Biomedical subjects

Paulette Spencer

Publications and source records attributed to Paulette Spencer.

At least 19 recordsLinked to original sources

PubMed2007

Relationship of solvent to the photopolymerization process, properties, and structure in model dentin adhesives.

The ratio of the double-bond content of monomer to polymer, i.e. degree of conversion (DC) has been used frequently as a convenient means of comparing the behavior and properties of dental composites and adhesives. The purpose of this investigation was to study the relationship of photopolymerization processes, bulk properties, and structure using model dentin adhesives cured in the presence of different ethanol content as an example. There was little difference in the DC of model BisGMA-based adhesives cured in the presence of ethanol concentrations ranging from 0 to 40 wt %, but there were substantial differences in the mechanical properties. Ultimate tensile strength (UTS) and modulus of elasticity decreased with an increase in ethanol content. Polymer structure was revealed by thermal behavior in the glass transition temperature (Tg) region; these measurements were obtained by modulated temperature differential scanning calorimetry (MTDSC) technology, which removes the competing irreversible effects associated with release of volatiles and residual curing. Glass transition temperature of model adhesives decreased substantially with an increase in ethanol content. The DC based on the quantity of remaining double bond has been used extensively to characterize and provide a relative assessment of the quality of dentin adhesives and dental composites. Since polymers differing in linearity, and therefore crosslink density, may have a similar degree of conversion, the measurement of monomer/polymer conversion does not necessarily provide complete representation of the quality or durability of the polymer structure.

Dentin-Bonding Agents↗

PubMed2007

Chemical profile of adhesive/caries-affected dentin interfaces using Raman microspectroscopy.

In clinical practice, dentists must frequently bond adhesives to caries-affected dentin substrates, but the bond that characteristically forms with these substrates does not provide the durability necessary for long-term clinical function. The purpose of this study was to characterize and compare the interfacial chemistry of adhesive with caries-affected and noncarious dentin using micro-Raman spectroscopy. The results indicated that the differences in the Raman spectra between noncarious and caries-affected dentin could not be accounted for by simple decreased mineralization. Both the structure of collagen and mineral in the caries-affected dentin has been altered by the caries process. The differences in structure and composition not only interfered with acid-etching process but also subsequent resin monomer penetration. It was shown that the interface between the adhesive and caries-affected dentin was wider and more complicated than that of the adhesive and noncarious dentin. As a result of adhesive phase separation, a structurally integrated hybrid layer did not form at the interface with either caries-affected or noncarious dentin. Using chemical imaging techniques, this study provides the direct evidence of adhesive phase separation at the interface with caries-affected dentin. Although our group previously reported adhesive phase separation at the interface with noncarious dentin, the chemistry of caries-affected dentin leads to greater variability and a more highly irregular composition along the length and breadth of the interface.

Adult↗

PubMed2007

Characterization of photopolymerization of dentin adhesives as a function of light source and irradiance.

Manufacturers have attempted to address the limitations associated with dentin bonding by eliminating as many steps as possible in the bonding protocol. Theoretically, this approach increases the efficiency of the procedure and reduces technique sensitivity. These trends are reflected in the introduction of all-in one, single-step adhesive systems; the increased concentration of acidic resin monomers in these systems allows for simultaneous etching and priming of the prepared dentin surface. Ideally, the degree of monomer conversion would be high enough that the acidic reaction would be self-limiting. The purpose of this study was to investigate the effect of light irradiance and source on the photopolymerization of three commercial dental adhesives by monitoring the double bond conversion as a function of time during and after irradiation. The photopolymerization curing efficiency of the commercial adhesives investigated in this study varied as a function of light source and distance. The use of LED performed better than the halogen light in terms of polymerization rate and degree of conversion for the commercial single-step, sixth generation adhesive, Adper Prompt. In contrast, polymerization of commercial single-bottle, fifth generation adhesive, Single Bond and One-Up Bond F, was mainly a function of exposure time, irrespective of the two light units or intensities.

