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G Kugel

Publications and source records attributed to G Kugel.

At least 19 recordsLinked to original sources
PubMed2003

Effect of nitrous oxide on intracellular events of GT1-7 GnRH-secreting neurons.

Exposure to nitrous oxide (N2O) may result in decreased fertility and other reproductive problems in women working in dental offices. This study explored direct effects of N2O on gonadotropin-releasing hormone (GnRH) neurons involved in pituitary-gonadal function. An immortalized GnRH-secreting GT1-7 cell line was used to evaluate the effects of 60% N2O exposure for 24 hours on pro-GnRH mRNA levels, KCl-stimulated GnRH levels, and certain signaling pathways. N2O exposure for 24 hours decreased pro-GnRH mRNA levels by approximately 80% without affecting cell viability or intracellular GnRH levels. The ability of KCl to release GnRH stores was also significantly reduced. Western blot analyses of ERK1/2, and p38 phosphorylation and IkappaB did not indicate any change in phosphorylation, although p63 tyrosine phosphorylation was increased after short-term N2O exposure. Levels of c-fos, a nuclear transcription factor, were not changed by N2O exposure. These results indicate that N2O significantly decreases evoked release of GnRH as well as GnRH mRNA levels either by decreased synthesis or by mRNA stability. These results may be important in understanding adverse effects of N2O on female workers in dental practice where the gas is not scavenged.

Analysis of Variance↗
PubMed2001

Orthodontic-restorative treatment of chipped or worn incisors.

PURPOSE: To evaluate the shear bond strength of esthetic adhesive restorations for worn or fractured incisal edges. MATERIALS AND METHODS: On 30 human extracted incisors the edge was reduced and a bevel was prepared in the thickness of enamel. Then, the incisal edges were restored, using a different adhesive system in each of the three groups to which the sample teeth had been randomly assigned. Group A: Scotchbond Multi-Purpose Plus, in combination with phosphoric acid, and Z100 as a restorative material. Group B: Scotchbond 1 after etching with phosphoric acid, plus Z100. Group C: F2000, a compomer, in combination with its Primer/Adhesive. The differences in the bond strength values among the three groups were tested for statistical significance. Also, the resistance to load of the restored teeth was compared with that of 10 intact incisors (Group D) (controls). A statistical analysis was performed to test the significance of the differences. RESULTS: No statistically significant difference in shear bond strength was found between Scotchbond Multi-Purpose Plus (17.6 MPa) and Scotchbond 1 (14.8 MPa), whereas F2000 gave significantly lower bond strength values (10.1 MPa). As compared with intact incisors, the teeth restored with either Scotchbond Multi-Purpose Plus or Scotchbond 1 did not perform significantly differently under load. On the other hand, the incisors restored with F2000 gave, as compared with the controls, a resistance to loads significantly lower and of a questionable reliability from a clinical standpoint. SEM observations performed on some of the samples revealed that when phosphoric acid was used to condition the substrate, a deep and uniform demineralization of the enamel was effected, and a mechanically retentive interlocking was created at the interface between resin and enamel. The Adhesive/Primer of F2000 was unable to produce an equally retentive morphology.

Acid Etching, Dental↗
PubMed2001

A clinical study evaluating a new chairside and take-home whitening system.

This study evaluated the efficacy of tooth color modifications with a 15% hydrogen peroxide in-office whitening system when applied for a 30-, 45-, or 60-minute period and combined with a 10% carbamide peroxide take-home system. Twenty-four patients participated in this randomized, parallel clinical evaluation. Six maxillary anterior teeth with a shade of A3 or darker were selected. Patients were randomly divided into 3 groups of 8: Group I patients received a 30-minute application, Group II received a 45-minute application, and Group III received a 60-minute application of the initial in-office treatment. All patients returned at 24 hours for shade evaluation and receipt of a whitening tray with a 10% carbamide peroxide for 7 consecutive days. Patients returned at 24 hours, 72 hours, and on the 8th day of take-home treatment for shade evaluation. Kruskal-Wallis ANOVA showed no statistically significant difference between the groups (P > .10) at completion of treatment. When all three groups were combined, a mean shade change > 8 was seen. No significant difference existed for tooth color modifications when varied application times of 30-, 45- or 60-minute in-office whitening with 15% hydrogen peroxide was used in combination with 10% carbamide peroxide take-home whitening.

