Salivary glands might not recover fully.

Saliva production decreases in the span of 1 week after starting radiotherapy in the head and neck and continues to decline with the progress of treatment. The severity of dry mouth depends on the radiation dose and the number of glands irradiated. Salivary glands in the upper section of the cheeks near the ears are more affected than other salivary glands. The partial recovery of the salivary glands can occur in the first year after radiotherapy, but the recovery is generally not complete, especially if the salivary glands irradiated directly. Salivary glands irradiated may not become more active to compensate for the loss of saliva glands destroyed.