Biomedical subjects

F R Tay

Publications and source records attributed to F R Tay.

At least 73 records · Page 4Linked to original sources

PubMed2001

Effect of delayed activation of light-cured resin composites on bonding of all-in-one adhesives.

PURPOSE: This study examined the effect of delayed activation of light-cured resin composites on the microtensile bond strengths of two all-in-one adhesives to sound dentin. MATERIALS AND METHODS: Flat dentin surfaces prepared from caries-free third molars were bonded with either Prompt L-Pop (ESPE) or One-Up Bond F (Tokuyama). Each adhesive was divided into 6 subgroups containing three teeth each. A hybrid composite was left to contact the cured adhesive surfaces for 0, 2.5, 5, 10 or 20 min before light activation. In the 6th subgroup, the cured adhesive was covered with a layer of nonacidic bonding resin before contacting the composite for 20 min. Composite-dentin beams, with average cross-sectional areas of 0.85 mm2 were prepared for microtensile bond testing. Representative fractured beams from the 0, 10- and 20-min delay subgroups were prepared for SEM examination. Additional specimens were prepared in the 0- and 20-min delay subgroups by replacing the hybrid composite with either a flowable composite or a composite liner to facilitate TEM preparation and examination. RESULTS: Kruskal-Wallis ANOVA and Dunn's multiple comparison tests showed that significant differences existed among the subgroups of each adhesive. Regression analyses showed that for each adhesive, there was an exponential decline in mean bond strength with increasing delay in light activation, and the correlation was highly significant (r = -0.99, p < 0.005 for Prompt L-Pop; r = -0.96, p < 0.01 for One-Up Bond F). SEM examination of fractured interfaces in the immediately light-cured subgroups revealed the absence of voids within the fractured composite. However, voids were consistently observed in the 10 min- and 20 min-delay subgroups. They corresponded to soapsuds-like blisters that were observed with TEM in the 20 min-delay subgroups. CONCLUSION: Adverse interactions between acidic adhesive resin monomers and tertiary amines in light-cured composites normally do not occur because of the fast rate of free-radical generation in photochemical redox reactions. However, such interactions can occur in all-in-one adhesives on prolonged contact of light-cured composites with the cured adhesive layer.

Composite Resins↗

PubMed2000

An ultrastructural study of the application of dentine adhesives to acid-conditioned sclerotic dentine.

OBJECTIVE: This in vitro study examined the ultrastructure of resin-infiltrated sclerotic dentine following the application of a self-etching primer, with or without the adjunctive use of phosphoric acid pre-conditioning. MATERIALS AND METHODS: Non-carious, natural cervical sclerotic lesions were hand-cleaned with a slurry of pumice and chlorhexidine and bonded without further cavity preparation. One group was bonded using Clearfil Liner Bond 2V (Kuraray Co. Ltd, Osaka, Japan) alone. Specimens from the other group were pre-conditioned with K-etchant (40% phosphoric acid gel, Kuraray) prior to the application of the same self-etching primer. Artificially prepared wedge-shaped lesions were also made in sound bicuspids, bonded using the two methods, and used as controls for the two groups. For SEM examination, each specimen was cryofractured into two halves through a pre-formed slit made on the lingual surface, after the respective conditioning treatment. Different locations within the lesions were examined after rinsing of the phosphoric acid/self-etching primer and specimen dehydration. For TEM investigation, specimens were bonded with the adhesive. Both demineralised and undemineralised ultrathin sections were prepared from the occlusal, gingival and deepest part of the wedge-shaped bonded lesions following specimen fixation, dehydration and resin embedding. RESULTS: A hypermineralised surface layer was present on the surface of etched sclerotic dentine. This layer was thicker in the deepest part of the natural lesions, where bacterial colonisation of the lesion surface was also apparent. Both treatment protocols were unable to effectively dissolve sclerotic casts that occluded the dentinal tubules. Depending upon the thickness of the surface layers at different locations in the natural lesion, self-etching primer treatment alone resulted in reduction of the thickness of the authentic hybrid layer (i.e. hybridised intertubular dentine). This was also true of phosphoric acid pre-conditioning along the deepest part of the natural lesions. Within this region, intertubular dentine completely devoid of an authentic hybrid layer could be seen in both treatment groups. Resin tags were also sparsely observed in such regions. CONCLUSIONS: Adhesive strategies that rely mostly on micromechanical retention alone may be compromised by the sporadic absence of the hybrid layer and resin tags in sclerotic dentine. Based on the ultrastructural features presented, it is further speculated that adaptive strategies such as removal of the surface layers and extended etching time may not be completely effective in improving bonding efficacy in highly sclerotic dentine. Interdisciplinary research should be continued to develop alternative procedures for bonding resins equally well to sound and sclerotic dentine.

