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Kuwait Dental Board General Dentistry study materials
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Kuwait Dental Board General Dentistry practice questions

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Question 1Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

After a difficult mandibular first molar extraction, a patient reports altered sensation over the buccal gingiva of that tooth. Which nerve most directly supplies this region?

  1. Lingual nerve
  2. Buccal branch of the mandibular nerve Correct answer.
  3. Inferior alveolar nerve
  4. Mylohyoid nerve

Explanation

The buccal branch (long buccal nerve) of the mandibular division of the trigeminal nerve supplies sensation to the buccal gingiva and mucosa adjacent to the mandibular molars. The lingual nerve supplies the lingual gingiva and tongue, while the inferior alveolar nerve supplies the teeth and chin. The mylohyoid nerve is primarily motor.

Question 2Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which cell type secretes the organic matrix that subsequently mineralizes to form enamel?

  1. Osteoblast
  2. Odontoblast
  3. Cementoblast
  4. Ameloblast Correct answer.

Explanation

Ameloblasts differentiate from the inner enamel epithelium and secrete enamel matrix proteins such as amelogenins and enamelins. As enamel matures, ameloblasts retreat and leave behind the highly mineralized tissue. Odontoblasts form dentin, cementoblasts form cementum, and osteoblasts form bone.

Question 3Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

In a healthy resting adult, which salivary gland contributes the largest proportion of total unstimulated whole saliva?

  1. Submandibular gland Correct answer.
  2. Minor salivary glands
  3. Sublingual gland
  4. Parotid gland

Explanation

The submandibular glands contribute roughly 60 to 70 percent of unstimulated whole saliva, making them the dominant source at rest. The parotid glands provide most saliva only during active stimulation. Sublingual and minor glands add smaller resting volumes.

Question 4Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Lidocaine prevents nerve conduction by blocking which target?

  1. Nicotinic acetylcholine receptors
  2. Gamma-aminobutyric acid receptors
  3. Voltage-gated sodium channels Correct answer.
  4. Voltage-gated potassium channels

Explanation

Local anesthetics such as lidocaine are weak bases that cross the axonal membrane and block voltage-gated sodium channels from the cytoplasmic side. This prevents sodium influx and raises the threshold for depolarization. Potassium channels, acetylcholine receptors, and GABA receptors are not their primary target.

Question 5Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which formulation change in a dental resin composite is expected to increase polymerization shrinkage?

  1. Increasing the resin matrix fraction Correct answer.
  2. Using larger filler particles at the same filler load
  3. Adding prepolymerized filler particles
  4. Increasing the filler volume fraction

Explanation

Polymerization shrinkage arises mainly from conversion of monomer to polymer within the resin matrix. A higher matrix fraction means more shrinkable resin per unit volume of composite. Increasing filler load or adding prepolymerized filler reduces shrinkage, while particle size alone has little effect at constant filler load.

Question 6Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which bacterium is most strongly associated with progression of an established dentinal carious lesion?

  1. Veillonella parvula
  2. Actinomyces viscosus
  3. Streptococcus mutans
  4. Lactobacillus species Correct answer.

Explanation

Mutans streptococci are strongly associated with initiation of enamel caries, but lactobacilli thrive in the acidic, retentive environment of cavitated dentin and correlate with lesion progression. Actinomyces species are linked more to root caries, and Veillonella is a lactate-fermenting genus rather than a primary driver of dentinal progression.

Question 7Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which muscle is the principal driver of mandibular protrusion when it contracts bilaterally?

  1. Temporalis
  2. Lateral pterygoid Correct answer.
  3. Medial pterygoid
  4. Masseter

Explanation

The lateral pterygoid pulls the condyle and articular disc forward, producing protrusion, and bilateral contraction also assists in mandibular depression. The masseter, medial pterygoid, and temporalis primarily elevate the mandible, with the temporalis also retruding it.

Question 8Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which principal periodontal ligament fiber group is best oriented to resist intrusive forces on the tooth?

  1. Oblique fibers Correct answer.
  2. Alveolar crest fibers
  3. Apical fibers
  4. Horizontal fibers

Explanation

Oblique fibers run from alveolar bone coronally toward cementum apically, so they are positioned to resist axial intrusive loading and convert it into tension in the ligament. Alveolar crest, horizontal, and apical fibers resist other force directions.