Analysis of Variance↗
PubMed2000

Self-focusing of a single laser pulse in a photorefractive medium

An original experimental and theoretical time-resolved study of a single laser pulse self-focusing in a nonlinear photorefractive medium is reported. The behavior of the self-focusing process is experimentally observed in a photorefractive Bi12TiO20 crystal during the 5 ns pulse duration of a doubled Nd:YAG (yttrium aluminum garnet) laser. A theoretical interpretation is provided, based on a simple model of photorefraction on the nanosecond time scale.

Journal Article↗
PubMed2000

Composite restoration wear analysis: conventional methods vs. three-dimensional laser digitizer.

UNLABELLED: The purpose of this study was to compare three-dimensional laser digitizing with subjective evaluations of wear in posterior resin-based composite restorations during a 24-month period. BACKGROUND: The authors describe an indirect method of analyzing wear in resin-based composite restorations. A computer-driven laser was used to scan stone casts of restorations and create three-dimensional computerized surface models of the teeth. A standard computer algorithm was used to superimpose the follow-up model images over the baseline model images and to calculate the amount of wear within 10 micrometers. METHODS: Patients were selected whose treatment plans required a Class II restoration. A total of 100 restorations were inserted at baseline and evaluated at six months, 12 months and 24 months. Polyether quadrant impressions were taken and casts were made. Twenty-one casts were selected for the three-dimensional laser digitizing technique. The same casts were evaluated via subjective evaluations using sets of 18 calibrated standard models, following the method developed by Leinfelder. RESULTS: Statistical analysis using the Wilcoxon test revealed significant differences (P < .01) between subjective wear evaluation and the three-dimensional laser digitizing wear analysis. CONCLUSION: The normalized three-dimensional laser digitizing technique is significantly more effective than subjective evaluations in establishing restoration wear rates.

Adult↗
PubMed2000

Disinfection and communication practices: a survey of U.S. dental laboratories.

BACKGROUND: The need to disinfect impressions is crucial to prevent the transmission of infectious diseases. The authors report the results of a survey of U.S. dental laboratory directors. The survey was designed to determine how well dental laboratory personnel are communicating with dentists regarding the disinfection of impressions, and, in turn, what laboratory technicians are doing to protect themselves against microbial cross-contamination. METHODS: Four hundred dental laboratory directors were selected in a blinded and random manner. To create a geographically representative sample, an equal number of laboratory directors from the East, Midwest and West were interviewed. A survey consisting of 16 open-ended questions was conducted by trained interviewers via 10- to 15-minute telephone interviews. All dental laboratory directors stated that they were thoroughly familiar with their laboratory's disinfection protocol. RESULTS: The survey documented that the majority of impressions were made of polyvinyl (57 percent) or polyether (27 percent) materials. Only 44 percent of the respondents stated that they knew if the impressions they received had been disinfected. Twenty-three percent of the laboratory directors did not know the method of disinfection used, and 47 percent did not know the length of time involved. Forty-five percent of the respondents reported that they receive inadequate instruction in regard to disinfection techniques. No one class of impression materials was found to be more problematic than others by the laboratory directors. CONCLUSIONS: The results indicate a significant and problematic lack of communication between these team members. The responses also suggested that laboratory-perceived problems with impressions were not linked to any particular type of material, but more to the disinfection technique used. PRACTICE IMPLICATIONS: Lack of communication between dentists, staff members and dental laboratory personnel, along with poor training of laboratory personnel in disinfection techniques, may have a direct effect on the prosthetic results achieved in dental practices.

