Tooth brushing with my son isnt going well. Help!

Hi my son who has ASD will not brush his teeth along with other Sensory issues this has been a constant battle since we first tried brushing his teeth and feel this is what we need to work on first. He has attended O.T sessions and they have given us some ideas such as using a cloth around his mouth to desensitise before brushing using pictures etc, and he attends a special care dentist. Nothing is working he is only 4 but obviously he needs to brush his teeth. He gets very aggressive with me if I attempt to go near him with the brush and won't allow me to use the cloth on his face, will hit me and himself. Does anyone have any other ideas or techniques they use? or is there somewhere else I can be referred to to get help? Many thanks