I85PREP
⌘ K
CDT study materials
CDT study resources

CDT practice questions

One question at a time. Build your CDT understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Complete Dentures

Which statement best describes the purpose of the posterior palatal seal in a maxillary complete denture?

  1. Maintaining the posterior border contact during function Correct answer.
  2. Relieving pressure over the incisive papilla region
  3. Improving retention by engaging the zygomatic arch
  4. Recording the mandibular rest position at the try-in

Explanation

The posterior palatal seal is placed at the junction of the hard and soft palate, where slight displacement of soft tissue compensates for processing shrinkage and functional movement. This keeps the posterior border in contact so that the border seal and the retention it provides are preserved.

Question 2Complete Dentures

Border molding a custom tray is carried out mainly to record:

  1. The functional depth and width of the sulcus Correct answer.
  2. The shade and mould of the anterior teeth
  3. The centric relation record at the correct vertical dimension
  4. The resting interocclusal distance measured with a gauge

Explanation

Border molding uses a plastic material such as modeling compound shaped by muscle movements to capture the functional limits of the vestibule and surrounding tissues. This gives the final impression an accurately contoured border, which is essential for an effective seal.

Question 3Complete Dentures

Centric relation is best described as a maxillomandibular relationship in which:

  1. The condyles rest in the most posterior part of the glenoid fossa
  2. The teeth are in maximum intercuspation and the lips are lightly touching
  3. The condyles are seated in the anterior-superior position against the eminence Correct answer.
  4. The mandible is suspended at the physiologic rest position with the lips apart

Explanation

Centric relation is a bone-to-bone relationship independent of the teeth, defined by the condyle-disc assemblies being in their most anterior-superior position against the articular eminence. It is a reproducible reference used to mount casts and to arrange teeth.

Question 4Complete Dentures

A normal interocclusal rest space (freeway space) for a complete denture wearer is approximately:

  1. 5 to 7 mm
  2. 8 to 10 mm
  3. 0.5 to 1.0 mm
  4. 2 to 4 mm Correct answer.

Explanation

The freeway space is the difference between the occlusal vertical dimension and the vertical dimension at rest. It usually measures about 2 to 4 mm at the incisors and allows the mandible to move without dislodging the dentures.

Question 5Complete Dentures

When arranging anterior teeth, the incisive papilla is a useful landmark for locating the:

  1. Maxillary first molars
  2. Mandibular canines
  3. Maxillary central incisors Correct answer.
  4. Mandibular first molars

Explanation

The incisive papilla usually lies about 8 to 10 mm behind the labial surfaces of the maxillary central incisors, so it serves as a reliable guide for their anteroposterior position. Posterior teeth are positioned using other landmarks such as the retromolar pad and the hamular notch.

Question 6Complete Dentures

The hamular notch is clinically significant in complete denture construction because it indicates the:

  1. Posterior limit of the maxillary denture border Correct answer.
  2. Midline of the hard palate
  3. Position of the greater palatine foramen
  4. Anterior limit of the maxillary denture border

Explanation

The hamular notch, or pterygomaxillary notch, lies between the pterygoid hamulus and the posterior border of the maxillary tuberosity. It marks the posterolateral limit of the denture base, and the border must be recorded into it without pressure.

Question 7Complete Dentures

The microorganism most commonly implicated in denture stomatitis is:

  1. Escherichia coli
  2. Staphylococcus aureus
  3. Streptococcus mutans
  4. Candida albicans Correct answer.

Explanation

Denture stomatitis is a chronic erythematous inflammation of the denture-bearing mucosa, most often caused by Candida albicans colonizing the fitting surface of the denture. Poor hygiene, continuous wear and an ill-fitting base are common predisposing factors.

Question 8Complete Dentures

The material most widely used for the definitive base of a complete denture is:

  1. Shellac resin
  2. Heat-polymerized polymethyl methacrylate Correct answer.
  3. Chemically activated polyvinyl siloxane
  4. Type IV dental stone

Explanation

Heat-polymerized polymethyl methacrylate remains the standard denture base material because of its adequate strength, dimensional behavior, ease of processing and repair. Chemically activated acrylic resin is used mainly for interim and repair work.

Question 9Complete Dentures

Which factor influencing balanced occlusion is determined by the patient's anatomy rather than by the dentist?

