A Clinical Overview of Removable Prostheses 3. Principles of Design for Removable Partial Dentures

L N E T IPCRS O S T H O D O N T I C S R E M O V A B L E RP ER M O SOTVH A OB DO

A Clinical Overview of Removable Prostheses: 3. Principles of Design for Removable Partial Dentures J. FRASER MCCORD, NICK J.A. GREY, RAYMOND B. WINSTANLEY AND ANTHONY JOHNSON Supporting Elements

Abstract: Removable partial dentures (RPDs) should not be made for patients unless they are necessary. Most partial dentures have the potential to cause some damage to the teeth and supporting tissues, however well they are designed and constructed; the criteria for selecting such devices were described in a previous article. In general there is merit in, wherever possible, reducing tissue coverage as much as possible when RPDs are being planned. This article, the third in a series on the prescription of RPDs, discusses the design principles involved. Dent Update 2002; 29: 474–481

Clinical Relevance: Correct design of RPDs will aid retention and minimize the risk of damage to supporting teeth and tissues.

These may be rests on the crowns of teeth, coronal restorations, root faces of teeth, mucosa or implants. Retaining Elements These are termed direct retainers and may be clasps, precision retainers, guiding plates acting on surfaces/ planes (e.g. in the RestPlane I-bar (RPI) system) or, on occasion, resilient insertions. As denture adhesives are not planned components of RPDs, they are excluded in this context. Connecting Elements

B

efore discussing basic principles of design of removable partial dentures (RPDs), it is important to discuss rudimentary aspects of such devices – their classification and constituent parts. The common classification system used in the UK for partial dentures is that devised by Kennedy.1 This classification, which will be familiar to most readers, is based empirically on the frequency of the partially edentulous state. It is descriptive of the J. Fraser McCord, BDS, DDS, FDS, DRD RCS (Edin.), FDS RCS (Eng.), CBiol, MIBiol, Professor and Head of Unit of Prosthodontics, University Dental Hospital of Manchester, Nick J.A. Grey, BDS, MDSc, PhD, FDS, DRD, MRD RCS (Edin.), Consultant/Honorary Senior Lecturer in Restorative Dentistry, Edinburgh Dental Institute, Raymond B.Winstanley,BDS,MDS,FDS RCS (Edin.), Senior Lecturer/Honorary Consultant in Restorative Dentistry, Charles Clifford Dental School, Sheffield, and Anthony Johnson, MMedSci, PhD, Lecturer in Dental Technology, Charles Clifford Dental School, Sheffield.

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anatomical form of the respective arch and merely provides an overall description of where the saddles are without outlining the size of the saddles or, indeed, of describing the denture. The classification advocated by Beckett2 outlines the source/s of support (see Table 1).

These may be major connectors, which join up the saddles, or minor connectors that join rests or direct retainers to the major connector.

Components of Partial Dentures

Denture Base Material and Flange The denture base material and denture flange may serve as one or more of the above components.

A sound understanding of the components of partial dentures, and the different potential forms for each component, is essential if dentures are to be designed appropriately for each patient. What is appropriate can be determined only by thorough examination of the patient and listening to their wishes and expectations – dentures cannot be designed appropriately by scrutinizing study casts in isolation and abdicating responsibility to the technician.

Anti-rotational Components Often referred to as indirect retainers, although they also function as supporting elements for the framework.

PRINCIPLES OF DESIGN Once it has been agreed that a RPD is to be fitted, the dentist should work to a rubric or skeleton when designing the prostheses, whether fixed or removable. We recommend the following: 1. Outline the saddles and determine which ones need to be restored. 2. Decide on the nature of the support. Dental Update – December 2002

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Classification Class or type

Comments/modifications

Kennedy

Class Class Class Class

Bilateral free-end saddles Unilateral free-end saddle Bounded saddle – posterior Anterior bounded saddle