Administrative Personnel↗
PubMed2000

The science of bonding: from first to sixth generation.

BACKGROUND: Adhesive dentistry has revolutionized restorative dental practice during the past 30 years. Improved adhesive materials have made resin-based composite restorations more reliable and long-standing. CLINICAL IMPLICATIONS: This article reviews the evolution of bonding from the first generation to current bonding materials. It discusses the composition and effectiveness of the various iterations. Current products are highlighted to improve clinical use and performance of the materials.

Adhesives↗
PubMed2000

Enameloplasty effects on microleakage of pit and fissure sealants under load: an in vitro study.

Enameloplasty has been implicated in the successful application of pit and fissure sealants. The present study aimed to evaluate the effect of enameloplasty technique on microleakage of sealants when occlusal force was applied on the teeth. The study also allowed a direct comparison of the effectiveness of enameloplasty, when two different burs were used. Six groups of ten human extracted wisdom teeth were tested. Group A: no load, conventional (no enameloplasty--control); Group B: no load, enameloplasty 1/2 round bur (Brasseler USA); Group C: no load, enameloplasty diamond fissure bur REF/UP 791 (Ultradent); Group D: load 500 N, conventional, Group E: load 500 N, 1/2 round bur; Group F: load 500 N, diamond fissure bur. Specimens were thermocycled for 500 cycles at 5 degrees C and 55 degrees C with a dwell time of 30 seconds after load application. Microleakage was scored as distance of dye penetration with 0 = no microleakage and 3 = microleakage to underling fissure. The Kruskal-Wallis One Way Anova and Mann-Whitney U test showed group D having the greatest degree of microleakage statistically significant (p < 0.05) comparing with other groups. Sealants prepared with the conventional technique (A, D) had statistically significant differences in microleakage with those prepared with enameloplasty (B, C, E, F) (p = 0.01). Enameloplasty in groups with no load (B, C) did reduce microleakage, but not significantly (p = 0.3). However, loaded teeth with enameloplasty appeared to perform superior, as compared to those without (p = 0.005). Regarding the effect of load, teeth without load (Groups A, B, C) were found to have significantly less microleakage than teeth where mechanical force had been applied (Groups D, E, F), (p = 0.01). Microleakage in Group A (conventional technique without load) was significantly less than microleakage in Group D (conventional technique with load), (p = 0.04). However, load did not seem to influence microleakage when enameloplasty had been performed. This finding was true for both round bur enameloplasty (p = 0.29), and fissure bur enameloplasty (p = 0.26). There was no statistically significant difference between Groups B, E (round bur) and C, F (fissure bur) (p > 0.05), or between Groups B and C (p > 0.05) and between Groups E and F (p > 0.05). The results of the study indicated that enameloplasty reduced microleakage of pit and fissure sealants, especially when load was applied to teeth, irrespective of what bur was used to enlarge the fissure, as there was no statistical significant differences between the round and fissured diamond burs. The application of occlusal force to the tooth produces significantly more microleakage, unless enameloplasty is performed.

Analysis of Variance↗
PubMed2000

Nontray whitening.

Explore the source record for details and available documents.

Administration, Topical↗
PubMed2000

Direct and indirect adhesive restorative materials: a review.

Esthetic restorative materials require a bonding procedure in order to be durable and reliable. In order to accomplish this ideal, the bonding system must be biocompatible, bond indifferently to enamel and dentin, have sufficient strength to resist masticator forces, have mechanical properties close to those of tooth structures, be resistant to degradation in the oral environment and easy to use. This paper reviews the published literature on direct and indirect adhesive restorative materials.

Biocompatible Materials↗
PubMed2000

Two-year clinical evaluation of a high-density posterior restorative material.

