Restoration Interface Research Articles

In Vitro Exploration and Finite Element Analysis of Failure Mechanisms of Resin‐Bonded Fixed Partial Dentures

The purpose of this study was to explore the debonding mechanisms of two-unit cantilevered and straight and bent three-unit fixed-fixed resin-bonded fixed partial dentures (RBFPDs) and to measure the failure loads needed for debonding. Failure load tests were performed using Bondiloy beams simulating both cantilevered and fixed-fixed RBFPDs, luted onto flat-ground buccal surfaces of bovine teeth with RelyX ARC, Panavia F2.0, and UniFix resin cements. The failure loads were recorded, and the debonded surfaces of both the enamel and the restorations were examined for details of interest. Finite element analysis (FEA) was used to calculate the stress concentrations within the cement layers at failure. Simulated two-unit cantilevered and straight three-unit fixed-fixed RBFPDs showed a significantly higher failure load than the simulated three-unit fixed-fixed RBFPDs with a curved appearance. The FEA models revealed the magnitude and stress locations within the cement layer, resulting in an explanation of the different failure modes. The low failure loads for the three-unit bent fixed-fixed RPFPDs, compared with their straight counterparts and the two-unit cantilevered RBFPDs, indicate that clinically a reserved attitude needs to be maintained with regard to three-unit fixed-fixed RBFPDs spanning a clearly curved part of the dental arch. The FEA results make it clear which part of the tooth restoration interface is subject to the highest stress levels, making it possible to design abutment preparations that avoid high interfacial stresses to help prevent debonding.

Effects of enamel anisotropy on stress singularities in restorations of premolar class II cavities

This paper studies the strength of inplane and antiplane stress singularities near the apex of a structure formed from the dental restoration of premolar class II cavity. In order to exclude the probability of failure, it is necessary to find the conditions such that singularity orders are kept to a minimum or inplane and antiplane stress fields are non‐singular.The effects of enamel anisotropy on the stress singularities are emphasized at two critical positions in the restoration structure: (1) the apex of the enamel and restoration interface, and (2) the apex of the enamel, dentine and restoration junction. In the second case, the interface between the restoration and enamel may be bonded or debonded. The results of this paper show that the recommended cutting angles are strongly affected by the ratio R of transverse stiffness to the longitudinal stiffness. Besides, if the stiffness of the restoration material is close to the transverse stiffness of the enamel, the singularity orders will be reduced. The results of previous studies, in which the enamel is considered to be isotropic, should be modified.

Composite resin degradation products from BisGMA monomer modulate the expression of genes associated with biofilm formation and other virulence factors in Streptococcus mutans

Bacterial microleakage along the tooth/composite resin dental restoration interface contributes to postoperative sensitivity, recurrent caries, and necrosis. Studies have confirmed that enzymes in human saliva degrade composite resin monomers 2,2-bis [4-(2-hydroxy-3-methacryloxypropoxy) phenyl] propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) to release methacrylic acid (MA), bishydroxypropoxyphenyl propane (Bis-HPPP), and triethylene glycol (TEG) at levels of 50 microM in vivo. Studies have found that TEGDMA degradation products alter the growth and gene expression of cariogenic Streptococcus mutans. Specifically, TEG was shown to alter S. mutans gene expression levels of gtfB, a known virulence factor, and yfiV, a putative transcriptional regulator of cell-surface fatty acid genes. The objective of this study was to examine the effect of BisGMA degradation products on the growth and gene expression of S. mutans NG8 cells. Results demonstrated slight inhibition of bacterial growth at Bis-HPPP concentrations of 1.0 x 10(2) and 2.5 x 10(2) microM at pH 5.5. Furthermore, both MA and Bis-HPPP affected gtfB and yfiV expression in a concentration-dependent manner. Because BisGMA is universally used across most dental restorative materials, with millions of placement procedures performed annually, these findings are relevant due to the potential influence of resin monomer-derived biodegradation products on biofilm formation, acid tolerance, and proliferation of S. mutans cells.

