Oligodontia and ectodermal dysplasia : on signs, symptoms, genetics and outcomes of dental treatment

Abstract: The general aim of this thesis was to broaden our knowledge of the signs and symptoms, genetics, and outcomes of dental implant treatment in individuals with oligodontia or ectodermal dysplasia. Article I is a population-based study in three Swedish counties of 162 individuals with oligodontia, which was a prevalence of 0.09%. The intent was to explore ways for dentists to assess symptoms from other ectodermal structures than teeth through a clinical interview and chair-side analyses. Thirty per cent had low salivary secretion rates while only 11% with no known syndrome reported symptoms from hair, nails, or sweat glands. These are, together with teeth, the ectodermal structures on which it is proposed that a clinical diagnosis of ectodermal dysplasia (ED) be based. Article II screened 93 probands with oligodontia for mutations in six genes known to cause oligodontia and hypohidrotic ED. Sequence alterations predicted to be damaging or potentially damaging were revealed in the AXIN2, MSX1, PAX9, and EDARADD genes in 14 (15%) of the probands. All mutations but one were novel. For the first time, EDARADD mutations were shown to cause isolated oligodontia. No individual who had reported ectodermal symptoms from hair, nails, or sweat glands had a mutation. Article III assessed orofacial function in individuals with different types of EDs using the Nordic Orofacial Test-Screening (NOT-S) protocol. Individuals with ED scored significantly higher in orofacial dysfunction than a healthy reference sample, especially in the Chewing and swallowing, Dryness of the mouth, and Speech domains. Article IV surveyed treatment outcome of dental implants in Swedish children up to age 16 years. In a 20-year period, only 26 patients were treated, 5 of whom had hypohidrotic ED and anodontia of the mandible. Individuals with ED had 64% failed implants compared to 6% among subjects with teeth missing due to trauma or agenesis. The main conclusions of this thesis were that (i) a check of whether one or more permanent incisors are missing will identify 65% of individuals with oligodontia and 84% of individuals missing nine teeth or more, (ii) evaluation of salivary secretion is indicated in children with oligodontia, (iii) a majority of individuals with oligodontia did not report other abnormal ectodermal organ function besides teeth, (iv) no clinical indicator discriminated between individuals with and without mutations in the tested genes, and more unidentified genes are involved in tooth morphogenesis, (v) EDARADD mutations are associated with isolated oligodontia, (vi) evaluation of orofacial function is indicated in individuals with ED, and many individuals with ED would benefit from orofacial skills training, (vii) dental implant placement is a rare treatment modality in children, (viii) individuals with hypohidrotic ED seem to present special challenges due to structural as well as direct effects of the mutations on bone, which seem to compromise osseointegration, (ix) central registers on signs and symptoms in individuals with rare disorders would help establish prevalences of various diagnoses and define treatment needs, and (x) quality registers for monitoring treatment outcomes of dental implants would promote early detection of risks and side-effects in individuals with rare disorders.