Applications of confocal laser scanning microscopy to dental bonding

Evaluation of two rehydration protocols for fractured tooth fragments for characteristics of penetration of resin tags using confocal laser scanning microscopy

BACKGROUND

Fragment reattachment is the recommended treatment modality in uncomplicated crown fractures. There is a paucity of literature regarding the mechanisms responsible for increased resistance to fracture after fragment rehydration in such cases. Hence, the aim of this proof-of-concept study was to decipher the microscopic changes in the penetration characteristics of resin in tooth fragments after different rehydration protocols.

MATERIAL AND METHODS

Sixty bovine incisors free of structural deformities were fractured as per a standard protocol and the fragments were stored in saline at 4°C. They were randomly allocated into three groups (n = 20)-Group 1: negative-control, no-rehydration, Group 2: rehydration by immersion in distilled water for 15 min, Group 3: rehydration by humidification for 15 min. They were subjected to the "experimental bonding protocol" using an eighth-generation bonding agent mixed with rhodamine-B dye. The samples were subjected to decalcification and sectioned into cubical blocks (2 × 2 × 2 mm3 ). They were embedded in paraffin wax, sectioned by an ultramicrotome and evaluated by using a confocal laser scanning microscope. The depths and width of the resin tags were assessed by image analysis software, and the number of tags was counted manually by blinded evaluators. Statistical analysis was done with Stata-14.

RESULTS

The depth of penetration of the resin tags was greatest in Group 2 (927.81 ± 280.38 μm) followed by Group 3 (902.03 ± 371.85 μm) and Group 1 (287.74 ± 124.80 μm). Similarly, the width of the penetrated resin tags was greatest in Group 2 (58.29 ± 21.15), followed by Group 3 (35.53 ± 22.15) and Group 1 (23.89 ± 6.88). The number of resin tags in the majority of the samples in Group 1 had less than 25 tags (65%), whereas there were more than 25 tags in Group 2 (70%) and Group 3 (75%). These differences were statistically significant (p < .05).

CONCLUSION

The resin penetration, as observed by the number of tags and their depth and width, was significantly affected by the rehydration of the fragments. The fragments rehydrated in the distilled water had greater penetration of resin tags than those rehydrated in a humidification chamber.

Traditional Microscopic Techniques Employed in Dental Adhesion Research-Applications and Protocols of Specimen Preparation

Microscopy is a traditional method to perform ex vivo/in vitro dental research. Contemporary microscopic techniques offer the opportunity to observe dental tissues and materials up to nanoscale level. The aim of this paper was to perform a literature review on four microscopic methods, which are widely employed in dental studies concerning the evaluation of resin-dental adhesive interfaces-confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The literature search was performed using digital databases: PubMed, Web of Science and Scopus. On the basis of key words relevant to the topic and established eligibility criteria, finally 84 papers were included in the review. Presented microscopic techniques differ in their principle of operation and require specific protocols for specimen preparation. With regard to adhesion studies, microscopy assists in the description of several elements involved in adhesive bonding, as well as in the assessment of the condition of enamel surface and the most appropriate etching procedures. There are several factors determining the quality of the interaction between the substrates which could be recognized and a potential for further implementation of microscopic techniques in dental research could be recognized, especially when these techniques are used simultaneously or combined with spectroscopic methods. Through such microscopy techniques it is possible to provide clinically relevant conclusions and recommendations, which can be easily introduced for enamel-safe bonding and bonding protocols, as well as optimal pretreatments in dentine preparation.

Comparative Evaluation of Resin Dentin Interface using Universal and Total- Etch Adhesive Systems on Sound and Eroded Dentin: In Vitro Study

Objective This study aimed to compare the resin-dentin interface of sound and eroded dentin using universal and total-etch adhesive systems.

