The objective of this retrospective study with 5-year follow-up was to compare crestal bone loss (CBL) and buccal bone thickness (BBT) around triangular cross-section neck (TN) to round neck (RN) implants retaining mandibular overdentures, using cone-beam computed tomography

CBL is a multifactorial entity including factors related to patients, surgical technique, prosthetic interventions, and implant design. Thus, new developments in implant micro- and macro-features, such as modifications of surface characteristics and chemistry, type of abutment connection, thread design, and neck design have been introduced over time parallel to recent advances in implantology not only for reducing CBL, but also for preserving buccal bone dimensions around implant. Furthermore, implant neck properties have been considered as a determinant factor involved in maintenance of crestal bone around implant in various trials. Nevertheless, there is no consensus with respect to the design of implant neck for reducing CBL.

The most common implant neck design is the circular one; recently, however, a newly designed implant with a triangular neck (TN) portion was introduced, which has reduction in the neck portion on three sides. This neck design provides compression-free area to alveolar crest during implant insertion to minimize CBL. In addition, TN design also would enhance the BBT by increasing the space between the flat part of the triangle and the buccal bone cortex. Based our previous study with one-year follow-up, despite the implants with novel neck design showed a better crestal bone preservation compared to conventional neck design, long-term clinical trials determining the effect of TN are missing for validating the success of this new design. Unfortunately, the data derived from only very few short-term comparative clinical trials to date do not provide an answer on benefits of TN design over the CN implants regarding preserving crestal bone level.

Thus, this retrospective study with up-to-x-month follow-up aimed to compare CBL and BBT around implants with TN and RN retaining mandibular overdentures. The null hypothesis was that there was a difference in CBL and BBT between two implant designs in the long-term follow-up.

Inclusion Criteria:

• Patients over 18 years old.
• Mandibular total edentulism.
• Presence of sufficient residual bone width (>5 mm) and length (>10 mm).
• Sufficient keratinized gingiva crestally (≥4 mm).
• Sufficient interarch space.
• Sufficient vestibular depth.
• Patients had their teeth extracted at least three months before surgery.

Exclusion Criteria:

• Patients with any systemic disease or condition that can/could compromise osteointegration (cancer, diabetes mellitus, osteopo- rosis, and cardiovascular diseases).
• Presence of any drug use that could affect bone metabolism.
• Presence of immunocompromising conditions.
• Presence of any pathology in the mandible.
• Allergy to any drugs used in the postoperative period.
• Patients who are smokers.

Healty patients who was inserted dental implants with two different designs