Why 30o Oscillating Reamers Produce Superior Results in Oval Canals and Thin Isthmuses

The reason is so obvious that it is hiding in plain site. The oscillating stainless steel twisted reamers are virtually invulnerable to separation. From a practical point of view that means a dentist or endodontist even on a bad day is not going to be able to separate an instrument when used in the 30o oscillating handpiece. That means the restrictions on their use are small compared to the precautions recommended for the safe usage of rotary instruments be they continuous or interrupted (reciprocation). Where rotary must stay centered with minimal deviation from the most direct pathway through the canal, the oscillating stainless steel reamers can and should be applied laterally and vigorously against all the canal walls. These reamers are not used in a crown-down fashion the way rotary is used. Rather the thinnest instruments those most likely to gain access to the apex with the least resistance are used first and given their thinness they have the best chances of entering and deriding any thin isthmus-like anatomy. The result is the preservation of more dentin and the entry of these instruments into pulpal configurations that rotary would never attempt.

My critic suggested that the up and down motion of the reamers used in the oscillating handpiece are likely to impact debris against the canal walls as they are applied vigorously against them.That is a theory that has not been substantiated with any evidence. What has been substantiated is the debris impacted bucco-lingually when a greater tapered rotary instrument first enters an oval canal. It shaves dentin from the narrower canal anatomy, namely the mesio-distal dimension?and impacts some of those shavings bunco-lingually as you can see in the video Dr. Ali Nasir made when performing that task. The impacted debris impairs irrigation and reduces the debridement we want in this third dimension.

Contrary to my critic’s theory, it is the greater tapered rotary instruments that present a greater challenge to cleansing the canal rather than the 30o oscillating thin reamers. The action of the initial thin reamers are removing far less dentin from the mesial and distal canal walls, depositing far less bucco-lingually and if indeed some is being deposited those same reamers are vigorously being applied to the buccal and lingual canal walls to assure their debridement. Rotary instruments precautioned to stay centered are far less likely to carry out this function and if they did would have a far greater task in removing the larger quantity of impacted debris.

The 30o oscillating reamers shave dentin away from the canal walls on the upstroke, but that action is accomplished via the rapid horizontal strokes generated by the handpiece. On the down stroke the vertically oriented flutes of the relieved reamer tend to bypass any debris present in the canal similarly to the way rotary instruments with a similar flute orientation would. So from the point of view of the down stroke the 30o oscillating reamers and the rotary instruments tend to bypass debris much the same way. The significant difference between the two is that the oscillating reamers are used first in their thinnest configurations far less likely to have intimate contact along the length of the canal and far less likely to impact debris than the greater tapered rotary instruments which is another reason why greater tapered instruments are used in a crown-down sequence.

It should also be noted that the relieved reamers gain depth via short arcs of motion that have been shown in several research papers to function similarly to the balanced force technique. So while, the reamers further cleanse the canals along its length on the upstroke, they advance in small increments and like those advancements with balanced force they have been shown in innumerable cases I have posted to stay true to the original canal anatomy. By substituting the 30o oscillating handpiece as the driving force for gaining undistorted apical length, the manual use is bypassed as well as the hand fatigue that would result. Given the high frequency of oscillations 3000-4000 cycles per minute or about 60 cycles per second, the task of instrumentation not only becomes far easier, but also much quicker.

What I am describing here and in many previous posts are the inherent advantages of implementing relieved stainless steel twisted reamers with short arcs of motions. Short arcs of motion are the key. It prevents instrument breakage and it prevents distortions. This was true from day one and did not require an endless array of innovations to overcome instrument breakage. That cannot be said for rotary NiTi. The problem of instrument separation became apparent quite quickly after their introduction in 1988 and for the past 30 years the resolution of that problem has been the main source of innovation, finding the means to reduce separation while delivering well derided canals without excessive loss of coronal tooth strucrture. No question that the NiTi companies have made progress. The martensitic properties of NiTi instruments have been accentuated making the latest instruments more flexible and less prone to breakage due to cyclic fatigue an unpredictable iatrogenic event particularly when shaping and debriding curved canals. As the martensitic properties are accentuated, the NiTi metal becomes softer and more flexible. The reduced tendency to separate should give the dentist a greater freedom to apply these instruments against the canal walls, but at the same time the increased flexibility causes them to increasingly deflect from the canal walls they touch, a problem most noticeable in the wider dimensions of oval canals.

Adopting these newer generations of rotary has led to an improved level of non-distortion of curved canals as noted in mesio-distal peripapical?radiographs. What is not seen is the increased lack of debridement in the bucco-lingual dimension of oval canals, something noted in the literature as a phenomenon that has yet to be solved. The introduction of rotary endodontics still requires ongoing innovation to solve the shortcomings. New metallurgy and constantly upgraded recommendations on their safe usage and how many times given the circumstances of the individual case can they be used is par for the course. This constantly shifting reality is reflected in the ever more sophisticated engines that run these instruments, controls that cover clockwise and counterclockwise arcs of motion, speed, torque controls with settings that are supposedly optimum for each instrument when used in a myriad of different conditions.

And in contrast there is 30o oscillations at high frequency using stainless steel relieved twisted reamers that present no limiting problems and can be used consistently in all situations. All it required were some small design improvements for optimal function and the dentists had a tool that was completely adaptable. I say this with some degree of confidence given the fact that we created this different approach and have been using it consistently and successfully for the past 30 or so years.

Finally, I am adding a small video that shows the extrusion of debris using a rotary system. Nothing unusual given the consistent findings in the literature that all instrumentation systems produce some degree of apically extruded debris. My critic wished to nullify all the benefits of three dimensional debridement based on a small amount of debris being extruded apically. Perhaps, he will soften his stance if and when he sees that extruded debris is a problem not completely solved that affects all systems developed to date.

Regards, Barry