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There are 3 leading causes of postoperative sensitivity after composite resin restoration, the good news for patients is that there are ways to reduce its occurrence with your restorative dentistry.
Postoperative sensitivity is a typical patient complaint after composite resin restoration. We look at the 3 leading causes of postoperative sensitivity and some ways to reduce its occurrence with your restorative dentistry.
Per the International Journal of Dentistry and Oral Health, there are 3 primary causes of postoperative sensitivity. These include:1
Built-up residual stress in the tooth after direct restorative material placement
Postoperative sensitivity from polymerization shrinkage also has to do with the C-Factor (cavity configuration factor), which Craig's Restorative Dental Materials (Fourteenth Edition) defines as a ratio determined by the bonded-to-unbonded surfaces of the restoration. While not proven by science, the C-Factor is the best explanation for clinicians attempting to manage polymerization shrinkage in their prep design for direct posterior composite restorations.2
All composites shrink, ranging from 2% to 5%, and usually toward the center of the restoration. Therefore, the shape of the prep, the number of opposing walls and how they are in opposition to one another, and the angle of that opposition affect the behavior of the composite shrinkage. In other words, parallel walls that traditional cavity preparations teach in dental school—originally meant for amalgam restorations—work against the dentist regarding postoperative sensitivity when the material shrinks during polymerization.2
The Primary Way to Prevent Postoperative Sensitivity is to Create a Stress-Free Bond
Richard Young, DDS, private-practice clinician, and Assistant Professor of General Dentistry At Loma Linda University School of Dentistry, says that ever since the mid-1980s when he first got out of dental school, he learned that the foundational element of preventing postoperative sensitivity with direct composite resin dentistry is not to stress the bond to the dentin. The system that he started using then was based on total etching of dentin, but it was very important to follow the manufacturer’s directions, which was 20-second applications of the components of the system, and Dr Young says they learned more than 20 seconds was better than less.
"I always ran an egg timer for 20 seconds, if that was the time shown in the directions of the system I was using,” Dr Young says.
Before flowable composites were available, Dr Young explained that dentists would then put a thin layer of their chosen material, as thin as .5 mm, in the deepest area of the box nearest the pulpal floor and cure it. Next, clinicians would use a similar thin layer of .5mm on the box connected to the floor. This 2-part ultra-thin layering technique helped minimize shrinkage and that stress pulling the bond off the pulpal floor where gaps would form.
"Every composite shrinks towards the strongest bond, so you have to control shrinkage, at the bond to dentin interface.”
In the late 80s and early 90s, clinicians learned a technique called “directed shrinkage.”Bisco's Bisfil™ 2B self-cured composite was hand mixed, then put into a Centrix syringe tip, and injected into the box and onto the plural floor 2 to 3 mm deep, depending on the depth of the cavity preparation, Dr Young explains.
“This technique worked extremely well in controlling shrinkage and post-op sensitivity on biting. Then, in the 90s, clinicians moved to using flowable composite in a similar way,” Dr Young says.
After the bonding process was completed and cured, Dr Young says clinicians used thin layers of flowable composite, 0.5mm to 1mm in thickness, in the box first and then over all the dentin.The first layer in the base of the box was the most critical.This was followed by horizontal layering in 2 mm increments of the final composite such as Herculite, Heliomolar, or APX, he explains.
“We were also careful to not apply our curing lights to intensely and the beginning of the curing process, known as ‘ramping’ of the curing light,” Dr Young says."The irony is that nothing has really changed, that technique is often referred to as ‘immediate dentin sealing and resin coating’ today.Everything we do today is based on the concepts that have been proven over time and presented in many research studies, as stress goes up, bond strength and long-term success go down.”
Providing good isolation and moisture control.A rubber dam has always been the preferred method since Dr Young was in dental school. Dr Young says other systems like DryShield®, Isolite®, and Ultradent’s Umbrella™, which are designed for areas where placing a rubber dam is a problem, can serve well here also.
