Symphyseal measurements may guide choice of suitable dental implant design

Overdenture with single symphyseal implant is one of the useful clinical approach for elderly edentulous patients. The loss of anterior mandibular teeth induces many changes of the symphysis, particularly regarding its shape and volume. These changes have been well described in the literature. They mainly occur during the first 6 months after tooth extractions, and often involve the loss of up to 50% of the initial volume.

Hence, Chloë Mense and colleagues from the Aix Marseille University, Marseille, France carried out this study to evaluate edentulous patients with regards to the relationship between dimensions, bone characteristics, cancellous densities, and cortical thickness of the mandibular symphyseal region using cone beam computed tomography (CBCT).

The authors analyzed 103 CBCT from pre-implant investigations. All included patients were healthy without any disorders affecting bone metabolism. 13 measurements for each patient was performed: 9 of height, width, and thickness (mm) and 4 of density (Hounsfield Units; HU). Fisher's exact test was applied to examine the association between two categorical variables, the Pearson correlation coefficient to measure the strength of linear relationship between two quantitative variables. The two-sample Student's t-test was used to compare mean symphysis height between men and women, the paired Student's t-test to compare mean lingual and buccal cortical thickness. For all tests, the threshold of significance was fixed at 5%.

The results showed that men and women significantly differed with regards to mean total symphysis height (p = 0.004) and the distribution of Cawood and Howell classifications (p = 0.033). Symphysis height was negatively correlated with mean density of cancellous bone (r = −0.453, p < 0.001). Mean lingual cortical thickness significantly differed from mean vestibular thickness (p < 0.001, paired Student's t-test).

Therefore, the authors laid out the following conclusions-

1. The reduction of symphyseal size is sex-related, with women showing greater reduction.
2. The decrease of symphyseal height is accompanied by an increased density of the central and lower portion of cancellous bone, and the thickness of the lingual and lower parts of cortical bone.
3. Symphysis size is an important parameter for selecting the design (form, thread, surface) of the implant to ensure optimal primary stability and quick osteointegration.