Acid Etching, Dental↗

PubMed2000

Marginal adaptation of a new compomer under different conditioning methods.

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

Acid Etching, Dental↗

PubMed2000

Mechanical disruption of dentin collagen fibrils during resin-dentin bond testing.

PURPOSE: To determine if collagen fibrils on the dentin side of failed resin-dentin interfaces undergo mechanical disruption during microtensile bond testing. MATERIALS AND METHODS: Extracted, caries-free human third molars were divided into four groups. The occlusal enamel was removed, leaving a flat dentin surface for bonding. Resin composite buildups were made after the acid-conditioned dentin was bonded with either Single Bond (S) or One-Step (O), and using either moist bonding (M) or air drying for 5 s (D). After storage in water for 24 h, the teeth were vertically sectioned into an array of 0.9 x 0.9 mm resin composite-dentin beams. They were stressed to failure using the nontrimming version of the microtensile bond test. Fractured dentin and resin composite sides of representative beams from each group that exhibited adhesive failures under light microscopy examination were prepared for scanning (SEM) and transmission electron microscopy (TEM). RESULTS: A two-way ANOVA showed that moist bond strengths were significantly higher than those made to dry dentin (M > D; p < 0.001), but that there was no difference between the adhesives (S vs O; p = 0.547). SEM analysis showed the presence of loose collagen fibrils within fractured hybrid layers in the dry groups, but not in the moist groups. TEM examination of the dry-bonded groups revealed collagen fibrils that were thinner and exhibited abnormally wide interfibrillar spaces when hybrid layers were intact. Within dry-bonded fractured hybrid layers, broad mechanical disruption zones could be seen, consisting of fibrils that were devoid of cross banding, defibrillation of the subfibrillar architecture, and gross disaggregation into microfibrils. In the moist-bonded groups, only short mechanical disruption zones were found along the torn edges of the collagen fibrils. The rest of the fibrils beyond the fracture site were intact and retained their periodicity. Mechanical testing of demineralized matrices yielded a maximum modulus of elasticity of 43.9 +/- 6.1 MPa. CONCLUSION: We speculate that adhesive resin has a protective function for demineralized collagen in well-infiltrated hybrid layers. We propose that both the collagen and resin contribute to load sharing during stress application until the final moment of rupture. On the other hand, collagen fibrils in poorly infiltrated hybrid layers, being unsupported by resin, undergo various degrees of irreversible mechanical disruption depending on how the stress is dissipated. The collagen fibril network has a much lower modulus of elasticity compared to those of resin-infiltrated fibrils or the demineralized dentin.

Acid Etching, Dental↗

PubMed2000

An ultrastructural study of the influence of acidity of self-etching primers and smear layer thickness on bonding to intact dentin.

