The Mysterious Molecular Culprit Behind Cold Tooth Pain: Researchers figured out how a jolt of discomfort gets from the damaged outside of your tooth to the nerves inside it (NY Times, March 26, 2021)
If you have ever had severe tooth pain, then you know how uncomfortable cold sensitivity can be. But how does cold signal pass through the hard enamel tissue of the tooth? A recent mouse model study elucidates how the cold signal gets passed through the tooth’s tissue boundaries. It involves a kind of stem cell beneath the surface of dentin (the calcified tissue layer beneath the enamel of a tooth; Figure below), called an odontoblast, which forms microscopic protrusions with special cold-detecting proteins.
Here’s what you need to know about odontoblasts: they are made in the dental pulp of a tooth and make dentin (Figure below). In addition to making dentin, the special cells monitor the external, oral environment. Odontoblasts detect the signals that would suggest something is awry in the oral cavity (e.g., pH, cytokines, inflammatory mediators). They do this via tiny microscopic channel protrusions (also referred to as tubules) in the dentin that poke into the enamel layer. In the event of damage, odontoblasts can then signal for dentin regeneration. Here is a paper dedicated to a discussion of the specialized cells.
Figure. Tooth structure and dental tissues. Image credit: Britannica
The microscopic odontoblast protrusions are where cold signaling happens, mediated by a type of cold-sensing transient receptor potential (TRP) ion channel, called TRPC5. When something cold makes contact with the tooth, there is a cascade of events that ultimately depolarizes cell membranes to signal the sensation. So odontoblasts can be considered both surveillance cells on the lookout for damage and receivers of the sensory signal, aided by TRPC5.
I am in awe of the sophisticated construction of the tooth and its intricate internal network of nerves that facilitate the kind of signaling discussed above. I look forward to continuing the discussion about understanding and preserving oral health over a lifespan in an upcoming podcast episode conversation.
Episode 441. Does Advertising Actually Work? (Part 2: Digital) (Freakonomics Radio, 25 November 2020)
This podcast episode takes a hard look at the evidence for the efficacy of digital advertising, such as the social media ads and email marketing. The podcast uses the example of eBay to illustrate the stark disparity between what we think is true about advertising and what may be actually true. To give you an idea, the company executives believed that about 5% of sales were driven by paid-search advertising, meaning that if they stopped paying for advertisements their sales would drop by 5%. In reality, sales dropped by about 0.5%. With that knowledge, the company slashed its paid-search marketing budget by 100 million dollars a year.
The upshot here is that it turns out ads don’t cause sales. Granted, it is a commonly held belief that ads are a big part of sales. Most of us think they are because we confuse causation and correlation, sometimes without knowing it. This confusion is somewhat understandable because teasing out the cause of sales, say on Black Friday when companies spend a lot on digital ads and sales increase, is really difficult to do. And the relationship can easily be reinforced with the wrong kind of analyses, ones that are not randomized experiments, for example.
What is staggering to me is that, even when companies learned about the eBay research results, no one pushed to replicate the results of their internal experiments. The reasons are complicated, surely, but it sounded all too familiar to me. Listening to the episode reminded me that the field of medicine is not the only area in which ideas that are tested, if found to be at odds with the prevailing dogma, are ignored or discarded. The episode raises an important observation about cognitive biases, which I discuss in a conversation with Carol Tavris and Elliot Aronson. If you work on something for the majority of your life, it becomes part of your professional identity and you strongly believe in it. To go against long-standing beliefs is easier said than done. To do so would stand to challenge not only the concept in question but also the person’s strongly held identity associated with it.