**5. Discussion**

Ultrasound is defined as sound frequency 20,000 cycles per second. Ultrasound travels through materials. It is the modality that is used for a number of purposes including diagnosis destruction of tissue and therapy. Ultrasonic energy generated at 1MHZ is transmitted through the more superficial tissues and absorbed primarily in the deeper tissue at depths of 3-5 cm. Patient should be in lying position with head support with pillow in continuous mode with duration of 5 to 8 min. The treatment head is moved continuously over the surface, while even pressure is maintained in order to iron out irregularities in sonic field. The pattern of movement can be series of overlapping parallel strokes, circles or figure of eight. The effect of ultrasound increases intracellular ca, increases skin and membrane permeability, increases macrophage response, promotes healing, reduces swelling, and increases blood flow.

Many studies recommend ultrasound is effective for TMD treatment. The beneficial effect of Ultrasound may be associated with the effect of micro-destruction. In addition to reduction of pain in TMJ treatment, ultrasound treatment shows improvement in jaw functions.

The therapeutic effect is persistent in follow-up period of 6 months with less than 3% recurrence rate after ultrasound treatment; therefore, ultrasound may be recommended for TMD treatment [17].

Shuang Ba et al. concluded that US has been shown to be able to reduce excessive cytokine content in the articular fluid and the apoptosis of chondrocytes. It promotes the proliferation of articular cartilage to repair cartilage defects and inhibits the secretion of inflammatory cytokines. Hence, treating by ultrasound reduces pain effectively [18].

Sanyuktha et al. state that the generated heat presumed to increase tissue cell metabolism, which in turn helps to promote soft tissue healing. The sound wave causes tissue vibration creating heat in the treatment field and thus increases the blood flow. The pain reduces with the resolution of information.

Zhou et al. explored the efficacy of US in terms of mandibular condylar cartilage repair *via* autophagy regulation. And it reduced the injury severity and upregulated the autophagy biomarkers [19].

Liang et al. stated that US has decreased the proliferation of chondrocytes and increased the osteoclast activity in the calcified cartilage layer [20].
