REVIEW OF DENSTISTRY

Removable Partial Denture Prosthodontics

What is meant by dental prosthetics?

The replacing of a missing natural tooth or teeth and associated structures with artificial substitutes.

What is prosthodontics?

Prosthodontics is the practice of that branch of dentistry pertaining to (1) diagnosis, restoration and maintenance of oral and facial function; (2) health, comfort and appearance by the replacement of missing natural teeth, oral and facial tissues with fixed and removable artificial substitutes; and (3) application or prescription of proper medicinals (Oral Health Committee of the Federal of Prosthodontic Organization).

What is a partial denture?

The type of prosthesis that supplies one or more artificial teeth and adjacent tissues in a partially edentulous arch.

1. Fixed partial denture: A partial denture that may be put in place or removed at will by the patient.
2. Removable partial denture: A partial denture that may be put in place or removed at will by the patient.

What is meant by support?

The foundation on which all prosthetic appliances rest; it is divided into three classes; tooth support, mucosa-ridge support and combination tooth-mucosa support.

What is retention?

The fixation of a removable partial denture in the mouth in such a manner that, although it may be removed easily, it may be placed and retained with sufficient firmness to withstand displacing stresses that may be brought to bear on it and do so without injury to the natural structures.

What is a retainer?

A mechanical appliance used for the fixation of a removable partial denture.

What is a direct retainer?

A retainer applied directly to an abutment tooth (it may be either a clasp or a frictional attachment).

What is a fulcrum line?

An imaginary line passing through any two teeth with direct retainers, around which line the appliance has a tendency to rotate when subjected to functional masticatory stresses.

What is an indirect retainer?

A mechanical device (rest, continuous clasp, or base), assisting in the fixation of a removable partial denture by functioning indirectly on the opposite side of a fulcrum line from the part to be retained.

What is a load line?

An imaginary line joining any two positive supports (A fulcrum line is always a load line; however, a load line may not be a fulcrum line).

What is a clasp guideline (surveyed line)?

A line produced on a tooth by the scriber of a surveyor, denoting the greatest height of contour in relationship to a given path of placement of a restoration.

What is the path of placement?

The direction in which a restoration is seated or withdrawn from the abutment teeth; this path is used in determining clasp guidelines of the abutment teeth.

Under biting stress, what prevents removable partial dentures from being displaced gingivally?

Positive supports or rests in stop seats.

What is the retention area of a tooth?

That portion of the crown of a tooth gingival to the clasp guideline, ordinarily referred to as the infrabulge, or undercut.

What is a master cast?

An accurate reproduction of the prepared supporting elements and denture area as recorded by the unaltered impression.

What is an investment cast?

A reproduction in a high=heat-resistant material of the master cast as altered survey procedures.

What is a clasp?

A metal wire or cast band that partially or wholly encircles a tooth (must encircle more than halfway around) and that functions for support, stabilization and fixation of the removable partial denture (it is called an external attachment).

What is a circumferential clasp?

The type of continuous tooth contact clasp that partially or wholly encircles a tooth circumferentially, the terminals of which must embrace more than half of the circumference to provide reciprocation.

What is a bar clasp?

The type of clasp whose arms are direct extensions from the base and/ or from a major connector, rather than from the occlusal stop or the body of the claps; its arms pass along soft tissue through much of their extent and contact the tooth at their terminals.

What are the functions of a clasp?

Support, stabilization and fixation (or retention).

What is a continuous clasp?

A continuous clasp (Kennedy bar), not a true clasp, is actually a continuous multiple rest.

What is occlusion?

Contact of the teeth in opposing jaws when closed in any position.

What is meant by centric relation?

The relation of the mandible to the maxilla when the condyles are in their most comfortable retruded position in the glenoid fossae, from which lateral movements can be made.

What is meant by centric occlusion?

The contact relation of the incisal and occlusal planes of the teeth when interdigitated and in the relationship provided by nature or when the greatest number of inclined planes are in contact.

What is meant by vertical overlap?

The vertical distance the upper anterior teeth overlap the lower anterior teeth in centric occlusion.

What is meant by horizontal overlap?

Horizontal space existing between the incisal edges of the lower anterior teeth and the lingual surfaces of the upper anterior teeth in centric occlusion.

What is the compensating curve?

The curve introduced in the construction of artificial dentures to compensate for the opening influence produced by the condylar and incisal guidance during laterqal and protrusive mandibular excursive movements.

What is articulation?

The contact-relation of the incisal and occlusal planes of the teeth during excursive movements of the mandible.

What is a lingual bar?

A major connector uniting two or more parts of a mandibular denture and placed lingually to the remaining teeth (a labial bar is the same, placed labially).

What is a palatal bar?

A major connector uniting two or more parts of a maxillary denture and crossing the palate.

What is a minor connector?

The connecting link between the major connector and any other part of the framework.

What is an impression?

A negative likness.

What is a removable bridge?

A unilateral removable partial denture supported wholly on remaining teeth.

What is a clasp partial denture?

A removable partial denture that is retained in its functional position by means of external attachments.

What is a precision attachment partial denture?

A removable partial denture that derives its fixation from frictional precision attachments (called internal attachments).

What is a precision anchorage, or attachment?

A type of direct retainer, utilizing proprietary male and female slotted attachments, the former being made a part of the removal partial denture, the latter being made a part of the abutment tooth restoration.

What is an interim partial denture?

A dental prosthesis supplying part of the teeth in an arch for a short interval of time for reasons of esthetics, mastication, occlusal support or convenience until permanent prosthetic dental treatment can be provided.

Essentials of Removable Partial Denture Components

What are the two different types of direct retainers?  Internal and external attachments.

How do these direct retainers differ in their retaining action?

External attachments engage undercuts.  Internal precision attachments retain by frictional resistance.

Do their functions differ?

No, both types of retainers have the functions of support, stabilization and retention.

Which is the more popular partial denture?

The clasxp partial denture – it is more simple to construct and more patients can affort it.

What are the component parts of a clasp partial denture?

