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Modern dentistry is undergirded by adhesive dentistry. Most of the restorations that are placed depend on the clinician's ability to bond materials to tooth structure. Unfortunately, a common complication of adhesive dentistry is postoperative sensitivity. Having patients return due to postoperative sensitivity creates frustration for both them and the clinician. In addition, it costs the dental team valuable chair time. Treating postoperative sensitivity is difficult once it has already occurred; therefore, the best solution is to prevent it from occurring in the first place. Ideally, it is prevented through the use of a proper adhesive technique. Factors that may contribute to postoperative sensitivity during adhesive procedures include the over-etching of dentin, overdrying, shrinkage stress, hyperocclusion, poor isolation, and underpolymerized restorations.
Over-Etching of Dentin
The aggressive use of phosphoric acid etchant on dentin may cause a host of complications. If 35% to 40% phosphoric acid etchant is allowed to sit on the dentin for too long, it will excessively demineralize it. During etching, the acid dissolves the hydroxyapatite in the dentin and reveals the collagen fibers. The hydroxyapatite is interwoven between the collagen fibers. If the dentin is excessively etched, the collagen collapses, and the adhesive cannot completely penetrate the dentin during bonding. This can result in voids that lead to fluid movement in the dentinal tubules,1 and fluid movement can trigger the sensation of sensitivity.2
To decrease the risk of excessive dentin etching, cut dentin should only be etched with phosphoric acid for 10 to 15 seconds.3 Alternatively, clinicians can utilize a self-etching primer on dentin. Self-etching primers employ acidic monomers such as 10-MDP to simultaneously etch and prime the tooth. These monomers tend to be weaker acids than the phosphoric acid used in the etch-and-rinse technique. Self-etching bonding agents do not remove the smear layer but rather modify and solubilize it.3
Overdrying
Overly drying dentin prior to restoration placement may also lead to postoperative sensitivity. Nakabayashi's work, which introduced the concept of the hybrid layer, demonstrated the significance of optimal dentin hydration.4 The collagen must stay hydrated within the dentin matrix to prevent collapse. If it collapses, the adhesive won't be able to completely penetrate the dentin, which once again, can lead to fluid movement in the tubules and sensitivity.5
After drying, the dentin should appear slightly shiny and moist. There should not be any visible fluid pooling, nor should the dentin appear chalky. If air drying, the clinician should intermittently and lightly dry the dentin.
Polymerization Shrinkage
As composite resin is cured, it shrinks. This is because the monomers begin in a loosely arranged network. As they are polymerized, they are rearranged into a cross-linked network, which results in shrinkage. The organization of the monomers into a cross-linked network causes the net spacing between the monomers to decrease. The higher the C-factor of a preparation, the higher the shrinkage stress. In that regard, certain preparation designs are more susceptible to shrinkage stress. Class I preparations have the highest C-factor.
Therefore, any time that clinicians use adhesive materials in dentistry, they must be conscientious of decreasing the stress. Using an incremental composite layering technique in which thin increments that are 2 mm or less are placed and cured at a time reduces the volume being cured and thus the shrinkage that occurs. An oblique layering technique may also decrease shrinkage stress.6
Organizations such as the International Caries Consensus Collaboration and the American Dental Association have authored publications discussing the need for a minimally invasive approach to caries removal.7 One such technique, selective caries removal, can preserve pulp vitality. However, because the bond to affected or infected dentin is of decreased strength, if it is left close to the pulp, there is a risk that as the composite shrinks, it will pull away from the carious dentin. This may lead to occlusal loading sensitivity.8 This phenomenon is oftentimes overlooked or mistaken for hyperocclusion.
Hyperocclusion
Postoperative pain from hyperocclusion can be prevented with a proper occlusal evaluation. Oftentimes, to evaluate occlusion, clinicians will have patients bite down on articulating ribbon at the end of the procedure. Any markings on the restoration from the ribbon are then removed, and the restoration is "taken out of hyperocclusion." The shortcoming of using articulating ribbon to evaluate occlusion is that the ribbon shows where the contact is, but it may be difficult to decipher if the contact is too strong.
The optimal way to create an ideal occlusal scheme on a restoration begins by evaluating the strength of the occlusal contacts of the adjacent teeth prior to tooth preparation. This can be done using shimstock, which is an occlusion foil that is 8 to 13 μm thick. The clinician should repeat this step after restoration placement. If teeth that were formerly occluding are no longer occluding, the restoration may be high and require adjustment.
Improper Isolation
Proper isolation is essential to the long-term success of adhesively placed restorations. Improper isolation may indirectly lead to postoperative sensitivity. Research has demonstrated that salivary contamination as minuscule as 1 μL can adversely impact shear bond strength.9 Frankenberger concluded that the leading cause of adhesive failure is contamination of the preparation.10 Preparation contamination, whether from blood or saliva, can lead to poor polymerization, adhesive layer degradation, and voids-all of which can result in postoperative sensitivity and pain. Moreover, contamination can result in incomplete adhesive penetration into the dentinal tubules. Consequently, microleakage, fluid movement, or bacterial ingress may arise, which can also lead to postoperative sensitivity and pain.
Underpolymerized Restorations
An oft-overlooked reason for postoperative sensitivity is underpolymerization. In some situations, clinicians discount how important it is to completely cure the restoration. When a restoration is cured, the top of it may feel hard; however, the bottom may still be uncured.11 Therefore, it is important to always follow the manufacturer's recommended curing time for the composite or cement used. In addition, manufacturer instructions regarding the composite's depth of cure must be adhered to. Bulk-fill composites can be placed in increments of 4 to 6 mm because they have more photoinitiators than standard composites. If standard composites are placed as though they are bulk-fills, it can lead to undercured portions.
The curing light used can be another factor in underpolymerization. Choosing the right curing light and properly maintaining it are critical. High-performance curing lights are more reliable than inexpensive LED curing lights. It is also advisable to routinely test the output of a curing light. Some curing lights are equipped with irradiance sensors, which can help ensure consistent performance.11
Conclusion
Treating postoperative sensitivity may not be feasible. Therefore, the best strategy is to prevent it from occurring in the first place by employing a proper adhesive technique. One way to enhance the prevention of postoperative sensitivity is to incorporate a desensitizing agent into the bonding protocol. Popular desensitizing agents are composed of glutaraldehyde (a cold sterilant) and HEMA. The glutaraldehyde blocks the dentinal tubules, thus preventing fluid movement, and the HEMA supports the formation of a polymer matrix in the tubules, which further prevents fluid movement.12 Research has shown that such desensitizers demonstrate effectiveness in preventing postoperative sensitivity.13 If a desensitizer is to be used, it must be applied carefully and according to the manufacturer's instructions. Failure to do so may result in decreased bond strength.
Although some postoperative sensitivity may be unavoidable in certain cases, preventing it or minimizing it by being vigilant in the proper execution of bonding protocols will improve patient satisfaction and trust. Many of the factors presented here that can result in postoperative sensitivity also have an effect on bond strength and occlusion, which can impact the long-term success of restorations, further underscoring the importance of adhering to proper technique.
Acknowledgement
The author would like to thank Richard Price, DDS, MS, PhD; Mark Latta, DMD, MS; and Joe Oxman, PhD, for their mentorship.
Queries regarding this course may be submitted to authorqueries@conexiant.com
About the Author
Melissa Seibert, DMD, MS
Diplomate
American Board of General Dentistry
Creator and Host
Dental Digest Podcast
US Air Force Dentist
Langley Air Force Base
Hampton, Virginia
Clinical Instructor
Creighton University
School of Dentistry
Omaha, Nebraska
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