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What is the inter-pupillary line and its significance in denture orientation?
The inter-pupillary line is an imaginary line between the two pupils of the eyes, used to orient the anterior occlusal plane of artificial teeth.
Describe the ala-tragus line and its role in denture construction.
The ala-tragus line is an imaginary line from the ala of the nose to the tragus of the ear, used to orient the posterior occlusal plane of artificial teeth.
What is the canthus-tragus line and how does it assist in dental prosthetics?
The canthus-tragus line runs from the outer canthus of the eye to the tragus of the ear and is used for the arbitrary location of the condyles.
Explain the nasio-labial sulcus and why it becomes more prominent with age.
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What is the vermillion border and its relationship with the orbicularis oris muscle after tooth loss?
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Define the labial tubercle and its changes post tooth resorption.
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Identify two extraoral landmarks used in complete denture orientation.
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Why is the angle of the mouth important in the context of complete dentures?
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What does the curvature of the mento-labial sulcus indicate in relation to maxillo-mandibular relationships?
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How is Angle Class II characterized in terms of the mento-labial sulcus?
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What is the philtrum and how can it be affected by dental issues?
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What condition is referred to as angular cheilitis, and what causes it?
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Define the modiolus and describe its significance in denture construction.
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What is a stress bearing area in the context of intraoral anatomy?
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How does the construction of dentures address issues with the angle of the mouth?
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What happens to the modiolus after tooth loss and alveolar bone resorption?
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What are the three criteria of a stress-bearing area in the upper arch?
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Define a relief area in the context of dental prosthetics.
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What role does the residual alveolar ridge play in denture support?
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What is the significance of the maxillary tuberosity in denture retention?
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Explain the importance of the median palatine raphe in denture fitting.
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What happens to the incisive papilla after tooth extraction?
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Why is relief of the incisive papilla necessary during denture construction?
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What are some supporting structures of the maxillary arch?
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How does the position of maxillary canines relate to the incisive papilla?
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What is the function of the palatine rugae in relation to speech?
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What is the significance of the torus palatinus in denture fitting?
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What are fovea palatinae and their anatomical location?
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Describe the composition and suitability of the residual alveolar ridge for stress bearing.
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What is the anatomical feature referred to as the crest of the ridge?
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What complications can arise from the presence of a torus palatinus during denture use?
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Identify two supporting structures of the mandibular arch.
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What is the function of the external oblique ridge in denture support?
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Why is the buccal shelf considered a primary stress-bearing area for dentures?
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Describe the location of the mental foramen and its significance in denture design.
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What anatomical structures are included in the retromolar pad and how does it support dentures?
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What is the significance of the pterygomandibular raphe in denture wearers?
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How does the presence of a torus mandibularis affect denture fitting?
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Explain the role of the retromolar pad in maintaining denture function.
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What could happen if the denture base extends beyond the external oblique ridge?
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Study Notes
Extraoral Landmarks
- Inter-pupillary Line: An imaginary line between the centers of the pupils when looking straight ahead. It helps to orient the anterior occlusal plane of artificial teeth.
- Ala-Tragus Line (Camper's Line): An imaginary line from the ala of the nose (side of the nose) to the tragus of the ear. This line is used to orient the posterior occlusal plane of artificial teeth.
- Canthus-Tragus Line: An imaginary line connecting the outer canthus of the eye (where the upper and lower eyelids meet) to the tragus of the ear. Used to arbitrarily locate the condyles (rotational axis).
- Nasio-labial Sulcus: A depression running from the ala of the nose laterally and downward to the corner of the mouth. It becomes deeper with age and can be restored through proper positioning of the anterior teeth and contouring of the upper denture flange.
- Vermillion Border: Transitional epithelium between the mucous membrane of the lip and facial skin. It is usually affected by resorption of the labial alveolar bone, resulting in a diminished appearance. Denture flanges and anterior tooth positioning can restore this.
- Labial Tubercle: A small bulge in the middle of the upper lip's vermillion border. Similar to the vermillion border, it loses support with age and can be addressed with appropriate denture flanges and anterior teeth positioning.
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Mento-labial Sulcus: A depression running horizontally between the lower lip and chin. Its curvature gives an indication of the maxillo-mandibular relationship:
- Angle Class I: Gentle curvature in a normal ridge relationship.
- Angle Class II: An acute angle in a retruded mandibular position.
- Angle Class III: An obtuse angle (greater than 180 degrees) in a protruded maxillo-mandibular relationship.
- Philtrum: A diamond-shaped area at the center of the upper lip, below the base of the nose. It can be distorted by tooth loss and bone resorption, but its original form can be restored with proper tooth arrangement and labial flange contouring.
