Molybdenum Oxide Nitrides of the Mo2(O,N,□)5 Type: On the Way to Mo2O5.

Blue-colored molybdenum oxide nitrides of the Mo2(O,N,□)5 type were synthesized by direct nitridation of commercially available molybdenum trioxide with a mixture of gaseous ammonia and oxygen. Chemical composition, crystal structure, and stability of the obtained and hitherto unknown compounds are studied extensively. The average oxidation state of +5 for molybdenum is proven by Mo K near-edge X-ray absorption spectroscopy; the magnetic behavior is in agreement with compounds exhibiting MoVO6 units. The new materials are stable up to ∼773 K in an inert gas atmosphere. At higher temperatures, decomposition is observed. X-ray and neutron powder diffraction, electron diffraction, and high-resolution transmission electron microscopy reveal the structure to be related to VNb9O24.9-type phases, however, with severe disorder hampering full structure determination. Still, the results demonstrate the possibility of a future synthesis of the potential binary oxide Mo2O5. On the basis of these findings, a tentative suggestion on the crystal structure of the potential compound Mo2O5, backed by electronic-structure and phonon calculations from first principles, is given.

Lithium Diffusion Pathway in Li(1.3)Al(0.3)Ti(1.7)(PO4)3 (LATP) Superionic Conductor.

The Al-substituted LiTi2(PO4)3 powders Li(1+x)Al(x)Ti(2-x)(PO4)3 (LATP) were successfully prepared by a water-based sol-gel process with subsequent calcination and sintering. The crystal structure of obtained samples was characterized at different temperatures using high-resolution synchrotron-based X-ray and neutron powder diffraction. Possible lithium diffusion pathways were initially evaluated using the difference bond-valence approach. Experimental 3D lithium diffusion pathway in LATP was extracted from the negative nuclear density maps reconstructed by the maximum entropy method. Evaluation of the energy landscape determining the lithium diffusion process in NASICON-type superionic conductor is shown for the first time.

Phases in the (1 - x)Na0.5Bi0.5TiO3-(x)CaTiO3 system.

The structures of (1 - x)Na(0.5)Bi(0.5)TiO(3)-(x)CaTiO(3) at room temperature have been investigated using neutron powder diffraction and dielectric studies. The system exhibits an orthorhombic (Pbnm) structure for x ≥ 0.15 and rhombohedral (R3c) for x ≤ 0.05. For x = 0.10, though the neutron diffraction pattern shows features of the orthorhombic (Pbnm) structure, Rietveld refinement using this structure shows a drastic reduction in the in-phase tilt angle (∼4°) as compared to the corresponding value (∼8°) for a neighbouring composition x = 0.15. The neutron diffraction pattern of x = 0.10 could be fitted equally well using a two-phase model (R3c + Pbnm) with orthorhombic as the minor phase (22%), without the need for a drastic decrease in the in-phase tilt angle. The dielectric studies of x = 0.10 revealed the presence of the polar R3c phase, thereby favouring the phase coexistence model, instead of a single-phase Pbnm structure, for this composition.

Clinical course of chronic periodontitis: effect of lifelong light smoking (20 years) on loss of attachment and teeth.

AIM: To examine the lifelong effect of light smoking on periodontal health. METHODS: The data were derived from a 20-year longitudinal study of a group of Norwegian, middle-class males. The patients were subset according to their smoking history. A total of 119 non-smokers and 17 smokers were examined, 20 years apart. RESULTS: Current smokers had significantly higher plaque indices than non-smokers after the age of 35 years, while before 35 years, there was no difference. Before 20 years of age, the non-smokers exhibited greater gingival indices, but after the age of 35, the smokers had significantly more sites that bled upon probing. Smokers demonstrated higher mean calculus indices after 35 years and as they approached 50 years of age. At baseline, the two groups showed similar attachment loss (0.14 mm), but with increasing age and approaching 50 years, the attachment loss progressed significantly faster in smokers than in non-smokers (2.31 and 1.57 mm, respectively). Linear regression indicated that ageing and light smoking were independently and significantly related to attachment loss. CONCLUSIONS: Lifelong light smoking could be confirmed as a risk factor for periodontal disease progression. However, in this population, smoking did not significantly increase the risk of tooth loss.

The clinical course of chronic periodontitis: V. Predictive factors in periodontal disease.

