Search PubMed⌕ Search

Biomedical subjects

R Hickel

Publications and source records attributed to R Hickel.

At least 55 records · Page 3Linked to original sources
PubMed2000

Determination of changes on tooth-colored cervical restorations in vivo using a three-dimensional laser scanning device.

The present study aimed at the determination of changes of tooth-colored cervical restorations in vivo using an optical 3-dimensional laser scanning device. The study was performed on 197 cervical restorations placed on incisors, canines, and premolars. Four different tooth-colored restoration materials, a composite, a polyacid-modified resin composite, and two resin-modified glass ionomer cements, were used for the restoration of the lesions. For the determination of changes, images were taken at baseline and 15, 24 and 36 months after the placement of the fillings using a 3D-laser scanning device. The images were superimposed automatically, and digital subtraction was made by a specially developed image analysis software. The total substance loss on the entire filling surface at 36 months for the resin-modified glass ionomer Photac-Fil was 44 (+/-23) microm, for Fuji II LC 45 (+/-26) microm, for Dyract 71 (+/-47) microm and for Tetric 18 (+/-12) microm. Differentiating between the class of lesion, a higher wear rate was observed at 36 months on restorations which had been placed in erosion/non-carious cervical cavities (66 (+/-33) microm). In conclusion, the composite material demonstrated a distinctly lower surface wear rate over time in comparison to the resin-modified glass ionomer cements and the polyacid-modified resin composite.

Adult↗
PubMed2000

Three-year clinical evaluation of direct and indirect composite restorations in posterior teeth.

STATEMENT OF THE PROBLEM: Objective long-term clinical data are necessary to assess the performance of modern posterior composites as direct and indirect restorations. PURPOSE: This prospective, long-term clinical trial evaluated direct and indirect composite restorations for clinical acceptability as posterior restoratives in single or multisurface cavities and provided a survey on the 3-year results. MATERIAL AND METHODS: Under the supervision of an experienced dentist, 9 dental students placed 88 composite restorations (Tetric, blend-a-lux, Pertac-Hybrid Unifil), 43 direct composite restorations, and 45 indirect inlays. Clinical evaluation was performed at baseline and in yearly intervals after placement by 2 other experienced dentists, using modified USPHS criteria. A third follow-up of 60 restorations took place within 33 to 36 months after placement. RESULTS: A total of 93% of indirect and 87% of direct restorations were assessed to be clinically excellent or acceptable. During the third year, 1 direct restoration in a molar failed because of margin opening. Indirect inlays exhibited a significantly better anatomic form of the surface than direct composite restorations. Premolars revealed a significantly better marginal integrity and anatomic form of the surface than molars. Restorations in molars exhibited a significantly higher failure rate compared with premolars. CONCLUSION: Posterior composite restorations provided a satisfactory clinical performance over a 3-year period, even if placed by relatively inexperienced but supervised students.

Bicuspid↗
PubMed2000

Root substance removal with Er:YAG laser radiation at different parameters using a new delivery system.

