Comparative Assessment of different degree of retention of ERA attachment on the supporting structures of implant supported mandibular overdenture

Objectives: This research was carried out to evaluate the effect of different degree of resiliency of ERA attachment; white and grey nylon male components in mini-implant retained mandibular overdenture on the peri-implant crestal bone level.
Materials and Methods: Twenty completely edentulous patients with maladaptive experience of wearing mandibular dentures were selected to participate in this study. Patients participating in this study were rehabilitated by maxillary complete denture and implant retained mandibular overdenture by four mini-implants with ERA head abutments. For all selected patients four mini implants 2.2 mm in diameter and 14 mm in length (ZIMMER ERA) were inserted in the inter-foraminal area following the non-submerged flapless surgical approach with the help of a modified transparent acrylic template. Standard clinical and laboratory techniques were followed for denture construction for all patients. Patients were randomly divided into two equal groups according to the resiliency of the male nylon insert. A white replacement insert was seated into the metal housing for group I, while a grey replacement insert was used for group II. Mesial, distal, buccal and lingual marginal bone height around the mini implants were evaluated, using the linear measurement system of the software (Ondemand 3D) with flat panel detector supplied by the cone beam CT. The measurements were carried out at the end of each follow-up appointment (at overdenture insertion, 6, 12 and 18 months post insertion). The marginal bone loss at different intervals was obtained by calculating the difference in bone height at that interval from the base line measurement and statistically analyzed.
Results: The results of this study showed that there was statistically significant increase in the marginal bone height loss around the mini implants in both groups at the end of 18 months follow up. Comparing the two studied retentive elements of ERA attachment; statistically significant difference between the two groups was found at the end of 18 months follow up period, where group I showed less bone resorption in comparison to group II. There was also significant difference between both groups concerning the distal and the labial surfaces after 18 months. Conclusion: ERA attachments in mini-implant retained mandibular overdenture fulfil the criteria of implant success as indicated by the measured amount of marginal bone loss. ERA attachments provide adequate retention and have the ability to control the amount of bone loss by changing the retentive elements. The lesser the retention the less significant bone loss around the implants