Problem solving in removable prosthodontics* Sybille K. Lechnert

(Received for publication October 1985.)

Success in removable prosthodontics depends on

1. The patient must be motivated to wear a

2. The patient’s neuromusculature control must

3. The denture must be technically adequate. Of these requirements, the dentist has full control

only of the third or least important aspect with the consequence that often little attention is paid to the first two. The importance of motivation and neuromuscular control, however, cannot be ignored. It is common knowledge that there are patients who enthusiastically wear inadequate dentures and also that there are those who cannot tolerate dentures which could be considered to be technically perfect. The problems which can be created in the areas of motivation and neuromus- cular control must be addressed before denture construction begins.

three things. These, in order of importance, are:

denture.

be such that the denture can be manipulated.

Complete denture motivation Since complete dentures are psychologically and

socially necessary for a great many people, it is tempting to assume that all edentulous patients want them. Further, it would be reasonable to suppose that if there were people who did not want dentures they would not present at the surgery for treatment. This premise is not strictly true, however. Some patients, particularly older patients, are not always in a position to make their own wishes readily known. The opinions of family, friends or staff of an institution should not influence a decision not to make a denture for a patient who feels no need for one.’

*From a Paper presented at the 24th Australian Dental Congress, Brisbane, 12-17 May 1985. ?Senior Lecturer in Prosthodontics, University of Sydney.

Other patients may not be able to cope with the loss of their dentition. Even though they may desperately want ‘teeth’, the whole concept of complete dentures horrifies them and they therefore cannot accept any denture made for them. Closely related to these is a third group who use their edentulous state as a convenient peg for a variety of psychological hang-ups. Such patients always want a new denture, but they do not want a denture which they can actually wear comfortably as it would interfere with the complex self-image they have built.

Patient motivation can best be assessed in a relaxed discussion session. Patients should be encouraged to talk about themselves and their dental problems. The dentist must learn to ‘hear between the lines’, assess the patient’s attitude to dentures and categorize the problems as dental or not. Vague, generalized complaints are more suspect than definite identifiable problems. A hostile attitude towards previous dental treatment is also often a danger sign.

While such a session is time consuming, an informed decision nor to accept a particular patient for treatment can save considerably more time and added frustration at a later date.

Neuromuscular co-ordination A denture is a foreign body and the instinctive

reaction of the oral musculature is to chew it up and swallow it, or to spit it out. To maintain a denture in the mouth during speech and to distin- guish during mastication which is a denture and which is food, which is to be held firmly in place while the other is swallowed, necessitates a highly sophisticated technique. Some patients have perfected this technique over many years and can do what may be termed ‘denture Olympics’, having the ability to eat corn on the cob with old ill-fitting dentures and other similar unlikely things.

While it is true that neuromuscular control is primarily input from the patient, it is possible for

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the old denture and the patient does not approve of them, the problems with those dentures may be quickly forgotten and the patient will remember only how stable, comfortable and efficient they were before adjustments were carried out. Those dentures will never again be the same as they are in the patient’s memory and the dentist could well be faced with the impossible task of making new dentures as comfortable as these old mythical ones.

By duplicating the old denture and making adjustments to the duplicate, it is possible to supply the patient with a basis for making a valid comparison between what has been worn and what may be expected with new dentures. A joint decision can then be made as to future procedures as the patient’s responses to the changes are gauged.

Duplicating an old denture for such diagnostic purposes is a relatively simple procedure.

1. Three grooves are cut into the back of an ordinary investment flask and the denture is invested using an elastic material such as irrever- sible hydrocolloid as investment instead of plaster (Fig. la). The lower half of the investing mould should be lubricated with petroleum jelly as a separating medium before investing is completed.

2. After investing is completed, the halves are separated and the denture removed and returned to the patient. The indentations left by the teeth are filled with tooth-coloured self-polymerizing acrylic resin.

3. When this has set it is removed and the gingival margin area is trimmed back to leave a chamfered space between the acrylic and the investing material (Fig. lb). 4. Channels are cut in the hydrocolloid from the

denture to the grooves in the flask. The two outer channels will serve as vents (Fig. lc).

5. The flask is reassembled and self-polymerizing pour acrylic* is poured into the centre hole until it rises in the vent holes (Fig. Id). The flask may be held together with strong elastic bands, keeping the sprue hole uppermost until the acrylic has set.

6. The denture is then trimmed, smoothed and polished (Fig. le).

If an upper denture is being duplicated, care must be taken to avoid overlapping of colours at the gingival margins in the anterior region. In other areas, such overlapping is not important.

