Retrofilling Cements Types: Selection and Techniques
Amalgam has been used for a long time, but it has several problems. There tends to be marginal adaptation and filtration. There is also a problem with biocompatibly. In subcutaneous and bone studies, amalgam was cytotoxic due to free mercury ion release (less cytotoxic when set). Amalgams with a higher content of copper or zinc were also cytotoxic due to ion release. In addition, a galvanic current is produced due to contact with metal posts and crowns. Finally, tatoos arise due to corrosion of amalgam/silver cones or leaving amalgam outside the cavity or removal of previous apico-ectomies with amalgam/old silver cones.
Amalgam studies show that success rates were as low as 44%, especially in studies longer than 5 years.
Zinc Oxide-eugenol (ZOE) Cements
Zinc oxide-eugenol cements have been used in the past decade to replace amalgams; but they contain eugenol which, in contact with tissue fluids, is hydrolyzed and released. Free eugenol has several dangerous effects depending on its concentration and length of exposure. It inhibits sensory nerve activity, mitochondrial respiration, and prostaglandin synthetase. It depresses vasoconstrictor response, and supresses or enhances effects on the inmmune response. It can be an allergen and eliminates native oral microorganisms.
Intermediate Restorative Material (IRM)
Intermediate Restorative Material is a modified ZOE cement that has been reinforced by the addition of polymethacrylate in the powder, eliminating the absorbability problem and eliciting a milder reaction.
Studies show a better biocompatibility and higher clinical success rate than amalgam.
Super ethoxybenzoic acid cement is an improved IRM. Super EBA is pH neutral, has low solubility, and has less leakage than amalgam. It produces minimal chronic inflammation in the apex. It has excellent adaptation to sectioned dentin edges, and collagen fiber apposition over the material has been observed.
However, it is a difficult cement to manage when a large cavity has to be sealed, because of its short setting time, and it is also greatly affected by moisture and disintegrates in acidic pH89.
In summary, superEBA cement is well tolerated by tissues, is fast-setting, polishable and dimensionally stable, and provides a good apical seal. Disadvantages are that is difficult to manage, sensitive to temperature, moisture and acidic pH, and is only moderately radiopaque. It has no capacity to regenerate cementum.
SuperEBA retrocavity obturation technique
TIP If drying of the retrocavity walls is not thorough, superEBA will not stick and will fall out.
SuperEBA cement is prepared with a 1:4 liquid/powder ratio. When the mixture is still shiny, additional powder is added and rolled until it loses its shine and the tip does not droop when picked up by a microspatula. Working time is 3-4 minutes and setting time only 2 minutes. Cement preparation for delivery should be thinner at the beginning and thicker at the end.
An appropriately sized plugger (0.25 mm width;) or a customized one should be delivered by the assistant right in front of the microcavity. For final filling, a round ball should be used in the same way as the plugger until a slight over-obturation of the microcavity has been achieved. After setting is complete, excess cement can be carved away by a curette or with a blade. Polishing is not necessary.
Final inspection of the area should be made at high magnification (25x) with a CX-1 explorer.
Glass lonomer Cement (GIC)
Glass ionomer cement consists of aqueous polymeric acid, such as polyacrylic acid, plus basic glass powders, such as calcium alumi-nosilicate. The cement can be either light- or chemically cured. Seal and marginal adaptation are better in the light-cured version. As with IRM (see above), it is greatly affected by moisture and blood during the initial setting time, resulting in increased solubility and decreased bond strength94 95; this significantly occurred in unsuccesful cases96. The cytotoxicity and tissue response is similar to ZOE-based cements9798.
Most of the earlier treatment failures with this material were related to poor adaptation of gutta-percha to the canal walls, space occupied by the sealer - even with a good looking radiograph - and after sealer degradation. Leakage can be seen in many surgical cases without using methylene blue.
Therefore, the surgeon cannot rely on cold- or heat-burnished gutta-percha and finish microsurgery after apicoectomy without preparing a 3 mm deep apical microcavity and obturating it with a well-sealing and dimensionally stable biocompatible cement.
MTA consists of tricalcium silicate, tricalcium aluminate, tricalcium oxide, and silicate oxide. It also has bismuth oxide powder for radiopacity. The crystals are composed of calcium oxide and the amorphous matrix is composed of 33% calcium, 49% phosphate, 2% carbon, 3% chloride, and 6% silica99. Calcium and phosphorous are the main ions. Iron is absent in the white MTA.
Hydration of the powder, which has a mean particle diameter of 10 nanometers, produces a colloidal gel that solidifies into a hard structure consisting of discrete crystals in an amorphous matrix.
Setting time is long (3 hours), meaning low contraction and good marginal adaptation. Addition of calcium chloride accelerates the setting by up to 20 minutes.
The compressive strength is quite low at 24 hours (40 MPa) but it increases to 67 MPa at 21 days after mixing.
The solubility of MTA is similar to amalgam and superEBA. Importantly, it is hydrophilic, so moisture and blood do not affect its setting.
Initially the pH is 10.2, but this increases to 12.5 at 3 hours after mixing". Its radiopacity is reasonable, being higher than superEBA and IRM.
MTA cement stimulates cementogenesis and hard tissue formation102-105 by osteocalcin gene expression of osteoblast cells106. It is currently the only available filling material that produces a cementum deposition layer over it, and only a minimal degree of inflammatory cell response, periodontal ligament regeneration thickness and osseous healing107-109.
MTA is the best filling material available today in terms of biocompatibility, sealing ability, dimensional stability. Disadvantages are that, although moisture is required for its setting, during packing, isolation is critical because just one drop of liquid can remove it from the retrocavity. Also, its setting time is very long, radiopacity is not high, and clinically is the least scientifically tested cement, so far.