Biomedical subjects

R Hickel

Publications and source records attributed to R Hickel.

At least 73 records · Page 4Linked to original sources

PubMed1998

Polishing and coating of dental ceramic materials with 308 nm XeCl excimer laser radiation.

OBJECTIVES: The polishing and coating of ceramic surfaces is recommended in order to improve the physical properties of dental ceramics. Conventional methods for the surface treatment of dental ceramic materials are not capable of creating a smooth surface without microcracks. The special radiation characteristics of XeCl excimer laser light indicate that it must be possible to treat ceramic surfaces in order to produce a polished finish. The aim of this study was to investigate the efficacy of XeCl excimer laser radiation for the polishing and coating of dental ceramics. METHODS: Samples (n = 64) of four different dental ceramic materials were irradiated with 308 nm XeCl excimer laser radiation at varying energy densities per laser pulse of 1.57, 3.14, and 6.28 J cm-2. In detail, the subjects for irradiation were samples of Ivoclar-Empress (leucite-reinforced feldspathic ceramic), In-Ceram Spinell (double crystalline spinell ceramic), In-Ceram Alumina (alumina oxide; continous interpenetrating phase composite ceramic) and Vita-Mark II (feldspathic ceramic). The roughness (Ra) of the laser-treated ceramic surfaces was measured using a profilometer. In addition, SEM and AFM investigations of the changes in surface structure were conducted. The changes in surface roughness due to laser treatment were analyzed for their statistical significance using ANOVA with the Scheffé test at a level of significance of 0.05% (p < 0.05). Depending on the type of ceramic material and the energy density of the radiation, varying reductions of the surface roughness were obtained. In general, minimum values of the roughness were measured on samples irradiated with maximum energy density of radiation. RESULTS: The lowest roughness value was obtained for the specimen of In-Ceram Spinell: 1.30 (+/- 0.19) microns. The mean value for minimal roughness of Ivoclar-Empress was 1.92 (+/- 0.35) microns, that for In-Ceram Alumina was 2.04 (+/- 0.49) microns, and that for Vita-Mark II was 2.72 (+/- 0.40) microns. Ultrastructural examination of laser-treated ceramics in part demonstrated both extensive fusion and inhomogeneous surfaces with blistering and the formation of microcracks. SIGNIFICANCE: It is concluded that the physical roughness of dental ceramic surfaces can be significantly reduced by 308 nm excimer laser irradiation. Nevertheless, the laser-treated surface was in no case completely fused and the formation of microcracks and blistering was observed. Therefore, after using an XeCl excimer laser for finishing dental ceramic alloys, further polishing of the laser-treated ceramic surfaces will be needed.

Aluminum Oxide↗

PubMed1998

The effect of working parameters on root substance removal using a piezoelectric ultrasonic scaler in vitro.

This study assessed defect depth and volume resulting from root instrumentation using a piezoelectric ultrasonic scaler with a slim scaling tip in vitro. Combinations of the following working parameters were analyzed: lateral forces of 0.5 N, 1 N, and 2 N; tip angulations of 0 degrees, 45 degrees, and 90 degrees; power settings of low, medium and high; and instrumentation time of 10 s, 20 s, 40 s, and 80 s. Defects were quantified using a 3D optical laser scanner. Overall, lateral force had the greatest influence on defect volume compared to instrument power setting and tip angulation (beta-weights 0.49 +/- 0.04, 0.25 +/- 0.04, and 0.14 +/- 0.04, respectively). The effects on defect depth were highest for tip angulation followed by lateral force and instrument power setting (beta-weights 0.48 +/- 0.04, 0.34 +/- 0.04, and 0.25 +/- 0.04, respectively). Interestingly, at all power settings, the highest defect volume and depth by far were found after combining 45 degrees tip angulation with 2 N of lateral force. The efficacy of the assessed piezoelectric ultrasonic scaler may be adapted to the various clinical needs by adjusting the lateral force, tip angulation, and power setting. To prevent severe root damage it is crucial to use the assessed scaler at a tip angulation of close to 0 degrees.

Dental Instruments↗

PubMed1998

New direct restorative materials. FDI Commission Project.

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 to aesthetics, but all material characteristics must be considered, such as mechanical properties, biological effects, and longterm clinical behaviour.

Biocompatible Materials↗

PubMed1998

Working parameters of a magnetostrictive ultrasonic scaler influencing root substance removal in vitro.

