Immediate versus one-month wet storage fatigue of restorative materials

Immediate finishing is a highly desirable property of restorative materials. In general, the resin composites, the polyacid-modified resin composites and resin-modified glass-ionomers are finished immediately after light-curing. For the conventional glass-ionomers a waiting period of 24 h is recommended. Therefore, the objective of this study was to investigate whether immediate finishing and application of cyclic loading under water spray on resin-modified glass-ionomers, a conventional glass-ionomer, a polyacid-modified resin composite and a resin composite are reflected in their Young's modulus and fatigue resistance after 1-month wet storage compared with a control group that could mature untroubled for 1 month. From this study, it could be concluded that there is a material-dependent response on immediate finishing. For the conventional glass-ionomer, the waiting period of 24 h is highly advisable. The resin composite suffered more than the other test materials. A second statement is that one must be cautious by the extrapolation of findings obtained on quasi static tests (Young's modulus) towards dynamic properties (flexural fatigue limit).

The clinical performance of adhesives

OBJECTIVES

Traditional mechanical methods of retaining restorative materials have been replaced to a large extent by tooth conserving adhesive restorative techniques. Because adhesives have been evolving so rapidly for the last few years, the timing is right for evaluating the clinical status of present day adhesives.

DATA SOURCES

Current literature with regard to the clinical performance of adhesives has been reviewed. An overview of currently available adhesive systems is provided and a categorization of these adhesives according to their clinical application procedure and their intended mechanism of adhesion is proposed. Parameters of direct relevance to the clinical effectiveness of adhesives are discussed in relation to the clinical effectiveness of today's adhesives.

CONCLUSIONS

The clinical performance of present day adhesives has significantly improved, allowing adhesive restorations to be placed with a high predictable level of clinical success. Most modern adhesive systems are superior to their predecessors, especially in terms of retention that is no longer the main cause of premature clinical failure. Recent adhesives also appear less sensitive to substrate and other clinical co-variables. As the remaining major shortcoming of modern adhesives, none of these modern systems however appears yet to be able to guarantee hermetically sealed restorations with margins free of discoloration for a long time.

A TEM study of two water-based adhesive systems bonded to dry and wet dentin

To keep the exposed collagen scaffold penetrable to resin, it has been recommended that the conditioned dentin surface be maintained in a visibly moist condition, a clinical technique commonly referred to as wet bonding. In this study, resin-dentin interfaces produced with two water-based adhesive systems--OptiBond (OPTI, Kerr) and Scotchbond Multi-Purpose (SBMP, 3M)--were compared by transmission electron microscopy, following the application of either a dry- or a wet-bonding technique. The hypothesis advanced was that the ultramorphology of the hybrid layer would differ depending on which bonding method was applied. A morphologically well-organized hybrid layer of collagen fibrils intermingled with resin in tiny interfibrillar channels was consistently formed by the OPTI system. The SBMP system was found to produce a hybrid layer with a more variable ultrastructure, less distinctly outlined collagen fibrils, and a characteristic electron-dense phase located at its surface. No major differences in hybrid layer ultrastructure were observed when the two adhesive systems investigated were bonded to either dry or wet dentin. When the adhesives were dry-bonded, no ultrastructural evidence of collapsed demineralized collagen, incompletely or not at all infiltrated by resin, could be detected. In addition, when the two adhesives were bonded to wet dentin, no signs of overwetting phenomena, that would have indicated that water was ineffectively removed, were apparent. It has been hypothesized that the amount of water provided with the hydrophilic primer solution of either of the two adhesive systems investigated suffices to re-hydrate and re-expand the gently air-dried and collapsed collagen network. Further research should be directed to determine whether this hypothesized self-rewetting effect can be extrapolated to other adhesive systems that provide water-based primers.

[Characterization of glass ionomer cements containing resin]

Recently, several new resin-modified glassionomers have been introduced on the dental market. At the moment a real confusion exists over the right terminology of the products and its limits in use. Therefore, an in vitro and in vivo study with simultaneously a comparison with conventional glassionomers and composite resins was really necessary. This study revealed that resin-modified glassionomers have physico-mechanical properties that are situated between those of conventional glassionomers and composite resins. The manufacturers have a different approach concerning the particle size distribution. The new materials give a rough surface. They are not indicated for posterior restorations, because their surface hardness is too low compared to that of enamel, and their fatigue resistance is insufficient. The elasticity decreases during setting and maturation. Consequently, they are mainly indicated in situations that require a moderate strength and esthetics, for patients with a high caries activity and when ease in use is requested.

[Micro-abrasion of the enamel: an alternative to the removal of demineralization and superficial decalcification]

Tooth discoloration's may cause serious damage to the aesthetic appearance of the patients. These discoloration's can be treated in several ways but up to lately tooth structure had to be removed in an irreversible manner in order to provide sufficient bulk for the new restorative material. Nowadays thanks to the work of T. Croll and others a method has been established in a scientific way whereby tooth discoloration's confined to the outermost layer of enamel can be removed, through the application of an compound called PREMA which will simultaneous erode and abrade the enamel surface. If carefully selected the discoloration can be removed with only a limited loss of tooth structure. The authors describe the historical background of the method. Furthermore patient's selection, specific instruments and materials are described in detail. The clinical procedure is explained step by step, followed by a complete report of the effects of the procedure on the different tooth structures. Finally the long term results are discussed and the possibility to enhance the result by combining this method with home bleaching.

In vitro interfacial relationship between human dentin and one-bottle dental adhesives

OBJECTIVES

One-bottle dentin adhesives combine primer and adhesive resin into a single solution. This study was conducted to determine the bond strengths to dentin of four one-bottle bonding systems and to evaluate their SEM interfacial morphology. The hypothesis to be tested was that the water-based bonding system would produce lower bond strengths and less complete penetration into dentin than other bonding systems that are dissolved in organic solvents.

METHODS

Forty extracted molars were ground to expose middle dentin and were randomly assigned to four groups (n = 10): Group 1--Experimental Single Bond (3M Dental Products Division); Group 2--Prime&Bond 2.1, pre-launch version (Dentsply DeTrey); Group 3--Syntac Single-Component (Vivadent); Group 4--Tenure Quik with Fluoride (Den-Mat Co.) The surfaces were treated according to manufacturers' instructions. After 24 h in water, the specimens were thermocycled, and the bond strengths were measured in shear. The data were analyzed with ANOVA and Duncan's test at a confidence level of 95%. Further, the adhesives were also applied to 600 microns thick dentin disks. After preparing polished cross sections, the bonded interfaces were demineralized, deproteinized, and observed under a FE-SEM. The morphological appearance of the resin-dentin interface surfaces was compared by screening the entire resin-dentin interface for each specimen.