BACKGROUND: The factors associated with initial periodontitis are not well understood and cannot be identified by cross-sectional studies. AIM: To identify the factors associated with the initiation of chronic periodontitis using ante-dependence modelling. MATERIAL AND METHODS: A 26-year longitudinal study of the natural history of periodontitis served as the basis for the study. In 1969, 565 Norwegian men aged 16-34 years were surveyed. Subsequent surveys were performed in 1971, 1973, 1975, 1981, 1988 and finally in 1995, with 223 remaining subjects. Plaque (PlI), gingival (GI) and calculus indices (CI) and loss of attachment (LoA) were recorded. Ante-dependence modelling using a Markov chain enabled the results of this sequence of examinations to be analysed longitudinally, taking into account serial dependence, describing temporal changes in patients' levels of disease and allowing for both progression and regression between disease categories. RESULTS: With age, the rate of disease regression decreased. Increasing calculus accumulation and smoking increased the rate of disease progression, while increasing GI increased the rate of regression. CONCLUSIONS: Increased mean CI and smoking were significant predictive covariates for progression, while increased mean GI and younger age predicted regression of initial periodontitis.

Structural phase transition study of the morphotropic phase boundary compositions of Na(0.5)Bi(0.5)TiO(3)-PbTiO(3).

Neutron, synchrotron x-ray powder diffraction and dielectric studies have been performed for morphotropic phase boundary (MPB) compositions of the (1-x)Na(1/2)Bi(1/2)TiO(3)-xPbTiO(3) system. At room temperature, the MPB compositions (0.10

Magneto-structural study of a Cr-doped CaRuO(3).

Temperature-dependent neutron powder diffraction, magnetization and XPS studies were carried out on an optimally Cr-doped CaRuO(3), i.e. CaRu(0.85)Cr(0.15)O(3) (CRC-15). XPS data revealed that Cr exist in 3+ and 6+ oxidation states. The charge dissociation preserves the overall 4+ nominal charge of the Ru site. Although ferromagnetic correlations develop around 100 K, the system exhibits a large coercive field below 50 K. The unit cell volume exhibits negative thermal expansion below 50 K since the lattice expansion due to the magnetostrictive effect outweighs the thermal contraction due to the phonon-driven mechanism.

Structural disorder of a new zeolite-like lithosilicate, K(2.6)Li(5.4)[Li4Si16O38].4.3H2O.

The framework structure of the synthetic microporous lithosilicate RUB-30 (K(2.6)Li(5.4)[Li4Si16O38].4.3H2O) is similar to that of the fibrous zeolites such as natrolite, edingtonite and thomsonite, since all their frameworks include the same secondary structural building unit, the so-called 4-1 T5O10 cluster of tetrahedra. Unique to the structure of RUB-30, each 4-1 unit consists of a LiSi4O10 moiety within which the single [LiO4] tetrahedron is strictly segregated from the other four [SiO4] tetrahedra. The connection of neighboring 4-1 units through edge-sharing [LiO4] tetrahedra results in a new framework topology. The present work reports an ;average' structure of RUB-30 solved by synchrotron X-ray single-crystal diffraction data collected at a second-generation source. A superstructure with a x 2b x c (relative to the subcell quoted above) could be seen in X-ray diffraction data collected with better resolution and higher brightness at a third generation source. Diffuse streaks along k with l = odd and unusual superstructure hkl reflections, with k = odd and l = odd only, indicate a more complicated real structure of the material. To explain this observation we propose two different structure types which are statistically, but coherently, intergrown in RUB-30.

The natural history of periodontal disease in humans: risk factors for tooth loss in caries-free subjects receiving no oral health care.

AIM: No long-term studies have reported on risk factors for tooth loss in subjects without home or professional dental care. The purpose of this report is to identify potential risk factors for tooth loss among male Sri Lankan tea labourers who participated in a 20-year investigation of the natural history of periodontal disease. MATERIAL AND METHODS: Data for this report were obtained from the 455 subjects who participated in multiple examinations over the 20-year period from 1970 to 1990. Analyses included data from interim examinations in 1971, 1973, 1977, 1982 and 1985. Oral health assessments included the following: (1) attachment levels in millimetres on all mesial and mesio-buccal surfaces, excluding third molars; (2) plaque index; (3) gingival index; (4) calculus index; (5) caries index; and (6) missing teeth. Other variables included age, history of smoking and betel nut use. Statistical analyses included descriptive statistics and multivariate repeated-measures modelling with generalized estimating equations. RESULTS: Tooth loss was significantly dependent upon interactions between the mean attachment loss and betel nut use (Z=3.40; p=0.0007) and history of missing teeth (Z=-3.70; p=0.0002). The effect of attachment loss on tooth loss was increased in the presence of betel nut and diminished when teeth were already missing at baseline. CONCLUSION: History of missing teeth, betel nut use and increasing attachment loss were significant predictors of tooth loss over time. Betel nut use increased the effect of attachment loss on loss of teeth, while history of missing teeth diminished the effect of attachment loss on tooth loss.

Anion diffusion in Y- and N-doped ZrO2.

