ResMed: The Empire Strikes Back!
Apparently, the 3-D Printers at RESMED have been very busy since last November, when I first wrote about the NarvalTM by RESMED and the D-SADTM (Digital Sleep Apnea Device) by Panthera. Referring to them as “New World” appliances, they were contrasted to the very well respected “Old World” hand-made Herbst appliance.
The Herbst, still offers superior lateral movement due to the advancement mechanism employed, can be used in cases where there is insufficient dentition to retain a New World appliance and can be advanced in smaller increments than the NarvalTM or D-SADTM. However, that about sums up the Herbst advantages and it turns out that the New World appliances have their own set of advantages.
New World appliances are manufactured by a 3-D printer and made of a nylon polymer. Lightweight, sleek, and attractive, they advance the mandible by replacing nylon straps of varying length and intrude minimally on tongue space. Their unique strap mechanism transfers forces in the horizontal plane thus reducing vertical forces and stress to the teeth, musculature and Temporomandibular joints. I am referring to the NarvalTM by RESMED and a device made by Panthera Dental now called the D-SADTM. Last November I stated that the device made by Panthera appeared to be a “more evolved NarvalTM” and suggested, “The Empire Must Strike Back”. Well, it has! RESMED is clearly paying attention.
The NarvalTM straps have been modified to address the concerns raised last November; It is now a much more substantial strap which allows it to better manage the stresses imposed by a heavy bruxer (although I personally have never witnessed any issues with the previous straps) and the numbers on them are now larger so they can be read by most without an optical aide. Finally, they are now available in 0.5mm increments. The D-SADTM appliance straps are also available in 0.5mm increments and although their basic strap is already quite substantial they now also provide a special “B” version of their straps for those heavy bruxers requiring the extra strength.
RESMED now allows you to isolate and exclude a tooth from being incorporated into it’s retention, which is useful when you are dealing with a compromised tooth. The lost retention is mathematically added to the surrounding dentition. Panthera had this capability all along. Regarding appliance overall retention, the Panthera people recommend full coverage (with no contact) on the mandibular anteriors which aides with mandibular retention; especially when the teeth are short. RESMED also provides this feature. The increase in retention appears to be due to an increase in stiffness allowing the undercut retention from one quadrant to play off the undercut retention in the other.
As hands-on experience continues the concern over lack of reparability is starting to diminish. At this point, I, and others in North America have been inserting these New World appliances for almost 2 years and durability has absolutely not been a concern. In fact, there have been a number of examples of surviving pet dog munching and the like which would simply never apply to an Old World appliance.
Adjustability of these New World appliances to accommodate new dentistry has not turned out to be as big an issue as I originally believed. The Nylon Polymer has demonstrated itself to be very strong, allowing much more adjustment to the appliance leaving the material much thinner than one would have expected possible. Furthermore, if retention is compromised as a result of these adjustments, techniques to help enhance retention are now better understood. So, lack of ability to accommodate new dentistry is no longer as much of a concern.
By now, those of us even moderately involved in providing this therapy have witnessed tooth movement and the fact that this movement varies based on the appliance used. This movement is of course a factor of the forces placed on the dentition by the appliance, which varies due to differences in appliance design. Having minimal intrusion on tongue space doesn’t come without a price. I, and others have witnessed flaring of the maxillary anteriors with these New World appliances, apparently due to forces from the tongue pushing on lingual surfaces of these teeth. Of course, we want the tongue out of the airway, but it is apparent that we also have to protect the teeth from the forces imparted by that same tongue. RESMED now allows us to choose from various designs allowing the strap attaching the posterior segments on both upper and lower to cover the anterior dentition completely, partially, Lingually or Buccally. This affords us the ability to protect the dentition from tongue forces that could cause tooth movement, and although this anterior section does not make contact with the dentition, the added rigidity seems to aide retention when it is needed due to shorter or missing teeth. The D-SADTM appliance also allows these options. Unfortunately, I have witnessed this anterior tooth flaring on an inconsistent basis, sometimes alarmingly quickly and in other cases minimally or not at all. So, depending on whether this type of tooth movement would be a great concern with your patient I would recommend playing it safe in your design; unfortunately, playing it safe means losing some of the coveted tongue space these devices afford us. This issue needs further attention.
I find that on occasion I still have to remove posterior contact chair-side with the Narval but that may simply be a symptom of my bite registration; not sure on this one. However, I have not found this concern with the D-SADTM appliance and Panthera claims that this is taken care of by their software and design.
Both these New World devices seem to be very accommodating regarding being fabricated at various verticals. However, once fabricated, the vertical is not easily altered. This is another issue for further consideration.
Regarding Warranty, the NarvalTM remains at 3 years and includes both breakage and retention. The D-SadTM remains at 5 years on breakage only, in the event retention becomes an issue during that time frame it can be dealt with using techniques that involve modifying the appliance chair-side or adding composite to the side of the tooth to provide more of an undercut. I have not personally witnessed either one of them break or even show any signs of breakage in the last 18 months. Old World appliances have been put into a position to compete with the longer Warrantees offered with the New World appliances; unfortunately, making them more robust often means making them bulkier, which can prove to be problematic from a lip seal and patient comfort perspective
Finally, I understand that the D-SADTM appliance is in the final stages of obtaining FDA approval. This is a good thing. Who ever said competition is not desirable just needs to read this article. Kudos to RESMED for the many valuable enhancements to an already great appliance.
These New World appliances have much to offer and address many concerns associated with the Old World appliances, especially overall size, forces placed on the dentition and oro-facial apparatus, durability and longevity. However, when retention is an issue due to short or insufficient teeth, an Old World design remains the way to go, at least for the time being. These appliances are well received by patients and boast many benefits over traditional Old World appliances. However, they are clearly a work in progress, and I look forward to continued enhancements from both RESMED and Panthera.
So, now that the Empire has struck back, we can all await “The Return of the Jedi”.
John Viviano BSc DDS D ABDSM