Beckett

Tooth–borne Tissue (mucosa) -borne Tooth and tissue -borne

I II III IV

mucosa covering the residual ridge(s) as the denture will tend to sink into the tissues and damage the periodontal tissues of the remaining teeth with time. If the teeth provide some support, then the sinking of the denture into the tissues is, in theory, minimized. Hence it is the design rather than the material which is important in this context (Figure 1). The advantages of acrylic resinbased RPDs primarily relate to ease of construction, lower production cost and their relative ease of adjustment/ alteration. They are light in weight but usually cover more tissue than a corresponding metal denture because of their inferior strength characteristics; in consequence they tend to be thicker than cobalt-chromium bases. The fitting surface is difficult to clean owing to its relatively rough finish, and it tends to take up stain more easily. However, in many cases it is possible to design a hygienic acrylic resin upper denture with a design similar to (but covering more tissue than) a metal denture of a plate design (Figure 2). Metal dentures, it is claimed, offer the advantage of transmission of temperature to the underlying tissues, but once again the fitting surface tends to be relatively rough because it is not possible to polish it without losing the accuracy of fit (not applicable to saddle areas which are resin covered). It is possible to make all acrylic partial dentures partly tooth supported by ensuring the palatal or lingual plate finishes on or above the survey line on the teeth, but this practice is considered risky as the resin may

Functional descriptor only – gives no indication of position in the arch

Table 1. Summary of the classification of dentures according to Kennedy1 and Beckett.2

3. Decide on how best to maximize retention. 4. Decide on how best to unite the saddles. These four steps are identical for both fixed and removable prostheses. 5. Decide whether anti-rotational devices are required and, if so, how this is achieved. 6. Re-assess for hygiene and, with an eye on the future, maintenance of the prosthesis (e.g. relining, repair and replacement of components of precision attachments) and the prognosis of the remaining dentition. 7. Decide on how the occlusion is to be planned and, at the same time, plan with appearance in mind. In the UK, it tends not to be the practice to cast primary impressions in the surgery, yet such a simple task is taught to every undergraduate and the advantages of casting primary impressions on-site must outweigh any potential disadvantages. The ability to cast study impressions on the premises facilitates denture design as study casts would be readily available to place adjacent to radiographs and other patient-related data when planning an appropriate design. Most dentists do not actually design partial dentures,3,4,5 preferring to delegate this task to the technicians; yet the responsibility for the design is a clinical one. Currently, only the dental surgeon is licensed to examine the patient, assess radiographs, interpret the condition of the mouth and, ultimately, fit the denture. Dental Update – December 2002

We endorse the philosophy, however, that provision of successful partial dentures is a team effort, and liaison with laboratory staff is essential to ensure the proposed design is technically feasible. This is particularly important if an unusual or more complex design is being considered.

MATERIALS The two main types of material used for construction of the base of RPDs are acrylic resin and cobalt-chromium alloys. The former is often thought to be ‘second best’ and the latter better but this is not necessarily the case. We consider that the selection of the most appropriate design is probably more important. The term ‘gum stripper’ is often associated with acrylic resin dentures but this tends to be related particularly to the mandibular partial denture, where the non-tooth supporting tissues are poorer, quantitatively and qualitatively, than in the maxilla. Any partial denture in the lower jaw may act as a ‘gum stripper’ if it is supported only by the

a

b

Figure 1. (a) Lower ‘gum-stripper’ partial denture. (b) Damage to the underlying tissues caused by this denture.

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a

b

Figure 2. Hygienic upper acrylic resin partial denture. (a) Facial view. (b) Palatal view.

fracture. It is also possible to incorporate cast gold rests into acrylic dentures but the cost of doing so is probably greater than making a cast cobalt-chromium base in the first place. Denture teeth for partial dentures are usually made of acrylic resin, rather than porcelain, because it is easier to grind them to fit in with the occlusion and apply them to the framework. Porcelain is not only much harder to adjust, but there is the danger of removing the diatoric holes which provide retention to the acrylic resin. In many cases of small-span saddles posteriorly, a metal ‘sanitary’-type

Figure 3. Metal ‘sanitary’ pontic between the maxillary molars.

pontic may be more appropriate with a metal partial denture rather than a conventional resin saddle (Figure 3). When designing metal dentures that incorporate anterior saddles, particularly where there is a ‘close bite’, it is preferable to have metal protection for the palatal/cingulum aspects of the denture teeth in order to prevent them being dislodged. The appearance of such a denture is of acrylic resin joining the anterior denture teeth to the metal major connector with an underlying meshwork for retention (Figure 4). This area of the denture is potentially weak and will offer little resistance to dislodgement. The technician needs to see the final position of the denture teeth if he or she is to know exactly how far to extend the waxing for the metalwork to provide protection. This necessitates an extra clinical stage, with a try-in (in wax on a baseplate) before the metalwork is constructed (Figure 5) – this was discussed in the second article in this series.6