Question 9Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

In response to hypocalcemia, parathyroid hormone raises serum calcium through which direct action?

  1. Increasing osteoclastic bone resorption Correct answer.
  2. Decreasing distal tubular calcium reabsorption
  3. Inhibiting 1-alpha-hydroxylase in the kidney
  4. Increasing renal phosphate reabsorption

Explanation

Parathyroid hormone increases bone resorption through osteoclast activation, increases distal renal tubular calcium reabsorption, and stimulates 1-alpha-hydroxylase to produce calcitriol. It also decreases renal phosphate reabsorption, promoting phosphaturia. These actions together restore serum calcium.

Question 10Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which statement best characterizes the microbiota of a primary endodontic infection?

  1. It is sterile unless the canal has been previously treated
  2. It is usually a single facultative streptococcal species
  3. It is dominated by obligate anaerobic bacteria Correct answer.
  4. It is composed mainly of Candida albicans

Explanation

Primary endodontic infections are polymicrobial biofilm infections dominated by obligate anaerobes such as Prevotella, Fusobacterium, and Porphyromonas. Facultative streptococci may be early colonizers but do not dominate the established community. Fungi such as Candida are more characteristic of persistent or secondary infections.

Question 11Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which muscle fibers retract the mandible?

  1. Anterior digastric fibers
  2. Posterior temporalis fibers Correct answer.
  3. Superficial masseter fibers
  4. Medial pterygoid fibers

Explanation

The posterior fibers of temporalis run almost horizontally and pull the condyle backward into the glenoid fossa. Masseter and medial pterygoid are mandibular elevators, while the anterior belly of digastric contributes to depression.

Question 12Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which region of the oral mucosa is normally covered by nonkeratinized stratified squamous epithelium?

  1. Attached gingiva
  2. Hard palate
  3. Dorsal surface of the tongue
  4. Buccal mucosa Correct answer.

Explanation

Lining mucosa covers the buccal mucosa, lips, and soft palate and is normally nonkeratinized. Attached gingiva and hard palate are masticatory mucosa with keratinized epithelium, and the dorsal tongue bears specialized keratinized papillae.

Question 13Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

In stimulated whole saliva, which buffer system predominates?

  1. Bicarbonate system Correct answer.
  2. Urea system
  3. Ammonia system
  4. Phosphate system

Explanation

Bicarbonate is the dominant buffer in stimulated whole saliva, and its concentration rises with salivary flow. Phosphate is more important intracellularly and in some resting secretions, while urea and ammonia are not the principal salivary buffers.

Question 14Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

According to the hydrodynamic theory, dentin hypersensitivity arises because:

  1. Tubular sclerosis exposes intratubular nerve fibers
  2. Acidic dentinal fluid activates acid-sensing channels
  3. Fluid shifts in dentinal tubules deform pulpal nerve endings Correct answer.
  4. Odontoblast processes fire action potentials directly

Explanation

The hydrodynamic theory states that thermal, osmotic, or mechanical stimuli shift fluid in patent dentinal tubules. This fluid movement deforms mechanosensitive nerve endings near the pulp, producing pain. Direct odontoblast action potentials are not the accepted mechanism.

Question 15Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

A patient with acute pulpitis reports inadequate anesthesia during an inferior alveolar nerve block. Which local anesthetic property best explains reduced efficacy in inflamed tissue?

  1. Rapid hepatic clearance of the drug
  2. Increased protein binding in inflamed tissue
  3. Low pKa relative to tissue pH
  4. Lower uncharged base fraction at acidic pH Correct answer.

Explanation

Local anesthetics cross the nerve membrane mainly in the uncharged base form. In inflamed, acidic tissue the fraction of uncharged base falls, so less drug enters the neuron; protein binding, pKa relationships, and clearance do not explain the acute failure.

Question 16Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which placement technique most directly reduces the configuration factor (C-factor) of a light-cured resin composite restoration?

