NEET MDS Prosthodontics and Crown & Bridge Syllabus

State Ante's Law as applied to fixed partial denture abutment selection.

Ante's Law: the combined periodontal (root) surface area of the abutment teeth should be equal to or greater than the periodontal surface area of the teeth being replaced by the pontics. It guides whether abutments can support the bridge load.

What is the recommended total occlusal convergence (taper) for a tooth preparation receiving a full crown, and why?

The ideal total occlusal convergence is about 6 degrees (roughly 2-3 degrees per wall). This taper provides adequate retention and resistance form while allowing a single path of insertion and complete seating; excessive taper reduces retention.

List the principles of tooth preparation for a cast restoration (name at least four).

Principles: (1) preservation of tooth structure, (2) retention and resistance form, (3) structural durability (adequate material bulk—occlusal reduction, functional cusp bevel), (4) marginal integrity (proper finish line), and (5) preservation of the periodontium.

Compare the chamfer, shoulder, and knife-edge finish lines used in crown preparation.

Chamfer: distinct curved margin, good for cast metal/metal margins of PFM—conservative, easy to read. Shoulder: 90-degree butt margin giving bulk for all-ceramic/PFM porcelain margin but removes most tooth. Knife-edge/feather: minimal reduction but produces over-contoured, hard-to-read margins—generally avoided.

What is the function of provisional (temporary) restorations in fixed prosthodontics? Name three requirements.

Provisionals protect the prepared tooth and pulp, maintain position (prevent drift/supra-eruption), and provide esthetics/function while the definitive restoration is fabricated. Requirements include marginal fit, adequate strength, biocompatibility, esthetics, and easy removal/cleansability.

Name two materials used to fabricate provisional crowns and a key property of each.

PMMA (polymethyl methacrylate): good polishability and esthetics but high exothermic heat and polymerization shrinkage. Bis-acryl composite (e.g., bis-GMA): lower exotherm, less shrinkage, good marginal fit and strength, easier chairside use but more brittle and costlier.

Differentiate temporary versus permanent luting cements and give an example of each.

Temporary luting cements (e.g., zinc oxide eugenol, non-eugenol ZOE) allow easy provisional removal. Permanent cements bond definitive restorations—examples include zinc phosphate, glass ionomer (GIC), resin-modified GIC, and resin cements (which provide highest bond strength and are needed for all-ceramic/bonded restorations).

What is the difference between conventional cementation and adhesive (resin) bonding for crowns?

Conventional cementation relies on mechanical retention/luting (zinc phosphate, GIC). Adhesive resin bonding chemically/micromechanically bonds restoration to tooth via etching and bonding agents, providing higher retention and reinforcing weaker ceramics—essential for resin-bonded bridges, veneers and glass-ceramics.

What is an osseointegrated dental implant, and who coined the concept of osseointegration?

An osseointegrated implant is a titanium fixture in direct structural and functional connection between living bone and the implant surface, with no intervening fibrous tissue. The concept was discovered/coined by Per-Ingvar Brånemark.

Name the main components of an endosseous root-form implant system.

Components: the implant fixture (placed in bone), the abutment (connects fixture to prosthesis), the abutment/cover screw and healing abutment, and the prosthesis (crown/bridge/denture) with its retaining screw or cement.

Differentiate a one-stage from a two-stage implant surgical protocol.

In a two-stage protocol the implant is submerged under the mucosa with a cover screw to heal undisturbed, then a second surgery exposes it. In a one-stage (non-submerged) protocol a healing abutment protrudes through the mucosa at placement, so no second surgical exposure is needed.

What is the difference between primary and secondary implant stability?

Primary stability is the mechanical anchorage achieved at the moment of placement (engagement of implant threads in bone). Secondary stability is the biological stability gained over time through osseointegration (new bone formation/remodeling around the implant).

During the implant prosthetic phase, what is the difference between cement-retained and screw-retained restorations?

Cement-retained crowns are luted to an abutment—better esthetics/occlusion and passive fit but risk of residual subgingival cement causing peri-implantitis and are hard to retrieve. Screw-retained restorations are secured by an access screw—easily retrievable and no cement, but require an access hole and precise implant positioning.

What is peri-implantitis and how does it differ from peri-implant mucositis?

Peri-implant mucositis is reversible inflammation of the soft tissue around an implant without bone loss. Peri-implantitis is inflammation accompanied by progressive loss of supporting marginal bone around an osseointegrated implant—a major late complication.

In maxillofacial prosthetics, define an obturator and state its main purpose.

An obturator is a maxillofacial prosthesis that closes/occludes a defect or opening (commonly a palatal/maxillary defect from surgery or congenital cleft). It restores the partition between oral and nasal cavities, aiding speech, swallowing and esthetics.

Differentiate surgical, interim, and definitive obturators by timing of use.

Surgical obturator: placed at the time of resection surgery to maintain function and support the surgical packing. Interim (temporary/treatment) obturator: used during healing as the defect changes. Definitive obturator: the final prosthesis fabricated after tissues have healed and stabilized (usually 3-6 months).

Name two commonly used materials for fabricating extraoral maxillofacial prostheses (e.g., facial/ocular).

