A comparative analysis of zinc and non-zinc alloys used in retrograde endodontic surgery. Part 1: Apical seal and tissue reaction

Biocompatibility of root-end filling materials: recent update

The purpose of a root-end filling is to establish a seal between the root canal space and the periradicular tissues. As root-end filling materials come into contact with periradicular tissues, knowledge of the tissue response is crucial. Almost every available dental restorative material has been suggested as the root-end material of choice at a certain point in the past. This literature review on root-end filling materials will evaluate and comparatively analyse the biocompatibility and tissue response to these products, with primary focus on newly introduced materials.

Periapical bone regeneration after endodontic microsurgery with three different root-end filling materials: amalgam, SuperEBA, and mineral trioxide aggregate

INTRODUCTION

The purpose of this study was to determine the bone regeneration potential to different root-end filling materials by evaluating the distance between the materials and newly regenerated bone after root-end surgery.

MATERIAL AND METHODS

Periapical lesions were induced in premolars and molars of five female beagle dogs. The teeth were treated endodontically after the development of the lesions. After 1 week, the teeth underwent root-end surgery using modern microsurgical techniques. Three different root-end filing materials were used: amalgam (Tytin; Kerr Mfg Co, Romulus, MI), SuperEBA (Bosworth, Skokie, IL), and mineral trioxide aggregates (MTA; Dentsply, York, PA). After 4 months, the dogs were sacrificed, and the jaws were prepared for histological sectioning. The distances from the root-end filling materials to the regenerated bone were determined by the evaluation of microradiographic images of the sections with imaging software (Sigma Scan/Image; Jandel Scientific Software, San Rafael, CA). The results were statistically analyzed with analysis of variance using Sigma Stat software (Jandel Scientific Software, San Rafael, CA).

RESULTS

The mean distances from the newly regenerated bone were 0.397 +/- 0.278 mm in the MTA group, 0.756 +/- 0.581 mm in the SuperEBA group, and 1.290 +/- 0.386 mm in the amalgam group. There was a statistically significant difference between the amalgam and MTA groups (p < 0.05). No significant differences existed for amalgam versus SuperEBA and SuperEBA versus MTA.

CONCLUSION

MTA showed the most favorable periapical tissue response. The distance from MTA to the regenerated bone was similar to the normal average periodontal ligament thickness in dogs.

Periapical Tissue Responses and Cementum Regeneration with Amalgam, SuperEBA, and MTA as Root-End Filling Materials

The purpose of this study was to compare the periapical tissue responses and cementum regeneration in response to three widely used root-end filling materials, amalgam, SuperEBA, and Mineral Trioxide Aggregate (MTA). These materials were placed using modern microsurgical techniques on endodontically treated dog premolars and molars. After 5 months, the cell and tissue reactions of surface-stained un-decalcified ground sections were evaluated by light microscopy and statistically analyzed. The major difference in the tissue responses to the three retrofilling materials were the degree of inflammation and types of inflammatory cells, number of fibrous capsule formations, cementum neoformation over these materials, osseous healing and resulting periodontal ligament thickness. MTA showed the most favorable periapical tissue response, with neoformation of cemental coverage over MTA. SuperEBA was superior to amalgam as a root-end filling material.

Cytotoxicity of endodontic materials

An in vitro cell culture model of human gingival fibroblasts and L-929 cells was used to measure the cytotoxicity of currently used root canal sealers Endomet, CRCS, and AH26 and root-end filling materials Amalgam, Gallium GF2, Ketac Silver, mineral trioxide aggregate (MTA), and Super-EBA. Cytotoxic effects were assessed using the MTT assay for mitochondrial enzyme activity and the CV assay for cell numbers. Using inserts culture and L-929 fibroblasts. All-Bond-2 was also evaluated. The statistical analysis of results showed that CRCS was the least cytotoxic sealer followed by Endomet and AH26. Among root-end filling materials, MTA was not cytotoxic; Gallium GF2 displayed little cytotoxicity; and Ketac Silver, Super-EBA, and Amalgam showed higher levels of cytotoxicity. All Bond-2 also displayed a high degree of cytotoxicity. CRCS was the best root canal sealer and MTA the best root-end filling material. The outcome was favorable also for Gallium GF2 as a retrofilling material.

Excisional wound healing following the use of IRM as a root-end filling material

Intermediate Restorative Material (IRM) has been advocated as a root-end filling material based primarily on reports of clinical success and various leakage studies. The objectives of this study were to determine the excisional wound healing responses of the periradicular tissues to IRM root-end filling material and to compare this with the wound healing responses to amalgam and orthograde gutta-percha root-end filling materials. Mandibular premolars in dogs were obturated, root-ends resected, and the healing responses associated with root-end fillings of IRM, amalgam, and orthograde gutta-percha were evaluated microscopically and radiographically at postsurgical intervals of 10 and 45 days. The excisional wound healing responses associated with IRM root-end fillings were normal at both postsurgical intervals. There was no evidence of inhibition of dentoalveolar or osseous wound healing associated with IRM, amalgam, or orthograde gutta-percha. Statistical analysis showed no difference in wound healing between the 3 root-end filling materials.

