Odontoblast morphology and dental repair.

OBJECTIVES: To investigate the changes in morphology and activity of pulp odontoblasts in response to cavity restoration variables and patient factors. METHODS: Class V non exposed cavities were prepared in the intact 1st or 2nd premolar teeth of 27 patients, aged between 9 and 17 years-old. Following tooth extraction, the area of reactionary dentine and the area of the odontoblasts were measured using computerised histomorphometry. RESULTS: The cytoplasm to nucleus ratio of the odontoblasts was found to increase beneath cut dentinal tubules, following the secretion of reactionary dentine. However, none of the patient or preparation variables were found to be correlated with changes in the odontoblast cytoplasm to nucleus ratio. CONCLUSIONS: Morphological changes in human odontoblasts is directly related to their capacity to repair dentine injuries and provide pulp protection. Changes in odontoblast morphology reflect secretory activity.

Two- versus three-dimensional in vitro differentiation of human pulp cells into odontoblastic cells.

The spatial organization of the pulp cells may modify the cytodifferentiation process. The purpose of this study was to compare the two- versus three-dimensional cell culture systems for differentiation of human odontoblastic cells in vitro. Pulpal cores from freshly extracted human third molars were cultured in vitro in a perfusion device on two types of membranes: polyester membrane (two-dimensional [2D] cell culture) and nylon mesh (three-dimensional [3D] cell culture). The cells were incubated with minimum essential medium containing (a) substitute serum, (b) 10% fetal calf serum (FCS), (c) 10% fetal calf serum + 2 mM beta-glycerophosphate (beta GP), and (d) 10% fetal calf serum + transforming growth factor (TGF) beta 1. Immunohistochemistry was used to evaluate the expression of collagen I, osteonectin, and nestin. Small differences were observed between 2D and 3D cell culture systems. This was particularly evident in the 10% FCS group. beta-Glycerophosphate in the 3D system seems to stimulate the osteogenic cell phenotype, as a considerable induction of osteonectin is observed.

Pulpal inflammatory responses following non-carious class V restorations.

The effects of inflammatory activity following surgical intervention can injure pulp tissues; in severe cases it can lead to pulpal complications. With this article, the authors report on the effects of cavity preparation and restoration events and how they can interact together to reduce or increase the severity of pulpal inflammatory activity in 202 restored Class V cavities. Although some inflammatory activity was observed in the absence of bacteria, the severity of pulpal inflammatory activity was increased when cavity restorations became infected. Zinc oxide eugenol and resin-modified glass ionomer cement prevented bacterial microleakage in cavity restorations, with no severe inflammatory activity observed with these materials. Bacteria were observed in cavities restored with enamel bonding resin and adhesive bonded composites and were associated with severe grades of inflammatory activity. The cavity remaining dentin thickness influenced the grade of inflammatory activity. In the absence of infection, the grade of inflammatory activity decreased after 20 weeks post-operatively. In the presence of infection, the grade of pulpal inflammation remained stable until a minimum of 30 weeks had elapsed.

Restorative pulpal and repair responses.

BACKGROUND: Each year, about 90 million new restorations are placed in the United States and 200 million are replaced. Controversy surrounds the pulpal reactions and frequency of bacterial microleakage associated with common restorative materials. The authors investigated and compared pulpal reactions to different types of restorative materials. METHODS: Two hundred seventy-two teeth with standardized rectangular Class V unexposed cavities were restored with resin-based composite bonded to dentin; resin-based composite bonded to enamel; resin-modified glass ionomers, or RMGI; amalgam lined with zinc polycarboxylate, or ZnPC; amalgam lined with calcium hydroxide, or Ca(OH)2; or zinc oxide-eugenol, or ZnOE. Teeth were extracted for orthodontic reasons between 20 and 381 days later. The authors categorized pulpal responses according to standards set by the Federation Dentaire Internationale and the International Organization for Standardization. Bacteria were detected using Brown-Brenn-stained sections. Pulpal responses were evaluated using histomorphometric analysis and analysis of variance statistics. RESULTS: The results showed that RMGI was the best material for preventing bacterial microleakage, and resin-based composite bonded to enamel was the worst. In regard to minimizing pulpal inflammatory activity, ZnOE was the best material and resin-based composite bonded to enamel was the worst. In terms of maximizing odontoblast survival beneath deep cavity preparations, Ca(OH)2, was the best material and RMGI was the worst. CONCLUSIONS: The results show that bacterial microleakage, pulpal injury and repair responses varied widely with different restorative materials. CLINICAL IMPLICATIONS: The authors recommend that RMGI be used to restore teeth with cavities that are shallow to moderate in depth, with the floor of deep cavities being lined with Ca(OH)2 before the teeth are restored with RMGI.

