Photobiomodulation Dose Parameters in Dentistry: A Systematic Review and Meta-Analysis

Abstract

Objective: This systematic review and meta-analysis of published randomized controlled trials examines a possible relationship between optical spot size at surface tissue, irradiance, radiant exposure, total energy delivered, operator technique and reported clinical outcomes.

Background: Clinical photobiomodulation (PBM) therapy has achieved a high level of evidence-based acceptance in the mitigation of oral mucositis associated with cancer radiotherapy and chemotherapy, and supportive clinical research in relation to orthodontic tooth movement, oral medical conditions, including burning mouth syndrome, xerostomia and lichen planus. Inconsistent outcomes have been reported not withstanding a substantial body of primary supportive research from clinical, in vitro and animal studies.

Materials and methods: PubMed, Cochrane Database of Reviews and Google Scholar search engines were applied to identify human clinical trials of PBM therapy in clinical dentistry. A total of 766 articles between February 2009 and June 2020 were identified and following a full text evaluation, 38 papers with sufficient data to permit analyses are included in this investigation.

Results: Following a detailed assessment of potential factors that may have an influence in clinical outcome, a clear trend is apparent associating optical spot size to a positive or negative effect. Furthermore, there is a clear difference in the reported results in relation to total energy applied, delivery techniques and optical parameters, which merits further investigation. Factorial statistical analyses identified an association between smaller optical surface applications and an overall lower level of reported clinical success in treating superficial and deeper targets, and correspondingly sub-surface larger target tissues were found to be more responsive to therapy by use of a larger optical surface spot size. Moreover, use of multiple small diameter probe applications was found to provide inconsistent results.

Conclusions: Many factors can confound clinical success including variations in anatomy, site location, clinical condition and subject individuality. To achieve higher levels of predictable outcome, a mature appreciation of these factors, plus an expanded understanding of laser parametry, tissue volume and target depth to deliver an adequate dose within current recommended guidelines, is essential.

Keywords: dentistry; diode laser; low-level laser therapy (LLLT); photobiomodulation (PBM); systematic review.

Figure 1

PRISMA flow-chart of selected criteria for the included study reports. [39].

Figure 2

Plots of mean ±95% confidence intervals for the large, medium and small spot size treaments at both deep (black) and superficial (red) target sites. ΔOutput Score represents differences determined between the mean clinical outcome score variables observed for the laser and control treatment groups, which was positive for all 38 studies reported.

Figure 3

Outcomes of optical transport at a target tissue result in significant energy loss (radiant exitance).

Figure 4

Three-dimensional render (left) and planar view (right) of the beam profile of two parallel optic beams 1 cm apart applied to a tissue sample. These images are offered as a guide to the reader to demonstrate the lack of lateral spread from the tips. Note the Gaussian distribution and the relative lack of lateral scatter.

Figure 5

Three-dimensional render of optical beam profile: transillumination through a 2 mm sample of porcine tissue. On the left: 810 nm 0.28 cm² spot size, 190 mW (0.5 J/cm²). On the right: 810 nm 1 cm² spot size, 500 mW (0.5 J/cm²).

Figure 6

Gaussian beam energy profile (left) compared to an optically rectified flat top beam (right). Images are intended to display solely differences in optical spatial profile only (different optical sources and parameters).