1. Occlusal stops (rests)
2. Clasps (primary or direct retainers)
3. Tangs (minor connectors)
4. Lingual bars (or lingual plates)
5. Palatal bars (major connectors)
6. Indirect retainers (secondary retainers)
7. Stress breakers and stress equalizers
8. Bases teeth

Occlusal stops

State the main functions of an occlusal stop. 

Transmitting occlusal stresses parallel to the long axis of the tooth and holding the clasp in its predetermined position.

Why is the occlusal stop or some other form of positive rest (such as an incisal rest) of such great importance?

It is the means of providing definite denture support under the stresses of mastication.

What should be the design of rests?

They should be heavy enough for strength, thin enough to preclude interfering with occlusion, and shaped to function in a seat rounded like the bowl of a spoon.

Should rests ever be supported on inclines sloping away from the tooth?

No, such support would result in drifting of the teeth and denture.

It is advisable to employ few or many rests? Many, as multiple supports distribute stresses to additional teeth.

Clasps

What are the functions of clasps?

Support, stabilization, and retention (fixation).

Is it necessary to have a great number of clasps on a given partial denture?  For retention alone, two clasps are generally adequate.

Then why are three, or even four clasps frequently used on a partial denture?  To distribute occlusal and lateral stresses further, to prevent tooth migration, and to stabilize additional teeth.

What is reciprocal action? The clasp action secured by distributing its contacts with the tooth more than halfway around.

Why must all types of clasps have reciprocal action  to be efficient? To prevent tooth soreness, migration and loss, since the pressure or action of one clasp component will be reciprocated for by its other parts.

How do clasps retain? By frictional and undercut resistance, mostly the latter.

Should clasps grip teeth tightly?

No.  On the contrary, when once seated, they should be absolutely passive, no longer exerting any pressure in any direction until activated by function.

What three things contribute most to maximum clasp efficiency?

1. Proper taper to provide maximum spring.
2. Narrow form to avoid broad tooth surface coverage and bulk.
3. Heat treatment for correct tempering when possible.

What type of clasp is least efficient for stabilization but kindest to clasped teeth and most favourable to tooth structure?

The long resilient bar type of clasp (only point contacts).

What type of clasp is most efficient for retention?

The bar type of clasp (push type).

What other type of clasp is nearly as kind to the abutment tooth as the bar clasp?

The wrought, circumferential, round wire type of clasp (only line contact).

Which clasp type is best for denture stabilization?

The cast circumferential type of clasp.

Tangs

What is the purpose of tangs?  To connect rests, direct retainers, and indirect retainers to lingual and palatal bars, other framework, and bases.

How should tangs be designed?  In cast work, tangs should be constructed with a finishing line, or ledge, to avoid feathered edges of base material.

Lingual bars

What are the principal functions of lingual bars (plates)? To correct two or more bases and to distribute stresses bilaterally.

What should be the design of lingual bars?

Lingual bars (plates) should be absolutely rigid and should provide clearance for tissues in the floor of the mouth, at the same time anticipating some subsequent settling of the denture.

Palatal bars

What are the main purposes of palatal bars?

To join two or more bases and to distribute stresses to both sides of the dental arch.

How should palatal bars be designed?

1. They should be rigid to distribute stresses bilaterally without spring action.
2. They should be positioned for least tongue interference
3. They should be shaped thin and wide rather than thick and narrow.
4. The edges of anterior bars should follow the grooves of the range.
5. The borders of bars should be beaded.
6. the edges of bars should be 3 mm or more from the free margins of the gingivae to prevent strangulation of tissues.,

Area two bars, anterior and posterior, always necessary?

In most cases, two are necessary for sufficient rigidity, stress distribution and avoidance of the palatal hard raphe.

Indirect retainers

What functions do indirect retainers serve?

Indirect (secondary) retainers distribute stresses and prevent displacement of free projecting bases by tongue and muscle movements, gravity and sticky food.  An indirect retainer functions indirectly on the opposite sided of the fulcrum line from a free-end base or bases.

What designs may an indirect retainer have?

An indirect retainer may be an occlusal stop, an incisal embrasure rest, a so called continuous clasp, or even another base.

Stress breakers

What is the purpose of stress breakers?

To relieve abutment teeth of all or part of the stress of mastication.

What are the two types of stress breakers?

1.            Complete, removing all occlusal stress from the abutment (e.g., Roach attachment).

2.            Partial, removing only part of stress (e.g., flexible wire connector).

Base

What are the main functions of bases?

To provide a supporting foundation for the teeth and a base to rest against the soft tissues, to reestablish the correct contour of the face, and to supply functional stimulation of supporting ridge tissues.

What attention should be given to the design of bases?

            Bases should have correct shape for esthetics and sufficient bulk for strength and, when free-end type, should be as large as possible for maximum tissue coverage.

Teeth
Do teeth perform any other important functions besides those of mastication and speech?

            Yes, to enhance esthetics and to prevent drifting of, and to provide function for, opposing natural teeth and tissues.

What should be the arrangement and design of teeth on bases?

1.      Small, when possible, to reduce occlusal stress.

2.      As few in number as feasible.

3.      Narrow buccolingually, with sharp cutting cusps.

4.      Positioned for favorable leverages.

5.      Provided with occlusal balance.

Do precision attachment partial dentures have the same component parts?

            The precision attachment takes the place of the clasp; otherwise, clasp and precision attachment partial dentures function alike and the essentials are the same.

What are the three main advantages of the frictional attachment partial denture?

1.      It is more esthetic, as there is no show of metal.

2.      It is least conducive to dental caries.

3.      Stresses are much better distributed to the abutment teeth.

Which teeth are the most suitable for clasping?

            Molars, bicuspids, and cuspids, in the order named.

What are the advantages of clasps?

1.      Make unnecessary the excessive cutting of sound teeth.

2.      Are simple in design.

3.      Are quite permanent when properly designed.

4.      Are relatively inexpensive.

5.      Can be easily cleaned.

6.      Permit normal movement of teeth and denture.

7.      Lend their construction to average technical ability.

How might one restore a carious abutment tooth with a gold inlay when new occlusal stop support for the partial denture is involved?

