Porous Bone Increases the Risk of Posterior Mandibular Implant Failure

Our recent study indicated that patients with osteoporosis had an increased risk for early and late implant failure perhaps due to a large cancellous space. Therefore, the purpose of the article is to explore the relationship between the amount of cancellous space in an implant site and implant failure.

The authors conducted a retrospective cohort study on patients who received dental implants in the posterior mandible at the senior author's practice from January 1, 2008 to October 1, 2019. The primary outcome variable was time to implant failure. The primary predictor variable was the amount of cancellous bone between the buccal and lingual cortices (cancellous space). Other study variables included demographic variables, medical history variables, and implant site measurements. Statistical analysis was performed using descriptive statistics, chi-squared tests, single variable and multiple Cox proportional hazard analyses.

The study cohort (n = 220) was composed of 62.3% women and the average age was 58.2 years. The median follow-up time was 3.5 years (range: 1-12). Five-year survival rates for patients with a cancellous space of <4 mm was 100%, with a cancellous space of 4-6 mm was 95.3%, with a cancellous space of 6-8 mm was 88.2%, and with a cancellous space of >8 mm was 64.1%. In the final multivariate Cox proportional hazard model adjusting for age, gender, smoking status, site and buccal cortex width, cancellous space remained significantly associated with time to implant failure (aHR 1.7 per millimeter change [1.4 - 2.2], P < .0001).

The width of the cancellous space and subsequent gap between implant and cortical bone should be considered when placing implants into the mandibular molar sites. When the patient presents for an implant in the mandibular molar region, if the cancellous space is large, the patient should be informed of the risk.