This study assessed defect depth and volume resulting from root instrumentation using a magnetostrictive ultrasonic scaler with a slim scaling tip (P 12) in vitro. Combinations of the following working parameters were analyzed: lateral forces of 0.5 N, 1 N, and 2 N; tip angulations of 0 degrees, 45 degrees, and 90 degrees; power settings of low, medium, and high; and instrumentation time of 10, 20, 40, and 80 seconds. Defects were quantified using a 3-dimensional optical laser scanner. Lateral force had the greatest influence on defect volume compared to tip angulation and power setting (beta-weights 0.53+/-0.04, 0.17+/-0.04, and 0.19+/-0.04, respectively). Lateral force and tip angulation had similar effects on defect depth, but both effects were greater compared to power setting (beta-weights 0.43+/-0.04, 0.49+/-0.04, and 0.19+/-0.04, respectively). The various combinations of the assessed working parameters showed synergistic effects resulting in a wide range of defect depths (14.1+/-1.7 microm to 410.5+/-51.1 microm) and volumes (0.0084+/-0.0057 mm3 to 1.3+/-0.079 mm3). Severe root damage (defect depth >50 microm) at 40 seconds instrumentation time occurred under most combinations of lateral force, angulation, and power settings. The only exceptions were combinations of: 1) 0 degrees angulation, 0.5 N and 1 N lateral force at any power setting and 2) 45 degrees angulation, 0.5 N lateral force at low and medium power setting. The efficacy of the assessed magnetostrictive ultrasonic scaler may be adapted to the various clinical needs by adjusting the lateral force, tip angulation, and power setting.

Dental High-Speed Equipment↗

PubMed1997

CAD/CAM--fillings of the future?

The development of computer aided technology in restorative dentistry has created a range of techniques for the modern dentist. The types of systems now available and the literature published thus far on long term clinical results of restorations created by such techniques are reviewed.

Ceramics↗

PubMed1997

Working parameters of a sonic scaler influencing root substance removal in vitro.

This study assessed defect depth and volume resulting from root instrumentation using a KaVo Sonic-flex Lux 2000 L sonic scaler with a slim scaling tip (Perio-Tip no. 8) in vitro. Combinations of the following working parameters were analyzed: lateral forces of 0.5 N, 1 N, and 2 N; tip angulations of 0 degree, 45 degrees, and 90 degrees; and instrumentation time of 10 s, 20 s, 40 s, and 80 s. Defects were quantified using a three-dimensional optical laser scanner. Instrumentation time had an almost linear impact on defect depth and volume. Although lateral force (beta-weight 0.55 +/- 0.062) had a greater influence on defect volume than tip angulation (beta-weight 0.29 +/- 0.062), their effects on defect depth were similar (beta-weight 0.43 +/- 0.052 and 0.50 +/- 0.052, respectively). The combination of force and angulation showed synergistic effects resulting in a wide range of defect depths (21.9 +/- 0.96 microns to 174 +/- 28.8 microns, at 40 s) and volumes (0.056 +/- 0.019 mm3 to 0.68 +/- 0.10 mm3 at 40 s). Severe root damage (> 50 microns/40 s) did not occur at any combination of 0.5 N lateral force and/or 0 degree tip angulation. By adjusting lateral force and tip angulation, the efficacy of the assessed sonic scaler may be adapted to various clinical needs.

Dental Instruments↗

PubMed1997

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

In the course of a prospectively designed long-term clinical trial, composite fillings and inlays were evaluated for clinical acceptability as restorative materials in one, two or more surface cavities of posterior teeth over a 1-year period. In 45 patients, 88 restorations were placed by nine student operators, under the supervision of an experienced dentist, to compare the two half sides using the composite resins Tetric (Vivadent), blend-a-lux (Blend-a-med), and Pertac-Hybrid Unifil (Espe). The first clinical follow-up check took place within a time period of 11-13 months after placement of the restorations using modified USPHS criteria. The interpretation of the clinical criteria showed satisfactory results over this time period: more than 85% of the inlays and direct fillings were rated "alpha" or "bravo", using the parameters of assessment defined in this study. Only three restorations (two fillings, one inlay), all in molars, were rated "delta", i.e., unacceptable. The reasons for their replacement were marginal opening, secondary caries, and loss of sensitivity. For the criteria "surface texture", "anatomical form of the surface", and "occlusion", composite inlays were significantly better than composite fillings. These results indicate that posterior composite restorations provide acceptable and excellent clinical service, even if they are placed by relatively inexperienced student operators.

Adult↗

PubMed1997

3D volume-ablation rate and thermal side effects with the Er:YAG and Nd:YAG laser.

