Risks and complications

Prosthetic technical complications

A recent epidemiological study screened almost 11,000 implants in Sweden after a mean follow-up period of 5.3 years. The study reported that technical complications requiring re-interventions by a dentist occurred in around 25% of implants (14% chipping and 11% screw loosening) (Karlsson et al. 2018). If we consider this statistic in practical terms, every clinician can expect to have to manage technical complications in roughly one in four implants.

“Every clinician can expect to have to manage technical complications in roughly one in four implants”

When managing a complication, the first step is to identify the implant system and have the appropriate tools to work with it. Next, you need to try to find out why the complication occurred. It is often the case that the restoration needs to be removed in order to properly examine the site. The patient must be informed of the risks involved when solving the technical problems.

A breakdown analysis should be performed to prevent future complications. The speaker outlined a four-step plan for this:

  1. Ensure that the screws are compatible and appropriately torqued
  2. Check the passivity between the framework and the abutments/implants
  3. Examine the restoration/abutment/implant interfaces on a radiograph using the parallel technique
  4. Verify that there is proper distribution of occlusal contacts, that there are no interferences and check whether the patient has any habits or para-functions which could be problematic

Framework misfit is more harmful in implants than in teeth. Since implant-bone interface cannot adapt to framework misfits, it can lead to bending of the framework which puts tension on the screws and the veneering porcelain.

“Framework misfit is more harmful in implants than in teeth”

The speaker explained that we should aim to minimise misfit as much as possible, since a mismatch of 150μ greatly increases the risk of fractures in the veneering material. A recent experimental study (Löfgren et al. 2017) tested misfit in partial fixed implant-supported restorations. The authors found that when screwing frameworks, gaps were no more visible in poorly-fitting frameworks than in normal ones, however the tension inside was much greater in the misfits. They found that the more dynamic cycles there were, the more cracks appeared in the porcelain. Under functional cyclic loading, framework misfits will result in complications due to fatigue. We should therefore always strive for passive fit, and should check the framework with light force.

We all know that in theory, veneering porcelain must be supported. But this is often forgotten in practice. To prevent fractures, the framework should support the veneering porcelain and this must be checked radiographically. The speaker explained that the causes for fracture and screw loosening are in fact the same.

“To prevent fractures, the framework should support the veneering porcelain and this must be checked radiographically”

Preloading ensures screw stability, but only 10% of the torqueing force translates into preload. The rest is dissipated in the friction between components, and this effect is magnified in misfits. The more friction, the more resistance needs to be overcome by the torqueing force and ultimately less preloading reaches the screw.

The amount of torque should correlate with the exact amount of combined friction the implant, abutment and screw have together. No more, no less.

There are a number of copycat materials available which claim to be compatible with abutments and screws. However, these have been shown to present critical differences in contact areas from the originals (Mattheos et al. 2015). Consequently, the fit and friction are not the same and accordingly the required torque is not either. The speaker said that we should be wary of using these copycat abutments and screws.

“We should be wary of using copycat abutments and screws”

The speaker also said that when trying to retrieve broken components, it is crucial to read the manufacturers’ manual and follow their instructions regarding which tools to use. The corresponding component retrieval kit should be used, recommended steps followed diligently and the correct magnification used.