The purpose of this study was to clinically evaluate SureFil high-density posterior composite for Class 2 restorations of permanent first and second molars. All teeth were restored in occlusion with the natural dentition. After cavity preparation, the enamel was etched for 15 seconds with 34% phosphoric acid. No liner/base material was used for the dentin. Prime & Bond 2.1 (two applications) was applied for adhesion to the exposed dentin and etched enamel. The first coat of adhesive was cured for 20 seconds with a curing light and the next coat was only spread thin with a gentle jet of air. The cavity was restored in 3-mm to 5-mm increments. Clinical evaluation (US Public Health Service method) and wear analysis (indirect cast comparison method) were conducted immediately after placement (baseline) and at 3 months, 6 months, 9 months, 1 year, and 2 years. A total of 25 restorations were inserted. At baseline and after 3, 6, and 9 months (n = 24), all restorations were graded Alfa in all categories. At the 1-year recall, 3 restorations (n = 22) were graded Bravo for surface staining. At the 2-year recall, an additional 3 restorations (n = 22) were graded Bravo for surface staining. No restoration was graded Charlie in any category at any time. Wear analysis revealed an average of 13.8 microns of wear at the 2-year recall (n = 22). No evidence of recurrent caries was observed. In conclusion, after 2 years, this high-density composite material demonstrated clinical acceptability and excellent wear characteristics in all categories, making it suitable for posterior restorations.

Acetone↗
PubMed2000

Tooth-whitening efficacy and safety: a randomized and controlled clinical trial.

A randomized, single-center, double-blind, parallel-group, placebo-controlled trial evaluated the whitening efficacy and safety of 2-week, twice-daily use of a 5.3% hydrogen peroxide tooth-bleaching gel delivered on polyethylene film. Efficacy was based on change in Vita shade scores from baseline to the end of treatment. Thirty-three patients in each group completed treatment. Use of the peroxide-containing gel led to a mean change in baseline Vita shade score of -3.70 +/- 0.35, compared with a change of -0.87 +/- 0.24 after use of a placebo gel. After adjustment for baseline scores, the mean difference in shade change between the peroxide gel-treated group and placebo-treated group was -2.85 +/- 0.41 (P < 0.0001). Both treatments were generally well tolerated. The strips offer ease of use, comfort, and shorter duration of wear compared with other at-home bleaching systems.

Adult↗
PubMed1999

Shear bond strength of techniques for bonding esthetic veneers to metal.

STATEMENT OF PROBLEM: New composites with improved qualities have been introduced to the dental profession as alternatives to porcelain. There is concern about the strength and reliability of new metal-resin bonding systems when these composites are used as esthetic veneers over metal frameworks. PURPOSE: This in vitro study compared the shear bond strength of 2 metal-resin bonding techniques with the bond strength of conventional porcelain fused-to-metal (PFM). Effects of water storage and thermocycling were also evaluated. MATERIAL AND METHODS: Ninety disks, cast in a medium gold, high noble PFM alloy, were divided equally into 6 groups, and received 3 treatments for veneering: conventional feldspathic porcelain on 1 group, and a composite (Artglass) bonded to the metal, using 2 metal-resin bonding techniques. Specimens were tested in shear, half of them after a 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling. Fractured specimens were evaluated under x10 magnification to determine the nature of failure. Statistical analysis was performed with 2-factor analysis of variance (ANOVA). RESULTS: Mean shear bond strength values before and after wet storage and thermocycling were 29.66 and 22.91 MPa for the PFM group; 21.43 and 17.92 MPa for the Siloc group; and 19.34 and 15.64 for the etched group, respectively. The PFM group exhibited significantly higher bond strength values compared with the other 2 groups (P<.001). All groups showed a significant decrease in bond strength values after wet storage and thermocycling (P<.001). CONCLUSION: Wet storage and thermocycling caused a significant decrease in shear bond strength of all specimens. Shear bond strength of conventional feldspathic PFM was significantly higher than that of the 2 metal-resin bonding techniques tested. The 2 latter techniques did not reveal any statistically significant differences.

