The clinical effects of treatment with 808- and 980-nm diode lasers as an adjunct to a uniform and consistent nonsurgical periodontal treatment protocol (NSPTP) for initial probing pockets ≥ 6 mm with a 10-year follow-up were evaluated. In total, 24 patients (16 test cases and 8 control cases) were treated with the NSPTP. The control group (CG) was treated only with nonsurgical conventional therapy, while the test group (TG) received treatment with thermal diode lasers (wavelength of 808 or 980 nm). All patients had recall visits every 3 months and were reevaluated at 1 year after NSPTP. Following the 1-year follow-up, patients were monitored at 4-month intervals for the remaining 9 years. In total, 646 teeth (433 in TG [124 multirooted teeth and 309 single-rooted teeth] and 213 in CG [64 multirooted teeth and 149 single-rooted teeth]) were included. The initial probing pocket depth (PPD) in single-rooted teeth from TG patients decreased from an average of 6.7 mm to 3.3 mm after 1 year, and to 2.3 mm after 10 years. The mean increase in clinical attachment level (CAL) was 3.8 mm. The initial PPD of single-rooted teeth in CG patients decreased from an average of 6.4 mm at baseline to 4 mm after 1 year and 3.3 mm after 10 years. The mean increase in CAL was 2.5 mm in CG. In the TG, the PPDs of multirooted teeth decreased from 6.2 mm to 3.3 mm after 1 year, where they remained stable for 10 years. The mean increase in CAL was 2.2 mm in this group. In the CG, the PPDs for multirooted teeth decreased from 7 mm to 5.8 mm after 1 year and were 5.1 mm after 10 years. The mean increase in CAL was 1.9 mm. The TG had significantly better clinical parameters than the CG, including reduced tooth loss. Compared to conventional debridement alone, the use of thermal diode lasers with NSPTP improves PPD and increases CAL in periodontal pockets ≥ 6 mm over the long term.