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Background: In this case report, we represent a healthy 26-year-old patient with an oral hairy leukoplakia who is HIV-seronegative. Case presentation: The histological sample showed all typical signs for oral hairy leukoplakia, including balloon cells; however, the in situ hybridisation showed a negative result for an EBV infection, which is the common sign for oral hairy leukoplakia. Conclusion: Therefore, we suggest the unusual diagnosis of "pseudo oral hairy leukoplakia" in this special case. Keywords: oral hairy leukoplakia, HIV-negative, pseudo oral hairy leukoplakia

Das orale Plattenepithelkarzinom zählt mit einer 5-Jahres-Überlebensrate von 59% der Frauen und 44% der betroffenen Männer zu den aggressivsten Karzinomen. Die Zahl der Neuerkrankungen in Deutschland steigt stetig an und manifestierte sich im Jahr 2008 mit 9520Initialdiagnosen unter Männern und 3490unter Frauen

Case Report: Mesiodens in monozygotic male twins: Diagnosis and surgical therapy. Introduction: The incidence of supernumerary teeth reported in the literature is 0.15 - 3.9% and it is five times more common in permanent dentition teeth. Mesiodens is defined as a tooth additional to the normal dentition, commonly seen in the maxillary arch, centrally located between the roots of the upper incisors. The overall incidence is 0.15% - 1.9%, with the ratio men to women being 2:1. The aim of this case report is the presentation of diagnostic and surgical treatment of mesiodens, including etiological factors in monozygotic twins. Clinic: We report on two 10-year-old monozygotic male twins. Evaluation of the DVT in the upper jaw showed a rudimentary, inverted conical mesiodens centrally located between the root apices of teeth 11 and 21, cranially limited by a thin cortical lamina to the nasal floor. Radiographic imaging of the single maxillary anterior region of his twin brother also revealed a mesiodens in the same region. The DVT showed a varied location of the rudimentary, slightly enlarged, inverted and conical mesiodens in the same region, in mirror-symmetrical position relative to the median sagittal plane. Surgical removal of the mesiodens in both twins was performed under local anesthesia, using intrasulcular vestibular incision and minimally invasive osteotomy. Discussion: The occurrence of mesiodentes in twins is rare, only few case reports depicted in the literature can elucidate the etiology and a presumed genetic component. The absolute incidence of monozygotic twins is 3.5 - 4 per thousand pregnancies and is independent of maternal age or race and is similar in all populations. Regarding the etiologic background, a zygote that divides prior to lateral differentiation will produce identical monozygotic twins. The division of the blastocyst at a later stage can lead to increased levels of asymmetry. The different relationship of twins to each other within the membranes of the placenta has an impact on the respective axial asymmetries. The mirror image of unilateral mesiodentes occurring in twins has been described. An autosomal dominant disorder with incomplete penetrance genes may play a role in the increased incidence among first-degree relatives. Even small differences of epigenetic influences on tooth development may be responsible for differences in the expression in monozygotic twins. So far, several theories have been put forward for the formation of mesiodentes. These include the theories of atavism, the dichotomy / schizodontia, hyperactivity of the dental lamina, family history, asymptomatic autosomal dominant holoprosencephaly and environmental factors such as radiation, and the influence of exogenous epidermal growth factor and vitamin A. Supernumerary teeth may occur in isolation or in combination with syndrome disorders. Complications related to mesiodentes are eruption in the nasal cavity, retention and abnormal root development of permanent front teeth, crowding and development of diastema, as well as the emergence of follicular cyst or keratocystic odontogenic tumour, which may lead to root resorption and rotation of the adjacent teeth. Early diagnosis and treatment is required to avoid complications. Conclusion: In monozygotic twins with a positive family history of supernumerary tooth germs, a radiological examination of the twin sibling may reveal a similar condition. A DVT is helpful for three-dimensional diagnostics and surgical planning. DVT is an excellent tool for the surgical removal of the mesiodentes in terms of protecting adjacent structures and for deciding whether surgery should be performed before or after the commencement of the completed root development of permanent incisors. Keywords: mesiodens, monozygotic twins, digital volume tomography, surgical removal