Narrow implants in hyperglycaemic patients: HbA1c mattered more than diameter

The posterior mandible with a distal-extension gap is where a clinician most often wonders whether a narrow implant is enough. Add hyperglycaemia, and the doubt doubles: will thinner fixtures in a metabolically compromised host lose more bone?

This stratified randomised controlled trial, published in Clinical Oral Implants Research, tested exactly that. Participants were first grouped by glycated haemoglobin (HbA1c 5.8% to below 7.0%, or 7.0% and above) and then randomised within each stratum to receive either ∅3.3 mm or ∅4.1 mm hydrophilic titanium-zirconium implants. Each participant received two implants supporting a multi-unit fixed dental prosthesis in a mandibular distal-extension situation. The primary outcome was the change in marginal bone level (MBL) 12 months after prosthesis delivery; secondary outcomes included implant stability quotient (ISQ), peri-implant indices, a healing index and patient-reported outcomes. The trial was prospectively registered.

Of 88 participants enrolled, 83 (166 implants) were evaluated. Implant survival was 100% and no peri-implantitis was recorded at one year. Marginal bone change did not differ significantly between diameters: the median was 0.27 mm in both groups (p = 0.078). The signal came from the metabolic side instead: participants with HbA1c ≥ 7% had roughly sevenfold higher odds of marginal bone loss of 0.5 mm or more than those below 7%. The ∅4.1 mm implants showed higher stability (ISQ 79.6 vs 76.1), while early soft-tissue healing was better with the ∅3.3 mm implants. Chewing ability improved markedly from baseline to 12 months, regardless of diameter or HbA1c category.

Clinical relevance: in this cohort, choosing a narrow Ti-Zr implant did not cost bone at one year, even in hyperglycaemic patients. What did track with clinically relevant bone loss was glycaemic control. The practical message is to spend less worry on the extra 0.8 mm of diameter and more on the patient's HbA1c, before and after placement. The limits are clear: a single-centre trial, one implant system, and a 12-month follow-up that cannot yet speak to long-term peri-implant health.