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PubMed1994

Cytotoxicity of components of resins and other dental restorative materials.

Cytotoxicity testing of dental restorative materials must be viewed as an assessment of hazards, that is the potential of the material to cause pulpal problems. In this context, composites, glass ionomers, amalgams, zinc-based cements and peroxide bleaching agents are all possible hazards to the pulp. The risks that these materials will cause pulpal toxicity in vivo can be partly estimated by assessing the cytotoxicity of the substances which are released from these materials in vitro and comparing these cytotoxic concentrations with those concentrations that are present in vivo. The resin components of composites, metal ions and hydrogen peroxide, all of which are released from dental restorative materials, have been shown to be cytotoxic in vitro in sufficient concentrations. The potencies of these substances are quite diverse. However, the cytotoxicity of these substances in usage tests, and therefore the risks of pulpal toxicity, depends on their ability to diffuse through the dentine and accumulate in the pulp.

Animals↗
PubMed1994

Effect of dentine on release of TEGDMA from resin composite in vitro.

Triethylene glycol dimethacrylate (TEGDMA) is a component of some resin composites which contributes to their cytotoxicity. The presence of dentine between resin composite and test cells reduces the cytotoxicity in vitro. To determine why dentine has this protective effect, the diffusion of TEGDMA from a composite resin through dentine to the pulp space was compared with release directly into aqueous solution in vitro. Both release rate and total cumulative release of TEGDMA for the two groups, at times up to 100 days, were determined using reversed-phase HPLC. Release rate directly into water was highest in the minutes immediately after immersion and declined thereafter. However, in the tooth model, using an equivalent mass and surface area of composite resin, no TEGDMA was detectable in the pulp space until 43 min after restoration placement. The rate of diffusion through dentine from that time until day 1 was less than 1% of the highest (initial) direct release rate. The rate declined thereafter. It is relevant, however, that by day 3 the total cumulative release of TEGDMA through dentine was 60% of the direct release. Dentine therefore appears to exert its protective effect principally by retarding or 'damping' the initial high release of TEGDMA to a substantial degree.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1994

Influence of dentine on the pulpward release of eugenol or acids from restorative materials.

The diffusion gradient which develops across dentine and the clearance into the capillary circulation at the pulpal side of the tissue both reduce the concentration of potential toxins applied to dentine, thus protecting pulpal cells. The data presented on eugenol indicates that when release of a potential toxin from a solid material is hydrolytic the limited wetness of dentine, i.e. the limited availability of water for hydrolysis, contributes to the protective effect of the tissue. The data on strong acids indicates that a third protective mechanism, buffering by hydroxyapatite, can contribute to dentine's protective effect in situations where the potential toxin is strongly acid. There may be other mechanisms by which dentine protects the pulp against chemical toxins from restorative materials. However, the three described: diffusion limitation; limited wetness for hydrolysis; and buffering by dentinal hydroxyapatite, appear to allow the relatively safe use of a wide range of tooth restorative materials.

Acids↗
PubMed1997

The influence of endodontic treatment upon periodontal wound healing.

The interrelationship between periodontal and endodontic disease has aroused much speculation, confusion, and controversy. Pulpal and periodontal problems are responsible for more than 50% of tooth mortality today. Diagnosis is often difficult since these diseases have been studied primarily as separate entities. The toxic substances of the pulp may initiate periodontal defects through canal ramifications and patent dentinal tubules, thus impairing wound healing in regenerative procedures. Although no studies exist addressing the direct effect of pulpal infection on the outcome of guided tissue regeneration (GTR) procedures, several studies do indicate that pulpal status may play a significant role toward the end results of GTR. This review article discusses the potential influence of endodontic treatment on the long-term outcomes of GTR. Potential pathways between the pulp and periodontal ligament, which may be responsible for the failure of the regeneration of new periodontal attachment apparatus, are explored. Examination and review of the clinical and research findings in the literature relating to perio-endo lesions are made to demonstrate that a negative influence may exist between GTR outcomes and the status of the pulp.

Bacterial Infections↗
PubMed1988

Cytotoxicity of dental composites and other materials in a new in vitro device.