An in vitro investigation of marginal dentine caries abutting composite resin and glass ionomer cement restorations

There are a number of studies citing the primary reason for replacing auto cure glass ionomer cements was due to recurrent caries. The purpose of this study was to use an in vitro model to measure caries at the dentine restoration interface of bonded composite resin and auto cure glass ionomer cement restorations and to measure the amount of surface degradation occurring in the restorative materials. Specimens of auto cure glass ionomer cements (Riva Fast, Fuji IX Fast, Ketac Molar Quick and Fuji VII) and bonded composite resin restorations (Ice, SDI) were placed separately at the dentino-enamel junction of 10 recently extracted human third molar teeth, disinfected and placed into the overflow from a continuous culture of S. mutans for two weeks. Restorations were sectioned and prepared for scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Restoration tooth interfaces were photographed and the distance from the surface of the teeth to the surface of the restorations measured. EPMA of percentage weights of calcium, phosphorous and fluoride were made outwards from the restoration surface 130pm at a depth of 10 microm below the surface of the dentine. There were significant differences between the surface heights of composite resin, auto cure glass ionomer cements compared to teeth surfaces. Percentage weights of calcium and phosphorus levels were similar to non-demineralized dentine in the auto cure glass ionomer cement samples but there were significant reductions in mineral content of dentine adjacent to bonded composite resin restorations. Fluoride levels were mixed. This study shows that placing a bonded composite resin restoration into dentine affords little protection to the surrounding tooth from caries attack although insignificant degradation of the restorative surface occurs. Placing a glass ionomer cement restoration into dentine protects the surrounding tooth from caries but degradation of the restoration surface occurs.

On the design of dental resin-based composites: A micromechanical approach

Adhesive resin-based restorative materials have the potential to considerably strengthen teeth and offer more economically viable alternatives to traditional materials such as gold, amalgam or ceramics. Other advantages are direct and immediate placement and the elimination of the use of mercury. However, polymerization shrinkage during curing of an adhesive restoration and mismatch in mechanical properties can lead to the initiation and development of interfacial defects. These defects could have a detrimental effect on the longevity of the restored tooth. The current study is focused on some design issues of resin-based composites affecting the longevity of the tooth–restoration interface. The theoretical approach is based on self-consistent micromechanical modelling that takes into account the effect of the material properties, volume concentration of the dispersed particle phase as well as the shape of these particles on the overall thermomechanical properties of the composite. Results obtained for resin-based composites reinforced with spherical, disc and short fibre particles highlight the advantages of disc shaped and short fibre particles.

Comparative study of nanomechanical properties of cements used in teeth restoration

The discipline of dental science includes the diagnosis of disease in the mouthand teeth, its manifestations and the procedures involved in the restoration oftheir integrity and function. Restoration of lost tooth structure with suitablematerials plays an integral part in the successful rehabilitation of oral tissues.Several factors influence the performance of dental restorations. These factorsinclude the type of cement used to bond crown restoration to prepared teeth.The nanoindentation method was used to explore the mechanical properties of differenttypes of resin cement polymerized using different techniques. A Nano IndenterXP (from MTS Nano Instruments, USA) was used for the experimental tests.A sample of 40 extracted human teeth were restored using two different resin cements:Variolink II (Ivoclar Vivadent, Liechtenstein) and Venus A2 (Heraeus Kulzer, Germany).Both resin cements are light-cured and one of them is self-cured so that the degree ofpolymerization would be higher.The data obtained for nanohardness and the Young’s modulus were analysed usingANOVA to evaluate the influence of different factors (the resin cement and polymerizationtechnique used, the position on the tooth–restoration interface) and to determine the bestperformance for restoration.The results obtained could give a useful indication of the choice of cementation techniqueand of the materials used for the restoration of lost tooth structure in different clinicalcases.

