MCQs on Dental Materials : Amalgams Part 1

Practice these 26 MCQs on Dental Amalgam (Part 1). These questions cover composition, phases, properties, and clinical manipulation.

---

1. The term "trituration" means:

• A. Lysing amalgam alloy
• B. Mixing of amalgam alloy and mercury
• C. Removal of excess of mercury
• D. None of the above

Click to Reveal Answer

Correct Answer: B

Explanation: Trituration (or amalgamation) is the process of mixing the alloy powder with liquid mercury to remove the oxide coating on the alloy particles and allow the mercury to wet the surface, initiating the setting reaction.

2. Dynamic creep is the:

• A. Continuing alloying between Silver-Tin alloy and mercury during the life of the restoration
• B. Deformation of set amalgam during function
• C. Process whereby alloy is wetted by mercury
• D. Spread of amalgam during packing

Click to Reveal Answer

Correct Answer: B

Explanation: Creep is the time-dependent plastic deformation of a material under a constant stress. "Dynamic creep" specifically refers to this deformation occurring under cyclic loads, such as mastication, which can lead to marginal ditching.

3. The highest mercury concentration in amalgam filling is typically found:

• A. At the margin of restoration
• B. In the centre of the restoration
• C. In the deepest part of the restoration
• D. None of the above

Click to Reveal Answer

Correct Answer: A

Explanation: During condensation, the mercury-rich matrix (which is the weakest part) rises to the surface. If this mercury-rich layer is not adequately carved away or if it pools at the margins, the margins will contain the highest mercury concentration, making them prone to fracture.

4. The dental amalgam is most resistant to:

• A. Compressive stress
• B. Impact stress
• C. Shear stress
• D. Tensile stress

Click to Reveal Answer

Correct Answer: A

Explanation: Amalgam is a brittle material with high compressive strength (similar to enamel) but very low tensile and shear strength. This necessitates cavity designs that rely on bulk to prevent fracture.

5. The ADA specification no. 1 for composition of amalgam alloy recommends:

• A. 65% silver, 32% tin and 3% copper
• B. 49% silver, 32% tin and 19% copper
• C. 65% silver, 29% tin and 5-6% copper
• D. None of the above

Click to Reveal Answer

Correct Answer: C

Explanation: For conventional (low copper) alloys, the classic composition is approximately 65% Silver, 29% Tin, and less than 6% Copper (often with <2% Zinc). High copper alloys have significantly higher copper content (>12%).

6. According to ADA sp. no. 1, the minimum compressive strength for silver amalgam after one hour should be:

• A. 80 Mpa
• B. 140 Mpa
• C. 260 Mpa
• D. 510 Mpa

Click to Reveal Answer

Correct Answer: A

Explanation: Early strength is critical to prevent fracture before the final set. The standard requirement is 80 MPa at 1 hour, though modern high-copper amalgams often exceed 250 MPa within an hour.

7. Which of the following phases of dental amalgam has minimum strength?

• A. Gamma 1
• B. Gamma 2
• C. Gamma 3
• D. Epsilon 1

Click to Reveal Answer

Correct Answer: B

Explanation: The Gamma-2 phase ($Sn_8Hg$) is the weakest and most corrosion-prone phase. High copper amalgams are designed specifically to eliminate this phase.

8. Admixed high copper alloy powder typically contains:

• A. 9-20% copper
• B. 13-20% copper
• C. 9-30% copper
• D. 13-30% copper

Click to Reveal Answer

Correct Answer: D

Explanation: High copper amalgams must contain enough copper to eliminate the gamma-2 phase (usually >12%). Admixed alloys typically range from 13% to 30% copper (e.g., Dispersalloy is ~12-13%, others go higher).

9. Compared to conventional amalgams, spherical amalgams:

• A. Require more mercury
• B. Require heavy compaction forces
• C. Have longer setting time
• D. None of the above

Click to Reveal Answer

Correct Answer: D

Explanation: Spherical alloys have a lower surface area, so they require less mercury (A is false) and are very plastic, requiring less condensation force (B is false). They generally set faster than lathe-cut alloys (C is false).