RESULTS

Two morphological characteristics were evaluated: 1) the depth of resin penetration into the tubules and 2) the thickness and density of the resin-dentin interdiffusion zone. Single Bond showed statistically higher mean shear bond strengths (p < 0.001) compared to the other three materials. Specimens prepared with Syntac Single-Component and Prime&Bond 2.1 were ranked in the intermediary Duncan's grouping. Specimens bonded with Tenure Quik with Fluoride exhibited the lowest mean shear bond strength. All materials penetrated and hybridized dentin. Single Bond formed a thick layer of adhesive resin on the top of the interdiffusion area without debonding, whereas some areas of debonding were observed on the top of the hybrid layers for Prime&Bond 2.1 and Syntac Single-Component. For the water-based adhesive Syntac Single-Component, the interdiffusion zone displayed a thick filigree pattern, containing scattered open spaces between the resin-enveloped collagen fibers. Tenure Quik with Fluoride did not thoroughly infiltrate the demineralized dentin zone, resulting in wide gaps in all specimens. Prime&Bond 2.1 formed the shortest resin tags, whereas Syntac Single-Component formed the longest resin tags.

SIGNIFICANCE

Bonding to dentin remains unpredictable using one-bottle bonding systems. The chemistry of each individual material may be more important than the type of solvent.

Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: a review of the literature

OBJECTIVES

The roughness of intraoral hard surfaces can influence bacterial plague retention. The present review evaluates the initial surface roughness of several intraoral hard materials, as well as changes in this surface roughness as a consequence of different treatment modalities.

METHODS

Articles found through Medline searches were included in this review if they met the following criteria: 1) stated threshold surface roughness values and reputed change in surface roughness due to different manipulation techniques; or 2) included standardized surface conditions that could be compared to the treated surface.

RESULTS

Recently, some in vivo studies suggested a threshold surface roughness for bacterial retention (Ra = 0.2 micron) below which no further reduction in bacterial accumulation could be expected. An increase in surface roughness above this threshold roughness, however, resulted in a simultaneous increase in plaque accumulation, thereby increasing the risk for both caries and periodontal inflammation. The initial surface roughness of different dental materials (e.g., teeth, abutments, gold, amalgam, acrylic resin, resin composite, glass ionomer or compomer and ceramics) and the effect of different treatment modalities (e.g., polishing, scaling, brushing, condensing, glazing or finishing) on this initial surface roughness were analyzed and compared to the threshold surface roughness of 0.2 micron. The microbiological effects of these treatment modalities, if reported, are also discussed and compared to recent in vivo data.

SIGNIFICANCE

Based on this review, the range in surface roughness of different intraoral hard surfaces was found to be wide, and the impact of dental treatments on the surface roughness is material-dependent. Some clinical techniques result in a very smooth surface (compressing of composites against matrices), whereas others made the surface rather rough (application of hand instruments on gold). These findings indicated that every dental material needs its own treatment modality in order to obtain and maintain a surface as smooth as possible.

Effects of a self-etching primer on enamel shear bond strengths and SEM morphology

PURPOSE

To study a dental adhesive system containing a self-etching primer, by evaluating the enamel shear bond strengths and comparing the SEM interfacial morphology.

MATERIALS AND METHODS

100 flat enamel bonding sites were prepared to 600-grit on proximal surfaces of caries-free human molars. The bonding surfaces were treated with Clearfil Liner Bond 2 as recommended by the manufacturer, or combined with various acidic etchants. A composite rod (Clearfil Photo Anterior) was applied to the bonding area in two increments in a Teflon mold and polymerized for 100 s. After 24 h of water storage, the specimens were thermocycled and the shear bond strengths measured using an Instron testing machine. Forty extra molar crowns were roughened and treated with Clearfil Liner Bond 2 and alternative etchants, as described. A low-viscosity resin was bonded to the occlusal surfaces of these crowns, which were further demineralized and deproteinized. Field-Emission SEM examinations were carried out to evaluate the effects of different treatments on enamel surfaces.

RESULTS

The mean shear bond strengths were in the range of 18.1 MPa to 25.9 MPa, without significant differences between pairs of means. The failures were predominantly of the adhesive type. The use of alternative etchants resulted in the deepest etching patterns. The use of Clearfil Liner Bond 2, according to manufacturer's directions, resulted in a poorly-defined etching pattern. Regardless of the alternative etchant used, the use of the self-etching primer did not affect the mean enamel shear bond strength.

Comparative physico-mechanical characterization of new hybrid restorative materials with conventional glass-ionomer and resin composite restorative materials

The recently developed hybrid restorative materials contain the essential components of conventional glass ionomers and light-cured resins. The objective of this study was to determine several physical and mechanical properties of eight such materials in comparison with two conventional glass ionomers, one micro-filled, and one ultrafine compact-filled resin composite. The two resin composites and two of the three polyacid-modified resin composites could be polished to a higher gloss than the conventional as well as the resin-modified glass ionomers. After abrasion, surface roughness increased for all materials, but not at the same extent, being the least for the conventional resin composites and one polyacid-modified resin composite, Dyract. In contrast to the later resin composites, of which the surface roughness is principally determined by the presence of protruding filler particles above the resin matrix, roughness of conventional and resin-modified glass ionomers results from both protruding filler particles and intruding porosities. The mean particle size of the hybrid restorative materials fell between the smaller mean particle size of the resin composites and the larger one of the conventional glass ionomers. The micro-hardness and Young's modulus values varied substantially among all eight hybrid restorative materials. For all the resin-modified glass-ionomer restorative materials, the Young's modulus reached a maximum value one month after mixing and remained relatively stable thereafter. The Young's modulus of the conventional and the polyacid-modified resin composites decreased slightly after one month. The conventional glass-ionomer materials undoubtedly set the slowest, since their Young's modulus took six months to reach its maximum. The flexural fatigue limit of the hybrid restorative materials is comparable with that of the micro-filled composite. From this investigation, it can be concluded that the physico-mechanical properties vary widely among the eight hybrid restorative materials, indicating that these materials probably have yet to achieve their optimum properties. Their mechanical strength is inadequate for use in stress-bearing areas, and their appearance keeps them from use where esthetics is a primary concern.