- Angle of the Mouth (Commissure): The point where the upper and lower lips meet. Drooping saliva and inflammation are termed angular cheilitis, often due to prolonged edentulism, dentures with reduced vertical dimension, or vitamin B12 deficiency. This can be improved with dentures that have proper vertical dimension and anterior tooth positioning.
- Modiolus: The point of meeting for facial muscle fibers. It is a depression located below and distal to the angle of the mouth. Resorption causes the modiolus to drop inward, but proper denture construction can help restore the appearance.
Intraoral Landmarks
- Supporting Structures: Areas that can withstand forces applied by the denture base without tissue ulceration, bone resorption, or denture dislodgement. They have horizontal surfaces, compact bone, and thick mucosa.
- Limiting Structures: Sensitive elevated areas that cannot withstand pressure and require relief in the denture base to reduce stress.
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Stress Bearing Areas: Intral oral areas that can withstand forces from the denture base.
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Maxillary Supporting Structures:
- Residual Alveolar Ridge: The remaining portion of the alveolar process and its covering soft tissue after tooth extraction. The highest point is the crest of the ridge. It’s the primary stress bearing area in the upper arch, covered with dense fibrous tissue.
- Maxillary Tuberosity: A rounded bony prominence at the distal end of the maxillary ridge. It should be covered by the denture for retention and support.
- Median Palatine Raphe: An area of firmly attached mucous membrane to bone with little submucosal tissue. It runs from the incisive papilla to the distal end of the hard palate covering the median palatine suture. It has no resiliency and should not be stressed. Relief of the median palatine raphe is important to prevent rocking, which leads to uneven pressure on the tissues.
- Incisive Papilla: Pear-shaped soft tissue elevation at the midline, palatal to the upper central incisors covering the incisive foramen (which houses the nasopalatine nerves and vessels). It migrates to the crest of the ridge after tooth loss. Needs relief in dentures to avoid interference with nerves and blood supply. Also acts as a guide for anterior tooth position.
- Palatine Rugae: Irregular ridges of dense connective tissue radiating from the midline. Assist the tongue with taste and speech functions. They can withstand stresses and serve as a secondary stress bearing area.
- Torus Palatinus: Bony bulge in the midline of the palate. It needs relief in the denture or surgical removal (for large ones) as it can cause trauma and irritation.
- Fovea Palatinae: Two small pits located on either side of the midline just behind the hard and soft palate junction. They are openings for minor salivary gland ducts. The posterior border of the maxillary denture should extend 2mm posterior to the fovea palatinae.
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Maxillary Supporting Structures:
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Mandibular Supporting Structures:
- Residual Alveolar Ridge: Similar to maxillary, it’s the remaining portion of the alveolar process after tooth extraction. It is formed of cancellous bone and can only bear minimal stress.
- External Oblique Ridge: A dense bony ridge descending diagonally from the ramus of the mandible towards the mental foramen. The lower denture should cover this ridge, but not extend beyond it to avoid denture displacement by the masseter muscle.
- Buccal Shelf of Bone (Buccal Plateau): A nearly horizontal bone shelf between the residual ridge crest and the external oblique ridge in the molar region. It is comprised of dense compact bone and should be covered for denture support. It’s considered a primary stress bearing area because it is nearly perpendicular to forces applied by the masseter muscle.
- Mental Foramen: Located on the buccal surface of the mandible (premolar region), between the roots of the first and second premolars. The mental nerve and vessels pass through this foramen. Relief is necessary to avoid numbness of the lower lip.
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Retromolar Pad: A pear-shaped soft tissue pad at the distal end of the mandibular ridge. It contains mucous glands, the temporalis tendon, pterygo-mandibular raphe, fibers of the buccinator and superior constrictor muscles. Needs to be covered by the denture for support and acts as a shock absorber due to its spongy nature. Helps maintain the occlusal plane.
- Anterior 2/3rd: Height of occlusal rims should not cross this area.
- Posterior 1/3rd: Helps in arranging the mandibular posterior teeth.
- The Pterygomandibular Raphe: The union of the buccinator and superior constrictor muscles. It extends from the hamular process to the retromolar pad. It stretches during mouth opening and may cause denture dislodgement.
- Torus Mandibularis: A bony prominence sometimes present on the inner surface of the mandible in the premolar region. It can be unilateral or bilateral and needs relief if covered by thin mucosa.
- Internal Oblique Ridge (Mylohyoid Ridge): A bony elevation located on the inner surface of the mandible.
- Genial Tubercles or Mental Spine: Bony projections found on the lingual surface of the mandible. They serve as attachment points for muscles and ligaments.
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Description
This quiz covers important extraoral landmarks used in dentistry, including the Inter-pupillary Line, Ala-Tragus Line, and more. Understanding these landmarks is crucial for properly orienting artificial teeth and improving dental aesthetics. Test your knowledge on these foundational concepts in dental anatomy.