BACKGROUND: The recently introduced Er:YAG laser radiation appears to be a promising alternative in treating dental hard tissue due to its thermo-mechanical ablation properties and the lack of thermal side effects. The present in vitro study attempted to evaluate the use of Er:YAG laser radiation in combination with a specially developed delivery system in removing calculus from root surfaces. METHODS: Fifty extracted anterior teeth, premolars and molars, were divided into 2 groups of 25 each with (group A) and without (group B) subgingival calculus. Source of radiation was an Er:YAG laser device with a wavelength of 2.94 microm, in the infrared optical spectrum, a pulse duration of 250 ns, and a pulse repetition rate of 15 pps. In each group, 6 teeth were irradiated with 300 laser pulses either at 60 mJ, 80 mJ, 100 mJ, or 150 mJ. The samples were continually moved linearly using a computer numeric controlled device. The volumetric evaluation of root substance removal was performed with a 3-dimensional laser scanning system (100,000 surface points per sample, accuracy: 5 microm) and special image analyzing software. A scanning electron microscopic (SEM) observation was performed to assess the laser induced ultrastructural changes on the root surfaces. Statistical analysis was carried out with ANOVA followed by the Scheff*e test and with regression analysis according to Pearson-Bravais at a level of significance of 5% (P <0.05). RESULTS: The linear measurement of substance removal on calculus samples (group A) revealed average depths between 174.38 (+/-16.13) microm and 501.85 (+/-111.01) microm. Defect depths on the teeth without calculus (group B) ranged from 37.78 (+/-14.03) microm to 484.44 (+/-80.63) microm. The SEM observation of laser-treated root surfaces revealed no signs of thermal damage; e.g., melting, fusion, or cracking. CONCLUSIONS: The results of the present study showed that a substance removal with Er:YAG laser radiation at lower energy densities is comparable, in effect, to that after conventional root surface instrumentation with curets. The results seem to indicate that calculus removal can be selectively done using lower radiation energies. Considering the favorable results of the SEM investigation, the use of the Er:YAG laser in periodontal therapy may be possible in the future.

Analysis of Variance↗
PubMed2000

Clinical results and new developments of direct posterior restorations.

PURPOSE: To (1) review the literature and analyze the longevity and reasons for failure of direct resin-based composite (RBC), amalgam, and glass-ionomer cement (GIC) restorations in stress-bearing posterior cavities and (2) to assess new material developments and treatment techniques to restore these cavities. MATERIALS AND METHODS: This work reviewed the dental literature predominately of the last decade for longitudinal, controlled clinical studies and retrospective cross-sectional studies. Only studies investigating the clinical performance of restorations in permanent teeth were included. Annual failure rates of direct resin-based composite, amalgam, and GIC restorations were determined and failure reasons were discussed. RESULTS: Annual failure rates in posterior stress-bearing cavities were determined to be: 0-9% for direct RBC restorations, 0-7% for amalgam restorations, and 1.9-14.4% for GIC restorations. The median annual failure rate of longitudinal studies for amalgam was calculated with 1.1%, for RBCs 2.1% and for GICs 7.7%. GIC is significantly worse compared with amalgam and RBC. Main reasons for failure were secondary caries, marginal deficiencies, fracture, and wear. Longitudinal studies showed a strong trend towards a higher longevity compared with cross-sectional investigations.

Composite Resins↗
PubMed1999

Effect of dental materials on gluconeogenesis in rat kidney tubules.

The effect of dental composite components triethyleneglycoldimethacrylate (TEGDMA) and hydroxyethylmethacrylate (HEMA) as well as mercuric chloride (HgCl(2)) and methylmercury chloride (MeHgCl) on gluconeogenesis was investigated in isolated rat kidney tubules. From starved rats kidney tubules were prepared and isolated by digestion with collagenase. Every 10 min up to 60 min 1-ml samples were drawn from the cell suspension for quantitating the glucose content. Glucose formation in controls was 3.3 +/- 0.2 nmol/mg. per min (mean +/- SEM, n=21). Relative rates of glucose formation were obtained by expressing individual rates as a percentage of the corresponding control. X-Y concentration curves (effective concentration, EC) of the substances were calculated by fitting a four-parametric sigmoid function to the relative rates of glucose formation at various test concentrations. At the end of the incubation period cell viability was assessed by trypan blue exclusion. Cell viability decreased within the 60 min interval from 90 to approx. 80% (controls), <25 (HEMA), <20 (TEGDMA), <10 (MeHgCl), and <10% (HgCl(2)). Values of 50% effective concentration (EC(50)) were calculated from fitted curves. EC(50) values were (mmol; mean +/- SEM; n=4): HEMA, 17.7 +/- 2.9; TEGDMA, 1.8 +/- 0.2; MeHgCl, 0.018 +/- 0.0005; and HgCl(2), 0. 0016 +/- 0.0005. The toxic effect of HgCl(2) was approximately 1000 or 10 000 higher than that of the dental composite components TEGDMA or HEMA, respectively.