Root end filling materials: a review

When non-surgical attempts prove unsuccessful or are contraindicated, surgical endodontic therapy is needed to save the tooth. The procedure usually consists of exposure of the involved area, root end resection, root end preparation and insertion of a root end filling material. Numerous materials have been suggested as root end filling materials. This article is a review of the literature on the suitability of various root end filling materials based on their leakage assessment, marginal adaptation, cytotoxicity, and usage test in experimental animals and humans.

Ten-year in vitro assessment of the surface status of three retrofilling materials

Sixty-one maxillary central incisors were collected, cleaned, and divided into six groups of 10 teeth, with one tooth as a control. Half of the teeth were resected with a high-speed bur and half with a slow-speed bur, and prepared for retrofillings. Retrofillings of EBA cement and Ketac cement were placed in 10 teeth, each of the high-speed and slow-speed groups. Similarly++, zinc containing amalgam was placed in 10 teeth of the high-speed group, and zinc-free amalgam was placed in 10 teeth in the slow-speed group. A single operator completed all retrofills. They were stored in physiological saline for 10 yr. After that period, the apical portions were photographed at X 30 magnification and evaluated by the authors for marginal discrepancies, root crazing, staining, voids, and roughness. Overall, EBA cement++ and amalgam rated better than Ketac cement in every category except root crazing. Perhaps, as some studies have suggested, EBA cement may replace amalgam as the retrofill material of choice.

The effect of retrograde cavity design on microleakage of amalgam fillings

A phantom head model was modified to simulate as closely as possible the limited access encountered during periapical surgery on maxillary anterior teeth. Extracted human maxillary anterior and mandibular canine teeth were placed in this model in a standardized position for root resection, retrograde cavity preparation and filling with amalgam. Three different designs of retrograde cavities were evaluated: the conventional class 1 cavity, the slot cavity and a previously unreported approach, the funnel cavity. Upon completion of the retrograde filling, the teeth were removed from the model and subjected to microleakage tests by placing radiolabelled lipopolysaccharide in a reservoir created coronal to the retrograde fillings. Leakage was quantified by measurement of radioactivity in scintillation counter. It was found that the retrograde fillings in the funnel cavity leaked significantly less than those in the other two cavity designs. There was no statistically significant difference in leakage between the conventional class 1 and the slot cavities up to the thirtieth day 30.

A study in vitro of threaded titanium pins used for retrograde obturation of root canals

The microleakage of four retrograde filling materials was compared in vitro. Fifty-three single rooted teeth were instrumentated and root filled with resin chloroform and gutta-percha. The gutta-percha cones were left extruding from the access opening. All teeth were apicected and retrograde fillings placed. The materials used were a non gamma 2 amalgam (Amalcap), a glass ionomer cement (ChemFil II), threaded titanium pins cemented with a glass ionomer cement (ChemFil II) and identical titanium pins cemented with a silicone material (Adheseal). After removal of the gutta-percha with tweezers, a radioactive isotope solution was placed in the teeth. Extraradicular samples were taken at 3, 7, 28, 77 and 104 days. All retrograde fillings showed some microleakage. The group with titanium pins cemented with silicone showed the least leakage: significantly less than the teeth with glass ionomer cement (P < 0.01) and with amalgam (P < 0.01). No significant differences were found between other groups.

Tissue reactions to endodontic materials implanted in the mandibles of guinea pigs

Teflon, Intermediate Restorative Material, and Prisma VLC Dycal were implanted in the mandibles of 16 guinea pigs. After experimental periods of 4 and 12 weeks, the animals were killed and tissue sections were prepared. No severe inflammatory response was noted in any of the groups except for a persistence of moderate inflammation in the poorly condensed Teflon group. Bone apposition occurred in the Prisma VLC Dycal group; none-to-mild inflammation and a thin fibrous capsule characterized the IRM group; and the Teflon group had a thick fibrous encapsulation except for samples where the Teflon material appeared to be poorly condensed and dispersed into the bony tissue. In areas where the teflon was loosely condensed, chronic inflammation and active phagocytosis were seen along the surface of the material.