Materials and Methods Forty caries-free extracted human premolars were collected, and the occlusal surfaces were ground by using slow speed diamond disc with copious water supply until a flat superficial dentin was exposed. The test group underwent erosive cycle (n = 20), and another group (n = 20) was reserved for control group. Erosive protocol consisted of immersion in 1.23% citric acid for 1 minute every 12 hours and stored in artificial saliva. Both the control and eroded teeth were further subdivided (n = 10) for composite restoration by using either self-etch or total-etch systems. Then the tooth samples were sectioned longitudinally and observed under confocal laser scanning microscope at ×10 magnification to evaluate resin tag length and hybrid layer thickness.

Statistical Analysis The data obtained were analyzed by using independent t-test.

Results The highest mean value of the resin tag length and thickness of hybrid layer was observed with total-etch system in sound dentin group compared with other groups (p < 0.001).

Conclusion The resin-dentin interface of sound dentin was found to be better than eroded dentin by using total-etch system. The resin-dentin interface of eroded dentin was superior to sound dentin by using self-etch adhesive system.

Graphene oxide-reinforced poly (ether-ether-ketone)/silica composites with improved mechanical performance and surface bioactivity

The control of interfacial interaction between polymers and fillers is essential for the fabrication of high-performance polymer composites. In this work, poly(ether-ether-ketone)/silica (PEEK/SiO₂) and PEEK/SiO₂/graphene oxide (GO) composite were prepared by ball milling-ultrasonic dispersion combined with melt extrusion injection molding. GO nanosheets were introduced as the interfacial enhancer to improve interfacial binding between SiO₂ and PEEK. Mechanical tests showed that the incorporation of SiO₂ and GO greatly optimized the modulus, strength, and fracture toughness of the composites. The tensile strength and Young's modulus of the PEEK/SiO₂ composites increases with the increase of SiO₂ content. The maximum tensile strength and Young's modulus of the PEEK/SiO₂ composites are approximate 95.9 ± 0.6 MPa and 4.007 ± 0.005 GPa at 30 wt% of SiO₂, an increase of 6.4% and 21.2% than that of pure PEEK. The maximum tensile strength and Young's modulus of the PEEK/SiO₂/GO composite are further improved to approximate 101.5 ± 0.7 MPa and 4.62 ± 0.08 GPa at a GO content of 1.5% wt, which is 12.6% and 39.4% higher than that of pure PEEK. In addition, SEM images show that numerous HA formed on the surface of the PEEK/SiO₂/GO composite after immersion in SBF for 7 days, and the HA layer becomes gradually thicker after 14 days, implying the good osteogenic activity of PEEK/SiO₂/GO composites. Therefore, these results suggest that the use of GO as a novel filler surface modifier for the preparation of high-performance composites may become a novel interfacial design strategy for the development of high-performance composites.

Comparison of microleakage of Scotchbond™ Universal Adhesive with methacrylate resin in Class V restorations by two methods: Swept source optical coherence tomography and dye penetration

Background:

One of the most important factors in restoration failure is microleakage at the restoration interface. Furthermore, a new generation of bonding, Scotchbond Universal (multi-mode adhesive), has been introduced to facilitate the bonding steps. The aim of this study was to compare the microleakage of Class V cavities restored using Scotchbond™ Universal with Scotchbond Multi-Purpose in two procedures.

Materials and Methods:

Eighteen freshly extracted human molars were used in this study. Thirty-six standardized Class V cavities were prepared on the buccal and lingual surfaces. The teeth were divided into three groups: (1) Group A: Scotchbond Universal with “self-etching” procedure and nanohybrid composite Filtek Z350. (2) Group B: Scotchbond Universal with “total etching” procedure and Filtek Z350. (3) Group C: Scotchbond Multi-Purpose and Filtek Z350. Microleakage at enamel and dentinal margins was evaluated after thermocycling under 5000 cycles by two methods of microleakage assay: swept source optical coherence tomography (OCT) and dye penetration. Wilcoxon's signed-rank test and Kruskal–Wallis test were used to analyze microleakage.

