The purpose of this study is to evaluate the vertical and horizontal graft bone resorption (GR) in grafted maxillary sinuses and the marginal bone loss (MBL) around implants placed in the sinuses with different prosthetic connections and to determine the effect of other clinical factors on these tissue responses at 6 and 18 months postloading.A total of 254 implants were placed in 150 grafted maxillary sinuses of 101 patients (51.5% female) with mean age of 52.2 years (range, 32-82 years). GR and MBL measurements were made in implants placed with two different prosthetic connections (internal and external) at 6 and 18 months postloading. The complex samples general linear model was used to analyze the influence of patient age, gender, smoking habit, history of periodontal disease, implantation timing (simultaneous vs deferred), and prosthetic abutment length on radiographic GR and MBL values.At 18 months postloading, the MBL ranged from 0 mm to 5.89 mm; less than 1 mm was lost around 49.0% (mesial) and 44.3% (distal) of the implants, while no bone was lost around 32.9% (mesial) and 26.7% (distal). The GR was significantly affected by smoking, remnant alveolar bone height, graft length, graft height, gender, and age, and it significantly decreased over time. The MBL was influenced by the type of connection, implantation timing, and prosthetic abutment length. The MBL was greater with longer postloading interval and higher patient age and in smokers.Resorption of grafts that combine autogenous cortical bone with anorganic bovine bone is dependent on the anatomic features of the sinus and is not affected by the time elapsed after the first 6 months. The MBL in implants placed in these grafted areas is time dependent and mainly related to potentially modifiable clinical decisions and patient habits.