            The cavity is prepared. Inlay wax is inserted into the cavity and carved. The proximal wax surface is left in excess. The involved partial clasp is heated cautiously, while the wax pattern is cooled in the mouth, and the entire denture is carefully seated. The warm clasp removes the excess wax to proper fit, and the occlusal stop shapes its own seat. On removal of the partial denture, the wax pattern is given minor refinements and then cast.

Should a gold clasp be placed in contact with an amalgam filling?

            Generally speaking, no. And certainly never against a new, recently placed amalgam. If a gold clasp rests against an old silver alloy restoration, a galvanic current may result (but not in all cases), causing intermittent pain and pulp death, all resulting from the difference in electric potential between the two metals. To be safe, abutment tooth restorations should be of precious metal.

What clasp type is most generally employed?

            The cast circumferential clasp, no doubt because of economic factors and average technical skill.

Name the different types falling under the heading of circumferential clasps.

1.      Cast circumferential.

2.      Wrought circumferential (round and half-round wire).

3.      Variations of the cast circumferential, designed by the operator to best suit the requirements of a restoration, but still strictly circumferential (i.e., cast plus wrought).

What types of bar clasp are used most often?

They are the C, L, U, T, I, and the so called mesiodistal grip clasp.

What is the chief difference in design between circumferential and bar clasps?

            The arms of the former lead off from the occlusal rest; those of the latter take origin from the base outline.

Can both types be used with equal ease?

            No. Bar clasps lend themselves better to all-metal base dentures than to those with plastic bases but are possible with either.

What are the advantages of the circumferential type of clasp?

1.      Is the best stabilizing clasp.

2.      Uses the least metal.

3.      Seldom bends or gets out of order.

4.      Can be used with any type of base.

5.      If necessary, can be easily repaired or adjusted.

6.      Is simple to design.

7.      Is least costly to finish.

8.      Catches stringy foods less than any other clasp.

9.      Is not bulky to the tongue and facial muscles.

What are the advantages of the bar type of clasp?

1.      Is least conducive to dental caries.

2.      Requires less display of metal (often).

3.      Is long and springy-kind to abutments.

4.      Is an open clasp-permits food to give normal gum massage

5.      Gives best retention.

6.      Permits quite normal tooth movement.

7.      Permits normal slight denture movement.

8.      Is most versatile-can be designed to meet any clasping problem.

What rule should govern the selection of clasp types?

            Bar clasps should be used where they are indicated by survey; circumferential clasps should be used where they will best serve.

Why cannot one type or design of clasp be used universally?

            Because different cast positions and shapes and leaning of teeth present varied clasping problems as indicated by the surveying spindle.

Besides surveyed lines, what things largely dictate the clasp design?

            Esthetics to avoid show of metal and the function required of the clasp.

What general rule for the overall removable partial denture should be observed?

            The denture should be as simple as feasible, consistent with required function.

Is a compromise sometimes necessary?

            Often. The indicated clasp must frequently give way to one of better esthetics or to another with a specified required function.

May bar and circumferential clasps both be used on the same restoration?

            Yes.

Should clasps and precision anchorages be used on the same restoration?

            No. Their functions are the same; however, their action is dissimilar, clasps allowing for much more denture movement.

GENERAL CONSIDERATIONS IN REMOVABLE PARTIAL

DENTURE PROSTHESIS

What classification of partial dentures is most commonly employed?

            Kennedy’s (Edward Kennedy, D.D.S.) classification.

Classify partial dentures according to Kennedy.

Class I: The bases are bilateral and lie posterior to the attachment teeth (most common).
Class II: The base is unilateral and lies posterior to the attachment tooth or teeth.
Class III: There is (are) tooth (teeth) missing on one side of the arch, the base having support anteriorly or posteriorly.

Class IV: The base is entirely anterior to the attachment.

Which class permits no modifications?

            Class IV. The loss of a tooth elsewhere would change it to a modified Class I, II, or III.

Is a classification of any assistance in arriving at a definite design?

            Not at all. Using a classification is merely a professional way of referring to specific problems.

In removable partial denture prosthetics, what should be the prime objectives?

            The preservation of those tissues that remain while providing desired function and esthetics.

To ensure a successful removable partial denture, what must be kept foremost in mind in its planning?

            Proper design and adequate support.

What principles ate ehie1y involved in correct designing?

            That leverages shall be favorable, not traumatic, to teeth, tissue, and ridges.

State simply what this means.

            To have favorable leverages, occlusal stress and unseating leverages must be of the short- arm type; controlling leverages must be of the long-arm type.

What is the immediate result of ideal leverages?

            Best possible denture stabilization, without transmitting tipping stresses or torque to abutment teeth.

Give the steps in surveying a cast.

            The master cast is mounted on the round movable base. The vertical carbon marker is placed against the teeth that are to be clasped, it is run up or down, as best suits the case, and is passed around the teeth by moving the movable base and swinging the horizontal arm. The point where the vertical side of the marker touches the tooth indicates the greatest circumference of the tooth. The undercut areas are indicated by space between the marker and the tooth below the greatest circumference of the tooth. The undesirable undercuts are eliminated and the desirable ones retained by manipulation of the cast on the movable base, which is done until this objective is best obtained. When this objective is accomplished, the position of the clasps is marked with the marker. Widely separated tripod points or vertical scratches are now located on the cast so that it (also the duplicate) can be repositioned repeatedly and exactly when necessary.

For what is the surveyor used in removable partial denture prosthetics?

1.      To scribe the survey lines (heights of contour) on teeth t be clasped.

2.      To determine the favorable path of placement and removal of a removable partial denture (in line with the stylus).

3.      To mark the extent of guiding planes to correlate with the path of placement.

4.      To decide on the best cast position to provide ideal undercuts for favorable clasp retention.

5.      To identify all hard and soft tissue undercuts-those that are desirable as well as those that are not acceptable.

6.      To aid in the slight recontouring of natural teeth.

7.      To enable the operator to exactly reposition a cast or casts repeatedly by means of tripod points or by orientation grooves.

