NEET MDS Lessons
Prosthodontics
LIMITING STRUCTURES
A) Labial, lingual & buccal frenum
- It is fibrous band extending from the labial aspect of the residual alveolar ridge to the lip containing a band of the fibrous connective tissue the that helps in attachment of the orbicularis oris muscle.
- It is quite sensitive hence the denture should have an appropriate labial notch.
- The fibers of buccinator are attached to the buccal frenum.
- Should be relieved to prevent displacement of the denture during function.
- The lingual frenum relief should be provided in the anterior portion of the lingual flange.
- This anterior portion of the lingual flange called sub-lingual crescent area.
- The lingual notch of the denture should be well adapted otherwise it will affect the denture stability.
B) Labial & buccal vestibule
- The labial sulcus runs from the labial frenum to the buccal frenum on each side.
- Mentalis muscle is quite active in this region.
- The buccal sulcus extends posteriorly from the buccal frenum to outside back corner of the retromolar region.
- Area maximization can be safely done here as because the fibers of the buccinator runs parallel to the border and hence displacing action due to buccinator during its contraction is slight.
- The impression is the widest in this region.
C) Alveololingual sulcus
- Between lingual frenum to retromylohyoid curtain.
- Overextension causes soreness and instability.
It can be divided into three parts:
i) Anterior part :
- From lingual frenum to mylohyoid ridge
- The shallowest portion(least height) of the lingual flange
ii) Middle region :
- From the premylohyoid fossa to the the distal end of the mylohyoid region
iii) Posterior portion :
- From the end of the mylohyoid ridge end to the retromylohyoid curtain
- Provides for a valuable undercut area so important retention
- Overextension causes soreness and instability
- Proper recording gives typical S –form of the lingual flange
D) Retromolar pad
- Pear-shaped triangular soft pad of tissue at the distal end of the lower ridge is referred to as the retromolar pad.
- It is an important structure, which forms the posterior seal of the mandibular denture.
- The denture base should extend up to 2/3rd of the retromolar pad triangle.
E) Pterygomandibular raphe
SUPPORTING STRUCTURES
A) Primary stress bearing area / Supporting area
1. Buccal shelf area
- Extends from buccal frenum to retromolar pad.
- Between external oblique ridge and crest of alveolar ridge.
Its boundaries are:
1. Medially the crest of the ridge
2. Laterally the external oblique ridge
3. Distally the retromolar pad
4. Mesially the buccal frenum
The width of this area increases as the alveolar resorption continues.
B) Secondary stress bearing area / Supporting area
1. Residual alveolar ridge
- Buccal and lingual slopes are secondary stress bearing areas.
RELIEF AREAS
A) Mylohyoid ridge
- Attachment for the mylohyoid muscle.
- Running along the lingual surface of the mandible.
- Anteriorly: the ridge lies close to the inferior border of the mandible.
- Posteriorly it lies close to the residual ridge.
- Covered by the thin mucosa which may be traumatized by denture base hence it should be relieved.
- The extension of the lingual flange is to be beyond the palpable position of the mylohyoid ridge but not in the undercut.
B) Mental foramen
- Lies on the external surface of the mandible in between the 1st and the 2nd premolar region.
- It should be relieved specially in case it lies close to the residual alveolar ridge due to ridge resorption to prevent parasthesia.
C) Genial tubercle
- Area of muscle attachment (Genioglossus and Geniohyoid).
- Lies away from the crest of the ridge.
- Prominent in resorbed ridges therefore adequate relief to be provided.
D) Torus mandibularis
- Abnormal bony prominence.
- Bilaterally on the lingual side near the premolar area.
- Covered by thin mucosa so it should be relieved
1. Ridge Shape Influences
-
Well-formed ridge
- Allows ideal tooth placement for esthetics and function
- Promotes stability and retention of prosthesis
-
Flat or resorbed ridge
- Teeth may need to be placed slightly lingual or palatal to improve stability
- Avoid placing teeth directly over the ridge crest to prevent tipping
-
Knife-edge ridge
- Avoid direct loading; place teeth slightly off the crest
- Use broader occlusal surfaces to distribute forces
-
Undercut ridge
- May require modified tooth positioning or surgical correction
- Risk of food impaction and prosthesis instability
2. Arch Form Considerations
| Arch Form | Tooth Arrangement Strategy |
|---|---|
| Square Arch | Teeth placed more centrally; good stability |
| Tapered Arch | Teeth may be flared slightly to maintain arch harmony |
| Ovoid Arch | Natural curvature followed; esthetically pleasing |
| Asymmetrical Arch | Requires customized arrangement to balance occlusion and esthetics |
3. Key Principles
- Follow the natural arch contour for esthetics and phonetics
- Avoid placing teeth directly over mobile or thin mucosa
- Ensure bilateral balance in occlusion for complete dentures
- Compensate for ridge resorption by adjusting buccolingual positioning
- Maintain neutral zone—especially in mandibular dentures—to prevent muscle interference
→ Following rules should be considered to classify partially edentulous
arches, based on Kennedy's classification.
Rule 1:
→ Classification should follow, rather than precede extraction, that might
alter the original classification.
Rule 2:
→ If 3rd molar is missing and not to be replaced, it is not
considered in classification.
Rule 3:
→ If the 3rd molar is present and is to be used as an abutment, it
is considered in classification.
Rule 4:
→ If second molar is missing and is not to be replaced, it is not
considered in classification.
Rule 5:
→ The most posterior edentulous area or areas always determine the
classification.
Rule 6:
→ Edentulous areas other than those, which determine the classification are
referred as modification spaces and are designated by their number.
Rule 7:
→ The extent of modification is not considered, only the number of additional
edentulous areas are taken into consideration (i.e. no. of teeth missing in
modification spaces are not considered, only no. of additional edentulous spaces
are considered).
Rule 8:
→ There can be no modification areas in class IV.