Histological, radiological, and clinical outcomes of sinus floor elevation using a lateral approach for pre- / post- extraction of the severely compromised maxillary molars: A split-mouth randomized clinical trial

INTERVENTION: Group 1:Sinus floor elevation before the extraction; Group 2:Sinus floor elevation after the extraction; CONDITION: dental impants PRIMARY OUTCOME: Post operative discomfort (pain); INCLUSION CRITERIA: 1. Patents with bilateral first/second molars which need to be extracted due to severe periodontal disease and need to be replaced by implants; 2. Residual alveolar bone height of these teeth is between 1‐4mm; 3. Patients aged 18 years old; 4. Patients with optimal oral hygiene and good compliance; 5. Patients with healthy maxillary sinuses; 6. The general of patient are suitable for implant placement and sinus floor elevation; 7. The patient who is willing to sign the informed consent and to follow the experimental follow‐up rules.