PURPOSE: The objectives of this study were (1) to determine the depth of demineralization into intact dentin using several self-etching primer systems with different pH values, and (2) to evaluate whether hybridization of intact dentin in Clearfil SE Bond may be affected by variation in the thickness of the smear layers. MATERIALS AND METHODS: Dentin disks were created from mid-coronal dentin in extracted, human third molars. Three self-etching primer systems (Clearfil Liner Bond II, Liner Bond 2V, and SE Bond) were applied separately to these disks to evaluate how deep self-etching systems penetrate through smear layers into intact dentin. Dentin treated with All-Bond 2 using the "no-etch" technique was used as a control group. In the second part of the study, dentin disks with different smear-layer thicknesses were produced. The cryofractured control group was devoid of a smear layer. The experimental teeth were ground with 60-, 180-, or 600-grit SiC paper and bonded using SE Bond. Dentin disks were bonded together and examined with TEM. RESULTS: All-Bond 2 did not etch beyond the smear layer. The three self-etching primers etched beyond the smear layer to form true hybrid layers within intact dentin. This layer was thickest with Liner Bond 2 (ca 1.2 to 1.4 microns), but very thin (0.5 micron) using both Liner Bond 2V and SE Bond. Application of SE Bond to dentin of different surface roughness produced hybridized smear layers of variable thickness. However, the thickness of the underlying true hybrid remained consistent for the four groups (ca 0.4 to 0.5 micron). CONCLUSION: Self-etching primers create thin hybrid layers that incorporate the smear layer. The suspicion that thick smear layers may interfere with the diffusion of self-etching primers into the underlying intact dentin was not confirmed.

Acid Etching, Dental↗

PubMed2000

Effect of smear layers on the bonding of a self-etching primer to dentin.

PURPOSE: The objective of this work was to evaluate the effect of the absence and presence of smear layers on bonds made to dentin using a self-etching primer system, Clearfil SE Bond. MATERIALS AND METHODS: Dentin surfaces with different smear layer thickness were created from mid-coronal sound dentin in extracted, human third molars. The control group was cryofractured to create a bonding surface that was devoid of a smear layer. The experimental teeth were ground with wet 60-, 180- or 600-grit SiC paper. They were bonded using SE Bond, followed by resin composite buildups. After 1 day, bonded specimens were sectioned into multiple 1- x 1-mm beams. Microtensile bond strengths were determined and the results analyzed with ANOVA and the Student Neuman Keuls test. Fractographic study of cross sections of failed interfaces from the dentin side of representative beams was performed using both SEM and TEM. RESULTS: SE Bond produced high bond strengths (ca 50 MPa) to both smear layer-free and smear layer-covered dentin. SEM examination was inadequate to define the exact nature of interfacial failures. TEM observations demonstrated a thin (ca 400 to 500 nm) hybrid layer in the fractured dentin and thicker (ca 1 to 4 microns) hybrid layers on smear layer-covered dentin. This included a thick, hybridized smear layer and a thin, underlying true hybrid layer in the intact dentin. Separation of the two hybrid layers was not evident in interfacial failures. CONCLUSION: Self-etching primers create thin hybrid layers that incorporate the smear layer. This study shows that formation of true hybrid layers occurs irrespective of smear layer thickness and that both hybrid layers may function as a unit during loading without separation. identification of secondary cracks from TEM fractographic analysis exemplifies the complex reaction to tensile stresses in multilayered joint systems that comprise materials of variable compliance.

Acid Etching, Dental↗

PubMed2000

Bonding of a self-etching primer to non-carious cervical sclerotic dentin: interfacial ultrastructure and microtensile bond strength evaluation.

