**3. Results**

The literature search resulted in 71 articles across the four databases (PubMed, Clinical Trials, Cochrane, Web of Science), of which 33 were reviewed after duplicates (*n* = 38) were removed (Figure 2). After screening with inclusion/exclusion criteria, six papers remained for the systematic analysis. Detailed summaries of final studies are included in Tables 1 and 2.

**Figure 2.** Flowchart of the systematic search based on PRISMA guidelines.


**Table 1.** General data of the eligible studies.

SRP—scaling and root planning.



*Nutrients* **2020**, *12*, 553

Two of the remaining six studies aimed to evaluate the relationship between plasma ascorbic acid levels and PD in systemically healthy and type 2 DM subjects, following the administration of vitamin C in similar 450–500 mg daily doses. Gokhale et al. [63] randomly divided participants into subgroups, using a coin-toss method: subgroup A (15 adults) receiving 450 mg chewable tablet associated with daily scaling and root planning and subgroup B (15 adults) receiving placebo as lemon-flavored sugar-free candy chewable tablets with scaling and root planning spaced over two appointments. It revealed that dietary ascorbic acid supplementation associated with scaling and root planning improved the sulcus bleeding index in subjects with gingivitis and diabetics with periodontitis. They also obtained additional results, by using Tukey's multiple post-hoc procedures, regarding the plasma ascorbic acid levels in subgroup A, which supported their conclusion [63]. Similarly, Kunsongkeit et al. [64] assessed the administration of daily 500 mg vitamin C tablets, for 2 months in 15 adults or placebo tablets in 16 adults, both groups receiving full scaling and root planning from baseline to the last administered tablet, comparing the results within groups using Bonferroni post-hoc test. Periodontitis patients with uncontrolled type 2 DM did not exhibit evident benefits by supplementation of 500 mg/day vitamin C [64], but the di fferences between their results may have been generated by the recently diagnosed type 2 DM patients included in the Gokhale et al. study and uncontrolled type 2 DM patients included in the Kunsongkeit el al. study. Therefore, the progression and severity of periodontitis were greater in patients with uncontrolled diabetes and perhaps the dosage of vitamin C should have been larger to sustain the conclusions revealed in the Gokhale et al. study. Even so, both studies assumed the bidirectional relationship between periodontitis and DM, which means further assessments should be aimed by other medical specialists.

Three studies from the ones selected [65–67] evaluated the e ffect of dietary intake of vitamin C, as an antioxidant and immunomodulatory agent, and the evolution of PD in patients with DM, without specifying certain consumed fruits or vegetables or dosage, but measuring plasmatic [65,67] or salivary concentration of ascorbic acid [66]. Thomas et al. [65] measured plasmatic ascorbic acid levels in their case-control study by using spectrophotometric quantitation on all three groups: 20 patients with type 2 DM and PD, 20 healthy patients with PD and 20 healthy patients without PD. This method was useful for comparing the micronutrient levels not only of vitamin C but also of zinc and copper in diabetic patients and healthy individuals with periodontitis, finally showing that diet plays a modifying role in the progression of periodontal disease. The idea was sustained by a statistically significant decrease in vitamin C levels in diabetic patients with periodontitis when compared to healthy individuals with periodontitis [65]. The same conclusion appeared in a cross-sectional survey, also held in India, by Patil et al. [67], even though vitamin C was measured by a di fferent chemical method (dinitro phenyl hydrazine method). They included an additional group consisting of patients who su ffered from gingivitis, an incipient form of PD, and a group of recently diagnosed patients who su ffered from periodontitis and diabetes, who had not received any antidiabetic medication, before the study onset [67]. Gumus et al. [66] conducted a case-control study in Turkey by measuring the total antioxidant capacity in patients with PD, divided into three groups: 16 patients with type 1 DM, 25 patients with type 2 DM and 24 patients with no associated disease. They used the Kruskal–Wallis test, followed by the Mann–Whitney U test for the group comparisons of the salivary antioxidant levels, as well as the clinical periodontal measurements; however, their conclusion was di fferent from the Indian studies, because vitamin C did not seem to play a major role in the pathogenesis of periodontal manifestations in diabetes. They mentioned the absence of a group with diabetes with a clinically healthy periodontium which would have enabled them to conclude whether the levels of salivary antioxidants are related to the diabetic status independently of the clinical periodontal situation [66]. This limitation of the Turkish study might have led to a di fferent conclusion regarding the ascorbic acid levels in patients with both diabetes and periodontitis than the one commonly presented in Indian studies.