Silicone (room-temperature or heat-vulcanized maxillofacial silicone elastomers) is the most widely used for facial prostheses due to lifelike texture and color. Acrylic resin (PMMA) is used for ocular prostheses and harder substructures.

In maxillofacial patient management, what is the difference between a maxillectomy and a mandibulectomy defect's prosthetic challenge?

A maxillectomy defect requires an obturator to seal the oronasal communication and restore the palate (challenge: retention against gravity and air leakage). A mandibulectomy defect disrupts continuity/occlusion and may need guidance prostheses or implant-supported reconstruction (challenge: mandibular deviation and occlusal stability).

What is occlusion, and define the terms "working side" and "non-working (balancing) side" in lateral movements.

Occlusion is the contact relationship of teeth during function and parafunction. In a lateral excursion the side toward which the mandible moves is the working side; the opposite side is the non-working (balancing/idling) side. Contacts on the non-working side are usually considered interferences in natural dentition.

Differentiate group function from canine-protected (mutually protected) occlusion.

Canine-protected (mutually protected) occlusion: in lateral excursion only the canines contact, disoccluding posterior teeth; posteriors protect anteriors in centric. Group function: multiple teeth on the working side share lateral contacts/load distribution. Both are accepted occlusal schemes depending on tooth condition.

In occlusal analysis, what is an occlusal interference and name the four types of interferences.

An occlusal interference is an undesirable tooth contact that prevents smooth, harmonious mandibular movement. Types: (1) centric (premature) interference, (2) working-side interference, (3) non-working/balancing-side interference, and (4) protrusive interference.

What is the purpose of occlusal adjustment (selective grinding) on natural dentition and what is the conservative sequence?

Occlusal adjustment removes interferences to distribute forces evenly, eliminate trauma and stabilize the bite. Conservative sequence: first eliminate centric (CR-CO) prematurities, then correct protrusive interferences, then working-side, then non-working/balancing-side interferences, reshaping cusps/fossae minimally.

Classify dental impression materials into elastic and inelastic groups with examples.

Elastic impression materials: hydrocolloids (reversible—agar; irreversible—alginate) and elastomers (polysulfide, polyether, condensation silicone, addition silicone/PVS). Inelastic (rigid) materials: impression plaster, impression compound, zinc oxide eugenol paste, and impression waxes.

Compare addition silicone (PVS/polyvinyl siloxane) and polyether impression materials on key properties.

Addition silicone: excellent accuracy, dimensional stability, high elastic recovery, hydrophobic (improved with surfactants), no byproduct (unless H2 release). Polyether: very accurate, hydrophilic (good in moisture), high stiffness/rigidity (hard to remove), and is dimensionally stable but absorbs water/distorts if stored wet.

Why is alginate (irreversible hydrocolloid) impression dimensionally unstable, and how should it be handled?

Alginate loses water by evaporation (syneresis/shrinkage) and absorbs water (imbibition/expansion). It must be poured immediately (within ~10-15 minutes), kept in 100% humidity if storage is unavoidable, and not stored in water, to prevent dimensional change.

Compare heat-cure and self-cure (cold/autopolymerizing) denture base acrylic resins.

Heat-cure PMMA uses heat to activate benzoyl peroxide—better polymerization, higher strength, lower residual monomer, superior properties (used for definitive denture bases). Self-cure uses a chemical activator (tertiary amine) at room temperature—faster but higher residual monomer, more porosity, lower strength, and slight color instability (used for repairs/relines).

What is the major connector material/alloy most commonly used for removable partial denture frameworks and why?

Cobalt-chromium (Co-Cr) alloy is most common for cast RPD frameworks because of its high modulus of elasticity (rigidity), high strength, low density (light), corrosion resistance and low cost compared with type IV gold alloys.

Compare metal-ceramic (PFM) crowns with all-ceramic crowns on esthetics and strength.

PFM crowns: strong metal substructure with porcelain veneer—durable, good for posteriors and long-span bridges, but the metal can show a gray margin/opacity reducing esthetics. All-ceramic crowns (e.g., lithium disilicate, zirconia): superior esthetics/translucency and biocompatibility; zirconia is very strong while glass-ceramics are more translucent but somewhat weaker than metal-ceramic for long spans.

Why is commercially pure titanium (and Ti-6Al-4V alloy) the material of choice for dental implants?

Titanium is highly biocompatible and spontaneously forms a stable titanium-dioxide passivating oxide layer that resists corrosion and promotes osseointegration (direct bone apposition). It has favorable strength-to-weight ratio; Ti-6Al-4V (grade 5) adds higher mechanical strength for the fixture/abutment.

What is the difference between the "setting" (working) and "final" forms of a cast restoration's marginal seal, i.e., compare zinc phosphate and glass ionomer luting cements?

Zinc phosphate: long clinical track record, high compressive strength, but is acidic on setting (pulpal irritation), brittle and not adhesive (purely mechanical). Glass ionomer (GIC): chemically bonds to tooth, releases fluoride (anticariogenic), is less soluble and more biocompatible, but has lower early strength and is moisture-sensitive during setting.