PURPOSE: The objectives of this study were 1) to examine the ultrastructural features of the resin-sclerotic dentin interface following the application of Clearfil Liner Bond II sigma to natural cervical wedge-shaped lesions, and 2) to evaluate the regional tensile bond strength of this self-etching primer at different locations on natural and artificially-created cervical lesions. MATERIALS AND METHODS: Deep cervical natural lesions were bonded using the self-etching primer. Micromorphology of the bonded interface at different locations within the lesions were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy/energy dispersive x-ray analysis (STEM/EDX). Ultrastructural features were further compared with the use of the same self-etching primer on artificial lesions created in sound cervical dentin. A nontrimming technique was used to evaluate the regional tensile bond strength from the occlusal, gingival, and the deepest central part of both natural and artificial cervical lesions. Beams with a mean area of 0.46 +/- 0.03 mm2 were prepared and were pulled to failure using a Bencor Multi-T testing device attached to an Instron universal tester. Bond strength results were evaluated using a two-way ANOVA design. RESULTS: A hypermineralized layer devoid of intact, banded collagen was invariably present on the surface of the natural lesions. Depending upon its thickness at different locations of the lesion, the action of a self-etching primer may be limited to this surface layer alone, producing a hybridized hypermineralized surface layer. Penetration of the self-etching primer into the underlying sclerotic dentin produced a hybridized complex containing a hybridized hypermineralized surface layer as well as a subsurface layer of hybridized intertubular dentin. Bacterial colonization of the lesion surface resulted in the formation of an additional zone of hybridized intermicrobial matrix over the surface of the lesions. Dentinal tubules remained blocked with sclerotic casts, and resin tags were rarely observed. Regional tensile bond strength results showed that the overall bond strength to natural sclerotic dentin was about 20% lower than sound cervical dentin, but was independent of the different locations within the lesions from which bond strength was evaluated. CONCLUSION: There were four factors that may have influenced the overall decrease in bond strength in natural cervical sclerotic lesions: a) the presence of a hybridized intermicrobial matrix together with entrapped bacteria may have weakened the bonds, b) inability of a self-etching primer to etch through a thick, hypermineralized surface layer, c) presence of a layer of possibly remineralized, denatured collagen at the base of the hypermineralized surface layer, and d) retention of acid-resistant sclerotic casts that obliterate the tubular lumina and prevent effective resin tag formation.

Acid Etching, Dental↗

PubMed2000

Self-contamination of deep dentin by dentin fluid.

PURPOSE: To compare, with the use of a resin replica technique, surface features of deep, acid-conditioned dentin from vital human molars that were anesthetized with an anesthetic: Group 1: without a vasoconstrictor (Mepivacaine 3%), and Group 2: containing a vasoconstrictor (Lidocaine 2% with 1:80,000 epinephrine). MATERIALS AND METHODS: 10 Class I cavities with dentin caries were included in each group. Following complete caries removal, a total-etch technique was performed with 32% phosphoric acid (Uni-Etch) for 15 s. After rinsing, each cavity was air-dried for 1 s, then a slow setting vinyl polysiloxane (President) impression was taken. As a control, impressions were taken from three additional cavities in teeth that were anesthetized with Mepivacaine 3% but not acid etched. A TEM-grade epoxy resin was used to prepare replicas from the impressions. Polymerized replicas were coated with gold and examined with a scanning electron microscope. RESULTS: In Group 1, fluid was visible leaving tubular orifices in all replicas. In addition, three were covered with a smooth, amorphous film that was different from the granular appearance of the smear layer in the control cavities. In Group 2, patent tubular orifices without fluid were observed in all specimens. Odontoblast process-like structures were seen from some dentin tubules.

Acid Etching, Dental↗

PubMed1999

Distribution of nanofillers from a simplified-step adhesive in acid-conditioned dentin.

PURPOSE: This in vitro study examined the interfacial ultrastructure of a nanofilled, simplified-step adhesive (Prime & Bond NT, Dentsply), to determine the distribution of nanofillers within the collagen network of the hybrid layer. MATERIALS AND METHODS: Twenty-four dentin discs were divided into two groups and bonded using two recommended conditioning techniques: Group I, NRC (Non-Rinse Conditioner), and Group II, Conditioner 36 (colloidal silica thickened 36% phosphoric acid). Following conditioning, a single coat of adhesive was applied and light-cured. Dentin discs were then bonded to form disc-pairs and processed for TEM examination. Demineralized, ultrathin sections were examined stained or unstained. Non-demineralized sections were used for STEM/EDX analysis of elemental distribution across the resin-dentin interface. In addition, four dentin discs were bonded with a generic adhesive (HEMA/TBBO) for TEM examination of stained collagen and proteoglycans. RESULTS: In unstained sections of both groups, nanofillers from the adhesive layer were congested around patent tubular orifices, but were not found within the interfibrillar spaces of the hybrid layer. EDX analysis of silicon (Si) showed predominant distribution within the adhesive layer and tubular orifices. Phosphorus (P) was present within the hybrid layer and adhesive layer in Group II. CONCLUSION: It is hypothesized that a) aggregation of the nanofillers within the adhesive resulted in filler clusters that are too large to infiltrate the interfibrillar spaces of the hybrid layer; and b) retention of ground substance within the demineralized intertubular collagen matrix may also have prevented the infiltration of the nanofillers.