Effective single particle potentials governing the motion of O2 and N3- anions have been determined by single crystal neutron diffraction at high temperatures for three samples of ZrO2 doped with different amounts of Y and N. Diffusion jumps take place directly to vacant nearest neighbour anion sites through the edges of the surrounding cation tetrahedra along (100)-directions. Activation enthalpies of migration for O (1.09 eV) and N (1.99 eV) are in good agreement with values obtained from tracer diffusion measurements (M. Kilo, C. Argirusis, G. Borchardt and R. A. Jackson, Phys. Chem. Chem. Phys., 2003, 5, 2219 and M. Kilo, M. A. Taylor, C. Argirusis, G. Borchardt, M. Lerch, O. Kaitasov and B. Lesage, Phys. Chem. Chem. Phys., 2004, 6, 3645). The diffusion process is facilitated by local short range order and anharmonic thermal vibrations. It is therefore advocated that the interactions with the phonons have to be taken into account in the description of the diffusion process.

The clinical course of chronic periodontitis.

AIM: The purpose of this study was to assess the long-term influence of gingival inflammation on tooth loss. MATERIAL AND METHODS: The data originated from a 26-year longitudinal study of Norwegian males, who practiced adequate daily oral home care and received "state-of-the-art" dental care. The initial examination in 1969 included 565 individuals aged between 16 and 34 years. Subsequent examinations took place in 1971, 1973, 1975, 1981, 1988 and 1995. Thus, the study covers the age range of 16-59 years. The teeth were divided into three tooth groups (I-III) reflecting the history of inflammation of the surrounding gingiva (gingival index (GI) scores) over 26 years: (I) teeth with surrounding gingival units scoring a minimum of one site with GI=0 and a maximum of three sites with GI=1, (II) teeth with surrounding gingival units scoring a minimum of one site with GI=1 and a maximum of three sites with GI=2 over the observation periods and (III) teeth with surrounding gingival units always scoring a minimum of GI=2 (bleeding on probing) at all sites over the observation period. RESULTS: At baseline (1969), out of possible 15,820 teeth (565 x 28), 15,383 teeth were present. Four hundred and thirty-seven teeth had already been missing for unknown reasons. By 1995, 13,159 teeth were reexamined, i.e. over the 26-year observation period only 126 (0.95%) teeth were lost. Only 16 (0.28%) of 5793 teeth belonging to GI-Severity Group I were lost. In the GI-Severity Group II, however, 78 (2.28%) out of 3348 teeth were lost, and 13 (11.21%) of 103 teeth with GI-Severity Group III were lost. Teeth with GI-Severity Group III yielded an odds ratio for tooth loss that was 46 times higher than that of teeth with GI-Severity Group I, and five times higher than that of teeth with GI-Severity Group II over 26 years. Furthermore, teeth with the GI-Severity Group II had a nine times higher risk for tooth loss than teeth with the GI-Severity Group I. The GI-Severity Group I retained 99.5% of the teeth after a tooth age of 51 years. The GI-Severity Group II retained 93.8% of the teeth after a tooth age of 50 years. However, in the GI-Severity Group III, 63.4% of the teeth were retained for a tooth age of 47 years. CONCLUSIONS: Teeth surrounded with inflammation-free gingival tissues were maintained for a tooth age of 51 years, while teeth consistently surrounded with inflamed gingivae yielded a 46-times higher risk to be lost. Only two-thirds of such teeth were maintained throughout the 26-year observation period. This documents the role of gingival inflammation as a risk factor for future tooth loss.

Clinical course of chronic periodontitis. I. Role of gingivitis.

OBJECTIVES: The purpose of this study was to determine the influence of long-standing gingival inflammation on periodontal attachment loss. On the basis of repeated examinations, the present report describes the influence of gingival inflammation on the initiation of periodontitis from 16 to 59 years of age. MATERIAL AND METHODS: The data originated from a 26-year longitudinal study of Norwegian males, who practiced daily oral home care and received state-of-the-art dental care. The initial examination included 565 individuals. Subsequent examinations took place in 1971, 1973, 1975, 1981, 1988 and 1995. Thus, the study covers the age range of 16-59 years. All tooth sites were divided into four categories according to their history of gingival inflammation over the entire observation period: sites always scoring GI = 0, GI = 1 and GI = 2 sites (GI = gingival index). Sites disclosing various GI scores at different observation periods were not considered. RESULTS: The mean cumulative attachment loss for non-inflamed (GI = 0) sites in individuals approaching 60 years of age was 1.94 mm. Sites always scoring GI = 1 yielded 2.42 mm, and sites that always scored GI = 2 exhibited 3.31 mm of periodontal attachment loss. At interproximal sites of all three groups where gingival trauma was assumed to be minimal or non-existent, only very few sites expressed attachment loss due to gingival recession (2-4%). At interproximal sites always scoring GI = 0, 20% loss of attachment was in the form of pocket formation by 59 years of age. The GI = 1 and the GI = 2 cohorts exhibited attachment loss with pocket formation in 28% and 54%, respectively. CONCLUSION: This study has shown that, as men approach 60 years of age, gingival sites that throughout the 26 years of observation bled on probing had approximately 70% more attachment loss than sites that were consistently non-inflamed (GI = 0). Before 40 years of age, there was a slight increase in periodontal attachment loss due to pocket formation, but after this, the frequency increased significantly. Loss of attachment due to gingival recession was very small in all three groups. The fact that sites with non-inflamed gingiva also exhibited some loss of attachment and pocket formation may be explained by fluctuation in the variations of tissue status during long observation intervals combined with the presence of subclinical inflammation.

