The objective of this study is to determine whether the use of a systemic antimicrobial (metronidazole) as an adjunct to periodontal surgery provides additional clinical and microbiological beneficial effects compared to periodontal surgery alone plus a placebo, in patients with non treated periodontitis (stage III and IV) positive to Porphyromonas gingivalis.

Design: pilot, randomized, parallel, placebo controlled and triple blind clinical trial.

Sample: Patients with generalized severe chronic periodontitis (stages III and IV) and positive to Porphyromonas gingivalis who potentially need periodontal surgery were recruited from those who attended the postgraduate program in periodontics at the Complutense University in Madrid.

Patients were randomly assigned to the test group (periodontal surgery + metronidazole) or control group (periodontal surgery + placebo).

Study visits:

• Examiner calibration

• Recruitment of patients. Screening. Data collection (clinical and microbiological variables)

• Phase I

  • Non surgical periodontal therapy (2 visits) performed by second year students.
  • Reevaluation at 6 weeks. Data collection (clinical and microbiological variables).

Identification of study participants (patients with probing pocket depth > 5mm in ≥ 2 teeth per sextant or those presenting multiple sites with probing pocket depth ≥ 5mm and bleeding on probing in ≥ one mouth quadrant and positive to Porphyromonas gingivalis.

The need of the surgical procedure was supervised in every case by more than one experienced periodontist (clinical teachers). Finally patients were randomly assigned to their study groups.

• Phase II. Surgical Periodontal Therapy

  • Periodontal surgery sessions performed by second year students. In the last surgery the patient received a recipient containing the pills (metronidazole or placebo according to randomization) and the instructions for use.
  • Suture removal 1 week after the surgery. Data collection 1 week after antibiotic consumption after the last surgery (patient-centered variables on the side effects of antibiotics). Pills recipients were collected in order to evaluate patient compliance. An individual not involved in the study protocol was in charge of doing the data and recipient collection.

• Phase III. Periodontal Maintenance.

  • Maintenance 1(3 months postsurgery). Data collection (clinical and microbiological variables)
  • Maintenance 2 (6 months postsurgery). Data collection (clinical and microbiological variables)
  • Maintenance 3 (9 months postsurgery).
  • Maintenance 4 (12 months postsurgery). Data collection (clinical and microbiological variables)

Security protocol:

Any patient exhibiting worsening in periodontal clinical parameters during the maintenance phase were excluded from the study and inestable sites were re-treated. Inestable sites were considered those exhibiting clinical attachment loss > 2mm between two consecutive visits (Haffajee et al. 1983) after the treatment.

Inclusion Criteria:

• Diagnosis of generalized severe chronic periodontitis (Armitage 1999) or periodontitis stages III or IV (Papapanou et al., 2018) that may require periodontal surgery.
• Have at least 10 teeth in function, excluding third molars.
• Present sites with pocket probing depth (PPD) ≥ 6mm in ≥ 2 teeth in ≥ one quadrant
• Present radiographic evidence of ≥ 30 % bone loss in ≥ 30% of the dentition
• Detection of Porphyromonas gingivalis in subgingival samples taken at the screening visit as well as in the post-scaling and root planing visit and processed by culture.
• Systemically healthy patients.

Exclusion Criteria:

• Pregnant or lactating women.
• Systemic pathology and/or taking medication that may affect the periodontal situation and/or patients requiring antibiotic prophylaxis.
• Have received systemic antimicrobial treatment 6 months prior to the beginning of the study.
• Have received periodontal treatment 6 months prior to the beginning of the study.
• Patients allergic to metronidazole.
• Patients allergic to cornstarch.
• Patients who refuse to sign the informed consent.

The subjects were randomly assigned to the treatment groups in ascending order according to a balanced distribution system through a computer generated random number design table (random block design). Randomization was balanced according to the smoking habit at the initial visit to ensure homogeneity in the treatment groups.

The method of allocation concealment selected were opaque envelopes. The research coordinator was responsible for the randomization and patient allocation.