Several in vitro methods have been developed over the years to improve correlation between screening tests and usage tests of dental restorative materials. Pulpal responses to restorative materials in usage tests are usually less severe than are responses of cells either in vitro screening tests or in implantation tests where there is direct contact between experimental materials and vital cells. In the "in vitro pulp chamber" device tested in the present study, dentin disks were interspersed between composite resins (as well as other dental materials) and the medium which served as the nutrient source for the Balb/c 3T3 test cell system. The dentin restricted the diffusion of materials into the "pulp chamber" to clinically relevant levels. The light-cured composite resins (Fulfil and P30), caused depression of protein synthesis only during the first 24 h postpolymerization, when placed on 0.5 mm but not 1.5 mm thick dentin dishes. The chemically-set composites (SILAR and P10) caused no significant inhibition of protein synthesis (as compared to negative controls) at any postpolymerization time on either 0.5 mm or 1.5 mm dentin disks.

Animals↗
PubMed1989

Aluminum oxalate/glycine solutions as pretreatment in the Gluma bonding system.

Dentin and enamel surfaces were treated with solutions of aluminum oxalate (AO), the pH of which was adjusted by glycine. Gluma as well as an enamel bonding agent were applied to the surfaces before the placement of a composite resin. On shear bond testing, there was obtained a strong adhesion that was influenced by the pH of the AO solutions. Dentin and enamel specimens for examination by scanning electron microscopy (SEM) were also prepared and treated as above. Enamel specimens showed a very definite etching pattern, and on the dentin surfaces a precipitate was observed. The amount of this product seemed to decrease as the pH increased.

Aldehydes↗
PubMed1993

The structure of dentin surfaces exposed for bond strength measurements.

The structure of dentin on three different levels, near enamel, central, and deep dentin, was examined. The solid area available for bonding was studied in a scanning electron microscope (JSM 840) connected to a computer-assisted image analysis instrument (IBAS 2). The number of tubule openings per unit area (frequency) and the area percentages of these tubule openings were recorded. Three dentin disks were obtained from both buccally and occlusally located dentin of a single tooth (third molars were used), and the two deeper levels were each 1.25 mm deeper than the level above. The disks showed an increasing number of tubules with an increasing diameter the deeper into the dentin they were cut. Disks from the occlusal part of the tooth showed, in general, a higher number and area percentage of tubule openings than the corresponding disks from the buccal part. The variation across each disk was also larger for disks from the occlusal part than from the buccal part of the tooth. This variation increased with increasing depth of dentin. The most solid dentin with the lowest variation was found in superficial disks of buccally located dentin.

Dental Bonding↗
PubMedDate not supplied

Facilitated diffusion by iontophoresis of vasoactive agents to the rat incisor pulp.

The use of iontophoresis for facilitated diffusion of vasoactive agents into the dental pulp was investigated in lower incisor teeth of anaesthetized rats. Acetylcholine, carbachol and noradrenaline were iontophoresed with anodal and sodium nitroprusside with cathodal direct current through a superficial dentin exposure. Pulpal blood flow was measured with laser Doppler flowmetry. Current intensities below 100 microA of both polarities, using sodium chloride as a medium, caused no or minor afferent nerve-induced vasodilation, but excited sympathetic fibres of the pulp in a current-dependent manner. The current threshold for facilitated diffusion of acetylcholine was about 20 microA. The vascular responses to the cholinergic and noradrenergic drugs appeared within a minute after the onset of current and they were abolished by systemic administration of atropine and phenoxy benzamine, respectively. Iontophoresis of acetylcholine (40-100 microA for 20-120 s) caused a 3-fold increase of pulpal blood flow which was not dose-dependent; carbachol provoked a high-magnitude, long-lasting vasodilation and so did sodium nitroprusside. Noradrenaline caused a long-lasting vasoconstriction. In denervated rats iontophoresis of carbachol had effects similar to those seen in intact animals. None of the drugs used locally had any effect on systemic blood pressure. The results of this study indicate that iontophoresis can be used for delivery of vasoactive agents from an exposed dentin surface into the pulp in sufficient quantity to elicit drug-specific local vascular responses without causing systemic vascular effects.

Acetylcholine↗
PubMedDate not supplied

The blocking effect of iontophoretic administration of lidocaine on neurogenic vascular reactions in rat dental pulp.

