The Mighty Molar
Molar teeth on dentures are often something we take for granted as they are not overly visual and have little bearing on the appearance aspects of the denture. They are however the workhorse of our chewing efforts with broad surfaces to trap food, and withstand bite forces in some cases of hundreds of pounds per square inch. In nature we work with whatever our genetic makeup has provided, but in dentures there are choices to be made based on a number of individual considerations.
Molars accomplish their task by crushing food that has been boxed in by our tongue and cheek walls. This crushing action is usually coupled with a slight rotary motion to grind the food between the mountain like cusps of the upper and lower tooth surfaces. With denture teeth these cusps are given a designation of 0°, 10°, 20°, or 33° based on the angle and height of their slopes.
33° being a very tall and aggressive chewing tooth, to 0°, which might offer very little rotary friction. At first one might assume everyone would want 33° molars as they are the most prominent or what a patient might refer to as sharp. There is however other considerations that come into play such as how tall are the ridges in the patient's mouth that the dentures will fit over. If a patient has minimal bone mass holding a lower denture in place, the heavy cusp design of 33° when locking together may cause the denture to shift from side to side while chewing. This movement can lead to sore tissues and potential problems of food entrapment under the denture. A less aggressive cusp of 10° or 20° would offer a better compromise between sharpness and stability in this situation. In cases where the lower ridge has dramatically resorbed, 0° molars often fit the bill as they provide the least resistance to lateral forces of chewing that might unseat a denture.
There are also many theories regarding the movements of the temporal mandibular joint or jaw joint. You may find your practitioner choosing the degree of molar incline based on your unique bite patterns. Size is also relevant, ideally a full compliment of two bicuspids and two molars per side is desired. Too big a selection may only leave room for three teeth, conversely too small a selection will make for a short chewing surface leaving a gap at the tail end of the denture.
Over the years there have been a number of unique designs that do not resemble the shape of natural dentition at all. They have had varying degrees of success, but are not commonly seen or sought out. Dr. French's molars are a design where the upper arch denture there would be a flat 0° type molar, while the opposing lower arch would have a single raised ridge running down the middle of the tooth creating a chisel to a flat surface type action.
An even less common application was the cutter bar. On these molars a raised ridge of steel would zig zag down the chewing surfaces on one denture with a flat 0° molar in opposition. Given the hardness of steel the opposing tooth would usually be made of porcelain, certainly materials designed for durability but fell way short of pleasing aesthetics.
So there you have some food for thought, (excuse the pun!), for the next time you are discussing tooth selection with your dental provider.