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Hans-Peter Weber

Publications and source records attributed to Hans-Peter Weber.

15 recordsLinked to original sources
PubMed2006

Hydrated Cs+-exchanged MFI zeolites: location and population of Cs+ cations and water molecules in hydrated Cs6.6MFI from in and ex situ powder X-ray diffraction data as a function of temperature and other experimental conditions.

Extending our previous investigation of dehydrated, Cs-exchanged MFI zeolites (J. Phys. Chem. B 2006, 110, 97-106) to hydrated analogues, we have determined the crystal structures of members of the Cs(6.6)H(0.3)MFI.xH(2)O series, for 0 < x < 28, from synchrotron-radiation powder diffraction data. In the fully hydrated phase, three independent Cs(+) cations and six water molecules are identified in difference Fourier maps. The populations of the cations amount to 2.79/3.40/0.41 Cs/unit cell (uc) for the Cs1/Cs2/Cs3 sites, respectively, and those of the water molecules to 4/4/4/4/8/4 H(2)O/uc for the Ow1/Ow2/Ow3/Ow4/Ow5/Ow6 sites, respectively. Close to water saturation, the Cs3 and Ow6 sites are near each other (approximately 1.44 A) and are not occupied simultaneously. At saturation, Cs cations and water molecules form three interconnected Cs(H(2)O)(n) clusters and one (H(2)O)(4) cluster in the MFI channel system: Cs2(H(2)O)(5) centered at x/y/z approximately -0.018/0.146/0.546 (midway between the intersection and the straight channels), Cs1(H(2)O)(4) centered at approximately 0.056/0.240/0.889 (the zigzag channel openings), Cs3(H(2)O)(2) centered at approximately 0.228/0.25/0.899 (in the zigzag channel), and the (H(2)O)(4) cluster (in the zigzag channel) bonded to Cs1 and Ow1. (H(2)O)(4) and Cs3(H(2)O)(2) exclude each other. The Cs2(H(2)O)(5) clusters are connected through weak Ow5...Ow5' hydrogen bonds (2.88 A) and form polymeric chains in the straight channel direction (010). During progressive hydration this Cs2 cation enlarges its hydration shell, stepwise, from Cs2(H(2)O)(2) to Cs2(H(2)O)(3), to Cs2(H(2)O)(4), and finally to a Cs2(H(2)O)(5) cluster. During the dehydration process, these extraframework species migrate, and it is shown that for varying total H(2)O/uc loadings the individual populations of the Cs(+) cations and H(2)O molecules strongly depend on experimental and measurement (in situ vs ex situ) conditions. The shapes of the channels change also; except for T > 150 degrees C, in all the Cs(6.6)H(0.3)MFI.xH(2)O phases, the straight channel D10R (double 10-ring) pore openings (1.16 < epsilon < 1.23) become strongly elliptical. The framework structure of all the investigated phases conforms to orthorhombic Pnma space group symmetry. Hydration and dehydration in Cs(6.6)MFI are fully reversible processes. From a knowledge of the Cs(+) locations, we are able to estimate, by computer simulations, the positions of H(2)O molecules in Cs(6.6)H(0.3)MFI.28H(2)O. The maximum theoretically possible water loading in an hypothetical and idealized cationless [Cs(6.6)H(0.3)]MFI structure amounts to 48 H(2)O/uc (nine independent water species), which is in fair agreement with existing high-pressure data (47 H(2)O/uc). This value is to be compared with the water saturation capacity obtained in a structural refinement of sealed-tube diffraction data of a proton-exchanged H(6.9)MFI.38H(2)O (seven independent water molecules). In the crystal structure of this H-ZSM-5 phase, the straight channel openings are almost circular (epsilon = 1.08). From this we conclude that the main factor responsible for the flexibility of the MFI framework is the presence of the Cs(H(2)O)(n)() clusters residing in, or close to, the straight channel double 10-rings.

Journal Article↗
PubMed2006

Dyggve-Melchior-Clausen syndrome and Smith-McCort dysplasia: clinical and molecular findings in three families supporting genetic heterogeneity in Smith-McCort dysplasia.