Analysis of Variance↗
PubMed1999

Simulation of the temporal behavior of soliton propagation in photorefractive media.

We consider the propagation of light beams in photorefractive media in the framework of a (1+1)-dimensional model. The Kukhtarev band transport model is introduced both in a time-dependent differential equation describing the evolution of the space charge field and in a nonlinear wave propagation equation. This latter is then numerically solved with a beam propagation method routine. The evolution in time and space of an initially diffracting laser beam is simulated as a function of initial profiles and waists. The beam is shown to go through a transient overfocused state prior to relaxing to a steady state soliton. Additional features such as the stability condition of the system or effects such as optical branching and soliton interactions are studied.

Journal Article↗
PubMed1999

Standardized microscopic evaluation of the bonding mechanism of NRC/Prime & Bond NT.

PURPOSE: To investigate the in vitro formation of hybrid layer, resin tags and adhesive lateral branches, when using Prime & Bond NT (PBNT) "one-bottle" enamel-dentin bonding system on conditioned and unconditioned human dental substrates. MATERIALS AND METHODS: The enamel dentin adhesive was tested on 18 dentin and 18 enamel flat preparations made on facial and occlusal surfaces, respectively, of extracted posterior teeth. Each experimental tooth substrates were randomly divided in six groups of six samples each: Group 1: PBNT on conditioned dentin (CD) with 36% phosphoric acid (PA), Group 2: PBNT on etched enamel (EE) with 36% PA, Group 3: PBNT on CD with NRC non-rinse conditioning (NRC); Group 4: PBNT on EE with NRC, Group 5: PBNT on dentin without any conditioning (UD), Group 6: PBNT on enamel without any conditioning (UE). In the experimental groups, PBNT was applied following the manufacturer's instructions. Over the PBNT, a layer of Dyract AP was placed and light-cured for 20 seconds. All samples were split-fractured along their long axis. One half of each sample was deproteinized and decalcified at the interface in order to visualize the hybrid layer and the other was completely dissolved in order to observe the morphology of resin tags with a scanning electron microscope. RESULTS: Groups 1, 2: The tested samples showed a micromechanical bonding mechanism to CD and EE with phosphoric acid. PBNT formed hybrid layer, resin tags and adhesive lateral branches on dentin. In the dentin samples of the first group, characteristic reverse cone-shaped tags with their corresponding adhesive lateral branches were evident. At the enamel site, traditional pattern of etch enamel was always observed with resin tags formation. Groups 3, 4: When the bonding system was applied on dentin conditioned with NRC, a thin hybrid layer was formed, resin tags were also noted but their shape was narrower than that observed in Group 1. At the enamel site, the conditioned surface showed presence of an etched pattern and of resin tags. Groups 5, 6: When PBNT was applied without any previous conditioning, the hybrid layer and resin tags formation were not evident on dentin, and no bonding mechanism was developed with unetched enamel.

Acid Etching, Dental↗
PubMed1999

Clinical evaluation of a one-bottle bonding system for desensitizing exposed roots.

