An intraoral phototherapy device (10, 30, 40, 80) for receiving light from an associated light source and propagating the light into an oral cavity of a patient, the device comprising: an external light source (72, 73, 240); and a light guide (12, 92, 94) that receives light from the external light source, the light guide comprising a main body portion (14, 32, 42, 88, 90) made of an optically transparent flexible biocompatible polymeric material sized and shaped to conform to contours of the oral cavity when inserted therein to direct the light to targeted regions of the oral cavity, wherein: the main body portion comprises a pair of laterally spaced side wings (16, 18, 34, 36, 48, 50) sized and shaped to be received between a patient's teeth and cheeks on opposite sides of the oral cavity for transmitting and directing the light to targeted regions of the oral cavity; and the side wings support one or more solid side light channels (44, 46) integrally molded with the side wings for transmitting and directing the light to targeted regions of the oral cavity; characterised in that each of the side light channels are generally cylindrical in shape and are selectively tapered along their length for controlled light emission therefrom or each of the side light channels have at least two branches (52, 54, 56, 58) to more evenly distribute the light to the targeted portions of the oral cavity. an external light source (72, 73, 240); and a light guide (12, 92, 94) that receives light from the external light source, the light guide comprising a main body portion (14, 32, 42, 88, 90) made of an optically transparent flexible biocompatible polymeric material sized and shaped to conform to contours of the oral cavity when inserted therein to direct the light to targeted regions of the oral cavity, wherein: the main body portion comprises a pair of laterally spaced side wings (16, 18, 34, 36, 48, 50) sized and shaped to be received between a patient's teeth and cheeks on opposite sides of the oral cavity for transmitting and directing the light to targeted regions of the oral cavity; and the side wings support one or more solid side light channels (44, 46) integrally molded with the side wings for transmitting and directing the light to targeted regions of the oral cavity; characterised in that each of the side light channels are generally cylindrical in shape and are selectively tapered along their length for controlled light emission therefrom or each of the side light channels have at least two branches (52, 54, 56, 58) to more evenly distribute the light to the targeted portions of the oral cavity. the main body portion comprises a pair of laterally spaced side wings (16, 18, 34, 36, 48, 50) sized and shaped to be received between a patient's teeth and cheeks on opposite sides of the oral cavity for transmitting and directing the light to targeted regions of the oral cavity; and the side wings support one or more solid side light channels (44, 46) integrally molded with the side wings for transmitting and directing the light to targeted regions of the oral cavity; characterised in that each of the side light channels are generally cylindrical in shape and are selectively tapered along their length for controlled light emission therefrom or each of the side light channels have at least two branches (52, 54, 56, 58) to more evenly distribute the light to the targeted portions of the oral cavity.