As an Endodontic specialist of almost 15 years practice, I have seen products and techniques come and go. Hydron, the magic hydrophilic filling material of the 80s is no more. Friction driven filling devices (McSpadden Compactor) have fallen out of favor as the endodontic community "warms" to the concept of pushing gutta-percha vertically under the influence of heat. Ultrasonics, the converted Cavitron touted in the mid 80s by Cunningham and Martin as the "Vegematic" of Endodontics (it cleans, shapes, sterilizes, implodes, produces less extrusion of debris etc etc) has been relegated to "electronic swizzle stick" status. Once research is performed by those not financially affiliated with the device or technique, the published results are inevitably less favorable than originally claimed.
The initial positive effects of endosonic/ultrasonic instrumentation were predicated on the free movement of the energized file in the canal. Once it was understood that contact of the file with the canal wall dampened and reduced the sonic vibration, the proposed in vitro effects were less clinically relevant or reproducible. Most studies began to show that in vivo cases were not shaped more quickly than conventional treatment. It was also noted that the tip of the instrument had the most amplitude and the body of the file the least. This is opposite to the desired endodontic result, minimal enlargement of the deepest portions of the canal and more enlargement in the body and cervical portions.
The most recent research suggests that both sonic and ultrasonics are equally effective in activating irrigation solutions once canals have been cleaned and shaped. The recommended time for activation of these canals is three minutes per canal. Therefore in maxillary molars, ultrasonics will increase the canal preparation time for most teeth by 12 minutes. Since the ultrasonically activated files must not contact the canal walls, they must be held in position manually. (Should Dentists choose to delegate this duty to assistant, there will no doubt be legal ramifications since in most states/provinces assistants are not allowed to perform this type of "treatment". Also, if a file breaks in the hands of an assistant, it is doubtful that the dentist's malpractice coverage would cover the consequences of this scenario.) It is also unlikely that clinicians will comply with an extra 12 minutes of instrumentation time per molar, especially when some Endodontic clinicians are claiming to clean and shape an entire tooth in only a few minutes with Ni-Ti engine rotary files.
There is no question that the use of sonics/ultrasonics in conjunction with endodontic irrigation can produce cleaner canals in many cases. Whether this technique is useful in teeth with difficult access or extremely curved canals, whether the increase in time and necessity for maintaining files in free space by hand are justified remains to be proven by unbiased research. Until this is verified, the claims of manufacturers and their paid advocates/lecturers should be viewed with the appropriate skepticism.