Electron probe microanalysis of ion exchange of selected elements between dentine and adhesive restorative materials

There have been numerous attempts to demonstrate the phenomenon of ion exchange between auto cure glass ionomer cements (GICs) and dentine. The purpose of this study was to employ an electron probe microanalysis (EPMA) technique to examine the interchange of elements between non-demineralized dentine and two types of restorative material, auto cure GICs and a resin composite. Restorations of auto cure GICs (Riva Fast, Fuji IX Fast, Ketac Molar Quick and Fuji VII) and a bonded composite resin were placed in each of 10 recently extracted human third molar teeth. After two weeks the restorations were sectioned and prepared for EPMA. Percentage weights of calcium, phosphorus aluminum, strontium and fluoride were calculated in the restorations 200 microm from the restorative interface and 200 microm into the dentine at 5 microm intervals. There was evidence of calcium and phosphorus in all five auto cure GICs to a depth of 50 microm. Aluminum and strontium ions were also present in dentine except subjacent to Ketac Molar restorations. There was evidence of element transfer into composite resin and resin-bonded dentine. The findings of this paper support the concept of ion exchange as a bonding mechanism between auto cure GIC and dentine. Element penetration into tooth structure and GIC exceeded beyond the "ion exchange layer" observed in scanning electron microscopy studies. Penetration of calcium and phosphorus into composite resin from dentine likely occurred as a result of the self-etching process dissolving calcium and phosphorus and incorporating these elements into the hybrid layer. The presence of Al and Sr ions in dentine were likely to be associated with resin tags extending into the dentine.

Restoration Interface Microleakage Using One Total-etch and Three Self-etch Adhesives

This study evaluated the efficacy of a total-etch and three self-etch adhesives in reducing microleakage after three months water storage and thermocycling. Thirty freshly extracted caries-free human premolars and molars were used. Class V standardized preparations were performed on the facial and lingual surfaces, with the gingival margin placed 1 mm below the CEJ. The teeth were randomly divided into four groups; Group I: Xeno III one-step self-etch adhesive (Dentsply/Caulk), Group II: Prime & Bond NT total-etch adhesive (Dentsply/Caulk), Group III: i-Bond one-step self-etch adhesive (Heraeus Kulzer) and Group IV: Clearfil SE Bond two-step self-etch adhesive (Kuraray Medical). The teeth were restored using 2 mm increments of shade A2 resin composite (Esthet-X, Dentsply/Caulk). Each layer was cured using the Spectrum 800 curing light (Dentsply/Caulk) for 20 seconds at 600mW/cm2. The teeth were stored in distilled water for 90 days. Samples were thermocycled 500x between 5 degrees C and 55 degrees C with a dwell time of 30 seconds, then placed in a 0.5% methylene blue dye solution for 24 hours at 37 degrees C. Samples were sectioned longitudinally and evaluated for microleakage at the occlusal and gingival margins under a stereomicroscope at 20x magnification. Dye penetration was scored: 0 = no penetration; 1 = partial dye penetration along the occlusal or gingival wall; 2 = dye penetration along the occlusal or gingival wall; 3 = dye penetration to and along the axial wall. A Mann-Whitney test was used to demonstrate significantly more dye penetration in Group III than in the other groups at both the occlusal and gingival scores (p < 0.0001). When comparing the occlusal and gingival scores for each group, the Wilcoxon Rank test showed no significant difference in dye penetration for Xeno III (p > 0.05), Prime & Bond NT (p = 0.059) and I Bond (p = 0.083), and Clearfil SE Bond yielded more dye penetration at the occlusal than at the gingival wall (p = 0.001).

