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Letter to the Editor

Editor, – As a clinician I was concerned to read the dental note by Michael McCullough (Aust Prescr 2011;34:181), in which the incidence of osteonecrosis of the jaw in bisphosphonate users was quoted as being 1/500 to 1/1500. The reference quoted is a retrospective survey of 13 946 individuals. It is worth noting that other studies, in some cases with much larger sample sizes, have concluded that the incidence is rather lower. One review estimated the risk with oral bisphosphonates for osteoporosis to be between 1/10 000 and less than 1/100 000 patient-treatment years.1 Another study of medical claims from 714 217 individuals concluded that intravenous, but not oral, bisphosphonates seem to be strongly associated with adverse outcomes in the jaws.2 This conclusion was reiterated by Canadian guidelines.3 It also appears that the risk of osteonecrosis of the jaw is substantially higher in patients being treated for cancer than it is in patients with senile osteoporosis.

My concern is that patients may be discouraged from using bisphosphonates because of concerns about osteonecrosis of the jaw. I understand that clinical experience with a patient suffering from this condition is likely to have a powerful effect on a practitioner, but we should aim to help our patients make quality decisions based on objective assessments of the risks and benefits.

Let us use the example of a 70-year-old woman who is estimated to have a 5% risk of sustaining a fractured neck of femur over five years, using a tool such as FRAX or the Garvan calculator. If we assume a 20% death rate in the 12 months following such a fracture, then the absolute risk of death is 1%. Intravenous zoledronate has been shown to reduce the incidence of hip fracture by 41%. Treating the patient would reduce the five-year hip fracture risk to 2.95%, in turn reducing the risk of death to 0.59%. This absolute reduction of the risk of hip fracture of 2.05% equates to a number needed to treat of 49 to prevent a hip fracture, or 243 to prevent a premature death subsequent to a hip fracture. This compares very favourably with the potential harms of bisphosphonate use, even assuming the higher rates quoted by Dr McCullough.

It is entirely appropriate to use bisphosphonates carefully, preferably having estimated absolute fracture risk, and to take steps to optimise oral health before starting treatment.

Simon Vanlint
Discipline of General Practice
University of Adelaide

Author's comment

Michael McCullough, author of the dental note, comments:

Dr Vanlint raises some very interesting points regarding the risk of bone fracture and osteonecrosis of the jaw. We agree that the careful use of bisphosphonates after clinical assessment and estimation of fracture risk is entirely appropriate and can have significant benefits for patients.

The discussion regarding the incidence of bisphosphonate-associated osteonecrosis of the jaw continues and it was once thought to be low and of an order of 1/10 000 to 1/100 000. More recent studies show the risk to be more likely around 1/1000 (95% confidence interval 1/500 to 1/1500).4 This was previously quoted in an information pamphlet produced for Australian doctors and dentists by both Osteoporosis Australia and the Australian Dental Association. Interestingly, some specialist single centre studies show the risk following dental extraction to be of the order of 1/300.5 Other ongoing studies will shed more light on the true incidence and risk factors for delayed dental healing and its association with bisphosphonate use.

Irrespective of the exact incidence of this adverse event, Dr Vanlint is entirely correct in stating that optimising oral health before bisphosphonate treatment is ideal, and will diminish the likelihood of osteonecrosis of the jaw occurring.

References

  1. Khosla S, Burr D, Cauley J, Dempster DW, Ebeling PR, Felsenberg D, et al. Bisphosphonate-associated osteonecrosis of the jaw: report of a task force of the American Society for Bone and Mineral Research. J Bone Miner Res 2007;22:1479-91.
  2. Cartsos VM, Zhu S, Zavras AI. Bisphosphonate use and the risk of adverse jaw outcomes: a medical claims study of 714,217 people. J Am Dent Assoc 2008;139:23-30.
  3. Khan AA, Sandor GK, Dore E, Morrison AD, Alsahli M, Amin F, et al. Canadian consensus practice guidelines for bisphosphonate associated osteonecrosis of the jaw. J Rheumatol 2008;35:1391-7.
  4. Mavrokokki T, Cheng A, Stein B, Goss A. Nature and frequency of bisphosphonate-associated osteonecrosis of the jaws in Australia. J Oral Maxillofac Surg 2007;65:415-23.
  5. Lo JC, O’Ryan FS, Gordon NP, Yang J, Hui RL, Martin D, et al. Prevalence of osteonecrosis of the jaw in patients with oral bisphosphonate exposure. J Oral Maxillofac Surg 2010;68:243-53.