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Friday, March 23, 2001

Prosthodontics MCQ Answer 16

Friday, March 23, 2001
0 comments

Answer is B

A Porcelain fused to metal crown has several advantages

  • The metal core supports the tooth.
  • It is strong enough to withstand the heaviest biting forces and resist fracturing.
  • It is durable and long lasting.
  • The porcelain can be made to closely match natural teeth.

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Prosthodontics MCQ Answer 15

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Answer is E

The Path of Insertion created by the preparation is dependent upon:

•Approximating contacts/contours
•Tooth inclination
•Esthetics
•Path of insertion of other abutment teeth
•Planned restoration contour
•Pulp size and location

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Prosthodontics MCQ Answer 14

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Answer is D

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Prosthodontics MCQ Answer 13

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Answer is A

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Prosthodontics MCQ Answer 12

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Answer is A

  • when tapers and prep heights are equal, the prep with the smallest diameter will be more resistant. This is because the tangent line is lower on the opposing wall, creating an increased resistant area. So, for retention you want a bigger diameter and for resistance you want a smaller one.
  • the resistance for a short, wide prep can be enhanced with boxes and grooves.
  • when prep height and diameter are equal, the prep with the greater taper will have a decrease in resistance.
  • the taper that provides resistance for a prep where the height is equal to the base is 2x that of a prep where the height equals ½ the base. So, a shorter prep needs to be more parallel. To achieve adequate resistance, the ht to base ratio should be at least 0.4 or greater, provided you have minimal taper. 3mm of prep ht should be adequate for anterior teeth while 4mm should be adequate for molars.

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Oral Medicine And Radiology MCQ Answer 01

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Answer is A

IPH has commonly been described as having a cobblestone appearance. It is a painless, firm, pink or red nodular proliferation more commonly found on the hard palate with occasional extension onto the residual ridge. When the papillary lesions are reddened, secondary infection with Candida is common. IPH is not pre-malignant; it is an inflammatory process with a fungal component.

More Notes

Inflammatory papillary hyperplasia, also known as papillary hyperplasia of the palate and erroneously as palatal papillomatosis, is almost always restricted to the mucosa under a denture base. First reported by Berry in 1851, it results from selective but severe edema and eventual inflammatory fibrosis of the connective tissue papillae between the rete processes of the palatal epithelium. It is found in three of every 1,000 adults .

The great majority of cases are seen beneath ill-fitting dentures of long use and in persons who do not take their dentures out overnight. The lesion seems to result from a combination of chronic, mild trauma and low-grade infection by bacteria or candida yeast. It is occasionally seen in patients without dentures but with high palatal vaults or with the habit of breathing through their mouths.

Clinical Features

Papillary hyperplasia is seen in middle-aged and older persons and there is a strong female predilection (2 females:1 male). The disease occurs on the bone-bound oral mucosa of the hard palate and alveolar ridges. It presents as a cluster of individual papules or nodules which may be erythematous, somewhat translucent or normal in surface coloration . Often the entire vault of the hard palate is involved, with alveolar mucosa being largely spared. White cottage cheese-like colonies of candida may be seen in clefts between papules. There is seldom pain, but a burning sensation may be produced by the yeast infection. Early papules are more edematous while older ones are more fibrotic and firm, being individually indistinguishable from irritation fibroma.

Pathology and Differential Diagnosis

Connective tissue papillae are greatly enlarged by edematous connective tissue, granulation tissue, densely fibrotic tissue, or a combination thereof, depending on the duration of the lesion . Small to moderate numbers of chronic inflammatory cells are present, perhaps admixed with occasional polymorphonuclear leukocytes. Each enlarged papilla produces a surface nodule which may be pedunculated or sessile, with deep clefts between nodules.