  1. Compensating curve
  2. Condylar guidance Correct answer.
  3. Incisal guidance
  4. Cuspal inclination of the posterior teeth

Explanation

Condylar guidance is fixed by the slope of the articular eminence and is transferred to the articulator with a protrusive record. Incisal guidance, cusp angulation and the compensating curve can all be modified by the dentist when arranging teeth.

Question 10Complete Dentures

When a patient with a monoplane (flat) occlusion protrudes the mandible, the posterior teeth:

  1. Intercuspate fully in the protruded position
  2. Contact only on the balancing side
  3. Contact only on the working side
  4. Separate, leaving a posterior gap Correct answer.

Explanation

With a flat occlusal plane and no compensating curve, the condyles move down the eminence while the teeth move forward on a flat plane, so posterior separation occurs in protrusion. This is Christensen's phenomenon and explains why a compensating curve or cusp angulation is used for balanced occlusion.

Question 11Complete Dentures

The neutral zone in complete denture construction is the region where:

  1. Alveolar resorption is slowest
  2. Masticatory load on the ridge is greatest
  3. The palatal vault is deepest
  4. Forces from the tongue, cheeks and lips are in balance Correct answer.

Explanation

The neutral zone is the potential space between the tongue and the buccal and labial musculature where the forces exerted by these muscles cancel each other. Teeth and polished surfaces placed within this zone are not displaced during function.

Question 12Complete Dentures

For a displaceable anterior maxillary ridge, the flabby tissue is best recorded by:

  1. A functional wash impression taken under occlusal load
  2. Border molding the area with modeling compound only
  3. A single-stage alginate impression made with heavy pressure
  4. A window in the tray so the area is recorded undistorted Correct answer.

Explanation

Flabby tissue is displaced easily, so recording it under pressure produces a denture that becomes unstable once the tissue rebounds. A window in the tray, or a separate light-bodied record, captures the tissue in its undistorted form.

Question 13Complete Dentures

A facebow transfer is used in complete denture construction to:

  1. Relate the maxillary arch to the hinge axis of the articulator Correct answer.
  2. Establish the incisal guidance for the anterior teeth
  3. Record centric relation at the correct occlusal vertical dimension
  4. Measure the interocclusal rest space

Explanation

The facebow records the spatial relation of the maxillary arch to the terminal hinge axis and transfers it to the articulator. This allows the casts to open and close about an axis comparable to the patient's, improving the reliability of eccentric records.

Question 14Complete Dentures

After the loss of the natural teeth, resorption of the residual ridges generally results in:

  1. Loss of maxillary ridge height that exceeds mandibular loss
  2. Loss of mandibular ridge height that exceeds maxillary loss Correct answer.
  3. Equal loss of maxillary and mandibular ridge height
  4. Upward and backward movement of the mandibular anterior ridge

Explanation

Resorption proceeds in the direction of the forces applied, so the maxilla resorbs upward and inward while the mandible resorbs downward and outward. Because the mandibular denture-bearing area is smaller and the forces per unit area are greater, mandibular ridge loss is usually more pronounced.

Question 15Complete Dentures

In a mucostatic impression technique, the impression material is:

  1. Applied only over the crest of the ridge
  2. Compressed firmly against the mucosa while it sets
  3. Border molded under functional muscle movement
  4. Fluid enough to record the tissues without displacing them Correct answer.

Explanation

Mucostatic impressions aim to record the mucosa in its resting form using a low-viscosity material and minimal pressure. The resulting denture base contacts the tissue without the rebound instability produced by compressing displaceable tissue.

Question 16Complete Dentures

The essential property of a record base used for jaw relation records is that it is:

  1. Transparent so that the tissue can be seen
  2. Soft and easily adapted to the tissues
  3. Limited to the crest of the ridge
  4. Rigid and dimensionally stable Correct answer.

Explanation

Record bases must reproduce the fit of the future denture base and must not deform under the forces of recording or handling. Rigidity and dimensional stability ensure the jaw relation record is not lost between appointments.

Question 17Complete Dentures

When the maxillary occlusion rim is shaped, the anterior occlusal plane is set parallel to:

  1. The ala-tragus line
  2. The interpupillary line Correct answer.
  3. The nasolabial angle
  4. The Frankfort horizontal plane

Explanation

The anterior occlusal plane is adjusted so that it is parallel to the interpupillary line, which gives an acceptable esthetic result and a level incisal display. The posterior segment of the plane is oriented to the ala-tragus line instead.

