Anatomical structure – Definition, Meaning & Synonyms

Question. Describe with diagrams the anatomical structures of

1. Maxillary Denture Bearing area.
   
2. Mandibular Denture-Bearing area
   Answer:

What Is A Maxillary Denture – Maxillary Denture Bearing Areas

Stress-bearing Areas

The residual ridge and most of the hard palate are considered the primary stress-bearing area in the upper jaw. The crest of the residual alveolar ridge is covered with a layer of fibrous connective tissue and the bone in the region of the crest of the upper residual ridge may be compact in nature, being made up of haversian systems. The above features help to provide primary support for the upper denture.

Read And Learn More: Complete Dentures Question and Answers

Anatomical Landmarks

1. Labial Frenum-   Labial Frenectomy

The maxillary labial frenum is a fold of mucous membrane at the median line with no muscle and has no action of its own. This band of tissue starts superiorly in a fan shape and converges as it descends and attaches to the labial side of the ridge. The labial notch in the labial flange of the denture must allow the frenum to pass through it without manipulation of the lip.

1. Labial notch
2. Labial flange
3. Buccal notch
4. Buccal flange
5. Coronoid contour
6. Alveolar groove
7. Maxillary tubercular fossa
8. Pterygomaxillary seal
9. Posterior palatal seal
10. Median palatine groove
11. Incisive fossa
12. Rugae

1. Labial frenum
2. Labial vestibule
3. Buccal frenum
4. Buccal vestibule
5. Coronoid bulge
6. Residual alveolar ridge
7. Maxillary tuberosity
8. Hamular notch
9. Incisive papilla
10. Median palatine raphe
11. Mental foramen area

2. Labial Flange

• The denture border between the labial and buccal frenum is known as the labial flange. The orbicular oris is the main muscle resting on the labial flange and teeth of the denture.
• Its tone depends on the support it receives from the thickness of the labial flange and the position of teeth. The fibers of the orbicularis pass horizontally through the lips and anastomose with fibers of the buccinator muscle.

3. Buccal Frenum

• The buccal frenum can be a single or double fold of mucous membrane which is broad and fan-shaped. The canines (levator anguli oris) attach beneath and affect the position of the buccal frenum. The orbicularis oris pulls the frenum forward and the buccinator pulls it backward.
• The buccal notch in the denture must be broad enough to allow this movement of the buccal frenum. The buccal frenum is a continuous band of tissue going from the maxilla through the modiolus to the buccal frenum on the mandible.

4. Buccal Vestibule

• The buccal vestibule is opposite the tuberosity and extends from the buccal frenum to the hamular notch. The size of the buccal vestibule varies with the contraction of the buccinator, the position of the mandible, and the amount of bone loss from the maxilla.
• The thickness of the distal end of the buccal flange of the denture should accommodate the ramus and coronoid process and the masseter as they function. If too thick, the ramus will push the denture out of place during opening or lateral movements of the mandible.

5. Incisive Papilla

The incisive papilla covers the incisive foramen and is located behind and between the central incisors. If adequate relief is not provided in this region it may cause interference with the blood and nerve supply.

6. Rugae

• The rugae are irregularly shaped rolls of soft tissue in the anterior part of the hard palate which should not be distorted during impression procedures.
• The rural area is set at an angle to the occlusal plane of the residual ridges and is thinly covered by soft tissues. It helps in secondary retention.

7. Median palatine Raphe

The submucosa in the region of the median palatal suture of the maxillary bones is extremely thin. Proper relief in the impression tray or the completed denture is essential for the accommodation of the histologic nature of this tissue.

8. Zygomatic Process

The zygomatic, or malar process, located opposite the first molar region, is a hard area found in mouths that have been edentulous for a long time. Some dentures require relief over this area to aid retention and prevent soreness of the underlying tissues.

9. Palate

• Divided into anterior and posterior parts. The posterior part consists of glandular tissue which aids in retention but does not provide significant support for the denture because of higher resiliency at this site.
• The mucus glands in this region are relatively thick and they cover the blood vessels and nerves coursing forward in the palate from the greater palatine foramen and they anastomose with vessels and nerves passing through the nasopalatine canal.