Covering epithelium is often atrophic but may be acanthotic, especially near the base of the inter-nodal troughs. Occasional lesions demonstrate extensive pseudoepitheliomatous hyperplasia. Basal cell hyperchromatism and basal layer hyperplasia often impart a false appearance of mild epithelial dysplasia. Surface ulceration is surprisingly rare and deeper tissues show few alterations beyond a mild chronic inflammatory cell infiltration.

While individual nodules may appear identical to pyogenic granuloma and irritation fibroma, the palatal location and the multinodularity of the lesion makes the diagnosis of papillary hyperplasia an easy one. Some of the more edematous papules may mimic the mucus extravasation of mucocele, but will be negative for mucus with the mucicarmine stain. A silver or periodic acid-Schiff (PAS) stain will frequently identify candida spores and hyphae in the superficial portions of the epithelium, especially in cases with severe acanthosis or pseudoepitheliomatous hyperplasia.

Treatment and Prognosis

The old concern that papillary hyperplasia of the palate held increased risk for cancer is no longer accepted. Even extensive lesions will continue indefinitely, waxing and waning in the early years but remaining more constant as nodules become more and more fibrotic. Occasional proliferations are so exuberant that clefts between nodules may be more than a centimeter deep.

Early lesions may completely disappear with cessation of denture use for 2-4 weeks, perhaps aided by topical antibiotic or antifungal therapies. Persistent lesions must be surgically removed or laser ablated if a proper base is to be prepared for a new and better-fitting denture.

References


Berry A. A partial set of teeth sustained by air chambers instead of clasps. Dent Reg West 1851; 9:114-116.

Bhaskar SN, Beasley JD III, Cutright DE. Inflammatory papillary hyperplasia of the oral mucosa: report of 341 cases. J Am Dent Assoc 1970; 81:949-952.

Priddy RW. Inflammatory hyperplasias of the oral mucosa. J Can Dent Assoc 1992; 58:311-315,319-321.

Bouquot JE, Wrobleski. Papillary (pebbled) masses of the oral mucosa, so much more than simple papillomas. Pract Perio Anesth Dent 1996; 8:533-543.

Salonen MAM, Raustia AM, Oikarinen KS. Effect of treatment of palatal inflammatory papillary hyperplasia with local and systemic antifungal agents accompanied by renewal of complete dentures. Acta Odont Scand 1996; 54:87-91.

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Pharmacology MCQ Answer 01

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Answer is B


Lidocaine is THE local anesthetic. It blocks activated AND inactivated Na+ channels, and it has its greatest effect in pts with ischemia.

  • It reduces ventricular automaticity but has no effect on the atria.
  • It has no anticholinergic effects.
  • Slight effect on the QT interval, mostly reduction (not prolongation), no prolongation of QRS. So it is not pro-arrhythmic. Lidocaine is probably one of the most useful of all the drugs we are going to be talking about. So ventricular only, no atria.
  • It has a very rapid hepatic metabolism; its clearance = hepatic blood flow.
  • MUST be given IV, by infusion, usually started with a few boluses; has no effect po.

Lidocaine is generally the drug of choice for almost all types of ventricular arrhythmias. Lidocaine is used most often in situations of ischemia (e.g.- CCU pts with early signs of ventricular ectopy).

The main adverse effect is on the CNS: drowsiness, nystagmus, confusion, speech disorders, parasthesias. In rare situations (toxicity) seizures can occur, usually in pts who have hepatic insufficiency and can’t metabolize the drug, or CHF, where clearance is reduced. Lidocaine is generally very well tolerated, though.

RARELY it can be associated with arrhythmias, although this is hard to prove because the pt was on the drug for arrhythmias, so it can be unclear whether there just was not enough of the drug (a break-through-like phenomenon) or whether they are an actual side effect of the drug.

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Prosthodontics MCQ Answer 11

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Answer is E





ANTERIOR GUIDANCE

Also known as: -

The influence of the contacting surfaces of teeth on mandibular movement

ARCON

Also known as:- ARTICULATED CONDYLE

Where the condyle part is attached to the lower member of the articulator. NON-ARCON is where the condylar part is attached to the upper member of the articulator.

