Objectives: The objective of the study was to evaluate the effectiveness of a prophylactic single preoperative dose of amoxicillin in decreasing complications after lower third molar surgery.

Materials and methods: The sample consisted of 400 patients randomly divided in two groups consisting of 200 patients per each group. The patients underwent third molar surgery at the Department of Oral Surgery, Clinical Hospital Dubrava, Croatia, in the period between April 2010. and November 2016. Unlike the patients from the second group, the first group of patients had never been diagnosed inflammation prior the surgical procedure. The main tested groups were further divided in two subgroups (control and tested): the tested subgroup (100 patients) received a prophylactic single dose of 2 g amoxicillin an hour prior the procedure, while the second control subgroup (100 patients) received a placebo. Complications, including swelling, alveolar osteitis (AO), infection at the surgical site (SSI), limited mouth opening, pain, bleeding, and increased body temperature, were evaluated postoperatively. Evaluation was done on the first postoperative day and 7 days after surgery.

Study design and sample description This prospective study was performed at the Department of Oral Surgery of Clinical Hospital Dubrava, Zagreb, Croatia, in the period from April 2010. through November 2016. All patients voluntarily agreed and written consent to participate in the study was obtained from each participant. The study was approved by Ethics Committee of the School of Dental Medicine, Zagreb, Croatia (81-2009). The identity of the subjects was protected in all phases of the study.

The exclusion criteria in this study were systematic diseases, with developing local infections, current smokers, pregnant women, lactating females, patients using oral contraceptive drugs and those under any antibiotic coverage.

The sample consisted of systematically healthy subjects between 18 to 40 years (both gender) and having semi-impacted lower third molars indicated for surgical removal randomly divided into two main groups of patients. Unlike the patients from the second group, the first group of patients had never been diagnosed inflammation prior the surgical procedure. The main tested groups were further divided in two subgroups (control and tested): the tested subgroup (100 patients) received a prophylactic single dose of 2 g amoxicillin an hour prior the procedure, while the second control subgroup (100 patients) received a placebo. The selection of third molars for control and study subgroup was made according to Pederson difficulty index (9). According to this index (Table 1), the patients are classified into 3 groups: easy, moderate and difficult. The patients from this study who were classified into a difficult group were excluded from the study due to a longer and complicated surgical procedure with an expected prolonged recovery period and possible postoperative complications.

The patients were recalled for follow-up on post-operative days one and seven. In all tested groups data had been obtained by using identical questionnaire. The following symptoms were assessed: pain, swelling, wound healing (AO, SSI), maximum inter-incisal opening of mouth, increased body temperature and hemorrhage. A postoperative follow-up was done always by the single experienced therapist. Patients evaluated their postoperative pain with grades from 0-10 using according to visual analogue scale (VAS) where the end points were marked as "no pain" (0) and "unbearable pain" (10). Surgeon evaluated the type of post-extraction alveolus healing as following normal healing, acute inflammation followed by infected alveolus and dry socket. The surgeon who assessed wound swelling did not know to which group the patient was allocated. The method of assessing the swelling was described in our previous study (10). The post-operative swelling was assessed on postoperative days 1 and 7, using four-point scale as 0=no swelling, 1=mild swelling, 2=moderate swelling, 3=severe swelling.

The maximum inter-incisal opening of the mouth was calculated from the mesioincisal angle of the ipsilateral mandibular central incisor to the mesioincisal angle of the ipsilateral mandibular central incisor using digital calliper (Caliper-Digital; Salvin Dental Specialties, Inc, Charlotte, NC).

Increased body temperature was measured by patient at home during postoperative period of seven days. Body temperature within 36.0ºC and 37.5ºC was evaluated as normal. The body temperature under 37.5 ºC was evaluated as increased. All temperatures were measured at the same time of the day, between 9:00 and 11:00 a.m.

Hemorrhage was observed by patient during next seven days after the surgical procedure. It was classified as absent or present through following days. Present hemorrhage was classified as light or intense.

The outcome variable was the presence or absence of an inflammatory complication after third molar surgery (SSI or AO). A diagnosis of SSI was identified by purulent discharge from the surgical site at any point postoperatively, fever, lymphadenopathy, or pain and edema warranting surgical intervention and/or systematic antibiotics. Alveolar osteitis was diagnosed in cases of an empty alveolar socket, increasing pain lasting more than 2 days after surgery, and exposed alveolar bone tissue.

Inclusion Criteria:

• systematically healthy subjects between 18 to 40 years (both gender) and having semi-impacted lower third molars indicated for surgical removal

Exclusion Criteria:

• The exclusion criteria in this study were systematic diseases, with developing local infections, current smokers, pregnant women, lactating females, patients using oral contraceptive drugs and those under any antibiotic coverage.

There was 400 participiants, patients and the same oral surgeon