Early and intermediate time response of the dental pulp to an acid etch technique in vivo.

PURPOSE: To present the ultrastructural features of the pulpal responses, following the application of All-Bond 2 to acid-conditioned, deep, unexposed coronal dentin and exposed pulps in human teeth. MATERIALS AND METHODS: Cylindrical Class V cavities were prepared in human premolars. In the non-exposure group an attempt was made to prepare the floor of the cavity to +/- 0.5 mm from the pulp. In the exposure group, the pulps were intentionally exposed. After hemostasis, the preparation was etched with 10% phosphoric acid. The teeth were restored with All-Bond 2. Histological evaluation was done at 0-7, 28-35, and > 90 days. RESULTS: A typical connective tissue response to injury was observed in the majority of the specimens. Irreversible injury to the odontoblasts closest to the site of cavity preparations resulted in the death of these cells. This was followed by an early neutrophilic response, a subsequent macrophage response and a fibroblastic response that led to the deposition of either reparative dentin or calcific bridge formation by odontoblast-like cells. However, another notable feature was the consistent observation of resin particulates within the dentin-pulp complex. These resin particulates could have been indirectly introduced into the pulp through the pertubation of the junctional complexes or the death of the odontoblasts. They may also enter the pulp directly through a pulpal exposure. In some specimens, the presence of these resin particulates appeared to have triggered a foreign body response, characterized by the presence of a mononuclear inflammatory infiltrate as well as the appearance of multinuclear giant cells. The persistence of unresolved chronic inflammation was associated with the lack of calcific bridge formation in these specimens.

Root-surface caries in rats and humans: inhibition by a non-antimicrobial property of tetracyclines.

The incidence of root caries has been found to increase as the population ages and as edentulism becomes less prevalent due to improved dental awareness and care, and as exposure of roots due to gingival recession has also increased in the elderly. The mechanism of root caries is thought to be mediated by both bacterial and mammalian proteases produced by plaque and the periodontal tissues, respectively. In the current study, a rat model of periodontal disease was used in which gnotobiotic rats were infected intra-orally with a periodontal pathogen (P. gingivalis). Infecting the rats with P. gingivalis increased the collagenase activity in the gingival tissue in association with severe alveolar bone loss. Treating P. gingivalis-infected rats with doxycycline or CMT-1 prevented the destruction of the periodontium by MMPs, thus preventing exposure of roots to subgingival bacterial plaque and host tissue collagenases and the subsequent development of root caries. In addition, a low-dose doxycycline (LDD, 20 mg bid, non-antimicrobial dose) for 3 months was used in humans predisposed to increased root caries as the result of heavy use of smokeless (chewing) tobacco, causing gingival recession, subgingival plaque accumulation with Gram-negative bacteria, increased gingival crevicular fluid flow (GCF), and elevated GCF collagenase. Daily administration of LDD in smokeless tobacco patients reduced the GCF collagenase and prevented the further development of root caries.

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.

Current concepts on adhesion to dentin.

This review examines fundamental concepts in bonding to dentin. Emphasis is placed on the structure and permeability characteristics of dentin and how they may influence its interaction with adhesive resin. Several new techniques to examine the interfaces between resin and dentin are reviewed along with some of their limitations. The advantages and disadvantages of acid etchants/conditioners vs. self-etching conditioners/primers are discussed. The problems of matching the surface tension of resin-bonding systems to the surface energy of the substrate are reviewed in terms of wetting the various components of dentin. The problems associated with matching the permeability of intertubular dentin to the diffusibility of bonding reagents are explored. Speculation is advanced on how to ensure polymerization and wetting of dentinal collagen. Theoretical problems associated with dentin bonding and with bond testing are reviewed to encourage future research in this rapidly developing area.

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.

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.

Microleakage of Class V composite, resin sandwich, and resin-modified glass ionomers.