  1. Using a lower-intensity curing light
  2. Preheating the composite before insertion
  3. Using oblique increments of 2 mm or less Correct answer.
  4. Bulk filling the cavity in one increment

Explanation

C-factor is the ratio of bonded to unbonded surface area, and high values increase contraction stress. Oblique increments of 2 mm or less keep some free surface available and reduce that ratio. Bulk filling raises C-factor, and preheating or low-intensity curing does not address it.

Question 17Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which microorganism is most characteristic of a persistent or secondary endodontic infection?

  1. Actinomyces viscosus
  2. Streptococcus mutans
  3. Porphyromonas gingivalis
  4. Enterococcus faecalis Correct answer.

Explanation

Enterococcus faecalis is a hardy facultative organism frequently recovered from persistent or secondary endodontic infections. Porphyromonas gingivalis is a periodontal pathogen, Streptococcus mutans is cariogenic, and Actinomyces viscosus is associated with root caries.

Question 18Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which periodontal ligament fiber group extends from the cementum of one tooth across the alveolar septum to the cementum of the adjacent tooth?

  1. Alveolar crest group
  2. Apical group
  3. Transseptal group Correct answer.
  4. Horizontal group

Explanation

Transseptal fibers pass from the cementum of one tooth across the interdental septum to the adjacent tooth. Alveolar crest, horizontal, and apical fibers attach the tooth to bone rather than linking neighboring teeth.

Question 19Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Which change in mixing a dental stone increases its setting expansion?

  1. Reducing the water-to-powder ratio Correct answer.
  2. Increasing the water-to-powder ratio
  3. Adding potassium sulfate to the mix
  4. Vacuum mixing under reduced pressure

Explanation

A lower water-to-powder ratio produces a denser mix with greater setting expansion and strength. Increasing water dilutes the mix and reduces expansion, potassium sulfate accelerates setting and lowers expansion, and vacuum mixing mainly reduces porosity.

Question 20Basic and Applied Dental Sciences (oral anatomy, histology, physiology, microbiology, pharmacology, dental biomaterials)

Hunter-Schreger bands in mature enamel are best described as:

  1. Incremental lines marking weekly apposition
  2. Retained enamel proteins near the dentinoenamel junction
  3. Alternating rod orientations producing optical decussation Correct answer.
  4. Zones of hypomineralization beneath the cusp tip

Explanation

Hunter-Schreger bands are optical bands caused by alternating directions of enamel rods, known as decussation, through the enamel thickness. Incremental lines reflect appositional growth, and the other options describe unrelated enamel features.

Question 21Operative (Restorative) Dentistry and Dental Materials

A light-cured resin composite contains barium glass filler and a silane coupling agent. What is the principal function of the silane coupling agent?

  1. It releases fluoride to inhibit secondary caries at the restoration margins.
  2. It initiates camphorquinone decomposition during light exposure.
  3. It lowers the coefficient of thermal expansion of the set material considerably.
  4. It bonds the inorganic filler particles to the organic resin matrix. Correct answer.

Explanation

Silane coupling agents such as γ-methacryloxypropyltrimethoxysilane hydrolyse to silanol groups that condense with hydroxyl groups on the filler surface, while the methacrylate end copolymerises with the resin matrix. This covalent bridge transfers stress from the weaker matrix to the filler and protects the interface from hydrolytic breakdown. Without silanisation the filler behaves as a void and the composite loses strength and durability.

Question 22Operative (Restorative) Dentistry and Dental Materials

A dental assistant triturates a zinc-containing amalgam capsule and the dentist notices that condensation produces a mix that later expands slowly, sometimes days after placement. Which alloy component is responsible for this behaviour when moisture is present?

  1. Mercury
  2. Zinc Correct answer.
  3. Copper
  4. Tin

Explanation

Zinc reacts with water contaminating the mix to form hydrogen gas, which accumulates slowly within the set mass and produces delayed expansion that can begin days later. This expansion can fracture the tooth or marginal enamel and cause postoperative pain, which is why zinc-free alloys are available for situations where moisture control is difficult.

Question 23Operative (Restorative) Dentistry and Dental Materials

The setting of a conventional glass-ionomer cement depends primarily on which reaction?