Bisphenol A-Glycidyl Methacrylate↗

PubMed2006

Effect of coinitiator and water on the photoreactivity and photopolymerization of HEMA/camphoquinone-based reactant mixtures.

It was reported previously that, in the presence of water, a commercially available light-activated BisGMA/HEMA adhesive underwent physical separation into solid BisGMA-rich particles and a fluid-like HEMA-rich phase. The HEMA-rich phase exhibited limited monomer conversion suggesting that the photoinitiator is localized to the hydrophobic phase or that the photoinitiator is not compatible with the hydrophilic HEMA. The objective of the present study was to identify photoinitiators that are compatible with the hydrophilic HEMA-rich phase, when the mixtures are prepared without and with water added. The photoinitiator was camphoquinone (CQ, 0.5 mol %), and the coinitiators (0.5 mol %) were 2,2'-dihydroxyethyl-para-toluidine (DHEPT), dimethylaminoethyl methacrylate (DMAEMA), and N-phenylglycine (NPG), and (1 wt %) diphenyliodonium chloride (DPIC). Reactivities were evaluated using photodifferential scanning calorimetry, at 37 degrees C, using visible light (>418 nm), with the parameters determined being enthalpy (DeltaH), the induction time (herein defined as the time for 1% of the photopolymerization to be complete), and the time at which the maximum exotherm occurred. The degree of monomer conversion was measured using micro-Raman spectroscopy. It was shown that the reactivity ranking (based on time to exotherm peak maximum and total enthalpy) was HEMA/CQ/DHEPT < HEMA/CQ/DMAEMA < HEMA/CQ/NPG. Reactivity was dramatically increased for CQ/DMAEMA and CQ/NPG in the presence of DPIC, but not for CQ/DHEPT. Water has a major effect on HEMA conversion. At 10% of water, the conversion level of HEMA formulated with CQ/DMEMA dropped from approximately 100% to 86%. In comparison, the conversion in 10% of water increased to nearly 96% when DPIC was used. The results suggest that DHEPT, which is commonly used in commercial adhesives, is not compatible with HEMA. Both NPG and DMAEMA appear compatible with the HEMA. The ionic hydrophilic iodonium salt, DPIC, enhances the polymerization of HEMA, even in the presence of water. Future studies on water-compatible photoinitiators should be performed to address the detrimental effects of water on dentin adhesive systems.

Calorimetry, Differential Scanning↗

PubMed2006

Interfacial chemistry of moisture-aged class II composite restorations.

Under in vivo conditions, the adhesive/dentin bond at the gingival margin of class II composite restorations can be the first defense against substances that may penetrate and ultimately undermine the composite restoration. Deterioration of this bond during aqueous aging is an area of intense investigation, but to date, the majority of our techniques have provided only an indirect assessment of the degrading components. The purpose of this study was to analyze the in situ molecular structure of adhesive/dentin interfaces in class II composite restorations, following aging in aqueous solutions. Class II preparations were cut from 12 unerupted human third molars, with a water-cooled, high-speed, dental handpiece. The prepared teeth were randomly selected for restoration with single bond (SB) and Z100 (3M). Teeth were restored, as per the manufacturer's directions, under environmental conditions that simulated humidity and temperature characteristics of the oral cavity. Restored teeth were kept in sterile Delbecco's phosphate saline for 48 h or 90 days. The samples were sectioned occlusogingivally and micro-Raman spectra were acquired at approximately 1.5 microm spatial resolution across the composite/adhesive/dentin interfaces at the gingival margins. Samples were wet throughout spectral acquisition. The relative intensity of bands associated with the adhesive in the interfacial region decreased dramatically after aqueous storage. This decrease in concert with the similar depth of dentin demineralization provides direct spectroscopic evidence of leaching of adhesive monomer from the interface during the 90 days of storage. SB adhesive infiltrated 4-5 microm of 12-microm demineralized dentin at the gingival margin. After 90 days of aqueous storage, SB adhesive infiltration was reduced to approximately 2 microm, leaving approximately 10 microm of demineralized dentin collagen exposed at the gingival margin. The unprotected collagen at the gingival margin of the aged class II composite restorations was disorganized, suggesting hydrolysis of the collagen, with 90 days of aqueous storage.