The 5-year clinical performance of direct composite additions to correct tooth form and position. I. Esthetic qualities

The aim of the study was to evaluate the esthetic performance of direct composite additions in correcting tooth form and position at 5 years. Composite additions were directly placed using the acid-etch technique and enamel bonding on 87 intact maxillary anterior teeth in 23 young patients (12-19 years old). The restorations were made by one operator using an ultrafine midway-filled densified restorative composite. Color slides were made at baseline and 5 years. At the 5-year recall, esthetic performance was assessed clinically by two evaluators at chair-side in subterms of color match, translucency/opacity, surface roughness, and anatomical form. Five additional examiners scored esthetics on the 5-year slides. Of the restorations, 89% were still esthetically satisfactory after 5 years of clinical service. The remaining restorations needed replacement, mainly because of severe loss of anatomical form, to a lesser degree because of severe color mismatch. Central incisors and small unilateral restorations generally showed the best results concerning color match (68% and 74%, respectively) and surface smoothness (84% and 100%, respectively). The slide scores on color match and translucency/opacity were generally similar or somewhat better than the direct clinical scores; however, the difference were not statistically significant (P > 0.05). As far as surface roughness is concerned, the results were significantly better (P < 0.05) when recorded indirectly than by direct clinical evaluation. In conclusion, direct composite additions are a valuable and effective procedure for esthetic and conservative treatment of malformed and misaligned anterior teeth. Loss of anatomical form due to wear points to a shortcoming of the composite material used, with which a durable esthetic result cannot always be guaranteed in the long term.

The 5-year clinical performance of direct composite additions to correct tooth form and position. II. Marginal qualities

The aim of the study was to evaluate the marginal performance of direct composite additions for the correction of tooth form and position at 5 years. Composite additions were directly placed using the acid-etch technique and enamel bonding on 87 intact maxillary anterior teeth in 23 young patients (12-19 years old). The restorations were made by one operator using an ultrafine midway-filled densified restorative composite. Color slides were made at baseline and 5 years. At the 5-year recall, marginal performance was assessed by two evaluators in terms of marginal adaptation and retention, clinical microleakage, and caries recurrence. Marginal adaptation and clinical microleakage were judged on the vestibular, palatal, and proximal planes. In addition, these planes were divided into a cervical and an incisal part. No caries recurrence was noted at 5 years and no restoration was lost. Concerning marginal adaptation, only four restorations (5%) presented a severe incisal chipping and needed replacement. The restorations showed a significantly (P < 0.05) higher percentage of perfect margins incisally (37%) than cervically (15%). Canines showed the best cervical marginal adaptation (29% with perfect margins), the best results being with small unilateral restorations. Concerning clinical microleakage, 7% of the restorations were rated as clinically unacceptable due to severe marginal discoloration. Clinical microleakage was significantly more often (P < 0.05) found among smokers. In conclusion, an ultrafine midway-filled densified composite is indicated for use in stress-bearing areas in the anterior region. The type and location of the restoration are determining factors for marginal integrity.

Three-year clinical effectiveness of four total-etch dentinal adhesive systems in cervical lesions

A 3-year follow-up clinical trial of two experimental Bayer total-etch adhesive systems and two commercial total-etch systems. Clearfil Liner Bond System and Scotchbond Multi-Purpose, was conducted to evaluate their clinical effectiveness in Class V cervical lesions. Four hundred twenty abrasion-erosion lesions were restored randomly using the four adhesive systems. There were two experimental cavity designs, in which the adjacent enamel margins either were or were not beveled and acid etched. Clearfil Liner Bond System and Scotchbond Multi-Purpose demonstrated high retention rates in both types of cavity design at 3 years. The two experimental Bayer systems scored much lower retention rates in both cavity designs at 3 years. None of the systems guaranteed margins free of microleakage for a long time. At 3 years, superficial, localized marginal discolorations were observed, the least for Clearfil Liner Bond System, followed by Scotchbond Multi-Purpose and the two experimental systems. Small marginal defects were recorded at the cervical dentin and the incisal enamel margin. Retention of Clearfil Liner Bond and Scotchbond Multi-Purpose appears to be clearly improved over earlier systems, but marginal sealing remains problematic. The two Bayer systems were found to be clinically unreliable.

[Damage to composite restorations]

The expression of damage in dental composite restoratives varies widely, going from some local damage as in attrition facets, to generalized failure or collapes of a restoration. However, crack growth lies on the basis of both aforementioned phenomena. It is therefore of primary importance to gain insight in the way structurally differing materials respond to external stress. It is the aim of the present review to summarize some recent in vitro studies that deal with simulation of wear and fatigue phenomena in dental composite restorative materials.

[Dental pulp reactions and pulp protection: traditional underlayers versus dentin adhesive lacquer]

The dental pulp possesses an intrinsic healing capacity, by which pulpal reactions remain initially localised; they are often completely reversible. The younger and healthier the pulp is, the greater its healing capacity will be. Only in case of bacterial infection will the sterile pulpal inflammation convert into a local necrosis of the pulpal tissue that gradually will expand apically until the whole pulp is contaminated. The profit-effect of pulpal protection by means of traditional calcium hydroxide medicaments is compared with a more modern adhesive dentin sealing. Potential pulpal response to restorative materials and procedures are reviewed. Finally, clinical guidelines for optimal pulpal protection and dentinal sealing are formulated.

[Resin-modified glass-ionomers in dentistry]

The resin-modified glass-ionomers contain the essential components of both a conventional glass-ionomer and a visible light-cured resin. They have several advantages like longer working time, shorter setting time, bonding to tooth structure, fluoride-release, better aesthetics than conventional glass-ionomers and ease in use. As disadvantages can be mentioned the polymerisation shrinkage, trapping of air-bubbles, difficulties in colour choice and contouring. A physical and mechanical characterisation was necessary to define the possibilities and limits of these materials. It can be stated that the strength and aesthetic appearance of resin-modified glass-ionomers are less than that of composites, but better than that of conventional glass-ionomers. Clinically, this is expressed in a rough and dull surface compared to a composite restoration. They are not indicated in stress bearing areas. Consequently, they are mainly indicated in cervical class V-restorations in the postcanine region, and probably restorations in pedodontics, geriatric dentistry and for patients with a high caries activity.

The interaction of adhesive systems with human dentin

PURPOSE

To investigate the interaction of six experimental and commercial bonding systems with dentin in vivo.