Amaliya et al. [68] organized a cohort study in Indonesia analyzing the intake of vitamin C from the dietary origin while monitoring all 98 patients using a full set of dental radiographs with long cone paralleling technique. Their results depended on the consumption of guava fruit over one month in all 53 women and 45 men, with an age range from 39 to 50 years, who were included in the study. Amaliya et al. stated that guava fruit contains 228 mg vitamin C per 100 g (USDA 2010), which implied that the consumption of one guava (without skin and kernel) results in an intake of about 400 mg vitamin C. Since the guava consumption varied between 0 and 30 guavas in the month preceding plasmatic ascorbic acid measurements, a grea<sup>t</sup> variation in the amount of vitamin C intake existed in their included population, possibly contributing to the significant association with alveolar bone loss. In their study, 45% of the population showed vitamin C depletion/deficiency, 70% were in a prediabetic state and 6% had untreated diabetes. Their new finding was that guava fruit consumption may play a protective role against periodontitis in the 10% malnourished population, which showed a relatively low body mass index. These conditions may have contributed to the extent and severity of alveolar bone loss in the population. It is important to mention that Amaliya et al. had a limitation because 70% of their population were in a prediabetic state and 6% had undiagnosed diabetes, which is why no relation could be assessed between HbA1c plasma levels and alveolar bone loss, probably due to the small number of subjects with HbA1c values ≥6.5% and insu fficient conclusive data of the study [68].

All studies included in our systematic review had in common the assessment indication for PD, which included certain parameters: alveolar bone loss, bleeding on probing, clinical attachment level (CAL > 3 mm), the community periodontal index, pocket depth or probing pocket depths (PPDs of ≥5 mm, along with the presence of attachment loss of ≥2 mm within at least three teeth (assessed at four sites per tooth)), plaque index and the sulcus bleeding index (SBI score of ≥2).

The plaque index had the following scoring criteria: score 0—no plaque, score 1—a film of plaque adhering to the free gingival margin and the adjacent area of the tooth, seen in situ only after the application of disclosure solution or by using the probe on the tooth surface, score 2—moderate accumulation of soft deposits within the gingival pocket, or the tooth and gingival margin, which can be seen with the naked eye, score 3—abundance of soft matter within the gingival pocket and/or on the tooth and gingival margin [63]. The assessment of gingival bleeding is done on a scale of 0–5 according to the following criteria: score 0—healthy appearance of the gingiva and no bleeding upon sulcus probing, score 1—apparently healthy gingiva showing no color or contour changes and no swelling, but sulcus bleeding on probing, score 2—bleeding on probing and color change caused by inflammation, but absent swelling, score 3—bleeding on probing, change in color and slight edematous swelling, score 4—bleeding on probing, obvious color change and swelling, and score 5—spontaneous bleeding on probing, color change, marked swelling with or without ulceration [63].

The parameters used to sustain the diagnosis of DM included body mass index (BMI), glycosylated hemoglobin (HbA1C > 7%), fasting blood sugar (FBS ≥ 126 mg/dL), two-hour postprandial glucose (PPG ≥ 200 mg/dL) and random blood sugar (RBS ≥ 200 mg/dL with symptoms such as polyuria, polydipsia and polyphagia).