Acid Etching, Dental↗

PubMed1998

Micromorphological spectrum of acid-conditioned dentin following the application of a water-based adhesive.

OBJECTIVES: The goal of this study was to illustrate the micromorphological spectrum along the resin-dentin interface when a water-based, dentin adhesive (Scotchbond Multi-purpose) was applied to acid-conditioned dentin under different dry and wet bonding conditions. METHODS: Twenty-eight 1 mm dentin discs were each conditioned with 10% maleic acid for 15 s. Twenty-four of these discs were randomly divided into four groups, based upon the status of the remaining surface moisture: Group I (30 s dry); Group II (3 s dry); Group III (visibly moist) and Group IV (overwet). They were bonded using Scotchbond Multi-purpose. The remaining four discs were bonded using an experimental water-based primer containing 35 vol.% HEMA (Group V). Laminated dentin disc pairs were prepared for transmission electron microscopic examination. RESULTS: In all groups, diffusion of the polyalkenoic acid copolymer component of the primer into acid-conditioned dentin was localized to the surface region of the hybrid layer. The remaining part of the hybrid layer (the subsurface region) appeared variable. In Group I (30 s dry), collagen fibrils were collapsed. In Group II (3 s dry) and Group III (visibly moist), stained collagen fibrils were surrounded by wide electron-lucent interfibrillar spaces. In Group IV (overwet), a marked diffusion gradient was observed representing dilution of part of the primer components. In addition, an electron-dense primer phase, containing electron-lucent globular domains was invariably observed, irrespective of the hydration status of the demineralized collagen matrix. This electron dense phase was absent when HEMA alone was used as the primer (Group V). SIGNIFICANCE: With the use of a water-based adhesive, one could briefly air-dry the acid-conditioned dentin and allow the water in the primer to rehydrate the collapsed collagen matrix, without the risk of incomplete hybridization or tubular seal along the resin-dentin interface. However, care should be exercised to minimize dilution of the water-soluble primer component.

Acid Etching, Dental↗

PubMed1998

Relation between water content in acetone/alcohol-based primer and interfacial ultrastructure.

OBJECTIVES: This study investigated the ultrastructure of the resin-dentine interface when a two-bottle primer system containing NTG-GMA (N(p-tolyl)glycine-glycidyl methacrylate) and BPDM (biphenyl dimethacrylate) was used with different concentrations of water as a part of the primer solvent: (I) an experimental version of All-Bond 2 with no water in primer A; (II) a commercial version of All-Bond 2 (Bisco, Itasca, IL, USA) with 5% water in primer A; and (III) a former version of All-Bond 2 with 17% water in primer A. METHODS: Thirty-six 1-mm thick dentine discs prepared from third permanent molar teeth were each conditioned with 10% phosphoric acid for 20 s and rinsed for 20 s. They were randomly divided into three groups: Group A, conditioned dentine surface air-dried for 30 s; Group B, air-dried for 3 s; and Group C, blot-dried so that the dentine surface remained visibly moist. The three categories of primers were applied to each disc in 8-10 coats, resulting in nine sub-groups. Discs in each sub-group were bonded together to form disc-pairs using a chemical cure resin, demineralized in ethylene diamine tetraacetic acid (EDTA) and prepared for transmission electron microscopic examination. RESULTS: With the use of the water-free primer version, sub-optimal hybridization was observed whenever dentine was dried prior to bonding (Groups IA and IB). In the 5% water version, prolonged desiccation resulted in compromised hybridization (Group IIA), while resin globules were observed on the surface of the hybrid layer when a moist technique was employed (Group IIC). In the 17% water version, surface blisters and globules characteristic of the 'overwet phenomenon' were observed in Groups IIIB and IIIC. CONCLUSION: Between the two extremes of a morphological spectrum of bonding conditions, the different primer versions exhibited different sensitivity ranges. There was a shift in the 'window of opportunity' for optimal hybridization and tubular seal depending on the water content of the primer system investigated.

