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Cones for use in root canal treatment

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Official DGZMK [German Society of Dental, Oral & Craniomandibular Science] and DGZ [German Society of Operative Dentistry] papers:

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Function of cones for use in root canal treatment

Paste fillings are not suitable as final root canal fillings; pastes that remain soft or are self-curing are inappropriate. On the one hand, precise length control of the root canal filling is not possible whilst on the other hand there is potential for entrapment of air and bubble formation during placement of the filling as well as contraction during the process of curing of the root canal paste leading to poor seal of the fillings against the margin. This quickly results in re-infection of the obturated root canal system. Therefore, pastes are clearly not suitable for being used alone as material for root fillings.
Root canal cones are less flexible than sealers. They are used for the condensation of root canal filling pastes and may consist of gutta-percha, metal, or synthetic materials.

The percentage of root canal cones used should be as high as possible in any root canal filling treatment because, unlike most sealers, they will not shrink during the setting process.

Furthermore, solid materials are usually biologically more inert than most pastes used for root canal filling.

Semi-solid cones for root canal fillings

Gutta-percha cones

Gutta-percha is a trans-isomer of polyisoprene (trans-1.4-polyisoprene), hence it has chemical properties which are similar to natural latex.
Depending on the temperature, the material exists in different crystalline forms, namely the alpha form, beta form, or gamma form. Dental gutta-percha cones correspond to the beta form which has the same mechanical properties as the natural alpha form but the melting point of which is lowered by 9°C. The consistence of alpha gutta-percha is more sticky and softer than that of beta gutta-percha; therefore, the alpha form is not suitable for the techniques commonly used for root canal filling. It is usually used for what is referred to as thermoplastic filling techniques.

Gutta-percha cones consist of:
  • gutta-percha (20 - 45 m%),
  • zinc oxide (33 - 61.5 m%),
  • waxes and synthetic materials as softeners (1.0 - 4.1 m%),
  • heavy metal sulphates as x-ray contrast media (1.5 - 31.2 m%),
  • colouring agents pursuant to ISO coding (1.5 - 3.4 m%), and
  • trace elements (below 1 m%: e.g. Cd, Cu, Fe, S, Ti).
The overall biocompatibility of gutta-percha cones is good. However, if excess gutta-percha penetrates the peri-apical tissue via the root apex, it will delay healing of an existing peri-apical lesion. This is probably due to the zinc oxide contained in gutta-percha cones. Therefore, if gutta-percha cones are used as root canal filling material, it is also essential not to allow escape of excess material into the peri-apical tissue.

Solid cones for root canal fillings

Solid cones for root canal filling are more rigid than gutta- percha cones. From the clinical point of view, this is disadvantageous as solid cones cannot be condensed inside the root canal due to their poor compressibility. This means that there is a significantly greater volume of root canal filling paste as a component of the overall filling which clearly increases the probability of edges not being tightly sealed.

Silver cones

Silver cones will corrode to variable extent when in contact with tissue fluid; sometimes they will even disintegrate.
Cytotoxic products (silver sulphides, silver chloride, silver sulphates and silver carbonates) develop which will frequently pass into the peri-apical tissue where they can cause blueish-black discolouration of the oral mucosa in the area of the root apex. Furthermore, these by-products of corrosion are often the cause for acute and/or chronic inflammatory reactions in peri-apical tissue. Overall, the use of silver cones is considered no longer indicated in modern root canal filling treatment.

Titanium cones

Under physiological conditions, these cones practically do not corrode and are mainly biologically inert.
However, like silver cones, they have the same disadvantage in that, due both to their circular cross-section and lack of compressibility, it may not be possible to achieve a tight and lasting seal.