ARTICULATION

Also known as: -

A relationship of the upper & lower teeth which exists during mandibular movement from one occlusion to another. It is a dynamic relationship & it may be balanced or unbalanced.

BALANCED ARTICULATION

Also known as: - FULLY BALANCED OCCLUSION

BALANCED DYNAMIC OCCLUSION

A multi-point contact relationship of the opposing teeth in which they guide smoothly over each other during mandibular movement without causing dislodgement of the dentures.

BALANCED OCCLUSION

Also known as:- BILATERALLY BALANCED OCCLUSION

BALANCED STATIC OCCLUSION (Dentures)

A multi-point contact relationship of opposing teeth in static contact.

BENNETT ANGLE

Also known as: - PROGRESSIVE SIDE SHIFT

The angle obtained after the non-working side condyle has moved anteriorly & medially, relative to the sagittal plane. The flatter the cusp the greater the side shift.

BENNETT SHIFT

Also known as: - BENNETT MOVEMENT

IMMEDIATE SIDE SHIFT

MANDIBULAR SIDE SHIFT

The bodily lateral movement of the mandible towards the working side during lateral excursions (approx. 0.3mm)

BRUXISM

Also known as: - PARAFUNCTIONAL ACTIVITY

Tooth contacting habits, which are not necessary in order to execute the normal physiological oral function. I.e. clenching & grinding.

CANINE GUIDANCE

Also known as: - CANINE PROTECTED OCCLUSION

The part of the anterior guidance that often occurs on lateral excursion, where the mandibular movement is dictated by mandibular canine-maxillary canine contacts

CENTRIC OCCLUSION (CO)

Also known as: - INTERCUSPAL POSITION (ICP)

HABITUAL OCCLUSION

INTERCUSPATION POSITION

MAXIMUM INTERCUSPATION

HABITUAL CENTRIC

AQUIRED CENTRIC

BITE OF ACCOMMODATION

The position of the mandible when the maxillary & mandibular teeth are at their most interdigitated. I.e. Maximum intercuspation of the teeth irrespective of the condyle to fossa relationship. This is only evident when an adequate number of occluding teeth are present.

CENTRIC RELATED OCCLUSION

Also known as: -

When CO & CRO are co-incidental. This the ideal that we aim for in an equilibrated mouth – simultaneous contact of all the teeth with the condyles in centric relation – see reorganized occlusion

CENTRIC RELATION OCCLUSION (CRO)

Also known as: - RETRUDED CONTACT POSITION (RCP)



The position of the mandible determined by tooth to tooth contact when the mandible closes in CR.

CENTRIC RELATIONSHIP (CR)

Also known as: - TERMINAL HINGE AXIS

TERMINAL HINGE RELATION

RETRUDED ARCH OF CLOSURE

RETRUDED AXIS POSITION (RAP)

LIGAMENTOUS POSITION

HINGE AXIS

The most retruded position of the mandible relative to the maxilla determined by the TMJ with the teeth separated I.e. Condyle to fossa relationship without tooth contact. Condyles in the upper most position in fossa.

CENTRIC STOP

Also known as: - CENTRIC STOP POSITION

Cusp tip used to achieve contact.


CONDYLE

Also known as: -

The rounded surface at the distal extremity of the ramus of the mandible, which fits into the Glenoid fossa to form the tempromandibular joint.

CONDYLAR ANGLE

Also known as: - CONDYLE PATH

The angle given by the downward & forward slope of the glenoid fossa. “S” shaped in life, this represented as a straight line in average value & semi-adjustable articulators.

CONDYLAR GUIDANCE

Also known as:- ANGLE OF EMINENCIA

The mechanism on an articulator which reproduces the paths down which the condyles travel on protrusion of the mandible.

