Background <p>This study aimed to describe changes in marginal bone levels (MBL) and peri-implant trabecular radiomorphometric patterns during the osseointegration period in posterior mandibular implants healed with either healing abutments or cover screws.</p> Methods <p>This retrospective radiographic cohort study included 53 posterior mandibular implants in 36 patients, classified into the healing abutment group (<i>n</i> = 22) and the cover screw group (<i>n</i> = 31), based on the immediate postoperative panoramic radiographs. Digital panoramic radiographs obtained before implant placement (T0), immediately after implant placement (T1), and after a 3-month osseointegration period (T2) were analyzed. Marginal bone level (MBL) changes and radiomorphometric indices, including fractal dimension (FD), lacunarity, bone area fraction (BAF), and mean gray value (MGV), were calculated.</p> Results <p>MBL values decreased significantly from T1 to T2 in both groups (<i>p</i> &lt; 0.05). No statistically significant between-group difference in MBL change was detected at either the mesial or distal surface (<i>p</i> &gt; 0.05). In the overall cohort, mean lacunarity decreased, whereas mean FD, BAF, and MGV increased. Group-based analyses showed significant longitudinal changes in all radiomorphometric parameters in the cover screw group, while only FD changed significantly in the healing abutment group (<i>p</i> &lt; 0.05). For the overall mean radiomorphometric values, no statistically significant between-group differences were detected at T2 (<i>p</i> &gt; 0.05).</p> Conclusions <p>Posterior mandibular implants showed MBL reductions and radiomorphometric changes during the 3-month osseointegration period. MBL changes did not differ significantly between groups, while radiomorphometric trajectories differed descriptively. These findings provide descriptive radiographic information on early peri-implant bone changes and should be interpreted within the limitations of the retrospective cohort design.</p>