By Dr.Swathi Pai on Tuesday 13 January 2009 with 0 comments

A prerequisite to fixed prosthodontic treatment is a healthy joint and supporting skeletal musculature.

Normal range of mandibular maximal opening is 53-58mm.

A restricted opening is less than 40mm.

Hard endfield = a discal problem

Soft endfield = a muscular problem

Biomechanics/Lever system

-Class I Lever: the “see-saw”----WORK FULCRUM FORCE

-Class II Lever: the “wheel barrel”----FULCRUM WORK FORCE

-Class III Lever: the “nut-cracker”----FULCRUM FORCE WORK

  • The class I lever delivers the most destructive forces and should be avoided.
  • The class II and III levers are less destructive and are representative of the human stomatognathic system.
  • Class III levers generate 4X the work in the molar region.

FM Angles:

-normal = 25 (Angle’s class I occl.)

-low = less than 20 (Angle’s class III occl.)---increased forces

-high = greater than 30 (Angle’s class II occl.)---decreased forces

Width of keratinized gingiva: must be 2mm or more to prevent chronic irritation around crown margins.

Biologic width: 2mm from bottom of sulcus to alveolar crest---1mm is junctional epithelium and 1mm is connective tissue. It’s 3mm total if you include free gingival margin. A 3mm distance is recommended between the finish line of a preparation or final margin of a restoration and the alveolar bone.

Timing of preparation after perio surgery: if esthetics is not a concern and the periodontium is thick, 8 weeks is enough time. If it’s an esthetic area or the periodontium is thin, 20 weeks is the recommended time.

6 indications for subgingival margins:

  1. caries

  2. pre-existing restorations

  3. esthetics

  4. root sensitivity

  5. cervical erosion

  6. root fracture

Crown contours: under-contouring is better than over-contouring---a 0 or concave emergence profile of crowns is recommended.

Embrasure design: when a connector for an FPD is reduced to ½ its original width, the resistance to deformation is likewise decreased by ½. When the height of the connector is reduced by ½, it has 1/8 the strength of the original connector. This concept is an example of “The Law of Beams.” Another example of this law involves the edentulous span length (deflection of an FPD). The deflection of an FPD is proportional to the cube of its length.

-the force on 1 pontic is 1X the distance

-the force on 2 pontics is 8X the distance

-the force on 3 pontics is 27X the distance

Accepted tapers for teeth:

-anterior teeth: 30

-premolars: 10

-molars: 8

-if axial alignment is greater than 25, then endo or ortho may be required.

Category: Prosthodontics Notes



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