Ideal Mechanical, Physical and Biological Properties of Obturation Materials
Characteristics of an Ideal Irrigation System
Physical flushing of debris
Disinfect and detoxify dentin and tubules of all microbial substances
Smear layer removal
Not affect physical properties of dentin
Factors Influencing Efficacy of Irrigation
Diameter of the irrigating needle
Depth of the irrigating needle engaged in root canal
Size of enlarged root canal (radius of tube)
Viscosity of the irrigating solution (surface tension)
Velocity of the irrigating solution at the tip of the needle (ultrasonic, sonic)
Orientation of the bevel of the needle
Traditionally, irrigation has been done using a syringe and side-slotted needle placed 3mm short of working length. Other techniques such as sonic, ultrasonic and apical negative pressure devices have been introduced and are currently available to the clinician. Research has indicated some of these systems may be safer and more efficient than others. Research evidence and experience should be used when deciding which system to incorporate into your technique based on its effectiveness and safety.
Criteria for Judging Technical Success of the Obturation Phase of Endodontic Treatment
Techniques vary by the way they accomplish a three-dimensional obturation of the canal system. The basic principles and criteria for technical success must be achieved regardless of the technique.
1. Clinical Evaluation. For a case to be considered successful, normal findings to routine tests such as percussion, palpation, periodontal probing and visual inspection of the final restoration should be obtained and recorded in the patient’s record at an appropriate follow-up visit. If the clinician is concerned about some aspect of therapy or the prognosis, the reevaluation visit should be scheduled in a few weeks. Routine reevaluation periods may be 6 months and 1 year. Patients
should be informed that if symptoms occur they should call the office for an appointment.
2. Radiographic Evaluation (Length, Shape and Density). (overfilled, overextended and underextended). Three qualities that should be observed, are length, shape and density. The length of an ideal fill should be from the canal’s apical minor constriction to the canal orifice unless a post is planned. The core restoration should complete this seal to the cavo-surface margin. The shape of the completed case is somewhat dependent on the obturation technique being used. Some require a more tapered canal than others. Voids should not be visible on the radiographic image. In terms of percentage rates of success, a meta-analysis of the literature showed that obturations 0 to 1mm short of the apex were better than obturations 1 to 3mm short of the apex; both were superior to obturations beyond the apex.
Regardless of the quality of the sealing of the root canal space, unless this space is protected against ingress of oral microorganisms, success may not be achieved. Notice the presence of an obturated lateral canal. A study of failed cases found that 59.4% of endodontically treated teeth failed due to restorative reasons, 32% for periodontal reasons and 8.6% for endodontic reasons. It is apparent from the literature that prevention of coronal microleakage is critical to success. The use of intra-orifice barriers, which are restorative materials placed over the canal orifices and covering the pulp chamber floor, has been strongly recommended. Criteria have been proposed for the ideal intra-orifice barrier. This material can be any material that will bond or seal the dentin and have a distinguishable color from dentin.
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.
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, 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.