Short Implant Versus Crestal Standard Length Implant to Retain Class 1 Removable Partial Denture.

Inclusion Criteria * adult patients aged 50 years or older with class 1 RPD with missing mandibular molars at least and complaining from instability of the prosthesis were recruited. * Medical history revealed no contraindication to implant therapy. * Patients have an amount of bone nearly equal to 8 mm length above the inferior alveolar canal to receive a 6 mm short implant with 2 mm subcrestal to the bone level with sufficient bone width ≥ 8mm on one side and an amount of bone equal to or more than 8 mm to receive a standard-length implant of 7.5, 9, or 10.5 mm placed at crestal bone level with sufficient bone width ≥ 8mm on the contralateral side which was examined by CBCT. Exclusion Criteria: * Presence of active infection or inflammation in the areas intended for implant placement; \*systemic diseases such as diabetes. * Pregnant and lactating patients. * Habit of severe bruxism or clenching. * Treatment with therapeutic radiation to the head within the past 12 months. * Treatment with bisphosphonate within the past 12 months. * More than 10 cigarettes/day smoking habit.