The blocking effect of lidocaine on nerve-induced vascular reactions was investigated in lower incisor teeth of anaesthetized rats. Pulpal blood flow was measured with laser Doppler flowmetry. Monopolar electrical stimulation of the rat incisor evoked a biphasic vascular response: an initial vasoconstriction was followed by a long-lasting vasodilation. Iontophoresis of lidocaine on a superficially exposed dentin surface with 60 microA of anodal direct current for 20 min blocked almost completely the stimulus-induced blood flow increase for about 25 min without any systemic effects. Iontophoresis of lidocaine with 40 microA for 20 min was almost without effect. Topical application of a mixture of lidocaine and prilocaine (25 + 25 mg/ml) in deep dentinal cavities was also without effect on the neurogenic reactions. Intravenous administration of lidocaine at 5 and 10 mg/kg in rats pretreated with phenoxybenzamine reduced the stimulus-induced increase in blood flow by an average of 29% and 54%, respectively, whereas the remaining alpha-adrenoceptor resistant vasoconstriction was not influenced. The present results show that iontophoresis of lidocaine on exposed dentin blocks nerve-induced vascular responses without causing systemic effects.

Anesthetics, Local↗
PubMed2004

The effect of a self-etching primer on the continuous demineralization of dentin.

Self-etching primers (SEP), used for adhesion of resin restorations, contain an acidic monomer that is not rinsed off after application; therefore, residual acid could further demineralize dentin, jeopardizing adhesion. This study evaluated whether dentin demineralization continues after a 20-s application of a SEP and also after polymerization of the adhesive. Surface recession was measured, using atomic force microscopy (AFM), between the masked surface and dentin etched with SEP (Clearfil SE Bond) or phosphoric acid (pH 1.94) immediately, 5 min, 2 h or 12 h after application. AFM-based nanoindentations were performed to determine mechanical property profiles across resin-bonded interfaces of two sequence groups: SG 1, where the adhesive was applied and polymerized immediately after application of the primer and specimens were immersed in Hank's solution after 5 min, 2 h and 12 h; or SG 2, where specimens were placed in an incubator before the application of the adhesive, for the same time periods. Significant surface recession occurred over time for all groups, except for SEP before desiccation. Nanoindentations yielded decreased hardness and elastic modulus below the hybrid layer after application of the initial primer, even after polymerization of the adhesive. The results reveal a demineralized dentin zone below the hybrid layer formed by the SEP, not fully protected by the adhesive, which could jeopardize bond strength.

Acid Etching, Dental↗
PubMed2005

In vivo degradation of resin-dentin bonds produced by a self-etch and an etch-and-rinse adhesive.

Resin-dentin bonds are known to degrade in the relatively aggressive oral environment. In order to obtain greater insight into the interfacial degradation process, we examined, by using transmission electron microscopy (TEM), the interfacial ultrastructure of two adhesives bonded to dentin after 1 yr in vivo. Class V cavities were prepared on the buccal surfaces of 14 intact teeth of two monkeys and then restored by using either the two-step self-etch adhesive, Unifil Bond, or the two-step etch-and-rinse adhesive, Single Bond, in combination with the restorative microhybrid composite, Z250. After 1 yr, 10 other teeth were restored by using the same materials (controls). One day later, the monkeys were killed, following which the microtensile bond strength to dentin was determined and the interfacial ultrastructure was examined by TEM. Whereas no noticeable changes in the morphology of the resin-dentin interface were observed between the 1-d and 1-yr specimens for Unifil Bond, Single Bond exhibited signs of interfacial degradation, in particular at the bottom of the 3 microm-deep hybrid layer. In conclusion, the adhesive interface produced by the etch-and-rinse adhesive was less resistant to degradation than that produced by the self-etch system.

Acid Etching, Dental↗
PubMed2004

Behavior of human periodontal ligament cells on CO2 laser irradiated dentinal root surfaces: an in vitro study.