Question 18Complete Dentures

At a wax try-in, which observation suggests that the occlusal vertical dimension is excessive?

  1. The lips meet with only slight effort
  2. The patient feels relaxed at rest
  3. The teeth contact evenly in centric occlusion
  4. The lips are visibly separated at rest Correct answer.

Explanation

When the occlusal vertical dimension is too great, the lips are strained and fail to close comfortably at rest, and the patient may show excessive tooth display. Comfortable closure at rest with even centric contacts indicates an acceptable record.

Question 19Complete Dentures

A patient reports a single localized sore spot 24 hours after denture insertion. The appropriate first step is to:

  1. Reduce the denture border along its entire length
  2. Place a permanent soft liner in the denture
  3. Advise leaving the denture out for one week
  4. Adjust the intaglio surface at the identified pressure point Correct answer.

Explanation

A localized sore spot usually reflects excessive pressure from a small area of the denture base. The pressure point is located with an indicator paste and relieved selectively, preserving the remainder of the fit and the border seal.

Question 20Complete Dentures

Compared with a reline, a rebase procedure:

  1. Is used only for immediate dentures
  2. Always requires new teeth to be set at a try-in
  3. Replaces the whole denture base while keeping the existing teeth Correct answer.
  4. Adds material only to the tissue surface of the denture

Explanation

A reline adds new material to the tissue surface of an existing base, whereas a rebase replaces the entire base and retains the existing tooth arrangement. Both are used to restore fit when the teeth are still serviceable.

Question 21Complete Dentures

For a patient with severely resorbed mandibular ridges and poor neuromuscular control, the preferred posterior tooth form is:

  1. Non-anatomic teeth with flat occlusal surfaces Correct answer.
  2. Semianatomic teeth with 20-degree cusps
  3. Metal posterior teeth with steep cusps
  4. Anatomical teeth with 33-degree cusps

Explanation

Flat, non-anatomic posterior teeth reduce the horizontal forces transmitted to a compromised ridge and are more tolerant of minor discrepancies in the jaw relation record. Steep cusps increase lateral loading and the risk of dislodgement and further ridge loss.

Question 22Complete Dentures

In a lingualized occlusion scheme, the maxillary lingual cusps occlude against:

  1. The incisal edges of the mandibular anterior teeth
  2. The broad central fossae of the mandibular posterior teeth Correct answer.
  3. The marginal ridges of the mandibular first premolars only
  4. The buccal cusps of the mandibular posterior teeth

Explanation

Lingualized occlusion concentrates occlusal contact on the palatal cusps of the maxillary teeth working in the central fossae of the mandibular teeth. This arrangement improves food penetration while reducing lateral forces on the mandibular ridge.

Question 23Complete Dentures

If the condylar guidance is fixed on the articulator and the incisal guidance is increased, balanced occlusion is maintained by:

  1. Increasing the compensating curve or the cuspal inclination Correct answer.
  2. Reducing the occlusal vertical dimension
  3. Reducing the number of posterior teeth in contact
  4. Flattening the occlusal plane completely

Explanation

The factors of articulation must remain in harmony, so a change in one requires compensation in the others. Greater incisal guidance must be offset by steeper cusps or a more pronounced compensating curve to keep posterior contacts balanced in excursion.

Question 24Complete Dentures

Which group of findings is most characteristic of combination syndrome?

  1. Resorption of the posterior mandible with anterior mandibular atrophy
  2. Uniform resorption of both ridges without soft tissue change
  3. Hypertrophy of the anterior maxillary ridge with atrophy of the tuberosities
  4. Resorption of the anterior maxilla with enlargement of the maxillary tuberosities Correct answer.

Explanation

Combination syndrome is seen when an edentulous maxilla opposes a mandibular arch that retains anterior teeth, typically an overdenture. The anterior maxilla resorbs, the tuberosities enlarge, the mandibular anterior teeth extrude and a soft tissue enlargement may appear in the anterior palate.

Question 25Complete Dentures

For a severely resorbed edentulous mandible, an implant-retained overdenture is preferred mainly because it:

  1. Removes the need for border molding
  2. Prevents resorption of the residual ridge completely
  3. Automatically corrects the occlusal vertical dimension
  4. Resists dislodgement from horizontal and rotational forces Correct answer.

