# A retrospective study on the impact of different antibiotic regimens in non-surgical periodontal therapy on microbial loads and therapy outcomes

## TL;DR

This study found that using metronidazole alone during non-surgical periodontal treatment can reduce harmful bacteria as effectively as combining it with amoxicillin.

## Contribution

The study shows that metronidazole alone may be sufficient as an antibiotic adjunct in periodontal therapy.

## Key findings

- Patients not receiving antibiotics had a 2.4-fold higher risk of not achieving the treatment target.
- Metronidazole alone reduced microbial loads as effectively as metronidazole plus amoxicillin.
- Residual bacterial levels were linked to not achieving the treatment target.

## Abstract

This study aimed to analyse the impact of different antibiotic regimens during non-surgical periodontal therapy on the microbial load of selected periodontitis-associated bacteria (PAB) and the primary therapy outcomes.

For this aim, 259 patients received steps I and II of periodontal therapy and were included in this clinical trial. 202 patients were treated without the adjunctive use of systemic antibiotics, 18 received amoxicillin (AMOX) as well as metronidazole (MET) and 39 only MET. Subgingival biofilm samples were quantitatively analysed for selected PAB using DNA-DNA-hybridisation-based detection assays for microbial loads of PAB before and 6 months after treatment. Changes in the microbial load of PAB and achievement of a “treat-to-target” endpoint (T2T) (≤4 sites with probing depth ≥5 mm) were analysed. Patients' subgingival microbial load was significantly reduced following therapy.

38.2% of the patients achieved T2T. Binary logistic regression adjusted for confounders indicated a relationship between residual PAB levels and not achieving T2T. In patients not receiving systemic antibiotics a 2.4-fold increased risk of not reaching T2T after steps I and II therapy was observed (none vs. MET aOR = 2.38 p = 0.44). Linear regression analysis adjusted for T0 PAB concentration and confounders revealed an increased reduction of PAB levels in patients with systemic antibiotics. No difference in PAB reduction or chance of achieving T2T was observed between MET and MET + AMOX.

Microbial loads of PAB were found directly associated with periodontal status. As antibiotic treatment with both MET and MET + AMOX similarly reduced microbial loads of PAB, treatment with MET alone may be sufficiently effective as adjunctive to non-surgical periodontal treatment. To confirm this, further prospective studies with bigger sample size are needed.