  1. Chelation of zinc eugenolate by calcium hydroxide.
  2. An acid-base reaction between polyalkenoic acid and fluoroaluminosilicate glass. Correct answer.
  3. Crystallization of gypsum from calcium sulfate hemihydrate.
  4. Addition polymerization of a dimethacrylate monomer initiated by camphorquinone.

Explanation

The polyalkenoic acid attacks the fluoroaluminosilicate glass, releasing aluminium and calcium ions that cross-link the polyacid chains into a silica hydrogel matrix; the unreacted glass particles act as the filler. Because water is essential to the reaction, freshly set cement must be protected from desiccation and from early moisture contamination.

Question 24Operative (Restorative) Dentistry and Dental Materials

A Class I cavity in a mandibular molar is 4 mm deep with a high configuration factor. Which placement technique best limits contraction stress at the bonded interface?

  1. Pre-warming the composite to 60 °C before a single bulk placement.
  2. Bulk filling with a single 4-mm increment of flowable composite.
  3. Oblique increments of no more than 2 mm placed against opposing walls. Correct answer.
  4. Placing the whole restoration and curing it through the occlusal surface for 60 seconds.

Explanation

The configuration factor is the ratio of bonded to unbonded surface, so a deep box-shaped cavity confines the material and converts polymerization shrinkage into interfacial stress. Thin oblique increments leave a free surface that lets the material flow and relieve stress before it sets, and keeping increments small also improves depth of cure. Bulk placement in a high configuration factor cavity maximises the stress transmitted to the adhesive interface.

Question 25Operative (Restorative) Dentistry and Dental Materials

Which statement about the smear layer in dentin bonding is correct?

  1. Self-etch systems dissolve the smear layer and incorporate its remnants into the hybrid layer. Correct answer.
  2. The smear layer increases dentin permeability and improves resin tag formation.
  3. Etch-and-rinse systems deliberately leave the smear layer intact so that resin can bond through it.
  4. Removal of the smear layer with EDTA is a mandatory step before any self-etch adhesive is used.

Explanation

Self-etch adhesives contain acidic phosphate or carboxylate monomers that simultaneously etch and prime, partially dissolving the smear layer and trapping its fragments within the hybrid layer. Smear plugs remain in the tubules, which reduces fluid flow and postoperative sensitivity but also limits resin tag length. Etch-and-rinse systems instead remove the smear layer completely with phosphoric acid before priming.

Question 26Operative (Restorative) Dentistry and Dental Materials

A lithium disilicate veneer is to be adhesively cemented with a resin cement. What is the appropriate treatment of the intaglio surface?

  1. Etch with 9.5% hydrofluoric acid for 90 seconds, rinse and dry without silane.
  2. Airborne-particle abrasion with 50 µm alumina and a phosphate-monomer primer only.
  3. Etch with 37% phosphoric acid for 60 seconds, then apply a dentin adhesive.
  4. Etch with 5% hydrofluoric acid for 20 seconds, then apply silane. Correct answer.

Explanation

Hydrofluoric acid selectively dissolves the glassy phase of lithium disilicate and leaves a microporous surface for micromechanical interlocking, and silane then forms a chemical bridge between the silica and the resin cement. The etching time must be respected because prolonged etching weakens a thin restoration. Phosphoric acid does not attack the glassy phase of this ceramic.

Question 27Operative (Restorative) Dentistry and Dental Materials

While placing a Class II composite in a maxillary premolar, the dentist inserts a wooden wedge from the buccal embrasure. What is the primary purpose of this wedge?

  1. To hold the matrix band, adapt it gingivally and slightly separate the teeth. Correct answer.
  2. To retain the rubber dam clamp in place during isolation.
  3. To burnish the matrix band firmly against the tooth after the composite has been placed.
  4. To transmit curing light to the proximal composite.

Explanation

The wedge stabilises the matrix band against the gingival cavosurface, prevents overhangs and gingival excess, and produces slight tooth separation so that a proper proximal contact can be re-established when the band is removed. A transparent wedge can also help transmit light, but that is a secondary benefit rather than the primary purpose.

Question 28Operative (Restorative) Dentistry and Dental Materials

A freshly triturated dental amalgam is dry, crumbly and does not cohere when squeezed in the amalgam carrier. What is the most likely cause?