8.      To ensure the proper shaping of fixed partial restorative procedures on abutment teeth.

9.      To ensure correct wax blackout procedures by using the stylus of the surveyor as a guide.

10.  To enable the operator (using the stylus of the surveyor) to wax up crowns for abutment teeth so that these crowns will have accurate guiding planes and ideal contours for clasping.

Are all three classes of leverage involved ri stabilizing as well as tending to displace movable partial dentures?

            Yes.

Which class of leverage is most advantageous?

            Class2.

In planning, how can one be sure of creating the most nearly ideal stability?

1.      By selecting abutments for direct retainers as far apart as is feasible.

2.      By selecting these abutments, if only two, so that the fulcrum line bisects stabilizing elements of the denture.

3.      By selecting these abutments, if three r four are going to be utilized, so that the geometrical figure (triangle or quadrangle) n-med by the several fulcrum lines will have the greatest area possible.

4.      By providing short hard-stress unseating leverages and long controlling ones.

What is meant by adequate support?

            Sufficient support to bear up indefinitely under the functional stresses of mastication.

How is this best accomplished?

            By distributing stresses among remaining teeth and over the greatest possible ridge area consistent with tolerance.

Do these rules, with reference to design, apply to precision attachment partial dentures as well as to clasp partial dentures?

            Yes, in exactly the same way.

What is the purpose of the preliminary examination?

            The preliminary examination is made to gather all the facts that bear on the subsequent phases of the service and should include surveyed diagnostic casts, x-ray films, and other data. The choice of restoration is made at this stage.

What mouth preparation must always be done before the final impression Tor a clasp denture is made?

            The preparation of the rest seats, the provision of satisfactory border contour, and a prophylaxis.

Are there other important mouth preparations?

            Yes, such as extraction of malposed teeth and roots, placement of fillings and crowns, and removal of bulbous tuberosities; however, these are not always encountered.

What impression materials may be used for making impressions for partial dentures?

1.      Impression compound.

2.      Plaster.

3.      Hydrocolloids (also with altered cast).

4.      Alginates (also with altered cast).

5.      Custom tray with rubber-base type of liner.

6.      Compound with alginate liner.

7.      Hydrocolloid or alginate taken over, and in combination with, a shellac tray previously corrected with a zinc oxide-eugenol paste (altered cast technique).

What is the most suitable material for making impressions for clasp partial dentures?

            The alginates-more versatile than the hydrocolloids. Alginates can be used in combination with more other materials, hot or cold; the tray can be extended for them with wax; and they have better body against distortion and fracture.

What areas should be included in an impression for a partial denture for the lower arch?

1.      All remaining natural teeth.

2.      Edentulous ridges.

3.      Retromolar pads.

4.      Mucobuccal and mucolabial folds with muscle attachment.

5.      Lingual, buccal, and labial surfaces of alveolar ridge.

What information is needed to make a diagnosis for a partial denture?

1.      Full-mouth x-ray films (also, bite- wings).

2.      Articulated diagnostic casts, surveyed.

3.      Complete chart of the mouth.

4.      Complete clinical examination of the mouth.

5.      Length of time the partial denture is anticipated to be used.

What areas are to be included in an upper impression for a partial denture?

1.      All remaining natural teeth.

2.      Entire palatal area.

3.      Junction of hard with soft palate.

4.      Tuberosities.

5.      Edentulous ridges.

6.      Mucobuccal and mucolabial folds with muscle attachment.

What are the advantages of the alginates in making impressions for clasp partial dentures?

            They require no special equipment. The powder is mixed with a measured quantity of water to make a paste. The paste sets in a few minutes to a rubbery mass that springs out of undercuts, returns to its original form, and gives an exact negative of the teeth and surrounding soft tissues.

What results if a tooth is lost and is not replaced by an artificial tooth?

1.      The remaining teeth drift away from their original positions.

2.      This drifting results in the loss of proper cusp interdigitation and tooth contacts.

3.      As a result of subsequent cusp interference and the tilting of the teeth adjacent to the space, an increased load must be borne by the investing tissues, and periodontal lesions may follow.

In what directions do teeth naturally drift?

1.      Mesial drift of the teeth posterior to the space.

2.      Distal drift of the teeth anterior to the space.

3.      Occlusal drift, especially if there are no opposing teeth.

What injuries may result from the lack of partial denture service?

1.      Exfoliation, extrusion, continued eruption, and elongation of teeth.

2.      Separation of contact points (driffing of teeth).

3.      Traumatic gingivitis.

4.      Exposed cementum.

5.      Decrease of natural cleansing of teeth.

6.      Excessive abrasion of remaining teeth.

7.      Loss of vertical dimension, resulting in Costen’s syndrome.

8.      Decrease in masticating efficiency of teeth.

9.      Impairment of speech and esthetics.

Classify partial dentures regarding supporting structures.

1.      Mucosa-borne dentures, for arches with very few natural teeth and for interim dentures.

2.      Tooth-borne dentures supported wholly or entirely by natural teeth.

3.      Tooth- and mucosa-borne dentures, for arches in which there are no distal natural teeth and the bases are free-end.

What are the requirements of partial dentures?

1.      That the partial denture may be worn with comfort and safety.

2.      That no needless impairment of the abutment teeth will be produced by the denture.

3.      That it will give a maximum of service if used with average care.

4.      That it will satisfy esthetic and functional masticatory requirements.

What is the value of mounted diagnostic casts?

1.      The design in general can be analyzed.

2.      Surveying and clasping can be studied.

3.      The possibility of fitting the artificial teeth into the spaces (interarch) can be considered.

4.      The location of recesses for rests can be noted.

5.      The nature of operative restorations can be decided on.

6.      Reshaping of crowns for better retention can be planned.

7.      An opportunity for consultation with patient, technician, and surgeon can be provided.

8.      The lasting permanent record for correct tooth position can be ensured.

9.      An accurate guide for tooth preparations and for oral surgery to be performed can be obtained.

What is the value of diagnostic casts over diagrams or charts in designing clasp partial dentures?

            Dentures can be designed on diagrams and charts, but the difficulties can be seen and studied best on mounted or related stone casts. Charts provide only flat planes. Casts lend to the case the third dimension and make possible study and analysis of the difficulties with a surveyor.