MATERIALS AND METHODS

One-Step, Clearfil Liner Bond 2, OptiBond, Permagen with 10% phosphoric acid, Permagen with 35% phosphoric acid, and Prime & Bond were applied in standard Class I occlusal cavities in premolars scheduled for extraction for orthodontic reasons, combined either with a self-cured or with a light-cured resin composite. The teeth were carefully extracted 5 minutes after resin polymerization and fixed in 2.5% glutaraldehyde. After fixation, the specimens were dehydrated, sectioned, and processed for field-emission SEM.

RESULTS

Although some systems produced gap-free intact interfaces in specific specimens, all of them showed detachment at the transition between the resin-dentin interdiffusion zone and the fluid resin placed over it. It was apparent that the presence of air-bubbles and/or thick layers of polymerized-filled fluid resin resulted in less frequent separation areas at the resin-dentin interface, providing support for the concept of the elastic cavity wall. It was also confirmed that some dentin adhesive systems do not form a thick layer over the dentin, otherwise the resin composite would not have penetrated the dentin tubules.

Morphological field emission-SEM study of the effect of six phosphoric acid etching agents on human dentin

OBJECTIVES

This study evaluated the effects of six phosphoric acid-etching agents on dentin, the independent variables being two acid concentrations (10% and 32%-37%) and three thickener conditions (no thickener, silica, and polymer). The tested hypothesis was that the use of different etchants with similar concentrations of phosphoric acid would result in similar depths of dentin demineralization.

METHODS

Thirty dentin disks were obtained from extracted human teeth by microtome sectioning. The dentin surfaces were etched with one of the etching agents, fixed, dehydrated and dried. The specimens were observed using a FE-SEM. The mean deepest demineralization of intertubular dentin was measured from fracture surfaces of the disks. These values were analyzed by ANOVA and Duncan's Test. The morphological appearance of the dentin surfaces was compared using the following observation criteria: 1) Presence of a cuff of peritubular dentin; 2) Relative thickness of the layer containing residual collagen or smear layer particles; and 3) Formation of a submicron hiatus at the bottom of the exposed collagen network. The pH of each of the etching agents was measured. A correlation analysis was made of the pH vs. the depth of dentin demineralization.

RESULTS

Silica-thickened etchants did not demineralize dentin as deeply as did polymer-thickened etchants and unthickened etchants. High magnifications revealed three distinct zones within the demineralized dentin layer; an upper porous zone of residual smear layer or denatured collagen and residual silica particles (in groups etched with silica-thickened etchants), an intermediate area with randomly oriented collagen fibers, and a lower zone with submicron hiatus, few collagen fibers, and scattered hydroxyapatite inclusions. This hiatus was observable in all the specimens etched with the polymer-thickened etchants, in 90% of the specimens etched with the unthickened phosphoric acid liquids, and in 60% of the specimens etched with the silica-thickened gels.

SIGNIFICANCE

The results obtained suggest that similar concentrations of phosphoric acid etchants containing distinct thickeners result in different demineralization depths as well as different morphology of etched dentin.

Restorative therapy for erosive lesions

More needs to be learned about the etiology of erosion lesions before they can be accurately diagnosed, confidently treated and, more importantly, prevented. The treatment is dependent on the location and the degree of erosion. The decision to treat an erosion lesion should be based on careful consideration of the etiology and progression of the condition. Reasons for restoring noncarious enamel/dentin lesions are discussed and various therapeutic measures are provided. Preventive and restorative therapeutic measures for noncarious abrasive/ erosive lesions are proposed such as: a change of dietary or behavior patterns; application of desensitization products; intensive fluoride therapy with or without iontophoresis; brushing with desensitizing dentifrices; adhesive penetration with dentin bonding agents; glass ionomers and compomers; resin composites; composite or porcelain veneers; crown and bridge work; occlusal adjustments and nightguard fabrication if the abfraction factor coincides. The clinical durability of restorative therapy and important clinical factors related to the restoration of multifactorial defects are discussed.

Clinical and semiquantitative marginal analysis of four tooth-coloured inlay systems at 3 years

OBJECTIVES

The marginal quality of four tooth-coloured inlay systems was clinically investigated and subjected to computer-aided semiquantitative marginal analysis under scanning electron microscopy (SEM) after 3 years of clinical service.

METHODS

Three of the restoration types were made using the Cerec CAD-CAM apparatus: one was milled from preformed glass ceramic blocks, and the two other inlay types were milled from preformed porcelain blocks. The fourth system was based on an experimental indirect resin composite inlay system. Each inlay type was luted with a different luting resin composite. The clinical evaluation was performed with a mirror and explorer by two clinicians separately, and the marginal analysis was conducted microscopically on replicas (SEM x 200).

RESULTS

After 3 years in situ, all the restorations were clinically acceptable. No recurrent caries was observed. Marginal analysis under SEM detected a high percentage of submargination for all four systems, which suggests that their respective resin composite luting agents were all subject to wear. The percentage of marginal fractures on the enamel side as well as on the inlay side did not increase dramatically compared to the 6-month results.

CONCLUSION

The first recall after 6 months of clinical service indicated how tooth-coloured inlays behave at their margins. The 3-year results confirmed the early findings, indicating that wear of resin composite lutes is important and present in all systems. The two ceramic materials showed a similar behaviour at the margins. The resin composite inlay performed better at the inlay site than at the enamel site.

Field emission SEM comparison of four postfixation drying techniques for human dentin

Critical-point drying (CPD) is generally considered essential for the preparation of biologic specimens for electron microscopy. Several attempts have been made to introduce alternative techniques. More recently, this problem has arisen in dentistry, because of the new developments in dentin bonding. The present study focuses on three alternative techniques to CPD: hexamethyldisilazane (HMDS) drying, Peldri II drying, and air drying. Twenty-four dentin disks were obtained from noncarious extracted human molars by microtome sectioning parallel to the occlusal surface. The dentin surfaces were etched with polymer-thickened, silica-free, 10% phosphoric acid semigel, fixed, dehydrated, and dried with one of the four techniques. The specimens were observed in two perpendicular planes, showing dentinal tubules in longitudinal view and cross-section, using a field emission scanning electron microscope. The intertubular demineralized dentin zone was composed of three different successive layers, which did not substantially differ between CPD and Peldri II drying, but were more evident in HMDS-dried specimens: first, an upper layer of denatured collagen and residual smear layer particles, with sectioned collagen fibrils and few open intertubular pores; second, an intermediate layer of closely packed cross-sectioned collagen fibers; and third, a deeper layer with unfilled spaces, scattered hydroxyapatite crystals, and few collagen fibers. HMDS drying seemed to preserve better the collagen network and the microporosity of the demineralized dentin surface. Moreover, HMDS drying is easy to perform. The air-drying method caused some artefacts, such as surface collapsing and thickening of the denatured collagen layer.