PURPOSE: To evaluate in vitro the extent of microleakage of Class V cavities restored with composite, and resin-modified glass ionomers. MATERIALS AND METHODS: Class V cavities were prepared in 35 extracted teeth and randomly divided into seven groups of five teeth each (10 restorations in each group). Group 1: Scotchbond Multi-Purpose Adhesive (SMP) and restored with Z100 resin placed with an incremental technique, Group 2: Lined with GC Fuji lining LC and restored with SMP and Z100. Group 3: Based with Fuji II light-cured glass ionomer restorative and restored with SMP and Z100. Group 4: Lined with Vitrebond and restored with SMP and Z100. Group 5: Based with Vitremer and restored with SMP and Z100. Group 6: Restored with Fuji II LC. Group 7: Restored with Vitremer. The teeth were subjected to thermocycling, stained with silver nitrate, then longitudinally sectioned. Dye penetration at the tissue/restoration interface was scored based upon the extent and location of the precipitated silver. RESULTS: All groups demonstrated minimal or no microleakage at both the enamel and gingival sites.

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.

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".

The overwet phenomenon: an optical, micromorphological study of surface moisture in the acid-conditioned, resin-dentin interface.

PURPOSE: To evaluate the morphological effect of different degrees of surface wetness on "wet bonding" upon the acid-conditioned, resin-dentin interface using an acetone-containing adhesive system (All-Bond 2). MATERIALS AND METHODS: Dentin surfaces were conditioned with 10% phosphoric acid (20 seconds), washed and air dried (3 seconds) or blot dried. RESULTS: The surfaces were characterized by the formation of an intact layer of resin impregnated dentin. Dentin tubules were sealed with solid cores of primers commonly below which were intratubular primer globules. Excess moisture on the dentin surface resulted in the creation of blister-like spaces at the primer-dentin interface. A layer of resin-impregnated intertubular dentin was present and below such spaces were incompletely sealed tubules. Primer globules were also observed on the dentin surface. The presence of microscopic voids at the primer-dentin interface may offer a morphological explanation for the published decrease in bond strength when this system was applied in the presence of excessive surface moisture.

Variability in microleakage observed in a total-etch wet-bonding technique under different handling conditions.

Using a stereoscopic clearing protocol and scanning electron microscopy, we investigated the extent and nature of microleakage in a total-etch, current-generation dentin adhesive by a wet-bonding technique under different handling conditions. The hypotheses were that inadequate light curing of the primer or incomplete drying of the primer solvent might adversely affect the sealing ability of an acetone-containing adhesive system. The study consisted of three experimental groups: (I) a control group with an adequate light source and with the primer solvent completely dried; (II) an "inadequate-light" group; and (III) an "incomplete evaporation of primer solvent" group. The extent of microleakage after silver staining and clearing of the specimens was scored based on a modified five-point scale. Nonparametric statistical analysis (Kruskal-Wallis ANOVA) followed by a multiple comparison test (Dunn test) indicated significant differences among the three groups (p < 0.05). SEM examination of the restorative interface revealed that microleakage appeared to be initiated from the bonding resin-hybrid layer interface in all three groups, representing the weak link in the adhesive system. In addition, microleakage was characterized by 5 zones, each delineating a stage in a continuous array of progressively deleterious microleakage patterns variously distributed among the three groups. It was suggested that, while the bonding resin-hybrid layer interface represented the intrinsic weakness in an already much improved dentin adhesive, extrinsic factors such as the adequacy of the curing light and, more importantly, complete removal of the primer solvents can and should be avoided to preserve the structural integrity of the marginal seal.

A method for microleakage evaluation along the dentin/restorative interface.

PURPOSE: To present a simple non-abrasive protocol in conjunction with the silver-staining method, enabling unobstructed visualization of well-defined microleakage patterns within the demineralized dentin-restorative interface. MATERIALS AND METHODS: Class V preparations were made with an occlusal margin on bevelled enamel and a gingival margin on dentin/cementum. After restoration with All Bond 2/P-50 and Scotchbond 2/Silux, storage in water at 37 degrees C for 7 days and thermocycling 300 times between 5 degrees and 55 degrees C, the specimens were placed in silver nitrate solution. After silver fixation, demineralization and clearing in methyl salicylate, silver stain location was scored ordinally. In addition, a three dimensional portrait of leakage pathways was illustrated using photographic and computer digitization. RESULTS: The Wilcoxon signed-rank test showed that the extent of silver penetration before and after acid demineralization was not significantly different (P > 0.05). This study also confirmed that microleakage is not uniform along the circumference of a restorative margin. Although the protocol is insensitive to microleakage occurring solely within enamel, the predominant concern over that occurring within dentin, in particular along the cervical restorative border, renders it a serviceable alternative for future investigation of the integrity of the marginal seal from clinically restored in vivo specimens.