10. Finishing and polishing of amalgam causes ___________ of the restoration.

• A. Increase in tarnish and corrosion resistance
• B. Increase in the marginal strength
• C. Decrease the tarnish and corrosion resistance
• D. Increase in the compressive strength

Click to Reveal Answer

Correct Answer: A

Explanation: Polishing creates a smooth surface with less surface area and fewer irregularities for plaque accumulation, thereby significantly increasing resistance to tarnish and corrosion.

11. Which of the following statements about high copper silver alloy compared to conventional alloy is NOT true?

• A. It has increased tensile and compressive strength
• B. It has poor tarnish and corrosion resistance
• C. Its edge strength is greater
• D. Mercury content in the final restoration is less

Click to Reveal Answer

Correct Answer: B

Explanation: This is the FALSE statement. High copper alloys have superior tarnish and corrosion resistance because they lack the highly corrodible Gamma-2 phase.

12. Setting time of amalgam is best controlled by:

• A. Using spherical particles
• B. Lathe cut alloy
• C. Altering Hg-alloy ratio
• D. Trituration time

Click to Reveal Answer

Correct Answer: D

Explanation: While manufacturers control particle shape, the clinician can most significantly alter the setting time by changing the trituration time. Over-trituration speeds up the reaction (shortens working time), while under-trituration results in a grainy, slow-setting mix.

13. Increase in the residual mercury in silver amalgam filling can:

• A. Cause fracture of the filling
• B. Cause tarnish and corrosion
• C. Increase in strength
• D. Decrease condensation pressure

Click to Reveal Answer

Correct Answer: A

Explanation: Excess residual mercury (>55%) leads to a higher volume of the weak gamma-2 and gamma-1 matrix phases. This drastically reduces strength, leading to fracture, and increases creep and corrosion.

14. High Cu alloys have all of the following EXCEPT:

• A. High tensile strength
• B. Low creep
• C. High corrosion
• D. None of the above

Click to Reveal Answer

Correct Answer: C

Explanation: High Copper alloys have LOW corrosion resistance (better properties). Therefore, saying they have "High corrosion" is the exception/false statement.

15. Chronic mercury toxicity results from:

• A. Ingestion while removing old amalgam
• B. Skin contact
• C. Mercury vapor
• D. All of the above

Click to Reveal Answer

Correct Answer: C

Explanation: Inhalation of mercury vapor is the primary route for chronic toxicity in dental settings. Ingested metallic mercury is poorly absorbed, and skin absorption is less significant than vapor inhalation.

16. In non-zinc containing dental amalgam alloy, the percentage of zinc present is:

• A. Less than 0.02 %
• B. Less than 0.1 %
• C. Less than 0.01 %
• D. None of the above

Click to Reveal Answer

Correct Answer: C

Explanation: According to ADA specifications, a "zinc-free" alloy must contain less than 0.01% zinc. Zinc-containing alloys usually have 0.01% to 1% (often ~1%).

17. In spherical alloys as compared to lathe cut:

• A. Less condensing force is required
• B. More condensing force is required
• C. Both require same condensing force
• D. Manipulation is easy

Click to Reveal Answer

Correct Answer: A

Explanation: Spherical particles slide over each other easily ("mushy" feel). They require larger condensers and lighter pressure compared to the high force needed to pack irregular lathe-cut particles.

18. High copper dental amalgams are superior to other amalgams because high copper dental amalgams:

• A. Have less marginal breakdown
• B. Are workable at lower Hg-alloy ratio
• C. Have a higher ratio of tensile to compressive strength
• D. Have less resistance to tarnish and corrosion

Click to Reveal Answer

Correct Answer: A

Explanation: The elimination of the weak Gamma-2 phase and lower creep values result in significantly less marginal breakdown (ditching) over time.