Retroperitoneal schwannoma

A case of an incidentally found retroperitoneal schwannoma is reported. A schwannoma is a rare, benign tumor affecting the soft tissues and the viscera. In the presented case, the US and CT images suggested the nature of this benign tumor. Angiography confirmed the mass effect on the portal vein and subsequently the potential risk of portal thrombosis. The diagnosis was confirmed at surgery.

In vitro fatigue behavior of restorative composites and glass ionomers

OBJECTIVES

This in vitro study was conducted to investigate the fatigue behavior of several dental restoratives, including composites, glass ionomers and a resin-reinforced glass ionomer.

METHODS

Fatigue was imposed under a reverse stress-controlled regimen, following a staircase approach. Samples were stored and tested under both dry and wet conditions. The following parameters were measured and analyzed: Young's modulus, restrained fracture strength, and flexural fatigue limit.

RESULTS

As a general trend, all products showed a decrease in Young's modulus following water sorption. For all products except the resin-reinforced glass ionomer, the same trend was seen in the restrained fracture strength. This is, however, no longer valid for the flexural fatigue limit: the trend is steady-state for the glass ionomers, status quo for the resin-reinforced glass ionomer, and all composites tested show a decrease.

SIGNIFICANCE

The diversity in structure of both composites and glass ionomers does not allow findings for one product to be extrapolated to other similar products.

In vitro flexural fatigue limits of dental composites

The flexural fatigue test equipment developed was used to study the fatigue behavior of dental restorative composites, using a "staircase" approach. Three commercial composites were tested after dry and wet storage conditions. The findings indicate that the method is accurate and reliable, and that changes due to water sorption are clearly reflected: The flexural fatigue limit decreases after water sorption. From the present results it seems that under environmentally controlled conditions, the fatigue behavior is characterized by a well-defined fatigue stress level above which the composites tested fail rapidly, and below which they survive.

Clinical status of ten dentin adhesive systems

Laboratory testing of dentin adhesive systems still requires corroboration by long-term clinical trials for their ultimate clinical effectiveness to be validated. The objective of this clinical investigation was to evaluate, retrospectively, the clinical effectiveness of earlier-investigated dentin adhesive systems (Scotchbond, Gluma, Clearfil New Bond, Scotchbond 2, Tenure, and Tripton), and to compare their clinical results with those obtained with four modern total-etch adhesive systems (Bayer exp. 1 and 2, Clearfil Liner Bond System, and Scotchbond Multi-Purpose). In total, 1177 Class V cervical lesions in the teeth of 346 patients were restored following two cavity designs: In Group A, enamel was neither beveled nor intentionally etched, as per ADA guidelines; in Group B, adjacent enamel was beveled and conditioned. Clinical retention rates definitely indicated the improved clinical efficacy of the newest dentin adhesives over the earlier systems. With regard to adhesion strategy, adhesive systems that removed the smear layer and concurrently demineralized the dentin surface layer performed clinically better than systems that modified the disorderly layer of smear debris without complete removal. Hybridization by resin interdiffusion into the exposed dentinal collagen layer, combined with attachment of resin tags into the opened dentin tubules, appeared to be essential for reliable dentin bonding but might be insufficient by itself. The additional formation of an elastic bonding area as a polymerization shrinkage absorber and the use of a microfine restorative composite apparently guaranteed an efficient clinical result. The perfect one-year retention recorded for Clearfil Liner Bond System and Scotchbond Multi-Purpose must be confirmed at later recalls.

Morphological characterization of the interface between resin and sclerotic dentine

Since dentine exposed to the oral environment undergoes important compositional and morphological transformations, bonding to it differs significantly from bonding to unaffected normal dentine. In this investigation, the interface between resin and sclerotic dentine, the dentine type clinically exhibited by cervical abrasive or erosive lesions, was morphologically characterized by scanning electron microscopy after an argon-ion-beam etching procedure. The microstructure of the resin-sclerotic dentine interface was compared with that produced to normal unaffected dentine in an attempt to find reasons for the reported less reliable bonding of adhesive resins to sclerotic dentine. A resin-dentine interdiffusion zone or hybrid layer with only a limited width was formed at the hypermineralized intertubular dentine. No or only short resin tags were developed in most dentinal tubules, since their orifices were obliterated due to increased peritubular dentine apposition, intratubular deposition of irregular minerals and formation of so-called sclerotic casts. Consequently, it is reasonable to predict that dentine adhesives with an adhesion strategy, which mainly involves micromechanical interlocking by the formations of a resin-dentine interdiffusion zone combined with resin-tag development into the dentinal tubules, will be less effective when applied to sclerotic dentine than to unaffected normal dentine. An adapted adhesive treatment may be necessary to make sclerotic dentine more receptive to bonding. Further research should be directed to develop adhesive systems that bond equally well to various kinds of dentine.

Clinical relevance of laboratory fatigue studies

From a clinical point of view, fatigue in dental restorative resins is discussed by the way that fatigue expresses itself in different forms in these materials. In vitro testing of the fatigue sensitivity of dental composites is far from conclusive: there is a need for standardized testing methodology. Some findings obtained with a recently developed fatigue machine, and interpreted as a function of masticatory stresses, indicate that the generalized form of fatigue will probably be limited to microfilled based composites.

Dual cure luting composites--Part II: Clinically related properties

Thirteen dual cure luting composites were compared in function of film thickness, consistency, and working time by using the American National Standard/American Dental Association (ANS/ADA) specifications for zinc phosphate cement and direct filling resins. The effect of temperature and setting reaction on the film thickness was also evaluated for some representative products. All three clinically related properties varied widely among the products investigated. A strong linear correlation was found between film thickness and consistency. This relation is supported by the temperature dependence of film thickness of dual cure luting composites. Cooling of the material increased the consistency, resulting in a larger film thickness, while heating reduced the film thickness because of the lower consistency. However, one product with a rather short working time at room temperature occasionally exhibited a dramatically enlarged film thickness after heating, probably caused by accelerated chemical polymerization. No correlation emerged between film thickness and maximum filler size or between consistency and filler weight content. Maximum filler size and filler weight content had been measured previously in Part I of this study. Scanning electron microscope (SEM) analysis of the cured film thickness samples revealed that the largest filler particles had been crushed under the heavy load pressure during film thickness measurement. The lack of correlation between consistency and filler weight content can be explained by the multifactorial determination of the consistency. It is concluded that the great diversity in the currently available luting composites makes clear specifications with regard to the optimum composition of luting composites urgently needed. Furthermore, more adequate methods for testing the film thickness of luting composites are also required.

