## 5 Discussion
_Delivery/spot size_: Across the groups, some variation was shown in the'spot' size, i.e., beam diameter, along with contact versus non-contact tip-to-tissue application. Non-contact, non-focused beams will undergo considerable variation in irradiation, which, in tandem with the effects of a non-linear Gaussian spectral beam profile, impacts the fluence values with even short distances. In many instances, no record of such measurements occurred. _Applied fluence/computed/relative to therapeutic optimal dose:_ during the past twenty years, a gradual acceptance of photonic 'dose' values relative to cellular and then whole-tissue radiation has defined therapeutic PBM delivery. Biphasic light-dose delivery may provide biostimulation, with ascending energy density values leading to a hormetic zone associated with cellular/tissue inhibition; at higher levels, this may lead to permanent damaging effects. Allowing for a nominal standard deviation, the biostimulatory fluence is observed at 5 Joules/cm\({}^{2}\); above 10 Joules/cm\({}^{2}\), with an average of 15 Joules/cm\({}^{2}\), cell/tissue inhibition may be observed. Moreover, an upper value of 30 Joules/cm\({}^{2}\) has been proposed as the threshold of damaging effects. However, the biological capacity of tissues to withstand photo-induced stress is a function of the rate of the dose delivery, expressed as irradiance (W/cm\({}^{2}\)). High-intensity photon exposure induces a potential damaging photothermal response; conversely, the accumulated energy expressed as fluence (J/cm\({}^{2}\)) may be high with extended low-value irradiance settings, as well as with repeated treatments. From our analysis of all groups, there is wide and significant variation in the fluence values applied, with most instances citing low or sub-therapeutic values. _Application/number/repetition/relative to anatomical site and dose variation with depth_: It has been seen earlier that because of the non-isotropic nature of oral soft and hard tissues, with dental hard tissue structures, considerable variation exists between the chosen laser wavelength and associated absorption of applied fluence. Additionally, such phenomena may influence the applied dose at depth, with the reduction in fluence approaching 70-90% at 10 mm in oral soft tissue. The analysis of the applied target dose at depth versus the surface value, across the treatment groups and individual treatment schedules, showed significant variation and may contribute to a compromise in the effectiveness of PBM irradiation at tissue depth. _Significance of outcomes_: Taken individually or collectively, the measurable variation in laser-relevant elements needs to be considered and set against the outcomes of individual randomised clinical trials. The consequence of this strict systematic review raises the significance of RCT data in defining ongoing evidence-based knowledge and the application of PBM therapy in dentistry. It is outside the scope of this review to define the extent of discipline to be applied to the parameters of clinical PBM delivery, but the study design and full disclosure of the delivery values should still be fully evaluated at the ethical approval stage of studies.