Acetone↗

PubMed1997

The overwet phenomenon in two-component acetone-based primers containing aryl amine and carboxylic acid monomers.

OBJECTIVES: The overwet phenomenon was first reported when a moist bonding technique was used with an earlier commercial version of All-Bond 2 (Bisco) that contained BPDM in primer B. This study investigated whether ultrastructural features of the overwet phenomenon could also be detected in other commercially available two-component acetone-based primers containing BPDM, PMDM and PMGDM, as well as an experimental two-component primer containing DSDM. METHODS: Thirty 1 mm dentin discs prepared from third molars were each conditioned with 10% H3PO4 for 20 s and rinsed for 20 s. They were randomly divided into 5 groups: Group I (Bond-It, Jeneric/Pentron:PMGDM); Group II (Wet Bond, Chameleon Dental Products:PMGDM); Group III (Tenure S, Den-Mat:PMDM); Group IV (present commercial version of All-Bond 2, Bisco:BPDM) and Group V (Experimental two-component primer system containing DSDM in primer B). Following a moist bonding technique using the respective system, discs from each group were further bonded together to form three disc pairs using a chemical-cured resin. Bonded disc pairs were demineralized in EDTA and processed for TEM examination. For this ultramicroscopical study, results such as the features of the overwet phenomenon were analyzed by visual inspection of the specimens in each group (n = 12). RESULTS: Isolated blister-like spaces of variable dimensions were observed within the primer layer in all groups and possessed the following characteristics: 1) a layer of resin-impregnated dentin was always present along the base of the primary blister; 2) surface primer globules, sometimes containing secondary blisters, were identified within these primary blisters; 3) dentinal tubules within the blister-like spaces were not completely sealed; 4) primer globules were circumscribed by a halo of fine kinked strands of material. SIGNIFICANCE: Although the technique of moist bonding is based on valid biological principles, incorporation of resin monomers that are immiscible with water rendered the application of current two-component, acetone-based primers very technique-sensitive in terms of tubular seal, when used on moist, acid-conditioned dentin. Further studies should be directed at elimination of this type of oil-in-water (O/W) "macroemulsion" formation through optimal micellar solubilization of these resin monomers in water.

Acetone↗

PubMed1997

Ultrastructure of the resin-dentin interface following reversible and irreversible rewetting.

PURPOSE: This study investigated the effect of reversible and irreversible rewetting on the application of One-Step, single-bottle, water-free, acetone-based primer/adhesive. MATERIALS AND METHODS: Thirty 1 mm dentin discs prepared from third molars were each conditioned with 10% H3PO4 for 20 seconds and rinsed for 20 seconds. They were randomly divided into five groups: Group 1 (positive control): conditioned dentin bonded visibly moist; Group 2: bonded after drying for 3 seconds; Group 3: drying for 3 seconds and rewetting with distilled water; Group 4 (negative control): drying for 3 seconds, stored in 8% glutaraldehyde for 15 minutes, rinsed with distilled water and dried for 3 seconds; and Group 5: drying for 3 seconds, stored in glutaraldehyde for 15 minutes, rinsed with distilled water and bonded visibly moist. One-Step was applied in two coats according to the manufacturer's recommendation and discs in each group were further bonded together to form a disc-pair using a chemical cure resin, demineralized in EDTA and prepared for TEM examination. RESULTS: Complete resin infiltration into the zone of demineralized dentin was observed in Group 1 and 3. In Group 2, resin infiltration was limited to the surface and base of the demineralized network apparently along the lateral branches of the dentin tubules. A middle zone of suboptimal infiltration was observed. In Group 4 and 5, minimal resin infiltration was only observed along the base of the demineralized network upon their fixation in a collapsed state with glutaraldehyde.

Collagen↗

PubMed1996

Micromorphological spectrum from overdrying to overwetting acid-conditioned dentin in water-free acetone-based, single-bottle primer/adhesives.