Dyggve-Melchior-Clausen syndrome (DMC) (MIM 223800) and Smith-McCort dysplasia (SMC) (MIM 607326) are rare allelic autosomal recessive spondylo-epi-metaphyseal dysplasias (SEMDs) characterized by similar skeletal manifestations. Both phenotypes have been mapped to chromosome 18q21.1 and mutations in the DYM (dymeclin) gene were identified in 13 families with DMC and in two families with SMC. Most mutations identified in DMC predict a loss of function, while those identified in SMC are mainly missense mutations, presumably associated with residual DYM activity and a less severe phenotype. We studied three consanguineous families from Turkey, Lebanon, and Georgia, one with SMC and two with DMC and identified different homozygous DYM mutations (IVS3 194-1G > A, 938_942delTGTCT) in the DMC families. No mutation was identified in the SMC family, possibly suggesting genetic heterogeneity of this disorder.

Adolescent↗
PubMed2006

Dehydrated and Cs+-exchanged MFI zeolites: location and population of Cs+ from in situ diffraction data as a function of temperature and degree of exchange.

H-MFI type zeolitic materials of different Si/Al ratios have been completely or partially cesium-exchanged (cesium content ranging from 0.7 to 7.7 Cs/unit-cell (uc)). Examined with synchrotron X-ray powder diffractometry, an anhydrous sample with the Cs6.6H0.3Al6.9Si89.1O192 chemical composition revealed at ambient temperature the presence of five discrete Cs locations: Cs1 located in the channel intersection near a 10-ring window of the zigzag channel; Cs2 and Cs2', both located in the straight channel but 1.23 A apart; Cs3 and Cs3', both located in the zigzag channel and rather close to each other (2.51 A). The populations of the Cs species amounted to 2.61/0.81/1.85/0.86/0.47/uc for Cs1/2/2'/3/3', respectively. The continuous but multimodal nature of the C2 split site is well-described by a joint-probability density function. The 10-ring of the straight channel in the framework is highly elliptical (epsilon = 1.218). The populations for the same sites were also determined at higher temperatures: 131, 237, 344, and 450 degrees C. At 450 degrees C, Cs2' has migrated toward the center of the channel intersection, and the site separation between Cs2 and Cs2' has lengthened to 2.23 A. Using a temperature-controlled laboratory X-ray diffractometer, similar studies were carried out on partially or almost totally Cs-exchanged samples from various sources with differing Cs contents. They show that over the 0.7 to 4 Cs/uc range all the individual Cs populations vary linearly as a function of total Cs/uc present. At higher total Cs/uc content (4 to approximately 7 Cs/uc) solely Cs1 continues to do so. For Cs2+Cs2' and Cs3+Cs3', the variation is almost linear over the whole concentration range. Computer simulations using a 6-exp-1 Buckingham-type atom-atom van der Waals interaction model yield six possible Cs sites in the actual Cs6.6MFI framework structure. Four of them lie very close to those determined from difference Fourier maps using the room temperature data. A fifth one is close to the Cs2' species after thermal migration at 450 degrees C, and the sixth one is close to the center of the channel intersection. However, this latter site is observed experimentally only in the case of hydrated CsMFI phases. In the anhydrous Cs6.6MFI phase at room temperature, the shortest Cs-framework oxygen distance is Cs3'-O25 = 3.08 A, and the next shortest distances are Cs1-O26 = 3.37, Cs2-O11 = 3.34, Cs2'-O22 = 3.47, and Cs3-O20 = 3.34 A. The framework T(Si,Al) sites most involved in these contacts are the T9, T11, T12, T10, and T3 sites. This implies that these sites are prime candidates for Si/Al substitution.

Journal Article↗
PubMed2005

Reproducibility of tooth color gradation using a computer color-matching technique applied to ceramic restorations.

STATEMENT OF PROBLEM: To reproduce tooth color precisely, an objective methodology based on color science is required. However, perception-based techniques are still the primary method for color matching in restorative dentistry. PURPOSE: This study evaluated the accuracy of reproduction of color gradation for ceramic restorations using a Computer Color Matching (CCM) technique employing a prototype program and spectrophotometric data measurements. MATERIALS AND METHODS: The colors of 10 target-shade tabs of the Vitapan 3D Master shade guide were measured at 4 regions of crowns from the cervical to the incisal area using a spectrophotometer. Tooth-shaped CCM ceramic specimens (30 specimens; 3 specimens for each of 10 target-shade tabs), the same size and shape as target-shade tabs, were fabricated according to the CCM prescriptions calculated using a prototype CCM program. The colors of CCM ceramic specimens and target-shade tabs were compared in 10 incremental areas from gingival to incisal (each measuring 1 mm high x 3 mm wide). The color differences, Delta E, Delta L* , Delta a* , and Delta b* , were calculated. The color difference Delta E values were analyzed by a repeated measures analysis of variance (P <.0001). Three prosthodontists evaluated CCM specimens by perception techniques. RESULTS: The mean color difference (Delta E) values were clinically acceptable (below 3.6) for incremental areas 3 through 10 and unacceptable for areas 1 and 2 (gingival area). Highly significant differences in the mean of Delta E values among target-shade tabs (P <.0001), areas (P <.0001), and target-shade tab-by-area interaction effects (P <.0001) were noted. However, perceptional evaluation indicated "Definitive match" or "Approximate match" for all CCM specimens. CONCLUSION: The CCM technique tested in this study utilizing 4 measurements on target-shade tabs could reproduce tooth color gradation from incisal to precervical regions with clinically acceptable results.

