Can combination syndrome influence functional performance and peri-implant bone remodeling in mandibular overdenture users? Results from a 5-year cohort study.

PURPOSE

This longitudinal clinical study aimed to investigate the circumferential peri‑implant bone level (CPBL), posterior mandibular resorption (PMR), and masticatory function (MF) in users of implant-retained mandibular overdentures (IMOs), comparing individuals with and without combination syndrome (CS) over a 5-year follow-up period.

MATERIALS AND METHODS

A total of 39 patients were enrolled and stratified into two groups: absence of CS (ACS; n = 23) and presence of CS (PCS; n = 16). Assessments were conducted at 1, 3, and 5 years. CPBL and PMR were measured using cone beam computed tomography. PMR parameters included total bone height, cortical and medullary bone height, percentages of cortical and medullary bone and bone density at 4 standardized mandibular regions. MF was assessed via masticatory performance (MP) and swallowing threshold (ST) tests.

RESULTS

The PCS group showed a significant reduction in CPBL over time (p ≤ 0.05), particularly at the mesial and distal surfaces, with average reductions of -1.09 mm (mesial) and -0.70 mm (distal) after 5 years. MF was also significantly impaired in the PCS group at 5 years, demonstrated by reduced bolus homogenization in both tests, MP and ST tests; prolonged masticatory cycles, and inferior performance in the ST (p ≤ 0.05). In contrast, the ACS group showed significantly greater PMR values (p ≤ 0.05), with increased total and medullary bone heights and higher medullary bone percentages. The ACS group also demonstrated lower cortical bone percentages at L1 and L2 distances.

CONCLUSIONS

The presence of CS is associated with accelerated peri‑implant bone loss and deterioration in masticatory function over time. Conversely, greater mandibular resorption was observed in the absence of CS, particularly affecting the medullary compartment. These findings underscore the influence of CS on both structural bone remodeling and functional outcomes in IMO users.

CLINICAL SIGNIFICANCE

Patients with CS would require stricter prosthetic maintenance protocols due to the impact of anterior hyperfunction. This functional overload accelerates peri‑implant bone resorption in the anterior region of mandible and can lead to maladaptive changes in the posterior mandible. As posterior occlusal support diminishes, masticatory function deteriorates, reinforcing the need for early intervention and ongoing monitoring to preserve oral function and implant stability.