The effect of cavity restoration variables on odontoblast cell numbers and dental repair.

OBJECTIVES: Dentinal repair following cavity restoration is dependent on several parameters including the numbers of surviving odontoblasts. The purpose of this study was to examine the effects of cavity cutting and restoration treatments on post-operative odontoblast numbers. METHODS: 353 Standardised non-exposed rectangular Class V cavities, were cut into the buccal dentin of intact 1st or 2nd premolar teeth of 165 patients, aged between nine and 25 years of age. Composite cavity restorations with various etching treatments were compared with resin-modified glass ionomer cements, enamel bonding resins, as well as polycarboxylate, calcium hydroxide, and zinc oxide eugenol materials. Following tooth extraction (20-381 days) for orthodontic reasons, the area of the reactionary dentine and the area of the odontoblasts was measured histomorphometrically. RESULTS: Odontoblast numbers and dentine repair activity were found to be influenced more by cavity restoration variables, than the choice of cavity filling materials or patient factors. The most important cavity preparation variable was the cavity remaining dentine thickness (RDT); below 0.25mm the numbers of odontoblasts decreased by 23%, and minimal reactionary dentine repair was observed. CONCLUSIONS: Odontoblast injury increased as the cavity RDT decreased. In rank order of maintaining odontoblast numbers beneath restored cavities with a RDT below 0.5mm, and using calcium hydroxide for comparison; calcium hydroxide (100%), polycarboxylate (82.4%), zinc oxide eugenol (81.3%), composite (75.5%), enamel bonding resin (49.5%) and RMGIC (42.8%). The vitality and dentine repair capacity of the pulp is dependent on odontoblast survival. Variations in the extent of odontoblast injury caused during operative procedures, may be the major underlying reason for the success or failure of restorative treatments.

Human dentin production in vitro.

The main hard tissues of teeth are composed of dentin and enamel, synthesized by the mesenchyme-derived odontoblasts and the epithelial-derived ameloblasts, respectively. Odontoblasts are highly differentiated post-mitotic cells secreting the organic matrix of dentin throughout the life of the animal. Pathological conditions such as carious lesions and dental injuries are often lethal to the odontoblasts, which are then replaced by other pulp cells. These cells are able to differentiate into odontoblast-like cells and produce a reparative dentin. In this study we reproduced this physiological event in an in vitro culture system using pulps of human third molars. Pulp cells cultured in presence of beta-glycerophosphate formed mineralization nodules, which grew all over the culture period. The immunohistochemical study revealed that, as odontoblasts, pulp cells contributing to the nodule formation express type I collagen, osteonectin, and nestin. By the exception of nestin, these proteins are also detected in the nodules. The composition of the nodules was also analyzed by Fourier transform infrared microspectroscopy. The spectra obtained showed that both the organic and the mineral composition of the nodules have the characteristics of the human dentin and differ from those of enamel and bone. Taken together, these results show that both the molecular and the mineral characteristics of the human dentin matrix are respected in the in vitro culture conditions.

Postoperative pulpal and repair responses.

