Thirty maxillary edentulous patients with previous mandibular All-on-4 screw retained prosthesis and their age ranged from 55 to 65 years were selected from the outpatient clinic, of prosthodontics Department, Faculty of Dentistry, Mansoura University from March 2022 to July2022 and 80% power was used to calculate patients sample according to the results of a previous study 1 which showed no significant difference was reported when comparing occlusal stability ,implant stability and periimplant soft tissue changes between different implants angulation of both groups. (Effect size=.70mm and α=.05). The power analysis was performed using the G*Power program (version 3.1.5, Kiel, Germany)

the aim of this study is to compare between All-on-Six distributed dental implants "Anterior 4 Implant Parallel and Posterior 2 Implant Distally Tilted" versus parallel distribution supporting screw retained maxillary single denture regarding soft tissue changes around implants, implant stability and occlusal stability.

The primary outcome is to study implant stability and occlusal stability. The secondary outcome is to evaluate periimplant soft tissue changes. The null hypothesis of this study will be there is no difference between the two studied groups.All patients were informed about the proposal of this study, the line of treatment, and the need for regular and frequent recalls. Their acceptance to participate in this study was confirmed and they signed the consent form of the ethical committee of the faculty of dentistry. This study gained the approval of the ethical committee of the Faculty of Dentistry, with approval number (A05080622).

all the patients were divided randomly into two equal groups as follows Group I patients received four axially placed anterior Implants(*General system) in lateral and first premolar region and two distally tilted 30 degree posteriorly in molar region relative to the occlusal plane supporting screw retained maxillary single denture.

Group II patients received 6 implants in parallel distribution in anterior, premolar and molar region

Inclusion Criteria:

• patient with maxillary edentulous alveolar ridges.
• patient complained from insufficient retention and stability of their maxillary single denture.

Exclusion Criteria:

• medically compromised patients.
• patients with parafunctional habits.

. Evaluation was done for all patients at three evaluation periods as follows: T0: immediately before screwing the final prosthesis.T6: 6 months after unscrewing of the final prosthesis.T12: 12 months after unscrewing of the final prosthesis.