# Seven-Year Retrospective Study on Conometric Retention for Complete Fixed Prosthesis
## 4 Discussion  
This retrospective study aimed at investigating MBL, implant, and prosthetic survival rate of four implant supported concentric retained fixed mandibular dentures after a follow-up period of seven years. The present study showed a high implant and prosthetic survival rate and an absence of marginal bone loss, revealing this solution to be stable and reliable in the long term. Implant supported prostheses, especially in the mandible have been shown to significantly improve patient quality of life, if compared to complete removable dentures [16]. Implant supported overdentures provide various advantages compared to full arch implant supported fixed rehabilitation, such as reduced treatment costs and better cleansability. However, according to a recent RCT [17], systematic review, and meta-analysis [6] patients tend to prefer the latter solution. Conometric retention can therefore be a valuable alternative to provide fixed retention to mandibular complete dentures, merging the advantages of the abovementioned rehabilitative options. Conometric retention uses the friction between the abutment and the titanium coping to retain the prosthesis without the use of screws or cement [18]. This system has shown outstanding prosthetic results in the short term, both for partial [18,19] and full-arch rehabilitations [12,13], with several advantages both for patients and clinicians. In detail, they can provide fixed support to full arch prostheses, permitting an easy and faster removal of the prosthesis, making professional cleaning and regular check-up easier to perform. Furthermore, the whole procedure can be conducted in the dental office, without the need of dental technicians, reducing the overall time and costs of the treatment. Also, the lack of cement and screws highly reduces the risk of mechanical or biological complications [20]. In the present study, after seven years, clinical and radiographical parameters were within health thresholds. Even if the mean PPD significantly increased during the observed period, with a mean difference of 0.55 mm between the baseline and the 7-year follow-up, at this timepoint the mean PPD value was 1.74 (\(\pm\)0.88) mm. This value results in being lower than those reported both for fixed (2.4 mm to 3.73 mm) [21,22] and removable \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & **Baseline Mean** & **2 y of Function** & **5 y of Function** & **7 y of Function** & **0-2 y Mean** & **0-5 y Mean** & **0-7 y Mean** \\  & **(\(\pm\)SD)** & **Mean (\(\pm\)SD)** & **Mean (\(\pm\)SD)** & **Mean (\(\pm\)SD)** & **Difference (\(\pm\)**SD)** & **Difference (\(\pm\)**SD)** & **Difference (\(\pm\)**SD)** \\  & & & & & **(\(p\)**-Value)** & **(\(p\)**-Value)** & **(\(p\)**-Value)** \\ \hline PPD & 1.18 (\(\pm\)0.39) & 1.21 (\(\pm\)0.41) & 1.36 (\(\pm\)0.48) & 1.74 (\(\pm\)0.88) & 0.02 (\(p\) = 0.67) & 0.17 (\(p\) = 0.001) & 0.55 (\(p\) \(<\) 0.001) \\ \hline MBL & 1.22 (\(\pm\)0.91) & 0.81 (\(\pm\)0.89) & 0.71 (\(\pm\)0.89) & 0.49 (0.86) & 0.41 (\(p\) \(<\) 0.001) & 0.51 (\(p\) \(<\) 0.001) & 0.74 (\(p\) \(<\) 0.001) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mean value and standard deviation for PPD and MBL, and results from the ANOVA test. Figure 3: Marginal Bleeding Index parameters on the different follow-up time points. (2.3 mm to 3.5 mm) [23; 24] implant supported prostheses after a minimum follow-up period of 6.5 years. It can be hypothesized that this lower PPD value might be related to better cleansability of the concentric-retained prosthesis, leading to high stability and health of the peri-implant soft tissue. This hypothesis could also explain the high stability of MBL along the investigated timepoints. In our study, the mean MBL after a follow-up period of seven years was 0.49 \(\pm\) 0.86 mm, meaning that the mean MBL was above the implant shoulder. However, a statistically significant mean marginal bone loss (0.74 mm) was found compared to the baseline.