Effect of long-term water storage on dentin bonding.

PURPOSE: To determine the effect of long term water storage on assembly bond strength and interfacial integrity of resin composite bonded to dentin. MATERIALS AND METHODS: Four groups, each containing 10 molar teeth, were established to measure the shear strength of All-Bond 2 and Amalgambond bonded P50 resin composite assemblies at 24 hours and after 6-month water storage at 37 degrees C. An additional four groups of similarly bonded Class V restorations were subjected to the same immersion periods. Marginal leakage was determined using eosin dye and the restoration interface was observed using polyvinyl siloxane impressions to determine gap location. RESULTS: The shear strength values (MPa) for All-Bond 2 were 32.68 +/- 7.12 and 23.29 +/- 5.77 at 24 hours and 6 months respectively. The mean values for Amalgambond were 26.03 +/- 5.94 and 12.90 +/- 6.90. The difference between the values at different immersion times was statistically significant (P < 0.05). There was no evidence of dye leakage in any of the teeth. No gaps were found at the margins of the restorations correlating with the absence of microleakage. Gaps were found commonly at the floor of the Amalgambond restorations.

Altered tissue contribution to interfacial bond strength with acid conditioned dentin.

PURPOSE: To measure the shear bond strength of resin composite to dentin using three fourth generation bonding agents in combination with three different acid treatments. One such treatment was followed by sodium hypochlorite. The purpose was to determine the contribution which the collagen rich, demineralized zone made to bond strength. MATERIALS AND METHODS: Three groups, representing (1) All Bond 2/BisFil, (2) Optibond Dual Cure/XRV and (3) Scotchbond Multi-Purpose/Z100, contained four sub-groups each comprised of 10 caries-free molar teeth whose dentin was exposed in a transverse mid-coronal plane. Dressed with 320 grit, wet silicon carbide paper, the dentin surface in each sub-group was conditioned with 10% maleic acid (15 seconds), 10% phosphoric acid (20 seconds), 2.5% nitric acid (60 seconds) and 10% phosphoric acid (20 seconds) followed by 5% sodium hypochlorite (120 seconds). The bonded resin composite assemblies were stored in water at 37 degrees C for 24 hours and then subjected to shear force at a crosshead speed of 5 mm/minute until failure. RESULTS: The mean and standard deviation values derived for the groups were not statistically different from each other (P < 0.05). It was concluded that the type of conditioning agent was not a factor in achieving optimal bond strength for the system tested. Furthermore, it was tentatively concluded that the collagen-rich zone offered no direct, quantitative contribution to the interfacial bond strength which is probably derived from complete resin diffusion into the porous, partially demineralized dentin below.

Adhesive restorations with amalgam: guidelines for the clinician.

The adhesive amalgam restoration technique combines the good properties of amalgam with the principles of tooth structure preservation and marginal seal inherent to adhesive materials. In spite of lack of longitudinal data, results of early clinical and laboratory tests are encouraging. If the present research is substantiated by clinical confirmation of their results, bonded amalgam restorations will become routine. The purpose of this article is to present a brief literature review on adhesive amalgam restoration and to introduce guidelines for its use.

Dentin bond strength after air drying and rewetting.