Results:

In silver nitrate dye penetration method, group A exhibited the minimum microleakage at dentin margins and group C exhibited the minimum microleakage at enamel margins (P < 0.05). Furthermore, in OCT method, group C demonstrated the minimum microleakage at enamel margins (P = 0.047), with no difference in the microleakage rate at dentin margins.

Conclusion:

Scotchbond Universal with “self-etching” procedure at dentin margin exhibited more acceptable performance compared to the Scotchbond Multi-Purpose with the two methods.

Determining Optimal Fluorescent Agent Concentrations in Dental Adhesive Resins for Imaging the Tooth/Restoration Interface

Fluorescent dyes like Rhodamine B (RB) have been used to identify the spatial distribution of adhesive restorative materials in the tooth/restoration interface. Potential effects of the addition of RB to dental adhesives were addressed in the past, but no further information is available on how to determine suitable concentrations of RB in these bonding agents for imaging in the confocal laser scanning microscope. This study provides systematical strategies for adding RB to viscous dental adhesive resins, focusing on the determination of the lowest range of dye concentrations necessary to achieve an acceptable image of the dentin/adhesive interface. It was demonstrated that optimized images of the resin distribution in dentin can be produced with 0.1-0.02 mg/mL of RB in the (tested) adhesives. Our approaches took into account aspects related to the dye concentration, photophysical parameters in different host media, specimen composition and morphology to develop a rational use of the fluorescent agent with the resin-based materials. Information gained from this work can help optimize labeling methods using dispersions of low-molecular-weight dyes in different monomer blend systems.

Nanoleakage evaluation at adhesive-dentin interfaces by different observation methods

The purpose of this study was to evaluate the capability and characteristics of different nanoleakage observation methods, including light microscope (LM), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and confocal laser scanning microscope (CLSM). Dentin specimens were bonded with either an etch-and-rinse adhesive (SBMP) or a self-etch adhesive (GB), and prepared for nanoleakge evaluation according to different observation methods. LM, FESEM and CLSM results demonstrated that the SBMP group showed more interfacial nanoleakage than the GB group (p<0.05); by contrast, no significant difference was found in TEM results (p>0.05), however, TEM illustrated concrete nanoleakage forms or patterns. The results suggested that different observation methods might exhibit distinct images and a certain degree of variations in nanoleakage statistical results. Researchers should carefully design and calculate the optimum assembly in combination with qualitative and quantitative approaches to obtain objective and accurate nanoleakage evaluation.

Analytical method to estimate resin cement diffusion into dentin

This study analyzed the diffusion of two resin luting agents (resin cements) into dentin, with the aim of presenting an analytical method for estimating the thickness of the diffusion zone. Class V cavities were prepared in the buccal and lingual surfaces of molars (n=9). Indirect composite inlays were luted into the cavities with either a self-adhesive or a self-etch resin cement. The teeth were sectioned bucco-lingually and the cement–dentin interface was analyzed by using micro-Raman spectroscopy (MRS) and scanning electron microscopy. Evolution of peak intensities of the Raman bands, collected from the functional groups corresponding to the resin monomer (C─O─C, 1113  cm(−1)) present in the cements, and the mineral content (P─O, 961  cm(−1)) in dentin were sigmoid shaped functions. A Boltzmann function (BF) was then fitted to the peaks encountered at 1113  cm(−1) to estimate the resin cement diffusion into dentin. The BF identified a resin cement–dentin diffusion zone of 1.8±0.4  μm for the self-adhesive cement and 2.5±0.3  μm for the self-etch cement. This analysis allowed the authors to estimate the diffusion of the resin cements into the dentin. Fitting the MRS data to the BF contributed to and is relevant for future studies of the adhesive interface.

Influence of erbium, chromium-doped: Yttrium scandium-gallium-garnet laser etching and traditional etching systems on depth of resin penetration in enamel: A confocal laser scanning electron microscope study

OBJECTIVE

This study was performed to assess the resin tag length penetration in enamel surface after bonding of brackets to identify which system was most efficient.

