important that denture bases are extended into the full denture-bearing area in order to maximise stability and retention – and this will be discussed further in the following chapters.
Removable prostheses are indicated primarily for the following clinical reasons (Figure 2.1):
Restoring masticatory function
Restoring appearance
Restoring speech
Restoring soft tissue bulk and providing soft tissue support
Acclimatisation during the transition to becoming edentulous
Removable prostheses are often indicated for the following technical reasons:
Restoring long edentulous saddles
Restoring multiple short edentulous saddles
Providing posterior stability and improving occlusal load distribution
Preventing undesirable tooth movements
Rehabilitating to an increased vertical dimension
Facilitating functional anterior guidance
In order to prescribe diastemata between prosthetic teeth
To avoid preparing abutment teeth for fixed prostheses
To avoid cantilevering from root-treated teeth
To aid planning and diagnosis, especially prior to implant placement
Finally, but by no means least, our patients may well request removable prostheses in order to:
Improve aesthetics
Restore social confidence
Improve their eating experience
Restoring vs improving
Notice that most of the clinical rationale is based around restoring or rehabilitating, whilst patient requests often centre around improving. This important subtlety can easily be lost when negotiating informed consent. Correcting technical deficiencies and restoring clinical function does not necessarily result in a patient-perceived improvement. Again, moderating patient expectations is critical at each stage of treatment.
Quality of life
One of the most profound moments as an undergraduate was when Professor Janice Ellis (Newcastle) asked us whether we would rather lose a leg, and have a prosthetic replacement, or lose all of our teeth and wear a denture? At the time this seemed like a ridiculous comparison to make – but actually as clinicians we do become desensitised to seeing edentulous patients or partially dentate patients. The bottom line is whether we really sympathise with our patients or not. By working on a daily basis with edentulous patients who are struggling to cope, it is relatively easy to sympathise with the condition – even if we are unable to fully empathise. However, if we converse with denture-wearers less frequently, then there is a chance that we forget about what Professor Ellis termed the ‘edentulous plight’. This reiterates why it is important that we take the time to listen to what our patients want, and that they feel comfortable enough to tell us.
Risks of removable prostheses
One of the most significantly overlooked aspects of denture provision is the potential negative impact on the hard and soft tissues. Primarily this relates more to the provision of partial prostheses – and patients should be made aware as part of the planning process (through informed consent) of the risks and benefits of receiving dentures. Do not assume that because your patient is already wearing dentures that there is no need to reiterate the potential risks.
Whilst the jury is probably out in terms of the impact on periodontal disease, there is clear evidence of an increased risk of plaque accumulation, gingivitis and root caries for patients wearing partial prostheses. Many well-conducted studies show that the key to minimising soft and hard tissue damage whilst wearing dentures is to maintain an optimal level of oral hygiene, and to attend regular review and maintenance appointments; this is very much a shared responsibility between clinician and patient. The patient must understand this, and the discussion should be well documented in the case notes.
3 Stability and retention
Stability and retention are fundamental principles for the construction of removable prostheses – consequently, problems with retention and stability often underpin the patient's perception of the prostheses.
Stability
This can be defined as the resistance to horizontal displacement or rotation – in complete dentures, or around large saddles, this is often determined by the underlying anatomy and ridge form; this is primarily assessed in terms of the cross-sectional profile of the ridge, and how much support the ridge is able to provide before it distorts or displaces.
From time to time you will notice ridges that present with fibrous aspects, which have a tendency to displace on palpation and loading. You may notice these presentations being referred to as flabby ridges, but this expression is not so well received with patients! Fibrous elements can affect the whole aspect of the ridge, or just the crestal tissues. The impact this has on denture stability will be determined by which anatomical features are affected and is discussed further in Chapter 17.
When considering shorter or bounded saddles, elements of stability will be derived from the way in which the denture base contacts the hard tissues (either acrylic or cobalt chrome) and engages undercuts. This is largely determined by the ‘path of insertion’ (POI) and is discussed further in Chapter 32. To a degree, the stability of the prosthesis is therefore dependent on how effectively the neighbouring teeth can support lateral loading. This is known as ‘bracing’. If there is inadequate bony support for the abutment teeth then they will also move pathologically, and cause denture instability. This will cause further damage, possibly resulting in secondary occlusal trauma. These aspects will be discussed further, later in the book, in relation to partial denture planning.
Retention
This can be defined as the ability of the prosthesis to withstand removal in an axial direction – with complete dentures or areas over large saddles, this is often determined by the degree of coverage (employing cohesive and adhesive contact forces) and whether a border seal can be achieved. It is also important to consider the extensions of the prosthesis when assessing retention – whilst the prosthesis