Immediate versus water-storage performance of Class V flowable composite restoratives

Objectives The aims of this investigation were to clarify the effects of 24 h water-storage and finishing time on mechanical properties and marginal adaptation to a Class V cavity of eight modern flowable resin-composites. Methods Eight flowable composites, plus two controls (one microfilled and one hybrid composite), were investigated with specimen sub-groups ( n = 10) for each property measured. The principal series of experiments was conducted in model Class V cavities with interfacial polishing either immediately (3 min) after setting or after 24 h water-storage. After the finishing procedure, each tooth was sectioned in a buccolingual direction through the center of the restoration, and the presence or absence of marginal-gaps was measured (and then summed for each cavity) at 14 points (each 0.5 mm apart) along the cavity restoration interface ( n = 10 per group; total points measured = 140). The shear bond-strengths to enamel and to dentin, and flexural strengths and moduli data were also measured at 3 min and after 24 h water-storage. Results For all flowable composites, polished immediately after setting, 14–30 summed gaps were observed (controls: 64 and 42). For specimens polished after 24 h, a significantly ( p < 0.05) reduced number of 8–17 summed gaps occurred for only 3 flowable composites; whereas for 5 flowable composites there were non-significantly-different ( p > 0.05) numbers (11–17) of summed gaps (controls: 28 and 22). After 24 h storage, shear bond-strengths to enamel and to dentin, flexural strengths and moduli increased highly significantly ( p < 0.001) for all materials, except Silux Plus. Significance A post-cure interval of 24 h resulted in enhanced mechanical and adhesive properties of flowable dental composites. In a minority of cases there was also a reduced incidence of marginal-gap formation. However the latter effect may be partly attributed to 24 h delayed polishing, even though such a delay is not usual clinical practice.

Use of fluorescent compounds in assessing bonded resin-based restorations: A literature review

This work reviews fundamental concepts involved with fluorescent imaging in the dental materials field. Fluorescent dyes have been widely used: incorporated into adhesive system components, placed in the pulp chamber and allowed to diffuse toward the restorative interface, as well as used as a visible tracer in microleakage tests. Although use of fluorescent imaging has substantially contributed to the existing knowledge base, there is no standardized methodology used, and as a result, interpretation of study results as well as comparison of results among studies remains questionable.

Evaluation of the biomechanical behavior of maxillary central incisors restored by means of endocrowns compared to a natural tooth: A 3D static linear finite elements analysis

Objective The present study aimed at evaluating different restoring configurations of a crownless maxillary central incisor, in order to compare the biomechanical behavior of the restored tooth with that of a sound tooth. Materials and methods A 3D FE model of a maxillary central incisor is presented. An arbitrary static force of 10 N was applied with an angulation of 125° to the tooth longitudinal axis at level of the palatal surface of the crown. Different material configurations were tested: composite, syntered alumina, feldspathic ceramic endocrowns and glass post resorations with syntered alumina and feldspathic ceramic crown. Results High modulus materials used for the restoration strongly alter the natural biomechanical behavior of the tooth. Critical areas of high stress concentration are the restoration–cement–dentin interface both in the root canal and on the buccal and lingual aspects of the tooth–restoration interface. Materials with mechanical properties underposable to that of dentin or enamel improve the biomechanical behavior of the restored tooth reducing the areas of high stress concentration. Significance The use of endocrown restorations present the advantage of reducing the interfaces of the restorative system. The choice of the restorative materials should be carefully evaluated. Materials with mechanical properties similar to those of sound teeth improve the reliability of the restoartive system.

Root-surface gap-formation with RMGIC restorations minimized by reduced P/L ratio of the first increment and delayed polishing