BACKGROUND: Each year in the United States, the success of 10 million surgically restored carious lesions depends on a favorable tertiary dentin repair response to preparation, restoration and patient factor variables. The authors investigated the relationship between these variables and dentinal response. METHODS: Standardized rectangular Class V restoration preparations were cut into the buccal dentin of intact first or second premolars of 27 patients without exposing the pulp and were restored. The patients were between 9 and 17 years of age. The treated teeth were scheduled for extraction for orthodontic reasons. After tooth extraction, the tertiary dentin was analyzed histomorphometrically. RESULTS: The area of tertiary reactionary dentin was found to be correlated using linear regression analysis of variance with restoration residual dentin thickness (P = .0024), age of the patient (P = .0045), restoration floor surface area (P = .0266) and restoration width (P = .0415). The authors did not find a correlation with the premolar position (P = .0594), sex of the patient (P = .650), pulpal inflammatory reaction (P = .613) or the time elapsed since surgery (P = .531). Restoration with zinc oxide eugenol was found to negatively influence tertiary dentin matrix secretion (post hoc analysis of variance, P = .030). CONCLUSIONS: The age of a patient at treatment, the choice of restorative material and the size of the restoration preparation are all factors that can positively or negatively affect the pulpal repair response. CLINICAL IMPLICATIONS: Age of the patient affects dentin repair capacity and may be a factor in treatment planning decisions. Minimizing the cutting of dentin, especially the width and base of the preparation, reduces the probability of recurrent pulpal complications.

Human odontoblast cell numbers after dental injury.

OBJECTIVES: The purpose of this study was to measure the changes in odontoblast cell numbers in response to cavity restoration variables and patient factors, and the effect these factors have on dental repair by tertiary dentinogenesis. The number of vital odontoblasts is a critical factor for pulpal repair following restorative surgery, and yet little information is available on these cell numbers. METHODS: Class V non-exposed cavities were prepared in the buccal surface of intact first or second premolar teeth of 27 patients, between 9 and 17 years of age. Following tooth extraction (28-163 days) the area of reactionary dentine and the area of the odontoblasts were measured histomorphometrically. RESULTS: Patient factors, as well as cavity preparation and restoration variables, had little effect on the numbers of odontoblasts per pulpal unit area. However, the age of the patient did appear to have an effect on the reactionary dentine secretory capacity of odontoblasts per unit area, and on the relative number of odontoblasts beneath cut dentinal tubules. CONCLUSIONS: Odontoblast cell numbers were maintained following the preparation of cavities cut into dentine with a 0.5mm residual dentine thickness. The repair capacity of the pulp-dentine complex would appear to be age dependent, this may explain differences in the success of various restorative treatments between patients.

Polymetallism and osseointegration in oral implantology: pilot study on primate.

In oral implantology, successful results in osseointegration are obtained in the medium term (6-12 months) with commercially pure titanium implants. However, current superstructures can be of a different nature (precious metal or titanium) and of different manufacture (cast or machine-produced). Polymetallism between the implant and the superstructure may lead to conditions of galvanic corrosion, and influence osseointegration. The study described establishes, on the one hand, the procedures of animal experimentation in primates and on the other, the techniques of analysis of histological sections. The first technique of analysis is based on histomorphometry and leads to the definition of an osseointegration index. The second technique of analysis consists of X spectrometry by dispersion of energy which enables a spectral analysis of selected points below the crestal neck of the implant (vulnerable area in the case of corrosive attack) to be obtained. It is noted that after 6months, two of which were of activation, osseointegration did not vary according to the nature of the superstructure (precious alloy or titanium). After 2 months, the presence of a precious alloy superstructure lead to titanium migration towards the area around the cervical region of the implant (10-50 microm). This phenomenon did not occur with a titanium implant. It can therefore be presumed that polymetallism leads to detectable corrosion after 2 months but without apparent modification of osseointegration.

Low-energy He/Ne laser in the prevention of radiation-induced mucositis. A multicenter phase III randomized study in patients with head and neck cancer.