What may be observed on the casts?

1.      Interdental and intermaxillary relationships.

2.      Leaning of teeth.

3.      Excessive contours of teeth.

4.      Hard, bony projections that would interfere with bars or bases-bulbous tuberosities and torus palatinus and torus mandibularis.

5.      Irregularities in occlusion. Forces of occlusion can be studied. Forces of mastication destroy more abutment teeth than do clasps.

6.      Fee requirements. Accurate estimates of cost can be made.

What do diagnostic casts provide for the operator?

1.      Excellent lasting record and protection for the dentist in the same way that the orthodontist is protected by models and the radiodontist by radiographs.

2.      Record for esthetics for complete dentures.

3.      Place to mark surgical and operative work yet to be completed.

4.      Accurate index for impression tray selection.

5.      Vivid means of convincing the patient of the necessity for various preparations, alterations, and extractions.

6.      Opportunity for the dentist to discuss the problem intelligently with the technician or with a specialist.

What are the indications for removable partial dentures?

1.      When mobility or weakness of teeth presents a need for bilateral bracing.

2.      When teeth have been recently extracted and reestablishment of the ridge is awaited; any case in which rapid change is expected; and when the denture needs to be accessible for alterations and repairs

3.      When nervous temperament of the patient is such that he cannot endure preparations for fixed restorations.

4.      When diseased conditions are being treated and further tissue changes are impending.

5.      When there is no caries in teeth adjoining edentulous spans.

6.      When the length of edentulous spans makes fixed restorations impracticable.

7.      When recontouring of facial features are made necessary through loss of tissue (soft or bony.

8.      When restoring lost vertical dimension.

9.      When base areas must support stresses of mastication.

10.  When restoring or closing a palatal cleft.

11.  When restoring teeth for children, where a fixed partial denture is impossible and allowance must be for continuing growth and development.

12.  When cost of mouth rehabilitation is too costly with fixed restorations.

What metals may be used in the construction of partial dentures?

            Gold alloys and non-precious metals.

Give steps in the construction of an all metal removable partial denture (precious metal).

1.      Mounting of cast on a survey or tilt table.

2.      Mounting cast, tripoding, and surveying.

3.      Marking undercuts on a master cast.

4.      Drawing the full design on a master cast, using undercut gauges.

5.      Preparing a master cast for duplication (wax ledges, relief).

6.      Duplicating.

7.      Drying of investment cast.

8.      Grinding in teeth on the master cast.

9.      Making of a plaster core to hold the position of teeth.

10.  Preparing teeth for boxing.

11.  Waxing up the design on an investment cast, clasps against ledges.

12.  Boxing of teeth individually.

13.  Orienting teeth on the investment cast by means of a plaster core.

14.  Uniting the boxing to other waxing and removing of the core.

15.  Waxing refinements, smoothing with eucalyptol, and washing with acetone.

16.  Spruing of the waxed design for casting.

17.  Painting with a wetting agent and investing.

18.  Burning out the wax from the investment

19.  Heating metal and casting.

20.  Plunging the casting to properly cool metal and disintegrate investment.

21.  Boiling the casting in 50% sulfuric pickle.

22.  Grinding and polishing the casting.

23.  Applying heat treatment to the finished casting.

Give contraindications for removable partial dentures.

1.      When it is possible, or seems feasible, to use a fixed restoration.

2.      When a restoration is unilateral (usually).

3.      When tooth restoration is anterior only.

4.      When very few teeth remain and financial considerations, rebasing, and servicing are involved.

5.      When the patient refuses to allow for proper mouth preparation.

6.      When the patient shows signs of poor mouth hygiene and is unappreciative of own teeth.

7.      When the patient lacks the finer sensibilities to appreciate adequately a work of art and a well-engineered appliance.

8.      When the patient’s teeth show a marked carious tendency.

9.      When the fee would constitute too great a financial hazard (complete dentures become the final solution).

Why is partial denture design a very difficult problem?

1.      Variations in the number and location of the missing teeth.

2.      Variations in the occlusal relations of the remaining teeth.

3.      Variations in the dental and periodontal health of teeth to which the denture is to be related.

4.      Variations in the condition of the alveolar ridge where teeth have been extracted.

What is meant by passivity of a partial denture?

            That with it in place and no masticating pressure, on it, there should be no binding, pulling, or pressure of any kind on the tissues and teeth.

What is the most important purpose of any restoration?

            The restoration of functional occlusion.

What is an important factor in the maintenance of a functional occlusion?

            The relining of partial dentures and restoring of lost vertical distance.

How is this best accomplished?

            By the use of a relining material with sufficient body and resistance to hold bases and their teeth in normal contact with their opponents during the relining procedure.

What is the material of choice for making an impression in relining a partial denture?

            Modeling composition is the best and most versatile material, adaptable to any problem, capable of being repeatedly softened to any degree of passivity or resistance, and always under the control of the operator. Available in a range of softening temperatures, it lends itself to any relining impression procedure.

What are the two generally accepted methods of making a reline impression?

1.      Static, or impression paste, method.

2.      Functional method.

What objectives are usually involved in a relining procedure for a mandibular distal extension partial denture?

1.      Repositioning the displaced metal framework.

2.      Reestablishing lost occlusal contacts.

3.      Making an impression that will ensure intimate tissue adaptation of the basal seat.

Do the self- and rapid-curing plastics used for relining result in a creditable product?

            Only as an emergency procedure. This method does not afford the same opportunity for precise border trim, uniform density of plastic bulk, unbroken color, excellent appearance, smooth borders, and refinement of finish as does the processed one; and not all objectives of relining can be attained.

What should be given due consideration in the design of a partial denture?

            The design of a partial denture should always provide for the possibility of future extractions of doubtful teeth or roots and for future inexpensive and simple replacement on the framework of the denture.

What conservation of teeth should be considered in designing partial dentures?

1.      Avoid the cutting of natural teeth, with possible pulp involvement or other sequelae, when possible.

2.      Avoid the removal of natural teeth as far as this is practical within biological, physical, mechanical, and economic limits.