Following the manufacturer’s instructions. If it says to scrub and apply the bond or primer for 20 seconds, then clinicians should do that.
Using a liner. He says this point is where flowable comes into play in a thin, .5mm layer first over the base of the box and pulpal floor curing each 0.5mm increment, and then all over the dentin.
Layering the composite in 2mm horizontal increments. Dr Young says that once you have laid this foundation for preventing polymerization stress, there should not be issues with postoperative sensitivity. DrYoung likes to use CLEARFIL™ Majesty Flow A1 or B1 for his flowable, and if it's a deep and extensive prep and he likes to replace the dentin with CLEARFIL AP-X horizontally layered in 2mm increments.Once he gets to the enamel layer, Dr Young likes to use CLEARFIL MAJESTY ES-2 Universal.
Use a Desensitizer.
In addition to using a liner, research indicates that a desensitizer can help prevent postoperative sensitivity. Per the Serbian Dental Journal, additional protection of the pulp in addition to proper prep design and the use of adequate layering technique reduces postoperative sensitivity.3
Researchers found that putting an oxalate-based desensitizer, BisBlock™ (BISCO Inc.), under the liner can also reduce the sensitivity after restoration. In their research, the group with restored teeth that had BisBlock had a 6.7% incidence rate of postoperative sensitivity versus 15.8% of the cases that did not restore with the desensitizer.3
Desensitizers reduce dentin hypersensitivity by reducing movement found within the dentinal tubules. Another explanation could be that it also reduces the nerve activation by the fluid's movement. BisBlock gets into the dentinal tubules and creates crystals of calcium oxalate there. However, the external surface of the dentin is still free to interface with the bonding agent. Therefore, the researchers conclude, the crystals prevent the fluid movement in the tubules without interfering with the bond.3
Don't Rush the Bonding Steps.
Another essential point to reiterate, Dr Young says, is not rushing the process. Unfortunately, he thinks that too many clinicians are looking for a shortcut, and not following the manufacturer’s directions in placement of the bond.Dr Young likes to say, “if saving 2 minutes of time is going to make a large difference in your overall practice profit then it’s time to rethink your management philosophies.
Review Your Technique and Equipment.
A fundamental review of your placement technique is essential. John Carson, DDS, PC, writes on Spear Education 4 tips to reduce postoperative sensitivity, which is related to technique.
After getting adequate isolation, proper etching and drying techniques are also essential. Over-etching the dentin can create problems after placing the restoration, so remember that timing is everything there, Dr Carson writes. In addition, you do not want to over-dry the dentin, which collapses the dentinal tubules. Moreover, the air source should not blow contaminants onto the area you want to dry. To test your instrument, Dr Carson suggests blowing air across your mirror; there should be nothing left behind on the mirror's surface.4
The curing technique can also contribute to postoperative sensitivity. So, checking your curing light's output and reviewing how close the light is to the composite's surface is essential. Also, ensure that the tip is free of debris and in good working order.4
If it Hurts, Take it Out and Start Over.
Post-op sensitivity has been a big problem for many clinicians over the years with posterior composites.Dr Young says that clinicians should understand what is causing the sensitivity. The first thing to do is to check if the bite is off or has a high spot. If so, adjusting the patient's occlusion will fix the postoperative sensitivity, usually over the next day or 2.
However, if the tooth does not settle down, Dr Young recommends having them gently bite in the middle of the composite with a device like the “tooth slooth” or a large round end plugger, or a small ball of composite cured on the end of a micro brush.If there is pain on release you most likely have a gap formation at the pulpal floor causing discomfort on biting.The only solution at that point, Dr Young explains, is to remove the composite and start over, carefully following all the stress reduction protocols outlined earlier in the article.
“It’s happened to all of us and one point or another,” Dr Young says. “In conclusion, as Unterbrink and Liebenberg said in 1999, ‘if the bonds can withstand the stress, the restorative technique will be successful.’”