Quantitative radioactive analysis of microleakage of four different retrograde fillings

Sealing properties of four different retrograde filling materials were investigated in vitro. Radioactive isotopes were applied in the root canal, and leakage into an extraradicular fluid was measured at regular intervals. The method permitted repeated observation of the specimens over prolonged periods of time. Forty single-rooted human teeth were biomechanically instrumented and obturated using calcium-hydroxide paste. Following obturation, an apicectomy was performed and retrograde cavities were filled with four different materials: group 1, non gamma 2 amalgam (Amalcap); group 2, glass ionomer cement (Ketac Silver); group 3, calcium-hydroxide-based root canal sealer (Sealapex); group 4, composite resin (Palfique Light-S). After removal of the calcium hydroxide, the teeth were immersed in a fluid. An isotope solution was then placed in the root canals. Samples were taken from the fluid at 0, 3, 7, 28, 56, 105, 210, 285 and 376 days to determine the radioactivity. It was found that Sealapex and Palfique Light-S showed significantly less leakage than amalgam and glass ionomer cement, which had the highest apical leakage.

Dye leakage in retrofilled dog teeth and its correlation with radiographic healing

In a previous study in beagle dogs, statistically significant differences in healing were observed radiographically 6 months after apicoectomy and retrofilling with amalgam and varnish, glass ionomer cement, or a composite resin. The purpose of this study was to compare the leakage of these retrofilling materials and to correlate leakage data with healing. After the dogs were sacrificed, 48 roots were extracted. Half of the roots had been irradiated with a CO2 laser on the bevelled root surface after retrofilling. The roots were coated with nail polish, except for their bevelled surface, and were suspended together with positive and negative controls in 2% methylene blue for 8 h. After the specimens were longitudinally split, they were ranked according to the severity of dye penetration, as observed with a dissecting microscope. The differences in dye leakage among the three retrofilling materials were not statistically significant. Consequently, dye leakage did not correlate with the previously assessed healing. Dye penetrated into the root through the bevelled root surface, regardless of CO2 laser exposure of that surface.

Retrograde approaches in endodontic therapy

The routine use of retrograde fillings during apical surgery, as well as the material of choice for that purpose, have been debated. A retrograde filling is placed so as to seal an infected root canal causing periapical pathosis. Therefore, retrograde root canal fillings should be performed routinely during apical surgery regardless of the apparent technical quality of the root canal obturation, unless orthograde endodontic treatment is performed in conjunction with surgery. When orthograde treatment is not performed, retrograde root canal filling enhances the prognosis of apical surgery. An array of potential retrograde filling materials have been extensively investigated in vitro and in vivo. Once that the biocompatibility of the materials is confirmed a clinical comparison, rather than in vitro sealability studies, is the most valid evaluation method. Some of the difficulties encountered in long term clinical studies in patients may be avoided in animal studies. The review of the relevant literature of the past decade suggests that amalgam used in conjunction with cavity varnish is the retrograde filling material of choice. It must be stressed, however, that retrograde filling is not comparable to debridement and obturation of the entire root canal. Therefore, when the only way to approach the root canal is from the apical direction, rather than placing an apical retrograde filling, a retrograde endodontic treatment of the entire canal should be preferred, if it is feasible.

In vivo efficacy of various retrofills and of CO2 laser in apical surgery

The purpose of the present study was to radiographically assess the efficacy of various retrofilling materials and of the use of CO2 laser in apical surgery. The mandibular premolars of six beagle dogs were infected, resulting in periapical lesions. Apical surgery was performed without root canal treatment. Amalgam with cavity varnish, glass ionomer cement and a lightcured composite resin were the retrofilling materials used. In half of the material CO2 laser was used on the root surface and the bone, for occlusion of the dentinal tubuli and sterilization. The healing following surgery was observed radiographically for six months. The highest success rate (89%) was found in the roots retrofilled with amalgam and varnish, and the lowest (60%) in those retrofilled with the composite resin. The difference between these groups was statistically significant. The success rate following retrofilling with glass ionomer cement was 69%, and was not significantly different from both the other groups. Under the conditions of this study, the use of CO2 laser during surgery did not affect the treatment results.

Effect of apical resections and reverse fillings on Thermafil root canal obturations

This in vitro dye leakage study examined the influence of apical root resection and reverse amalgam fillings on the apical seal of root canals obturated with Thermafil. Fifty human canine teeth were instrumented and obturated with either laterally condensed gutta-percha or Thermafil using Roth's zinc oxide-eugenol Type I regular sealer. After 24 h, one of the following additional procedures was performed on 30 of the teeth: 2-mm apical resection, 4-mm apical resection, and 2-mm apical resection plus reverse amalgam filling 2 mm in depth and diameter. The external root surfaces were coated with enamel paint and the teeth were exposed to 1% methylene blue dye at 37 degrees C for 2 wk. The roots were split longitudinally and the depth of linear dye penetration was measured through a stereozoom microscope. Statistical analysis showed no significant differences in the linear dye penetration among the various groups of teeth.