The most important adjustment which may be tried on an old denture or duplicated old denture is re-establishment of occlusal integrity by

‘Kulzer Palaprcss. Kulzer Australia Ltd, North Sydney.

Australian Dental Journal 1986;31:4.

adjustment of the occlusal table. It is interesting to note that this alone often improves fit, stability and even retention in the patient’s eyes. Relining the denture with temporary lining materials such as tissue conditioners may not be necessary unless tissue damage is evident.

Other important adjustments may include changes in the inclination of the occlusal plane to improve the direction of functional forces and also changes in buccolingual tooth positions and polished surface contours. These changes can easily be accomplished by the addition or removal of resin.

Where an old denture is not available for such experimentation, but where the prognosis is doubtful because of physiologic or psychologic difficulties a ‘diagnostic denture’ can be a very useful tool. Such a denture is made like any other denture except that it is composed entirely of acrylic so that adjustments to it can be more easily carried out. Its advantages lie in the fact that the ‘diagnosis’ part of it is presented as a diagnosis of whether the patient will be able to cope with it or not. If this purpose can be made clear to the patient, it puts the onus of manipulating the denture squarely on the patient where it belongs. Any major adjustments carried out on a diagnostic denture come under the heading of ‘diagnosis’. Any major adjustments which have to be done to a ‘final’ denture could quite easily come under the heading of ‘failure’.

When success has been achieved with a duplicate old denture or a diagnostic denture, a new denture can be made which copies its extensions, contours and occlusal table (Fig. 2).

If the adjustments carried out do not overcome any problems and satisfy the patient, then two possi- bilities exist:

1. The patient is ‘unsatisfiable’; 2. The dentist does not have the necessary

knowledge or skills to cope with this particular case. In either event it would be to no one’s advantage

to proceed in such circumstances.

Technical considerations The most common problems found in removable

prosthodontics relate to the complete lower denture and concern instability and ‘sore spots’, the two often being related. As regards instability, it is important to help the patient by planning polished surface contours and buccolingual tooth placement to lie in the neutral zone between tongue and

This is especially true for the resorbed mandible where discussions of tooth placement in relation to ‘the ridge’ become meaningless. Research has shown that there is a natural space in the oral

275

Fig. 2.-Diagnostic denture and final denture which has been constructed to follow extensions, contours, and occlusion of

successful diagnostic denture.

Fig. 3.-Typical variations in flange width found in resorbed mandibles. a, Distolingual: very thin. b, Mesiolingual: shorter and wider. c, Midlingual: restricted. d, Distobuccal: restricted. e, Midbuccal: wide and convex. f, Anterior: variable, depending

on mobility of orbicularis oris.

cavity both around a dentition and where a patient is edentulous and that this space is remarkably consistent in its outline.2 The denture should fill this space to gain as broad a bearing area as possible and will thus have flanges which vary both in length and thickness (Fig. 3).

The position of a natural tooth in relation to the underlying alveolus can be seen in Fig. 4a. Forces of mastication are directed through the root and into the alveolus. If a large ridge remains after tooth extraction, artifical tooth placement can copy nature to give a similar result. However, where gross ridge resorption has occurred, such tooth placement will only give stability while an actual bolus of food is exerting pressure on the tooth. At all other times,

for example, at rest or during speech and swallowing, the denture will be unstable as it is lifted by the force of the tongue in the posterior part of the mouth (Fig. 4b).

Placing the teeth buccally while still preserving ‘anatomic’ contours on the buccal surface may allow stability during rest and speech but will cause tilting of the denture during mastication and possible soreness at the periphery (Fig. 4c).

T o achieve a successful result for the grossly resorbed mandible, the denture must have a broad base, taking advantage of the entire area available. The polished surface contours must be a record of muscle function rather than anatomic correctness, and buccolingual tooth position must be in the centre of the denture bearing area (Fig. 4d). This may entail the use of posterior teeth which are very narrow buccolingually.

‘Sore spots’ or areas of mucosal irritation are of two kinds. Those caused by an inaccuracy of the tissue-fitting surface of the acrylic and those caused by a shunting of the denture over the tissues. The latter are usually caused by an occlusal discrepancy and cannot be successfully eliminated by grinding away the tissue fitting surface of the denture. It is not always a simple matter to differentiate between such areas. One way is to check with finger pressure whether the denture hurts when it is seated, that is, in its correct relationship to the underlying mucosa, or whether it only hurts under occlusal loading, that is, it is hurting because the occlusion has forced the denture into an incorrect position. Sore spots may be located using disclosing wax.t Small localized areas showing through the wax are

tA mixture of 3 parts Keds Disclosing Wax and 1 part petroleum jelly.