Collagen↗

PubMed2006

Comparison of interfacial characteristics of adhesive bonding to superficial versus deep dentine using SEM and staining techniques.

OBJECTIVES: A primary reason for premature failure of Class II composite restorations is recurrent decay at the gingival margin. The integrity of the gingival margin depends on the bond formed with dentine. Using scanning electron microscopy (SEM) and histomorphologic technique, the purpose of this study was to characterise the adhesive/dentine (a/d) bond in dentine sections from the dentinoenamel junction (DEJ) and the cementoenamel junction (CEJ) with commercial adhesives of varying hydrophobic/hydrophilic composition. MATERIALS AND METHODS: The occlusal 1/3 of the crown was removed from 20 human third molars, this exposed the surface used for the DEJ sections. The teeth were sectioned occluso-gingivally into equal halves: one-half representing the DEJ; the remaining half was sectioned 4mm deep to the exposed surface (CEJ). Each half was treated with the same adhesive. The teeth were randomly selected for treatment with Single Bond (SB, 3M) or Dentastic UNO (UNO, Pulpdent) using wet bonding technique as per manufacturers' instructions. Thin (3-5mum) sections of native a/d interfaces were cut and stained with Goldner's trichrome for light microscopic (LM) examination. Companion slabs were polished and acid-bleach treated, then analysed with SEM. RESULTS: DEJ sections: SB/dentine specimens had approximately 4mum exposed protein at the interface, UNO infiltrated the depth of the demineralised dentine and encapsulated exposed protein. CEJ sections: SB/dentine specimens had highly variable interface structure with localized exposed protein, UNO/dentine exhibited 3-5mum exposed protein at the interface. The quality of the interface was exaggerated and the above differences were not revealed based on SEM characterisation. CONCLUSIONS: As a result of adhesive phase separation, SB does not form structurally integrated a/d bonds at the DEJ or CEJ. The increased hydrophilic composition of UNO contributes to the formation of an integrated a/d bond at the DEJ, but structural differences and increased moisture leads to unprotected protein at the a/d interface in the CEJ sections. The inability of the SEM technique to reveal the complexity of the interface could be related to the modifications of the a/d interface caused by polishing and acid-bleach treatment.

Adhesives↗

PubMed2006

Fuzzy clustering of Raman spectral imaging data with a wavelet-based noise-reduction approach.

Raman spectral imaging has been widely used for extracting chemical information from biological specimens. One of the challenges is to cluster the chemical groups from the vast amount of hyperdimensional spectral imaging data so that functionally similar groups can be identified. In this paper, we present an approach that combines a differential wavelet-based data smoothing with a fuzzy clustering algorithm for the classification of Raman spectral images. The preprocessing of the spectral data is facilitated by decomposing them in the differential wavelet domain, where the discrimination of true spectral features and noise can be easily performed using a multi-scale pointwise product (MPP) criterion. This approach is applied to the classification of spectral data collected from adhesive/dentin interface specimens where the spectral data exhibit different signal-to-noise ratios. The proposed wavelet approach has been compared to several conventional noise-removal algorithms.

Adhesives↗

PubMed2005

Interfacial chemistry of class II composite restoration: structure analysis.

The gingival margins of class II composite restorations are particularly vulnerable to marginal leakage and secondary caries. In identifying the factors contributing to caries development, the molecular structure and differences in the structure at the proximal and gingival margins have been largely overlooked. The purpose of this study was to compare the molecular structure at the adhesive/dentin interface of the proximal and gingival walls of class II composite restorations. Class II preparations were cut in 12 unerupted third molars with a water-cooled high-speed dental handpiece. The prepared teeth were randomly selected for treatment with Single Bond (SB) + Z100 (3M). Teeth were restored, per manufacturer's directions, under humidity and temperature characteristic of the oral cavity. Restored teeth were kept in sterile Delbecco's phosphate saline for 48 h. The samples were sectioned occluso-gingivally and micro-Raman spectra were acquired at approximately 1.5-microm spatial resolution across the composite/adhesive/dentin interfaces. Samples were wet throughout spectral acquisition. Raman spectral characteristics at the proximal and gingival margins were distinctly different; the depth of demineralized dentin was 6-7 microm at proximal margin, 12-13 microm at gingival margin. SB adhesive penetrated the depth of demineralized dentin in a gradient at the proximal margin. The "single bottle" adhesive used in this study, gradually penetrated the depth of the demineralized dentin at the proximal margin but failed to infiltrate the depth at the gingival margin, leaving a thick exposed collagen layer.