Analysis of Variance↗
PubMed2005

Achieving immediate function with provisional prostheses after implant placement: a clinical report.

When using a conventional implant treatment protocol in edentulous patients, reduced function and comfort for up to 6 months after implant surgery is inevitable until bone healing is complete and a prosthesis is securely attached to the implants. The following report highlights 2 treatment modalities that enable immediate function by inserting provisional prostheses immediately after implant placement.

Aged↗
PubMed2004

The charge density of urea from synchrotron diffraction data.

The charge density of urea is studied using very high precision single-crystal synchrotron-radiation diffraction data collected at the Swiss-Norwegian Beam Lines at ESRF. An unprecedented resolution of 1.44 A(-1) in sin theta;/lambda is obtained at 123 K. The optimization of the experiment for charge-density studies is discussed. The high precision of the data allowed the refinement of a multipole model extending to hexadecapoles and quadrupoles on the heavy and H atoms, respectively, as well as a liberal treatment of radial functions. The topological properties of the resulting electron density are analysed and compared with earlier experimental results as well as with periodic Hartree-Fock calculations. The properties of the strongly polarized C-O bond agree with trends derived from previous experimental results while the ab initio calculations differ significantly. The results indicate that the description of the C-O bond requires more flexible basis sets in the theoretical calculations. The calculated integrated atomic charges are much larger than the observed ones. It is suggested that the present experimental results provide new target values for validation of future ab initio calculations. The molecular dipole moment derived from the integrated atomic properties is the same as the one obtained from the multipole model even though the individual atomic contributions differ. Comparison with literature data for urea in solution and the gas phase yields a dipole enhancement in the solid of about 1.5 D. The thermal expansion of urea is determined using synchrotron powder diffraction data. With decreasing temperature, an increasing anisotropic strain is observed.

Journal Article↗
PubMed2004

Mandibular two-implant telescopic overdentures.

To stabilize mandibular overdentures in edentulous patients, various connector types which can be attached to between two and four implants placed in the anterior mandible are possible. Treatment using non-rigid telescopic connectors on two interforaminal implants for overdenture stabilization began in 1989. The objective of this study is to investigate soft- and hard-tissue conditions as well as prosthesis function after a period of 10 years. This also involved an evaluation of correlations between radiographic and clinical parameters. Twenty-three subjects with 46 interforaminal implants (ITI solid screw implants, 12 mm in length, 4.1 mm in diameter; 10.4 years in situ, range, 8-12.8 years) were investigated. Modified plaque index (mPI), sulcus fluid flow rate (SFFR), modified sulcus bleeding index (mBI), probing depth (PD), distance from implant crown margin to the coronal border of the peri-implant mucosa (DIM), attachment level (AL), width of keratinized mucosa (KM), Periotest values (PTVs) and prosthesis function were evaluated. In the radiographic evaluation, the distance between implant shoulder and first crestal bone-implant contact (DIB) in mm and the horizontal bone loss (HBL) in mm were measured. The relatively high mPI scores (mean, 0.82; score, 0 in 44.4%; SD, 0.83) did not result in increased SFFR scores (mean, 12; min, 3, max, 38; SD, 7.43) or higher mBI scores (mean, 0.35; score, 0 in 70.8%; SD, 0.59), which was commensurate with healthy peri-implant mucosa. A mean PD value of 2.15 mm (min, 1 mm; max, 5 mm; SD, 0.96) and a mean DIM value of 0.28 mm (min, 0 mm; max, 2 mm; SD, 0.52) were measured. The implants were stable, showing a mean Periotest value of -1.91 (max, 02, min, -6; SD, 1.76). A mean DIB of 3.19+/-0.95 mm (range, 1.3-5.16 mm) and a mean HBL of 1.6+/-1.52 mm (range, 0.28-8.33 mm) were calculated. A correlation was found between DIB and the parameters SFFR (P=0.060), DIM (P=0.042), AL (P=0.050) and especially PTV (P<0.01), leading to the assumption that these clinical parameters may be useful indicators of peri-implant bone loss. The results of the 10-year follow-up examination show that non-rigid telescopic connectors with two interforaminal implants for overdenture stabilization appear to be an efficient and effective long-term treatment modality in severely resorbed edentulous mandibles. Particularly in geriatric patient treatment this concept may provide advantages in terms of handling, cleaning and long-term satisfaction.

