The effects of different restorative materials on periodontopathogens in combined restorative-periodontal treatment

Abstract Objective The aim of the study was to evaluate the association between subgingival restorations and the target periodontopathogenic bacteria (Pg, Td and Pi) in subgingival biofilm during one year after combined restorative-periodontal treatment. Material and Methods Seventeen systemically healthy subjects, who were positive for the presence of three cervical lesions associated with gingival recessions in three different adjacent teeth, were included in the study. A total of 51 combined defects were treated with connective tissue graft plus a nanofilled composite resin (NCR+CTG), a resin-modified glass ionemer cement (RMGI+CTG) and a fluoride-releasing resin material with pre-reacted glass (PRG), called giomer (Giomer+CTG). Periodontal clinical measurements and subgingival plaque samples were obtained from all combined defects at baseline and at 6 and 12 months after the surgery. The number of bacteria were evaluated by the real-time polymerase chain reaction (qPCR) method. Results No statistically significant difference in the amount of DNA copies of Pg, Td and Pi was observed in any of the groups at any time points (p>0.05). In addition, there was no statistically significant difference in the amount of DNA copies of the bacteria at baseline and at 6 and 12 months postoperatively, regardless of treatment group (p>0.05). Conclusion This study suggests that subgingivally placed NCR, RMGI and giomer restorations can show similar effects on periodontopathogenic bacteria in the treatment of gingival recessions that are associated with noncarious cervical lesions (NCCLs).


Introduction
Gingival recessions and noncarious cervical lesions (NCCLs) are frequently associated with the same tooth surface, forming a combined defect, and are closely related 34 . These combined defects result in numerous aesthetic and functional problems, and a comprehensive treatment approach is required to address the issue. A combined restorative-periodontal therapy, in which the restorative therapy is completed before mucogingival surgery, has been proposed for the treatment of gingival recession that is associated with NCCLs 14,27,36 . Following the healing period after surgery, the soft tissue is positioned over a part of the restorative material and the apical border of the restoration is in the subgingival area. However, the response of the gingival tissues to the restorative materials is very important, and this relationship has been thoroughly investigated over many years 18 . It has been reported that subgingival restorations are associated with greater plaque accumulation, bleeding on probing, and attachment loss 17  It has been suggested that some members of this composition, known as "keystone pathogens", could regulate biofilm virulence and modulate the host immune response 9,11,13 . Longitudinal studies have shown that periodontal disease progression can be predicted by the levels of Porphyromonas gingivalis (Pg) and Treponema denticola (Td) in subgingival plaque 3,9,12 . Moreover, it has been reported that Pg and Prevotella intermedia (Pi) are more frequently associated with deeper periodontal pockets 31 .
Various dental materials and surgical approaches have been used to manage these combined defects, in order to provide the most predictable combined restorative-periodontal treatment 14 . In this treatment method, resin composites or resin-modified glass ionomer cements (RMGIs) have been commonly used to restore NCCLs 19 , and gingival recessions have been treated using the coronally advanced flap (CAF) technique, either alone or in combination with a connective tissue graft (CTG) 14,21,24,28 . Some of the previous studies evaluated the effects of subgingivally placed restorative materials on periodontopathogenic bacteria in the combined restorative-periodontal treatment 23,28 . However, there is a lack of information in the current literature regarding the effect of subgingival restorations that are carried out using nanofilled composite resin (NCR), RMGI and giomer on periodontopathogenic bacteria in the treatment of gingival recessions associated with NCCLs.
The primary objectives of this study were to evaluate the association between subgingival NCR, RMGI and giomer restorations and three periodontopathogenic bacteria (Pg, Td and Pi) in subgingival biofilm during one year after combined restorative-periodontal treatment, and to examine the correlations between these pathogens and the clinical data.

Study design and population
This was a prospective, 12-month split-mouth clinical study. A total of 23 individuals, who were admitted to the Department of Periodontology, at the NCCLs were randomly allocated to three treatment groups using a computer-generated randomization scheme, as follows: NCR+CTG group, in which the combined defects were restored with NCR and treated by CTG; RMGI+CTG group, in which the combined defects were restored with RMGI and treated by CTG; Giomer+CTG, in which the combined defects were restored with giomer and treated by CTG.
The sample size was calculated considering a 0.5

Clinical measurements
Periodontal clinical measurements and subgingival plaque samples were obtained by an examiner that was blinded to the treatment allocation. All of the following clinical measurements were recorded immediately before surgery (baseline), and at 6 and   The restoration margin was then established using a diamond bur. The exposed root surface apical to the restoration was planed with curettes, and a CTG was obtained with a single incision technique 10 . Grafts were positioned to cover the exposed roots and then sutured to interdental papillae using 5-0 resorbable  Table 1.

Discussion
In this study, the influence of different subgingival     the pathogenesis of periodontal disease 33 and is highly related to clinical parameters, such as periodontal pocket depth and bleeding on probing 3 . It has also been found that the second group of bacterial species, known as the "orange complex" and including Pi, is also associated with clinical parameters of disease.
Both complex microorganisms are generally found together, and evidence shows that colonization by the red complex species is preceded by colonization and proliferation of the orange complex 30 . In our study, no significant relationship was found between the amount of DNA copies of all bacteria and PD values in the treatment groups at any of the study periods (p>0.05).

Conclusion
Within the limitations of this study, it was shown that subgingival placement of restorative materials did not negatively affect the subgingival microflora during the 12-month period after performing combined restorative-periodontal treatment. In addition, the study indicated that NCR, RMGI and giomer showed similar effects on periodontopathogenic bacteria in the treatment of gingival recessions that are associated with NCCLs.