Article
Edentulous patients are demanding higher levels of comfort and functionality, and are looking to implant-retained overdentures to provide stability. However, all components experience wear through use and it can sometimes be difficult to identify whether the wear has occurred to the attachment or the retainer. Accurately diagnosing the cause of the loss of retention is important from a patient satisfaction and financial viewpoint. This simple diagnostic method for assessment of the wear of an implant-retained overdenture using an analogue of a ball abutment will reduce perceived levels of complexity of routine maintenance treatments.
The prevalence of edentulism continues to fall in western society. Between 1998 and 2009, the overall level of edentulism has more than halved from 13% to 6%, demonstrating that this is a current and relevant changing pattern in oral health status within the population.1
Implant-retained overdentures rely on both the denture-bearing area and the implants for support and retention. Maxillary dentures are commonly supported by four or six implants,2 whilst mandibular dentures more usually may only have two implants.3,4 Commonly, ball or bar abutments are attached to the implants, and clips or ‘O’-ring matrices are embedded into the fitting surface of the denture.
Ball and stud-retained overdentures benefit from parallel implant alignment for the successful construction of the overdenture prosthesis. Mild divergence can be overcome, but will often result in greater wear and tear on components and higher maintenance requirements.
Retrospective studies looking at the maintenance requirements of implant-retained overdentures have generally concluded that, in the first year, there are more maintenance visits required for adjustments of the overdenture and the retaining components.5,6 In the long term, all components will eventually wear, although at different rates. It can be difficult sometimes to identify whether the wear has occurred to the housing insert or the abutment. In these cases, using components which are known to be retentive to test the part suspected to be worn can prevent replacing unnecessary elements which would result in additional cost to the patient with no benefit achieved.
Clinical example
A 53-year-old female patient presented at the Newcastle Dental Hospital for a review of an implant-supported mandibular overdenture (ISMOD). Two Brånemark Mk III 11.5 mm implants had been placed in the LR2 and LL2 positions approximately 5 years previously when she had first been treated within the Newcastle Dental Hospital. They supported a complete lower removable prosthesis, which initially exhibited good extensions and stability. Lack of retention on the left-hand side ball abutment had been noted on multiple occasions and had led to replacement of the dentures. Although the new dentures were technically sound, there remained ongoing problems with the retention around the left-hand side ball abutment.
To diagnose the source of the lack of retention in the nine-month-old dentures, an unused Brånemark ball abutment laboratory analogue of the same system was tried with the matrix in the fitting surface of the denture (Figure 1). This had positive seating in the right-sided matrix, but was very loose on the left-hand side. This illustrates that there was wear in the insert and the left-hand side matrix was therefore replaced. Retention of the left matrix now matched the retention of the right matrix with the analogue ball attachment.
When placed back in the patient's mouth, there was still a reduced retention when compared to the right-hand side ball abutment. Direct comparison between the retention on the analogue and that in the patient's mouth provided confirmation that it was the wear on the patient's ball abutment that was the primary source of the poor intra-oral retention (Figure 2). A change of the ball abutment was planned for the future based on this finding.
Discussion
When ball abutments are studied, significant changes are measured in the ball diameter after one year of usage, with this continuing to wear significantly until around three years of use (Figures 3a and b). Approximately 30 μm of diameter has been measured to have been lost in this time period, with this having the potential to reduce the effectiveness of retention in the components.7
Accurately and confidently diagnosing the cause of the loss of retention is important from a patient satisfaction and financial viewpoint. Replacement or adjustment of a matrix to increase retention after loss due to cycling of loads during mastication and denture removal is a relatively inexpensive and simple procedure. Failing to diagnose a worn bar or ball abutment will result in multiple patient appointments with little improvement in retention. The technique described is an inexpensive and easy method to diagnose the source of the loss of retention at the chairside confidently.
Conclusion
Practical and inexpensive solutions to common problems are necessary in modern dentistry for patient and dentist satisfaction and reduction in unnecessary costs. With the projected increase in numbers of implant-retained overdentures and the consequential increase in number of patients needing maintenance of their prostheses, creating simple diagnostic methods for identifying appropriate courses of treatment will hopefully increase the number of general dental practitioners who will take on these necessary procedures by reducing perceived levels of complexity of routine maintenance treatments and therefore increase provision and choice for patients.