METHODOLOGY

Our study was based on a more robust confocal microscopy for visualizing the resin tags in enamel. Totally, 100 extracted human first and second premolars have been selected for this study and were randomly divided into ten groups of 10 teeth each. In Group 1, the buccal enamel surface was etched with 37% phosphoric acid (3M ESPE), Group 2 with 37% phosphoric (Ultradent). In Groups 5, 6, and 7, erbium, chromium-doped: Yttrium scandium-gallium-garnet (Er, Cr: YSGG) laser (Biolase) was used for etching the using following specifications: Group 5 (1.5 W/20 Hz, 15 s), Group 6 (2 W/10 Hz, 15 s), and Group 7 (2 W/20 Hz, 15 s). In Groups 8, 9, and 10, Er, Cr: YSGG laser (Biolase) using same specifications and additional to this step, conventional etching on the buccal enamel surface was etched with 37% (3M ESPE) after laser etching. In Groups 1, 5, 6, 7, 8, 9, and 10 3M Unitek Transbond XT primer was mixed with Rhodamine B dye (Sigma-Aldrich, Germany) to etched surface and then cured for 20 s. In Group 2, Ultradents bonding agent was mixed with Rhodamine B. In Group 3, 3M Unitek Transbond PLUS, Monrovia, USA, which was mixed with Rhodamine B dye (Sigma-Aldrich, Germany). Group 4, with self-etching primer (Ultradent-Peak SE, USA) was mixed with Rhodamine B dye (Sigma-Aldrich, Germany). Later (3M Unitek, Transbond XT, Monrovia USA) [Figure 1] was used to bond the modified Begg brackets (T. P. Orthodontics) in Groups 1, 3, 5, 6, 7, 8, 9, and 10. In Groups 2, 4 Ultradent-Peak LC Bond was used to bond the modified brackets. After curing brackets were debonded, and enamel depth penetration was assessed using confocal laser scanning microscope.

RESULTS

Group J had a mean maximum depth of penetration of 100.876 μm, and Group D was the least having a maximum value of 44.254 μm.

CONCLUSIONS

Laser alone groups had comparable depths of penetration to that of self-etching groups but much lower than conventional acid etched groups.

Influence of fluorescent dye on physical-mechanical properties of luting cements for confocal microscopy analysis

AIMS

To evaluate the influence of a fluorescent dye (rhodamine B) on the physical and mechanical properties of three different luting cements: a conventional adhesive luting cement (RelyX ARC, 3M/ESPE), a self-adhesive luting cement (RelyX U-200, 3M/ESPE), and a self-etching and self-adhesive luting cement (SeT PP, SDI).

MATERIALS AND METHODS

The cements were mixed with 0.03 wt% rhodamine B, formed into bar-shaped specimens (n = 10), and light cured using an LED curing unit (Radii, SDI) with a radiant exposure of 32 J/cm(2) . The Knoop hardness (KHN), flexural strength (FS), and Young's modulus (YM) analyses were evaluated after storage for 24 h.

RESULTS

Outcomes were subjected to two-way ANOVA and Tukey's test (P = 0.05) for multiple comparisons. No significant differences in FS or YM were observed among the tested groups (P ≥ 0.05); the addition of rhodamine B increased the hardness of the luting cements tested.

CONCLUSION

The addition of a fluorescent agent at 0.03 wt% concentration does not negatively affect the physical-mechanical properties of the luting cement polymerization behavior.

Sealing ability of mineral trioxide aggregate, calcium phosphate and polymethylmethacrylate bone cements on root ends prepared using an Erbium: Yttriumaluminium garnet laser and ultrasonics evaluated by confocal laser scanning microscopy

Background:

Surgical endodontic therapy comprises of exposure of the involved root apex, resection of the apical end of the root, preparation of a class I cavity, and insertion of a root end filling material. Mineral trioxide aggregate (MTA) is now the gold standard among all root end filling materials. MTA is however difficult to handle, expensive and has a very slow setting reaction.

