Oro-facial Implant Axis in the Anterior Maxilla: a Pilot Study

Purpose: Screw retention is recommended for implant supported and retained prostheses in the anterior maxilla. This is because machined components have improved fit charactersitics and excess cement removal is difficult when restorative margins are located greater than 2mm subgingivally. Recently, in order to increase predictability of an aesthetic result, restorative options have increased. The use of screw-retained customized abutments in conjunction with cement retained crowns is one of these options. This procedures is associated with several advantages. Machined components can be utilized deep in the ginigival sulcus and the cement line is moved coronally where it is readily accessible. The use of customized abutments also increases the degree of flexibility for the oro-facial implant axis, as restorative inclination can be modified in the abutment.It is common for the oro-facial implant axis to change between screw and cement retention. In other words, the oro-facial implant axis needs to be set up toward palatal side of the incisal edge for a screw retained implant prosthesis. On the other hand, the oro-facial implant axis of cement retained implant prostheses requires an implant axis that passes through the incisal edge. This gives a more ideal emergence profile and improves cement line location. The difference between these axes influences traditional contour (particularly emergence) of the prosthesis. Therefore, it is possible that differences the oro-facial implant axis (and the use of this inclination as a measureable parameter) may help in obtaining and predicting aesthetic treatment results. For this study, the angle between planned implant axis for screw and cement retention was measured using the Cone-Beam CT (CBCT) images. Materials and Method: Adequate bone volume in the anterior maxilla is necessary for optimal restoration-based implant placement. Measurements were initially performed using CBCT images of maxillary central incisal areas characterized by an absence of periodontal disease or prosthesis. The angle formed between the axis of an implant planned for cement retention (Point A), and the axis of an implant planned for screw retention (Point B) was measured. Furthermore, the distance between the buccal alveolar crest (point C) and the palatal alveolar crest (point D) was measured. Result and Conclusion: The oro-facial implant axis of implants planned for screw and cement retained prostheses was examined using the CBCT images of the normal maxillary central incisor region. Proceedings of the 3rd ITI Consensus Conference identified the optimal three-dimensional implant position. Accordingly, when the implant axis for screw retention inclines unfavorably in comparison to the implant axis for cement retention, the prosthesis tends to become a ridge-lap design with aesthetic compromise. The tolerance level of this angle made between implant axes planned for screw and cement retention is one of the important factors for ensuring a satisfactory emergence profile and optimal aesthetic result. Keywords: Oro-facial Implant Axis, Anterior Maxilla, Cone-beam CT