Diverse surgical approaches, such as resective, reconstructive, and combined therapy, have been proposed for peri-implantitis treatment. A resective surgical approach with an adjunctive modified implantoplasty refers to the modification of the implant body into a constricted area to mimic a “waist” silhouette. This modified technique forms an adequate concave smooth area that may favor the outcomes of resective surgical therapy for soft tissue adaptation, biofilm control, and possible peri-implant bone gain over the long term. The present case series aimed to exhibit the long-term clinical and radiographic outcomes of resective surgery with adjunctive implantoplasty over a 6- to 11-year follow-up. Four patients presenting four implants (one per patient) diagnosed with peri-implantitis (according to an established case definition) were included in the present case series. Patients underwent resective surgery, a modified implantoplasty approach, and implant surface decontamination. After surgical therapy, clinical and radiographic outcomes such as bleeding on probing (BoP), suppuration on probing (SoP), probing depth (PD), marginal recession (MR), modified plaque index (mPI), and marginal bone levels (MBLs) were recorded over a long-term follow-up period. Over the 6- to 11-year follow-up, mean BoP, PD, and SoP scores amounted to 17% ± 24%, 3.2 ± 0.66 mm, and 0%, respectively. Mean BoP, PD, and SoP scores were reduced by 67% ± 24%, 2.5 ± 1.26 mm, and 100%, respectively. Radiographic analysis revealed a mean radiographic bone gain of 3.1 ± 1.84 mm. Peri-implant marginal bone loss surface area decreased by 5.7 ± 3.77 mm² over the long-term follow-up. Resective therapy with adjunctive implantoplasty promoted favorable clinical and radiographic outcomes at treated peri-implantitis sites over a long-term period.