  1. Excess mercury was added during mixing.
  2. The alloy has a high copper content.
  3. The mix was over-triturated and became too warm.
  4. The alloy was under-triturated. Correct answer.

Explanation

Under-trituration leaves the alloy particles insufficiently wetted by mercury, so amalgamation is incomplete and the mass is dry, crumbly and weak, with poor condensation and higher porosity. Properly triturated amalgam forms a shiny, plastic mass that coheres and holds its shape. Over-trituration produces the opposite problem: a hot, sticky mass with a shortened working time.

Question 29Operative (Restorative) Dentistry and Dental Materials

A monolithic zirconia crown is to be adhesively luted with a resin cement. Which pretreatment of the intaglio surface gives the most durable bond?

  1. Etching the intaglio surface with 9.5% hydrofluoric acid for 60 seconds, then applying a silane coupling agent.
  2. Airborne-particle abrasion with 50 µm alumina followed by a 10-MDP-containing primer. Correct answer.
  3. Etching with 37% phosphoric acid followed by an unfilled resin.
  4. Applying a two-step etch-and-rinse adhesive without any surface pretreatment.

Explanation

Zirconia is a polycrystalline ceramic with essentially no glassy phase, so hydrofluoric acid cannot create retentive porosity. A durable bond requires micromechanical roughening by airborne-particle abrasion at controlled pressure plus chemical bonding, in which the phosphate group of 10-MDP forms a stable bond with zirconium oxide. Combining both approaches gives the most hydrolytically stable interface.

Question 30Operative (Restorative) Dentistry and Dental Materials

After a small, non-bleeding pulpal exposure has been directly capped with a hard-setting calcium hydroxide liner in a deep cavity, a resin-modified glass-ionomer base is placed before bonding a composite. What is the main reason for this base?

  1. To neutralize the acidic phosphoric acid etchant that will be applied.
  2. To etch the dentin surface selectively so that resin tags can form and improve retention.
  3. To increase the total volume of composite that can be placed in the cavity.
  4. To seal the pulp cap from resin monomer and provide a bondable base. Correct answer.

Explanation

Calcium hydroxide is brittle, slightly soluble and has a high pH that can interfere with resin polymerization, and it is a poor substrate for adhesive bonding. A resin-modified glass-ionomer base seals the capped site, prevents resin monomer from diffusing toward the pulp and provides a rigid floor to which the adhesive can bond. It also contributes a chemical seal and some fluoride release.

Question 31Operative (Restorative) Dentistry and Dental Materials

When etching sound enamel before placing a resin composite, which protocol provides the most reliable micromechanical bond?

  1. 37% phosphoric acid applied for 15 to 30 seconds Correct answer.
  2. 10% phosphoric acid applied for 60 seconds
  3. 37% phosphoric acid applied for 5 seconds
  4. A self-etching primer without separate phosphoric acid

Explanation

Phosphoric acid at 30–40% concentration for 15–30 seconds produces the characteristic type I and type II enamel etch patterns needed for micromechanical retention. Extending the time does not improve the etch and may increase the risk of dentin contamination, while 5 seconds is inadequate. Self-etch primers bond less reliably to intact enamel.

Question 32Operative (Restorative) Dentistry and Dental Materials

In a conventional low-copper amalgam, which microstructural phase is the weakest and most susceptible to corrosion?

  1. The gamma phase (Ag3Sn)
  2. The epsilon phase (Cu3Sn)
  3. The beta phase (Ag-Sn)
  4. Gamma-2 (Sn7-8Hg) Correct answer.

Explanation

Gamma-2 (Sn7-8Hg) is the weakest and most corrosion-prone phase in set amalgam. High-copper alloys reduce or eliminate it, which improves strength and corrosion resistance. The gamma phase (Ag3Sn) is the main reactant and is stronger.

Question 33Operative (Restorative) Dentistry and Dental Materials

A 70-year-old with dry mouth has an active, leathery root caries lesion on the buccal surface of a mandibular premolar. Moisture control is difficult. Which restoration is most appropriate?