In the construction of partial dentures, what are the indications for internal attachments?

1.      When there is difficulty in getting adequate clasp retention.

2.      When there is unusual susceptibility to dental caries.

3.      When the esthetics of the removable partial denture demands elimination of the buccal arm of the clasps.

4.      When the tongue is irritated by the clasps.

5.      When the denture will be totally tooth-supported.

What are most necessary for internal attachment?

            Paralleling of all attachment receptors and sufficient crown length to accommodate an effective length of the female element

What forces from a partial denture are the greatest sources of injury to the supporting tissues of the teeth?

            Forces applied in a direction not parallel with the long axis of the teeth.

How should lateral forces be distributed to abutment teeth?

            By the clasp arms in the case of clasp partial dentures and by the male elements working against the side of the sleeves and as near the center of rotation as possible in the frictional attachment type.

What will reduce the lateral forces on the, abutment teeth?

            The lateral forces on the abutment teeth are reduced as the number of teeth used to carry the appliance is increased.

How is the greatest value from bilateral support of a partial denture secured?

            By the use of rigid lingual or palatal bars

What are the requirements of retainers for natural teeth?

1.      Adequate retention.

2.      Fixation in relation to the teeth.

3.      Minimum metal display.

4.      Minimum risk of fracture or distortion.

5.      No contact with vulnerable enamel areas that are caries prone.

6.      No contact with gingival tissues or cementum.

7.      No orthodontic movement when in position (passive contact).

8.      No lateral movement of the tooth on insertion or removal.

9.      No galvanic action.

10.  Minimum food pack areas.

What is galvanic action?

            It is the electric current, resulting a shock, set up between two dissimilar metals of different electric potential when they make and break contact in an acid saliva.

What is the most important quality that a removable partial denture should possess?

            Stability, as this perpetuates functional occlusion.

What is the most important step in the construction of a clasp-retained partial denture?

            Surveying the cast of the dental arch

What three main factors must be considered in positioning the cast in surveying?

            Interference during insertion or removal, retention, and esthetics

What is the most important factor in the construction of a removable partial denture?

            An accurate impression. It should be an accurate negative likeness of the exact contour of the remaining teeth and surrounding tissues.

What is meant by retention in removable partial dentures?

            Retention is obtained by constructing the denture in such a manner that it is easily removed and replaced by the patient but is retained in the mouth with sufficient firmness to resist displacement during speech and mastication of food, without injury to the remaining tissues.

How is retention obtained?

            Retention is obtained by retaining devices attached to one or more teeth.

How can the survey lines be transferred from the master cast to the investment cast?

1.      By scratching fine lines in the master cast, which will be reproduced in the duplicate.

2.      By drawing the lines with an indelible pencil.

3.      By making three small and widely separated pits on the master cast while surveying it and then repositioning the refractory cast.

4.      By building wax ledges up to the bottom of the clasp outlines.

5.      By placing vertical tilt lines on the base of the cast so that the duplicate cast can be resurveyed.

What determines the life expectancy of a removable partial denture?

1.      Case history.

2.      Patient’s general systemic condition and oral health.

3.      Care of the mouth.

What three factors should be considered in the hygienic construction of removable partial dentures?

1.      In the construction of fixed restorations as supports for partial dentures, there must be no surface that may hold food debris that cannot be readily removed with the toothbrush and floss silk.

2.      The placing of ill-fitting bands, crowns, clasps, or other retaining appliances around the necks of teeth will, eventually, cause resorption of the gingiva and the establishment of a point for the entrance of bacteria into the pericementum.

3.      The willful destruction of pulps of teeth and the failure to make an aseptic and perfect root canal operation will produce an apical infection.

What points should be checked when a partial denture is placed in the mouth?

1.      Clasps for tention and passivity.

2.      Impingement on soft tissues.

3.      Lateral stress on teeth.

4.      Occlusion.

5.      Displacement during various movements.

6.      Comfortable fit with no binding.

What are the causes of failures of removable partial dentures?

1.      Inadequate diagnosis of structures available to support the denture and poor treatment planning.

2.      Failure of the denture to preserve the foundation on which it is placed.

3.      Lack of proper care by the patient as well as the dentist after completion of service.

How may unstable dentures be balanced?

            By using indirect retainers and by later relining or “rebasing”

Does alveolar absorption occur more rapidly under mucosa-borne than under toothbome partial dentures?

            There is pressure atrophy under a mucosa-borne denture and disuse atrophy under a tooth-borne denture. It is believed that absorption is more rapid under a mucosaborne denture.

What injuries may result from poor partial denture service?

1.      Dental caries from faulty clasps.

2.      Rapid resorption of the alveolus.

3.      Defective speech such as lisping and whistling.

4.      Changes in the expression of the lower third of the face.

5.      Injury to the salivary mechanism.

6.      Injury to the nervous mechanism.

7.      Injury to the trachea and esophagus-accidental swallowing.

8.      Interference with the tongue.

9.      Early loss of the teeth by overloading.

10.  Impaired masticating efficiency.

What is meant by surveying the cast?

            Surveying the cast consists of locating the heights of contour of the teeth and soft tissues in relation to each other and also locating the undercuts.

Why is it necessary to survey the cast in the construction of partial dentures?

1.      A partial denture is similar to an inlay or a bridge, and undercuts must be eliminated for it to reach its proper position.

2.      To determine the adequacy of undercuts on the teeth for clasp retention-and to obtain the most favorable distribution of those undercuts to secure the greatest and most uniform retention. This may involve tilting of the cast in making the survey of the cast.

3.      To help arrive at a design that is properly stabilized.

4.      To determine the most favorable path of placement that will permit the denture to go into place, avoiding excessive tooth and tissue undercuts.

What are the possible paths of insertion of partial dentures?

1.      At right angles to the occlusal plane, which is often the most desirable.

2.      Anterior tilt.

3.      Posterior tilt.

4.      Right lateral tilt.

5.      Left lateral tilt.

What is the purpose of tilting the cast in surveying?

            To provide the most desirable path of placement of the denture and to determine the location of the most desirable undercuts for retention.