Use of the low-energy helium-neon laser (LEL) appears to be a simple atraumatic technique for the prevention and treatment of mucositis of various origins. Preliminary findings, and significant results obtained for chemotherapy-induced mucositis in a previous phase III study, prompted a randomized multicenter double-blind trial to evaluate LEL in the prevention of acute radiation-induced stomatitis. Irradiation by LEL corresponds to local application of a high-photon-density monochromatic light source. Activation of epithelial healing for LEL-treated surfaces, the most commonly recognized effect, has been confirmed by numerous in vitro studies. The mechanism of action at a molecular and enzymatic level is presently being studied. From September 1994 to March 1998, 30 patients were randomized. Technical specification: 60 mW (25 mW at Reims, 1 patient), He-Ne, wavelength 632.8 nm. The trial was open to patients with carcinoma of the oropharynx, hypopharynx and oral cavity, treated by radiotherapy alone (65 Gy at a rate of 2 Gy/fraction, 5 fractions per week) without prior surgery or concomitant chemotherapy. The malignant tumor had to be located outside the tested laser application areas (9 points): posterior third of the internal surfaces of the cheeks, soft palate and anterior tonsillar pillars. Patients were randomized to LEL or placebo light treatment, starting on the first day of radiotherapy and before each session. The treatment time (t) for each application point was given by the equation : t(s)= energy (J/cm2) x surface (cm2)/Power (W). Objective assessment of the degree of mucositis was recorded weekly by a physician blinded to the type of treatment, using the WHO scale for grading of mucositis and a segmented visual analogue scale for pain evaluation. Protocol feasibility and compliance were excellent. Grade 3 mucositis occured with a frequency of 35.2% without LEL and of 7.6% with LEL (P<0.01). The frequency of "severe pain" (grade 3) was 23.8% without LEL, falling to 1.9% with LEL (P<0.05). Pain relief was significantly reduced throughout the treatment period (weeks 2-7). LEL therapy is capable of reducing the severity and duration of oral mucositis associated with radiation therapy. In addition, there is a tremendous potential for using LEL in combined treatment protocols utilizing concomitant chemotherapy and radiotherapy.

In vitro cytotoxicity of one-step dentin bonding systems.

The cytotoxicity of resinous monomers may vary on mixing, calling into question the cytotoxicity of the new dentin bonding agents that are mixed in a single vial. The cytotoxicity of fourth and fifth generation dentin bonding agents was compared in vitro. All-Bond 2, One-Step, Scotchbond Multi-Purpose, Scotchbond One, Syntac, Syntac Single Component, Tenure, and Tenure Quick were tested uncured. The cytotoxicity of several dilutions of fourth generation dentin primer, dentin bonding agent, dentin primer + dentin bonding agent, and fifth generation single component products diluted at 10(-1) to 10(-8) in culture medium was recorded with a MTT assay on L929 fibroblasts. Only one synergistic (increased cytotoxicity after mixing primer and bonding agent) cytotoxic effect was observed with Tenure at 10(-5) dilution. An antagonistic effect (decreased cytotoxicity after mixing primer and bonding agent) was observed with All-Bond 2 between 10(-4) and 10(-8) dilutions. Scotchbond and Syntac fifth generation dentin bonding agents were less cytotoxic than their fourth generation counterparts. All-Bond and Tenure fifth generation dentin bonding agents were more cytotoxic than their fourth generation counterparts only in low dilutions. Clinical studies should confirm these good results, because no dramatic synergistic cytotoxic effect could be detected.

Relationship between dentine hydraulic conductance and the cytotoxicity of four dentine bonding resins in vitro.

OBJECTIVES: Dentine modifies pulpward diffusion of monomers leaching from restorative materials. Thus, remaining dentine thickness must be taken into account during in vitro cytotoxicity tests. This in vitro study was designed to determine the influence of dentine permeability on the outcome of a cytotoxicity test. METHODS: Dentine slices were made from 36 human third permanent molar teeth. The 36 dentine slices were divided into two groups according to their hydraulic conductance: high or low hydraulic conductance. The cytotoxicity of four dentine bonding agents of similar cytotoxicity was tested on dentine slices from each group. Four dilutions of the experimental culture medium were tested: undiluted, 1:2, 1:10 and 1:100. An analysis of variance was used to compare the cytotoxicity of the dentine bonding agents tested on high versus low hydraulic conductance. RESULTS: The cytotoxicity of the high hydraulic conductance (Lp) group was higher than that of low Lp group when tested with the undiluted test culture medium (p = 0.001). No difference was obtained with the 1:2, 1:10, 1:100 dilutions. CONCLUSIONS: Under the conditions of the study, the dentine bonding resins were more cytotoxic when applied onto dentine slices of high hydraulic conductance.

