A method for manufacturing multi-coloured positive tooth models that are suitable for manufacturing orthodontic appliances by means of pressure moulding or vacuum moulding a sheet of transparent thermoplastic material comprisies a three-dimensional, bi-coloured powder bed inkjet head printing process. For models which remain in place within the mould whilst the appliance is excised from the moulded sheet, printing teeth and gums different colours provide a visible orientation cut line representing the boundary of the appliance and along which the appliance has to be excised from the mould.
