Postoperative complications following odontectomy of impacted mandibular third molar is a common observation seen by the patient and the oral and maxillofacialsurgeon.The aim of this study was to compare three different flap designs on pain, swelling, trismus and pocket depth of distal aspect of the mandibular second molar following odontectomy of impacted mandibular third molar and to answer the question of whether or not the complications and side effects would be observed more in the envelope, triangular and modified triangular flap techniques after odontectomy of impacted mandibular third molar.The present study was performed on 30 patients presented at the Department of Oral Surgery, Faculty ofOral and Dental Medicine, Cairo University, seeking extraction of impacted mandibular third molars. Selected Patients had no preexisting medical conditions or medications with age ranging from 20 to 35 years and free from inflammatory symptoms in the oral cavity at the time of the operation or allergy to any drug used in the study.Patients were dividedr and omlyinto 3 equal groups 10 patients each, all cases were selected as class 1 position B impacted mandibular third molar according to Pell and Gregory classification (159) of impacted mandibular third molar, and each group received a specific flap design.Group A (2 males and 8 females), received the envelope flap that involve a sulcular incision from the mesiobuccal line angle of the first mandibular molar to the second mandibular molar and distal releasing incision along the external oblique ridge to the mandibular ramus. Group B (4 males and 6 females), received the triangular flap including an incision at the distobuccal edge of the second mandibular molar dropping down to alveolar mucosa of the vestibulum. The second part of the incision as group A and Group C (6 males and 4 females) received the modified triangular flap involve an incision at the distobuccal edge of the second mandibular molar dropping at a slight oblique angle curving forward into the mandibular vestibule (into the attached gingiva). The second part of the incision is a releasing incision as in group A and B.The study protocol was explained to each patient in details and subjects who met the criteria of the study were informed about the operative procedures and postoperative instructions after which a written consent was obtained before surgery. All clinical measurements was assessed preoperative and 2nd, 5thand 10th day postoperative except pain was measured 24, 48 and 72 hours postoperatively.Edema was measured by double assessment techniques were used to ensure a high degree of accuracy. A caliper used for measurement of cheek thickness, one tip of the caliper placed inside the lingual embrasure between mandibular first and second molars on the side of the jaw where surgery was performed, while the other tip of the caliper placed on the outer surface of the cheek at the anterior border of the masseter muscle were the teeth are closed on the arm of the caliper, postoperative swelling measured by subtracting the postoperative reading from preoperative reading of the caliper, care should be taken to ensure that both tips of the caliper are in a line parallel to a mandibular occlusal plane. The second method was the linear facial measurements between five fixed anatomical soft tissue points marked by indelible marker with a graduated tape.The mouth opening was measured by Vernier Caliper that measuring interincisal distance in millimetersbetween the incisal edges of maxillary and mandibular left central incisors.Pain was measured by Visual Analog Scale (VAS). A (VAS) is a horizontal line, 100 mm in length. The patients mark on the line the point that they feel represents their perception of their current state of pain. The VAS score is determined by measuring in millimeters from the beginning of the line to the point that the patient marks in a printed questionnaire.The pocket depth was measured on distobuccal and distolingual surfaces of the mandibular second molar using graduated periodontal probe. The graduated periodontal probe measure the distance in millimeters from the free gingival margin to the bottom of the pocket.The collected data were tabulated and statistical analysis was carried out to detect the influence of envelope, triangular and modified triangular flap designs on pain, swelling, trismus and distal pocket depth of ipsilateral second mandibular molar.The study was proven that flap design has no effect on pain, trismus, edema, or distal pocket formation at the second molar following odontectomy of the mandibular third molars.In conclusion, the present study concluded that there were no significant differences postoperatively among the three flap designs in pain, swelling, trismus and distal probing depth of the ipsilateral second mandibular molar. We recommend the double measurement method by linear facial measurement and with the caliper to reach maximum degree of accuracy when measuring the postoperative edema.From the results of this study and the literature reviewed it would appear that flap design didn’t influence postoperative pain, swelling, trismus and distal probing depth of the ipsilateral mandibular second molar following odontectomy of impacted mandibular third molar and the flap designs is a matter of surgical preference.