DESIGN OF THE RPD

go, and it enables the technician to overcome one of the problems of the prescription form – rotated teeth or spaces smaller than the missing teeth can be indicated in the design more clearly. Once it has been decided that a partial denture is necessary, the study casts should be articulated and the occlusion examined to confirm the clinical examination and identify any problems this may pose for the construction of the RPD (e.g. space for components of the RPD such as occlusal rests, clasp assemblies etc.). Study casts must be accurate; alginate (irreversible hydrocolloid) is the most commonly used impression material and ought therefore to be cast within 10 minutes of removal from the mouth or kept at the correct humidity until it can be cast. Distortion, blows on the occluding surfaces of the teeth and general lack of detail are not conducive to satisfactory partial denture design.6 However, accuracy is needed only in those areas directly related to where the denture will fit, or the occlusion. A blow or deficiency in the sulcus related to teeth that will not involve the

Figure 5. Upper RPD with a cobalt-chromium backing for the denture teeth to prevent them being dislodged by occlusal forces.

General Considerations

Figure 4. Acrylic resin joining the anterior denture teeth to the metal framework. The cobalt-chromium meshwork can be seen through the PMMA and the thin resinous connector tends to be prone to fracture. 476

Most laboratories will provide prescription forms for the design to be outlined, and some dentists may provide their own. The exact format of the form is unimportant, provided the necessary information can be included. We prefer to draw the design on the study cast/s (Figure 6) as well as on the prescription form. In this way it can be seen exactly where each component will

Figure 6. The partial denture design has been drawn on the study cast. Dental Update – December 2002

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Figure 7. Lingual bar.

denture is not of major importance. Care with casting the impression is also necessary to help prevent defects. Pouring the mix in from one side and letting the stone run around the teeth in the arch while vibrating the impression helps to prevent air blows. In both surgery and plaster room, care should be taken to prevent distortion of the heels of the impression. The areas of tooth preparation can be noted, and the depth of rest seats related to the occlusion. It is necessary at this stage to make use of the surveyor and mark the path of insertion of the denture, undercuts on the teeth, depth of any undercuts, and the presence of unwanted undercuts, which will need to be blocked out. The first article in the series7 referred to the need to assess the patient’s oral state and the perceived ability of remaining teeth and soft tissues to support a prosthesis. The patient’s history of denture wearing is important. If they have previously worn dentures satisfactorily, it may be sensible to make new ones to the same design as the old one provided its design was conducive to good oral health. If, in the estimation of the clinician, a previous design was poor but no damage has been caused and the patient has worn it for a long time without problems, there is a good case to be made for reproducing this design in the new denture. However, if it was predisposing to disease, a more satisfactory design should be chosen and the reasons explained to the patient.

Outlining the Saddles This is a good practice, as it enables the clinician to identify the edentulous 478

area(s) present and to determine the places where it is intended to place RPD saddle areas.7 The intended saddles areas are perhaps the easiest part of the design, since these are the areas of the missing teeth. With distal extension dentures, the saddle should extend around the tuberosities with upper RPDs, and up onto the retromolar pads with lower RPDs. These landmarks should normally be combined with maximum extension into the functional depth of the buccal and lingual sulci. Exceptions may be where the bounded saddles are short or where it has been decided to ‘gum fit’ the denture teeth when large alveolar undercuts are placed.

Selecting the Major Connector Drawing the design on the study cast enables all the denture components and their position to be identified so that the technician can reproduce the design exactly. Once the material of the denture has been decided upon, the major connector can be drawn and the particular type chosen depending on the position of the edentulous saddles. Maxilla In the maxilla, if the major connector is selected to be acrylic, then it will most probably be a plate design (even the spoon denture is essentially a plate design). However, with a stronger material as a major connector (e.g. cobalt-chromium alloy), then a larger range of options is available – a plate, strap, horseshoe or ring design. l The ring design, and all bar types of major connector, tends to have a number of edges noticeable to the tongue, and are thicker although they cover less tissue. Plate designs tend to be thinner and less noticeable, but do cover a wider area of the palate. l With anterior saddles, a spoon denture or an ‘every’ type denture may be suitable, depending upon the number of anterior teeth missing and the presence of

