whether it was possible to cover all of the dentin that had been exposed during the preparation of a tooth for a crown.² In 1998, Didier Dietschi, DMD, PhD, presented this concept as part of his protocol for the preparation and restoration of posterior teeth with composite.³ He was already thinking that sealing the dentin and waiting a bit would lead to a stronger bond. In 2002, Pascal Magne, DMD, MSc, PhD, published a fantastic book, Bonded Porcelain Restorations in the Anterior Dentition,⁴ which asserted that dentin contamination and the susceptibility of the bond area (ie, the hybrid layer) to collapse is the primary problem with establishing a strong bond to dentin. How do we overcome this problem? By sealing off the dentin. In 2005, Magne published another article with the rationale for immediate dentin sealing⁵; however, further literature on this topic was limited until the last 2 to 3 years or so, when it became very popular. Suddenly, everyone wanted confirmation of whether or not immediate dentin sealing lead to stronger bonds and, subsequently, increased resistance to fracture, less sensitivity, less contamination, and other advantages. More evidence began to emerge. A 2019 study by Sinjari and colleagues utilized a scanning electron microscope to identify areas where residual impression material was present after immediate dentin sealing.⁶ The results indicated that immediate dentin sealing prevented the impression material from getting inside the dentin tubules and remaining there, which compromises adhesion.

ID: After a few weeks of temporization, what protocol is used to refresh the bond before placing an indirect restoration?

AR: The answer to that question requires consideration of the immediate dentin sealing technique used. Pashley and De Gee initially only proposed the use of an early bonding agent. Later, Magne recognized the benefits of using a new filled adhesive instead of a very thin material to coat the dentin. This filled adhesive had a bit more body, which not only offered advantages in terms of mechanical properties but also better protected the tooth from thermal injury and bacteria. Because of the added thickness, the bonded surface could be gently pumiced to refresh it prior to placing an indirect restoration. Eventually, self-etch adhesives were introduced, and we learned that the self-etch method is not the best for bonding to enamel without first selectively etching, but it can produce a very strong, predictable bond to dentin. Nonetheless, self-etch materials were still used in conjunction with other products because the adhesives themselves were not as filled. The latest approach entails using a self-etch adhesive but then adding a very thin layer of flowable composite to supplement it. This creates a slightly thicker layer, which is advantageous because the dentist does not need to worry as much about removing too much material during pumicing. Because of this, air abrasion can be utilized, and the use of 40-µm to 60-µm aluminum oxide powder has now become the standard to refresh the composite and create that frosty, high-energy surface that will facilitate a strong connection to the bonding agent and to the additional composite placed over it for cementation.

ID: Can you offer any tips for preventing provisional restorations, such as those made from bis-acryl material, from bonding to the immediately sealed dentin without failing during the temporization period?

AR: When I started performing immediate dentin sealing approximately 3 to 4 years ago, I was using whatever adhesive I had available, and that created certain issues. Once the thin layer of composite has been added, the interproximal gaps between the preparations and the adjacent teeth must be considered. The composite must be completely polished so that there is no oxygen-inhibited layer remaining to react with the material used for temporization. In addition, the temporization material must lock into the interproximal spaces. This can be accomplished by using a self-curing bisacryl material that includes disinfectant solution and other ingredients to maintain the area and prevent contamination. This type of material can be placed into the spaces interproximally, and it is safe to leave there for a couple of weeks until the permanent restoration is ready. Another method is to use a temporary blockout material. These materials can be injected into the interproximal spaces to maintain the position of the tooth without entirely covering it. Because parts of the preparation that would traditionally be exposed have been sealed with adhesive and a thin layer of composite via immediate dentin sealing, the tooth will not become sensitive or contaminated, and the surfaces will later be refreshed with air abrasion. The issue that remains is maintaining the space and preventing the neighboring teeth from migrating during the time that it takes for the laboratory to fabricate and deliver the permanent restoration. When a material such as blockout resin is injected into the interproximal spaces around the preparation, it creates a small stop that not only prevents the adjacent teeth from being able to move but also prevents the preparation itself from supraerupting because it is somewhat locked into place from the sides.

ID: Are there any other studies that are particularly noteworthy in validating the effectiveness of immediate dentin sealing?

AR: In 2005, Magne and colleagues published a study involving tests on three groups: a control group prepared using a direct immediate bonding technique, a delayed dentin sealing group in which the preparations had a temporary restoration on them for 2 weeks before they were cleaned and the restoration was bonded, and an immediate dentin sealing group in which the preparations underwent immediate dentin sealing prior to placement of the temporary restoration.⁷ Although the control group achieved bond strengths of 45 MPa to 60 MPa. The delayed dentin sealing group demonstrated much lower, inconsistent bond strengths with a mean of approximately 12 MPa. The immediate dentin sealing group produced consistent bond strengths in the 50- to 60-MPa range with very reduced standard deviations. That is strong evidence in favor of immediate dentin sealing. Of course, critics of the study have noted that the bonding agent was not cured; however, the protocol used really does a good job of mimicking what is done in the clinic. In another noteworthy study published by van den Breemer and colleagues, immediate dentin sealing techniques were compared with control groups that used several variations of delayed bonding techniques, and in all cases, immediate dentin sealing lead to significantly higher bond strengths.⁸ One criticism is that bonding to dentin will always eventually lead to degradation. Regardless, when bonding to dentin is necessary, utilizing immediate dentin sealing will produce better results than bonding to dentin that is contaminated. You will achieve a higher bond strength.

ID: You have mentioned sensitivity a few times. Are there any studies that assess postoperative sensitivity as it relates to immediate dentin sealing?

AR: This issue is interesting because one would think that coating the preparation and sealing the tubules would make the tooth less sensitive, but a very recent study featured a complete systematic review, and it concluded that there was no reduction in postoperative sensitivity associated with teeth restored using immediate dentin sealing when compared with teeth restored using a delayed bonding approach.⁹ The bond strength achieved by immediate dentin sealing has been demonstrated to be superior, unquestionably, but postoperative sensitivity is a different issue. We cannot categorically say that immediate dentin sealing will provide any advantage related to postoperative sensitivity.