This in vitro study evaluated the effect on interfacial gap-formation around resin-modified glass-ionomer (RMGIC) root surface restorations with (a) variations in powder/liquid ratio (P/L) of the first increment of an incremental procedure, compared with a bulk restoration technique, and (b) delayed versus immediate polishing, to permit maturation. Cavity preparations were placed in premolar teeth on upper facial root surfaces. Two RMGICs were studied (Fuji II LC and Vitremer), with their associated conditioner or primer, applied with an incremental technique. The P/L ratio of the first increment was reduced to fractional (normalized) values between 0.2 and 1.0 of the manufacturers' recommended P/L, and the manufacturers' P/L was used for the second increment. Control groups were bulk filled. After polishing, either: (i) immediately after light-activation or (ii) after 24h storage, the restored teeth were sectioned in a buccolingual direction through the center of the restoration and the presence or absence of marginal gaps was measured at x 1000 magnification at 14 points (each 0.5-mm apart) along the cavity restoration interface; (n=10; total points measured per group=140). For both RMGICs, significant differences (p<0.05) in gap-incidence were observed between polishing (i) immediately and (ii) after one-day storage. In the former case, 30-70 gaps were found, with or without the incremental technique. In the latter case, only 2-14 gaps were observed. With fluid mixes (normalized P/L ratios between 0.3 and 0.6) for the first increment, gap-formation was greatly reduced, especially with Fuji II LC. To minimize gap formation, more fluid mixes could be used especially with Fuji II LC to give improved adaptation to the dentin. Secondly, whenever possible, polishing should be delayed on the final increment to permit maturation and minimize mechanical disruption of both increments.

Structural optimization of dental restorations using the principle of adaptive growth

In a restored tooth, the stresses that occur at the tooth-restoration interface during loading could become large enough to fracture the tooth and/or restoration and it has been estimated that 92% of fractured teeth have been previously restored. The tooth preparation process for a dental restoration is a classical optimization problem: tooth reduction must be minimized to preserve tooth tissue whilst stress levels must be kept low to avoid fracture of the restored unit. The objective of the present study was to derive alternative optimized designs for a second upper premolar cavity preparation by means of structural shape optimization based on the finite element method and biological adaptive growth. Three models of cavity preparations were investigated: an inlay design for preparation of a premolar tooth, an undercut cavity design and an onlay preparation. Three restorative materials and several tooth/restoration contact conditions were utilized to replicate the in vitro situation as closely as possible. The optimization process was run for each cavity geometry. Mathematical shape optimization based on biological adaptive growth process was successfully applied to tooth preparations for dental restorations. Significant reduction in stress levels at the tooth-restoration interface where bonding is imperfect was achieved using optimized cavity or restoration shapes. In the best case, the maximum stress value was reduced by more than 50%. Shape optimization techniques can provide an efficient and effective means of reducing the stresses in restored teeth and hence has the potential of prolonging their service lives. The technique can easily be adopted for optimizing other dental restorations.

Evaluation of enamel dental restoration interface by optical coherence tomography

Evaluation of molar dental restorations on enamel is performed using optical coherence tomography (OCT) with 10 microm resolution. Images of approximately 50 microm failure gaps in the restorations are demonstrated and the OCT images are compared with x-ray and optical microscopy pictures. The results demonstrate the potential of the technique for clinical evaluation of dental restorations.

Marginal and internal adaptation of extended class I restorations lined with flowable composites

Objectives. Cavity lining with flowable composites has been proposed to reduce interfacial stress due to its strain-absorbing capacity. The purpose of this in vitro study was to evaluate marginal and internal adaptation of large Class I restorations filled in bulk after cavity lining with flowable composites. Methods. Forty standardised large Class I cavities with enamel margins not supported by dentin, were randomly assigned to four groups and either restored in bulk after lining with flowable composites or in two oblique layers of high-viscosity composites. Two adhesives and flowable resins were used: Tetric Ceram, Tetric Flow, Excite (Vivadent, Schaan, Liechtenstein) vs. Prodigy Condensable, Revolution, Optibond Solo (Kerr Co., Orange, CA, USA). Immediately after restorative procedure marginal quality and the internal restoration interface of two bucco-oral sections were quantitatively assessed by SEM using replica technique. Results. Marginal gaps were almost not seen in all test groups (<0.001%), whereas marginal enamel fractures frequently occurred (>23%). No differences in marginal adaptation were detected for both application techniques if the same adhesive was used (ANOVA, Tukey, p<0.05). Lining with Revolution resulted in a significantly higher percentage of marginal continuity (MC) and less enamel fractures (EF) compared to Tetric Flow (MC: 73 vs. 45%; EF: 23 vs. 50%). Gaps at the inner interface were rarely observed (<0.05%). Conclusions. Large Class I restorations without dentin supported cavity margins showed a high amount of marginal enamel fractures directly after placement. Lining with Revolution proved to have the highest potential to initially maintain the marginal integrity.

