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Influence of endodontic access on the fracture resistance, retention and microleakage of full-coverage restorations in vitro: A systematic review and meta-analysis.

BACKGROUND: Endodontic access through retained full-coverage restorations (FCRs) is a preferred option for patients because of its high cost-effectiveness. However, the clinical performance of FCRs after repaired access cavity remains insufficiently characterized. This systematic review investigates the effects of endodontic access cavity preparation through retained FCRs on fracture resistance, retention, and microleakage based on in vitro studies. METHODS: A comprehensive search was performed in PubMed, Web of Science, and Scopus databases. Studies investigating the influence of endodontic access on the fracture resistance, retention, and microleakage of FCRs were included. Two independent reviewers conducted study selection, data extraction, and risk-of-bias assessment using the QUIN tool. Meta-analysis was employed to estimate fracture resistance and retention, with sensitivity analysis and subgroup evaluation also performed. Microleakage was summarized qualitatively. RESULTS: Twentythree studies were included: fracture resistance (n = 15), retention (n = 5), and microleakage (n = 3). Endodontic access significantly reduced fracture resistance for zirconia (p = 0.0002) and lithium disilicate (LD) restorations (p = 0.007), but not for resin-matrix ceramic (RMC) restorations (p = 0.25). Abutment tooth type contributed to heterogeneity within the LD and RMC subgroups. Retention was significantly reduced when access cavities were left unrepaired (p = 0.03), whereas appropriate repair protocols restored or enhanced retention relative to baseline. Accelerated aging increased microleakage in retained FCRs. Surface pretreatments and flowable resin liners tended to reduce microleakage, but findings were inconsistent. CONCLUSIONS: Endodontic access significantly reduces fracture resistance of zirconia and LD FCRs, whereas RMC restorations show no significant change. Appropriate repair protocols can restore or improve retention, potentially exceeding original values. Limited evidence suggests that effective sealing is achievable with appropriate materials. However, well-designed and in-vivo researches are needed to provide more detailed clinical guidance. CLINICAL SIGNIFICANCE: When performing endodontic access through retained FCRs, reduced fracture resistance must be carefully considered for zirconia and LD restorations, while RMC restorations may be exempt from this concern. Loss of retention with access can be restored after repair. Surface pretreatment and flowable resin liners help decrease microleakage.

Humans

Effects of burnishing on microleakage in an amalgam system.

No significant increase or decrease in microleakage occurred as a result of single or double burnishing of amalgam. When cavity varnish use was compared with no use of cavity varnish, significantly less microleakage was noted with the nonburnished control, single-burnish, and double-burnish techniques utilizing the cavity varnish. It was concluded that burnishing is not a factor in microleakage when using Optaloy, but microleakage can be reduced by the use of a cavity liner such as Copalite.

Autoradiography

Microleakage along composite restorations in human premolars after treatment with different cleansing agents.

Cavities prepared on extracted human premolars wereeee treated with different cleansing agents and by different procedures. The cavities were filled with a composite restorative material and microleakage was assessed by recording the penetration of basic fuchsin dye. Only acid agents which removed the smeared layer, producing an etch pattern on the enamel cavity walls, were able to prevent microleakage.

Bicuspid

Microleakage of amalgam restorations with high-copper content.

An in vitro study of microleakage of the margins of Class II restorations of several high-copper-content amalgams found that in general, leakage increased between 24 hours and a month, but decreased below the 24-hour values after six months; there were some differences in leakage among the products at 24 hours, but not aftersix months: the depth of leakage was not correlated with adaptation of the cavosurface margins; and the high-copper-content amalgams were similar to the conventional composition amalgam tested in regard to microleakage.

Copper

Marginal adaptation and microleakage of thixotropic and injection-capsule composites, an in vitro study.

