A system (100) for detecting tissue inflammation, and gingivitis specifically, including a light emitter (102) configured to emit light at a tissue region (104) within a user's mouth; a light detector (106) configured to detect optical signals diffusely reflected through the tissue region over a period of time; a controller (130) configured to: determine a slope signal (Q) based on at least two signals (R(λ1), R(λ2)) from the optical signals, the at least two signals including at least one signal from a hemoglobin-dominated wavelength range; determine one or more characteristics of the slope signal; and select a best measurement signal based on the one or more characteristics of the slope signal. The system further includes a user interface (116) configured to provide information regarding a position of a probe for accurate detection of tissue inflammation based on the one or more characteristics of the slope signal.