posterior edentulous saddles. l A ‘T’ design of denture is suitable for metal or acrylic in many cases of anterior missing teeth. l Where there is a torus, or the patient wishes to avoid too much palatal coverage, a horseshoe design or ring design is indicated. The authors’ preference where posterior teeth only are missing is a mid-palatal plate, the width and tissue coverage depending on the number of teeth being replaced. Mandible There are a number of choices for major connector in the mandible. With acrylic resin, a plate design may be used, but this should be restricted to a temporary or transitional partial denture because of the potential gingival damage. A more satisfactory connector in these cases is the wrought stainless steel lingual bar. For a ‘permanent’ lower partial denture cast metal should be used as the major connector, to enable as much tooth support as necessary (and possible) to be incorporated into the design, thus minimizing the possibility of ‘gum stripping’. The lingual bar is hygienic since it does not cover over the teeth (Figure 7), but a depth of functional lingual sulcus of at least 8 mm is required to combine stability of the denture with health to the remaining dentition. The lingual bar is considered to be more noticeable to the tongue, and cannot act, on its own, as an indirect retainer with distal extension cases. It is D-shaped in cross-section and requires a width from the lingual gingival margins of the remaining incisor teeth to the reflection of the lingual sulcus of 8 mm. The lingual plate is considered more acceptable to the tongue and can act as an indirect retainer, but it does of course cover over the lingual surfaces of the lower anterior teeth, thus predisposing to caries and gingival/ periodontal irritation. The appearance may also be poor if there is spacing between the teeth. A good alternative is the sublingual Dental Update – December 2002

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Outlining Support

Figure 8. Sublingual bar.

bar (Figure 8), which fits in the lingual pouch beneath the tongue and is less noticeable. Although more bulky than a lingual bar (it is half pear-shaped and requires a 10 mm space from lingual gingival margins to the lingual reflection), it is much more rigid. However, careful attention must be paid to the impression technique, using functional tongue movements to roll the impression material while it is setting. The technician must preserve this roll to safeguard denture stability. The dental bar may be used where there is a limited lingual sulcus, but as this fits onto the cingulum region of the teeth and has to be bulky for strength, it may not be readily acceptable to the patient. The labial or buccal bar is recommended for lingually inclined lower anterior teeth such as Skeletal III cases (Figure 9) but usually there are more acceptable alternatives. The Kennedy bar (Figure 10) is a combination of a continuous clasp on the lingual surfaces of the lower anterior teeth and a lingual bar. This type of major connector tends not to be well perceived by patients owing to the number of edges that are in contact with the tongue.8

Once the major connector has been drawn on the cast, the positions of any rests are also drawn and joined to the major connector with the minor connectors. Molars, premolars and canines are the most suitable teeth for rests, but incisal rests are valuable for ensuring forces are directed down the long axes of the teeth (although they are restricted to patients for whom aesthetics is not a high priority). It is often thought that rest seats should be prepared only to ensure there is sufficient room from the opposing tooth or teeth. However, preparation is a prerequisite to direct forces down the long axes of the teeth, because these are the forces teeth can withstand much better than lateral or ‘jiggling’ forces. Additionally, a definite seat ensures there are no sharp edges to irritate the tongue. (For details on preparation of occlusal rests, readers are referred to standard textbooks of prosthodontics.) Rests also act as indirect retainers for Kennedy Class I and Class IV partial dentures (see below). Where crowns are being provided, conventional wisdom would indicate that the wax try-in be made so that the supporting and retaining elements of the RPD may be incorporated into the crowns.

Retaining Elements Direct retainers are any components that provide retention for a partial denture – for example, frictional retention of the denture base against the teeth will give direct retention. However, the term is usually understood to mean the clasps used for retention. Two broad divisions of clasp are gingivally approaching and occlusally approaching, referring to their relationship to the clinical crowns of the abutment teeth. There are many weird and wonderful designs of clasp, and they can be very confusing.

Figure 10. Kennedy bar.

gingival tissues and thereby having a tendency to irritate them as well as leading to the accumulation of food. They are more easily distorted with misuse, and are not aesthetically pleasing. However, they do work effectively, especially on premolars. The simplest type of clasp in this category is the ‘I’-bar type (Figure 11). Occlusally Approaching Clasps Occlusally approaching clasps approach the undercut on the tooth from an occlusal position. They are intended to stay closely in contact with the tooth but, again, are not aesthetically pleasing. From the myriad of designs, two types are usually preferred: l the single-arm clasp (which, together with an occlusal rest and a reciprocal arm, is called a three arm clasp; Figure 12); and l the ring clasp. The latter is particularly useful on lone-standing molars, the retentive tip engaging lingually on the lower and buccally on the upper owing to the way in which these teeth tend to tilt when they do not have an adjacent

Gingivally Approaching Clasps

Figure 9. Labial/buccal bar. This example is incorporated in a Swinglock design. Dental Update – December 2002

