Treatment procedures

These are designed to reflect the simplicity of the overdenture modality, with clinical and technical requirements proving less demanding than for full fixed bridgework. Nonetheless, the clinician would be well advised to follow through a fuil clinical programme that includes articulation on a semi-adjustable articulator and try-in of dentures prior to insertion.

It is clear that a patient who presents with unsuccessful dentures, as in figure 7-4, may only require a degree of professional care to provide an optimised set of conventional dentures that offer a better fit and a more balanced occlusion. A great deal of information can be learnt from previous sets of dentures, such as hygiene ability and patient tolerance, which is often reflected by the number of sets the patient has in their shopping bag!!

It is important that an evaluation of the patient's requirements are well understood. If aesthetics alone are the source of disquiet, this may not necessarily be improved by implant support. A patient treatment planned for implants to solve such a presenting complaint may well prove dissatisfied with the result, even if chewing efficiency is markedly improved.

For bar splinted Implants, impression techniques are the same as for fixed bridge reconstruction utilising direct impression copings, abutments and cylinders (see chapter 5). The laboratory technique only varies in that the bar is usually prefabricated rather than cast and as such it is soldered to the prefabricated cylinders (Fig 7 - 5). For the ball {Fig 7-6) and magnet (Fig 7-7) attachments, the Astra Tech system recommends the use of the 45° Uni-Abutment™ (Fig 3 - 9), which acts to reduce the vertical infringement of the implant/abutment complex on the bulk of the denture. This compares to the bar splinted technique in which the vertical height of a bar and clip may compromise the available interocclusal space and hence the strength and bulk of the overdenture. As such it may be necessary to provide additional strength by means of a thinner palatal or lingual Co/Cr veneer. Impression techniques for the ball and magnet also vary, in that impressions are taken of the attachments themselves and not the abutments.

For the ball and socket a ball impression coping is placed over the ball attachment (Fig 7-8), which is screwed directly to the abutment and additionally secured by the use of a bonding agent, such as cyanoacry-late or Ceka Bond (Ceka NV, Antwerp, Belgium). Another alternative, is to use a one piece ball abutment, which screws directly into the fixture.

The copings remain within the impression on withdrawal. Ball abutment replicas can now be placed into the impression and incorporated into the master cast (Fig 7-9). For the magnet attachment, techniques are further simplified, with an elastic or hydrocolloid impression being taken directly over the magnet keepers, which are secured to the abutments in a similar manner. On pouring up the master cast, stone replicas are apparent (Fig 7-10). For the bar and ball attachment systems, the opposing components are activated and secured into place on the master cast (Fig 7-11), Forthe magnet system, magnets are secured to the stone replicas by means of cyanoacrylate (Fig 7-12). It is necessary to block out all undercuts and use spacers where indicated by the manufacturers, A baseplate incorporating the attachments is waxed up and processed in clear acrylic.

This protocol will allow an assessment of the accuracy of fit of the precision attachments, by means of a baseplate try-in (Fig 7-13). At this appointment it is necessary to determine not only the accurate location

Fig 7-4 A patient who presents with dentures like those pictured above, may only need a degree of professional care to provide a new optimised set of conventional dentures. If problems still persist, it is then reasonable to treatment plan for implants.

Fig 7-5 Prefabricated bars are usually available in 50 mm lengths. The bar is sectioned accordingly and soldered to the cylinders on the master model, A metalwork Iry-in will be necessary to ensure passive fit.

Fig 7-6 Ball attachments are ideally placed in the canine regions. Though two balls provide adequate retention, the placement of four balls prevents rocking of the denture, which can occur when the incisal table is anterior to Ihe Iwo balls.

Fig 7-7 Position of implants for magnet attachments should be well spread with preferably two magnets in the premolar regions and two in the canine regions. In the case shown all four implants were placed in the premaxilla, which was only possible by means of a nasal floor lift procedure. The remaining maxilla was of "egg shell" thickness.

Fig 7-8a (above) and Fig 7-8b (below) show how the ball Impression coping snaps over the ball attachment, but remains in the impression on withdrawal.

Fig 7-8b

Fig 7-9 Laboratory ball analogues (ball replicas) are seated in to the ball impression copings, prior to casting The master cast therefore incorporates balls that relate exactly to the clinical status.

Fig 7-10 No analogues are required for the flat top magnet keeper Instead a direct impression is cast, revealing stone replicas of the keepers. In an effort to increase the strength of the replicas, it is possible to pour cold cured acrylic into the impression of the keepers, prior to casting up.

Fig 7-11 Clips for the bar and balls are activated on the bench top and located on the master cast. Spacers may be recommended by the manufacturers. All undercuts will need to be blocked out in plaster, prior to waxing up the baseplate.

Fig 7-12 The magents are simply stuck to the stone or acrylic replicas using cyanoacrylate. The undercuts are blocked out in plaster prior to waxing up the baseplate.

Fig 7-13 Baseplates should be cured in clear acrylic so that a baseplate try-in will reveal the accurate location of the attachments and the displacement of tissues in the denture bearing area.

Fig 7-14 The incorporation of a midline diastema, slight imbrication or other imperfections will often serve to personalise the otherwise regimental set up so often characteristic of the standard denture, A balanced occlusion at the correct vertical dimension is of course paramount.

Fig 7-15 Aesthetics are defined not only by the textbook ideal, but by patient preference. The patient should be encouraged to take an active role in determining the iinal aesthetic result.

of the attachments but also the overall displacement of soft tissues in the denture bearing areas. The patient is afforded the first opportunity to appreciate the retentive powers of the future overdenture. In addition to baseplate try-in, a metalwork try-in is also indicated for bar splinted overdentures in order to assess passive fit. Any evidence of poor location of one or more cylinders. or the presence of pressure on securing the bar to the abutments, will necessitate sectioning, indexing and resoldering of the bar. Subsequent repositioning of the clips in the baseplate may also be necessary. It is now possibletoadd wax occlusal rims and proceed with bite registration as recommended in standard texts for the fabrication of conventional dentures.27 It is of course essential to register the correct occlusal plane and vertical occlusal dimension, along with a recording of midline, high smile line and canine lines within the wax rim. Bite registration and wax try-in are facilitated by the presence of well retained baseplates.

The fabrication of aesthetic dentures that provide adequate soft tissue support Is paramount and necessitates a wax try-in. To help achieve aesthetics thai wili serve to satisfy the patient, it is always useful to ask if any photographs are available showing the patient smiling with their natural teeth. Patients will often comment that they do not wish to reproduce the look of their natural teeth, however it can be equally as useful to know what the patient does not want by provision of the same photograph.

The incorporation of a midline diastema, slight imbrication or other imperfections will often serve to personalise the otherwise regimental set up so often characteristic of the standard denture (Fig 7-14). The inclusion of amalgam restorations, may also lend a more authentic character to the occlusal table. The insertion appointment should allow for an assessment of all parameters recorded during previous visits as listed in Table 7-2. The patient will need to be instructed on how to remove the prosthesis in a manner that does not differentially load the supporting implants with unfavourable tensile forces. The prosthesis should be withdrawn by applying thumb pressure eitherto the midline or with equal pressure either side of the midline. On first attempt patients will often be alarmed at the degree of retention and the perception of tensile forces on the implants. However, they soon become accustomed, preferring to remove the denture themselves on subsequent appointments, rather than allowing the clinician to remove them.

Recall Appointments

These appointments should be arranged for one week, one month and then six monthly. It will not be uncommon for the patient to complain of pressure sores after the first week. These should be highlight-

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