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Samples of two duckweed species, Spirodela polyrhiza and Lemna minor, were collected around small ponds and investigated concerning the question of whether natural populations of duckweeds constitute a single clone, or whether clonal diversity exists. Amplified fragment length polymorphism was used as a molecular method to distinguish clones of the same species. Possible intraspecific diversity was evaluated by average-linkage clustering. The main criterion to distinguish one clone from another was the 95% significance level of the Jaccard dissimilarity index for replicated samples. Within natural populations of L. minor, significant intraspecific genetic differences were detected. In each of the three small ponds harbouring populations of L. minor, based on twelve samples, between four and nine distinct clones were detected. Natural populations of L. minor consist of a mixture of several clones representing intraspecific biodiversity in an aquatic ecosystem. Moreover, identical distinct clones were discovered in more than one pond, located at a distance of 1 km and 2.4 km from each other. Evidently, fronds of L. minor were transported between these different ponds. The genetic differences for S. polyrhiza, however, were below the error-threshold of the method within a pond to detect distinct clones, but were pronounced between samples of two different ponds.
Abstract
Objectives
To examine the association between third molars and orofacial pain. We hypothesized that impacted third molars are a cause of orofacial pain.
Methods
Magnetic resonance images of 1808 participants from two population‐based cohorts from Northeastern Germany were analysed to define the status of third molars according to the Pell and Gregory classification. A self‐reported questionnaire and a clinical dental examination were used to detect chronic and acute complaints of orofacial pain, masticatory muscle pain, migraine and other types of headache. Logistic regression models were used to analyse the associations between third molar status and orofacial pain.
Results
Individuals with impacted third molars in the maxilla had a higher chance of chronic orofacial pain than those with erupted third molars (odds ratio 2.19; 95% CI 1.19‐4.02). No such association was detected for third molars in the lower jaw. Third molars were not associated with masticatory muscle pain, migraine or other types of headache.
Conclusions
Impacted maxillary third molars might be a cause of chronic orofacial pain. Thus, physicians should consider the eruption/impaction status of third molars in their decision‐making process when treating patients who complain of orofacial pain.
Weisheitszähne, deren Behandlung und Extraktion gehören zur täglichen Arbeit von Zahnärzten, Kieferorthopäden, Oralchirurgen und Mund-, Kieferund Gesichtschirurgen. Es besteht jedoch noch immer ein Mangel an validen Daten zum Vorkommen von Weisheitszähnen, ihrer Retention, der Angulation im Unterkiefer und der Lage zur Kieferhöhle im Oberkiefer in der Allgemeinbevölkerung. Deshalb wurde diese Thematik im Rahmen der randomisierten und kontrollierten SHIP-MRT-Studie an einer sehr großen Kohorte aus Vorpommern untersucht. Da das bildgebende Verfahren der Magnetresonanztomographie in der Befunderhebung des Zahnstatus in der Praxis bisher kaum eine Rolle spielte, soll diese Studie auch dazu beitragen, weitere Anhaltspunkte über die Eignung der MRT für diese Diagnostik zu liefern.