Explanation

Conventional mandibular dentures on severely resorbed ridges fail largely because of movement under horizontal and rotational loads, which a retained overdenture resists through the implants. Border molding and careful jaw relation records are still required, and some ridge remodeling can continue.

Question 26Complete Dentures

The average interocclusal rest space (freeway space) in both dentulous and edentulous individuals is approximately:

  1. 0.5 to 1 mm
  2. 10 to 12 mm
  3. 6 to 8 mm
  4. 2 to 4 mm Correct answer.

Explanation

The interocclusal rest space is the difference between the vertical dimension of rest and the vertical dimension of occlusion, and it averages about 2 to 4 mm when measured at the incisors. This value is used as a guide when establishing the occlusal vertical dimension for complete dentures.

Question 27Complete Dentures

The main function of the posterior palatal seal in a maxillary complete denture is to:

  1. provide a vertical stop that fixes the occlusal vertical dimension
  2. relieve pressure over the midpalatal raphe
  3. maintain the posterior border seal during function Correct answer.
  4. increase the rigidity of the acrylic resin base

Explanation

The seal is created by compressing the soft tissue at the junction of the hard and soft palate, forming a valve that opposes displacement of the denture. It also compensates for the volumetric shrinkage of acrylic resin that occurs during processing.

Question 28Complete Dentures

Border molding of a custom impression tray is most commonly carried out with:

  1. zinc oxide-eugenol paste
  2. modeling plastic compound Correct answer.
  3. irreversible hydrocolloid
  4. light-bodied elastomer

Explanation

Modeling plastic becomes pliable when softened in a water bath and sets rigid enough to record the functional movement of the vestibular and lingual tissues. Its rigidity allows the recorded border to be trimmed and re-adapted at the chairside.

Question 29Complete Dentures

The primary (preliminary) impression of an edentulous arch is most often made with:

  1. addition silicone
  2. polyether
  3. irreversible hydrocolloid Correct answer.
  4. zinc oxide-eugenol paste

Explanation

Irreversible hydrocolloid flows readily under light pressure, is inexpensive, and records the denture-bearing area accurately enough for a custom tray to be fabricated. Final border detail and tissue adaptation are then refined in the secondary impression.

Question 30Complete Dentures

Christensen's phenomenon refers to:

  1. increased posterior contact on the working side
  2. lateral shift of the mandible toward the first contact
  3. loss of posterior contact in a protrusive position Correct answer.
  4. separation of the anterior teeth in centric occlusion

Explanation

When the mandible protrudes, the condyles descend the articular eminences and the posterior teeth separate, so a protrusive record shows a gap posteriorly. This separation is reproduced on an articulator only when the condylar guidance is correctly set.

Question 31Complete Dentures

The retromolar pad is important in mandibular complete denture construction because it:

  1. is the principal stress-bearing area of the mandibular denture
  2. indicates the position of the lingual nerve
  3. guides the posterior extent and the occlusal plane height Correct answer.
  4. must be relieved to prevent impingement of the inferior alveolar nerve

Explanation

The pad is a reliable landmark: the denture should cover it to gain support and seal, and the occlusal plane is usually set level with its lower third. It is preferred over the retromolar fossa because it is easily palpated and relatively stable.

Question 32Complete Dentures

When the maxillary anterior teeth are arranged, the labial surfaces of the central incisors are usually placed how far labial to the incisive papilla?

  1. 2 to 3 mm
  2. 8 to 10 mm Correct answer.
  3. 14 to 16 mm
  4. 4 to 5 mm

Explanation

The incisive papilla is a stable landmark that does not resorb, and the natural central incisors lie roughly 8 to 10 mm labial to its centre. This guide helps restore the original lip support when the anterior ridge has resorbed.

Question 33Complete Dentures

The compensating curve is incorporated into the arrangement of artificial posterior teeth primarily to:

  1. simplify the arrangement of the anterior teeth
  2. increase the masticatory efficiency of the dentures
  3. reduce the load transmitted to the residual ridge
  4. provide balanced occlusion in protrusive movements Correct answer.

Explanation

The anteroposterior curvature of the occlusal plane, together with the cuspal angulation, allows the posterior teeth to remain in contact as the mandible moves forward. This contact is what maintains balanced occlusion in the protrusive excursion.