Animals↗
PubMed1999

Bond strength of a compomer to dentin under various surface conditions.

This study determined the influence of different dentin pretreatments on the shear bond strength of an adhesive system and corresponding compomer material. One hundred and twenty freshly extracted human molars were ground with wet SiC paper to expose flat oral/buccal surfaces of superficial dentin. The teeth were assigned to 12 treatment groups (n = 10) based on dentin surface finish (600-grit SiC vs. air abrasion vs. 40 microns diamond bur), surface conditioning (acid etching vs. no etching), and moisture content of the dentin (moist vs. dry). Cylinders of Compoglass F compomer were bonded to the dentin with Syntac Single-Component. After 24-h storage in distilled water, the specimens were debonded in shear mode. Bond strengths in MPa (SD) were calculated and bonding sites were analyzed for the mode of failure. Three-way ANOVA revealed significantly higher bond strength values for acid etched specimens (P = 0.001). Moisture content of the dentin surface (P = 0.614) and mechanical surface finish (P = 0.367) had no significant influence on the results. Debonding in unetched groups ranged from 94 to 100% adhesively. Acid etched groups showed adhesive failures ranging from 56 to 100%. To obtain a more reliable bond it is recommended that dentin is acid etched prior to the bonding of a compomer.

Acid Etching, Dental↗
PubMed1999

Two-year clinical evaluation of direct and indirect composite restorations in posterior teeth.

STATEMENT OF PROBLEM: Few long-term clinical studies have reported data of modern posterior composites as direct and indirect restorations. PURPOSE: This prospective, long-term clinical trial (1) evaluated direct and indirect composite restorations for clinical acceptability as posterior restoratives in single or multisurface carious teeth and (2) provided a survey on the 2-year results. MATERIAL AND METHODS: Nine dental students placed 88 composite restorations (Tetric, blend-a-lux, Pertac-Hybrid Unifil), 43 direct composite restorations and 45 indirect inlays, under the supervision of an experienced dentist. The first clinical evaluation was performed 11 to 13 months after placement by 2 other experienced dentists, using modified USPHS criteria. A second follow-up of 60 restorations took place within 20 to 26 months after placement. RESULTS: A total of 93% of indirect and 90% of direct composite restorations were assessed to be clinically excellent or acceptable. Two restorations (1 indirect composite inlay and 1 margin of a direct composite restoration) failed during the second year because of fracture. Indirect inlays demonstrated a significantly better "anatomic form of the surface" than direct composite restorations. Premolars revealed a significantly better margin integrity and postoperative symptoms than molars. CONCLUSION: Posterior composite restorations provided a satisfactory clinical performance over a 2-year period when placed by relatively inexperienced but supervised students.

Bicuspid↗
PubMed1999

Effects of surface finish and fatigue testing on the fracture strength of CAD-CAM and pressed-ceramic crowns.

STATEMENT OF PROBLEM: All-ceramic molar crowns can be fabricated with CAD-CAM or laboratory methods with different materials, and a polished or oven-glazed surface. PURPOSE: This in vitro study determined the fracture strength of various all-ceramic crowns, with and without prior cyclic loading. MATERIAL AND METHODS: Standardized molar crowns were fabricated with a CAD-CAM machine (Cerec 2), software with machinable ceramic materials (Vita Mark II and ProCAD), and also conventional heat-pressed IPS Empress crowns fabricated at 2 dental laboratories. Groups of 40 crowns of each material were manufactured with either a polished or an oven-glazed surface finish. Cyclic loading that simulated oral conditions were performed on half of each group. Afterward, all crowns were loaded until catastrophic failure.Results. Fracture loads of the polished ProCAD crowns without prior cyclic loading was 2120 +/- 231 N, significantly higher than that of the polished Vita Mark II crowns (1905 +/- 235 N), but was not significantly different from the strength of 2 laboratory-fabricated Empress crowns. Oven-glazing of ProCAD crowns improved the fracture strength significantly, up to 2254 +/- 186 N. Prior cyclic loading decreased the strength of all tested crowns significantly, but the reduction was less for the Cerec crowns than the Empress crowns. CONCLUSION: Cerec ProCAD crowns demonstrated significantly greater strength than the Vita Mark II crowns, better resistance to cyclic loading and lower failure probability than the laboratory-fabricated IPS Empress crowns. Prior cyclic loading significantly reduced the strength of all-ceramic crowns, but had less effect on Cerec crowns than on the IPS Empress crowns. Oven-glazing of ProCAD crowns resulted in significantly higher strength and higher resistance to cyclic loading than surface polishing.

