Birth of a conspiracy theory? In defense of oral hygiene.

“Historical perspectives on advertising and the meme that personal oral hygiene prevents dental caries”   by Hujoel V.P.,  Gerontology, 2018

This alarming article states that insufficient amounts of vitamin D rather than dental plaques caused by mouth bacteria cause tooth decay thus contradicting the consensus (Bowen, 2016; Selvitz et al., 2007; Tvetman S. et al., 2003; ). The author also calls dental hygiene, in particular, using fluoride products “a meme” introduced by the pharmaceutical industry and adopted by the dental profession because of professional dental association financing by toothpaste manufacturers.

To confirm this, the author uses blatant misinformation. He writes in the abstract that “over a hundred subsequent controlled trials, conducted over seven decades, largely confirmed  [that dental caries prevention required the proper mineralisation of teeth and that vitamin D could achieve this goal.]”.

To back this up, in the introduction he cites two metanalyses published in 1952 and 2013. The latter _by the same author_ states that “Twenty‐two of the 24 CCTs predated modern clinical trial design… The relative‐rate estimates of the 24 CCTs exhibited significant heterogeneity (P < 0.0001), and there was evidence of significant publication bias (P < 0.001)…”.

On closer inspection “over seven decades” mean the earliest trial (if we can call it this) was in 1918 followed by a cluster of them in the 1930s and 40s, a gap of  40 years, two trials in 1975 and one in 1989. The gap that significantly changes the hypothesis perception from “for seventy years people were finding strong evidence but ignored it” to  “revisiting badly collected data 40 years later shows some significance”, 1989 – 1930 = 59.

In other words, the literature shows a possible significance of Vitamin D that does not contradict the widely accepted theory of plaque formation and necessity of oral hygiene to prevent it.

Extraordinary claims require very strong supporting evidence. The claim that dental hygiene prevention of dental caries is a ‘meme’ rather than an established paradigm is certainly an extraordinary claim. The author not only fails to provide strong evidence but distorts the evidence he has. Moreover, the article has hallmarks of a conspiracy theory, namely “bad pharma”.

I wonder if the article would’ve been accepted in a journal with a similar impact factor  if the author wasn’t on the  “Gerodontology” editorial board.

I don’t dispute that caries is a complicated process dependent on the multitude of factors, including genetic, microbiome and nutritional components that determine teeth resilience to caries-causing bacteria. I also don’t doubt that the pharmaceutical industry has been making exaggerated claims about dental hygiene efficiency. But all this does not support the idea of modern oral hygiene futility.

Literature:

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Birds do it, bees do it, even West Ham supporters do it

 

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Starling murmuration – an example of metachronal wave (Image by , via wikimedia Commons, CC-BY)

The world’s most renowned TV naturalist, Sir David Attenborough,  stands in a tropical forest. It’s dark. Suddenly a pinpoint of green light flashes underneath him, in the grass. Another flash, and another until they become too numerous to count. And then a pattern emerges – instead of random light flashes, which would create a steady background, like individual drops of rain create steady rain noise, the flashing fireflies synchronise. They create a rhythm, not unlike flashing traffic lights – or a lighthouse.

The synchronising of rhythms of individual insects is not limited to the fireflies. Perhaps less surprisingly, bees, the notorious collective, do it. Not the torch-like flashing but they shimmer in response to hornet approach.  So do starlings and fish that create mesmerising collective movements.

This type of movement is called metachronal rhythm or metachronal wave.  It’s produced by the sequential action (as opposed to synchronized) of structures such as cilia, segments of worms or legs. These movements produce the appearance of a travelling wave.

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A Mexican wave in Brazil. (Image by Danilo Borges via Wikimedia Commons, CC-BY 3.0)

It’s made by reacting and repeating the movement of your neighbours be it cilia  in a single cell organism or a human.  West Ham football supporters (and all the rest of them) succumb to a metachronal rhythm during a Mexican wave.

Literature:

Restless Creatures: The Story of Life in Ten Movements by Matt Wilkinson, 
  • ASIN: B01B39IRJ2

On origin of life: Packman goes forth

The line between life and non-life is becoming increasingly blurred.  We use biological molecules as molecular machines and even as a base of computing. On the other side of the spectrum, inorganic materials are constructed to display a cell-like behaviour.

But there’s a gap between these organisation levels and the most primitive living cells capable of matter and energy exchange with the environment (metabolism) and reproduction. Experiments that bridge the gap between complex inorganic and a living cell brings us closer to understanding how life came to be.

phagocytic-article

Two consequent of optical microscopy images showing spontaneous transfer of silica colloidosome (red object, dotted line) into a magnetic droplet through a fatty acid stabilized aperture. Scale bar = 100 µm. (Image by University of Bristol).

Magnetite + organic solvent =

The authors of a recent article in Nature materials (Rodrigues-Arco et al. (2017), DOI: 10.1038/NMAT 4916) tried to bridge the gap between inorganic and organic. They mixed magnetic particles of iron oxide (magnetite) with droplets of an organic solvent and water. The particles with diameter of 500 ± 250 µm self-assembled on the surface of the solvent and were stable for several weeks.

Applying a magnetic field to the magnetic droplets opened the spheres along the surface, but they didn’t lose structural integrity and returned to the spherical shape. 

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Magnetite droplets open and close on   magnetic field application (Image by  Fr4zer  via Wikimedia Commons)

Increasing pH of the water phase to 10.5 and oleate concentration led to the creation of Matryoshka structures: parts of droplets remained covered by magnetic nanoparticles, and the rest of the structure was bordered by a monolayer of organic molecules.  At an optimal concentration, 3/4 magnetite with 1/4 water surface droplets resembled the hero of the classic game, Packman in appearance and behaviour.

 

Adding silica 

Under the same conditions, silica particles form smaller spheres, 50 ± 20 µm in diameter.  Silica colloids mixed with magnetic spheres do not interact in the absence of oleic acid. However, applying a magnetic field to the mix opened apertures in the magnetic spheres led to their self-propelled movement and random engulfment of colloidosomes. Only spheres with apertures – Packmen –  were able to move. The authors call this the engulfment ‘phagocytic-like behavior’ after ameba-like white blood cells that eat bacteria.

Particles movement explained by Marangoni effect – a movement due to surface tension gradient because of the uneven distribution of oleate on the surface of magnetic particles.  As the oleate gradient dissipate, the droplets moved only for several seconds. 

The authors proposed a model of ‘phagocytosis’. Non-magnetite covered surface Packman aperture covered by oleic acid molecules acts as a single layer proto-membrane. The silica colloidosomes have this layer as well. Fusion of molecular layers on the surface of Packmen aquatic opening and release of colloidosomes into the inner space creates semi-double membrane particles.

See the pictures and models on Nature web-site.   If by some miracle you have access to the original paper, do look into the supplemental videos of Packmen moving, Packmen ‘eating’, it’s mesmerising.

What is it good for

The authors propose using composite droplets mixtures for development of new material and nanoscale engineering approach, for example in microfluidics and delivering reagents for spatially controlled reactions. This sounds plausible and the author’s intention to mimic predation and chemical communication even more interesting.

However,  the scientists also call droplets ‘protocells’ and talk about ‘populations’ and their ‘collective behaviour’. In my opinion, this is a bridge too far. Life is characterised by sustained metabolism and ability of self-propagation. Magnetite and silica droplets display neither.  The reports about creating synthetic life is overhyping, the chronic disease of modern science.