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The Perfect Rapid Palatal Expander |
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Originally published September 2007
The Perfect Rapid Palatal Expander
If only we lived in a perfect world. Perfection, especially in the world of the orthodontic lab, can be an eternally elusive quality. On the other hand, if we can find products and services that closely match our needs at a price we are willing to pay, aren’t we close to technician Nirvana? When it comes to RPE’s, the reality of perfection for you may simply be the expander that works great, is easy to fit, and is trouble-free. Brand selection in your lab may be influenced by many things - doctor preference, reliability, size, availability, price, special features (such as ratchet stops), ease of use, or your relationship with a particular supplier - but as any experienced lab tech knows, preferences are often compromises between what is readily available and the value proposition of a particular product. Here is our perspective on a few factors that effect price and performance in the RPE market:
Spindle Tolerance
Tolerances are what determine the precision and repeatability of a machined part. As tolerances (+/- range of acceptable sizing) go down in machined assemblies, precision and consistency go up. Higher precision translates to higher predictability, and RPE’s machined to tighter tolerances have a tendency to resist “backing up” more than those that have looser (wider range) tolerances. The trade-off the technician experiences for a tighter, more reliable screw (beyond the higher price) is that the placement of the screw is more technique sensitive. If placement does not sufficiently account for equalization of expansion forces, binding of the spindle may occur, turning a great screw into an apparently defective one. Spindle tolerances on ratchet screws can be much looser than on standard types, since the tolerance isn’t what accounts for “back-up” resistance. For this reason, ratchet screws can be much more forgiving in placement while still providing a positive locking action on expansion.
Laser Welding
Laser welding is essential as the method of attaching the legs to the body of the RPE. This hi-tech joining technology minimizes heat in critical areas thereby reducing the possibility of subsequent wire failure, particularly when making leg adjustments close to the body. Laser-welding also enhances the fit and finish of the guide pins, guaranteeing a smooth travel through the entire range of expansion.
Center Bridge
A fixed center bridge is a nice option in that it stabilizes the RPE through the entire expansion range. This support structure ensures symmetric expansion and provides the added bonus of providing a “stop” preventing the adjustment key from coming in contact with palatal tissue.
Bent Legs vs. Straight Legs
One of the most popular RPE’s on the market comes with straight legs, so it’s certainly OK with a lot of technicians. We just find that it is easier to start with a preform bend in a palatal contour that reduces stress and fracture potential when bending close to the RPE body. Time is money, and whatever labor-saving elements you can incorporate into your basic components, the better the opportunity for profitability. Reducing material cost is important, but remember that in today’s labs across the USA, material costs account for 10% or less of the cost of doing business. Labor efficiency is where significant gains can be made, and preforms are a good place to start.
Check out the selection of RPE’s that Wehmer offers. All are designed to give you features, reliability and performance that are consistent from one order to the next.
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2009 Laboratory Equipment and Products (3962)