This paper deals with lossy compression of medical images in dentistry. For this purpose, we use AGU-M coder based on discrete cosine transform. A peculiarity of the proposed approach is that visually lossless compression is carried out without iterations and, due to this, in a fast way. Invisibility of introduced distortions and/or artifacts is provided by a proper setting of a fixed scaling factor that controls compression. This allows reaching a desired quality of compressed images characterized by PSNR-HVS-M. Experiments are performed for a set of dental images produced by Morita imaging system. Image visual quality has been analyzed by a group of dentistry experts. It is shown that the proposed approach provides several benefits compared to earlier designed counterparts, in particular, a larger compression ratio.