CONFORMATIVE

Also known as: -

When restorations are fabricated to the existing jaw relationship.

CROSSOVER INTERFERENCES

Also known as: -

Once the canine has moved into a position that is labial to the upper canine & the tips have crossed over, the mandible has then entered into the crossover position.

DISCLUSION

Also known as: - DISCLUDING


The separation of teeth during excursive movements e.g. on protrusion, as the mandibular anterior teeth slide over the palatal surfaces of the maxillary teeth the posterior teeth often disclude.


FOSSAE

Also known as: - FOSSA

A depression.

FREEWAY SPACE

Also known as: - INTEROCCLUSAL CLEARANCE

INTEROCCLUSAL SPACE



The space between the occlusal surfaces of the maxillary & mandibular teeth when in the rest position. It is usually measured in the premolar region.


FUNCTIONAL CUSP

Also known as: -


The palatal cusps of maxillary teeth & buccal cusps of mandibular teeth, which occlude with opposing fossae.


GROUP FUNCTION

Also known as: - SHARED FUNCTION


Guidance of the mandible when a number of posterior teeth are in contact in lateral and protrusive excursion.

INTERFERENCE

Also known as: - OCCLUSAL INTERFERENCE

DEFLECTIVE CONTACTS

An uneven, early contact arising on one or more teeth during a excursive movement causing disclusion of guiding teeth


INTERCONDYLER DISTANCE

Also known as: -

The distance between the condylar heads at any point.

LATERAL EXCURSION

Also known as: - LATRUSION

Sideways movement of the mandible.


LINGUALIZED OCCLUSION (LO)

Also known as: - PALATALISED OCCLUSION

It is where only the maxillary posterior palatal cusps occlude with shallow mandibular central fossae.

LONG CENTRIC

Also known as: - FREEDOM IN CENTRIC OCCLUSION


Freedom of the mandible to slide forward at the same vertical dimension.


MALOCCLUSION

Also known as: -

A deviation from normal occlusion of one or more teeth in the dental arches.

MUTUALLY PROTECTED OCCLUSION (MPO)

Also known as: -

That in centric relation there is only posterior tooth contact. The maxillary palatal cusps & mandibular buccal cusps should occlude with there opposing occlusal fossae. Thus, anterior teeth positively disclude the posterior teeth in all excentric excursions, protecting the posterior teeth (of implants) from harmful lateral forces.

NON-WORKING CONDYLE

Also known as: - ORBITING CONDYLE

The condyle on the non-working side, which undergoes a mainly translatory movement during function on the working side.


NON-WORKING MOVEMENT

Also known as: - NON-WORKING SIDE

NON-FUNCTIONING

BALANCING

CONTRALATERAL

ORBITING SIDE

The side the mandible is moving away from.

NON-WORKING SIDE INTERENCES

Also known as: -

Is a posterior contact on the non-working side which interferes with ideal anterior guidance, thus when the mandible moves in one direction, if a tooth on the opposite side interferes with ideal anterior guidance, this is classed as a non-working side interference.


PANTOGRAPHIC READING

Also known as: -

A reading from a device that accurately traces mandibular movements with two main component parts similar to two face bows; one is attached to the maxillary arch & one to the mandibular arch. On being transferred to a fully adjustable articulator, the resulting three-dimensional tracing of border movements can be used to programme the articulator to reproduce mandibular movement with a high degree of accuracy.

PATH OF CLOSURE

Also known as: - LINE OF CLOSURE

The path taken from rest to occlusal positions. It is usually traced at the incisal edges of the lower central incisors.


PREMATURE CONTACT

Also known as: - CLOSURE INTERFERENCE

FIRST POINT OF CONTACT

An uneven contact arising only on one tooth as the mandible closes to centric occlusion.


PROPRIOCEPTIVE

Also known as: -

The sensory perception of the occlusal load due to the periodontal ligament that attaches the teeth to the alveolus.

