Solubility of dental core build-up materials in electric fields.

BACKGROUND/PURPOSE: Over 250 years has been researched over the consequences of oral galvanism. Previous studies have already examined the influence on dental fixation materials. The aim of this study was to investigate the electro-chemical solubility behavior of different dental core build-up materials in a pseudo-realistic galvanic experimental setup. MATERIALS AND METHODS: The composite Admira (Voco, Cuxhaven, Germany) and two glass ionomer cements, Ketac Molar and Photac (3M-Espe, Seefeld, Germany), were examined. Test specimens were exposed to electric field strengths of 10-27 V/m in 0.9% saline solution. After 1, 2, 3, and 24 h, 2 ml of the electrolyte was removed for analysis. Aluminum and calcium were selected as parameters to measure the solubility of the products. Differences between the test samples and controls were ascertained using the two sample t-test. RESULTS: For all of the test groups, Admira demonstrated minimal solubility compared to Ketac and Photac. However, after 24 h in an electric field of 27 V/m, Admira demonstrated the highest increase in solubility compared to the controls (3.47 vs control at 0.76 µmol/l). The second highest increase yielded the conventional glass ionomer cement Ketac (8.62 vs control at 5.28 µmol/l), and a minor increase in solubility showed the composite-based glass ionomer material Photac (38.73 vs control at 31.78 µmol/l) compared to the controls. CONCLUSION: This study demonstrated that galvanic processes increase the solubility of glass ionomer and composite. Therefore, the time of storage, electric field strength, and contact of the material with the electrodes significantly influenced their solubility.

Loss of Aß-nerve endings associated with the Merkel cell-neurite complex in the lesional oral mucosa epithelium of lichen planus and hyperkeratosis.

The Merkel cell-neurite complex initiates the perception of touch and mediates Aß slowly adapting type I responses. Lichen planus is a chronic inflammatory autoimmune disease with T-cell-mediated inflammation, whereas hyperkeratosis is characterized with or without epithelial dysplasia in the oral mucosa. To determine the effects of lichen planus and hyperkeratosis on the Merkel cell-neurite complex, healthy oral mucosal epithelium and lesional oral mucosal epithelium of lichen planus and hyperkeratosis patients were stained by immunohistochemistry (the avidin-biotin-peroxidase complex and double immunofluorescence methods) using pan cytokeratin, cytokeratin 20 (K20, a Merkel cell marker), and neurofilament 200 (NF200, a myelinated Aß- and Aδ-nerve fibre marker) antibodies. NF200-immunoreactive (ir) nerve fibres in healthy tissues and in the lesional oral mucosa epithelium of lichen planus and hyperkeratosis were counted and statistically analysed. In the healthy oral mucosa, K20-positive Merkel cells with and without close association to the intraepithelial NF200-ir nerve fibres were detected. In the lesional oral mucosa of lichen planus and hyperkeratosis patients, extremely rare NF200-ir nerve fibres were detected only in the lamina propria. Compared with healthy tissues, lichen planus and hyperkeratosis tissues had significantly decreased numbers of NF200-ir nerve fibres in the oral mucosal epithelium. Lichen planus and hyperkeratosis were associated with the absence of Aß-nerve endings in the oral mucosal epithelium. Thus, we conclude that mechanosensation mediated by the Merkel cell-neurite complex in the oral mucosal epithelium is impaired in lichen planus and hyperkeratosis.

The growth of Staphylococcus aureus and Escherichia coli in low-direct current electric fields.

Electrical potentials up to 800 mV can be observed between different metallic dental restorations. These potentials produce fields in the mouth that may interfere with microbial communities. The present study focuses on the impact of different electric field strengths (EFS) on the growth of Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) in vitro. Cultures of S. aureus and E. coli in fluid and gel medium were exposed to different EFS. Effects were determined by calculation of viable counts and measurement of inhibition zones. In gel medium, anodic inhibition zones for S. aureus were larger than those for E. coli at all field strength levels. In fluid medium, the maximum decrease in the viable count of S. aureus cells was at 10 V⋅m(-1). Field-treated S. aureus cells presented ruptured cell walls and disintegrated cytoplasm. Conclusively, S. aureus is more sensitive to increasing electric field strength than E. coli.

Induction of apoptosis and up-regulation of cellular proliferation in oral leukoplakia cell lines inside electric field.