  1. High-copper spherical amalgam
  2. Conventional glass-ionomer cement Correct answer.
  3. Zinc phosphate luting cement
  4. Light-cured microfilled resin composite

Explanation

Conventional glass-ionomer cement bonds chemically to moist dentin, tolerates a less dry field, and releases fluoride, which is advantageous in xerostomia and active root caries. Resin composite needs strict isolation, amalgam has no fluoride release and adapts poorly to root surfaces, and zinc phosphate is a luting cement.

Question 34Operative (Restorative) Dentistry and Dental Materials

What is the maximum recommended increment thickness when placing a bulk-fill resin composite cured from the occlusal surface?

  1. 2 mm, which is the standard increment for all composites
  2. 1 mm, because light penetration is limited by filler load
  3. 4 to 5 mm Correct answer.
  4. 3 mm, provided the composite is translucent

Explanation

Bulk-fill composites are formulated to allow 4–5 mm increments depending on the product, because their translucency and photoinitiator system permit adequate depth of cure. Conventional composites are placed in 2 mm increments. Placing a bulk-fill material thicker than the manufacturer's limit risks uncured resin at the base.

Question 35Operative (Restorative) Dentistry and Dental Materials

A tooth has been restored with a provisional crown cemented using a zinc oxide-eugenol cement. Before adhesively bonding a composite restoration, what is the main concern?

  1. Residual eugenol may inhibit resin polymerization Correct answer.
  2. Eugenol acts as a co-initiator and accelerates polymerization
  3. Eugenol causes rapid demineralization of etched enamel
  4. Residual zinc oxide particles may increase the enamel bond strength

Explanation

Eugenol from zinc oxide-eugenol provisional cements can penetrate dentin and inhibit the polymerization of resin composites and adhesives, reducing bond strength. The cavity should be cleaned and a non-eugenol provisional cement used when adhesive restorations are planned.

Question 36Operative (Restorative) Dentistry and Dental Materials

In a deep carious permanent molar, the lesion extends close to the pulp but the pulp is vital and not exposed after peripheral caries removal. Which approach is best supported by current evidence?

  1. Perform a pulpotomy before restoring the tooth
  2. Apply a calcium hydroxide liner and leave soft dentin at the periphery
  3. Remove all softened dentin to hard, sound dentin
  4. Leave leathery dentin over the pulp and seal the cavity Correct answer.

Explanation

Evidence supports selective caries removal: peripheral caries is removed to hard dentin, but leathery, affected dentin is left over a vital pulp to avoid exposure. The cavity is then sealed with an adhesive restoration. Removing all softened dentin increases the risk of pulpal exposure without improving outcomes.

Question 37Operative (Restorative) Dentistry and Dental Materials

After light curing the final increment of a composite restoration, a glossy surface remains. What is the correct management before finishing?

  1. Apply fresh unfilled bonding resin and leave it uncured
  2. Leave it intact to improve the marginal seal
  3. Cure for an additional 60 seconds without wiping
  4. Remove the oxygen-inhibited layer Correct answer.

Explanation

The glossy surface is an oxygen-inhibited layer of unpolymerized resin. It should be removed before finishing and polishing because it is weak and can discolor. It should not be left in place or covered with more unfilled resin.

Question 38Operative (Restorative) Dentistry and Dental Materials

A Class II composite restoration in a maxillary premolar shows a weak proximal contact and poor contour after matrix removal. Which change in technique is most likely to correct this?

  1. Cure through the matrix before removing it
  2. Fill the box in one bulk increment from the occlusal
  3. Use a sectional matrix with a separation ring Correct answer.
  4. Use a flat Tofflemire band without wedging

Explanation

A precontoured sectional matrix with a separation ring provides better proximal contour and tight contact than a flat band, especially in premolars. The ring separates the teeth slightly and holds the matrix against the adjacent tooth. Bulk filling or curing through the matrix does not correct a deficient contact.

Question 39Operative (Restorative) Dentistry and Dental Materials

Which mechanism best explains the gradual loss of resin-dentin bond strength over several years with etch-and-rinse adhesives?