Analysis of Variance↗
PubMed1999

Bactericidal effects of 2.94 microns Er:YAG-laser radiation in dental root canals.

The purpose of this study was to investigate the antimicrobial properties of Er:YAG-laser radiation in dental root canals. The root canals of 90 freshly extracted anterior teeth were enlarged mechanically, sterilized, and randomly divided into subgroups of 10 samples. The root canals were inoculated with Escherichia coli or Staphylococcus aureus for 2 h. The laser treatment groups were exposed for either 15 or 60 s to Er:YAG-laser radiation (pulse energy: 50 mJ; 15 pps). Additionally, for each bacterial strain, one sample group was rinsed with a NaOCl solution (1.25%), and one was left untreated as control. After irradiation or irrigation, the number of bacteria was evaluated using the surface spread plate technique. In the case of S. aureus, the primary bacterial load (control group) of the root canals was reduced to 0.15% after 15 s and 0.06% after 60 s of laser treatment. In the E. coli group, the number of bacteria was diminished to 0.13%, with the shorter radiation time and to 0.034% after 60 s of radiation. Irrigating the root canals with NaOCl, a reduction of the number of bacteria to 0.033% for S. aureus and to 0.020% for E. coli could be obtained. As the results confirm, Er:YAG-laser radiation exerts very effective antimicrobial properties in dental root canals, depending on the time of radiation.

Colony Count, Microbial↗
PubMed1999

Substance removal on teeth with and without calculus using 308 nm XeCl excimer laser radiation. An in vitro investigation.

It was the aim of this in vitro study to determine the potential effects of 308 nm XeCl excimer laser radiation on root surfaces when used for removing calcified deposits. The source of laser radiation was a XeCl-excimer laser (MAX 10, Fa. Medolas, Germany) emitting ultraviolet radiation at a wavelength of 308 nm with a pulse duration of 60 ns. Subjects of irradiation were 60 extracted teeth which were divided into 2 groups of 30 samples each with (group 1) and without calculus (group 2). Specimens were irradiated with 800 laser pulses at 5 different energy-densities per pulse of 1.0 J/cm2, 2.0 J/cm2, 3.0 J/cm2, 4.0 J/cm2 and 5.0 J/cm2. For each parameter 6 samples (n=6) were exposed to 308 nm excimer-laser radiation. The ablation of hard tissue on the treated root surfaces was measured 3-dimensionally with a laser scanning device (100,000 surface points per sample; accuracy: 5 microm) and evaluated with a special image analyzing software (volume, mean, median, standard deviation). In addition, a scanning electron microscopic (SEM) evaluation of the irradiated root surfaces was performed. Statistical analysis was done using ANOVA with the Scheffé-test. The lowest amount of ablation on teeth without calculus was induced with 14.01 (+/-5.86) microm using laser radiation at an energy density of 2.0 J/cm2. Maximum tissue removal in this sample group was obtained with 56.67 (+/-21.05) microm with laser treatment at an energy density of 5.0 J/cm2. While no ablation of dental cementum was detectable after irradiating root surfaces without calculus at 1.0 J/cm2, a strong removal of calculus with a mean value of 31.91 (+/-4.2) microm was observed under these conditions. The results seem to indicate that a selective removal of subgingival calculus creating a homogenous shape of the root surface with 308 nm excimer laser radiation is possible. Furthermore, no signs of the formation of a smear layer nor the induction of thermal side-effects were observed.