[Adhesion of composite to dentin. Mechanical and clinical results]

Although an efficient bond of resin composites to enamel can be realized since quite a long time, reliable dentine bonding is nowadays still a clinical problem. After the failure of the dentine-etch technique, followed by the misfortunes of the chemical dentine adhesion technique, modern dentine adhesive systems are believed to function by a micromechanical attachment mechanism. Based on a morphological study of the resin-dentine interface, a broad selection of dentine adhesive systems was classified following their adhesion-strategy. In a second part, eight dentine adhesive systems were clinically tested in terms of retention.

Chemical characterization of the resin-dentin interface by micro-Raman spectroscopy

The chemical nature of the interface between dentin and adhesive resin materials was characterized by micro-Raman spectroscopy. The resulting chemical profiles were correlated with photomicrographs obtained by SEM after an argon-ion-beam etching treatment of the sample surface. Two commercially available dentin adhesive systems, of which one was also applied with a different conditioning agent, were investigated. Raman spectra, which were recorded along line scans across the interface with a step increment of 1 micron, revealed that resin effectively penetrated 4 to 6 microns deep into the superficially decalcified dentin zone. Across the interface, a gradual transition from resin to dentin over the interdiffusion zone with a mixed contribution of both substances was noticed. Finally, resin appeared to penetrate to the entire decalcification depth of dentin regardless of the aggressiveness of the conditioning procedure.

Evaluation of two dentin adhesives in cervical lesions

The clinical effectiveness of two dentin adhesives, Clearfil New Bond and Scotchbond 2, was evaluated in two different cavity designs. Group A was without enamel bevel or acid etch and with a butt-joint cavity; and group B had enamel bevel, acid etch, and feather-edged cavities. The retentive rate and marginal adaptation were monitored for 2 years. In the Clearfil system, 21% of group A restorations failed after 2 years, whereas virtually all the group B restorations (99%) were retained. In addition, after 2 years, the total of debonded group A restorations in the Scotchbond 2 system expanded to 13%, whereas no restorations from group B were lost. There was clearly marginal deterioration in time irrespective of the bonding system. Nevertheless, the marginal adaptation of cervical lesions restored with Clearfil New Bond adhesive in combination with Clearfil Ray composite resin revealed fewer defects compared with the Scotchbond 2 adhesive with Silux Plus composite resin restorations. SEM evaluation disclosed composite resin remnants on the dentin surface in cavities with lost fillings, which indicates partial cohesive failure of the adhesive joint.

Assessment by nano-indentation of the hardness and elasticity of the resin-dentin bonding area

The hardness and Young's modulus of the successive layers across a resin-dentin bonding area were determined by nano-indentation for four commercially-available dentin adhesive systems, of which two were also applied with a different conditioning agent. With a computer-controlled nano-indentation technique, minute triangular indentations were made within a small area of a few micrometers' diameter at a load of a few milli-Newtons. The load and displacement of the indenter were continuously monitored during the loading-unloading sequence, so hardness and Young's modulus could be computed as a function of the indenter geometry and the applied load. The hardness of the resin-dentin interdiffusion zone was significantly lower than that of unaltered dentin. A gradient of moduli of elasticity was observed from the rather stiff dentin over a more elastic resin-dentin interdiffusion zone and adhesive resin layer to the restorative composite. That gradient was more substantial in those systems that produced relatively thick adhesive resin layers or supplementally provided a filled low-viscosity resin as an intermediate layer between the adhesive resin and the bulk restorative composite. Such an elastic bonding area might have a strain capacity sufficient to relieve stresses between the shrinking composite restoration and the rigid dentin substrate, thereby improving the conservation of the dentin bond and, as a consequence, the marginal integrity and retention of the restoration.

Composite resins in the 21st century

Human enamel and dentin should be used as the physiologic standards with which to compare composite resins, especially in the posterior region. The intrinsic surface roughness of composite resins must be equal to or lower than the surface roughness of human enamel on enamel-to-enamel occlusal contact areas (Ra = 0.64 microns). Roughness determines the biologic strength of composite resins. The nanoindentation hardness value of the filler particles (2.91 to 8.84 GPa) must not be higher than that of the hydroxyapatite crystals of human enamel (3.39 GPa). Composite resins intended for posterior use should have a Young's modulus at least equal to, and preferably higher than, that of dentin (18.500 MPa). The compressive strength of enamel (384 MPa) and dentin (297 MPa) and the fracture strength of a natural tooth (molar = 305 MPa; premolar = 248 MPa) offer excellent mechanical standards to select the optimal strength for posterior composite resins. The in vivo occlusal contact area wear rate of composite resins must be comparable to the attritional enamel wear rate (about 39 microns/y) in molars. Differential wear between enamel and composite resin on the same tooth is a new criterion for visualizing and quantifying the wear resistance of composite resins in a biologic way. Posterior resins must have a radiographic opacity that is slightly in excess of that of human enamel (198% Al). Based on these standard criteria, it can be concluded that in the 21st century the ultrafine compact-filled composite resins may be the materials of choice for restoring posterior cavities.

Two-year clinical evaluation of two dentine-adhesive systems in cervical lesions

Two commercially available dentine-adhesive systems, Tenure and Tripton, were tested in two different cavity designs by placing 132 Class V composite restorations in cervical lesions of 35 patients. In Group A, the cervical restorations were placed totally in dentine without any intentional enamel involvement. In Group B, they were placed in dentine with adjacent enamel margins bevelled and acid etched. The retention rate, the evidence of clinical microleakage, and the marginal integrity were monitored over a 2-year period. The results of this clinical investigation indicate a high failure rate when only dentinal bonding was involved. A loss rate of 30% for Tenure and 55% for Tripton was noted in Group A after 2 years of clinical service. However, both adhesive systems used in combination with micromechanical retention on the enamel border (Group B) performed extremely well with only one restoration each having debonded over the 2-year period. Identically, marginal integrity and evidence of clinical microleakage more severely deteriorated with time for the Group A restorations in comparison with their Group B counterparts. In summary, the overall results were more positive for Tenure than for Tripton. It is concluded that micromechanical retention by acid etching of the enamel margin is still indispensable for the clinical success of cervical Class V composite restorations, primarily for retention and clinical microleakage and also, but to a lesser degree, for marginal adaptation.

