Question: How does a denture hold its position in the mouth without falling out when the person is talking?

Answer: A well-made denture is one that has a good peripheral seal and is held in place by negative pressure very much like a suction cup.

How does one explain the basic principles of denture retention to a group of young and aspiring dentists? Based on the answer to the above question, can you understand or visualise the principles of denture retention?

One way to illustrate the basic principles of denture retention is to use prior knowledge or experience. For example, some of us may have tried pulling a large rubber bung from a sink outlet only to discover that it does require quite some effort; others may have tried opening a refrigerator door immediately after slamming it shut only to find that it does not give way to a small tug.

In the first instance, once the rubber bug's seal is disturbed, it comes off the sink outlet easily. Likewise, when the pressure on the outside and inside of the refrigerator door is equalised, it swings open effortlessly. The same principle applies to denture retention; no matter how tight the denture is, one sneeze is all it takes to send it flying!

To explain the principles of denture retention, a teacher can go by way of physics and show students equations for pressure and surface tension and so on, or use prior knowledge or experience (e.g. the rubber bung and the refrigerator door) to help learners draw a parallel between the two situations. However, teaching such a new idea will be challenging when learners have neither knowledge of physics nor any prior experience with 'negative pressure'. While a person with some prior knowledge can get the idea immediately, someone without such knowledge may not know how to direct his/her thoughts and will probably never arrive at the answer.

The university is a place for students to learn how to form opinions and synthesise information by drawing from their past experiences and knowledge through discussion, interaction, exploration and thinking. As many subjects in science are evidence-based, students often need to rote learn basic facts and formulae to direct their thoughts in the right direction. However, in this information age, there is a misconception that it is no longer necessary to memorise facts as one can easily get them from the Internet and books.

Nevertheless, I believe that a good clinician must have a thorough knowledge of his field so that he can arrive at an accurate diagnosis promptly. For example, when someone walks into the consultation room with a toothache in the upper right molar, the dentist does not have the luxury of time to type 'toothache on upper molar' into a search engine on the Internet and wait for the relevant information to show up. The dentist has to quickly think through the possibilities: Pulpits? Tooth decay? Cracked tooth? Gum infection? Sinusitis? Headache? Mumps? Heart attack? Then, he has to mentally sieve through the list of clinical signs and symptoms of each ailment as he examines and questions his patient. A skilled dentist can usually arrive at the answer within seconds for the run-of-the-mill diagnosis of pulpitis due to tooth decay. Mumps may take the dentist a little longer to diagnose. Sometimes medical practitioners treat the patient for mumps when they actually have pulpitis! (this happened to one of my close friends when we were in university). Sometimes dentists perform a root canal procedure for pulpitis instead of prescribing treatment for sinusitis.

How do these mistakes happen? Prior knowledge or the lack of it! If the medical practitioner has a good knowledge of his field these mistakes can be avoided. A knowledgeable doctor will be able to diagnose a toothache and refer the patient to a dentist. By the same token, a well-informed dentist should be able to diagnose mumps or sinusitis and refer the case to a doctor.

In any field of study, one must strike a balance between two extremes-processing skills without sufficient knowledge and rote learning facts without application. Do not go overboard with too much emphasis on 'thinking skills' and forget that mastery of facts is fundamental to guiding the thinking.