What are the advantages of gold in the construction of removable partial dentures?

1.      Gold satisfies all the requirements of a restorative metal.

2.      The technique of its use is similar to that of small gold castings, with which most dentists are familiar.

3.      It is easy to repair. Soldering technique is simple and can be done in any dental office.

4.      Dependence on commercial laboratory techniques is avoided when desired.

5.      Gold clasp arms are elastic and by springing avoid stress shock to abutment teeth.

What determines the amount of relief necessary for a lingual bar?

            The amount of relief required varies according to the inclination of the tissues over which the bar will pass.

            How can one alter a cast to permit a grip of the acrylic resin on the frame?

            Apply 0.5 to 1 mm. thickness of wax where the gold frame is to rest on the cast, thus keeping the entire metal part off the ridge.

What instructions should be given a patient regarding the home care of artificial dentures?

1.      Dentures should generally be removed at night to rest the tissues and to prevent any undue resorption of tissues and decay of the normal teeth. This procedure is not always acceptable to the patient.

2.      The denture should be removed after each meal, if possible, to rinse away food particles.

3.      Abutment teeth, especially, should be kept as clean as possible to prevent caries.

4.      Tooth-contacting clasp surfaces must be kept free from food debris.

5.      Every 6 months the denture should be cleaned at a dental office to restore the smooth, highly polished surface.

6.      The denture is unsupported when out of the mouth-fragile. Handle with care.

7.      Regular periodic servicing of the denture and natural teeth is necessary.

Give some points regarding the mucostatic impression technique.

1.      It depends on surface tension for retention.

2.      It does not depend on the sealing of the border by folds of tissue.

3.      To obtain strong retention, the margins must be on immovable tissue, even though the area is small.

4.      The tissues must not be distorted in any way while the impression is being made.

5.      The cast must be absolutely accurate. No separating medium is permitted, for the casting investment must be poured directly into the impression.

6.      Only a hard metal will retain the absolutely accurate fit of the appliance.

7.      The tissue side of the cast must not be polished, as this might ruin the fit.

8.      The polishing may warp the frame; therefore care must be used in this process.

9.      The edge of the casting must be thin and square.

10.  The denture must be built on the base.

11.  No clasps or occlusal rests are used on partial dentures.

12.  All bars must fit the tissues the same as the base.

13.  There is minimum tissue resorption, and long life of the denture is claimed, as well as excellent retention. No food gathers under the bases.

14.  This type of impression technique is especially recommended by its proponents for both complete and partial dentures.

What is the etiology of congenital cleft palate?

            Unknown. Most evidence available today points to heredity

What is the rate of occurrence of cleft palates?

            About 1 in every 800 births

What is the purpose of a prosthetic restoration for cleft palate?

            To aid in the closure of the nasal passageway and to restore arch and vault form for resonance and phonetics

What is an obturator?

            An appliance constructed to fit and close a cleft in the hard palate.

What is an artificial velum?

            A rubber or plastic appliance constructed to restore the loss of or to supply the lack of tissues in the soft palate.

Name the steps in the construction of a prosthetic appliance for a cleft palate.

1.      Preliminary examination and survey of the mouth.

2.      Securing the impressions for record casts and for working casts.

3.      Making the casts.

4.      Molding and carving the models or patterns for the artificial palate and for the denture.

5.      Making the molds.

6.      Producing and assembling the com ponent parts.

Why should the wax setup be tried in the mouth before finalizing a partial denture?

1.      No articulator will reproduce accurately the movements of the mandible. It is advisable to do the best that is possible on the articulator and then to make corrections in the mouth.

2.      The fit on the ridge should be carefully checked and also the comfort of the design in the mouth.

3.      Centric occlusion should be checked.

4.      The various movements of the mandible, i.e., lateral, incisal, should be checked.

5.      The esthetics of the denture should be carefully checked.

6.      All possible necessary changes should be made at this time.

Is canal therapy advisable for a tooth to be used for retention?

            It has been shown by experience that if the root canal is properly filled, the tooth will usually last beyond the life of a partial denture. A root canal filling should be made if it is essential to the success of a partial denture or if it means the difference between a complete or a partial denture. The health of the patient should be first, last, and always in the mind of the dentist in making a diagnosis in the case of a questionable tooth.

What care must be given to acrylic dentures?

            It is absolutely necessary to keep the dentures in water when out of the mouth. Acrylic dentures undergo dimensional changes, particularly shrinkage, that materially affect their fit and comfort. It is also desirable to use only warm or cold water to wash the dentures, as hot water will cause shrinkage and warpage.

SAMPLE QUESTIONS

True-False

1.      The primary objective of partial dentures is to preserve those tissues that remain in a state of health. (T)

2.      Patient education is an important part of partial
denture service. (T)

3.      Hydrocolloids may be used for making impressions for removable partial dentures. (T)

4.      Impression compound is commonly used in making impressions for removable partial dentures. (F)

5.      The classification of partial dentures helps in arriving at a definite design for removable partial dentures. (F)

6.      The anterior teeth are most suited for clasps. (F)

7.      Surveying the cast is an important step in the construction of a clasp-retained partial denture (T)

8.      A clasp is a retentive device for a removable partial denture and encircles a varying amount of the tooth. (T)

9.      The terminals of the clasp must contact at least two opposing surfaces. (T)

10.  Dental caries may occur under clasps. (T)

11.  Amalgam may be used for making restorations on abutment teeth. (F)

12.  Clasps act as secondary retainers. (F)

13.  A rest should be used on each abutment tooth on a removable partial denture. (T)

14.  Rest seats are usually not necessary on removable partial dentures. (F)

15.  The rest seats should be prepared at right angles to the long axis of the tooth, or even slightly inclined. (T)

16.  The rest seat may be box shaped in a gold restoration (T)

17.  A rest helps to transmit occlusal stresses parallel to the long axis of the tooth. (T)

18.  The preparation for the rest should extend through the enamel. (F)

19.  One of the functions of a partial denture base is to carry the teeth to be supplied. (T)

20.  Removable partial dentures may not be used where tooth support is needed. (F)

21.  The base for removable partial dentures should rest firmly on the gingival margin. (F)

22.  An overload of the mucosa will occur when bases of too small an area are placed on it. (T)

23.  The path of placement should not be chosen before the clasps are designed. (F)

24.  All clasps have at least two arms. (F)

25.  The path of placement of a partial denture is best chosen as a single direction. (T)

26.  A vertical path of placement may be used. (T)

27.  Occlusion is an important consideration in partial dentures. (T)

28.  Precision attachments may be utilized for the retention of a removable partial denture. (T)

29.  Removable partial dentures may not be used for young patients where the roots are not fully formed. (F)

Completion

1.      The portion of the tooth that extends occlusally and incisally from the gingival attachment is referred to as the ______________ (clinical crown)