OBJECTIVES: The aim of this investigation was to determine the influence of a variety of parameters on the effectiveness of hard substance ablation and the thermal side effects when using Er:YAG laser (Key I and II, KaVo) and Nd:YAG laser (SunLase 800, Sunrise Technologies/Orbis). METHODS: For this study, ablation and temperature measurements were carried out on 170 dentin slices and 170 extracted teeth via computer-controlled cavity preparation. The Er:YAG laser settings varied from 250-400 mJ/pulse, 3-15 pps and 20-180 s processing time, and in the case of the Nd:YAG laser from 83-100 mJ/pulse, 10-20 pps, and 20-260 s processing time. The ablation rate was measured volumetrically via a 3D sensor. Temperatures were measured for each setting both on the dentin slice and in the pulp of the extracted teeth. The results were analyzed using a t-test for independent samples and a one-way ANOVA (Bonferroni). Also a liner regression analysis was done using Pearson's coefficient. RESULTS: The results show that with the Er:YAG laser, in combination with water-spray cooling, an effective 3D ablation rate (up to 0.017 mm3/pulse = 50 microns linear) can be achieved without raising the temperature of the surrounding tissue. In the case of the Nd:YAG laser, no measurable ablation rate was evident without conditioning of the dentin surface and, in the case of conditioning with black ink, a low ablation rate (0.00004 mm3/pulse = linear 0.2 micron/pulse) was found. SIGNIFICANCE: In contrast to the Er:YAG laser, it is apparent, that with the Nd:YAG laser from a total energy of 80 J onwards, the rise in temperature in the pulp is above 8 degrees C. For that reason, the use of the Nd:YAG laser at higher total energies is not recommended. The temperature rise with the Nd:YAG laser is dependent on the direction of the dentin tubuli. Dentin tubuli running parallel to the surface prevent significant heat penetration, whereas those running in a transverse direction to the surface (= parallel to the laser beam) support the penetration of heat. This finding supports the light-propagating theory for spreading effects of laser beams in dentin.

Aluminum Silicates↗

PubMed1997

A new optical 3-D device for the detection of wear.

For the clinical performance of new dental restorative materials to be accurately assessed, the three-dimensional anatomical changes of the functional surfaces of the restoration must be elucidated over time. To this end, a highly accurate 3-D optical scanner has been developed that utilizes the principles of triangulation and a reference-free automated 3-D superimposition software. The aim of this study was to assess the accuracy and the precision of the new system with and without referenced positioning. Additionally, the ability of the system to determine wear of posterior fillings three-dimensionally has been shown. Gypsum replicas of restored teeth were evaluated. The tooth surfaces were scanned with a resolution of 250,000 surface points within a measuring time of 20 to 40 sec. The results show that the precision and accuracy of 3-D data acquisition depend on the surface inclination. Up to an angle of 60 degrees, the precision is better than 3 microns, and the accuracy is better than 6 microns. If exact repositioning of the object before and after occlusal loading is possible, e.g., with in vitro studies, differences on the surface can be determined with a precision of 2.2 microns. In reference-free measurements, which are a necessity in clinical studies, the 3-D data acquisition in combination with the automatic matching program can detect wear with an accuracy of 10 microns. The application of this measuring device for the detection of wear of a composite filling functioning in the mouth has been shown. Since this measuring technique is automated, and measurements of high accuracy can be attained in a short period of time, this system offers the possibility for complex analyses of three-dimensional wear to be conducted on a large number of samples in clinical studies.

Algorithms↗

PubMed1997

Compartmental transfer of mercury released from amalgam.

The number of amalgam-covered surfaces and the occlusal area of the fillings, the concentrations of total mercury in plasma, erythrocytes and urine, the urinary excretion rate, and the absorbed daily doses estimated by two separate methods from intra-oral Hg emission were determined in 29 volunteers with a low amalgam load. The transfer of Hg from the fillings via the oral cavity and blood to urinary excretion was evaluated by multiple correlations between these variables. In addition, the combination of variables most representative of the entire compartmental transfer of amalgam Hg was determined. Urinary excretion (1), Hg concentration in plasma (2) and absorbed dose (3) were most closely correlated to each other, followed by correlations with the variables of the fillings (4). Correlation coefficients were 0.75 for variables 1 vs 2 and 2 vs 3, and 0.49 for variables 3 vs 4. It was concluded that variables 1-3 best reflected the transfer of mercury from amalgam fillings throughout the organism and that they were 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↗

PubMed1994

Clinical investigation into the incidence of direct damage to the lingual nerve caused by local anaesthesia.

The aim of this study was to investigate the amount of damage to the lingual nerve by mandibular block anaesthesia alone. For this purpose the records of 12,104 patients in whom mandibular block anaesthesia was administered without any type of surgery were reviewed. The reason for treatment in those patients was, in 72.4% fillings and crown preparations, in 27.13% periodontal procedures and in 0.30% other treatment. The records showed a lingual sensory disturbance in 18 out of 12,104 patients (0.15%). In 17 out of these 18 patients the tongue sensation recovered after a period of 6 months. Only in one patient (0.008%) was there a slight sensory diminution of the tongue, even after one year.

Anesthesia, Dental↗

PubMed1993

In vivo bonding of orthodontic brackets with glass ionomer cement.