Analysis of Variance↗
PubMed1999

Effect of rubber dam on mercury exposure during amalgam removal.

It was the aim of this investigation to treat 20 volunteers with maximally 5 amalgam fillings by the same comprehensive protocol in which all removals with (n = 8) and without (n = 12) rubber dam had been performed within a few months. Nine amalgam-related parameters indicated a close matching of both groups before removal. In the group without rubber dam, mercury (Hg) levels in plasma increased significantly above preremoval values at days 1 and 3 after removal; they decreased significantly below preremoval values at day 30 in the rubber-dam group and at day 100 in both groups. Excretion rates did not increase significantly in either group, but decreased significantly at day 100 in the protected group. Peak plasma-Hg was 0.6 ng/mL on average at day one and decreased with halftimes of 3 and 43 d in subjects protected by rubber dam. The results indicated that concentrations of total mercury in plasma responded rapidly to changes in the amalgam status and reflected the actual absorption most reliably. Notably, plasma-Hg levels were sensitive enough to detect a transient attenuation of the additional exposure by using rubber dam during the removal of only a few fillings. However, being small in magnitude and lasting 100 d at best, the rubber-dam effect had minor toxicological relevance.

Absorption↗
PubMed1999

Esthetic compomer restorations in posterior teeth using a new all-in-one adhesive: case presentation.

UNLABELLED: Compomers have continually gained in importance since their introduction in 1993, especially because of their ease of handling. The main indications are cervical lesions, Class III restorations, and restorations in the primary dentition. To extend the indications of compomers to esthetic Class I and II restorations in the permanent dentition, improvements in wear resistance and bond strength need to be accomplished. Studies have shown an improved bond strength and less marginal gap formation between compomers and enamel and dentin with acid etching of the tooth before application of conventional mild self-etching adhesives. Newly formulated, improved self-etching adhesives with a higher demineralization potential recently have been developed. The objective of this case presentation is to demonstrate step-by-step the clinical procedure for the application of a newly developed self-etching adhesive with high demineralization potential in combination with a compomer material in occlusal cavities. CLINICAL SIGNIFICANCE: Improved self-etching adhesives provide a faster and simplified application technique and allow effective conditioning and priming of enamel and dentin in one step, without waiving sufficient bond strengths. With limited indications, compomers are used in combination with these self-etching primers to restore occlusal cavities in posterior teeth. Evidence-based dentistry requires exact scientific data to evaluate whether this new trend results in benefits for patients. However, until clear evidence from controlled clinical studies supports the use of improved compomer systems in Class I and II cavities in the permanent dentition, dentists should be careful with this indication.

Bicuspid↗
PubMed1999

Current state of development and perspectives of machine-based production methods for dental restorations.

The rapid domination of practically all working processes by computer and automation technology has also changed dentistry in recent years. Especially in the automatic production methods for dental restorations, the high quality of the materials used and cost reduction have opened up new possibilities in therapy. In this survey article, the current state of analog and CAD/CAM systems, together with their development potential, is described and advantages and disadvantages are analyzed.

Ceramics↗
PubMed1999

[New direct restorative materials].

People worldwide have become increasingly aware of the potential adverse effects on the environment, of pollution control and of toxic effects of food, drugs and biomaterials. Amalgam and its potential toxic side effects (still scientifically unproven) continue to be discussed with increasing controversy by the media in some countries. Consequently, new direct restorative materials are now being explored by dentists, materials scientists and patients who are searching for the so-called 'amalgam substitute' or 'amalgam alternative'. From a critical point of view some of the new direct restorative materials are good with respect in aesthetics, but all material characteristics must be considered, such as mechanical properties, biological effects, and longterm clinical behaviour.

Biocompatible Materials↗
PubMed1998

Systemic transfer of mercury from amalgam fillings before and after cessation of emission.