A new in vitro model for the study of microbial microleakage around dental restorations: a preliminary qualitative evaluation.

The aim of this study was to develop an in vitro model to replicate microbial microleakage at a tooth/ restoration interface using a constant depth film fermentor (CDFF). Amalgam restorations were placed in machined bovine dentine cylinders and sealed externally with varnish, leaving a 1-mm perimeter exposed around the tooth/restoration interface. The dentine cylinders were housed in a CDFF and 300-microm thick microcosm dental plaques were grown over their exposed surfaces. The biofilms were maintained with a mucin-containing artificial saliva for up to 8 weeks. Cylinders were aseptically removed from the CDFF (at 1, 2, 4, & 8 weeks) and surface-decontaminated with validated protocols prior to splitting and sampling of apposing amalgam and dentine surfaces. Scanning electron microscopy (SEM) was used to ascertain the position and structure of the bacterial aggregates. Bacterial viability was determined by vital staining of the bacteria in situ. At all sampling times, SEM showed cocci, rods and filaments on both amalgam and dentine surfaces; some originated as cascades from the surface biofilm and extended into the tooth/restoration microspace. Vital staining showed the majority of bacteria from both dentine and amalgam surfaces to be viable. This preliminary investigation showed that the CDFF may be a valuable tool for the in vitro study of the dynamics of microbial microleakage around dental restorations.

Technique sensitivity: biological factors contributing to clinical success with various restorative materials.

Since the 1950s, clinicians have relied on various formulations of Ca(OH)2 to stimulate dentin bridge formation. Various studies (Kozlov and Massler, 1966; Massler, 1967; Brännström, 1978; Cox et al., 1987; Snuggs et al., 1993) have demonstrated that pulp healing and dentin bridging can occur against a pH spectrum of materials. Recent studies (Akimoto et al., 1998; Cox et al., 1998, 1999; Tarim et al., 1998; Kitasako et al., 1999; Hafez et al., 2000) have reported successful pulp healing and dentin bridging using adhesives for direct capping of exposed pulps. However, others (Costa et al., 1997; Stanley and Pameijer, 1997; Pameijer, 1998; Hebling et al., 1999; Carvalho et al., 2000) have reported unsatisfactory results when exposures were direct-capped with adhesives. Biological and technical factors, or a combination of both, might be postulated to explain these differences. Recent studies have demonstrated that biological success is dependent upon proper hemorrhage control at the exposure site. This review explores the differences and common factors influencing successful dentin bridging, focusing on data derived from animal studies conducted according to ISO usage guidelines for cavity preparation and material placement. In the past, there has been concern that etching of vital dentin leads to immediate pulp death due to low pH. Recent studies have reported that acidic cements cause breakdown of only the smear layer and fail to seal the restoration interface, leading to inflammation and necrosis. A properly hybridized dentinadhesive interface provides a "bacteriometic" seal to both dentin and pulp tissues. Recent ISO usage studies have shown a high incidence of dentin bridging with adhesives following proper hemorrhage control and removal of both operative debris and biofilm at the dentin-pulp interface by agents such as NaOCl. These are important technique-sensitivity factors to be considered for pulp healing and dentin bridge formation.