Gingivally approaching clasps, also known as bar clasps, approach the undercut on the tooth from a gingival position, passing over the alveolar and

Figure 11. I-bar on distal aspect of anterior abutment tooth. 479

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Figure 12. Three-arm clasp on the maxillary second molars. Note the anterior placement of the retaining clasp tips. The occlusal rests and the posterior palatal bar will thus serve as indirect retainers

tooth in contact mesially. We do not recommend the use of cast cobalt-chromium occlusally approaching clasps on premolar retainers since they are too short to be flexible or too thin and liable to fracture. It would appear, however that, in spite of the recommendations by Bates,9 this design of clasp is incorporated into many designs. Clasps It should be emphasized at this stage that clasps are passive when the denture is in the mouth. They become active only on removal and insertion of the denture, when passing out of or into undercuts on the teeth. For this reason, they require reciprocation with a rigid component on the other side of the tooth to the direct retainer in order to counteract lateral forces exerted on the teeth by the clasps when the denture is removed and inserted. The most common ways of achieving reciprocation use a component similar to a single arm retentive clasp on the other side of the tooth (but which is rigid) or fit the denture base against the tooth on the opposite side to the retentive clasp. A ring clasp gains its reciprocation from the rigid arm being on the opposite side of the tooth from the retentive tip, or via a cingulum rest if the tooth concerned is a canine. With all reciprocation, the reciprocal elements should act against a vertical surface on the tooth so that, as the denture starts to be removed, the reciprocal element does not lose contact with the side of the tooth; it should be 480

at the same vertical level as the retentive tip for the same reason. This will entail tooth preparation of the teeth to be clasped, which will also provide guide planes for improved seating of the denture. Reciprocation can also be obtained via the denture base and may take the form of a rest or a minor connector. It is doubtless redundant to state that true reciprocation is possible only when (replacement) crowns are milled to receive the components of a denture. The position of clasps, together with the reciprocation, rests (see below), and the minor connectors joining them to the denture base can now be drawn on the study cast. The type of clasp to be used, and its material, will depend on the amount of undercut available on the tooth, as determined when the study casts were evaluated with the surveyor. Whenever possible, clasps should be designed to be clear of the gingival margins to reduce the possibility of trauma and plaque accumulation (see first article, Figure 27). Composite additions to the crowns of natural teeth where the undercut is near the gingivae are worth considering in these circumstances.

Incorporation of Anti-rotation Components The final components of the denture base to be drawn on the design of the RPD are the indirect retainers. These are not necessary with all partial dentures, but are valuable with distal extension (free end saddle) partial dentures and those with anterior saddles. The easiest way to understand the principle of indirect retention is to visualize a bilateral free end saddle lower partial denture with the second premolars and all the molars missing and a lingual bar major connector. Clasps on the first premolars will give an axis of direct retention as an imaginary line between them. If the patient chews something sticky the saddles will lift up, rotating around the line of direct retention. On the opposite side of this axis the lingual bar will rotate downwards.

Figure 13. There is no need to restore the edentulous spans with two premolars and two molars; the occlusal table should be reduced in width and length to reduce occlusal forces on the residual ridges.

In the same partial denture but using a lingual plate as the major connector, the connector cannot rotate downwards as the plate rests on the lingual surfaces of the lower anterior teeth which are (relatively) incompressible. The saddles therefore cannot rotate upwards. In this case the lingual plate is acting as an indirect retainer as well as the major connector. Obviously this is all relative, and with the best will in the world a bilateral free end saddle lower partial denture will still tend to lift when eating sticky foods - but the indirect retention will help to reduce this tendency. Other examples of indirect retainers are rests so, when designing the support for a partial denture, the requirement for indirect retention should be borne in mind when positioning the rests (on a horizontal surface). In the maxilla, an extension of the denture base posterior to the axis of direct retention on the hard palate (which again is relatively incompressible) for a partial denture with an anterior saddle will provide indirect retention (Figure 12). The further the indirect retainer is away from the axis of direct retention, the more effective it is.