276 Australian Dental Journal 1986;31:4.

a b

C d

Fig. 4. -a, First molar showing forces of occlusion directed into alveolus. b, Denture duplicating natural tooth position directs forces of occlusion correctly into bone but risks dislodgement by forces of tongue. c, Denture tooth placed buccally into neutral zone but preserving ‘anatomic’ buccal contour will tilt buccally under occlusal load. d, Denture with narrow teeth placed in neutral zone and base widened to take advantage of full bearing

area is stable at rest and during function.

likely to be tissue surface discrepancies or overex- tensions. Larger diffuse areas on and around the denture bearing areas are likely to be occlusion related.

The most common problem encountered with complete maxillary dentures is lack of retention. This is most often due to under extension in the posterior region. Dentures are sometimes cut back at the request of a patient who feels they are causing nausea. If the posterior extension of the denture is on the ‘uh’line, cutting it back will more than likely compound the problem by causing loss of retention, with consequent movement in this vulnerable area. Unless the patient has an abnormal gag reflex, feelings of nausea are as often due to stimulation of the posterior part of the dorsum of the tongue as to stimulation of the soft palate. If the denture extends to, and not beyond, the ‘ah’ line, the patient’s nausea is probably due to tongue stimu- lation and can usually be relieved by thinning of the posterior border to allow a smooth transition from the denture to the surrounding tissues.

Palatally placed teeth or an excessively low occlusal plane can also contribute to feelings of nausea.

A denture which is very retentive at rest but dislodges during speech may actually be over- extended in the post dam region. The retention observed at rest will be found to have its basis in compression of the soft palate. During function the soft palate lifts away from the denture, the seal is broken and the denture dislodges. In such a case it is necessary to reduce the over-extension and relocate a new post dam seal.

Other causes of lack of retention are flanges which are over or underextended. Not only the length, but the width of the peripheries must be correctly reproduced if an adequate seal is to be maintained.

As with mandibular dentures, incorrect tooth placement will cause tongue interference where teeth are set too far palatally, or mechanical insta- bility where they are set too far buccally beyond the confines of the denture base. Occlusal discrepancies will also contribute to poor retention.

Occlusion The ability to record maxillo-mandibular

relationship, transfer the record to an articulator, and establish balanced occlusion is arguably the single most important technical consideration in complete denture work. Ill-fitting, over- or under- extended dentures often feel as if they fit better and have better retention when the occlusion is adjusted. Even ‘roaming sore spots’ tend to diasppear.

While it is not possible to cover so large a subject as occlusion in this paper, there are several points particularly germaine to problems associated with complete dentures.

The current extensive interest in occlusal correction for the dentate patient has tended to cloud the special problems pertinent to recording occlusion for the edentulous one. It is well to remember that in taking records for the edentulous patient one has not only to establish the correct relationship of the mandible to the maxilla, but also to maintain the correct relationship of the denture bases to the underlying mucosa. This can most easily be done with the patient sitting up and with the dentist standing in front and facing the patient. To stabilize a lower denture base on a resorbed alveolus, it helps to rest the forefingers on small shelves of wax added to the buccal surface of the denture in the second bicuspid/first molar region while recording centric (Trebitsch F. Personal communication.) (Fig. 5). These wax shelves will not form part of the base. They are merely a helpful device which is added just before the record is taken

Australian Dental Journal 1986;31:4 277

Fig. 5.- Wax shelves used to stabilize lower denture while centric relation is recorded.

and removed again immediately afterward. This addition can be used at any stage during or after denture construction and is extremely effective in preventing the base from sliding away over the mucosa.

Another difficult situation is where resorption of the maxillary alveolus has left a flabby ridge so that shunting of the entire denture base and underlying tissues occurs under even the lightest pressure. In such a case it is often impossible to prevent small movements of the upper base in the last moment of closure when recording centric by the conven- tional means of closure into softened wax. In these cases the following method may be used. (Graham CH. Personal communication.)

Softened wax cones are placed bilaterally in the mid-occlusal areas and a record is taken with closure stopping at a point where the teeth (or rims) are approximately 1 mm apart at their closest point. The cones are chilled and carved to give point contact with the opposing denture. These point contacts then act as stabilizing stops while centric is recorded using a non-compressible material$ (Fig. 6 ) . After recording of maxillo-mandibular relationship and transfer of the dentures to an artic- ulator, adjustment should achieve not only a maximum distribution of contacts in centric relation, but also smooth unhampered movements into eccentric positions to give balanced occlusion.

tKerr's Bite Registration Paste.