Question 34Complete Dentures

Pressure indicating paste is used at the insertion visit of a complete denture to:

  1. reveal areas of excessive pressure on the mucosa Correct answer.
  2. show the polished surface contour required
  3. measure occlusal force in the molar region
  4. record the denture borders in function

Explanation

The paste is painted on the intaglio surface and, where the mucosa has been compressed, it is displaced to leave a clean area on the denture. These clean areas identify the points that must be relieved before the next visit.

Question 35Complete Dentures

A space of about 1 mm is provided in a custom impression tray to:

  1. provide room for the border molding material
  2. reduce the setting time of the impression material
  3. allow a uniform thickness of impression material Correct answer.
  4. prevent distortion of the tray during curing

Explanation

A uniform space ensures that the impression material flows evenly over the whole denture-bearing area rather than being squeezed thin in some regions. Uniform thickness gives more even dimensional change on setting and more accurate tissue contact.

Question 36Complete Dentures

The closest speaking space is used clinically to:

  1. determine the extent of the posterior palatal seal
  2. record centric relation
  3. verify the occlusal vertical dimension Correct answer.
  4. set the angle of the incisal guidance

Explanation

While the patient counts rapidly, the teeth approach each other to within about 1 to 2 mm without touching, giving a functional check on the vertical dimension. If the teeth click together during speech, the vertical dimension is probably excessive.

Question 37Complete Dentures

When posterior teeth are arranged for a complete denture, the central fossae of the mandibular posterior teeth should lie:

  1. far lingual to the ridge to enlarge tongue space
  2. at the buccal border of the retromolar pad
  3. on the buccal slope of the residual ridge
  4. over the crest of the residual ridge Correct answer.

Explanation

Placing the occlusal forces over the crest of the ridge directs the load onto the most favourable stress-bearing bone and reduces tipping moments on the base. A lingual or buccal displacement produces leverage that promotes resorption and instability.

Question 38Complete Dentures

During selective grinding, a working-side prematurity between the buccal cusp of a maxillary premolar and the buccal cusp of the opposing mandibular tooth is corrected by grinding:

  1. the buccal cusp of the mandibular tooth
  2. the buccal cusp of the maxillary tooth Correct answer.
  3. the lingual cusp of the maxillary tooth
  4. the lingual cusp of the mandibular tooth

Explanation

The mnemonic BULL directs that in working-side interference the buccal cusp of the upper tooth and the lingual cusp of the lower tooth are reduced, because these are the surfaces that ride over the opposing incline during lateral excursion. Grinding the non-interfering supporting cusps would destroy centric stops.

Question 39Complete Dentures

A prominent torus mandibularis lies within the lingual border area of a planned mandibular denture. The appropriate management is to:

  1. border mold the torus area under heavy pressure
  2. relieve the denture base over the torus Correct answer.
  3. arrange the posterior teeth lingual to the torus
  4. extend the lingual flange over the torus to gain retention

Explanation

The mucosa over a torus is thin and non-compressible, so pressure there rapidly produces ulceration and pain. Relief in the denture base, or surgical removal when the torus is very large or undercut, allows the border to be extended without impingement.

Question 40Complete Dentures

In a bilaterally balanced occlusion, contact on the non-working side during a lateral excursion occurs between:

  1. maxillary lingual cusps and mandibular buccal cusps Correct answer.
  2. maxillary buccal cusps and mandibular lingual cusps
  3. buccal cusps of both maxillary and mandibular teeth
  4. lingual cusps of both maxillary and mandibular teeth

Explanation

On the non-working side the mandible moves medially, so the maxillary lingual cusps pass over the buccal inclines of the mandibular buccal cusps and maintain contact. This crossing contact is what balances the working-side contacts and stabilizes the bases during function.

Question 41Removable Partial Dentures

A partially edentulous arch has edentulous areas on both sides of the arch, each located posterior to the remaining natural teeth. How is this arch classified in the Kennedy system?

  1. Class IV
  2. Class III
  3. Class II
  4. Class I Correct answer.

Explanation

Kennedy Class I describes bilateral edentulous areas that lie posterior to the remaining natural teeth, giving two distal extension bases. Class II is a unilateral posterior space, Class III is a bounded posterior space with natural teeth both anterior and posterior to it, and Class IV is an anterior space crossing the midline.

Question 42Removable Partial Dentures

According to Applegate's rules, how is a missing third molar that will not be replaced handled when the arch is classified?