Aim:

(1) To compare the sealing ability of MTA, polymethylmethacrylate (PMMA) bone cement and CHITRA Calcium phosphate cement (CPC) when used as root end filling material using Rhodamine B dye evaluated under a confocal laser scanning microscope. (2) To compare the seal of root ends prepared using an ultrasonic retroprep tip and an Er: YAG laser using three different root end filling materials.

Statistical Analysis:

Statistical analysis was performed using a one-way ANOVA and a two-way ANOVA, independent samples t-test and Scheffe's post hoc test using SPSS Version 16 for Windows.

Results:

All the three materials, namely MTA, PMMA BONE CEMENT and CHITRA CPC, showed microleakage. Comparison of microleakage showed maximum peak value of 0.86 mm for MTA, 0.24 mm for PMMA bone cement and 1.37 mm for CHITRA CPC. The amount of dye penetration was found to be lesser in root ends prepared using Er: YAG laser when compared with ultrasonics, but the difference was found to be not statistically significant.

Conclusion:

PMMA bone cement is a better material as root end filling material to prevent apical microleakage. MTA still continues to be a gold standard root end filling material showing minimum microleakage. Er: YAG laser is a better alternative to ultrasonics for root end preparations.

Depth of resin penetration into enamel with 3 types of enamel conditioning methods: a confocal microscopic study

INTRODUCTION

The clinical efficiency of a bonding material relies on its bond strength and debonding characteristics; the depth of resin penetration into enamel affects both of these factors. The depth of resin penetration has been previously studied by researchers using laborious, indirect methods, including the scanning electron microscope and the optical microscope.

METHODS

We used a more direct method, confocal microscopy, to visualize the resin tags in enamel. Thirty maxillary first premolars were selected and divided into 3 groups. In group A, the buccal enamel surfaces were conditioned with 37% phosphoric acid; in group B, a self-etching primer was used; and group C was treated with air abrasion. Transbond XT adhesive (3M Unitek, Monrovia, Calif) was used to bond a modified bracket. Transbond XT primer (3M Unitek) mixed with rhodamine B fluorescent dye (Chennai Chemicals, Chennai, India) was applied in groups A and C. In group B, rhodamine was mixed with self-etching primer. After curing, the brackets were debonded, and the teeth were visualized under the fluorescent channel of the confocal microscope.

RESULTS

Maximal resin penetration of 53.9 μm was observed in group A, followed by group B at 40.5 μm and group C at 39.9 μm.

CONCLUSIONS

Confocal microscope evaluation showed that enamel conditioning with 37% phosphoric acid produced greater depths of resin penetration than did self-etching primer or air abrasion.

Effect of conventional and resin-modified glass-ionomer liner on dentin adhesive interface of Class I cavity walls after thermocycling

OBJECTIVE

The aim of this in vitro study was to analyze the effect of glass-ionomer cement as a liner on the dentin/resin adhesive interface of lateral walls of occlusal restorations after thermocycling.

MATERIALS AND METHODS

Occlusal cavities were prepared in 60 human molars, divided into six groups: no liner (1 and 4); glass-ionomer cement (GIC, Ketac Molar Easymix, 3M ESPE) (2 and 5); and resin-modified glass-ionomer cement (RMGIC, Vitrebond, 3M ESPE) (3 and 6). Resin composite (Filtek Z250, 3M ESPE) was placed after application of an adhesive system (Adper Single Bond 2, 3M ESPE) that was mixed with a fluorescent reagent (Rhodamine B) to allow confocal microscopy analysis. Specimens of groups 4, 5 and 6 were thermocycled (5°C-55°C) with a dwell time of 30 seconds for 5000 cycles. After this period, teeth were sectioned in approximately 0.8-mm slices. One slice of each tooth was randomly selected for confocal microscopy analysis. The other slices were sectioned into 0.8 mm × 0.8 mm beams, which were submitted to microtensile testing (MPa). Data were analyzed using two-way ANOVA and Tukey test (p<0.05).

