Dental Problems

Polycarbonate Crown as Semi permanent Restoration

tooth-5One amongst the moderately recent advancement in semi permanent restoration is polycarbonate crown. These are recommended for the restoration of lost tooth structure and to stabilize it with prefabricated crowns. In this article, there is a brief discussion on the polycarbonate crown as semi permanent restoration. Read on to know more.

Polycarbonate crown as a semi permanent restoration

In pedodontic practice, the most common lesion in anterior teeth is likely to be the result of the nursing bottle caries. These lesions will occur beginning on the labial face of the anterior side and they progress rapidly as a diffused demineralization of the entire surface of all existing teeth.

The best that can be offered at this time is the stabilization of the lesion without much in the way of a complete rebuild of the coronal anatomy. It is suggested that the first step should be to develop a clean periphery around the lesion using a small round bur whilst leaving the central portion of the affected dentin intact and undisturbed for fear of producing a pulp exposure.

This will make it possible to develop the ion exchange with glass ionomer and allow development of an effective seal.

Polycarbonate crowns

are the temporary crowns that could be given as a fixed prosthesis to the deciduous anterior tooth which would get exfoliated in future.

These are contraindicated in the following:

  • Severe bruxism
  • Excessive abrasion
  • Deep bite

Polycarbonate crowns are designed to provide various advantages which are listed below:

  • They are easy to trim
  • They save time and
  • They can be easily adjusted with piers

Technique for construction:

  1. Crown is selected according to mesiodistal width and cervio-mesial length of the tooth while keeping in mind the shade of the tooth.
  2. The tooth is reduced by about 0.5mm to allow space for the crown from labio-lingually.
  3. Mesio distally the reduction removes the contacts.
  4. 1-2 mm of incisal reduction is carried out.
  5. Crown is selectively ground at gingival aspect.
  6. It is then lined with acrylic or composite material.
  7. The preparation and the surrounding gingival is lubricated with water or saliva and the crown is then seated. As the acrylic starts to set, the crown is removed from the preparation and reseated a number of times. This dissipates the heal during polymerization and prevents blocking into undercuts.
  8. The margins are trimmed and finished and the crown is cemented with luting acrylic cement. Blanching of gingival tissues should be checked to avoid over extension into the sulcus.

Cementation of the polycarbonate crown:

Polycarbonate crown

used as semi permanent restorations are cemented with the glass or phosphate ionomer cements.

Disadvantages of polycarbonate crown:

  • These polycarbonate crowns are difficult to place.
  • They have poor retention
  • They are prone to excessive wear
  • They are brittle and also have a high incidence of crown fracture

Conclusion of polycarbonate crowns:

Ceramic and metal orthodontic brackets are bonded to the temporary polycarbonate crowns. These most likely do not withstand the orthodontic forces and biomechanics. However, sandblasting

polycarbonate crowns

will consistently cause an increase in the shear bond strength of ceramic and metal brackets.

Use of a diamond bur will effectively roughen the polycarbonate crown surface but without any in gain in the bond strength. Similarly, an etching on the surface of the polycarbonate crown with hydrofluoric acid (9.6%) is likely to be ineffective. Ceramic brackets which are bonded to the sandblasted polycarbonate crowns produce highest mean of 2.87 MPa of shear bond strength. This value is although far below the bond strengths with the natural tooth surfaces.

The above article discusses briefly about the polycarbonate crown as a semi permanent restoration.

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