Hardness and Young's modulus determined by nanoindentation technique of filler particles of dental restorative materials compared with human enamel

The recently developed nanoindentation technique was used to measure hardness and Young's modulus of small filler particles in resin composites and other dental restoratives. This technique eliminates the need to visualize indentations. Load and displacement are continuously monitored during a loading-unloading sequence, and hardness as well as Young's modulus are then calculated from the load-displacement curves taking into account the geometry of the indenter. Thirteen posterior composites, 3 dental ceramics for CAD/CAM restorations, 1 sintered porcelain, and 1 amalgam were investigated in this study. The results were compared to the hardness and Young's modulus determined by nanoindentation of human enamel. Of the dental materials tested, only five materials contain inorganic filler particles with a nanohardness not statistically different from that of enamel. The predominant fillers in all other materials, except amalgam and the prepolymerized resin fillers in Bell Firm PX, were found to be significantly harder. The dental restorative materials, except the alloy phase in amalgam, were composed of particles with a Young's modulus significantly lower than that of human enamel. The alloy phase in amalgam had a Young's modulus value comparable to that of enamel.

Three-year follow-up of five posterior composites: in vivo wear

The wear of five posterior composites at occlusal contact areas (OCA) and contact free occlusal areas (CFOA) was evaluated in Class II cavities over a 3-year period with an accurate 3D-measuring technique. A clinical evaluation was also performed. The ultrafine compact-filled composites (Willems et al., 1992) showed acceptable OCA-wear rates ranging from 110 to 149 microns after 3 years. This is very similar to the OCA-wear rate of human enamel on molars, which is about 122 microns after 3 years. The fine compact-filled composite had an unacceptable OCA-wear value of 242 microns after 3 years. The ultrafine midway-filled composite showed an exceptionally high CFOA-wear value of 151 microns after 3 years, which gave the impression of it being gradually washed out of the cavity. Clinically, 70% of the restorations made with the ultrafine midway-filled composite showed excellent colour match after 3 years. For most of the compact-filled composites slightly opaque fillings were noted and 63% of the restorations made with one of these materials were clearly opaque. It can be concluded that the investigated ultrafine compact-filled composites can be considered as amalgam alternatives as far as their wear resistance is concerned.

Three-year follow-up of five posterior composites: SEM study of differential wear

Assessing the wear of both enamel and composite at a shared occlusal contact area offers the opportunity to determine the differential wear between enamel and composite on the same tooth. Differential wear measurements were carried out on five posterior composite materials with an accurate 3D-measuring technique. The distinct wear step between enamel and composite was visualized by means of scanning electron photomicrographs. Both investigated ultrafine midway-filled and fine compact-filled composites (Willems et al., 1992a) have a considerably higher differential wear value and are, therefore, less suitable for rehabilitation of posterior teeth than are the ultrafine compact-filled composites, which have, in this study, a very satisfactory differential wear rate and appear to be highly wear resistant materials suitable for use in stress-bearing areas.

[Amalgam. IV. Metabolism of mercury]

After absorption in the body by four ways, each type of mercury undergoes a specific metabolism. Elementary mercury as mercury vapour becomes rapidly oxidized to Hg2+ and, afterwards, is metabolized as an inorganic mercurial compound. From the blood circulation mercury reaches target organs like the kidneys, the central nervous system, the liver and the hypophysis, in which mercury accumulates. The retention time varies by organ and is longest in the brain. Mercury is mainly eliminated with urine and faeces, to a lesser degree with transpiration and mother's milk and sometimes by respiration.

Dual-cure luting composites: Part I: Filler particle distribution

Fourteen dual-cure luting composites were analyzed for their filler particle shape, predominant and maximum filler size, and filler weight in function of their clinical use. Polished surfaces were etched with an argon ion beam and studied by means of scanning electron microscopy. The type of filler particles, either inorganic or prepolymerized, could clearly be recognized. Their shapes were angular, rounded or spherical, depending on the product. The maximum filler size varied extremely from less than 1 micron to 250 microns. A particle-size distribution analyser disclosed a bell-shaped filler-size distribution. The predominant filler size for all the products was much smaller than the maximum filler size. The filler weight varied from 36 to 77%. After ion etching, some products showed small areas with a low degree of filler loading. A classification of the luting composites based on the maximum filler size is proposed. Since the particle size varies widely within the group of products analyzed, a standard specification for luting composites is urgently needed.

Comparative SEM and TEM examination of the ultrastructure of the resin-dentin interdiffusion zone

The resin-dentin interdiffusion zone produced by a dentin-adhesive system that removes the smear layer and concurrently decalcifies superficial dentin was morphologically examined by both scanning and transmission electron microscopy. Cross-sectioned resin-bonded dentin discs were etched with an argon-ion beam to make the resin-dentin interface observable by SEM. For the TEM examination, the sections were partly decalcified by an aqueous EDTA solution to facilitate ultramicrotomy and to disclose the ultrastructure of the interdiffusion zone. Both SEM and TEM confirmed the presence of the resin-dentin interdiffusion zone as the junction between the deep unaltered dentin structure and the restorative resin. Within the interdiffusion zone, three sublayers with characteristic ultrastructure and staining were identified by TEM. An upper diffuse black layer contained few structural features. Underneath, partially-altered collagen fibrils were closely packed, mostly running parallel with the interface and perpendicular to the dentinal tubules. Their outline was electron-dense, forming tunnel-like structures. At the base of the upper layer, several stained projections were found to bulge out into the underlying collagen network and appeared to be confined by obstructive, parallel-running collagen fibrils. Finally, the third dense layer, containing hydroxyapatite crystals, demarcated the superficially demineralized dentin layer from the deeper unaltered dentin. Resin diffusion into the decalcified dentin surface layer was evident, but diminished with depth, presumably reducing deeper resin impregnation into the interfibrillar spaces. The citric acid dentin-pretreatment probably caused denaturation of the superficial collagen fibrils. Its decalcifying effect gradually weakened with depth, leaving behind hydroxyapatite crystals at the base of the interdiffusion zone.(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital intrahepatic porto-systemic shunt

An asymptomatic case of intrahepatic shunt between a portal and hepatic vein is presented. Ultrasound examination combined with Doppler sonography showed a communication between a dilated portal vein and a hepatic vein. Computed tomography and angiography confirmed the findings. Porto-hepatic venous shunting is very rare and has previously been reported in association with cirrhosis. The vascular malformation we present is believed to be a congenital anomaly, as no signs of cirrhosis or trauma were found.

