Dose Delivery Parameters in Photobiomodulation Therapy

Photobiomodulation (PBM) offers the potential to optimise the biological capacity of tissues to withstand cellular stress, along with the promotion of effective and uneventful healing. In addition, PBM has anti-inflammatory and analgesic properties, and can stimulate the immune system response to infection. Furthermore, in oncology, PBM is an invaluable tool to prevent and mitigate chemotherapeutic ally- and radiotherapeutically induced oral mucositis. The additional aspects of PBM utilisation indicate that this may reduce patient morbidity from other recognised complications of cancer therapies, as well as promote the effectiveness of oncology interventions. Retrospective case series and a number of double-blind randomised clinical trials throughout the last decade indicate that this is a safe and effective measure which can be associated with a reduced incidence of cancer recurrence, in addition to an improvement in life expectancy in such patients when compared to relevant control groups. The majority of dental and medical conditions have in common a root cause associated with acute or chronic inflammation, a compromised immune response and infection. Also, post-active disease stage legacy issues may present a clinical challenge in the form of loss of function in view of tissue destruction, as well as acute or chronic pain. Surgical interventions to arrest, or attempt to reverse, this tissue damage are inherently associated with post-operative pain and swelling. Furthermore, in an ageing population, together with the large cohorts of patients with one or more pathologies, e.g. those associated with obesity, coronary artery disease, diabetes or respiratory disorders, the potential and capacity of the patient’s ability to heal may be severely compromised. In addition, there may be added confounding factors adversely affecting good quality healing and repair associated with many commonly prescribed systemic medications such as analgesics, steroids, anti-depressants, and anti-hypertensives, for example. There is therefore a profound requirement for safe non-toxic adjuncts and, if possible, alternatives to reduce this need and/or ameliorate the harm that may result from sustained systemic medications which can have a “broadsword” effect with negative consequences (such as immunosuppression as seen with long-term steroid use). In view of this multiple set of problems, it is perhaps not a surprise that based on the established knowledge base of the potential gain from PBM as an interventional adjunct treatment, and that its clinical application has generated very considerable interest represented in the scientific literature. However, despite efforts spanning over fifty years, the benefits and adoption of PBM as a treatment adjunct remain at a nascent stage in clinical care. In an effort to identify successful management strategies, this doctoral study was undertaken to reappraise the published PBM evidence base in dentistry. The adopted tools of systematic review and meta-analysis enable clinicians and researchers to identify processes with a proven track record of success and also to refine these to optimise the outcome. Also, by virtue of a fundamental reappraisal of the proposed mechanisms associated with PBM, a targeted approach can be applied by extrapolation in order to manage a wider range of clinical conditions with a common core, for example, inflammation. The outcome of the research presented here is also directed towards developing a thorough understanding of the processes associated with optical delivery to both surface and sub-surface target tissues. With the innovation of dedicated PBM devices which can deliver a higher output power than previously used, as well as equipment designs built around concepts based on theory, there is an evident need to focus on safety aspects, as well as clinical proficiencies and outcomes. Hence, an experimental in vitro model is presented which employs analysis of optical beam characteristics in relation to optical delivery techniques. Also, a thermographic study is presented, which assesses the relative effects of many varied parameters, including surface optical spot size, wavelength and the delivery techniques adopted. As a thesis by concurrent publication, the outcome of the included studies is described within the context of a linked discussion, based on the author’s wider research activities with colleagues at De Montfort University, as well as those with similar interests worldwide. The conclusions support the adoption of PBM as an evidence-based approach, and recommendations are made to assist both clinicians and researchers. In summary, the findings made support the application of higher surface energy with larger surface applicators, for both superficial as well as sub-surface conditions. The choice of wavelength and its relationship with dosimetry is presented, with proposals to support safety as well as to derive effective parameters. It is the opinion of the author that this represents a major medical advancement in process, to which the hindrance is one of the need to conduct safe, well designed and executed quality randomised clinical trials. This poses a heritage problem, since the majority of PBM researchers have based their work on the application of low power outputs, with small surface-applicator devices. The outcome of the research described here may lead to future well-designed controlled randomised clinical trials being adopted to address some of the cardinal issues associated with the management of trauma, disease and age-related disorders.