OBJECTIVE: In dentistry, metallic alloys are used for dentures, restorative materials, and orthodontic devices. Electric voltages up to 950 mV may occur between different dental alloys in the oral cavity. This study aimed to investigate physiologic reactions of oral leukoplakia cells in vitro to electric fields. STUDY DESIGN: A human leukoplakia cell line (MSK-LEUK1), cultivated in keratinocyte growth medium (KGM-2) supplemented with growth factors in 5% CO(2) humidified air at 37°C, was exposed to electric field strength of 1-20 V/m for 24 hours in a custom-made pulse chamber. The cells were then analyzed for proliferation with the use of BrdU assay and for apoptosis with the use of TUNEL assay. Findings were assessed with the use of fluorescent microscopy. Ultrastructural changes were studied by transmission electron microscopy. RESULTS: Electric field strength of 1-10 V/m led to up-regulation of cell proliferation rate from 10.64% to 44.06% (P = .0001). The apoptotic index increased significantly (P = .0001) from 20.03% at 1 V/m to 46.56% at 10 V/m. Individual cell keratinization was seen in leukoplakia cells treated with 16 V/m. CONCLUSIONS: Oral galvanism induces subcellular changes in oral precancer cells in vitro that closely simulate some of the morphologic features of oral squamous cell carcinoma cells in vivo.

Indirect sinus floor elevation for osseointegrated prostheses. A 10-year prospective study.

The aim of this study was to evaluate the indirect/closed maxillary floor elevation technique for the insertion of osseointegrated implants to support fixed prostheses clinically. Thirty-one patients (19 female, 12 male) with a mean age of 62 +/- 9 years were selected for this study. All patients needed implants in the posterior maxillary region to support osseointegrated prosthesis. Forty-seven implants were inserted using the indirect/closed sinus floor elevation method, and another 31 implants were placed in the same individuals as intra-individual control. No augmentation material was used along with implantation. The mean bone height before sinus lift was 9.78 +/- 1.68 mm (minimum 5.6 mm), and for controls it was 15.62 +/- 3.44 mm. The average length of the implants used was 12.00 +/- 1.70 mm, whereas for controls it was 13.39 +/- 1.60 mm. The patients were recalled for periodic checkups every 6 months, and the radiographic controls were made every 12 months. One control fixture failed after uncovering; 77 implants were loaded, and 5 of them failed (2 controls and 3 of the sinus lift group) between 3 and 59 months following loading. One hundred nineteen months after surgery (112 months following loading), the censored survival rate (Kaplan-Meier) was 93.6% for sinus lift implants and 90.3% for controls. The crestal bone level changes were not significant either before loading or after loading for both sinus lift and control implants. None of the remaining implants showed any signs of mobility or peri-implant disease, and none of the patients exhibited sinus problems during the entire observation period.

Direct current electrical fields induce apoptosis in oral mucosa cancer cells by NADPH oxidase-derived reactive oxygen species.

The presence of more than one dental alloy in the oral cavity often causes pathological galvanic currents and voltage resulting in superficial erosions of the oral mucosa and eventually in the emergence of oral cancer. In the present study the mechanisms of apoptosis of oral mucosa cancer cells in response to electromagnetic fields was investigated. Direct current (DC) electrical fields with field strengths between 2 and 16 V/m, applied for 24 h to UM-SCC-14-C oral mucosa cancer cells, dose-dependently resulted in decreased cell proliferation as evaluated by Ki-67 immunohistochemistry and upregulation of the cyclin-dependent kinase (CDK) inhibitors p21(cip1/waf1) and p27(kip1), which are associated with cell cycle arrest. Electrical field treatment (4 V/m, 24 h) increased apoptosis as evaluated by immunohistochemical analysis of cleaved caspase-3 and poly-(ADP-ribose)-polymerase-1 (PARP-1). Furthermore, robust reactive oxygen species (ROS) generation, increased expression of NADPH oxidase subunits as well as Hsp70 was observed. Electrical field treatment (4 V/m, 24 h) resulted in increased expression of Cu/Zn superoxide dismutase and decreased intracellular concentration of reduced glutathione (GSH), whereas the expression of catalase remained unchanged. Pre-treatment with the free radical scavenger N-acetyl cysteine (NAC) and the superoxide dismutase mimetic EUK-8 abolished caspase-3 and PARP-1 induction, suggesting that apoptosis in oral mucosa cancer cells is initated by ROS generation in response to DC electrical field treatment.

Regulation of the multidrug resistance transporter P-glycoprotein in multicellular prostate tumor spheroids by hyperthermia and reactive oxygen species.

