Earthquakes and Oralquakes

October 2006

By: Dr. Scott R. Harden

There are many times in dentistry when it is challenging to convey a concept to a patient. You attempt to explain an idea several different ways, but you still receive that deer in the headlights look. A wonderful technique for communicating is the use of analogies. Analogies offer a terrific way to better illustrate a concept to a patient by utilizing a familiar reference for them that they can relate to and better comprehend. It is always better to have an approving nod than a blank stare.

Just the other day a new patient, Jerry, was asking questions about partial dentures. He was very interested in the design of a new denture because his previous three dentures were too uncomfortable for him to wear. He was specifically unhappy with the metal clasps on his old dentures because they were unattractive and put so much force on his teeth that one of his teeth became loose and needed extraction. Jerry was an engineer and thought about load vectors, force vectors sheer strengths and engineering stuff. This created the need for an analogy.
In comparison to modern sky scrapers that must be built and engineered to withstand the effects of an earthquake, partial dentures (tooth supported dentures) are rigid structures, accurately connected to teeth, sitting upon mobile tissue and related to a jaw that itself is moving. One could venture to say that the mouth is essentially a miniature earthquake, or perhaps an “oralquake”. Historically, many partial dentures were designed with brilliant interlocking precision attachments, engineering marvels that were very rigid and very much doomed to failure. The use of rigid metal clasps that hook over your teeth to anchor a partial denture in your mouth is one variation of this, and often can cause serious damage to teeth.

Buildings in earthquake areas transformed from rigid structures and became equipped with modern shock absorber systems to disseminate the earthquake forces. Dentures also evolved by developing flexible attachments that can move as the denture moves and similarly disseminate the oralquake forces.

Skyscrapers must withstand the vertical force of gravity and the horizontal force of wind. Most skyscrapers can easily move several feet in either direction, like a swaying tree, and account for this by use of hydraulic systems connected to counter-weights that shift as the building shifts. This keeps the foundational support of the building from being weakened over the years from wind or suddenly from an earthquake.
By comparison, partial dentures must withstand vertical and horizontal forces from chewing. Partial dentures are supported by teeth and a soft-tissue ridge where teeth were extracted. The partial denture places tissue pressure on the ridge and over time causes the tissue and underlying bone to resorb or shrink. Now the denture will undesirably teeter-totter using the teeth as the fulcrum point. This puts pressure on the teeth and if the anchorage to the teeth is rigid, like metal clasps, the teeth will become loose.

Like skyscrapers, modifications were developed in partial dentures to work with the force rather than try to resist it. Partial dentures can now be designed with a semi-rigid attachment on the back of the anchor teeth that work similar to a ball-and-hitch for connecting a trailer to back of your car. They are termed “Bredent Partial Dentures”. The anchor point, a round ball, is placed low on the anchor tooth, near the gum line, and thus reduces stress on the tooth. A nylon clip inside the denture snaps onto the ball and pivots freely without stressing the tooth. This is completely opposite to conventional metal clasps that were placed high on a tooth and acted to virtually extract teeth slowly as the tissue support changed and patients did not have their dentures relined to account for this tissue change.

Denture design remains a crucial factor in the success of patient comfort and esthetics. Another great benefit of this Bredent design is there are no unsightly metal clasps that show when you smile; the anchorage is all hidden. This would equate to a building having large metal cables attached from the top of the building to the ground instead of internal stabilizers. But that is yet another analogy.

Jerry was excited about his denture being engineered without clasps. He was also happy to learn about my long-term success rate of hundreds of dentures made based upon this design with terrific stability and patient satisfaction. This overshadows national statistics that states 80% of patients do not where their lower dentures. The lifelike esthetic design was a bonus for Jerry and his engineering background was truly satisfied with the approach of the analogy between earthquakes and oralquakes.

Analogies remain a great tool for communication between doctors and their patients.