It is important to choose an appropriate analgesia/sedation technique in pediatric dental treatment. Premedication combined with intravenous anesthesia is often used in deep sedation technique for pediatric dental treatment and it's a routine in most hospitals. Deep sedation has its unique advantages such as avoiding the airway damage with an enhanced recovery.

Dexmedetomidine is suitable for intranasal mucosal administration as a premedication drug. It has been proved with several beneficial characteristics in other clinical procedures.

This study intends to further explore the characteristics of nasal dexmedetomidine as premedication in pediatric oral treatment under deep sedation.

Inclusion Criteria:

1. children in need of deep sedation for dental treatment aged 3-7 years.
2. anticipated operation time 1-2hours

Exclusion Criteria:

1. any known medical records with neural or mental disorder
2. any known medical records with severe systemic disorder
3. history of sedation drug administration in recent 1 months
4. any known allergic history of dexmedetomidine, midazolam or propofol
5. morbid obesity
6. history of OSAHS or acute respiratory infection in 2 weeks
7. other conditions which the attending considers to be unfit for the trial