RESULTS

There was no detectedstatistical difference on bond strength among groups (α<0.05). Confocal microscopy analysis showed a higher mean gap size in group 4 (12.5 μm) and a higher percentage of marginal gaps in the thermocycled groups. The RMGIC liner groups showed the lowest percentage of marginal gaps.

CONCLUSIONS

Lining with RMGIC resulted in less gap formation at the dentin/resin adhesive interface after artificial aging. RMGIC or GIC liners did not alter the microtensile bond strength of adhesive system/resin composite to dentin on the lateral walls of Class I restorations.

Analysis of resin tags formation in root canal dentine: a cross sectional study

AIM

To evaluate the length, density and quality of resin tags formed by penetration of various types of adhesive systems into dentinal tubules at various cross section levels of the root canal in correlation to the density of dentinal tubules.

METHODOLOGY

Thirty mandibular premolars were instrumented and fibre posts were inserted with three different adhesive systems with and without activator: etch & rinse XP Bond and XP Bond/Self Cure Activator; self-etch (two-step) AdheSE and AdheSE/AdheSE DC Activator and self-etch (one-step) Hybrid Bond and Hybrid Bond/Hybrid Brushes. The resin tags were evaluated from slices obtained from sections perpendicular to the long axis of the teeth at 3, 6, and 9 mm from the root apex under a Confocal Laser Scanning microscope.

RESULTS

In all groups, lack of continuity of resin tag length, density and quality was observed not only from the cervical to the apical region of each root canal, but also in a mesio-distal direction to the long axis of the root. Application of etch & rinse adhesive in contrast to the self-etch adhesives provided the formation of the shorter, but considerably denser, more homogeneous and not interrupted resin tags with similar length. Use of the activator for all types of adhesives significantly increased the completeness (P = 0.014) and continuity (P = 0.024) of resin tags.

CONCLUSIONS

None of the investigated adhesives were able to completely infiltrate the dentinal tubules in the entire root canal. Use of the etch & rinse adhesive system and the activators significantly increased the density and the quality of resin tags.

Quantitative measurements obtained by micro-computed tomography and confocal laser scanning microscopy

OBJECTIVES

To compare measurements obtained by micro-CT with those obtained by confocal laser scanning microscope in simulative internal resorption cavities.

METHODS

An extracted human maxillary central incisor tooth was divided into two in the coronal plane. Four artificial internal resorption cavities were prepared with standardized burs on each section, and diameters and volumes were measured using a laser scanning electron confocal microscope and a desktop cone beam micro-CT-40. Differences between means of quantitative measurements for both methods were tested using the paired t-test; the correlation between quantitative measurements was tested by regression analysis.

RESULTS

Mean diameter and volume differences between the two methods were 0.061 mm and 0.004 mm(3), respectively. Average diameter and volume calculations obtained by micro-CT were significantly lower (P < 0.001 for diameter and P < 0.01 for volume). A significantly strong relationship was found in the average diameters (R(2) = 92.9%) and calculated volumes (R(2) = 91%), (P < 0.001).

CONCLUSIONS

Although a strong correlation between both methods was found, micro-CT significantly underestimated the diameters and volumes.

Confocal laser scanning microscopic analysis of the depth of dentin caries-like lesions in primary and permanent teeth

This study analyzed comparatively, by confocal laser scanning microscopy (CLSM), the depth of caries-like lesions produced by biological and chemical artificial models in permanent and primary dentin. Six primary molars and six premolars were used. The occlusal enamel was removed and a nail polish layer was applied on the specimens, except for a 4 x 2 mm area on dentin surface. Half of specimens were immersed in acid gel for 14 days (chemical model) and the other half was immersed in BHI broth with S. mutans for 14 days (biological model). After development of artificial caries, the crowns were longitudinally sectioned on the center of the carious lesion. Three measurements of carious dentin depth were made in each specimen by CLSM. Measurements depths were compared between the caries models and between tooth types by one-way ANOVA and Tukey test (a=5%). For permanent teeth, the biological model showed significantly higher (p<0.05) caries depth values than the chemical model. For primary teeth, no statistically significant difference (p>0.05) was found between the caries models. The artificial caries model influenced caries depth only in permanent teeth. There was no difference in carious dentin depth between permanent and primary teeth, regardless of the artificial caries model.