  1. Osmotic expansion of enamel crystallites beneath the adhesive
  2. Continued polymerization that embrittles the hybrid layer
  3. Hydrolysis of resin and enzymatic collagen breakdown Correct answer.
  4. Remineralization of the hybrid layer by salivary calcium

Explanation

Etch-and-rinse bonds degrade partly through hydrolysis of hydrophilic resin components and by matrix metalloproteinases that break down exposed collagen in the hybrid layer. This is why hydrophobic resin layers, MMP inhibitors, and improved infiltration are studied. Continued polymerization and remineralization do not explain the loss.

Question 40Operative (Restorative) Dentistry and Dental Materials

A fractured metal-ceramic crown has lost its buccal porcelain, exposing the base-metal framework. Which intraoral repair sequence gives the most durable bond of composite to the exposed metal?

  1. Etch the metal with 9.5% hydrofluoric acid and apply silane
  2. Air-abrade the metal and apply an MDP-containing primer Correct answer.
  3. Apply a total-etch adhesive without surface roughening
  4. Polish the metal and use a flowable composite alone

Explanation

For exposed base-metal framework, airborne-particle abrasion cleans and roughens the surface, and an MDP-containing primer bonds to the metal oxide layer. Hydrofluoric acid etches glass ceramics, not metal, and silane alone does not bond to metal. A total-etch adhesive without roughening gives poor metal bond strength.

Question 41Operative (Restorative) Dentistry and Dental Materials

A clinician is light-curing a 2-mm increment of a dark, highly opaque resin composite in a posterior tooth. Which property of the composite most directly limits the depth of cure?

  1. Composite shade and opacity Correct answer.
  2. Elastic modulus of the set material
  3. Radiopacity of the restoration
  4. Filler particle size distribution

Explanation

The depth of cure of a light-activated composite is limited by how much light reaches the material; darker and more opaque shades attenuate and scatter more light, reducing conversion at depth. Filler particle size, elastic modulus and radiopacity do not primarily control light penetration.

Question 42Operative (Restorative) Dentistry and Dental Materials

Which setting mechanism describes a resin-modified glass-ionomer cement used as a restorative material?

  1. Light-activated polymerization alone
  2. An acid-base reaction alone
  3. Acid-base plus light polymerization Correct answer.
  4. Chelation with dentin collagen

Explanation

Resin-modified glass-ionomer cements set by two mechanisms: an acid-base reaction between the glass powder and polyacid, and light-activated free-radical polymerization of the resin components. The acid-base reaction continues even where light is limited, which is why the material is not purely light-cured.

Question 43Operative (Restorative) Dentistry and Dental Materials

A mandibular molar has a mesio-occlusal amalgam and a distal marginal ridge crack that reaches the gingival margin. The remaining distal cusp is 1.5 mm thick, and the pulp is vital and asymptomatic. Which restorative approach is most appropriate?

  1. Replace the amalgam with a direct composite without cuspal coverage
  2. Remove the crack and restore with cuspal coverage Correct answer.
  3. Perform root canal treatment and place a post and core
  4. Place a direct composite and monitor the crack

Explanation

A crack reaching the gingival margin with a remaining cusp only 1.5 mm thick indicates that the cusp is unsupported and at high risk of fracture. Removing the crack and unsupported tooth structure and restoring with cuspal coverage protects the remaining tooth; direct composite without cuspal coverage does not address the structural failure. Root canal treatment is not indicated because the pulp is vital and asymptomatic.

Question 44Operative (Restorative) Dentistry and Dental Materials

Which is the main disadvantage of placing a flowable composite as a liner beneath a posterior resin composite restoration?

  1. It releases eugenol and inhibits polymerization
  2. It prevents the overlying composite from curing
  3. It has lower filler content and higher shrinkage Correct answer.
  4. It bonds only to enamel and not to dentin

Explanation

Flowable composites have lower filler content than conventional posterior composites, so they shrink more on polymerization and wear faster in occlusal contact. They are useful as liners or in low-stress areas, but they should not replace a properly filled posterior composite in stress-bearing regions.

Question 45Endodontics

During chemomechanical preparation of a necrotic mandibular molar, which irrigant is the primary agent for antimicrobial action and dissolution of organic tissue?