PROTRUSIVE EXCURSION

Also known as: - PROTRUSION

Forward movement of the mandible.


REORGANISED

Also known as: -

When restorations are fabricated to the patients jaw position in centric relation. Deflective contacts & occlusal interference’s are removed, allowing the muscles of mastication to move the mandible free from proprioceptive influence of these contacts.

REST POSITION

Also known as: - POSTURAL REST POSITION

POSTURAL POSITION

The position the mandible adopts when standing or sitting upright, when the musculature is at rest. Determined by muscle tone & tension of surrounding tissues.


SAGITAL PLANE

Also known as: -

The longitudinal vertical plane that divides the mouth into two halves (left & right)

THE ALERT FEEDING POSITION

Also known as: -

The head is tilted 30 degrees forward. The aim is to have no deflective contacts on the maxillary anterior teeth as the mandible closes in its acquired position.



WORKING CONDYLE

Also known as: -

The condyle on the non-working side, which undergoes a mainly rotational movement during function on the working side.


WORKING MOVEMENT

Also known as: - WORKING SIDE

FUNCTIONING SIDE

ROTATING SIDE

The side the mandible is moving to during excursive movement


WORKING SIDE INTERFERENCES

Also known as: -

The term working side is still most commonly used to describe the side to which the mandible is moving during a lateral excursion. A working side interference is a posterior contact on the working side, which interferes with the ideal anterior guidance.



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Dental Anatomy MCQs Answer 06

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Answer is C

Embrasure: The space between two teeth which opens out from their contact point.

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Saturday, March 17, 2001

Dental Anatomy MCQs Answer 5

Saturday, March 17, 2001
0 comments

Answer is C

DENTIN

It consists of about 80% hydroxyapatite (by dry weight) and 20% of organic matrix (collagen, proteoglycans, glycosaminoglycans) and is pervaded by the dentinal tubules. On the outside, the dentin is covered either by enamel (anatomical crown) or by cementum. On its inner surface facing the pulp chamber and the root canal, the dentin is lined by the odontoblasts, which are columnar cells arranged in a single layer (fig. 19). Each odontoblast sends a cytoplasmic process into one dentinal tubule, reaching as far as 1/2 the thickness of the dentin. Odontoblasts are not separated from the pulp by a basement membrane. A plexus of capillaries extends within the odontoblast layer close to the predentin (a thin uncalcified layer of dentin matrix facing the pulp chamber).

The odontoblasts are of mesenchymal origin, synthesizing and secreting the components of the dentinal matrix. They secrete first a layer of predentin, which stains pale in H&E and PAS preparations. The odontoblasts furthermore secrete a phosphoprotein that is deposited specifically at the predentin-dentin junction. Apparently this phosphoprotein initiates the calcification of dentin. Dentin stains strongly with H&E and PAS.

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120 MCQs in Prosthodontics Answers

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The Correct option is C

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119 MCQs in Prosthodontics Answers

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The Correct option is C

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118 MCQs in Prosthodontics Answers

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The Correct option is B

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117 MCQs in Prosthodontics Answers

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The Correct option is E

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116 MCQs in Prosthodontics Answers

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The Correct option is A

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115 MCQs in Prosthodontics Answers

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The Correct option is E

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114 MCQs in Prosthodontics Answers

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The Correct option is B

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113 MCQs in Prosthodontics Answers

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The Correct option is D

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112 MCQs in Prosthodontics Answers

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The Correct option is C


Guiding planes assist with the placement of the RPD but they also can limit rotation of abutment teeth. Retentive clasps should be bilaterally opposed (buccal retention on one side of arch should have buccal retention on other side of arch), unless guiding planes will control the path of insertion/removal and stabilize abutments against rotational movements.

