Principles of Attachment Selection for Implant Supported Overdentures

ridge resorption are good candidates for studs or magnetic attachment assemblies. However, magnets provide the least amount of retention compared to the other attachments, and they very soon lose their initial retention capacity. Studs are ideal for patients with a narrow ridge because in these cases, a bar would interfere with the tongue space.

Different types of attachment assemblies are listed in Table 2. Rigid telescopic copings transfer most of the masticatory force to the supporting implants. This increases the risk for implant fatigue and eventual fracture of the implant or its components. With rigid or minimally resilient attachment assemblies there is minimum load transfer to the posterior alveolar ridge. Therefore, patients experience the least amount of alveolar bone ­resorption.

Biomechanical Considerations

Factors that influence the design and ­resiliency of the attachment assembly are listed in Table 3. One hypothesis suggests that the bar connecting the implants should be parallel to the hinge axis. Although this rule has been followed by many clinicians, no

studies have supported this claim. One long-term study (5 years) analyzed the influence of placing the bar parallel to the hinge axis on peri-implant parameters, including the clinical attachment level.1 The outcome of the type of retention (i.e., splinted versus unsplinted) was also assessed. No significant correlations were found.

Distal Extension to the Bar

Distal extensions provide a high level of stability against lateral forces, particularly in the mandible, and can protect the denture bearing tissue from loading forces. Distal extensions should not extend beyond the position of first premolar of the mandibular prosthesis, and they cannot compensate for a short central segment. When distal extensions are used, the implants’ splinting

SROMS

Volume 19.6