This protocol was preregistered in the Open Science Framework (OSF) Registries (ID: qfs6p) [19]. This protocol, as presented in its entirety below, follows the 2015 PRISMA-P (Preferred Reporting Items for Systematic Review and Meta-Analysis for Protocols) checklist (Multimedia Appendix 1) [20]. It is also intended that this systematic review will contain the items of the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, 2020 version [21].

The search will include all articles indexed in the PubMed, Web of Science Core Collection (Clarivate), EBSCOHost, Scopus, and ProQuest databases published in the English language from January 2000 to May 2024. In addition, we will also consider an additional exploration of the reference lists and bibliographies of all potential full-text articles. EndNote software (version X7.0.1; Clarivate) will be used to facilitate reference management.

In Table 1, the search terms are presented exactly as they will be used in each specific database. A Boolean search strategy was elaborated, considering also those key terms previously used in existing systematic reviews [8,16]. For the PubMed database, Medical Subject Headings terms were used to ensure a more comprehensive and precise search.

The selection process will be in accordance with PRISMA guidelines. Data collection will be carried out using a specific spreadsheet, with parameters selected after a pilot study involving approximately 10 included studies. In addition, 2 reviewers, identified as participating researchers, will conduct the assessment independently. In case of disagreement, a third researcher with expertise in the field will resolve discrepancies.

If there is unclear or omitted information from the selected studies, such as missing data or incomplete text, the authors will be contacted by email, and weekly attempts will be made for a maximum of 5 weeks. If there is no response from the authors, the study will be excluded.

Studies meeting the inclusion criteria will undergo validation and data extraction.

The relevant data extracted from each study will describe the designated PECO measures: author’s name and date of publication; country; study design; participant characteristics; periodontal treatment; definition of psychological stress; stress diagnosis (stress scale or biomarkers used); clinical parameters (probing depth, clinical attachment level, bleeding on probing, and plaque index); monitoring and outcome measures of interest to the review (regular clinical monitoring to monitor the effectiveness of treatment); authors’ conclusions; and source of funding.

Subsequently, the “best evidence synthesis method” will be applied to classify the level of evidence [22]. It will be considered strong (consistent findings observed among multiple high-quality studies), moderate (consistent findings observed among multiple moderate-quality studies and/or 1 high-quality study), limited (findings provided by 1 moderate-quality study and/or only low-quality studies), conflicting (when inconsistent findings were observed), or “no evidence”(when there were no available studies) [22]. Consistency will be defined as ≥75% of studies report results in the same direction, and inconsistency will be defined as <75% of studies report results in the same direction.

A total of 2 authors (KRVV and KOS) will independently evaluate the methodological quality of each included study using the Newcastle-Ottawa Scale [23]. This scale is specifically designed for nonrandomized studies. The authors will use a “star” system for each study, considering 3 main components: (1) quality of study participant selection, (2) comparability, and (3) exposure and outcome. The maximum score is 9 points for case-control studies and 10 points for cross-sectional studies. The total score will categorize the studies into three groups: (1) high quality (total score: 7 to 9 or 10), (2) moderate quality (total score: 4 to 6), and (3) low quality (total score: 0 to 3). To determine consistency, the interrater agreement will be calculated using the Cohen κ coefficient.

Furthermore, the risk of bias in the outcomes or interpretations will be independently determined for each included study. This will be done using the Risk of Bias Assessment Tool for Non-Randomized Studies [24]. Each element will be evaluated as presenting low, high, or unclear risk concerning participant selection criteria, potential confounding variables, accuracy of exposure measurement, blinding of outcome assessments, handling of incomplete outcome data, and selective outcome reporting.

If there are a sufficient number of studies and no substantial variations in the methods used among them, the results may also be presented through a meta-analysis (quantitative synthesis). Regardless of whether the final manuscript meets the criteria for a quantitative synthesis, a qualitative synthesis will be conducted using the best evidence synthesis method. In addition, a table with the main characteristics of the studies will be included.

We will also consider the statistical analyses used in the selected studies, including different types of regression models to adjust for confounding variables. This may include multiple linear regression for continuous dependent variables, multiple logistic regression for binary stages, and multivariable ANCOVA. In addition, we will also include other statistical analyses, such as clarification analysis, as applicable.

Studies have shown a correlation between psychological stress and various inflammatory diseases [27,28]. Research in the field of dentistry shows systematic reviews that explore the association between psychological stress and periodontitis [16,17,25] or psychological stress as a possible risk factor for periodontal diseases [8,18,26]. However, to date, no systematic review has focused on understanding how psychological stress specifically influences periodontal treatment outcomes.

There is evidence that psychological stress affects the body’s inflammatory response [29,30], which together may increase susceptibility to periodontal disease [16,17,31,32] and hinder adherence to periodontal treatment, resulting in slower healing and less favorable clinical outcomes [32,33]. Therefore, it is hypothesized that the results of the selected studies confirm a significant influence of psychological stress on periodontal treatment. Patients with high levels of stress are likely to show worse periodontal treatment outcomes compared with those with lower levels of stress. A study [34] evaluated the effects of psychological stress on periodontitis healing in rats and the contribution of baseline fibroblast growth factor expression to the healing process; it observed that psychological stress could delay periodontitis healing, which may be mediated in part by down-regulation of baseline fibroblast growth factor expression in the periodontal ligament. Therefore, it is important to investigate whether patients with elevated levels of psychological stress may require personalized, lifestyle-changing interventions to optimize treatment outcomes.

A strength of this review is the rigorous methodology, which reinforces the validity of the results. In addition, this review will provide an updated, specific, and detailed view of how psychological stress directly affects periodontal treatment outcomes, highlighting the importance of considering psychosocial factors. However, there may be limitations to consider, such as variability in the measurement of psychological stress among the included studies, which may introduce bias.

For future research, it would be useful to explore the effectiveness of psychological interventions integrated into periodontal management to improve clinical outcomes. In addition, this review will identify other knowledge gaps, encouraging further studies to fill these gaps and thus improving the overall understanding of the topic, which will benefit clinical practice in the future.

To maximize the impact of these findings, several dissemination strategies are planned. These include publication in high-impact scientific journals and collaborations with dental professional societies to promote the integration of these findings into clinical practice. In addition, educational materials and workshops for oral health professionals will be developed, highlighting the importance of addressing psychological stress in periodontal treatment.

This review will provide current information on how psychological stress affects the outcome of periodontal treatment, the results of which can serve as a basis for creating broader health strategies aimed at addressing psychosocial factors in promoting oral health.