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111 MCQs in Prosthodontics Answers

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The Correct option is E

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110 MCQs in Prosthodontics Answers

0 comments

The Correct option is D

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109 MCQs in Prosthodontics Answers

0 comments

The Correct option is D

THE KENNEDY-APPLEGATE-FISET CLASSIFICATION SYSTEM

  • Class I Bilateral posterior edentulous areas
  • Class II An unilateral posterior edentulous area
  • Class III A unilateral tooth bounded edentulous area
  • Class IV An anterior tooth bounded edentulous area which crosses the midline
  • Class V A unilateral tooth bounded edentulous area where the anterior tooth is weak and incapable of providing support for the RPD

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108 MCQs in Prosthodontics Answers

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The Correct option is D

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107 MCQs in Prosthodontics Answers

0 comments

The Correct option is E

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106 MCQs in Prosthodontics Answers

0 comments

The Correct option is D

Major connectors must posses the following five qualities:

  1. Rigidity.
  2. Provide vertical support and protection of the soft tissues.
  3. Provides means of obtaining indirect retention where indicated.
  4. Provide an opportunity of positioning the denture bases where needed.
  5. Maintain patient comfort.

The first requirement of a major connector is rigidity. This allows stresses that are applied to the partial denture to be distributed effectively over the entire supporting area, including the teeth, underlying, bone and soft tissue. Other components of a partial prosthesis can only be effective if the major connector is rigid. Flexibility allows forces to be concentrated on individual teeth or edentulous ridges causing damage to those areas.

Major connectors must avoid impingement of the free gingival margin. The major connector must never terminate on gingival tissue. In maxillary castings the border of the major connector should be at least 6mm to 8mm from the gingival margin of the teeth and in the mandibular it should be at least 3mm from the gingival margin.

Patient comfort should be a consideration when designing the major connector and food traps must be avoided where possible.

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105 MCQs in Prosthodontics Answers

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The Correct option is C


Occlusal Rest

Located on the occlusal surface of molars and premolars. The size should be (approx.) half the buccolingual width and a quarter the mesiodistal width of the tooth on which it is to be seated. Rest seats may be prepared by the Dentist, therefore they need to be filled to the dimensions of the preparation. The occlusal rest is used to provide vertical support of a removable prosthesis.

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104 MCQs in Prosthodontics Answers

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The Correct option is C

Reciprocal Arm.

A rigid non retentive clasp arm placed occlusal to the height of contour on the opposing side of the tooth to the retentive arm. It should, where possible, resist the tipping force applied to the tooth by the retentive arm as it passes over the height of contour. The arm also helps stabilize the prosthesis against lateral movement. It can also contribute to vertical support as it is occlusal to the height of contour.

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103 MCQs in Prosthodontics Answers

0 comments

The Correct option is B


If a removable partial denture is not supported by natural teeth at each end of the edentulous saddle area, some provision must be made for the prosthesis to resist rotational forces that are exerted. This may also apply to long span bounded saddles (anterior especially).

Rotational movement around the fulcrum line, either toward the tissue or away from the tissue, may occur as forces are applied to the denture base. Movement toward the supporting ridge will be limited by the amount of compressible mucosa, or the amount of bone resorbption since the prosthesis was made. This movement to the ridge can only be controlled by accurate denture base adaptation. An indirect retainer does not control this movement.

Movement also occurs away from the tissue. This movement may be caused by sticky foods or other matter lifting the denture base; the tongue or buccinator muscles when they are activated by speech, mastication or swallowing. Gravity may also exert dislodging forces on a maxillary prosthesis. The reason for the use of the indirect retainer is to counter the movement produced by these forces.

The indirect retainer in free-end prosthesis uses the mechanical advantage of leverage by moving the fulcrum line farther from the force. The indirect retainer may contribute to the support and stability of the prosthesis.

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102 MCQs in Prosthodontics Answers

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The Correct option is B

Reference: http://www.feppd.org/ICB-Dent/campus/manufacturing_aspects/Casting.htm

Gypsum based investment

The gypsum based investments have traditionally been used for casting of gold alloy inlays, onlays, crowns and fixed partial dentures.