  1. 17% EDTA solution
  2. 0.9% sterile saline
  3. Sodium hypochlorite 1–5.25% Correct answer.
  4. 2% chlorhexidine digluconate

Explanation

Sodium hypochlorite is the only irrigant routinely used that combines broad antimicrobial activity with the capacity to dissolve necrotic pulp tissue and organic debris. It is delivered in concentrations of about 0.5–5.25% and must be frequently replenished because it is inactivated by organic material. EDTA and chlorhexidine have complementary roles but cannot replace this tissue-dissolving action.

Question 46Endodontics

A 34-year-old reports sharp pain in a mandibular first molar that continues for about 30 seconds after the cold stimulus is removed. The tooth is tender to percussion. Which pulpal diagnosis fits best?

  1. Reversible pulpitis
  2. Symptomatic irreversible pulpitis Correct answer.
  3. Asymptomatic irreversible pulpitis
  4. Pulpal necrosis

Explanation

Pain that lingers well beyond removal of the stimulus indicates a pulp that can no longer recover, and tenderness to percussion shows that inflammation has extended into the periapical region. Together these define symptomatic irreversible pulpitis. Reversible pulpitis produces sharp pain that resolves immediately once the stimulus is removed.

Question 47Endodontics

Why is rubber dam isolation regarded as the standard of care for root canal treatment?

  1. It permits preparation of shorter canals to the radiographic apex
  2. It prevents aspiration of instruments and irrigants Correct answer.
  3. It chemically disinfects the canal system during instrumentation
  4. It removes the need for an intracanal medicament between treatment visits

Explanation

A rubber dam protects the airway and gastrointestinal tract from swallowed or inhaled files, irrigants and debris, and at the same time gives a dry, aseptic field with better visibility. It does not sterilise the canal, replace an interim medicament, or change how working length is determined. Clinical guidelines treat adequate isolation as mandatory before any file enters the root canal system.

Question 48Endodontics

Which final irrigant regimen is used to remove the smear layer from the canal walls before obturation?

  1. Chlorhexidine digluconate 2%
  2. Hydrogen peroxide 3%
  3. 17% EDTA, a chelating agent Correct answer.
  4. Sodium hypochlorite at a higher concentration

Explanation

EDTA chelates calcium ions and dissolves the inorganic component of the smear layer, while a subsequent sodium hypochlorite rinse removes the organic component and exposes clean dentinal tubules. This alternating sequence is what prepares the walls for sealer adaptation. Hypochlorite alone leaves the smear layer largely intact whatever its concentration.

Question 49Endodontics

A clinician operates a nickel-titanium rotary file at the recommended rotational speed but with the torque limit set far above the manufacturer's range. What is the most likely consequence?

  1. Improved cutting efficiency with no effect on the instrument
  2. Reduced risk of screw-in and taper lock in curved canals
  3. Progressive straightening of the canal curvature
  4. Increased risk of torsional failure and file separation Correct answer.

Explanation

An excessive torque limit allows the flutes to lock into dentine until the elastic limit of the alloy is exceeded, producing torsional fracture; this is a different mechanism from cyclic fatigue caused by canal curvature. Torque should be set at or below the manufacturer's recommendation, with a slow, controlled advance and adequate irrigation. Canal curvature is not altered by torque settings.

Question 50Endodontics

A patient returns 24 hours after starting root canal treatment of a necrotic molar with pain, buccal vestibular swelling and a temperature of 38.2°C. The access was left open at the previous visit. What is the most appropriate immediate management?

  1. Leave the access open for drainage and defer cleaning to a later visit
  2. Drain, re-clean, medicate, seal and prescribe systemic antibiotics Correct answer.
  3. Prescribe analgesics alone and review the patient in one week
  4. Extract the tooth immediately under antibiotic cover

Explanation

A flare-up with systemic signs such as fever and diffuse swelling requires drainage of the swelling and of the canal space, thorough chemomechanical cleaning, an intracanal medicament, a properly sealed access, and systemic antibiotics. Leaving a tooth open gives no sustained drainage and permits continuous recontamination of the canal. Extraction is reserved for unrestorable teeth or infection that cannot be controlled.