Ideal Mechanical, Physical and Biological Properties of Obturation Materials
Many materials and techniques for obturation are available on the market. Dr. Louis I. Grossman, one of the founders of the specialty of endodontics, determined the ideal properties of obturation materials listed in taking these into consideration, the clinician should realize that material: (1) content; (2) toxicity; and (3) physical properties are controlled by the manufacturer. The clinician’s choice of obturation materials should be based on: (1) purchasing materials meeting the American Dental Association and the American National Standards Institute specifications; (2) assuring their compatibility with patient’s medical history; and (3) those that best match the instrumentation and obturation techniques being used. These materials are divided into two basic groups—sealers and core materials—each of which can be found in a large variety of materials and brands. Materials approved by the International Standards Organization and the American Dental Association should be used.
A. Sealers
Sealers are used between dentin surfaces and core materials to fill spaces that are created due to the physical inability of the core materials to fill all areas of the canal. Traditionally desirable characteristics were to adhere to dentin and the core material as well as to have adequate cohesive strength. Newer generation sealers are being engineered to improve their ability to penetrate into dentinal tubules and bond to, instead of just adhering to, both the dentin and core material surfaces. Various types of delivery systems such as auto-mix syringes have improved not only the efficiency of mixing, but also the quality of the mix and ultimately the properties of the set material. Various types of sealers include zinc oxide-eugenol, as well as polymer resins, glass ionomer, bio-glass and silicon-based materials.
B. Core Materials
1. Gutta-Percha: This material was first used in dentistry in the late 1800s as a temporary restorative material and then to obturate root canal systems. During the Civil War, a material called Hill’s stopping (which contained gutta-percha, quick lime, quartz and feldspar) and gutta-percha were advocated by Taft and Harris as temporary filling materials. Its use as a temporary filling material continued until 1950. Used without sealer, gutta-percha does not provide a seal. It is derived from the Taban tree (Isonandra perchas). The natural chemical form of gutta-percha is 1, 4-polyisoprene. It is an isomer of natural rubber and has been used for various purposes such as coating the first trans-Atlantic cable and for the cores of golf balls. Gutta-percha undergoes phase transitions when heated from beta to alpha phase at around 115° F (46° C). At a range between 130° to 140° F (54° to 60° C) an amorphous phase is reached. When cooled at an extremely slow rate the material will recrystalize to the alpha phase. However, this is difficult to achieve and under normal conditions the material returns to the beta phase. The softening point of gutta-percha was found to be 147° F (64°C). The phase transformation is important in thermoplastic obturation techniques.
Gutta-percha is soluble in chloroform, eucalyptol, and halothane and less well in turpentine. This property of gutta-percha allows it to be removed for post preparation and in the retreatment of nonhealing cases.
Any method manipulating gutta-percha using heat or solvent will result in some shrinkage (1-2 %) of the material. Shrinkage of the core material is not desirable when attempting to seal a canal. Dental gutta-percha is not pure
or even mostly gutta-percha. Its major component is zinc oxide (50-79 %), heavy metal salts (1-17 %), wax or resin (1-4 %) and only 19-22 % actual gutta-percha. The variations in content are because of different manufacturers and distributors desiring different handling properties. Some formulations are softer than others. Some clinicians choose the brand of gutta-percha depending on the technique being used. Compaction with spreaders, condensers or carriers is usually the means used to attempt to compensate for this shrinkage of the core material. In any case, some means of compensation for this shrinkage must be incorporated into the technique being used. An important characteristic of gutta-percha and of clinical importance is the fact that when it is exposed to air and light over time it becomes more brittle. Storage of gutta-percha in a refrigerator extends the shelf life of the material.
2. Resilon: Resilon™, a new, synthetic resin-based polycaprolactone polymer has been developed as a gutta-percha substitute to be used with Ephiphany®, (Pentron® Clinical Technologies, Wallingford, Conn.) a new resin sealer in
an attempt to form an adhesive bond at the interface of the synthetic polymer-based core material, the canal wall and the sealer. Advocates of this technique propose that the bond to the canal wall and to the core material creates
· It should be easily introduced into the root canal system.
· It should seal the canal laterally as well as apically.
· It should not shrink after being inserted.
· It should be impervious to moisture. It should be bacteriostatic or at least not encourage bacterial growth.
· It should be radiopaque.
· It should not stain tooth structure.
· It should not irritate periapical tissue.
· It should be sterile or easily and quickly sterilized immediately before insertion.
· It should be easily removed from the root canal if necessary.