Dental Materials↗

PubMed2005

Parametric study of the effect of phase anisotropy on the micromechanical behaviour of dentin-adhesive interfaces.

A finite element (FE) model has been developed based upon the recently measured micro-scale morphological, chemical and mechanical properties of dentin-adhesive (d-a) interfaces using confocal Raman microspectroscopy and scanning acoustic microscopy (SAM). The results computed from this FE model indicated that the stress distributions and concentrations are affected by the micro-scale elastic properties of various phases composing the d-a interface. However, these computations were performed assuming isotropic material properties for the d-a interface. The d-a interface components, such as the peritubular and intertubular dentin, the partially demineralized dentin and the so-called "hybrid layer" adhesive-collagen composite, are probably anisotropic. In this paper, the FE model is extended to account for the probable anisotropic properties of these d-a interface phases. A parametric study is performed to study the effect of anisotropy on the micromechanical stress distributions in the hybrid layer and the peritubular dentin phases of the d-a interface. It is found that the anisotropy of the phases affects the region and extent of stress concentration as well as the location of the maximum stress concentrations. Thus, the anisotropy of the phases could effect the probable location of failure initiation, whether in the peritubular region or in the hybrid layer.

Adhesives↗

PubMed2005

Elastic anisotropy of bone and dentitional tissues.

The calculation of the scalar compressive and shear anisotropy factors developed for single crystal refractory compounds has been adapted to the anisotropic elastic stiffness coefficients determined by a number of ultrasonic measurements of bone based on transverse isotropic symmetry. Later, this work was extended to include the ultrasonic measurements of bone based on orthotropic symmetry. Recently, the five transverse isotropic elastic constants for both wet and dry human dentin were determined using resonant ultrasound spectroscopy. The five transverse isotropic elastic constants for wet bovine enamel and dentin had been calculated based on modeling of ultrasonic wave propagation measurements and related data in the literature. The scalar compressive and shear anisotropy factors have been calculated from both these sets of data and are compared with a representative set from those published previously for both human and bovine bone and both fluoro- and hydroxyl-apatites.

Animals↗

PubMed2005

Moisture effect on polyether and polyvinylsiloxane dimensional accuracy and detail reproduction.

PURPOSE: This investigation evaluated and compared the dimensional accuracy and surface detail reproduction of two hydrophilic polyvinylsiloxane (PVS) and two polyether (PE) impression materials when used under dry and moist conditions. METHODS: Impressions were made of stainless steel dies as described in ANSI/ADA specification no. 19, with two vertical and three horizontal lines inscribed on the die superior surface. Impressions were made under dry and moist conditions (17 impressions per condition for each material). Dimensional accuracy was measured by comparing the average length of the middle horizontal line in each impression with the same line on the metal die using a measuring microscope with an accuracy of 0.001 mm. Surface detail reproduction was evaluated by using criteria similar to ADA specification no. 19: continuous replication of at least two of the three horizontal lines. RESULTS: The mean percent dimensional change and SD values ranged from -0.135% (0.035) to 0.053% (0.031). A two-way analysis of variance (ANOVA) indicated that moisture did not cause significant adverse effects on the dimensional accuracy of any material (p > 0.05); however, significant differences were found between the materials (p < .05). The surface detail evaluation indicated that moisture had a significant effect on detail reproduction of PVS materials (Pearson's Chi square, p < 0.05). Under dry conditions, all materials produced satisfactory detail reproduction 100% of the time; however, under moist conditions, only 29% of Aquasil and Genie Ultra PVS impressions produced satisfactory detail reproduction, while 100% of Permadyne Garant and Impregum Penta Soft PE impressions still met the surface detail criteria. CONCLUSIONS: Although moisture may not adversely affect the dimensional accuracy of either PE or hydrophilic PVS material, the evidence suggests that PE material is more likely to produce impressions with superior detail reproduction in the presence of moisture.

