So good, one set simply isn’t enough. Teeth are arguably the most underestimated of all bodily structures. Without teeth, eating would become a near-on impossible task, particularly amongst our ancestors who did not have access to cutlery and relied on a tougher vegetable based diet. There are a whole host of interesting questions surrounding the nature of human teeth. Why do mammals only have two sets? What are our wisdom teeth’s purpose? Do our changing diets mean we rely on our teeth less than we used to?
Many species have multiple sets of teeth. This makes a whole lot of evolutionary sense; teeth are rapidly worn down as we eat and an ability to replace them with a brand new set allows the maintenance of optimal feeding levels throughout our life. Studies within our very own department of Animal and Plant Sciences here at the University of Sheffield have just discovered the gene network which allows sharks to develop multiple sets of teeth throughout their lifetime. Mammals do not have this luxury; they are diphyodonts, meaning they only possess two sets of teeth throughout their lifetime. One advantage of having fewer sets is it allows for precise occlusion, our upper jaw teeth fit perfectly with our lower jaw teeth allowing an increase to our feeding efficacy.
Why haven’t mammals scrapped having multiple sets of teeth all together then? The answer lies in another feature which makes mammals unique: lactation. During infancy, breastfeeding ensures that the development of a strong set of teeth are not necessary - it is better to provision one’s resources in developing other more crucial structures. By the time mammals stop breast feeding our adult teeth should be ready to replace what have become suboptimal ‘baby’ teeth. Interestingly a societal change in western cultures has reduced the time span across which parents remain breastfeeding their children. A 2011 survey on the American population concluded that although 79% of newborns are breast fed, by the time they reach one year old this figure plummets to 27%. Given that the average age at which adult teeth appear is 6 years, it can be suggested that we are forcing ‘baby’ teeth to fill an adult function.
By the time humans reach their late teens a third set of molars erupt at the back of the mouth. This is the age upon which an adult is considered mature, supposedly, leading to their more common name of wisdom teeth. The common consensus is that these teeth appear at maturity to allow increased chewing and grinding power, which would be particularly beneficial to our early ancestors with their vegetable based diets. With the increased consumption of soft foods such as processed grains combined with the widespread use of tools which can undertake the job of teeth externally (eg knifes), wisdom teeth are now considered redundant structures. This makes the fact that numerous people have difficulties when their wisdom teeth emerge even more frustrating. One estimate has suggested that as many as 80% of us cannot maintain our wisdom teeth without any complications, making their removal one of the most common medical procedures in the UK. Over the last 10,000 years, human jaw sizes have been decreasing, meaning that our mouth has essentially become overcrowded with teeth. By the time that wisdom teeth are ready to emerge the gums are already lined with teeth, increasing the chances that a cyst will develop or the tooth will enter at an angled position. Periodontist Dr. Danenberg has attributed the loss of jaw size in modern humans to two main factors. Firstly, an increase in processed food and sugar intake has decreased the levels of nutrient dense grains consumed, resulting in compromised bone metabolism. Secondly, a decrease in breastfeeding in western societies means that from a young age we are missing out on optimal oral mechanical stimulation required for our jaws to develop to a larger size.
Changes to our diet and behavior have meant that teeth have a changed and less important role to play in an individual’s life. Wisdom teeth now join a wealth of structures found in humans which are relics of our evolutionary history, similar to our appendix which also reflects our ancestor’s reliance on a vegetable based diet. Discussions on the role that teeth play in modern humans give us a timely reminder that we too play by evolution’s rules.