  1. It automatically places the arch in Class I
  2. It is not considered in the classification Correct answer.
  3. It is counted as an additional edentulous area
  4. It is treated as an anterior edentulous space

Explanation

Applegate's rules state that if a third molar is missing and will not be replaced, the space is disregarded when applying the Kennedy classification. Only spaces that will actually be restored by the prosthesis influence the class.

Question 43Removable Partial Dentures

A mandibular removable partial denture is planned for a patient whose floor of the mouth is high and whose lingual frenum lies close to the gingival margins of the incisors. Which major connector is most appropriate?

  1. Labial bar
  2. Palatal strap
  3. Lingual bar
  4. Lingual plate Correct answer.

Explanation

A lingual plate is chosen when there is insufficient vertical space between the gingival margins and the functional floor of the mouth for a lingual bar. The plate is carried onto the lingual surfaces and cingula of the anterior teeth, so it is not limited by the height of the floor of the mouth.

Question 44Removable Partial Dentures

What is the primary function of an occlusal rest on a removable partial denture abutment?

  1. To prevent food packing beneath the major connector
  2. To direct occlusal forces along the long axis of the abutment tooth Correct answer.
  3. To retain the framework by engaging an undercut
  4. To provide reciprocation against the retentive arm

Explanation

A rest seat converts occlusal loading into a force directed essentially along the long axis of the abutment, which the periodontal ligament tolerates best. It also maintains the vertical relationship of the framework and prevents the prosthesis from settling into the tissues.

Question 45Removable Partial Dentures

Which part of a circumferential clasp engages the undercut and provides retention?

  1. The minor connector
  2. The reciprocal arm
  3. The occlusal rest
  4. The terminal third of the retentive arm Correct answer.

Explanation

Retention is produced by the tapered terminal third of the retentive arm flexing as it crosses the height of contour and springing back into the undercut. The amount of retention depends on the depth of the undercut and the taper and length of that terminal portion.

Question 46Removable Partial Dentures

What is the main purpose of surveying a cast before designing a removable partial denture?

  1. To select the shade of the artificial teeth
  2. To establish the plane of occlusion
  3. To locate the most favourable path of insertion and the available undercuts Correct answer.
  4. To measure the thickness of the residual ridge

Explanation

The surveyor identifies the height of contour of each abutment and, by tilting the cast, allows the designer to choose a single path of insertion that gives adequate retention with minimal tooth preparation. It also reveals interferences and guides preparation of guiding planes and rest seats.

Question 47Removable Partial Dentures

Which material is most commonly used for the denture base that carries the artificial teeth in a removable partial denture?

  1. Type IV dental stone
  2. Autopolymerizing epoxy resin
  3. Polymethyl methacrylate resin Correct answer.
  4. Cobalt-chromium casting alloy

Explanation

Acrylic resin, usually heat-polymerized polymethyl methacrylate, is the standard base material because it is easy to process, repair and reline, and can be shaped to fit the ridge. The cobalt-chromium alloy forms the framework and connectors, not the tooth-bearing base.

Question 48Removable Partial Dentures

What is the chief purpose of an indirect retainer in a Kennedy Class I removable partial denture?

  1. To limit rotation of the denture base about the fulcrum line Correct answer.
  2. To replace the need for a major connector
  3. To provide direct retention on the terminal abutment
  4. To splint periodontally involved anterior teeth

Explanation

The indirect retainer is placed on the side of the fulcrum line opposite the distal extension and resists the lifting rotation of the base that occurs when the patient closes on the anterior teeth. Because it acts at a distance from the fulcrum, it also reduces the torque transferred to the terminal abutments.

Question 49Removable Partial Dentures

Which clasp assembly is described as a mesial rest, a proximal plate and an I-bar?

  1. RPI Correct answer.
  2. Roach clasp with a distal rest
  3. RPA
  4. Akers clasp

Explanation

RPI stands for rest, proximal plate and I-bar, with the rest placed mesially on the abutment adjacent to the distal extension. This combination is designed so that the I-bar disengages when the extension base moves towards the tissue, reducing torque on the abutment.

Question 50Removable Partial Dentures

How does the RPA clasp design differ from the RPI design?

  1. It uses a distal rather than a mesial rest
  2. It omits the rest seat
  3. It omits the proximal plate
  4. It uses a circumferential cast clasp arm instead of an I-bar Correct answer.

Explanation

Both designs share a mesial rest and a proximal plate; the difference is the retentive element. RPA uses an Akers circumferential clasp arm, which is stiffer and provides more bracing than the I-bar used in RPI.