Nonsurgical periodontal therapy aims to remove supragingival and subgingival biofilm to restore periodontal health. This systematic review aims to assess the clinical effectiveness of manual and/or ultrasonic instruments and to determine whether other therapies can improve periodontal clinical outcomes. Case-control, cross-sectional and cohort studies and clinical trials of patients undergoing nonsurgical periodontal therapy with ultrasonic and/or manual instruments (and any adjunctive therapies, such as glycine, erythritol, ozone, laser and glycine) from 2013 to 2023 were analyzed using Pub-med/MEDLINE, Scopus and Google Scholar. To assess the risk of bias in this review, blinding, randomization, allocation concealment, outcome data and outcome recording were assessed. No differences between treatments were found; all methods, including manual and ultrasound, were helpful in improving clinical parameters (primary outcome). Although the results were mixed, adjunctive therapies seemed to be helpful in the treatment of periodontal disease. The results of this systematic review are consistent with the previous scientific literature and have shown that both manual and ultrasonic instruments are effective in nonsurgical periodontal therapy. This review could not show how complementary therapies could further improve nonsurgical periodontal therapy. For future research, it would be good to standardize the sample with regard to the degree and stage of periodontal disease and to evaluate the risks and benefits of the instruments (manual and ultrasonic scalers).