OBJECTIVE: The aim of this study was to investigate the in vitro attachment behavior of human periodontal ligament fibroblasts on periodontally involved root surface after conditioning with CO2 laser and to compare its efficacy with chemical conditioning agents, namely tetracycline hydrochloride, citric acid, hydrogen peroxide (H2O2) and EDTA, using scanning electron microscopy. METHODS: A total of 84 scaled and root-planed specimens from periodontally involved single-rooted human teeth showing hopeless prognosis were selected and assigned to two groups. One group was lased with a CO2 laser (from 5 cm at 3 W for 0.8, 1.0 and 1.2 s), and the other group was treated with either tetracycline hydrochloride (2.5%), citric acid (saturated solution, pH 1), H2O2 (6%) or EDTA (5%; pH 7.4) for 3 min. The specimens were then seeded with human periodontal ligament fibroblasts, incubated for either 12 h or 24 h, and then the cell attachment behavior was observed. RESULTS: CO2 laser irradiation for 1.0 s was found to be the most efficient, showing consistently good cell attachment with the highest mean value (15.00 +/- 3.41 cells/10,000 microm2 after incubation for 12 h and 29.17 +/- 2.04 cells/10,000 microm2 after 24 h), followed by irradiation for 0.8 s (13.11 +/- 3.04 cells/10,000 microm2 after incubation for 12 h and 22.91 +/- 7.10 cells/10,000 microm2 after 24 h). Charring was observed following irradiation for 1.2 s. Amongst chemical conditioning agents, citric acid was found to be the most efficient, with a mean cell attachment of 17.82 +/- 2.16 cells/10,000 microm2 after incubation for 12 h and 23.62 +/- 1.94 cells/10,000 microm2 after 24 h. EDTA and H2O2 did not do well in the study. CONCLUSION: The results suggest that CO2 laser irradiation for 1.0 s may promote comparatively better attachment of periodontal ligament fibroblast on dentinal root surfaces than the conventional chemical conditioning agents used in the study.

Analysis of Variance↗
PubMed1989

Barriers to diffusion of Ledermix paste in radicular dentine.

Freshly extracted human single-rooted teeth with a single root canal were used to study the effects of 2 irrigation regimens and the effect of cementum on the diffusion of corticosteroid and antibiotic tracer molecules from Ledermix paste placed in the pulp space. An irrigation regime that combined the use of 15% EDTAC and 1% NaOCl resulted in a significant increase in the permeation of the trace molecules through dentine compared with teeth that were irrigated with Savlon solution. Mechanical removal of the cementum also resulted in a significant increase in the permeation of the trace molecules. This study demonstrated that neither the smear layer nor the cementum were complete barriers to diffusion. The data obtained appeared to be of clinical relevance and provided further understanding of the dynamics of drugs in tooth roots.

Adult↗
PubMed1991

Epinephrine permeation across dentin in vitro.

The permeation of epinephrine across human dentin discs was studied in vitro. Permeation was measured across dentin of two different thicknesses, with and without the presence of smear layers. Epinephrine was readily detected at the earliest measured time (10 min) and reached peak concentrations between 30 and 50 min. Epinephrine flux (concentration multiplied by the volume of the effluent per min) increased with decreasing thickness of the discs and increased significantly with the removal of the smear layer. The T 1/2 (half-time in min necessary to reach steady-state diffusion of epinephrine) decreased as dentin thickness was reduced and fell further in the absence of the smear layer. This study suggests that the permeation of epinephrine across dentin is inversely related to dentin thickness and retarded by the presence of a smear layer. Also, the topical use of 1 mg/ml epinephrine produced therapeutically useful drug concentrations, but the rate of permeation was relatively slow.

Dental Pulp↗
PubMed1991

Effect of bleaching time and temperature on the radicular penetration of hydrogen peroxide.

Extracted human premolars were treated endodontically and bleached intracoronally. The teeth were bleached with 30% hydrogen peroxide for periods of 5, 20, 40 and 60 min at temperatures of 24 degrees C, 37 degrees C and 47 degrees C. A correlation for both bleaching time and temperature and the radicular penetration of hydrogen peroxide was found. No penetration was found after 5 min bleaching at any of the temperatures tested. Prolonging the bleaching time after 5 min increased the hydrogen peroxide penetration at each of the temperatures tested. A rise in the bleaching temperature also increased the hydrogen peroxide penetration although not significantly for all tested periods. It is therefore suggested to minimize the bleaching time and temperature when hydrogen peroxide is used as the oxidizing agent. Bleaching should be limited to separate 5-min periods rather than being performed over a long continuous period.

Adult↗