19. Well premeasured capsules of amalgam can release mercury vapor during:

• A. Mulling
• B. Carving
• C. Condensation
• D. Trituration

Click to Reveal Answer

Correct Answer: D

Explanation: The heat and friction generated during the high-speed oscillation of trituration can cause mercury vapor to leak from capsules if they are not perfectly sealed.

20. The largest component of amalgam alloy is:

• A. Silver
• B. Tin
• C. Zinc
• D. Copper

Click to Reveal Answer

Correct Answer: A

Explanation: Silver is the primary constituent, typically making up 40% to 70% of the alloy composition depending on the type (High Cu vs Low Cu).

21. In a high copper amalgam, the phase which is eliminated is:

• A. Gamma 1
• B. Gamma 2
• C. Gamma 1 and Gamma 2
• D. No phase is eliminated

Click to Reveal Answer

Correct Answer: B

Explanation: The defining feature of high copper amalgam is the reaction of Tin with Copper to form the Eta phase ($Cu_6Sn_5$), preventing Tin from reacting with Mercury to form the weak Gamma-2 phase ($Sn_8Hg$).

22. During amalgamation, trituration is done to:

• A. Dissolve the alloy in mercury
• B. Coat the alloy particles with mercury
• C. Remove excess mercury from amalgam
• D. Dissolve Hg in alloy

Click to Reveal Answer

Correct Answer: B

Explanation: Trituration abrades the oxide layer on the alloy particles, allowing the mercury to wet (coat) the surface of the particles so the chemical reaction can proceed. The alloy does not fully dissolve; it is a surface reaction.

23. Moisture contamination of amalgam can lead to:

• A. Marginal breakdown
• B. Shrinkage
• C. Delayed expansion
• D. Increased stresses

Click to Reveal Answer

Correct Answer: C

Explanation: In zinc-containing alloys, moisture reacts with zinc to produce hydrogen gas. This gas pressure causes a delayed, painful expansion of the restoration starting 3-5 days after placement.

24. Amalgam restorations give the best clinical service when the residual mercury content is:

• A. 38-42%
• B. 48-52%
• C. 58-62%
• D. 68-72%

Click to Reveal Answer

Correct Answer: B

Explanation: The optimal mercury content is generally cited as 48-52% (approx 50%). Levels above 55% significantly degrade properties. (Note: Spherical alloys may use even less, around 42-45%).

25. Discoloration of silver alloy is due to:

• A. Tarnish
• B. Tarnish and corrosion
• C. Wet corrosion
• D. Dry corrosion

Click to Reveal Answer

Correct Answer: A

Explanation: Tarnish is a surface discoloration (sulfide layer) that does not necessarily compromise the mechanical integrity. Corrosion is the actual chemical degradation of the body of the material.

26. Percentage of tin in low copper alloy is:

• A. 30-35%
• B. 26-28%
• C. 13-32%
• D. 22-30%

Click to Reveal Answer

Correct Answer: B

Explanation: The traditional $Ag_3Sn$ (Gamma) phase composition generally requires Tin to be around 26-28%. If it is too high, more Gamma-2 forms; if too low, contraction occurs.

Tooth Sensitivity / Dentin Hypersensitivity

Introduction
The Canadian advisory board on dentin hypersensitivity ( 2003 ) defined Dentin hypersensitivity (Tooth sensitivity) as “a short, sharp pain arising from exposed dentin in response to stimuli typically thermal, evaporative, tactile, osmotic or chemical and which cannot be ascribed to any other form of dental defect or disease.”  It has been described as the “common cold of dentistry” by some and
“toothbrush disease” by others when it occurs in the presence of gingival recession (Pashley et al. 2008 ).

Prevalence and Distribution
The condition is mostly prevalent among the young population in the 3rd and 4th decades. The prevalence may shift in the future to a younger age group because of the increase in acidic food/drink intake and the influence of greater oral hygiene awareness and measures (Chabanski et al. 1997; Clayton et al. 2002 ). Various intraoral locations can be affected with Dentin hypersensitivity. Sites of predilection in descending order are canines and first premolars, incisors and second premolars, and molars (Dababneh et al. 1999 ). The buccal surfaces are mostly affected, followed by labial, occlusal, distal, and lingual. Incisal and palatal surfaces are the least affected (Splieth and Tachou 2012; Amarasena et al. 2011 ).

