Free DMD Biomedical and Dental Sciences Questions and Answers — Questions and Answers
Question 1: According to Socransky's microbial complexes, which group of bacteria, known as the 'Red Complex', is most strongly associated with the progression of chronic periodontitis and increased probing depths?
- Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola (Correct answer)
- Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus
- Aggregatibacter actinomycetemcomitans, Capnocytophaga species, Eikenella corrodens
- Actinomyces viscosus, Streptococcus sanguinis, Veillonella parvula
Correct answer: Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola
The 'Red Complex,' identified by Socransky and colleagues, consists of Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola. This group is considered the most pathogenic and is strongly implicated in the destructive phase of chronic periodontitis, being frequently found in deep, bleeding periodontal pockets. [1, 2, 13] The other answer choices list bacteria primarily associated with dental caries, aggressive periodontitis, or early, healthy biofilm formation.
Question 2: A dentist administers a conventional inferior alveolar nerve block (IANB) for a procedure on a mandibular first molar. Despite achieving profound anesthesia of the lip and chin, the patient reports sharp pain when the tooth is touched. Which of the following is the most likely reason for this anesthesia failure?
- The injection was administered too low, missing the mandibular foramen.
- The long buccal nerve, which innervates the pulp, was not anesthetized.
- The lingual nerve was inadvertently anesthetized instead of the inferior alveolar nerve.
- Accessory sensory innervation was provided by the mylohyoid nerve. (Correct answer)
Correct answer: Accessory sensory innervation was provided by the mylohyoid nerve.
The mylohyoid nerve, which branches from the inferior alveolar nerve before it enters the mandibular foramen, typically provides motor function but can also carry sensory fibers that innervate the mandibular molars. [9, 10, 26] When a standard IANB fails despite signs of successful anesthesia (e.g., numb lip), this accessory innervation is a common cause. The other options are incorrect because a low injection would likely result in no anesthesia, the long buccal nerve innervates soft tissue (not pulp), and anesthetizing only the lingual nerve would not affect the tooth's pulp.
Question 3: The development of a unilateral cleft lip is primarily caused by the failure of fusion between which two embryonic structures?
- The two medial nasal processes in the midline.
- The maxillary process and the medial nasal process. (Correct answer)
- The lateral nasal process and the maxillary process.
- The right and left mandibular processes.
Correct answer: The maxillary process and the medial nasal process.
A unilateral cleft lip results from the failure of the maxillary process on one side to fuse with the merged medial nasal processes during the 4th to 7th week of embryonic development. [7, 11, 15] This fusion event is critical for forming the philtrum and lateral portions of the upper lip. Failure of the two medial nasal processes to fuse causes a rare midline cleft, while failure of the mandibular processes to fuse results in a cleft of the lower lip.
Question 4: A 10-year-old patient presents for an initial examination. Clinically, the teeth have a characteristic blue-gray opalescent hue. Radiographs reveal bulbous crowns with marked cervical constriction and near-complete obliteration of pulp chambers and root canals in both the primary and permanent dentitions. What is the most likely diagnosis?
- Amelogenesis Imperfecta
- Regional Odontodysplasia
- Tricho-Dento-Osseous Syndrome
- Dentinogenesis Imperfecta (Correct answer)
Correct answer: Dentinogenesis Imperfecta
Dentinogenesis Imperfecta (DI) is a hereditary disorder affecting dentin formation. The clinical and radiographic findings of opalescent teeth, bulbous crowns, cervical constriction ('tulip shape'), and progressive obliteration of the pulp are pathognomonic for this condition. [6, 17, 20] Amelogenesis Imperfecta affects enamel, Regional Odontodysplasia is a localized 'ghost teeth' phenomenon, and Tricho-Dento-Osseous Syndrome involves other specific systemic features not described.
Question 5: Which of the following best describes the primary post-eruptive mechanism by which topical fluoride inhibits the caries process?
- It directly kills cariogenic bacteria like Streptococcus mutans.
- It enhances remineralization by forming less acid-soluble fluorapatite. (Correct answer)
- It physically blocks the orifices of dentinal tubules.
- It stimulates an increase in salivary buffering capacity.
Correct answer: It enhances remineralization by forming less acid-soluble fluorapatite.
The principal mechanism of topical fluoride is its interaction with the tooth mineral at the plaque-enamel interface. When present during an acid attack, fluoride ions adsorb to the demineralized crystal surfaces and attract calcium and phosphate from saliva. This process enhances remineralization, forming fluorapatite, which is chemically more stable and less soluble in acid than the original hydroxyapatite. [5, 16, 28] While fluoride has some antimicrobial effects, its primary role is altering demineralization/remineralization dynamics.
Question 6: When taking a final impression for a multi-unit fixed partial denture, which property of an elastomeric impression material is most critical for ensuring the prosthesis will fit accurately?
- Hydrophilicity
- Tear strength
- Dimensional stability (Correct answer)
- Working time
Correct answer: Dimensional stability
For a multi-unit prosthesis, the spatial relationship between the abutment preparations must be captured perfectly and maintained until the stone cast is poured. High dimensional stability ensures that the impression does not shrink, expand, or warp over time, which would lead to a distorted master cast and a poorly fitting bridge. [8, 12, 19] While hydrophilicity, tear strength, and working time are important properties, they are secondary to dimensional stability for the ultimate accuracy of a large-span restoration.
Free DMD Biomedical and Dental Sciences Questions and Answers
According to Socransky's microbial complexes, which group of bacteria, known as the 'Red Complex', is most strongly associated with the progression of chronic periodontitis and increased probing depths?