The Dual Effects of Bariatric Surgery on Oral Health: Periodontal Improvement versus Dental Erosion—A Retrospective Self-Controlled Study

Background Obesity shares a bidirectional pathophysiological relationship with periodontitis, primarily driven by chronic inflammation. While bariatric surgery (BS) effectively reduces systemic inflammatory load, the resulting anatomical and dietary changes may adversely affect dental hard tissues. This study aimed to retrospectively evaluate the dual effects of BS on periodontal health and dental hard tissues. Methods This single-center, retrospective, self-controlled study enrolled patients who underwent bariatric surgery (Roux-en-Y Gastric Bypass [LRYGB] or Sleeve Gastrectomy [LSG]) between January 2018 and December 2022. Clinical data, including Body Mass Index (BMI), C-reactive protein (CRP), periodontal parameters (Bleeding on Probing [BOP], Probing Depth [PD], Clinical Attachment Loss [CAL]), and dental hard tissue indices (Decayed, Missing, and Filled Teeth [DMFT]; Basic Erosive Wear Examination [BEWE]), were collected at baseline (pre-operative) and 12 months post-operative. Paired t-tests or Wilcoxon signed-rank tests were used for analysis. Results A total of 156 patients were included. At 12 months post-surgery, mean BMI decreased significantly (38.5 ± 4.2 kg/m² vs. 26.8 ± 3.5 kg/m², P  < 0.001), accompanied by a marked reduction in serum CRP. Periodontal inflammation improved significantly, with BOP% decreasing from 45.2% ± 15.3% to 26.8% ± 12.1% ( P  < 0.001). Conversely, dental health showed signs of deterioration: the DMFT index increased (8.4 ± 3.2 vs. 9.1 ± 3.5, P  = 0.032), and the risk of high-grade enamel erosion (BEWE score ≥ 2) increased by 2.4-fold. Multivariate regression identified post-operative Gastroesophageal Reflux Disease (GERD) symptoms as an independent predictor of dental erosion (OR = 3.12). Conclusion Bariatric surgery yields significant periodontal benefits via the attenuation of systemic inflammation; however, it concurrently poses a substantial risk for dental erosion and caries due to increased acidic exposure. Integrated multidisciplinary care addressing oral hygiene and acid management is recommended for bariatric patients.