Mechanism
Brännström’s ( 1962, 1992 ) hydrodynamic theory of dentin sensitivity proposed that hydrodynamic
stimuli (hot or cold, tactile, evaporative or osmotic) caused sudden minute shifts of dentinal fluid that activate pulpal mechanoreceptors to cause sharp, well-localized tooth pain, thought to be due to A-delta sensory nerves (Narhi et al., 1992 ).

Causes and Predisposing Factors
The most important factor to be present for tooth sensitivity is the loss of tooth structure and the exposure of dentin to the oral cavity. The dentin may be exposed to the oral cavity by either the loss of enamel or cementum and overlying periodontal attachment apparatus or loss of both at the same time. Following the exposure, the patent dentinal tubules remain wide open and thus are predisposed to any stimulus, called the phase of “lesion initiation.” However, not all exposed dentin is sensitive (Rimondini et al. 1995 ).

The loss of enamel may be either due to attrition, erosion, abrasion, abfraction or abrasion due to tooth brushing (most commonly cervical abrasion). Similarly, loss of cementum due to various causes and periodontal attachment loss may cause exposure of dentinal tubules. Some medical conditions like Bulimia Nervosa, Gastroesophageal reflux disease, Chronic alcoholism, Salivary hypofunction, etc. may also cause dentin hypersensitivity.

Diagnosis
Diagnosis of dentin hypersensitivity can be made by applying any of the mechanical, chemical, thermal or electrical stimuli. Electronic pulp testers (EPT), mechanical pressure stimulators, air jet stimulator, ethyl chloride, thermoelectric device, cold water testing, ice testing, etc. can be used for challenging the affected tooth.

Treatment 
Two treatment approaches are mainly practiced in the treatment of dentin hypersensitivity. They are:

•  Use of dentin blocking agents that occlude patent (open) tubules (fluoride, strontium salts, oxalate, calcium phosphate, restorative materials, etc.), and
• Nerve desensitization agents that reduce intradental nerve excitability (e.g. potassium ions, guanethidine) in order to prevent a response from intra dental nerves to the stimulus- evoked fluid movements within the dentin tubules

 Application of these successfully tested products may either involve ‘in-office’ procedures by a clinician using a restorative approach (for example, restorative materials in the form of dentin bonding agents, glass ionomer cements (GIC), and periodontal surgical techniques) or by a clinician recommending an over-the-counter (OTC) approach (involving toothpastes, gels, mouthwashes).

Furthermore, the causative agent has to be identified and avoided as much as possible and the patient should be educated about the proper brushing technique to prevent mechanical abrasion due to toothbrushing in the future.

By : Raman Dhungel, 

B.P. Koirala Institute of Health Sciences, Dharan, Nepal

References:

1. Canadian Advisory Board on Dentin Hypersensitivity (2003) Consensus-based recommendations for the diagnosis and management of dentin hypersensitivity. J Can Dent Assoc 69(4):221–226

2. Pashley DH, Tay FR, Haywood VB, Collins MA, Drisko CL (2008) Consensus-based recommendations for the diagnosis and management of dentin hypersensitivity. Inside Dentistry 4(9 (Special Issue)):1–35

3. Chabanski MB, Gillam DG, Bulman JS, Newman HN (1997) Clinical evaluation of cervical dentine sensitivity in a population of patients referred to a specialist periodontology department: a pilot study. J Oral Rehabil 24(9):666–672

4. Clayton DR, McCarthy D, Gillam DG (2002) A study of the prevalence and distribution of dentine sensitivity in a population of 17-58-year-old serving personnel on an RAF base in the Midlands. J Oral Rehabil 29(1):14–23, 805 [pii]