Completion of Design The design should be reappraised and the clinician should determine that the denture base covering the saddles is sufficient to achieve prosthodontic norms. The denture base extension, however, is not suggestive of the number of teeth on the saddle, which should be kept to a minimum consistent Dental Update – December 2002

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with function (Figure 13). To reduce loading on a mandibular distal extension saddle the buccolingual width of the teeth may be reduced, and premolars rather than molars used. Teeth should never be placed on the ascending slope of the lower ridge unless it is necessary to oppose teeth in the opposite jaw. With an upper anterior saddle, the extent of the flange may vary depending on the individual case. l If only one or two anterior teeth are being replaced, ‘gum fitting’ or a small partial flange is acceptable. l Marked labial undercuts may necessitate less than full extension into the sulcus, although this area should be palpated clinically to determine the degree of compressibility. l A full-depth flange is to be preferred where there is a shallow palate in order to provide anteroposterior stability, particularly where a large number of anterior teeth are missing. l The presence of a high or low lip line will also affect the extent of the flange. A high lip line might cause the clinician to plan for a ridge-lap or even a ‘gum-fitted’ appearance to avoid the potentially unsightly flange. Where the lip line is low or where the mobility of the upper lip is reduced, the flange may not present an aesthetic problem. In the lower jaw, a full labial flange is necessary to provide stability because of the poor support available from a lower edentulous ridge.

TOOTH PREPARATION Preparation of the teeth after the design has been finalized is an important stage in the construction of successful partial denture, although care has to be taken when carrying this out.

Guide Planes Guide planes have already been mentioned in relation to reciprocation for clasps. In some patients, guide Dental Update – December 2002

planes exist naturally; others require some preparation of guide planes by grinding interproximal enamel to enable a more satisfactory denture to be constructed. Guide planes consist of parallel surfaces on the axial walls of the supporting teeth which then give a definitive single path of insertion for the denture, increase the direct retention due to the areas of contact, and avoid ‘wedging’ the teeth as the denture is inserted and removed. Guide planes can also be prepared on the mesial/distal surfaces of the teeth on either side of the edentulous spaces. Such preparations should not extend all the way down the axial walls; they should begin below the marginal ridge and end well before the gingival margin. With anterior edentulous spaces, the preparation of guide planes can lead to a partial denture with improved aesthetics.

Occlusal Adjustments It is poor clinical practice to reduce an opposing cusp tip in order to eliminate an interference when fitting a partial denture. However, as part of a planned preparation of the teeth, this is perfectly satisfactory before taking the master impression. Rest seats should be prepared for reasons already stated, but caution must be exercised: a deep preparation would not be recommended on a young patient or someone with a high caries rate where there is a possibility of extending into dentine (in fact with the caries prone patient a partial denture should be avoided if possible), but in an elderly patient with pulpal recession and a healthy mouth this may be perfectly acceptable. All enamel surfaces of the teeth that have been prepared should be polished afterwards. Preparation of a rest seat in a restored tooth requires care. For example, with a Class II amalgam restoration, rest seat preparation may thin down the amalgam at the axiopulpal line angle to the extent that the restoration fractures. A radiograph may help to determine the thickness of amalgam, but if there is any doubt it is

sensible to replace the amalgam carefully, taking care to ensure it will have sufficient bulk in the appropriate place.

R EFERENCES 1.

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8. 9.

Kennedy E. Partial Denture Construction. New York: Dental Items of Interest Publishing Co., 1928; pp.3–8. Beckett LS. The influence of saddle classification on the design of partial removable restorations. J Prosthet Dent 1953; 3: 506–516. Basker RM, Davenport JC. A survey of partial denture design in general dental practice. J Oral Rehabil 1978; 5: 215–222. Basker RM, Harrison A, Davenport JC, Marshall J. Partial denture design in general dental practice – 10 years on. Br Dent J 1988; 165: 245–249. Davenport JC, Basker RM, Heath JR, Ralph JP, Glantz PO, Hammond P. Communication between the dentist and the dental technician. Br Dent J 2000; 189: 471–474. McCord JF, Grey NJA, Winstanley RB, Johnson A. A clinical overview of removable prostheses: 2. Impression making for partial dentures. Dent Update 2002; 29: 422–427. McCord JF, Grey NJA, Winstanley RB, Johnson A. A clinical overview of removable prostheses: 1. Factors to consider in planning a removable partial denture. Dent Update 2002; 29: 376–381. Farrell J. Partial denture tolerance. Dent Pract Dent Rec 1969; 19: 162–164. Bates. The mechanical properties of cobaltchromium alloys and their relation to partial denture design. Br Dent J 1965; 120: 79–83.

NOVEMBER Self-Assessment Answers 1. A, B, D

6. A, B, C

2. A, B, D

7. B, C, D

3. A, B, D

8. B, C, D

4. A, C, D

9. A, B, C, D

5. A, B

10. B, C

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