Local anesthesia is the keystone to dental treatment. Fortunately blocks of the various nerves in the oral cavity are remarkably consistent and relatively easy to perform. Studies have shown blocks take about eight minutes to take effect, while infiltrations take about three minutes to complete anesthesia. We do not like to admit we ever miss a block or infiltration. However, other studies have shown the failure rate is close to 15% to 20%.Some claim that a greater success rate can be achieved by using larger diameter needles. Any needle smaller than a 25 gauge will curve some as it penetrates the tissue; intuitively, the bigger the needle, the greater the pain. There has been some research to show that there is no difference in pain when using a 31-gauge or a 25-gauge needle. Personally I have always used 27-gauge needles for blocks with good success, but I am not opposed to using a larger gauge. Regardless of the gauge, there is some pain when the needle pierces the tissue. Topical anesthesia has been used to prevent this pain. Numerous studies have shown that topical anesthesia is no more successful than a placebo at preventing this pain when true double-blind studies were done with flavored Vaseline. If neither the dentist nor the patient knew which was used, there was no advantage to the topical anesthesia. There have been studies to show that we do get a placebo effect from the topical. A few years ago, a new topical anesthetic was introduced, EMLA, a eutectic mixture of two local anesthetics, lidocaine and prilocaine, in a cream. It has been used for starting IVs, particularly with children. The EMLA is spread on the skin where the IV will be placed and a dressing is placed to keep the EMLA undisturbed for 20 to 30 minutes. The EMLA will anesthetize intact skin, making the IV placement painless. Studies have shown that EMLA works on the oral mucosa. In a slightly different form, it has been used to control the discomfort of periodontal scalings. I have also used it in root canal chambers as a lubricant for instrumentation when I was unable to get complete anesthesia on difficult-to-numb teeth. It is usually suggested that topical should be given five minutes to take effect.The pain from injections comes from piercing the tissue and from stretching the tissue while the solution is being injected. The pain of injecting can be eliminated by very slow injections. Piercing of the tissue is a different issue. I have used distraction by jerking the face at the moment of needle penetration. Quick penetration helps but there still is some pain from piercing the mucosa. What is the answer to preventing this pain?I did a study using electronic anesthesia to perform dentistry. I completed more than 800 cases with one of three techniques: just a Transcutaneous Electronic Nerve Stimulator (TENS), just nitrous oxide/oxygen sedation, or a combination of TENS and nitrous oxide. I did a variety of operative procedures from simple single-surface restorations through crown and bridge preps. The combination failed about 20% of the time. TENS alone or nitrous oxide/oxygen alone failed at a greater and unacceptable rate. When I failed, I would give local anesthesia to complete the procedure. Many patients said it was the best injection I have ever given. It took a while, but it dawned on me that maybe I should be using TENS in place of topical anesthetic for the administration of local anesthesia.I did a smaller study comparing TENS to topical. The patients preferred TENS to topical 3 to 1. Those who preferred topical usually stated that the TENS injection caused less pain than the injection that used topical, but they did not like the electronic sensation. In this study, topical was placed and allowed to work for five minutes. With the TENS technique, the needle puncture happened less than 15 seconds after the TENS was turned on. It was much faster than the topical technique and caused much less pain. TENS machines can be purchased online by doing a search for “TENS.” You want a TENS device that generates a signal of 150 Hz or more and that has an adjustable amplitude. Most machines will have two channels. You only use one channel at a time. These machines cost less than $100. TENS machines are most commonly used for muscle and joint pain. They come with adhesive electrodes. These pads do not work well for our purposes. I have found that two probes, one held on either side of where we are going to pierce the tissue, work better than the adhesive electrodes.After getting the TENS device, you must next make probes. I purchase small brass tubes at model hobby shops. I take the wooden applicator tips I use to apply topical and slide the wooden end into tubes until I find a diameter that accommodates the wooden end but not the cotton end. The cotton end is wet and serves as a contact with the tissue to conduct the current from the brass rod to the tissue. I cut the brass tubing into eight-inch lengths.Next, I went to an electronic hobby shop and got shrink tubing that the brass rod would slide into. This tubing serves to insulate the electrical signal so if the rod touches other tissue of the mouth, the signal is not diverted from where we want it. The TENS machines come with a wire harness that connects to the electronic pads. Most of the harnesses have a male pin about 1 mm in diameter that slides into a female connector of the pad. I put this pin into the end of the brass rod and crimp the rod tightly around the pin. The pin can also be soldered to the rod. Next, slide the shrink tubing over the brass rods. I shrunk the tubing to the brass rod by holding it over a flame. The probes are now ready to use with a rod attached to each wire. I have the dental assistant hold the TENS machine with the controls pointing at me. In her other hand is the anesthetic syringe that she holds by the needle cap out of the patient’s field of view. I take the probes and hold them like chopsticks. Each has a cotton applicator tip in its end that the assistant has previously dampened. I palpate the landmarks where I am going to inject with the probes spaced about three-quarters of an inch apart. Once I find the proper spot, I reach for the dial on the TENS machine and tell the patient to give me a grunt when he or she first feels a signal. I rapidly turn up the signal amplitude until I get the patient’s sign. I then slowly increase the signal strength while telling the patient to again tell me when the stimulation is strong. Sometimes you will see facial muscles contract due to the signal. I stop here even if the patient has not signaled. Holding onto the needle cap, the assistant passes me the anesthetic syringe, so that when I take the syringe the needle is uncapped. I pierce the tissue and give a very slow injection. Patients usually do not feel the needle penetrate. And if I inject slowly, they do not feel any of the injection. This all takes about 15 seconds from start to beginning the slow injection. For a short video of this technique, go to
http://youtube.com and search for “dentistry TENS.” The video also shows the use of a vibrating device to further block the pain of injection that will be a future topic.It is my opinion that the ultimate injection starts with the inhalation of a mixture of nitrous oxide and oxygen followed by the use of a TENS and vibration signals. With the rapid
induction technique, the patient is relaxed in less than a minute. Add a TENS device and a vibration injection device for another 15 seconds and you have the ultimate in pain control for dental injections.