Effect of Pulp Pressure on the Micropermeability and Sealing Ability of Etch & Rinse and Self-etching Adhesives

Etch & rinse adhesives are much more micropermeable and affected by pulp fluid compared with self-etching adhesives. Pulp pressure reduces dentin sealing with etch & rinse adhesives but not with self-etching adhesives. Pulp pressure has no effect on enamel sealing, which is lower when self-etching adhesive is used.

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

OBJECTIVES

This work reviews fundamental concepts involved with fluorescent imaging in the dental materials field.

DATA

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.

CONCLUSIONS

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.

Resin penetration through submicrometer hiatus structures: A SEM and CLSM study

The purpose of this study was to confirm the existence of submicrometer hiatus structures and to examine the degree of resin penetration through these formations. Dentin disks 2.0 mm in thickness were sectioned from 48 human molars with the use of a microtome saw. Three different fifth-generation (total-etch, combined primer/resin) dentin adhesive systems were used to bond a light-cured, resin-based composite to the dentin disks (n = 16 each group). Bonded disks from the three groups were then sectioned. Half of each group was examined with the use of a scanning electron microscope (SEM) (n = 8), and the other half with the use of a confocal laser scanning microscope (CLSM) (n = 8). The frequency of submicrometer hiatus formation was recorded and documented with associated imaging techniques. Resin penetration within submicrometer hiati were observed in 41.7% (10/24) of SEM specimens and 83.3% (20/24) of CLSM specimens. The location and size of these structures were found to be quite uniform. Submicrometer hiati approximated 200 microm in each of the three dentin bonding systems examined. Resin penetration through submicrometer hiati does not appear to be an artifact of desiccation. These structures were clearly identified within the hybrid layer of each dentin adhesive system used in this study.

Surface characteristics of dentin experimentally exposed to hydrofluoric acid

The purpose of this study was to test the effect of hydrofluoric acid (HF) on the surface characteristics of dentin in vitro. Dentin was exposed in 50 human molars and divided into five groups according to different etching schedules: (i) no etching, (ii) 15 s HF, (iii) 15 s H3PO4, (iv) 15 s HF and 15 s H3PO4, (v) 15 s H3PO4 and 15 s HF. Teeth were examined under a scanning electron microscope equipped with energy-dispersive X-ray (EDX) or two layers of fluorescence-labeled primer followed by the composite were applied, and the teeth were sectioned and examined using confocal laser scanning microscopy (CLSM). With scanning electron microscopy, no openings of dentinal tubules were found in groups (i), (ii), and (iv). In group (v) only a few tubules were opened and in group (iii) the smear layer was completely removed and tubules appeared open. The EDX analysis revealed that fluoride was incorporated into the dentin surface when HF was used. With CLSM, distinct hybrid layers could be detected only in group (iii). In group (v) the hybrid layer appeared less established compared with group (iii). No dentin hybridization was found in groups (i), (ii), and (iv). It is concluded that HF has the ability to close the openings of dentin tubules which were opened due to etching by phosphoric acid and cannot dissolve the smear layer.

Characterization of lipid in mature enamel using confocal laser scanning microscopy

OBJECTIVE

To characterize the lipid components of organic matrix in mature human enamel using Confocal Laser Scanning Microscopy (CLSM) coupled with a hydrophobic fluorescent probe.

