Most common reason for midline fracture of the maxillary denture

 # The most common reason for midline fracture of the maxillary denture is due to: 

A. Alignment of posterior teeth too far buccally

B. Lack of strength of the material itself

C. Thin palatal portion of the denture

D. Internal porosity which is common in palatal portion

The correct answer is A. Alignment of posterior teeth too far buccally.

Denture base resins are subjected to a variety of stresses during function:

• Midline fractures of dentures during function are considered a flexural fatigue failure due to cyclical deformation of the base during function. This is usually more evident in ill fitting or poorly designed dentures.

• Impact fracture may result from patients accidentally dropping the dentures.

Ref: Boucher's Prosthodontics, 13th Edition Page 137 

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Zero degree cusp teeth are preferred over anatomic teeth:

 # Zero degree cusp teeth are preferred over anatomic teeth:

A. When muscles of mastication is very powerful

B. Diabetic patients

C. Patients with well developed residual ridge

D. Patients with very less retention and stability

The correct answer is D. Patients with very less retention and stability.

Zero degree teeth are defined as, “Artificial posterior teeth having no cusp angles in relation to the horizontal occlusal surfaces” - GPT.

Advantages

• In patients with bruxism non-anatomic teeth decrease the forces acting on the basal tissues.

• Greater range of movements is possible.

• In patients with neuromuscular disorders where accurate jaw relation cannot be recorded, cuspless teeth are preferred.

• In cases with highly resorbed ridge, cuspless teeth are preferred as they do not get locked and displace the denture during lateral movements.

Disadvantages

• Flat occlusal surfaces and artificial contours give an unaesthetic appearance.

• Masticatory efficiency is less.

• Balanced occlusion cannot be obtained.

• Occlusion is in two dimensions, whereas the mandibular movement is in three dimensions.

• Any attempt to correct these teeth by occlusal grinding will decrease their efficiency.

Reference: Nallaswamy, 2nd Edition, Page No 9

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Metal margin is preferred over ceramic margin in metal ceramic restoration:

 # Metal margin is preferred over ceramic margin in metal ceramic restoration:

A. Margins are easy to prepare for metal during tooth preparation

B. Tooth preparation is going to be more conservative

C. Only when margin is subgingival

D. Marginal adaptation is better in metal margin rather than ceramic margin

The correct answer is C. Only when margin is subgingival.

Metal ceramics: These materials require extensive tooth reduction. The junction between the metal

and the ceramic is very unaesthetic. For aesthetic reasons the margins of the restoration is placed

subgingivally which frequently leads to periodontal problems. 

Reference: Nallaswamy, 2nd Edition, Page 495

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The support of partial denture is usually

 # The support of partial denture is usually:

A. Tooth support

B. Mucosa support

C. Occlusal rest support

D. Tooth and mucosa support

The correct answer is D. Tooth and mucosa support.

Watt et al Classification

He proposed the classification in 1958. It was based on the type of support derived.

• Entirely tooth borne: The entire denture rests on the abutment teeth.

• Entirely tissue borne: The entire denture rests on the soft tissue.

• Partially Tooth borne and partially tissue borne: These dentures rest on both the teeth and the tissues. Generally most of the removable partial dentures come under this category.

Reference: Nallaswamy, 2nd Edition, Page 284

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