Aged↗
PubMed2004

Immediate restoration and loading of dental implants: clinical considerations and protocols.

The use of dental implants to assist in the treatment of partial and complete edentulism is well documented. Most of the implant literature, however, reports results associated with implant survival and success when there has been adherence to rigid placement and loading protocols. Conventionally, these protocols call for the undisturbed healing of the implant-3 months in the mandible and 4 to 6 months in the maxilla. This article evaluates the literature and develops protocols for clinical procedures for the early or immediate restoration or loading of dental implants. Criteria are established for defining immediate loading, immediate restoration, early loading, and early restoration as compared to conventional protocols. The review assesses factors that influence accelerated loading and restoration decisions, including bone quality and quantity, implant design, splinting of implants, and prosthetic design. Conclusions and recommendations are made based on the experience of the consensus group charged with considering these procedures and on the current literature published on these protocols.

Bone Density↗
PubMed2003

Protonation site and hydrogen bonding in anhydrous and hydrated crystalline forms of doxazosin mesylate from powder data.

The three-dimensional solid-state structures of two modifications of doxazosin mesylate (C23H26N5O5)+.(CH3SO3)-, 4-amino-2-[4-[(2,3-dihydro-1,4-benzodioxin-2-yl)carbonyl]piperazin-1-yl]-6,7-dimethoxyquinazoline methanesulfonate, a commonly used antihypertensive agent, have been determined by synchrotron X-ray powder diffraction. An anhydrous form (A) and a dihydrate form (dG) crystallize in monoclinic space groups. In both forms the doxazosin molecule is protonated at the N1 atom of the quinazoline bicycle. The N1 atom, and the amino H atoms and O atoms of the mesylate moieties are involved in three-dimensional hydrogen-bonding networks, while solvent water molecules and carboxamide O atoms are also incorporated in a hydrogen-bonding network in dG.

Crystallization↗
PubMed2002

Secondary caries in crowned teeth: correlation of clinical and radiographic findings.

STATEMENT OF PROBLEM: The diagnostic value of radiographs for interproximal caries detection on nonrestored teeth is well investigated. However, little is known about the use of radiographs in the diagnosis of secondary caries localized at crown margins. PURPOSE: The aim of this study was to correlate clinical findings with regard to secondary caries with the findings of a radiographic evaluation. MATERIALS AND METHODS: One hundred randomly selected patients who underwent restorations with fixed prostheses and were exhibiting at least one secondary carious lesion were included in the study. A total of 820 restorations (test group, 730 interproximal surfaces of 365 single crowns and 910 interproximal surfaces of 455 fixed partial denture retainer crowns) and 1024 interproximal surfaces of 512 nonrestored teeth (control group) were investigated clinically, with the use of modified California Dental Association criteria, and radiographically for interproximal carious lesions. The extension of the lesions was rated to be initial (with no cavitation), early (with cavitation limited to orthodentin), or deep (with cavitation). The data were statistically analyzed for normal distribution, and the frequency of the findings was calculated in absolute numbers and as a percentage. Statistically significant differences were determined by use of the chi(2) test (P<.05). A linear regression model was applied for the correlation between the percentage of secondary caries and the duration of the crowns in situ. RESULTS: Secondary caries was diagnosed clinically in 11.2% of 1640 interproximal surfaces but only in 8.3% radiographically. In contrast, the frequency of interproximal carious lesions diagnosed clinically in nonrestored teeth increased with the use of radiographs from 3.3% to 4.1%. CONCLUSION: Within the limits of this study, the results confirm that radiographs improve the diagnostic sensitivity for interproximal caries in nonrestored teeth. However, for the diagnosis of secondary caries in crowned teeth, the clinical examination is more reliable than the radiographic evaluation.

Chi-Square Distribution↗
PubMed2002

Histologic and radiographic assessment of caries-like lesions localized at the crown margin.