Analysis of Variance↗

PubMed2005

Evaluation of the interface between one-bottle adhesive systems and dentin by Goldner's trichrome.

PURPOSE: To evaluate the hybrid layers in interfaces between dentin and six contemporary one-bottle adhesive systems using a nondestructive differential staining micro-technique. METHODS: The adhesive systems used in this study were divided to three groups based on hydrophilic/hydrophobic component ratios (i.e. ability to dissolve in water), from highest to lowest as follows: Group 1 (Dentastic UNO.DUO, PermaQuick PQ1) > Group 2 (One-Step, Primer&Bond NT) > Group 3 (Optibond Solo, Single Bond). The occlusal third of the crown was removed from 36 extracted, unerupted human 3rd molars. Smear layers were created by abrading the dentin with 600 grit SiC under water. The exposed dentin was treated with one of the adhesive systems per manufacturer's instructions. After 24 hours in water, 3-5 microm thin sections of the adhesive/dentin (adhesive/dentin ) interface were cut with a microtome and stained with Goldner's trichrome. Stained thin sections from each prepared tooth were imaged with light microscopy. RESULTS: The thickness and color difference of adhesive/dentin interfaces among these one-bottle adhesive systems were clearly visualized. The width of the hybrid layers varied, ranged from 4.1-9.2 microm for six adhesive systems. The color differences in the stained sections are reflected to the extent and degree to which the adhesive envelops the exposed collagen. Among these six bonding systems, resin encapsulation of collagen varied from highest to lowest as follows: Group 1 (UNO, PQ1) > Group 2 (OS, PBNT) > Group 3 (OP, SB). The differences in collagen encapsulation are dependent on the adhesive composition, or the ability to tolerate water during the infiltration of the wet demineralized matrix.

Azo Compounds↗

PubMed2004

Micromechanical analysis of dentin/adhesive interface by the finite element method.

The interfacial microstructure and spatial distribution of the modulus of elasticity have a profound effect on load transfer at the dentin/adhesive (d/a) interface. The microstructure is influenced by the varying degree of demineralization of intertubular and peritubular dentin during etching as well as the depth of adhesive penetration into the hybrid layer. These factors lead not only to a unique microstructure in the vicinity of the dentinal tubules, but also to a mechanically graded hybrid layer. This article investigates the micromechanical stress distribution at a d/a interface with the use of finite element analysis (FEA). Such analysis is now feasible given the newly measured moduli of elasticity at micro- and nanoscales. The results indicate that the morphological and micromechanical properties of the d/a interface affects the stress field such that the fracture/failure is likely to initiate in the stress-concentration zone of peritubular dentin next to the hybrid/exposed-collagen layer. The results suggest that devising a full-depth high modulus hybrid layer may considerably reduce the stress concentration zone and the magnitude of stress concentration in the peritubular dentin next to the hybrid/exposed-collagen layer.

Adhesives↗

PubMed2004

Overestimating hybrid layer quality in polished adhesive/dentin interfaces.