Fig. 6.-a, Record taken on small wax cones placed bilaterally in mid occlusal areas, for example, second bicuspid. Closure is stopped short of tooth contact. Wax cones are then chilled and carved to give point contact with the opposing occlusion. b, Centric is recorded using bite registration paste. c, C e n t r i record showing small stabilizing wax stops in centre of occlusal table.

c.

270 Australian Dental Journal 1986;31:4.

Fig. 7.-a, Double layer of softened wax is placed on the occlusal table and pushed well down over the remaining dentition. b, Centric relationship is recorded and the wax is chilled. c, Indentations in the wax record the remaining dentition in correct relationship with the denture. d, Mounted dentures with plaster filling indentations in the wax made by remaining dentition.

e, Mounted dentures with wax removed ready for occlusal adjustments to be carried out.

Partial dentures A recent survey on partial dentures highlights the

fact that here too, patient adaptation and attitude are extremely important in the successful wearing of denture^.^.^ Patients who had previously worn a denture successfully were much more likely to be satisfied than those who had been unhappy with a previous denture or who had never had one.

Technically, the most significant factor contributing to patient comfort was the ability to achieve centric occlusal contacts between the

natural dentition and the opposing occlusal table. Such contact should therefore be provided wherever possible.

Other problem areas are distal extension saddles. Where the patient has a large distal extension saddle, denture design must be concerned mainly with saddle design rather than focusing only on the few remaining teeth. Such a saddle should be treated as a section of a complete denture. Impressions should be taken in a custom tray so that stress bearing areas and both the length and

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contour of peripheral extensions can be recorded with greenstick compound. The impression material used in such a prepared tray must be capable of acting as a wash over the greensticked areas. A rubber base or silicone material would therefore be preferable to an irreversible hydrocolloid. As with complete dentures particular care must also be given to buccolingual tooth placement and polished surface contours.

A removable partial denture must be passively stable and able to be retained by the patient even without clasps. The clasps can then add an extra measure of security. They should never be used to attempt to retain an unstable denture against the forces of the musculature and/or occlusion.

Achieving precise occlusal contacts is of prime importance but can pose some problems with the large distal extension saddle. Intra-oral occlusal adjustment is very often the method of choice for tooth-bounded saddles but can become arduous and often inaccurate when dealing with distal extension saddles. Even when the dentures are to be mounted on an articulator, where very few natural teeth remain the saddle areas of the denture will often not fit the master case in precisely the same manner that it fits the mouth. It is necessary to use a method for mounting the dentures which not only records centric relationship but at the same time establishes the correct relationship of the denture to the remaining dentition. To record these relationships, a double roll of softened wax is placed onto the occlusal table and pushed well down over the remaining dentition (Fig. 7a). Centric relationship is then recorded (Fig. 7b) and the wax is chilled before the denture is removed from the mouth (Fig. 7c). The denture can then be mounted using this record while at the same time the indentations left by the teeth are filled with the plaster (Fig. 7d). When the plaster has set, the wax is removed (Fig. 7e) and occlusal adjustments can be carried out.

Summary To solve problems in removable prosthodontics

it is necessary to establish harmony in three areas. The first area is with the patient’s psyche. More

than in any other field of dentistry, removable prosthodontics needs good rapport between the patient and the dentist. There must also be rapport between the patient and the concept of a denture.

The second area is with the surrounding musculature. It is necessary to find the neutral zone and place in it a denture which does not interfere with muscular movement and yet which takes full advantage of all available bearing areas.

The third area is harmony between the dentures themselves: harmony of occlusion.

If harmony can indeed be achieved in these three areas then, with a little luck, there should be very few problems left to solve.

References 1 .

2.

3.

4 .

5.

6.

Lechner SK. Overcoming adaptational problems with complete and partial dentures. Int Dent J 1982; 32: 32-38. Lechner SK. Prosthetic management of the geriatric patient. Aust Dent J 1974; 19: 17-24. Beresin VE, Schiesser J. The neutral zone in complete and partial dentures. 2nd edn. St. Louis: CV Mosby, 1978. Schiesser FJ. Neutral zone and polished surface contours. J Prosthet Dent 1964; 14: 856-65. Lechner SK. A longitudinal survey of removable partial dentures. I. Patient assessment of dentures. Aust Dent J 1985;

Breustedt A. Physiological and social factors of importance for the older edentulous patient. Int Dent J 1979; 29: 276-84.

30: 112-7.

Requests for reprints: Department of Prosthodontics,

Faculty of Dentistry, University of Sydney,

2 Chalmers Street, Surry Hills, NSW 2000.

280 Australian Dental Journal 1986;31:4.