OBJECTIVES: The goal of this study was to illustrate and define the micromorphological spectrum which exists at the resin-dentin interface when two water-free, acetone-based, single-bottle primer/adhesive systems (One-Step, Bisco, and Prime & Bond, Dentsply/L.D. Caulk) were applied to acid-conditioned dentin under different dry and wet bonding conditions. METHODS: Forty-eight 1 mm dentin discs were each conditioned with 10% phosphoric acid and rinsed for 20 s. They were randomly divided into 4 groups based upon the status of the remaining surface moisture; Group I (30 s dry); Group II (3 s dry); Group III (blot dry) and Group IV (overwet). Bonded dentin disc pairs were then demineralized in EDTA and embedded in epoxy resin for transmission electron microscopic examination. RESULTS: The micromorphological spectra of the two bonding systems were essentially similar. Both were effected by even mild desiccation (3 s), resulting in incomplete intertubular resin infiltration. Optimal intertubular resin infiltration was achieved when the collagen network was kept moist and appeared relatively unaffected by the presence of excess surface moisture. On the other hand, intratubular resin infiltration was severely compromised in the presence of excess water within the dentinal tubules and at their openings in the dentin surface. The continuity of the resin layer deteriorated; blister-like spaces formed on the dentin surface and resin globules were found around the tubular orifices and on the surface of the hybrid layer. In addition, a complex phase separation pattern was observed in Prime & Bond that was characterized by phase inversion in the presence of surface moisture. SIGNIFICANCE: The "window of opportunity" for optimal interfacial integrity for both water-free systems appeared to depend upon keeping the demineralized collagen network moist, coupled with the complete evaporation of excess and "displaced" water from tissues prior to light-curing the prime/adhesives.

Acetone↗

PubMed1996

Resin permeation into acid-conditioned, moist, and dry dentin: a paradigm using water-free adhesive primers.

Preservation of the morphological integrity of demineralized dentin collagen in its hydrated state may account for the success observed in wet-bonding procedures. This study investigated the micromorphological differences between moist- and dry-bonding techniques with the use of: (a) Aelitebond, an alcohol-based, water-free, single-component dentin adhesive primer system; and (b) a water-free, acetone-based experimental primer similar to the acetone-based, water-containing All-Bond 2, a two-component primer system. In the wet groups, acid-conditioned dentin surfaces were blotted so that they remained visibly moist prior to bonding. In the dry groups, dentin surfaces were air-dried for 30 sec. Following the bonding procedures, dentin discs in each group were laminated together by means of a chemical-cure resin and processed for scanning electron microscope (SEM) and transmission electron microscope (TEM) examination. Conditioning with 10% H3PO4 for 20 sec. produced complete demineralization of the outer dentin. In the wet groups, banded collagen and interfibrillar spaces could be observed at the surface of the acid-conditioned dentin. Complete wetting of the loosely arranged collagen fibrils by the resin resulted in the formation of a hybrid layer. In the dry groups, only a very thin hybrid layer was observed on the dentin surface, along the walls of the tubules, and along the course of their lateral branches. The absence of banded collagen and interfibrillar spaces within these areas suggested the existence of a collapsed dentin matrix along various liquid-vapor boundaries that restricted resin permeation into the subsurface intertubular matrix, producing an incompletely infiltrated "hybridoid region".

Dental Bonding↗

PubMed1996

Quantitative contribution of the collagen network in dentin hybridization.

