A.J. van Wijk

Nitrogen cycling in acid forest soils subject to increased atmospheric nitrogen input

Nitrogen cycling was studied in four forest ecosystems in the Netherlands, characterized by increased atmospheric nitrogen input. The study involved in situ incubation experiments to measure nitrogen transformation rates in the ectorganic (L + F + H) layer and the top 5 cm of the mineral soil. Throughfall and lysimeter data were collected from two of these sites to determine nitrogen solute fluxes and the proton production related to nitrogen cycling. The annual nitrogen input by throughfall ranged from 22 to 55 kg N ha−1 year−1. On the basis of the nitrogen budget, three of the forests could be characterized as nitrogen saturated. In two of these three forests high nitrification rates (16 kg N ha−1 year−1) were measured in the ectorganic layer and in the top of the mineral soil. At the other sites relatively low nitrate production rates (5–6 kg N ha−1 year−1) were measured. Net mineralization rates ranged from 26 to 71 kg N ha−1 year−1 in the investigated layers. A strong positive relationship between net nitrogen mineralization and nitrification rate was found at the two sites with high nitrification rates. Nitrification rate relative to net mineralization rate ranged from 22 to 29%. A comparison between incubation and lysimeter data revealed a quantitative discrepancy. It was concluded that the in situ incubation technique underestimates nitrogen transformation rates. Nitrogen solute fluxes indicated that in the nitrifying site, high nitrate production rates in the ectorganic layer coincided with large nitrate fluxes underneath this layer, while the nitrate produced in the top of the mineral soil had no net effect on the nitrate flux underneath that layer. As a result, high proton production rates (4.7 kmol H+ ha−1 year−1) as a result of nitrogen transformations, were calculated for the ectorganic layer of this forest.

A review and meta-analysis of the heritability of specific phobia subtypes and corresponding fears

Evidence from twin studies suggests that genetic factors contribute to the risk of developing a fear or a phobia. The aim of the present study was to review the current literature regarding twin studies describing the genetic basis of specific phobias and their corresponding fears. The analysis included five twin studies on fears and ten twin studies on specific phobias. Heritability estimates of fear subtypes and specific phobia subtypes both varied widely, even within the subtypes. A meta-analysis performed on the twin study results indicated that fears and specific phobias are moderately heritable. The highest mean heritability (±SEM) among fear subtypes was found for animal fear (45%±0.004), and among specific phobias for the blood-injury-injection phobia (33%±0.06). For most phenotypes, variance could be explained solely by additive genetic and unique environmental effects. Given the dearth of independent data on the heritability of specific phobias and fears, additional research is needed.

Predictors for the development of temporomandibular disorders in scuba divers

The aim was to determine predictors for the development of complaints of temporomandibular disorders (TMD) in a large sample of Dutch scuba divers who were free of any TMD complaints before they started diving actively. Five-hundred and thirty-six scuba divers (mean ± SD age = 40.4 ± 11.9 years; 34.1% women) completed a specifically developed questionnaire, either online or on paper. Stepwise forward logistic regression analysis was performed to predict the presence of TMD pain, with several potential risk factors as predictors. Four hundred and eighty-five of the 536 respondents were free of any TMD pain before they started diving actively. In this sample, TMD pain was present in 214 persons (44.1%). Four predictors contributed significantly to the presence of TMD pain, viz., clenching (OR = 2.466), warm water (OR = 1.685), biting on the mouthpiece (OR = 1.598), and the quality rating of the mouthpiece (OR = 0.887, that is, a higher rating means a smaller odds of having TMD pain). TMD pain is a common complaint among scuba divers who were free of such complaints before they started diving actively. Clenching, biting on the mouthpiece, and a low rating of the mouthpiece are predictors for the presence of TMD pain in scuba divers, while diving in cold water serves as a protective factor for TMD pain.

Associations of pain intensity and pain-related disability with psychological and socio-demographic factors in patients with temporomandibular disorders: a cross-sectional study at a specialised dental clinic

The study assessed whether psychological and socio-demographic factors, including somatisation, depression, stress, anxiety, daytime sleepiness, optimism, gender and age, are associated with pain intensity and pain-related disability in patients with temporomandibular disorders (TMDs). In total, 320 TMD patients were involved in the study. The psychological status of each patient was assessed with questionnaires, including the Symptom Checklist-90 (SCL-90), Epworth Sleeping Scale (ESS), stress questionnaire and Life Orientation Test-Revised (LOT-R). TMD pain, including pain intensity and pain-related disability, was assessed with characteristic pain intensity (CPI) and disability points scales. The associations of psychological and socio-demographic factors with pain intensity and pain-related disability were assessed through logistic regression analyses. Higher pain intensity was significantly associated with more severe anxiety (P = 0·004), more severe somatisation (P < 0·001), more severe depression (P < 0·001), more severe stress (P = 0·001) and lower optimism (P = 0·025) in univariate regression analyses. However, multiple regression analysis showed that only somatisation was significantly associated with pain intensity (P < 0·001). Higher pain-related disability was significantly associated with more severe anxiety (P < 0·001), more severe somatisation (P < 0·001), more severe depression (P < 0·001), more severe stress (P < 0·001) and lower optimism (P = 0·003) in univariate regression analyses. However, multiple regression analysis showed that only depression was significantly associated with pain-related disability (P = 0·003). Among the psychological and socio-demographic factors in this study, somatisation was the best predictor of pain intensity, while depression was the best predictor of pain-related disability.

A comparative study of the Osstell™ versus the Osstell Mentor™ to evaluate implant stability in human cadaver mandibles.

The aim of this study was to assess the primary stability of dental implants by resonance frequency analysis (RFA) using the Osstell™ and Osstell Mentor™ devices and to investigate the reproducibility and comparability of the results obtained with these devices. Twenty-four Straumann implants (Straumann AG, Basel, Switzerland) were placed in the anterior mandible of 12 fresh edentulous human cadaver mandibles. The implant stability quotients (ISQs) were measured with the Osstell™ and Osstell Mentor™ when implants were inserted at 50% of their length and following their complete insertion. The Osstell™ device measured lower scores compared with the Osstell Mentor™. This was significant for the full position (mean difference = 9·9), t (11) = 7·4, P < 0·001 and for the halfway position (mean difference = 5·9), t (11) = 2·41, P = 0·03. In conclusion, the Osstell™ produced relatively lower ISQ scores than the Osstell Mentor™.