Marginal adaptation of a new compomer under different conditioning methods

Objectives: This in vitro study evaluated the marginal adaptation of compomer restorations placed using three different conditioning protocols. Materials and methods: Thirty extracted caries-free molars with 3 mm diameter cylindrical cavity preparations were divided randomly into three groups based upon the conditioning treatment used: (I) 36% phosphoric acid; (II) non-rinse conditioner (NRC, Dentsply DeTrey); and (III) no conditioning. Cavities were restored with Dyract AP using Prime&Bond NT (Dentsply DeTrey) as an adhesive. Silicone impressions of the briefly etched enamel surfaces were taken after finishing the restorations. Each sample was then longitudinally sectioned and impressions were taken. Epoxy resin replicas were prepared for SEM analysis. Qualitative and quantitative assessment were performed separately for the enamel– and dentine–restorative interface. Results: Enamel fractures and open margins along the enamel–restorative margin were observed in some specimens in each group. No statistically significant difference was found in the percentage of gaps/cohesive failures between specimens prepared using different conditioning methods. For the dentine–restorative interface, uniform hybrid layers and long resin tags were often observed in Groups I and II. The hybrid layer in Group III was irregular and discontinuous along the interface. A significant difference ( p<0.01) in the proportion of marginal gap was found between Group I (2%) and Group III (30%). Conclusions: Pre-treating the cavity with 36% phosphoric acid significantly improved the adaptation of the compomer and adhesive to dentine compared with no etching. The marginal quality at the enamel–compomer interface was not affected by the conditioning method used.

Microleakage of Class V resin-modified glass ionomer and compomer restorations

Statement of problem. Resin-modified glass ionomers and polyacid-modified resin composites (compomers) have been introduced to provide esthetic restorations. However, there is concern about the marginal sealing ability of these materials, especially at the dentin (cementum) aspects of restorations. Purpose. This in vitro study evaluated the microleakage of Class V restorations made with resin-modified glass ionomers or a compomer. Material and methods. Thirty noncarious human molar teeth were used. Standardized kidney-shaped Class V cavity preparations were placed in the buccal and lingual surfaces at the cementoenamel junction. Teeth were randomly assigned to 3 experimental groups of 10 teeth each and restored as follows: group 1, Fuji II LC; group 2, Vitremer; and group 3, Dyract. In all cases, the manufacturers’ instructions were strictly followed. All materials were placed in a single increment. Unfinished restorations were immediately coated with the respective manufacturers’ sealer or varnish and this was either light cured for 20 seconds or allowed to air-dry. After 24 hours, teeth were finished to contour and to the cavosurface margins, coated with nail varnish except for 1 mm around the restoration margin, thermocycled (1000×, 5-55°C) and placed in a solution of 2% basic fuchsin dye for 24 hours at room temperature. The staining along the tooth restoration interface was recorded. Results. Kruskal-Wallis 1-way analysis of variance revealed significant differences among all restorative materials for the overall, occlusal, and gingival scores ( P =.03, P =.01, P =.01, respectively). Occlusal and gingival scores for each matched pair of restorative materials using the Wilcoxon test showed statistically significant differences between Fuji II LC glass ionomer cement and Dyract composite, both for the occlusal ( P =.005) and gingival ( P =.005) margins and also as an overall evaluation ( P =.01), with Fuji II LC showing the least dye penetration. Vitremer revealed dye penetration scores not significantly different from Fuji II LC glass ionomer cement or Dyract composite. Conclusion. Resin-modified glass ionomers showed less or similar microleakage than the polyacid-modified composite resin tested. (J Prosthet Dent 1999;81:610-5.)

Dentine permeability and tracer tests

Objectives: This paper reviews the evidence for dentine's permeability in order to clarify and emphasize its confounding effect on leakage test measurements, and hence the need to use special test designs to avoid its effects. Methods: The literature on the subject between 1887 and 1997, including 249 articles. Conclusions: The prerequisite condition for any tracer penetration test is that unflawed specimens are themselves impermeable to tracer. Entry of tracer then can be used to indicate correctly the location or severity of flaws. The relative impermeability of intact dental enamel permits such testing of the enamel–restoration interface seal, but the same is not true when using dentine, which is usually frankly porous to most tracers through its tubules. False positive results are very likely. Recent intense interest in dentine bonding agents has increased the need and frequency of these tests with dentine, but this serious confounding factor has so far generally remained unstated, and has only been controlled adequately in one study. If tracer penetration test results are to be meaningful, then adequate control is required.