In vitro vibrational wear under small displacements of dental materials opposed to annealed chromium-steel counterbodies

In vitro vibrational wear tests were performed on 17 composites and one amalgam with human enamel as a reference. The specimens were fixed on a computer-controlled X-Y translation table that generated an oscillatory movement under small displacements. The dental material specimens were in permanent contact with an annealed chromium-steel counterbody. The tests were performed in ambient air of normal humidity at room temperature under non-lubricated sliding conditions. The friction between the counterbody and each of the various materials was measured on-line. After completion of the tests, the wear volumes were determined by contactless profilometry, and the wear pattern was studied with SEM. The simple vibrational test used in this study allowed a fast classification of different dental materials in terms of the relative wear on either the specimen or the counterbody material. The ratio of the wear volume of the counterbody versus the wear volume of the dental material specimen was used to accurately classify the materials according to their in vitro wear behavior, especially when this ratio was related to the total wear volume of the dental material specimen and the counterbody. From an analysis of the wear behavior of the both contacting materials, it became obvious that neither the wear of the dental materials nor of the chromium-steel counterbody appears to correlate with either the inorganic filler hardness, the intrinsic surface roughness, the surface hardness or the Young's modulus of the dental materials.

A classification of dental composites according to their morphological and mechanical characteristics

The on-going search for a biologically acceptable restorative material has brought a confusing variety of composites on the dental market. In the present study, commercially available composites are categorized as a function of their mean particle size, filler distribution, filler content, Young's modulus, surface roughness, compressive strength, surface hardness, and filler morphology. Out of this information, it can be concluded that the materials of choice for restoring posterior cavities at present are the Ultrafine Compact-Filled Composites because their intrinsic surface roughness, Young's modulus and, indirectly, their filler content, compressive strength, and surface hardness are comparable to the same properties of enamel and dentin. The Ultrafine Midway-Filled Composites seem to be very satisfactory materials for anterior use.

Morphological aspects of the resin-dentin interdiffusion zone with different dentin adhesive systems

Cross-sections of resin-dentin interfaces were etched with an argon-ion beam to make their substructure detectable by scanning electron microscopy. The dentin adhesive systems were categorized morphologically into three groups, and an attempt was made to clarify their adhesive mechanism. The first group of products removed the smear layer. The argon-ion bombardment clearly disclosed a hybrid or resin-impregnated dentin layer. It is hypothesized that conditioning with acidic or chelating agents demineralized the dentin surface-layer to a certain depth, leaving behind a collagen-rich mesh-work. Hydrophilic monomers are then believed to alter this collagen-fiber arrangement in a way that facilitates penetration of the adhesive resin, resulting in a mechanical, intermingled link between collagen and the adhesive resin. The second group preserved the smear layer. In this case, the dentinal tubules were obliterated with globular particles at their orifices and remained patent underneath these smear plugs. This type of adhesive system aims at the incorporation of the smear layer into the hydrophilic monomers, which have an affinity for the organic and/or inorganic components of the underlying dentin. Finally, a third, small group only partly dissolved the smear layer, creating a thin resin-impregnated dentin layer and a resin-impregnated smear plug. This study clearly showed that the application of recent adhesive systems induced structural changes in the dentin surface morphology, creating a retentive interface, called the inter-diffusion zone, between the deep, untouched dentin layers and the composite filling material. This resin-dentin interdiffusion zone offers bonding sites for copolymerization with the resin composite and, concurrently, might have protective potential for the pulp tissues.

Marginal accuracy of CAD/CAM inlays made with the original and the updated software

The software driving the Cerec CAD/CAM system has recently been updated. In this study, the marginal accuracy of computer-machined porcelain inlays was determined using the original and the updated software. Two types of MOD cavities in Frasaco resin teeth were prepared with either sharp or rounded box corners. The distance of the occlusal and proximal marginal interface was determined using a measuring microscope. The mean occlusal interfacial distance was 52 microns for both programs. Only the box corners showed a significantly larger space, of which the mean value was approximately 200 microns. The updated version improved the marginal accuracy at the box corners. Further reduction of the interfacial distance was accomplished by rounding the sharp box corners.

Stress-induced cervical lesions

The increasing occurrence of dental lesions at the cervical surfaces requires more knowledge of the causes of the process. Acidic and abrasive mechanisms have clearly been documented as causes but the stress theory by Lee and Eakle is still controversial. This report describes several incidences of possible stress-induced lesions according to the characteristics described by Lee and Eakle. The occurrences of subgingival lesions lend credence to the stress-induction theory by exclusion of other superimposing etiologic factors. With the current concepts, a perceptive approach to the treatment of cervical lesions can be executed.

Dentin- and enamel-bonding agents

The introduction of bonding agents in restorative dentistry has made it possible to adhere restorative materials to tooth structure. Since bonded restorations were introduced by Buonocore in 1955, extensive research has been conducted to develop systems that bond equally effectively to enamel and dentin. Researchers have identified a micromechanical retention mechanism for the attachment of hydrophobic resin restorative materials to both enamel and dentin that works if appropriate conditioning or priming steps are applied. At the dentin site, the modes of action of current adhesive systems converge to create a resin-dentin interdiffusion zone between the deep dentin structures and the filling material. To incorporate or remove the smear layer in this interdiffusion zone, different adhesion strategies are followed to obtain a resin-dentin bond. In the clinical situation, these modern dentin-bonding systems are more technique sensitive; the thickness of the interface, its elastic capacity, the polymerization efficiency and initiation of the bonding agent, and, finally, the application technique used for the restorative material play an important role in the final result.

Marginal adaptation of four tooth-coloured inlay systems in vivo

This study investigates the margin quality of four different tooth-coloured inlay systems using computer-aided quantitative margin analysis under scanning electron microscopy. Three types of restorations involved chairside procedures using a commercial CAD-CAM apparatus: one type of inlay restoration was milled from preformed glass ceramic blocks, the other two inlay types were milled from preformed porcelain blocks. The fourth system was based on an experimental indirect composite inlay system. Each inlay type was luted with its respective dual-curing luting composite, which was supplied with the system. After 6 months of clinical service, all four systems revealed a significant percentage of submargination indicating occlusal wear of the luting composite. The porcelain inlays and the composite inlays luted with their respective experimental luting composite showed the best marginal adaptation. Luted glass ceramic inlays, in particular, suffered from a significantly higher percentage of inlay margin fractures (9 per cent) and marginal openings (4 per cent) than the other systems. A possible explanation is that the glass ceramic subsurface structure at the inlay-lute interface was weakened by etching with ammonium bifluoride.