Immunocytochemical detection of apoptosis in human odontoblasts.

Pulpal chamber size decreases on ageing due to primary and secondary dentin deposition. This work was designed to find out the consequences of this pulp chamber reduction on odontoblast number and distribution. Twenty-one healthy human premolars were equally divided into three groups from 11-, 12.5- and 14-yr-old adolescents, respectively). The external and the internal perimeters of dentin were recorded on vestibulo-lingual sections, from buccal to lingual cemento-enamel junction using an image analysis system. Nuclei of the odontoblasts were recorded on 12 automatically selected fields. On nine erupted premolars (3 teeth from each 11-, 12.5- and 14-yr-old patients), apoptosis was detected by confocal microscopy using a modification of the original TUNEL method. Apoptotic cells were labeled in central pulp fibroblasts, perivascular endothelial cells, and in odontoblasts. When the pulp volume decreases due to primary dentin production, the decrease of the surface available for odontoblasts is compensated for by a multilayer distribution of cells. Secondary dentin deposition, associated with odontoblasts reorganization in a single layer, results in a hyperbolic decrease of the odontoblasts number. This decrease seems to result from a programmed cell death, which eliminates half of the odontoblasts over a 4-yr period.

Effects of desensitizing agents on human dentin permeability.

PURPOSE: To compare the in vitro effects of three desensitizing agents on hydraulic conductance of human dentin: Protect (n = 10), Gluma Desensitizer (n = 10), MS Coat (n = 10) (Pain-Free in the USA). MATERIALS AND METHODS: Dentin discs were prepared from 40 freshly extracted normal human third molars. The pulpal side of the dentin discs was etched with 37% phosphoric acid for 15 s and then rinsed under tap water. The coronal side was sequentially ground and the dentin discs were sonicated for 30 min. The hydraulic conductance was measured filtering 20% serum in phosphate buffered saline under a pressure of 15 cm H2O. The hydraulic conductance of each dentin specimen was measured before using the desensitizing agent and this value was designated as 100%. Thirty dentin discs were treated, the hydraulic conductance was remeasured and expressed as a percentage of the hydraulic conductance of that specimen before treatment. The teeth were stored for 1 month at 37 degrees C in deionized water and the hydraulic conductance of the 40 dentin discs was recorded again. Ten dentin discs were left untreated to serve as a control. RESULTS: No statistical difference was found between the immediate hydraulic conductance of the three groups after treatment. After 1-month storage, the control group showed a statistically higher hydraulic conductance than the three treated groups. There was no statistical difference between the three dentin desensitizing agents evaluated.

Eugenol diffusion through dentin related to dentin hydraulic conductance.

OBJECTIVES: The purpose of this study was (1) to find an easy way of evaluating the concentration of eugenol in cell culture fluids; (2) to confirm the relationship between the concentration and the cytotoxicity of eugenol in vitro; (3) to evaluate the cytotoxicity of four temporary eugenol-based filling materials: IRM, super EBA, Kalsogen and zinc oxide-eugenol cement; and (4) to establish a relationship between dentin permeability, eugenol diffusion and cytotoxicity. METHODS: (1) The concentration of eugenol was measured with a spectrofluorimeter; (2) the cell viability of L 929 cells cultivated for 24 h with eugenol-containing medium was evaluated by the MTT assay; (3) after measurement of hydraulic conductance, occlusal cavities in human teeth in vitro were filled with the restorative materials. The cytotoxicity was measured with undiluted test medium and with various dilutions in culture medium; (4) after Lp measurement, the eugenol concentration in the media in the pulp chamber that diffused from IRM and 10(3) mol/l eugenol solution was measured. RESULTS: (1) A proportional relationship (p = 0.001 and r = 1) was found between the concentration of eugenol; (2) eugenol started to be cytotoxic at 10(-5) mol/l and killed 95% of the cells at 10(-3) mol/l; (3) zinc oxide-eugenol cement was the most cytotoxic filling material when tested with the 1:100 dilution; (4) a significant relationship was found between Lp and cytotoxicity (p = 0.04) depending on the dilution of the test medium. A significant relationship was found between Lp and eugenol diffusion from a 10(-3) mol/l solution (p = 0.03) but not between Lp and eugenol diffusing from solid IRM (non significant). SIGNIFICANCE: Eugenol diffusion from zinc oxide-eugenol cement appears to depend more on the role of hydrolysis of eugenol from zinc oxide-eugenol cement than on dentin permeability.