The marginal integrity of MOD adhesive restorations of a thixotropic test composite (ZKP-A-5) and of two injection-capsule composites (Concise -capsule composite and Compocap-S) was examined. Dy penetration tests measured microleakage and scanning electron microscope evaluated marginal adaptation. The test restorations showed no improved micromorphological marginal adaptation when compared to those of a standard paste-paste composite (Concise). Compocap-S demonstrated better prevention of microleakage than did the other test preparations. The marginal quality of these thixotropic and injection-capsule composite restorations was improved from 34% to 52% with utilization of a sealer application (ZKP-A-2), (Concise-Enamel Bond). The application of a sealer prior to insertion of thixotropic and injection-capsule composites is, therefore, definitely indicated when these materials are used. The resultant restorations obtained with these test materials plus sealer correspond qualitatively to those of standard composites Concise or Adaptic [6,7]. The newly developed, complete composite systems (Nimetic, GC's Epolite 100/Epobond) demonstrated in comparison to Concise and Adaptic [6,7] inferior results.

Adhesiveness

Microleakage around preventive composite fillings in occlusal fissures.

The purpose of this study was to evaluated the microleakage around preventive composite fillings used in occlusal fissures with incipient caries, and to assess the influence of the consistency of the composite resin upon the leakage. The fissure enamel of 30 extracted maxillary premolars were partially removed using a small round bur (Ash No. 1/2). Dentin was not exposed. The cavities were etched with phosphoric acid and filled with undiluted composite (Adaptic) or composite diluted with different amounts of liquid resin (Adaptic Bonding Agent). Five teeth were not etched before filling, and served as a control group. The teeth were cycled thermally between two dye solutions and the marginal penetration of dye was evaluated by examining sections of the crowns in a dissection microscope. Marginal leakage occurred in all the control teeth and in none of the acid-etched teeth. It may be concluded that the preventive composite filling therapy provides good sealing of pits and fissures with incipient caries, and that the consistency of the composite used is not of primary importance.

Acid Etching, Dental

Microleakage around preventive composite fillings in loaded teeth.

The purpose of this study was to evaluate the microleakage around preventive composite fillings in teeth subjected to mechanical loading and thermal cycling, and to assess the influence of the consistency of the composite resin upon the leakage. The fissure enamel was partially removed without dentin exposure in 30 extracted maxillary pre-molars. The cavities were etched with phosphoric acid and filled with undiluted composite (Adaptic) or composite diluted with varying amounts of liquid resin (Adaptic Bonding Agent). Five teeth were not acid etched and served as a control group. All teeth were mechanically loaded and unloaded, simulating masticatory forces, and subsequently thermally cycled between two dye solutions. Extensive leakage was seen around all fillings in the control group, while slight leakage, restricted to the feather-edge margin, was seen in five teeth with acid etched cavities. Three of these contained undiluted composite fillings. Twenty teeth showed no leakage. The results show that preventive composite filling provides good sealing of occlusal fissures, and that the seal is resistant to those thermal and mechanical stresses which may be expected in vivo. The use of diluted composite resin in preventive composite fillings is recommended.

Acid Etching, Dental

Marginal microleakage in cemented complete crowns.

An in vivo study was developed to observe the penetration of 131INa around the margins of complete crown castings cemented with zinc phosphate cement with and without the application of different protective agents, with the following results. 1. Complete crowns cemented with zinc phosphate cement showed 131INa marginal leakage differences depending on the protective material used prior to cementation. 2. The best protective agent against marginal leakage according to this study was two layers of cavity varnish applied to the margins. 3. The amount of marginal leakage can be influenced by crown adaptation and the film thickness of the cement. 4. There were no differences between test periods of 1 hour or 21 days after cementation.

Anti-Infective Agents

Microleakage of several amalgam systems: an animal study.

Restorations placed without the application of cavity varnish to the cavity walls and the cavosurface angle exhibited significant marginal leakage after 24 hours and 3 months. At the end of 6 months a decrease in leakage was exhibited with all alloys. With the exception of two specimens, restorations placed after coating the cavity walls and the cavo-surface angle with cavity varnish demonstrated slight or no marginal leakage at all time intervals. The results of this study indicate that the marginal leakage of a conventional filing alloy, a conventional spherical alloy, and two high-copper alloys are approximately the same. The corrosion-resistant high-copper alloys showed the same degree of marginal leakage as the conventional alloys. The results of this study agree with those of a previously reported in vitro study on amalgam leakage.