The most popular techniques for determining the quality of the hybrid layer (HL) have relied on morphologic characterization of the polished adhesive/dentin (a/d) interfaces before and after acid-bleach chemical treatment. Using these techniques, the existence of smooth, acid-resistant layers has been consistently reported for most adhesive systems. The purpose of this study was to determine whether popular specimen preparation techniques that include polishing and acid-bleach treatment modify the a/d interface, mask the complexity of the HL, and lead to inaccurate assessment of the quality of the HL. To understand the impact of specimen preparation techniques on the morphology of the resin-dentin interface, polished and unpolished specimens from the same tooth were closely compared after different acid-bleach chemical treatment procedures. Two one-bottle adhesives, that is, 3M Single Bond and Pulpdent UNO, exhibiting distinct differences in hydrophilic/hydrophobic composition, were used in this investigation. Using specimens from the same tooth, the effect of chemical treatments on the morphology of the resin-dentin interdiffusion zone and the differences in the morphology of polished and unpolished specimens after these same treatments were studied with scanning electron microscopy. It was shown that conventional specimen preparation techniques that include polishing and acid-bleach treatment can adversely affect and even obscure the structural detail of the a/d interface in specimens that possess a porous HL. The results indicated that the Pulpdent UNO/dentin interface had better quality than the 3M Single Bond/dentin interface. The difference in the quality of HL can be attributed to factors such as compositional differences that impact the adhesive interaction with water, that is present within the substrate during wet bonding. The inability of the conventional acid-bleach procedure to reveal the differences in the scanning electron microscopy interfacial morphology was overcome in this investigation by using a multistep technique.

Acid Etching, Dental↗

PubMed2004

Physiochemical interactions at the interfaces between self-etch adhesive systems and dentine.

OBJECTIVES: The purpose of this study is to provide direct and comprehensive information regarding morphology, quality and chemistry of the interfaces between three self-etching primers/adhesives and dentine. MATERIALS AND METHODS: The occlusal one-third of the crown was removed from 18 unerupted human third molars. The prepared dentine surfaces were randomly selected for treatment with one of three commercial self-etching bonding agents according to manufacturers' instructions. One two-step self-etching adhesive (Clearfil SE Bond) and two one-step self-etching adhesives (One-Up Bond F and Prompt L-Pop) were selected. Five-micron-thick sections of adhesive/dentine interface specimens were cut and stained with Goldner's trichrome for light microscopy. Companion slabs were analysed with micro-Raman spectroscopy and scanning electron microscopy (SEM). RESULTS: It was shown that the difference in aggressiveness of these three contemporary self-etching systems produced different thickness of hybrid layer. Staining technique showed a distinct coloured line/zone at the adhesive/dentine interfaces for all three bonding systems. The width of this line varied, and was approximately 1, 1-2, 2-3 microm for Clearfil SE Bond, One-Up Bond F and Prompt L-Pop, respectively. The colour differences in the stained interface sections, which is reflected by the extent to which the adhesive encapsulates the demineralised dentine matrix, indicated that collagen fibrils at the interfaces were not totally encased in all three self-etching adhesives. Raman results showed that Prompt L-Pop is the most aggressive systems in this study. It almost totally demineralised the 2-microm deep subsurface dentine, while Clearfil SE is mild, only partially demineralised the first micron deep dentine. CONCLUSIONS: The complementary techniques, i.e. SEM, staining and micro-Raman spectroscopy, hold considerable promise for comprehensive physicochemical characterisation of self-etching adhesive/dentine interfaces. In comparison with two-step self-etching system, the aggressive one-step system produces more complex interfaces.

Azo Compounds↗

PubMed2004

Effect of acid etching time and technique on interfacial characteristics of the adhesive-dentin bond using differential staining.

Dentin bonding using the total-etch method has been claimed to be technique-sensitive. The aim of this study is to examine the effect of acid-etch variations on the dentin demineralization and interfacial structure of the adhesive-dentin bond using a differential staining technique. Single Bond adhesive with 35% phosphoric acid gel was used. The occlusal one-third of the crown was removed from 60 extracted, unerupted human third molars. Smear layers were created by abrading the dentin with 600 grit SiC under water for 30 s. The prepared teeth were randomly assigned to four groups according to etching time (Group 1, 10 s; Group 2, 15 s; Group 3, 30 s; Group 4, 60 s). In each group, the etching gel was: (i) applied and spread to the dentin surface and left to stand undisturbed; (ii) applied and gently agitated during etching; (iii) applied without using dispensing tips for the syringe and left for the same period as above. After rinsing, the etched dentin was then treated with the adhesive per manufacturers' instructions. 3-5 micro m thin sections of the adhesive/dentin (a/d) interface were cut with a microtome and stained with Goldner's trichrome. Stained, thin sections from each prepared tooth were imaged with light microscopy. The depth and extent of dentin demineralization, and the a/d interdiffusion zone were clearly visible by this differential staining microtechnique. The thickness of the interdiffusion zone increased as a function of etching time. However, the etchant gel application methods have a significant influence on dentin demineralization. Although agitating acid gel facilitates the penetration and etching into dentin, it should not be recommended, especially for longer etching time. These results indicated that the etching technique has a large effect on the profile of both dentin demineralization and interfacial structure.