10. Posterior Palatal Area

As the posterior palatine foramina are thickly covered by soft tissue they do not need to be relieved except in extreme cases of resorption. Anterolaterally, the submucosa of the hard palate contains adipose tissue and posterolaterally it contains glandular tissue.

11. Maxillary Tuberosity

The tuberosity region of the maxilla often hangs low if in cases where the maxillary posterior teeth are retained after the mandibular molars have been lost and not replaced, the maxillary teeth extrude, bringing the process with them. This excess soft tissue can prevent the proper location of the occlusal plane if it is not removed.

12. Pterygomaxillary (hamular) notch

• The hamular notch is situated between the tuberosity of the maxilla and the hamulus of the medial pterygoid plate. It is used as a boundary of the posterior border of the maxillary denture back of the tuberosity.
• The posterior palatal seal must be placed through the center of the deep part of the hamular notch since no muscle or ligament is present at a level to prevent the placement of extra pressure.

13. Palatine Fovea Region

The foveae palatine are indentations near the midline of the palate formed by the coalescence of several mucus gland ducts. They are close to the vibrating line and always in soft tissue, which makes them an ideal guide for the location of the posterior border of the denture.

14. Vibrating Line of The Palate

• The vibrating line is an imaginary line drawn across the palate that marks the beginning of motion in the soft palate when the patient says “ah”. It extends from one pterygomaxillary notch to the other and passes about 2 mm in front of the foveae palatine.
• The vibrating line is always on the soft palate. The direction of the vibrating line varies according to the shape of the palate. In a mouth with a flat vault, the vibrating line is usually farther posterior and has a gradual curvature, with a broader posterior palatal seal area.
• The distal end of the upper denture should end 1 or 2 mm posterior to the vibrating line and cover the tuberosities and extend into the hamular notches.
• The submucosa in the region of the vibrating line on the soft palate contains glandular tissue. The submucosa of the mucous membrane contained within the hamular notch is thick and made up of loose areolar tissue.
• The anterior vibrating line is an imaginary line located at the junction of the attached tissues overlying the hard palate and the movable tissues of the immediately adjacent soft palate.
• One way to locate the anterior vibrating line is to have the patient perform the Valsalva maneuver, which requires that both nostrils be held firmly while the patient blows gently through the nose.
• Another method is for the patient to say “ah” with short vigorous bursts. Due to the projection of the posterior nasal spine, the anterior vibrating line is not a straight line between both hamular processes. The anterior vibrating line is always on soft palatal tissues.
• The posterior vibrating line is an imaginary line at the junction of the aponeurosis of the tensor veli palatine muscle and the muscular portion of the soft palate.
• It represents the demarcation between that part of the soft palate that has limited or shallow movement during function and the remainder of the soft palate that is displaced during functional movements.
• The posterior vibrating line is visualized by instructing the patient to say “ah” in short bursts in a normal, unexaggerated fashion.
• The posterior vibrating line marks the most distal extension of the denture base. The posterior palatal seal area lies between the anterior and posterior vibrating lines and is cupids bow-shaped.

Mandibular Basal Seat Area 

1. Crest of the residual ridge:

The crest of the residual ridge is covered by fibrous connective tissue if closely attached to the bone it can resist externally applied forces.

2. Labial frenum

The mandibular labial frenum contains a band of fibrous connective tissue that helps attach the orbicularis oris.

3. Labial flange

The part of the denture that extends between the labial frenum (labial notch) and the buccal frenum (buccal notch) is called the mandibular labial flange which is limited by the fibers of the orbicularis oris and the incisive labii inferioris.

4. Mental Foramen Area

Severe resorption of bone near the mental foramina can result in a superficial location of mental foramen on the crest of the residual ridge. If relief is not provided in the denture base in this area this can lead to numbness of the lower lip due to pressure on the mental nerve.

5. Buccal Frenum

The buccal frenum connects as a continuous band through the modiolus at the corner of the mouth to the buccal frenum in the maxilla.

6. Buccal Flange

• The buccal flange area starts immediately posterior to the buccal frenum and extends to the anterior portion of the masseter, swings wide into the cheek, and is nearly at right angles to the biting force.
• Hence able to provide the greatest surface for resistance to vertical occlusal forces. The buccal flange may extend to the external oblique ridge, or even over it, depending on the location of the mucobuccal fold.

