**5. Conclusions**

During the last few decades, new approaches through salivary diagnostics have been developed to evaluate the possible useful biomarkers for predicting the disease. This study indicated that patients who have periodontitis and CAD presented lower serum and salivary vitamin C and antioxidant levels compared to patients with periodontitis and healthy subjects. Moreover, this study suggests that mainly CAD acts as a key factor on serum and salivary vitamin C and antioxidant levels through a pathway mediated by the CRP. This pilot study is promising and demands further studies with a larger sample and longitudinal observation in saliva, serum, and gingival crevicular fluid in order to better understand the role of vitamin C levels during periodontitis.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2072-6643/11/12/2956/s1: Table S1. STROBE Statement—checklist of items that should be included in reports of observational studies.

**Author Contributions:** G.I. conceived the idea and wrote the paper. G.I., A.P., S.M., and A.L.G. reviewed the collected data. G.I. and R.L. were responsible for editing, original data, and text preparation. All authors took responsibility for the integrity of the data that is present in this study.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
