This study was conducted to radiographically evaluate peri-implant and alveolar bone height changes of locator attachments used for three implant assisted mandibular complete overdenture using two different pick up protocols.

This clinical trial was done to evaluate the effect of using block-out spacer during picking up of locator attachments used for retaining 3 implant mandibular complete overdenture regarding peri-implant and alveolar bone height changes.

Eighteen egyptian completely edentulous male patients were chosen from the Outpatient Clinic of the Prosthodontics Department, Faculty of Dentistry, Mansoura University, Egypt.

Patients received three implants one anterior in midline area and two posterior at first molar area .

Patients free from any systemic diseases relating to the bone resorption, not taking any drugs that interfere with bone quality .Patients with absolute contraindication for surgical implantation, general contraindication , relative contraindication ,local contraindication for surgical implantation , allergic reactions to titanium or to local anesthesia were excluded.

The main question it aims to answer is whether to use block-out spacer during picking up of locator attachments used for retaining 3 implant mandibular complete overdenture or not.

• Participants were given antibiotic prophylaxis (clavulanic acid with amoxicillin 1 gm twice/day) one hour prior to surgery and continued for 6-7 days postoperative .Also, 50 mg of non-steroid anti-inflammatory tablets and analgesic (Declophenac tab) were given twice daily for one week after surgery. In addition to, Antiseptic mouth wash (0.2% chlorohexidine) was started ten minutes before surgery and continued one week after surgery twice daily.
• Patients were asked for radiographic evaluation immediately (T0) and 6 (T6) then 12 months (T12) after picking up of locator attachments.

Researcher compared between Block out spacer group (BOS-G) and Without block out spacer group (WBOS-G)which were randomly assigned into two equal groups to see if using block out spacer during picking up of locator attachments used for retaining 3 implant mandibular complete overdenture is more beneficial regarding peri-implant and alveolar bone height changes or not.

Inclusion Criteria:

• Good oral hygiene practiced by edentulous patients.
• Completely edentulous maxillary and mandibular arches (at least six months since last extraction) .
• Mandibular residual alveolar ridge mucosa was healthy, firmly attached, well keratinized, free from any ridge flabbiness and even compressible mucosa as detected by palpitation with the blunt end of the mirror .
• Mandibular residual alveolar ridge form was U-shaped with accepted bone width, height and density as assessed by cone beam computed tomography.
• Angle's class I maxillo-mandibular relationship.
• Sufficient restorative space vertically not less than (8.5mm) and horizontally not less than (9 mm) which were verified by tentative jaw relation record and mounting on the articulator .

Exclusion Criteria:

• Systemic diseases relating to the bone resorption(e.g. osteoporosis , uncontrolled diabetes, osteogenesis imperfecta…etc).
• Administrated drugs that interfere with bone quality (e.g. corticosteroids, thyroxin, levothyroxine... etc).
• Patients with absolute contraindication for surgical implantation (recent myocardial infarction, cerebrovascular accident, valvular prosthesis surgery, immunosuppression, bleeding issues….etc).
• General contraindication for surgical procedures such as patient with head and neck radiotherapy and hepatic patients.
• Patients with relative contraindication: history of para functional habits such as bruxism, clenching and bad habits such as smoking and alcoholism .
• Local contraindication for surgical implantation (close proximity to vital structure, pathological lesion, remaining root not indicated for removal , localized bone defects or poor bone quality (D4)).
• Allergic reactions to titanium or to local anesthesia

The selected patients were stratified according to age, gender, years of mandibular edentulism, number of old non-satisfactory dentures.

Patients were assigned to one of two groups using balanced randomization procedure to ensure comparability between groups.