Sunday, 30 October 2011

Tuesday, 25 October 2011

Tacit knowledge

This paper, which QMUL staff and students can access with their college logon details raises the problem of communicating tacit - or unspoken - knowledge in clinical teaching. What it suggests is that learners learn much more from their own experience and their clinical tutor's demonstration than they do from 'codified' knowledge (i.e. written stuff).

It also suggests that there is room for confusion in relation to the use of evidence if tutors are not explicit about whether they are teaching something from their own tacit knowledge ("it's always worked for me") or from evidential knowledge ("the research suggests this approach").

My reading of this is that as tutors we should work hard to be clearer about what type of knowledge we are communicating and that learners themselves ask their tutors to be explicit so they can make sense of the knowledge for themselves.

Tacit knowledge in dental clinical teaching

Wednesday, 5 October 2011

Swans and differential diagnoses

Sir Karl Popper, swans, and the general practitioner -- Berghmans and Schouten 343 --

This BMJ article raises a really important point for all clinicians involved in making a diagnosis: we need to question our quick diagnoses and think of differential diagnoses if we are to be better able to help our patients. And we need to accept that we can be wrong, like all other humans, but be willing to change our decisions.

Tuesday, 4 October 2011


I happened to be working beside a periodontist on clinic today and had been to a lecture by another last week. The former was using Emdogain on a patient with a 3 wall defect on an upper first molar. The latter had been enthusing about the benefits of Emdogain to treat infrabony defects. Ever the one to find my own evidence I did a quick search for Emdogain in the Cochrane Library (all databases).

There was a Cochrane systematic review of Emdogain versus placebo or other bone regeneration techniques from 2010. 13 trials (parallel and split-mouth) involving 653 patients were included. There didn't appear to be any more recent clinical trials so I make the assumption that this is the most up-to-date evidence.

"periodontal attachment loss improved 
by a mean difference of 1.1 mm"

When the data from the individual studies were combined in a meta-analysis, periodontal attachment loss (PAL) improved by a mean difference of 1.1 mm (95% CI 0.61 to 1.55) and periodontal pocket depth (PPD) reduction was 0.9 mm (95% CI 0.44 to 1.31) when compared to placebo or control treated sites over 1 year. When only those studies thought to be at lower risk of bias were included the PAL gain shrank to 0.62mm (95% CI 0.28-0.96). I have copied and pasted the Forest Plot from the Cochrane study below:

Reproduced from: Esposito M, Grusovin MG, Papanikolaou N, Coulthard P, Worthington HV. Enamel matrix derivative (Emdogain®) for periodontal tissue regeneration in intrabony defects. Cochrane Database of Systematic Reviews 2009, Issue 4. Art. No.: CD003875. DOI: 10.1002/14651858.CD003875.pub3

Overall the quality of the evidence according to GRADE criteria was low. The studies seem to have been very heterogenous with some including various antibiotic regimens and chorhexidine rinsing alongside the surgical treatment. All the studies appear to have included infrabony defects of 3-4mm or greater. I guess then that 1mm attachment gain is relatively significant but I wonder if in deeper defects the benefit would be proportionally similar (i.e. 2mm gain in a 6mm defect) or just 1mm. If the latter the benefit becomes less significant as the defect deepens I suppose.

At a cost of around £350 for a pack of 3 syringes (if we were only treating one defect we would use one syringe but it may get spread between 2 or 3 defects if these existed I am guessing), that makes it potentially £117 a pop for the material. If you were the patient with one of those 6mm attachment gains one sees in presentations (for example, see the bottom of this page) I reckon it would be worth it - but for 1mm or nothing? mmm....

Monday, 3 October 2011

Reckoning with risk

Having studied statistics for years and always struggled, this book makes the point over and over again that most other people have the same problem. As a clinician wanting to explain risk to patients, this book has been a very useful nudge and Gerd Gigerenzer repeatedly demonstrates that explaining risk using frequencies rather than probabilities means more people understand what's going on - both doctors and patients.

A simple thing I picked up was indicating to patients the risk of failure of a procedure. For example, one could say that a molar treated tooth has a chance of success of 80-90% over, say, 10 years (this is just an example figure!). A patient, though, may well understand the following better: Out of ten molar teeth treated with endodontics, 8 or 9 will be successful after 10 years.

More complex ideas are dealt with using frequencies too. For example, if a male heterosexual in a particular area gets tested for HIV and it turns out it's positive, what is the likelihood that he is indeed HIV positive? Here, the prior probability comes into play - something I think we pay little attention to most of the time (susbstitute oral cancer if you're a dentist). The book explains how, despite the HIV test having a sensitivity of 99.9%, the chance of that man actually having HIV is 1 in 2. i.e. there's an equal chance he isn't HIV positive despite having the positive test (sorry for not explaining how this occurs but I won't explain it nearly as well as it is explained in the book!).

If you've read about prior probability, absolute risk reduction, risk ratios and similar and wondered what's going on then this book guides you in a gentle manner to better understand the risks and benefits of doing things and not doing things.