METHODS

Twenty-four longitudinal sections of human enamel were fixed with 3.7% paraformaldehyde (PFA), partially decalcified with 0.5 M of EDTA, and labelled with a fluorescent probe (Nile red) before CLSM characterization. Based on the fluorescence spectra of Nile red in ethanol (1 microgram/ml), each enamel section was evaluated with 543 nm light source and with 590 nm long pass filter. Spectrophotometric analysis was carried out to characterize the autofluorescence and Nile red lipid fluorescence in mature enamel. Special optical parameters of the microscope were chosen to rule out the intrinsic fluorescence of the samples, and that induced by PFA.

RESULTS

The intensity of autofluorescence and PFA-induced fluorescence were negligible above 565 nm; whereas the fluorescence of Nile red peaked at around 600 nm. Lipid material was identified in the cross-striations, the lines of Retzius, the Hunter-Schreger bands, inter-prismatic spaces, and inter-prismatic spaces in the mature human enamel.

CONCLUSIONS

This technique successfully revealed the distribution of lipid components of organic matrix in mature human enamel and may be promising in assessing the changes of enamel organic elements in the developmental, pathological or experimental conditions.

The effect of NaOCl dentin treatment on nanoleakage formation

The term "nanoleakage" has been introduced to explain a penetration pathway within hybrid layers of the dentin-composite junction in the absence of gap formation. This phenomenon is argued in the literature to be a risk factor for the quality of the dentin bonding. NaOCl is a well-known agent used to remove collagen layers that are exposed after acid etching. The purpose of this study was to determine the influence of an NaOCl treatment of dentin to the formation of nanoleakage. Class V cavities were prepared in 40 human molars with the cervical margins located in dentin. After etching with phosphoric acid, 20 samples were treated with 10% NaOCl for 60 s, and 20 samples were used as control. Composite restorations were placed using two different bonding systems. The specimen were exposed in silver nitrate solution and then in developer. After embedding, the teeth were sectioned, dried, coated with gold, and analyzed by SEM. For all the specimen in the control group, backscatter images indicated a silver penetration within the hybrid layer. There was no penetration of silver detectable in the teeth that were treated with NaOCl. We conclude that the removal of the collagen layer by using NaOCl avoids the formation of nanoleakages with the materials tested.

Interaction patterns between dentin and adhesive on prepared class V cavities in vitro and in vivo

The interface between dentin and an acetone-based single-component adhesive system (Prime&Bond 2.1, DeTrey Dentsply, Germany) was morphologically investigated by scanning electron microscopy (SEM). Interaction patterns of human teeth were correlated in vivo and in vitro. The SEM examination proved that the formation of a hybrid and an adhesive layer, the peri- and intratubular adhesive penetration, as well as hiatus and nanoleakage formation were no different on vital and nonvital dentin within the limitation of the experimental arrangement of this study.

The ultrastructure of a compomer adhesive interface in enamel and dentin, and its marginal adaptation under dentinal fluid as compared to that of a composite

OBJECTIVES

To visualise the ultrastructure of the interface of SCA compomer adhesive and of Optibond composite adhesive in enamel and dentin, and to relate the findings to the marginal adaptation of these two products in mixed class V restorations.

METHODS

The ultrastructure was investigated using a scanning electron microscope (SEM) with and without prior argon ion etching, an environmental SEM, a field emission SEM, a confocal laser scanning microscope, and a transmission electron microscope. The marginal adaptation was quantified in mixed class V restorations by using the replica technique and a SEM under simulated dentinal fluid before and after simultaneous mechanical and thermal loading.

RESULTS

The ultrastructure of the compomer adhesive interface differed from those of the composite. However, no significant difference was discerned as regards the percentage of "continuous margin" in the enamel marginal area before loading, and in the dentin area before and after loading (p < 0.05; unpaired t-test). Only after loading, the percentage of "continuous margin" in enamel was significantly (p < 0.05; unpaired t-test) better than that of the compomer.

SIGNIFICANCE

The results indicated that the ultrastructure of the adhesive interface allowed no clear conclusions to be drawn as to the quality of marginal adaptation.

Dental materials: 1997 literature review

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.