The purpose of this study was to investigate the effect of air drying and remoistening of dentin on resin composite bond strength and to determine the extent to which the outermost, collagenous network and surface area of chemically conditioned dentin contributed to interfacial strength. Three components made up the experimental design: The first component comprised 12 experimental groups each containing 10 caries-free molar teeth. Shear bond strength values with dentin were measured for conditioned and non-conditioned dentin to which All-Bond 2 and BisFil were applied. The following values (MPa) were obtained for the groups conditioned with 10% phosphoric acid for 20 seconds: Group 1 (wet control) 24.20 +/- 2.03; Group 2 (10 seconds dried) 19.83 +/- 5.42; Group 3 (30 seconds dried) 11.56 +/- 4.93; Group 4 (10 seconds dried, 5 seconds. remoistened) 25.38 +/- 3.89; Group 5 (30 seconds dried, 5 seconds, remoistened) 24.66 +/- 4.54; Group 6 (5% NaOCl/wet) 25.97 +/- 3.61. For the non-conditioned groups the values were: Group 7 (wet control) 21.54 +/- 4.07; Group 8 (10 seconds dried) 14.62 +/- 3.55; Group 9 (10 seconds dried, 5 seconds remoistened) 16.95 +/- 4.04; Group 10 (5% NaOCl/wet) 13.67 +/- 4.39; Group 11 (air abrasive action) 18.78 +/- 3.62; Group 12 (air abrasive/5% NaOCl) 19.87 +/- 2.03.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemically conditioned dentin: a comparison of conventional and environmental scanning electron microscopy findings.

OBJECTIVES: The purpose of this study was to compare the structure of acid-conditioned dentin in its wet and dry state. METHODS: Using conventional and environmental scanning electron microscopy, conditioned dentin was examined in a wet, air-dried and critical point-dried state. Six different treatments were used including citric, maleic, nitric, oxalic and phosphoric acids in their commercial formulations and applied in accordance with manufacturer's instructions. RESULTS: Loss of moisture from acid-conditioned dentin through simple air drying and drying under controlled conditions of environmental scanning microscopy resulted in morphological alteration of the fibrous, collagenous structure. Critical point drying preserved the fibrous integrity of the outer mineral-depleted zone. This observation was true for all the acids used. SIGNIFICANCE: While the ultrastructure of dentinal collagen may be chemically stabilized or relatively unaltered by acid conditioning, it is nonetheless subject to morphological degradation and collapse during water loss. Only critical point drying can control the interfacial stress accompanying water transport and loss at the fiber boundary. Confirming previous observations, this study supports the concept of maintaining the moist state of dentin and the morphological integrity of the collagen so as to facilitate optimal resin infiltration in the bonding procedure.

A new method to test the cohesive strength of dentin.

The cohesive plateau theory states that the strength at a bonded interface should equal the strength, cohesively, of the substrate with which it is bonded. A new method was developed to test cohesive strength of dentin so as to offer an opportunity to compare the data against shear bond strength values of commercially available dentinal bonding agents using the same test assembly. The method applied a shear force to a standard circular column of dentin continuous with the tooth from which it was cut with a tubular diamond drill. The mean cohesive strength of dentin in the shear mode, based on 30 specimens, was 36.18 +/- 6.81 MPa.

Structural evidence of a sealed tissue interface with a total-etch wet-bonding technique in vivo.

The resin-dentin interface of in vivo specimens restored with the All-Bond 2 system by use of a total-etch wet-bonding technique on vital deep human dentin was investigated by: (a) SEM examination of cryofractured specimens; (b) SEM examination of acid-rinsed, highly polished, embedded specimens; and (c) TEM examination of demineralized ultrathin sections. Ultrastructural features that were pertinent to the formation of an effective clinical seal were characterized. It is suggested that the establishment of an effective seal of the patent dentinal tubules following total etching is accomplished by: (1) the formation of an outer zone of a solid resin plug surrounded by a circumferential cuff of resin-impregnated dentin; and (2) the formation of an inner zone of a hollow resin sheath with resin globules along the internal walls of the tubules, closely adapting to the odontoblast process. The structural appearance and functional implications of these two zones were strikingly similar, with the sealing of exposed dentinal tubules in arrested carious lesions or cervical abfraction lesions. It appeared that there is a common denominator in physiologic isolation defense mechanisms and the total-etch, wet-bonding technique in the All-Bond 2 system in preserving the biological and morphological integrity of the pulpo-dentinal complex.