The adhesion of orthodontic bracket bases was examined in vivo 24 to 32 hours after bonding with glass ionomer cement (GIC). In contrast to bonding with composite resin, with GIC there is no need to etch the enamel surface of the tooth. Conventional metal brackets with mesh pad, bonded with GIC, showed an average shear bond strength of 3.6 +/- 1.1 MPa, approximately one-fourth the bond strength of composite resin. Fracture sites were found exclusively at the mesh/GIC interface. Bonding between GIC and enamel must, therefore, be stronger than bonding between conventional resin and enamel. An experimental attachment with a modified base, consisting of brass rings 4 mm in diameter with a retention groove, was designed. In these experimental cases, fractures were found at the base/GIC interface and at the enamel/GIC interface. Shear bond strength of the experimental base was as high as 5.8 +/- 1.0 MPa. These values approached those of brackets bonded with composite resin and acid etching. Bond strengths of up the 3 MPa which occur during orthodontic treatment were achieved. Clinical trials with GIC bonding thus seem feasible and are being initiated.

Acid Etching, Dental↗

PubMed1992

[The factors affecting the risk for the loss of resin-bonded bridges].

1310 three-unit resin-bonded bridges were examined for their failure rates. After five years 86% (+/- 4%) were still in situ. 64% (+/- 5%) didn't need rebonding. Significant prognostic factors were: preparation of abutments, surface treatment (net retention, silicoating), type of luting agent (Bis GMA) and mobility of the abutments.

Adolescent↗

PubMed1991

[Individually controlled sedation using Midazolam].

Midazolam might be an alternative to general anesthesia for noncooperative children. 40 children were treated during 94 midazolam sedations to evaluate the potential dental therapy. An average of 2 fillings and 1 endodontic treatment was possible per sedation. The initial Midazolam dosage was 0.6 mg/kg. Every 15 min another 0.3 mg Midazolam/kg were administered to maintain the treatability of the children. 30 min after the initial Midazolam dosage dental treatment could be started. The average duration of a sedation was 76 min. Our results suggest that sedations complement under dental treatment general anesthesia.

Anesthesia, Dental↗

PubMed1991

[Adverse side effects of amalgam? An interdisciplinary study].

In an interdisciplinary study starting 2.5 years ago patients with various symptoms, which they associate with amalgam fillings, were examined. According to the first results of this study with 50 patients, the Hg-concentration in urine does correlate with the amount of amalgam fillings before and after taking DMPS (2,3-Dimercapto-1-propane-sulfonic-acid), but with a maximum of 66.4 micrograms Hg (24 h urine) the amounts of mobilization measured were significantly below toxicologically critical limits. Only in 3 patients did the individual immunological values (CD4/8 ratio, antinuclear antibodies) by far exceed standard values. In one case an allergy to amalgam is suspected. 40% of the patients showed a pathological psychiatric status (neurosis, depression, etc.). Another quarter had psychological problems like alcoholism or drug abuse. There is no reason at the moment to reject amalgam as filling material either because of the measured Hg-concentrations or because of any immunological or allergological findings.

Adolescent↗

PubMed1991

[Treatment of deciduous teeth under rectal Midazolam sedation].

Individual controlled sedation using Midazolam proves to be a valuable addition to the range of therapeutic options for non-cooperative children. In a clinical study the oral and rectal routes of administration were compared with each other. Rectal application allowed considerably better dose adjustment. While the quality of sedation and the therapeutic range were equal with both routes, rectal application had the advantage that treatment can be commenced sooner. The sedation was of shorter duration and left the patient with less unpleasant memories. Rectal application was easier and required a smaller amount of Midazolam than oral administration.

Administration, Oral↗

PubMed1990

[The eruption of deciduous teeth in children with various forms of Down's syndrome and congenital heart defects].

This study demonstrated that both congenital cardiovascular defects and the cytogenetic form of trisomy 21 have considerable effects on the chronology of the first dentition. The delay in the eruption of the deciduous teeth was even greater in children with congenital heart defects than in those with free trisomy 21. So-called mosaic-types of Down's syndrome, on the other hand, were associated with almost regular times of eruption.

Chromosomes, Human, Pair 21↗

PubMed1990

[Possibilities of crowning damaged primary teeth].

Supply of extensively destroyed primary molars with preformed stainless steel crowns has been a method approved for decades and can be carried out in practice without taking a lot of time and financial costs. Maintenance and reconstruction of primary anterior teeth by ready made or individually manufactured crowns is necessary also for phonetic reasons. Depending on the grade of destruction of the clinical crown different possibilities for restoration are available: that is for the group of preformed types pedoformstripcrowns, polycarbonate crowns and stainless steel crowns with a composite facing, and for the group of individual manufactured crowns as resin crowns and short-pin crowns.

Child↗