Animals

Reinforced matrices for pin-amalgam restorations reduce microleakage.

The considerable decrease in microkeakage in the compound-reinforced restorations may be due to the tighter fit of the matrix band at the gingival wall of the preparation, which allows better condensation and marginal sealing of the restoration. The compound prevents lateral migration of the band during condensation pressures.

Dental Amalgam

Effect of composite resin bond agent on microleakage and bond strength.

A study was conducted to evaluate the efficacy of the bonding agents supplied with three composite resins in improving the sealing ability of the materials to tooth structure and the bond of the resins to enamel. When the enamel was not etched prior to insertion of the resin, the use of the bonding agents did not improve marginal seal. Little or no marginal leakage was detected when the restorations were placed by means of the acid etch technique, either with or without use of the respective bonding agents. A slight improvement in the bond of the resins to unetched enamel was secured by use of the bonding agents; however, this advantage was lost when the specimens were thermal cycled. Acid etching of the enamel significantly improved the bond of the strength of all three resins, both when the specimens were thermal-cycled and when stored at a constant temperature. Only one of the commercial bond agents enhanced the bond of its respective composite resin to etched enamel subjected to cycling.

Acid Etching, Dental

The investigation of microleakage in root canal therapy. An electrochemical technique.

An electrochemical technique employing zero-resistance ammetry is described for evaluating the quantity, rate, and areas permeated in the canal system of a root-filled tooth by 1 per cent potassium chloride. Single-rooted extracted teeth were root-filled by a vertical condensation gutta-percha technique. The teeth were coated from the cementoenamel junction to 3 mm. from the apex with a stopping-off medium, so that the apical foramen and the accessory canals in the area would play a role, but not the lateral canals in the gingival area. The teeth were placed in a potassium chloride solution. When the potassium chloride permeated the apical seal and reached a mild steel rod placed through the occlusal access opening extending 2 mm. into the coronal end aspect of the canal, corrosion of the steel was established and was measured for quantity and rate. This technique suggests the possibility of another pathway for tissue fluid to effect coronal dentinal discoloration. The technique also suggests a quantitative means of measuring apical sealing procedures.

Corrosion

Microleakage and marginal adaptation of composite resin restorations.

It has been shown that the use of a sealant offers no advantage with respect to the retentive strength of a composite resin restoration. However, for the improvement of marginal seal and adaptation, the present findings indicate that enamel etching and the application of a sealant, in conjunction with use of a cavity geometry which reduces shrinkage strain, are absolute necessities.

Acid Etching, Dental

Microleakage and enamel finish.

Cavity preparations that are finished with hand instruments allow significantly less marginal leakage than those which are completed only with rotary instruments. This does not mean that hand-instruments walls are perfectly smooth; it only means that these walls allow less marginal leakage. Cavity preparations restored with composite resin showed more marginal leakage than those restored with amalgam. Also, the degree of marginal leakage was greater in cavity preparations restored with composite resin than in those restored with amalgam. Cavity preparations are more prone to marginal leakage at sharply defined cavosurface acute angles than at the smooth or straight surfaces of the cavity. This pattern of marginal leakage was true for both amalgam restorations and composite restorations, but the degree of marginal leakage was greater when composite resin was used as a restorative material. Since less marginal leakage was found in the finished cavity preparations, it is obvious that all cavity preparations must be finished with hand instruments. This may not completely eliminate the problem of marginal leakage, but it will reduce the potential secondary caries both in degree and frequency. Also, since sharply defined acute angles did exhibit more marginal leakage, this part of the cavity preparation needs special attention. With amalgam and composite restorations at least, these angles should not be sharply defined but should be slightly round, so that better condensation of restorative materials can be obtained. This may reduce the degree of marginal leakage.

Composite Resins