The main constituents of the gypsum based investment are a - hemihydrate of gypsum and quartz. The a-hemihydrate of gypsum serves as a binder and gives strength to the investment.

When heated to high temperatures, gypsum on its own shrinks and can fracture. Its change in dimension with temperature can be described as follows: it shrinks at a temperature range between 200 and 400oC, it slightly expands between 400 and 700oC and than it undergoes significant shrinkage beyond 700C. Because of this property, the gypsum should not be heated beyond 700C. In order to compensate for this shrinkage (which could cause the pattern void to expand) the pure gypsum moulds are significantly undersized.

Silica is added to provide a refractory component. As explained above, gypsum shrinks considerably with increase in temperature. However, if silica is added to the investment, this shrinkage can be reduced or even turned into expansion.

Setting time

The setting time of the investment is usually between 5 and 25 minutes, with the modern investments setting initially between 9 and 18 minutes.

Effects on setting expansion of the investment

· The amount of expansion of the investment is proportional to the portion of the silica component.

· It also depends on the size of the silica particles, the smaller the particles the higher the expansion.

· The higher the water/powder ratio of the investment wet mixture, the less hygroscopic setting expansion it will develop.

· The hygroscopic expansion is reduced as the mixing time is reduced.

· Duration of the immersion, especially before the initial set.

· Effect of the confinement offered by the casting ring.

Effects on thermal expansion

Thermal expansion of the investment is affected by:

· Amount and type of silica in the mixture which counterbalances shrinkage of the gypsum phase, and is in equilibrium at about 75% silica content.

· Water / Powder ratio – more water introduced in mixing leads to less thermal expansion.

· Chemical modifiers – small amounts of sodium, potassium or lithium chlorides could completely prevent any thermal shrinkage caused by the gypsum phase.

· Thermal contraction once it starts to cool down.

Phosphate based investments

The spread of use of phosphate based investment is caused by an increase in use of metal ceramic prosthesis, which require higher melting temperatures gold alloys. These temperatures are too high to be cast adequately in the gypsum based investments. Also, use of the less expensive base metal alloys forces the use of the phosphate based investments. CP titanium and titanium alloys also require use of specially formulated investments.

The investment consists also of binders and refractory filler, which are the same as for the gypsum based investments. However, the binder in this case is magnesium oxide and a monoammonium phosphate. Carbon is also often added to the investment in order to help to produce a clean casting and to encourage easier divesting of the casting from the mould. Differently to the gypsum based investments, these investment in practice do not show signs of setting shrinkage, but rather of slight expansion.

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101 MCQs in Prosthodontics Answers

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The Correct option is D



Stone, E.R. Tripping Action of Bar Clasps. JADA 23:596-617,1936.

Purpose: To compare the effects of the tripping action of bar clasps to horizontal type clasps

Discussion:

1. Definition: "Tripping Action": stumbling action which operates in many of the bar clasps, but not in the horizontal or diagonal circumferential clasps.

* tripping action is greatest when the arm of the bar clasp, under tension, approaches the plane of the undercut at a right angle to its origin.

2. Comparative analysis between push (bar) and drag (horizontal) type clasps

a) push: maximum tripping action, greater retention

b) drag: no tripping action

3. Retention: the direct gripping or clutch action of the clasp, influenced by - tension, length, mass and x-sectional shape of the clasp arm, torsion, tripping action.

4. Stabilization: influenced by - width, thickness, x-sectional shape and tension of the clasp arms, the distance from the occlusal rest to the lowest point of that same clasp-bearing area toward the gingiva, the distance from each occlusal rest to the farthest point of the denture base, tripping action

5. Types of teeth which are greatly influenced by the tripping action:

a) Short teeth where undercuts are hard to locate or lacking entirely (positive influence)

b) Long, bell-shaped teeth with excessive gingival recession or excessive inclination (negative influence)

6. Two clinical cases were presented.

Conclusion: The tripping action of bar clasps make them a more favorable clasp design choice in most clinical situations. The horizontal clasp should be used only in cases wherein malposed or tilted teeth and deep undercuts make it impractical to use the bar clasp.