Acid Etching, Dental↗

PubMed2004

In vivo versus in vitro microtensile bond strength of axial versus gingival cavity preparation walls in Class II resin-based composite restorations.

BACKGROUND: Gingival margins in Class II composite restorations are a site of frequent failure. The purpose of the authors' study was to compare the microtensile dentin bond strength of gingival and axial restored cavity preparation walls of Class II composite restorations under in vivo and in vitro conditions. METHODS: After obtaining informed consent, the authors placed Class II resin-based composite restorations in 14 premolar teeth from five patients, under in vivo or in vitro conditions. The teeth were sectioned to obtain rectangular specimens from axial and gingival walls with a surface area of approximately 0.5 square millimeter. The authors tested 85 microtensile adhesive samples from the 14 teeth on a testing instrument (Universal Instron, Model 125, Instron, Canton, Mass.) until failure. RESULTS: The mean (+/- standard deviation) mircotensile dentin bond strengths in mega-pascals were as follows: in vivo axial, 36.5 (14.9); in vivo gingival, 17.6 (11.6); in vitro axial, 49.5 (13.9); in vitro gingival, 34.0 (13.1). A two-way analysis of variance found a statistically significant difference between in vitro and in vivo conditions and between the axial and gingival walls (P < or = .001). Eighty-eight percent of the fractured samples involved the adhesive layer as observed under scanning electron microscopy up to x2,500. Seventeen of the gingival samples and two of the axial samples debonded during the preparation phase and could not be tested. CONCLUSION: The dentinal microtensile strength of adhesive/resin-based composite bonded to the gingival wall was significantly weaker than the bond to the axial wall, and in vivo conditions produced significantly weaker bond strengths than did in vitro conditions. CLINICAL IMPLICATIONS: The dentinal adhesive bond of resin-based composite to gingival walls is significantly weaker and thus more subject to failure than the bond to axial walls. In vitro bond strength studies may overestimate the bond strength of adhesives in in vivo applications.

Adolescent↗

PubMed2004

Identification of collagen encapsulation at the dentin/adhesive interface.

PURPOSE: The purpose of this study was to investigate the dentin/adhesive interfacial characteristics of three current commercial adhesives with different relative hydrophilic/hydrophobic composition, using a nondestructive staining technique. MATERIALS AND METHODS: Dentin surfaces of 18 unerupted human third molars were randomly selected for treatment with one of three commercial dentin bonding agents according to manufacturers' instructions for the "wet" bonding technique. The adhesives were ranked based on hydrophilic/hydrophobic component ratios (ie, ability to dissolve in water), highest to lowest, as follows: Uno (Pulpdent) > Prime&Bond NT (PBNT, Dentsply Caulk) > Single Bond (SB, 3M ESPE). Dentin/adhesive (d/a) interface sections were stained with Goldner's trichrome, a classical bone stain, and examined using light microscopy. RESULTS: The extent and degree to which the adhesive encapsulates the demineralized dentin matrix is reflected in the color differences in the stained sections. The depth of demineralization appeared comparable among these bonding systems, but adhesive infiltration varied from highest to lowest as follows: Uno > PBNT > SB. CONCLUSIONS: The differential staining technique provided a clear representation of the depth of dentin demineralization and extent/degree of adhesive encapsulation of the exposed collagen at the d/a interface. This technique provides a mechanism for readily identifying vulnerable sites at the d/a interface. The composition of the one-bottle adhesive systems has a substantial effect on the interfacial structure of the d/a bond.

Acid Etching, Dental↗