STATEMENT OF PROBLEMS: Little is known about the impact of crown margins on the demineralization and remineralization process or on the interpretation of radiographs for the detection of early secondary caries. PURPOSE: The aim of this study was to correlate the findings from 2 different radiographic techniques with the results of a histologic assessment of carieslike lesions at the crown margin. MATERIAL AND METHODS: Ten fully impacted third molars were extracted and restored with complete metal crowns with chamfer preparations. For each tooth, the prepared margin ended in enamel on one side and extended into cementum/dentin on the other. After being thoroughly cleaned, the teeth were covered with wax except for a 2- x 3-mm window at the crown margin in each of 2 test areas localized at the interproximal enamel and cementum/dentin junction. During demineralization with 6% hydroxyethyl cellulose gel at pH 4.9, direct digital radiographs or conventional radiographs were made at baseline and after 7, 14, 21, and 28 days. Each radiograph was blinded and examined for the presence/absence of lesions by 3 calibrated observers who used predetermined criteria required for receiver operating characteristic (ROC) analysis. After 28 days, the teeth were imbibed with methyl methacrylate and serially ground sectioned for assessment of the lesions in polarized light. Morphometric analysis of lesion extension included the calculation of mean values and standard deviations. Kappa and ROC analysis were applied to assess radiographs made at different demineralization time periods, localization of the crown margins in enamel or cementum/dentin, and direct digital and conventional radiographs. Data were tested for normal distribution (QQ plot), and statistical differences were calculated with Tukey's honestly significant difference post hoc test. RESULTS: Radiographic evaluation revealed only slight interexaminer agreement (Kappa) for enamel lesions (direct digital 0.19, conventional radiographs 0.2) and a fair interexaminer agreement for cementum/dentin lesions (direct digital 0.35, conventional radiographs 0.33). ROC analysis revealed no differences between the radiographic techniques. Lesions localized in cementum/dentin (direct digital 0.86 +/- 0.14, conventional radiographs 0.86 +/- 0.09) were diagnosed more reliably than those in enamel (direct digital 0.79 +/- 0.05, conventional radiographs 0.72 +/- 0.10). As microscopically assessed, the depth of lesions in enamel was less than that of lesions in cementum/dentin (49.3 +/- 7.3 microm vs 89.5 +/- 13.2 microm). Erosions were found in cementum/dentin (depth 25.2 +/- 5.3 microm). CONCLUSION: Within the limitations of this study, small artificial lesions were detected equally well by conventional and direct digital radiography. However, because of low interexaminer agreement, the radiographic assessment did not reproduce true histopathologic lesion characteristics documented by morphometry of serial ground sections.

Adolescent↗
PubMedDate not supplied

Peri-implant pathology caused by periapical lesion of an adjacent natural tooth: a case report.

An implant was removed 6 months after restoration because of peri-implant pathosis. The implant had been placed adjacent to the mandibular right second premolar and close to a periapical lesion of the endodontically treated adjacent first premolar. Along with removal of the failed implant and an apicoectomy of the problem tooth, guided bone regeneration was used to restore the alveolar ridge defect at the site of the failed implant. A replacement implant was placed 6 months later and successfully restored after healing.

Adult↗
PubMedDate not supplied

Voids and interlayer gaps in Class 1 posterior composite restorations: a comparison between a microlayer and a 2-layer technique.

OBJECTIVE: The main objective was to compare the presence of interlayer gaps between 2 hybrid composites placed using a microlayer and a 2-layer technique. METHOD AND MATERIALS: Standardized Class 1 cavities were prepared in 40 extracted posterior teeth. Two resin composite materials were used. The control group, group A, consisted of samples of the materials extruded out of the manufacturers' syringes. Group B consisted of 10 teeth restored using 2 layers per restoration. Group C consisted of 30 teeth restored using 6 microlayers per restoration. A scanning electron microscope was used to detect voids in the samples. RESULTS: Round, well-defined voids were found in 85% to 100% of the samples within the bulks of the resin composite materials only. A statistically significant relationship between the type of composite and presence of bubbles (Fisher exact test, P = .04) was found among the 2-layer technique group. No statistically significant difference (Fisher exact test, P = .48) was found among the microlayer technique group. Irregular interlayer gaps were found in 5% to 15% of specimens within areas between bulks of composite, as detected by an electron microscope based on the different densities of the bulks of composite and the interlayer areas. No such statistically significant relationship was found (Fisher exact, P = .62) among the study groups. CONCLUSIONS: Voids are routinely found in bulks of composite materials. Higher incidences of interlayer gaps in the 2-layer samples suggest that the use of a microlayering technique may result in fewer gaps.

Acrylic Resins↗