5. Dababneh RH, Khouri AT, Addy M (1999) Dentine hypersensitivity – an enigma? A review of terminology, mechanisms, aetiology and management. Br Dent J 187(11):606–611; discussion 603. doi: 10.1038/sj.bdj.4800345a , 4800345a [pii]

6. Brännström M (1992) Etiology of dentin hypersensitivity. Proc Finn Dent Soc 88(Suppl 1):7–13

7. Brännström M (1962) The elicitation of pain in human dentine and pulp by chemical stimuli. Arch Oral Biol 7:59–62

8. Närhi M, Jyvasjarv E, Vitanen A, Huopaniemi T, Ngassapa D, Hirvonen T (1992) Role of intra dental A and C type nerve fibers in dental pain mechanisms. Proc Finn Dent Soc 8(Suppl 1):507–516

9. Dababneh RH, Khouri AT, Addy M (1999) Dentine hypersensitivity – an enigma? A review of terminology, mechanisms, aetiology and management. Br Dent J 187(11):606–611. doi: 10.1038/sj.bdj.4800345a ; discussion 603

10. Clinician’s Guide to the Diagnosis and Management of Tooth Sensitivity ; Sahar Taha, Brian H. Clarkson ISBN 978-3-642-45163-8 ISBN 978-3-642-45164-5 (eBook) DOI 10.1007/978-3-642-45164-5

11. Rimondini L, Baroni C, Carrassi A (1995) Ultrastructure of hypersensitive and non-sensitive dentine. A study on replica models. J Clin Periodontol 22(12):899–902

12. Ling TYY, Gillam DG (1996) The effectiveness of desensitizing agents for the treatment of cervical dentine sensitivity (CDS) – a review. Periodontal Abstr 44(1):5–12

13. Orchardson R, Gillam D (2006) Managing dentin hypersensitivity. J Am Dent Assoc 137(7):990–998

Download these Textbooks of Dentistry as soon as possible

These are the important textbooks in Dentistry.

Oral Anatomy and Histology
1. Wheeler's Dental Anatomy, Physiology, and Occlusion    - Stanley J. Nelson
2. Woelfel's Dental Anatomy   - Rickne C. Scheid, Gabriella Weiss
3. Ten Cate's Oral Histology: Development, Structure, and Function    - Antonio Nanci
4. Orban's Oral Histology and Embryology  - G.S. Kumar
5. Oral Anatomy, Histology, and Embryology  - B.K.B. Berkovitz, G.R. Holland & B.J. Moxham

Oral Medicine and Radiology
1. Burket's Oral Medicine  - Michael Glick
2. Oral Radiology: Principles and Interpretation  - Stuart C. White, Michael J. Pharaoh

Oral and Maxillofacial Surgery
1. Peterson's Principles of Oral and Maxillofacial Surgery
2. An Introduction to Oral and Maxillofacial Surgery  - David A. Mitchell
3. Handbook of Local Anesthesia   - Stanley F. Malamed

Pediatric Dentistry / Pedodontics
1. Dentistry for the Child and Adolescent     - Ralph E. McDonald, David R. Avery
2. Principles and Practice of Pedodontics      - Arathi Rao

Orthodontics
1. Contemporary Orthodontics   - William R. Proffit
2. Orthodontics The art and Science - S.I. Bhalajhi
3. Orthodontics - Current Principles and Techniques - Graber, Vanarsdall ang Vig

Public  Health Dentistry
1. Jong's Community Dental Health   - George M. Gluck & Warren M. Morganstein
2. Dentistry, Dental Practice, and the Community  - Brian A. Burt, Stephen A. Eklund
3. Park's Textbook of Preventive and Social Medicine  - K. Park

Prosthodontics
1. Prosthodontic Treatment for Edentulous Patients     -    Zarb, Hobkirk, Eckert and Jacob
2. McCracken' Removable Partial Prosthodontics    - Alan B. Carr & David T. Brown


