Prostho 1 Finals Part 3 (Dental Ceramics, Pontic Design)

Dental Ceramics

Dental Ceramics or Porcelains

  • Finely ground ceramic particles that are pigmented to provide colors that are approximate to natural tooth surface

Dental porcelains according to fusing temperature

  1. High fusing 

    1. (1288 - 1371C)

    2. (2350-2500F)

    3. used to manufacture artificial denture teeth but rarely for tooth restoration

  2. Medium fusing 

    1. (1093-1260C) 

    2. (2000-2300F)

    3. fabrication of all ceramic restorations such as porcelain jacket crown (except PFM)

  3. Low Fusing 

    1. (871 - 1066 C)

    2.  (1600 - 1950F)

    3. used to fabricate PFMs / metal-ceramic crowns

Composition of Dental Porcelains

  1. Feldspar (85%) - provides a glassy phase and serves as matrix for the quartz

  2. Quartz (12-22%) strengthener

  3. Kaolin (4%) - hydrated aluminum silicate (that acts as a binder to increase modability of unfired porcelain)


  • Vitrification - porcelain solidifies with a liquid structure instead of a crystalline structure

  • Frits - internal stress or cracks produced when medium and low fusing porcelain are quenched in water

  • Fritting - process of quenching in water

  • Glass formers - principal ion of glass is oxygen which forms stable bonds with multivalent atom such as silicon, boron, germanium on phosphorus which forms random network in glass

  • Dental porcelain use basic silicon-oxygen network as the glass forming matrix but with the additional properties of oxides to the silicate matrix. These properties result in the ff:

    • Low fusing temperature

    • High viscosity

    • Resistance to devitrification

Oxides incorporated in silicon-oxygen matrix

  1. Potassium

  2. Sodium

  3. Calcium

  4. Aluminum

  5. Boric oxide

There are glass modifiers that act to interrupt the integrity of the silicate network and acts as fluxes.

Fluxes - lowers the softening temp of glass by reducing the amount of cross linking between the oxygen and glass forming elements.


Types of layers of porcelain

  1. Opaque porcelain - used to obscure the metal coping

  2. Body porcelain - used to build up the anatomic configuration of the restoration

  3. Incisal porcelain - used to give the restoration a tooth-like appearance

Special types of porcelain

  1. Color frits - added to the dental porcelain to obtain the various shades needed to simulate a natural tooth. 

    1. These coloring pigments are produced by fusing metallic oxides together with fine glass and feldspar and then regrinding them to a powder

  2. Stain - employed as surface colorants or used to replicate enamel checklines, hypocalcification areas or other tooth defects in the body of porcelain restoration

  3. Overglazed or applied glazes - ceramic powders that are painted on the surface of the porcelain restoration which is first at a maturing temperature lower than that of the restoration to produce a transparent glassy layer on the surface.

Pontic Design

Pontics

  • artificial teeth of a FPD that replace missing natural teeth, restoring function and appearance

  • should be designed to meet hygienic requirements

  • prevent irritation of the residual ridge (particular attention must be given to form and shape of gingival structure

    • prevent plaque accumulation

  • carefully designed and fabricated not only to facilitate plaque control of the tissue surface and the adjacent abutment teeth and also to adjust existing occlusal condition


Paradigm of Successful Pontic Design

  • Biologic

    • Cleansable tissue surface

    • Access to abutment teeth

    • No pressure on ridge

  • Mechanical

    • Rigid to resist deformation

    • Strong conenctors

    • Metal ceramic framework

  • Esthetics

    • Shaped to look like tooth it replaces

    • Emergence profile - Appearance to grow  out of the edentulous ridge

    • Sufficient space for porcelain.


Pretreatment Assessment

  1. Pontic space - the function of an FPD is to prevent tilting or drifting of the adjacent teeth into the edentulous space. 

    1. If such movement has already occurred, creating an acceptable appearance without the benefit of orthodontic repositioning is difficult.

    2. Modification of abutments with complete coverage retainers is the only solution.

  2. Residual ridge contour

    1. Edentulous ridge and topography should be evaluated for the following:

      1. Shape of the ridge - smooth, regular of attached gingiva which facilitates maintenance of plaque free environment

      2. Height and width of the ridge - allow placement of a pontic that appears to emerge from the ridge and mimics the appearance of neighboring teeth

      3. Frenum attachments - must be free of frenum attachments and adequate facial height to sustain the appearance of interdental papillae



Classification of residual ridge deformities according to Siebert

  1. Class I defect - faciolingual loss of tissue width with normal ridge height

  1. Class II defect - loss of ridge height with normal ridge width

  1. Class III defect - combination in loss of both dimension


Pontic design classification

  1. Mucosal contact

    1. Ridge lap

    2. Modified ridge lap

    3. Ovate

    4. Conical

  2. No mucosal contact

    1. Sanitary (hygienic)

    2. Modified sanitary (hygienic)


Mucosal Contact

Saddle ridge lap

  • Concave fitting surface that overlaps the residual ridge buccolingual simulating the contours and emergence profile of the missing tooth on both sides of the residual ridge

  • Should be avoided because the concave gingival surface of the pontic is not accessible to cleaning with dental floss


Modified Ridge Lap

  • Combines the features of the hygienic and saddle pontic designs combining esthetics with easy cleaning

  • Overlaps the residual ridge on the facial (to achieve the appearance of the tooth emerging from the gingiva) but remains clear on the ridge on the lingual

  • The gingival surface must have no depression to 


Conical Pontic

  • Egg-shaped, bullet shaped or heart shaped, conical pontic is easy for the patient to keep clean

  • Should be made convex with only one point of contact at the center of the residual ridge

  • Design is recommended for replacement of mandibular posterior teeth where esthetics is a lesser concern

  • Unsuitable for all residual ridge because the emergence produce is associated with the small tissue contact point creates areas of food entrapment


Ovate Pontic

  • Most esthetically appealing pontic design

  • Convex tissue surface resides in a soft tissue depression or hollow in the residual ridges which makes it appear that the tooth is literally emerging from the gingiva

The gingiva surrounding the pontic heals and adapts to it.


No mucosal contact pontic

Sanitary or hygenic pontic

  • The primary design features of the sanitary pontic allows easy cleaning because the tissue surface remains clear of the residual ridge

  • This hygienic design permits easy plaque control by allowing gauze strips and other cleaning devices to passed under the shoe shine fashion.

  • Its' disadvantage include entrapment of food particles which may lead to tongue habits that may annoy the patient

  • Least tooth like design of all pontic


Modified sanitary pontic

  • Its gingival portion is shaped like an archway between the retainers. 

    • This geometry permits increased connector size while decreasing the stress concentrated in the pontic and connector.

  • It is less susceptible to tissue proliferation that can occur when a pontic is too close to the resıdual ridge