Hyperthermia is an important component of many cancer treatment protocols. In our study the regulation of the multidrug resistance (MDR) transporter P-glycoprotein by hyperthermia was studied in multicellular prostate tumor spheroids. Hyperthermia treatment of small (50-100 microm) tumor spheroids significantly increased P-glycoprotein and mdr-1 mRNA expression with a maximum effect at 42 degrees C, whereas only moderate elevation of P-glycoprotein was found in large (350-450 microm) tumor spheroids. Hyperthermia caused an elevation of intracellular reactive oxygen species (ROS). Inhibition of ROS generation with NADPH-oxidase inhibitors diphenylen iodonium (DPI) and 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF) abolished P-glycoprotein expression but did not affect its transcript levels following heat treatment. This indicates that P-glycoprotein levels are controlled by regulating its translation rate or stability. Hyperthermia incubation resulted in a differential activation of p38 mitogen-activated protein kinase (MAPK), extracellular regulated kinase 1,2 (ERK1,2), and c-jun N-terminal kinase (JNK) immediately, 4 hr and 24 hr after treatment. Furthermore, upregulation of hypoxia-inducible factor 1alpha (HIF-1alpha) was observed. Elevation of HIF-1alpha and P-glycoprotein expression following hyperthermia treatment were abolished upon coadministration of the p38 inhibitor SB203580. In contrast the JNK inhibitor SP600125 and the ERK1,2 inhibitor UO126 resulted in increase of HIF-1alpha and P-glycoprotein in the control as well as the hyperthermia-treated samples, indicating negative regulation of intrinsic HIF-1alpha and P-glycoprotein expression by ERK1,2 and JNK signaling cascades. In summary our data demonstrate that hyperthermia-induced upregulation of P-glycoprotein and HIF-1alpha is mediated by activation of p38, whereas ERK1,2 and JNK are involved in repression of P-glycoprotein and HIF-1alpha under control conditions.

Effect of laboratory procedures and thermocycling on the shear bond strength of resin-metal bonding systems.

STATEMENT OF PROBLEM: During fabrication or repair of removable partial dentures, resin-to-metal or resin-to-denture tooth bonds may be stressed by laboratory procedures. PURPOSE: The purpose of this in vitro study was to evaluate the effect of steam cleaning, boiling, ultrasonic cleaning (laboratory procedures), and thermocycling on shear bond strength of resin bonds to metal and denture teeth. MATERIAL AND METHODS: Resin-metal bonding systems and their specific veneer resins (Rocatec, Sinfony; Rocatec, Visio-Gem, HLC-BOND, Zeta LC and Ducera experimental veneer resin) were tested on a Co-Cr alloy (Wirobond C). The veneer resins were bonded to resin denture teeth. The experimental groups (n=7) were subjected to the following conditions: 24-hour storage of the specimens in air (group I, control group), storage in air and treated with simulated laboratory procedures (2 minutes steam cleaning, 15 minutes ultrasonic cleaning at room temperature, 1 hour boiling in water, group II), storage in air with thermocycling (5000 cycles, 5 degrees to 55 degrees C, group III), storage in air with laboratory procedures followed by thermocycling (group IV), and storage in air with thermocycling followed by laboratory procedures (group V). Shear strength tests (MPa) were performed with a universal testing machine until fracture. After shear bond testing, the failure mode of the resin-metal and resin-denture tooth bonds was assessed. Statistical analysis of the results was carried out with one-way analysis of variance and Bonferroni-Dunn's multiple comparisons post hoc analysis for test groups (alpha=0.05). RESULTS: Except for Ducera/denture tooth specimens (groups III to V: 8.7 +/- 3.4-9.1 +/- 1.7; 10.8 +/- 1.9 MPa control group), the Wirobond C and denture tooth specimens (groups III, IV and V: 1.4 +/- 0.9-11.9 +/- 2.3 MPa), showed significantly lower shear bond strengths than the corresponding control groups (7.5 +/- 2.9-21.0 +/- 3.4 MPa, P<.05). The shear bond strengths of group II of Sinfony/Wirobond C (11.6 +/- 3.3 MPa, P<.0001), Visio-Gem/Wirobond C (7.4 +/- 1.9 MPa, P<0.0001), Ducera/Wirobond C (11.8 +/- 2.9 MPa, P<.0001) and of Zeta/denture tooth (3.9 +/- 1.6 MPa, P=.0005) were significantly decreased by steam, boiling, and ultrasonic procedures compared with the corresponding control groups (21.0 +/- 3.4 MPa; 14.7 +/- 4.0 MPa; 19.1 +/- 2.3 MPa; 7.5 +/- 2.9 MPa, respectively). No significant differences were noted among groups III, IV, and V. Co-Cr specimens subjected to the Rocatec system and bonded with Sinfony and HLC BOND/Zeta specimens showed cohesive failure. Adhesive failure was observed for the experimental veneer resin on the Co-Cr specimens and for all veneer resins on the denture teeth. CONCLUSION: Simulation of laboratory procedures and thermocycling caused a significant drop in shear bond strength of metal-resin and denture tooth-resin bonds for most of the tested veneer resins. Thermocycling before shear testing had the same effect on veneer resin bond strength as the simulated laboratory procedures.