7. Buccal Vestibule

• The buccal vestibule extends from the buccal frenum posteriorly to the outside back corner of the retromolar pad and from the crest of the residual alveolar ridge to the cheek.
• The buccinator, in the cheek, extends from the modiolus (anteriorly) to the pterygomandibular raphe (posteriorly). Its lower side attaches to the molar region in the buccal shelf of the mandible.

8. Buccal Shelf

• It is the primary stress-bearing area of the mandible denture base. The buccal shelf area extends from the mandibular buccal frenum to the anterior edge of the masseter.
• It is bounded medially by the crest of the residual ridge, anteriorly by the buccal frenum, laterally by the external oblique line, and distally by the retromolar pad.
• The inferior part of the buccinator is attached to the buccal shelf of the mandible and thus contraction of the muscle does not lift the lower denture. It is covered with good smooth cortical bone which is usually at right angles to the occlusal forces.

9. Masseter Muscle Region

• The distobuccal borders of the mandibular denture converge rapidly to avoid displacement due to contracting pressure of the anterior fibers of the masseter muscle, which passes outside the buccinator in this region.
• When the masseter contracts, it alters the shape and size of the distobuccal end by pushing inward against the buccinator muscle and suctorial pad of the cheek.

10. Retromolar Region and Pad

• The retromolar pad is a triangular soft pad of tissue at the distal end of the lower ridge which must be covered by the denture to perfect the border seal.
• It contains glandular tissue, some fibers of the temporalis tendon, buccinator fibers enter it from the buccal side, and fibers of the superior pharyngeal constrictor enter it from the lingual; the pterygomandibular raphe enter the pad at its super posterior inside corner.

11. Lingual Frenum and lingual flange

The anterior part of the lingual flange over the sublingual gland is usually shallow because of the mobility of the tissues controlled indirectly by the mylohyoid muscle hence only a short flange is usable.

12. Mylohyoid Ridge

• Soft tissue usually hides the sharpness of the mylohyoid ridge, which can be found by palpation. The lingual border of the mandibular impression extends into the undercut below
• the mylohyoid ridge. The mylohyoid muscle arises from the whole length of the mylohyoid line, extending from about 1 cm back of the distal end of the mylohyoid ridge to the lingual anterior portion of the mandible at the symphysis.
• Medially the fibers join those from the mylohyoid muscle of the opposite side and posteriorly they continue to the hyoid bone.
• The posterior part of the mylohyoid muscle in the molar region affects the lingual impression border in swallowing and moving the tongue.
• If the mylohyoid ridges are bulbous, irregular, and severely undercut or extremely thin and sharp it is the cause of aggravation and soreness for edentulous patients.

13. Sublingual Gland Region

It is in the premolar region on the lingual side of the ridge. The sublingual gland rests above the mylohyoid muscle and when the floor of the mouth is raised, this gland comes close to the crest of the ridge reducing the vertical space available for flange extension.

14. Alveololingual Sulcus

The alveololingual sulcus is the space between the residual ridge and the tongue extending posteriorly from the lingual frenum to the retro mylohyoid curtain. The alveololingual sulcus is divided into three regions.

1. The anterior region
   • Extends from the lingual frenum to where the mylohyoid ridge curves down below the level of the sulcus. The mylohyoid fossa can be palpated as a depression and a corresponding prominence, the mylohyoid eminence, can be seen on impressions. The mylohyoid fossa results from the concavity of the mandible joining the convexity of the mylohyoid ridge.
2. The middle region
   • This part extends from the mylohyoid fossa to the distal end of the mylohyoid ridge curving medially from the body of the mandible. The curvature is caused by the prominence of the mylohyoid ridge.
3. The posterior region
   • This part is the retro mylohyoid space or fossa. It extends from the end of the mylohyoid ridge to the retro mylohyoid curtain, being bounded on the lingual by the anterior tonsillar pillar and superior constrictor and on the buccal by the mylohyoid muscle, mandibular ramus, and retromolar pad.

• • The projection of the mylohyoid ridge toward the tongue and the existence of a retro mylohyoid fossa at the distal end of the alveololingual sulcus causes the border of the lingual flange to assume an “S” shape when viewed from the impression surface.