PURPOSE: To determine the quantitative contribution of dentin hybridization to bonded assembly strength and demonstrate the micromorphology of the interface with and without collagen present. MATERIALS AND METHODS: Four groups of 10 molar teeth were finished to a 320 grit dentin smear layer. Two groups served as controls and two experimental groups were subjected to collagenase digestion of the collagen exposed by acid conditioning. All-Bond 2 and Amalgambond were used to bond Bisfil and Epic resin composite, respectively. Stored in water at 37 degrees C for 24 hours the assemblies were tested in a shear mode at a crosshead speed of 5 mm/minute. Means and standard deviations were subjected to analysis for statistical significance. Twenty four teeth in four groups were examined by scanning (SEM) and transmission electron microscopy (TEM) for the relationship between resin and conditioned dentin with and without the collagen network. RESULTS: All-Bond 2 and Amalgambond controls were 28.41 +/- 3.9 and 19.04 +/- 5.96 MPa, collagenase-treated groups scored 26.43 +/- 2.90 and 19.70 +/- 4.25 MPa respectively. No significant difference existed between the control and experimental groups. SEM showed an intertubular collagen network with patent tubules and a pronounced porous, irregular dentin topography following collagen digestion. A distinct hybrid zone and tubular penetration was observed but the collagenase-treated specimens showed only resin in the tubules and their lateral extensions. TEM confirmed the absence of a distinct hybrid zone in the collagenase groups with a tight, gap-free junction between the resin and the undemineralized dentin. An electron dense zone (< 50 nm) at the leading edge of conditioning was observed for All-Bond 2 and Amalgambond groups. It was concluded that the resin-reinforced or hybridized, collagenous network does not detract from, nor contribute any significant quantitative value per se to dentin bonding with the systems tested.

Acid Etching, Dental↗

PubMed1996

The overwet phenomenon: a transmission electron microscopic study of surface moisture in the acid-conditioned, resin-dentin interface.

PURPOSE: To identify ultrastructural features resulting from possible primer-water interaction when a two-bottle, acetone- and alcohol-based dentin adhesive (All-Bond 2) was applied to acid-conditioned dentin in the presence of excess water. MATERIALS AND METHODS: Three groups (3-second dry, visibly moist, overwet), each comprising eight dentin discs prepared from human third molars, were established and bonded with All-Bond 2 under different degrees of surface moisture. Variations in the ultrastructural appearance of the resin-dentin interface from laboratory demineralized and epoxy resin embedded disc pairs were examined either with en bloc ruthenium red pre-staining alone or further stained with uranyl acetate and lead citrate. RESULTS: Displacement of water by the volatile primer solvents resulted in the formation of a layer of resin-impregnated dentin in the three groups. Interaction of the primer with water following the evaporation of the volatile primer solvents resulted in phase separation of the primer components. Ultrastructural features observed within the previously water-filled blister-like spaces on the dentin surface in the visibly moist and overwet groups recapitulated what was observed within partially water-filled dentin tubules in the 3-second dry group. The overwet phenomenon appeared to be a result of emulsion polymerization, involving irreversible interaction of water-soluble bifunctional primer components with those that are water-immiscible, through the formation of micelles, resulting in the absence of total interfacial integrity.

Acid Etching, Dental↗

PubMed1996

The overwet phenomenon: a scanning electron microscopic study of surface moisture in the acid-conditioned, resin-dentin interface.

PURPOSE: To study with the scanning electron microscope the interfacial phenomenon that occurred in the presence of excessive surface moisture following the application of an acetone-based adhesive to acid-conditioned dentin. MATERIALS AND METHODS: Specimens consisted of flat dentin discs that were divided into three groups based upon the status of remaining surface moisture: (1) 3-second dry group, (2) blot-dry group, with the conditioned dentin surface remaining shiny as opposed to matte, and (3) overwet group: an additional 40 mL of distilled water spread thin on the dentin surface after blot-drying. Polished resin-dentin interfaces were brought into relief using plasma-etching and examined without further embedding. RESULTS: Although a hybrid layer was observed in all three groups, there was (1) a sequential deterioration of the bonded assembly along the hybrid layer-resin interface, and (2) loss of complete tubular seal as the quantity of surface moisture increased. Intratubular resin globules were observed beneath short resin plugs in the 3-second dry group. Small, isolated blister-like spaces, trapped within the resin layer, were observed along the surface of the hybrid layer in the blot-dry group, while similar, but larger spaces were found in the overwet group. The blister-like spaces, which were often continuous with incompletely sealed tubular orifices, were partially filled with extraneous resin globules dispersed within an amorphous matrix.

Acid Etching, Dental↗