PURPOSE: To evaluate the effectiveness of a one-bottle adhesive system as a desensitizing treatment, with or without a prior phosphoric acid-etch step. MATERIALS AND METHODS: Two different clinical procedures using a one-bottle adhesive bonding system were tested for its efficacy on desensitizing exposed roots. Thirty subjects with a history of dentin hypersensitivity were selected and 60 exposed sensitive teeth were divided into two groups (n = 30). In Group 1 samples, Scotchbond 1 bonding system (Single Bond in USA) was applied without a prior acid-etching, while in those of Group 2, the exposed sensitive roots were acid-etched with 35% phosphoric acid for 15 seconds, prior to application of bonding agents. The sensitivity was evaluated at 0, 1, 2, 4 weeks and 3 months using cold air blast stimuli, and recorded using a visual-analogue scale. The scores were analyzed as non-parametric data by means of the Mann-Whitney and Sign tests. Five samples from each group were randomly selected in order to make scanning electron microscope observations of the sensitive dentin surfaces at baseline and at each recall using the replica technique. RESULTS: At baseline, after both desensitizing procedures all the patients reported distinct reductions in dentin sensitivity. At 1- and 2-week recalls, 20 teeth of Group 1 and 17 teeth in Group 2 exhibited a return of sensitivity, and in five teeth in each group, the sensitivity score was between 5-8. During the first recall (1-2 weeks), the sensitive teeth were retreated and showed an immediate reduction of sensitivity. At the 1-month recall, eight teeth in Group 1 and four teeth in Group 2 showed a return of some sensitivity, and in six teeth in Group 1 and in three teeth in Group 2, old amalgam restorations were replaced and this procedure almost completely resolved the sensitivity. At the 3-month recall, only five teeth from each group showed residual mild sensitivity (score 1-2). For both Groups 1 and 2 there was a statistically significant (P < 0.0005) reduction in sensitivity levels between the baseline pain scores and immediately after treatment, and between the first recall pre-treatment pain scores and the last recall pain scores. Overall, the two methods of treatment demonstrated a general decrease in sensitivity in both groups over the 3-month study period, adequately solving the clinical and patients' perception of the discomfort of sensitivity. The SEM observations of the replicas showed a progressive loss of the adhesive resin from the treated surfaces. This fact was more evident in the non-etched samples (Group 2) than in those in Group 1. The results of this study showed that exposed root dentin sealed with Scotchbond 1, with or without prior acid-etching, did not show spontaneous sensitivity after 3 months.

Acid Etching, Dental↗
PubMed1999

Influence of tissue characteristics at margins on leakage of Class II indirect porcelain restorations.

PURPOSE: To evaluate the sealing ability of Class II porcelain inlays with margins placed in cementum-dentin and enamel, luted by two new different cementing materials. MATERIALS AND METHODS: Thirty extracted molars, free from caries and restorations, were selected. The sample cavities were prepared in a standardized manner and then were divided in three groups (n = 10) at random. Group 1: The cervical margin was located 1 mm below the CEJ and the inlays were luted with EBS Multi (Espe) bonding system in combination with Compolute 1.0 Aplicap (CLA 1.0, Espe) experimental resin cement. Group 2: The cervical margin was placed 1 mm below the CEJ and Syntac bonding system (Vivadent) and Variolink II resin cement (Vivadent) were used. Group 3: The cervical margin was placed 0.5 mm above the CEJ and the same materials selected for Group 1 were used. IPS-Empress (Ivoclar) inlays were made following manufacturer's instructions. After luting procedures and 2500 thermal cycles (5 degrees and 55 degrees C), the samples were processed and evaluated for marginal leakage at cervical and occlusal site. Samples of Group 3 were first sectioned in the center of the restorations as in Group 1 and 2 and scored (Group 3A) and then two other cuts were made along the buccal and lingual areas (Group 3B) and also scored. After scoring dye penetration of Group 1 and 2 samples, half of the sections were randomly selected to evaluate: (1) resin cement thickness, (2) Hybrid layer formation at the interface between adhesive material and dental substrate and (3) to observe the morphology of the Class II cavity margins. The leakage data were statistically evaluated with the Mann-Whitney U test (P < 0.5). RESULTS: Statistically significant differences were found between Groups 3A and 3B at the occlusal site, and not at the cervical site. Samples of Group 1 showed a cement thickness of 92 microns, and 68 microns in Group 2. Hybrid layer and resin tag formation was evident in Group 1. In Group 2 samples, the hybrid layer formation was less evident and thinner than in Group 1. At cervical margins, an outer layer, not identifiable as sound dentin, of 200-300 microns thick, was noted. This layer was present in all three groups between outer margin and sound dentin. The margins located both cervically and axially in enamel mainly showed prisms cut along their long axis and a low level of structured etch pattern.

Aged↗