Periodontology
1. Carranza's Clinical Periodontology  - Newman, Takei, Klokkevold & Carranza
2. Clinical Periodontology and Implant Dentistry   - Niklaus P. Lang & Jan Lindhe

Operative Dentistry
1. Sturdevant's Art and Science of Operative Dentistry  - Harald O. Heymann, Edward J. Swift & André V. Ritter
2. Pickard's Manual of Operative Dentistry  - Avijit Banerjee & Timothy H. Watson

Oral Pathology
1. Shafer's Textbook of Oral Pathology  -  R. Rajendran & B. Sivapathasundharam
2. Oral and maxillofacial Pathology  - Neville, Damm, Allen, and Bouquot
3. Oral Pathology : Clinical pathologic Correlation  - Regezi, Sciubba & Jordan

BPKIHS Past Question : Endocrinology and Reproductive System - 2nd year MBBS

B.P. Koirala Institute of Health Sciences, Dharan

2^nd Year MBBS

Unit - 4

Internal Assessment, January 2000

Paper - IIA

(Endocrines & Reproduction)

Time: 2 hour                                                                                                                                Maximum Marks: 125

Short Answer Questions

Please answer each section in a separate answer book.

                                             Section 'A'

Anatomy

1.                Draw a neatly labeled histological diagram of a mature ovarian follicle (Grafian follicle).

Explain how theca externa is formed.                                                                                    3+1

2.            Define deep perineal pouch. Enlist six components of the deep perineal pouch.               2+3

3.            Explain in brief why incisions into the breast are usually made radially ?                             3

4.            Explain in brief the embryological basis of  thyroglossal cyst.                                              3

Acrylic Teeth Vs Porcelain Teeth

Property	Acrylic Teeth	Porcelain Teeth
Abrasion Resistance	Low	High
Adjustability	Easy	Difficult
Bonding	Chemical	Mechanical
Staining	Easily stained	Does not stain
Percolation	Absent when acrylic denture base is used	Present when acrylic denture base is used
Clicking Sound	Absent	Present
Ease of Fabrication	Easy	Difficult
Ease of rebasing	Difficult to remove acrylic teeth	Esay to remove porcelain teeth
Trauma to dental bearing area	Less	More

Anatomical Landmarks in Maxilla and Mandible for Complete Denture Fabrication

Anatomical Landmarks in Maxilla and Mandible for Complete Denture Fabrication

MAXILLA

Primary Stress bearing area	Residual alveolar ridge
Secondary stress bearing area	Rugae or anterior hard palate Maxillary Tuberosity
Tertiary stress bearing area and secondary retentive area	Posterolateral part of the hard palate
Relieving areas	Incisive papilla Mid palatine raphe Cuspid eminence Fovea palatinea
Primary retentive area	Posterior palatal seal area

MANDIBLE

Primary stress bearing area	Buccal shelf area
Secondary stress bearing area	Slopes of edentulous ridges
Primary retentive and primary peripheral seal area	Retromolar pad
Secondary peripheral seal area	Anterior lingual border
Relief areas	Crest of the residual ridge Mental foramen Mylohyoid ridge

Classification of Composites and their Properties

Type	Properties
Conventional Composite	Contain filler particle size of 8-12 micrometers It is the composite with largest filler size High strength and hardness Less water soprtion and Coefficient of thermal expansion Polishing is difficult and results in rough surface that tends to retain stains
Micro filled Composite	Contain smallest filler particles of size 0.04 - 0.4 micrometers Colloidal silica is used as a filler It has lowest filler content of 50% weight Lowest strength and hardness Highest thermal expansion coefficient and water sorption Excellent esthetics due to the increased smoothness
Small Particle	Contain filler particles of size 1 - 5 micrometers It has good surface smoothness like microfilled composites and improved physical properties like conventional composite It has the highest compressive strength of all composites
Hybrid Composite	It has filler particle size of 0.6 - 1 micrometer They have smooth finish and better esthetics than small particle but yet have similar physical properties.