Pulmonary risk of intraoral surface conditioning using crystalline silica.

PURPOSE: This study evaluated the pulmonary risk caused by possible respirable dust of Al2O3 and SiO(x) resulting from chairside tribochemical sandblasting procedures in a dental office. MATERIALS AND METHODS: Dust was collected using a trap near the working field, and quantitative morphologic determination and identification were performed with SEM and EDAX. Forty blasting processes (total time 20 minutes) were aimed at a dummy to obtain maximum pollution of the workplace. Respirable dust fraction was measured using personal air samplers with an 8-microm cellulose-nitrate filter and a volume flow rate of 2 L/min. Mass of the respirable dust fraction was determined, and respirable free crystalline silica was identified with the help of infrared spectroscopy. RESULTS: Blasting of metal or ceramic surfaces with tribochemical agents produces respirable and potentially harmful SiO(x) and Al2O3 particles with a diameter of less than 5 microm, showing a total concentration in the air of less than 0.3 mg/m3. With and without dental suction, the concentration of the respirable free crystalline silica was smaller than 0.02 mg/m3. CONCLUSION: Concern regarding the risk of chairside tribochemical methods and possible impairment of health of patients and dental staff is unfounded, even under extreme conditions or without protective measures, since the concentrations of SiO(x) found in the air of the workplace were far below the current threshold value of 0.15 mg/m3.

Clinical study on the reasons for and location of failures of metal-ceramic restorations and survival of repairs.

PURPOSE: A recently introduced technique, the Cojet system, using SiOx (Al2O3 coated with silisic acid), provides ultrafine mechanical retention by sandblasting, as well as a chemicophysical bond between the metal-ceramic and the composite resin. This study determined the reasons for and locations of failures of metal-ceramic restorations and evaluated the survival of the intraoral silica-coating system used for the repair of failed restorations. MATERIALS AND METHODS: A total of 153 patients possessing 289 fractured crowns were involved in this study; 255 of these fractures were on fixed partial dentures, whereas 34 were on single crowns. The mean observation period was 34.6 months. The materials used for the repair process were ESPE-Sil for silane; Visiogem, Sinfony, and Dentacolor as opaquers; and Pertac II Aplitip, Sinfony, and Charisma as repairing composite resins. RESULTS: The majority of the failures (65%) occurred in the anterior region. Sixty percent of the failures were observed at the labial, 27% at the buccal, 5% at the incisal, and 8% at the occlusal regions. The fractures were mainly in the maxilla (75%), predominantly at the labial surface. The overall cumulative survival rates of the repairs (89%) showed that the first failures happened mostly from 1 week to 3 months after the repair, without any difference between the composite resins. CONCLUSION: The original failures happened mainly during chewing function or because of accidents, iatrogenic factors, and surgical operations, whereas secondary failures after repair using intraoral silica coating and composite resin were due to trauma, chewing function, or lack of rubber dam application.

Articulator-related registration--a simple concept for minimizing eccentric occlusal errors in the articulator.

PURPOSE: The purpose of this study was to develop an easy-to-use procedure for individual registration and to test its accuracy. Unlike common principles, the method should be based on a transfer of the articulator geometry to the patient. MATERIALS AND METHODS: The system consists of an articulator holding a bite plate in a standard position. The bite plate connects to an electronic recording system, which transfers the articulator's condylar points virtually to the patient's mandible by a centric relation record. The trajectories of the transferred points are recorded during mandibular protrusions and laterotrusions. From the trajectories, sagittal condylar and Bennett angles are measured and are adjusted at the articulator after mounting of the casts via the bite plate. Using a mechanical testing device, the accuracy of the measured angles was examined by comparison with preset values varying from 10 to 60 degrees (condylar angle) and from 0 to 40 degrees (Bennett angle) in 10-degree increments. RESULTS: The mean deviations of measured condylar angles from preset values ranged between 1.5 and 0 degrees. The mean deviations of the Bennett angles ranged from -0.5 to -1.3 degrees. CONCLUSION: The transfer of articulator geometry to the patient reduces the number of individual parameters necessary to imitate jaw motion to the condylar and Bennett angles. This leads to a significant simplification in registration and cast transfer. Since the required parameters are recorded with high accuracy, the method could be an alternative to traditional sophisticated instrumental registration.