Clinical course of chronic periodontitis. II. Incidence, characteristics and time of occurrence of the initial periodontal lesion.

AIM: The purpose of this study was to assess the initiation and progression of periodontal disease during adult life. MATERIALS AND METHODS: In a 26-year longitudinal investigation of the initiation and progression of chronic periodontitis that started in 1969 and included 565 men of Norwegian middle class, 223 who had participated in some, but not all, intermediate examinations presented at the last survey in 1995. Fifty-four individuals were available for examination in all seven surveys. RESULTS: Covering the age range from 16 to 60 years, the study showed that at 16 years of age, 5% of the participants had initial loss of periodontal attachment (ILA > or = 2 mm) at one or more sites. Both the subject incidence and the site incidence increased with time, and by 32 years of age, all individuals had one or more sites with loss of attachment. As age progressed, new lesions affected sites, so that as these men approached 60 years of age approximately 50% of all available sites had ILA. An assessment of the intraoral distribution of the first periodontal lesion showed that, regardless of age, molars and bicuspids were most often affected. At and before the age of 40 years, the majority of ILA was found in buccal surfaces in the form of gingival recession. By 50 years, however, a greater proportion of sites presented with attachment loss attributed to pocket formation or a combination of pocket formation and gingival recession. As individuals neared 60 years of age, approximately half of the interproximal areas in posterior teeth had these lesions. CONCLUSION: This investigation has shown that, in a well-maintained population who practises oral home care and has regular check-ups, the incidence of incipient periodontal destruction increases with age, the highest rate occurs between 50 and 60 years, and gingival recession is the predominant lesion before 40 years, while periodontal pocketing is the principal mode of destruction between 50 and 60 years of age.

Clinical course of chronic periodontitis. III. Patterns, variations and risks of attachment loss.

AIM: The purpose of this study was to assess the rate of attachment loss during various stages of adult life in a well-maintained middle-class population. MATERIAL AND METHODS: The data originated from a 26-year longitudinal study of Norwegian males who had received regular and adequate dental care and practised daily oral home care. The initial examination in 1969 included 565 individuals aged between 16 and 34 years. Subsequent examinations took place in 1971, 1973, 1975, 1981, 1988 and 1995. Thus, the study covers the age range of 16-59 years. The rate of the annual attachment loss was calculated as the difference between the individual mean attachment loss between two examinations divided by the years between examinations. The mean annualized relative risk of attachment loss was calculated as the frequency distribution of sites with initial periodontal attachment loss (loss of attachment at the first time of occurrence > or = 2 mm) and healthy sites (loss of attachment always < 2 mm). For comparison of significant changes in annual attachment loss rates between the age groups and mean annualized relative risks of attachment loss as they proceeded through adult life, the Wilcoxon Mann-Whitney U-test was used. RESULTS: The mean overall individual attachment loss during 44 years (between 16 and 59 years) totaled 2.44 mm (range 0.14-2.44 mm), averaging an annual mean rate of 0.05 mm/year. The highest annual rate of attachment loss occurred before 35 years of age (0.08-0.1 mm/year), after which the mean annual rate decreased to about 0.04-0.06 mm/year for the next three decades of life leading to 60 years. The mean annualized relative risk of initial attachment loss increased significantly from adolescence (1.2%) to the maximum at 30-34 years of age (6.9%). After the age of 34 years, the risk of initial attachment loss decreased again, but after the age of 40 years, another continuous increase was observed. CONCLUSIONS: Over a 26-year period, 25% of the subjects went through adult life with healthy and stable periodontal conditions. The remaining 75% developed slight to moderately progressing periodontal disease with progression rates varying between 0.02 and 0.1 mm/year with a cumulative mean of loss of attachment of 2.44 mm as they approached 60 years of age. The annual mean rate and the mean annualized risk of initial attachment loss were highest between 16 and 34 years of age. Only 20% of the sites continued to lose further attachment during the remainder of the observation period, and less than 1% of the sites showed substantial loss of attachment (> 4 mm).