In 29 volunteers with a low amalgam load, the number of amalgam-covered tooth surfaces and the occlusal area of the fillings were determined. Concentrations of total mercury were measured in plasma and erythrocytes as well as in urine together with the excretion rate. Absorbed daily doses were estimated from intraoral Hg emission by two separate methods. The transfer of Hg from the fillings via the oral cavity and blood to urinary excretion was evaluated according to the most representative combination of parameters. This consisted of urinary excretion (1), Hg concentration in plasma (2), absorbed dose (3), and occlusal area (4). Pairwise correlation coefficients were 0.75 for parameters 1 vs 2 and 2 vs 3 and 0.49 for parameters 3 vs 4. Within 9 days after removal of the fillings, a transient increase was observed in plasma Hg levels only. This was reduced in those volunteers to whom a rubber dam had been applied during removal. Peak plasma Hg was 0.6 ng/ml on average and decreased with halftimes between 5 and 13 days. A significant decrease in Hg excretion was noted not before 100 days after removal. Being relatively insensitive to dietary mercury, the determination of total mercury in plasma and of its urinary excretion rate appears, under practical aspects, most suitable for the investigation of Hg uptake from amalgam.

Adult↗
PubMed1998

[Oro-dental injuries during intubation anesthesia].

Injuries to the oro-dental tissue are still one of the most frequent mishaps during endotracheal intubation and general anaesthesia. However, damage to the soft and hard tissues in most cases involves oral structures already showing advanced pathogenic alterations. Injuries to the teeth are therefore rather more often due to the disease of the teeth than to mistakes during anaesthesia. The risk of injuries to the teeth can be ascertained by means of a presurgical inspection of the oral cavity and evaluation of the individual anatomical conditions in the head and neck region, which may well interfere with the endotracheal intubation. In contrast to anaesthetic pitfalls causing severe disturbance of general health, dental trauma can be treated with quite satisfying functional and aesthetic results. However, in order to maintain conditions for the complete restitution of injured teeth immediate dental therapy is recommended. In preterm infants which need mechanical ventilation during the postnatal period direct laryngoscopy as well as mechanical alterations caused by an oral tube can cause injuries to the tooth germs of the first and second dentition and deformation of the maxillary skeleton. In consequence the patient will need intensive therapy of the resulting disturbances for several years. This review gives information about the causes and types of injuries to the oral and maxillofacial region during general anaesthesia. In addition, the anatomical conditions and pathological changes associated with an increased risk for oro-dental injuries and the facilities for prevention are discussed. Finally, the main aspects of emergency treatment of injuries to the dental hard tissues are presented.

Anesthesia, Inhalation↗
PubMed1998

One-year clinical evaluation of composite and ceramic inlays in posterior teeth.

STATEMENT OF PROBLEM: There are only a few studies available that deal with the clinical behavior of composite and ceramic inlay systems as potential substitutes for amalgam restorations. PURPOSE: This prospective clinical trial evaluated composite and ceramic inlay systems for clinical acceptability as restorative materials in single or multisurface cavities of posterior teeth and provided 1-year results. MATERIAL AND METHODS: Forty-seven composite inlays (Tetric, Blend-a-lux, Pertac) and 24 heat-pressed ceramic inlays (IPS Empress) were placed in 45 patients by 7 student operators under the supervision of an experienced dentist. The first clinical evaluation was performed 11 to 13 months after placement of the restorations and used modified United States Public Health Services criteria. RESULTS: Satisfactory results over this period were found, as 100% of ceramic inlays and 94% of composite inlays were assessed to be clinically excellent and acceptable. Only 3 composite inlay restorations were scored delta (unacceptable). Two inlays exhibited secondary caries and 1 demonstrated loss of pulp vitality. For the criteria "anatomic form of the surface" and "marginal integrity," ceramic inlays were significantly better than composite inlays. CONCLUSION: Posterior tooth-colored inlays provided acceptable and excellent clinical service, even if they are placed by relatively inexperienced student operators.

Adult↗