2.      The impression material most frequently used for making impressions for removable partial dentures is the ______________ (alginates)

3.      Rest seats should be prepared at right angles to the _____________________ of the tooth. (long axis)

4.      The minimum number of clasps usually necessary for the retention of a partial denture is ______________ (two)

5.      The clasp terminals should be placed of a tooth to act as a primary retainer. ______________ ______________ (below the height of contour)

6.      The part of the denture joining the teeth to the base is called the _____________________ (attachment)

7.      The _____________________ is the part of the denture that comes in direct contact with the mucosa. (base)

8.      ______________________ are simple retainers applied to two or more convex or sloping surfaces of remaining natural teeth. (Clasps)

9.      A ______________________ is a major connector uniting two or more parts of a maxillary denture and crossing the palate. (palatal bar)

10.  A retainer that is attached to a tooth directly without interlocking parts is a _____________ (simple direct retainer)

11.  The periodontal membrane of teeth used to retain partial dentures must be healthy, and at least _____________________ of the normal amount of bone must be remaining. (two thirds)

12.  The path of placement of a partial denture need not correspond to the direction in which it is depressed into the displaceable mucosa during ______________. (function)

13.  The position of the _____________________ depends on the path of placement. (guideline)

14.  The position of the guideline on a given tooth varies with the ______________ (path of insertion)

15.  The Roach clasp system includes many different types, chief of which are ______________ (T,U,L,I,C)

16.  The parts of a partial denture that join the base to the retainers or to the occlusal rest are the ______________ (connectors)

17.  Partial denture designs should always be made by the ____________________. (dentist)

18.  A lack of continuity of the roof of the mouth throughout the whole of or part of its length is a ___________________. (cleft palate)

19.  Palate defects may be corrected by a __________ (prosthetic appliance)

20.  For the correction of congenital palate defects, there is a choice between _________________ (surgery and prosthetic appliances)

21.  For the correction of acquired palatal defects of any extent, only
are indicated in the treatment. ______________ (prosthetic appliances)

22.  A removable partial denture should be scrubbed with a stiff brush, soap, and water after ______________ (each meal)

Multiple Choice

1.      The support of partial dentures is usually (a) tooth support, (b) mucosa support, (c) occiusal rest support, (d) tooth and mucosa support. (d)

2.      A retentive device for a removable partial denture that encircles a varying amount of tooth is a (a) rest, (b) connector, (c) bar, (d)clasp. (d)

3.      The shape of the rest seats in natural posterior teeth should be (a) box shaped, (b) flat, (c) convex, (d) saucer shaped. (d)

4.      The clasps for partial dentures should be made of (a) silver, (b) platinum, (c) gold, (d) iridioplatinum. (c)

5.      The teeth most suitable for clasping are (a) incisors, (b) molars, (c) bicuspids, (d) cuspids. (b)

6.      The most important step in the construction of a partial denture is (a) clinical examination, (b) designing the appliance, (c) surveying the case, (d) preparing the rest seats. (c)

7.      One of the retaining devices for partial dentures is a (a) stress breaker, (b) base, (c) tang, (d) clasp. (d)

8.      If a first molar is lost, the second molar drifts to the (a) distal, (b) mesial, (c) buccal, (d) lin gual (b)

9.      The most important quality that a partial denture should possess is (a) esthetics, (b) retention, (c) stability, (d) cleanliness. (c)

10.  One of the most important functions of clasp is to (a) give resiliency, (b) distribute stresses, (c) give strength,(d) give flexibility. (b)

11.  The termination bf a free-end clasp is referred to as the (a) stop, (b) tang, (c) finger, (d) arm. (c)

12.  The most important result of poor partial denture service is (a) dental caries, (b) resorption of the alveolus, (c) impaired masticatory efficiency, (d)interference with the tongue. (a)

13.  The main purpose in tilting the cast in surveying is to (a) locate the undercuts, (b) locate the line of contour, (c) provide the most desirable path of placement, (d) aid in designing. (c)

14.  The location of the clasps is determined by (a) clinical examination, (b) radiographs, (c) surveying the cast, (d) the position of the re main in teeth. (c)

15.  A rubber or plastic appliance to restore the loss of or to supply the lack of tissues in the soft palate is a(an) (a) obturator, (b) mold, (c) cast, (d) artificial velum. (d)

16.  A Class I partial denture that needs relining is properly positioned by (a) closing against opposing teeth, (b) the impression material lining the bases, (c) finger pressure against the framework, (d) noting occlusal markings made
on articulating paper. (c)

17.  An alginate impression for a partial denture will (a) record the anatomical form of the tissues, (b) result in a cast providing a physiologically based partial denture, (c) displace the tissues to functional form, (d) record areas
with varied pressures. (a)

18.  A circumferential clasp resists lateral horizontal stresses by the (a) occiusal stops, (b) clasp terminals, (c) shoulders of the clasp, (d) rigid tang attachment to the clasp. (c)

19.  The scriber of a surveyor (a) marks the clasp outline, (b) guarantees undercut retention, (c) dictates the removable partial design, (d) marks the greatest convexity of the tooth. (d)

20.  The precision attachment, under masticatory stresses against the partial denture, (a) tends to torque the tooth, (b) directs all stresses parallel to the long axis of the tooth, (c) employs all fibers of the periodontal ligament, (d) lacks allowance for sufficient tooth movement. (C)