Low energy Helium-Neon laser in the prevention of oral mucositis in patients undergoing bone marrow transplant: results of a double blind randomized trial.

PURPOSE: To evaluate the efficiency of Helium-Neon (He-Ne) laser in the prevention of oral mucositis induced by high dose chemoradiotherapy before autologous bone marrow transplantation (BMT). METHODS AND MATERIALS: Between 1993 and 1995, 30 consecutive patients receiving an autologous peripheral stem-cell or bone marrow transplant (BMT) after high dose chemoradiotherapy were randomized to possibly receive prophylactic laser to the oral mucosa after giving informed consent. Chemotherapy consisted of cyclophosphamide, 60 mg/kg intravenously (I.V.) on day (d)-5 and d-4 in 27 cases, or melphalan 140 mg/kg I.V. on d-4 in three cases. Total body irradiation (TBI) consisted of 12 Gy midplane dose in six fractions (4 Gy/day for three days). He-Ne laser (632.8 nm wavelength, power 60 mW) applications were performed daily from d-5 to d-1 on five anatomic sites of the oral mucosa. Oral examination was performed daily from d0 to d + 20. Mucositis was scored according to an oral exam guide with a 16 item scale of which four were assessed by the patients themselves. Mean daily self assessment scores for oral pain, ability to swallow and oral dryness were measured. A daily mucositis index (DMI) and a cumulative oral mucositis score (COMS) were established. Requirement for narcotics and parenteral nutrition was recorded. RESULTS: The COMS was significantly reduced among laser treated (L+) patients (p = 0.04). The improvement of DMI in L+ patients was also statistically significant (p < 0.05) from d + 2 to d + 7. Occurrence and duration of grade III oral mucositis were reduced in L+ patients (p = 0.01). Laser applications reduced oral pain as assessed by patients (p = 0.05) and L+ patients required less morphine (p = 0.05). Xerostomia and ability to swallow were improved among the L+ patients (p = 0.005 and p = 0.01, respectively). Requirement for parenteral nutrition was not reduced (p = NS). CONCLUSION: Helium-Neon laser treatment was well tolerated, feasible in all cases, and reduced high dose chemoradiotherapy-induced oral mucositis. Optimal laser treatment schedules still needs to be defined.

Low versus high pressure for in vitro determination of hydraulic conductance of human dentine.

The purpose of this study was to evaluate the effect of applied pressure and measurement time on the in vitro measurement of hydraulic conductance of human dentine. Dentine slices were prepared from 50 third molars. Water was forced through the slices under a constant hydrostatic pressure. Five pressures were tested: 1.3 kPa (n = 10), 13.3 kPa (n = 10), 26.6 kPa (n = 10), 40 kPa (n = 10) and 53.3 kPa (n = 10). The volume that went through the slices was recorded every 10 min for 3 h. The volume, the fluid flow rate and the hydraulic conductance under the five pressures were compared. The volume increased with time and pressure. The fluid flow and hydraulic conductance decreased with time under 13.3, 26.6 and 40 kPa, but remained constant under 1.3 and 53.3 kPa. Used of a low pressure (1.3 kPa) may permit water to pass through dentinal tubules without disturbing intratubular contents. Medium pressures (13.3, 26.6, 40 kPa) seemed to disturb tubule contents progressively, resulting in decreased fluid flow and therefore a decreased hydraulic conductance with time. Under these pressures, the calculated values of hydraulic conductance may be unreliable because they are time-dependent. High pressure (53.3 kPa) seemed to pack the tubule contents against intratubular resistances immediately, resulting in low fluid flows and low hydraulic conductances.