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Friday, March 16, 2001

100 MCQs in Prosthodontics Answers

Friday, March 16, 2001
0 comments

The Correct option is C

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99 MCQs in Prosthodontics Answer

0 comments

The Correct option is A

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98 MCQs in Prosthodontics Answer

0 comments

The Correct option is B

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97 MCQs in Prosthodontics Answer

0 comments

The Correct option is C

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96 MCQs in Prosthodontics Answer

0 comments

The Correct option is D




EIGHT FUNCTIONS OF RPD COMPONENTS

1. Support: Resistance to movement of the prosthesis toward the edentulous ridge. Support is the means by which occlusal forces are transferred to the teeth and denture bearing tissues for dissipation.

2. Retention: Resistance to movement of the prosthesis away from the edentulous ridge along the path of placement.

3. Reciprocation: The means by which forces acting on one part of a RPD are counterbalanced, counteracted or negated by another part of the RPD.

4. Bracing: The resistance to horizontal forces from mastication and the tongue.

5. Indirect Retention: The resistance to rotational movement of a tooth-tissue supported denture base and palatal major connector away from the denture foundation area when occlusal forces (sticky foods) are applied to the denture base.

6. Esthetics/Occlusion: The replacement of the esthetic and functional qualities of the missing natural teeth by prosthetic (artificial) teeth.

7. Connection: The means by which one component of an RPD is connected or attached to another.

8. Stability: The resistance to movement of a prosthesis due to functional forces. Stability of a RPD is obtained by all the factors which provide support, retention, reciprocation, bracing, indirect retention, occlusion, and connection. Stability also depends on the manner in which the patient uses the prosthesis.

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95 MCQs in Prosthodontics Answers

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The Correct option is A

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94 MCQs in Prosthodontics Answers

0 comments

The Correct option is C

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93 MCQs in Prosthodontics Answers

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The Correct option is B

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92 MCQs in Prosthodontics Answers

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The Correct option is C


COMBINATION SYNDROME, is a description of a dental condition that is the result of long term use of a few, usually remaining lower anterior teeth, #22-27 and a complete upper denture with no other natural remaining teeth and a lower free end Kennedy class I removable partial denture. Kelly considered that there were five changes which tended to occur in the cases which he studied. These are:

  • Loss of bone from the anterior part of the maxillary ridge
  • Overgrowth of the tuberosities
  • Papillary hyperplasia in the hard palate
  • Extrusion of the lower anterior teeth
  • The loss of bone under any (mandibular) partial denture bases

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91 MCQs in Prosthodontics Answers

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The Correct option is D

  • Zinc is used in crown and bridge alloys primarily as an oxygen scavenger. Zinc readily combines with oxygen that may have dissolved in alloy when it was in a molten state. This prevents the oxygen from forming gas porosity in the casting.

  • In PFM formulations, zinc also lowers the melting range, increases strength and hardness, and raises the thermal expansion.

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Saturday, March 10, 2001

90 Prosthodontics MCQs Answer

Saturday, March 10, 2001
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The Correct option is E

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89 Prosthodontics MCQs Answer

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The Correct option is D

Beryllium is a very toxic substance but is nevertheless still used in certain dental materials.

Beryllium is not used as an implant substance, although it can be found a component of nickel chromium alloys.

Beryllium in base metal alloys can present a dental occupational health problem. There is strong evidence that occupational exposure to certain nickel compounds is associated with increased incidence of specific types of cancer.
Skinner, p 559.

The best method to etch a beryllium-free base metal alloy is with 0.5 normal nitric acid.

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