In vitro cytotoxicity of dental adhesive systems under simulated pulpal pressure.

OBJECTIVES: Most of the devices used to evaluate the cytotoxicity of resin-based composites in vitro use a dentin barrier test. However, it is difficult to obtain the number of freshly extracted teeth, all on the same day, that is necessary for powerful statistical analysis. Tooth cryopreservation provides a way to build up a supply of teeth. This in vitro study compared cryopreserved teeth and freshly extracted teeth in an evaluation of the cytotoxicity of resin-based composites. In addition, this study also evaluated the effects of pulsatile pressure and the importance of dentin permeability on the cytotoxic response to bonding resins. METHODS: Forty freshly extracted and forty cryopreserved third molars were used. A standardized Class I cavity was prepared within the dentin. The hydraulic conductance of each tooth was recorded. The cavities were filled either with Scotchbond Multi-Purpose Plus and Z 100 (3M Dental Products) or with Optibond and Herculite (Kerr). A plexiglas device was designed to permit 24 h long contact between culture medium and the roof of the pulp chamber while a pulsatile pulpal pressure was simulated. The viability of L 929 cells cultured with a control medium and evaluated by an MTT assay was compared to that of L 929 cells cultured with medium which remained for 24 h in contact with the pulp chamber of restored teeth. A three-way ANOVA was used to compare the cytotoxicity among the different groups. A simple least-squares linear regression was used to seek a relationship between the hydraulic conductance of dentin and the cytotoxicity of composite restorative materials. RESULTS: No significant differences in cytotoxicity were found between the freshly extracted teeth and the cryopreserved teeth (p = 0.53). The cytotoxicity of the resin adhesives was statistically higher when a pulsatile pulpal pressure was simulated (p = 0.04). A significant relationship was found between the hydraulic conductance of dentin and the cytotoxicity of resin-based composites (p = 0.02). SIGNIFICANCE: Cryopreserved teeth can be used for in vitro evaluation of the cytotoxicity of resin adhesives. Pulsatile pulpal pressure simulations increased the in vitro cytotoxicity of the tested materials.

Helium-neon laser irradiation is not a stressful treatment: a study on heat-shock protein (HSP70) level.

BACKGROUND AND OBJECTIVE: Helium-neon (He-Ne) laser irradiation has been clinically used to reduce chemotherapy-induced mucositis. This work was designed to find out if this treatment is stressful at the cellular level by studying its effects on the level of the stress-inducible heat shock proteins. STUDY DESIGN/MATERIALS AND METHODS: Human desmodontal and mouse L929 fibroblasts were irradiated using a 60 mW laser by a single application of 1.5 and 3J/cm2 in continuous mode. Heat shock protein level was studied by gel electrophoresis and Western blotting using monoclonal antibodies. RESULTS: He-Ne treatment does not induce heat shock protein synthesis in human desmodontal nor in mouse fibroblasts at the energy densities used in this study. CONCLUSIONS: These results indicate that the treatment is not stressful at the cellular level.

Effect of masticatory cycles on tooth compression and resultant leakage of amalgam retrofills.

This study was carried out to investigate the effect of changes in tooth structure due to masticatory cycles on amalgam retrofillings performed to different cavity depths. Forty upper maxillary first molars were tested. In the obturated palatal root apical amalgam was inserted to different depths (1.5 and 3 mm). Eight casts were built, each having four sample molars. To block the teeth, the vestibular roots were embedded in resin (palatal root was left free). The eight remaining retrofilled teeth served as controls and were not submitted to occlusal forces. A mechanical device to simulate masticatory cycles subjected the teeth to 500,000 to three million cycles. Leakage was assessed from dye penetration observations. The values of microleakage were analyzed and compared, and strain gauges were used to assess structural modifications to the tooth. The leakage of all retrofilled obturations increased in correlation with the number of masticatory cycles. At three million cycles, root length compression was 0.3 +/- 0.02%. Leakage was significantly less for the deeper cavity preparations at all stages. This in vitro study suggests a significant effect by root compression due to masticatory loads on the leakage of retrofilled amalgam obturations.