Of the various malocclusions, unilateral posterior crossbite has often been associated to skeletal and muscular asymmetrical growth and function. To assess, by systematically reviewing the literature, the association between unilateral posterior crossbite (UPCB) and morphological and/or functional asymmetries (i.e. skeletal, masticatory muscle electromyographic (EMG) performance, bite force, muscle thickness, and chewing cycle asymmetries). A literature survey covering the period from January 1965 to June 2015 was performed. Two reviewers extracted the data independently and assessed the quality of the studies. The search strategy resulted in 2184 citations, of which 45 met the inclusion criteria. The scientific and methodological quality of these studies was medium–low, irrespective of the association reported. In several studies, posterior crossbite is reported to be associated to asymmetries in mandibular skeletal growth, EMG activity, and the chewing cycle. Fewer data are available on bite force and masticatory muscle thickness. The relationship between unilateral posterior crossbite and skeletal asymmetry is still unresolved. To date, most of the studies available report a skeletal asymmetric growth. EMG activity of masticatory muscles is different between crossbite and non-crossbite sides. Subjects with UPCB show smaller bite force than non-crossbite subjects. There is no consistency of studies reporting masticatory muscle thickness asymmetry in UPCB subjects. UPCB is associated to an increase in the reverse chewing cycle. The literature available on the subject is of medium–low scientific and methodological quality, irrespective of the association reported. Further investigations with higher sample size, well-defined diagnostic criteria, rigorous scientific methodologies, and long-term control are needed.

Background The effect of complex alleles in cystic fibrosis (CF) is poorly defined for the lack of functional studies. Objectives To describe the genotype–phenotype correlation and the results of either in vitro and ex vivo studies performed on nasal epithelial cells (NEC) in a cohort of patients with CF carrying cystic fibrosis transmembrane conductance regulator (CFTR) complex alleles. Methods We studied 70 homozygous, compound heterozygous or heterozygous for CFTR mutations: p.[Arg74Trp;Val201Met;Asp1270Asn], n=8; p.[Ile148Thr;Ile1023_Val1024del], n=5; p.[Arg117Leu;Leu997Phe], n=6; c.[1210-34TG[12];1210-12T[5];2930C>T], n=3; p.[Arg74Trp;Asp1270Asn], n=4; p.Asp1270Asn, n=2; p.Ile148Thr, n=6; p.Leu997Phe, n=36. In 39 patients, we analysed the CFTR gating activity on NEC in comparison with patients with CF (n=8) and carriers (n=4). Finally, we analysed in vitro the p.[Arg74Trp;Val201Met;Asp1270Asn] complex allele. Results The p.[Ile148Thr;Ile1023_Val1024del] caused severe CF in five compound heterozygous with a class I–II mutation. Their CFTR activity on NEC was comparable with patients with two class I–II mutations (mean 7.3% vs 6.9%). The p.[Arg74Trp;Asp1270Asn] and the p.Asp1270Asn have scarce functional effects, while p.[Arg74Trp;Val201Met;Asp1270Asn] caused mild CF in four of five subjects carrying a class I–II mutation in trans, or CFTR-related disorders (CFTR-RD) in three having in trans a class IV–V mutation. The p.[Arg74Trp;Val201Met;Asp1270Asn] causes significantly (pT] and a class I–II mutation had mild CF or CFTR-RD (gating activity: 18.5–19.0%). Conclusions The effect of complex alleles partially depends on the mutation in trans. Although larger studies are necessary, the CFTR activity on NEC is a rapid contributory tool to classify patients with CFTR dysfunction.

Among different malocclusions, posterior crossbite is thought to have a strong impact on the correct functioning of the masticatory system. To assess, by systematically reviewing the literature, the association between posterior crossbite and different temporomandibular disorder (TMD) diagnosis: disc displacement and masticatory muscle pain. A literature survey covering the period from January 1965 to April 2012 was performed. Two reviewers extracted the data independently and assessed the quality of the studies. The search strategy resulted in 2919 citations, of which 43 met the inclusion criteria. The scientific and methodological quality of these studies was found to be medium-low, independently by association reported. In several studies, posterior crossbite is reported to be associated to the development of disc displacement, muscular pain, and tenderness, possibly linked to a skeletal and muscular adaptation of the stomatognathic system. However, the lack of consistency of the results reported deeply reduces the external validity of the studies, with a consequent impossibility to draw definite conclusions. It is not possible to establish an association between posterior crossbite, muscle pain, and disc displacement because the distribution of the studies supporting or not supporting the association is similar. The consequences of posterior crossbite on the development of TMDs deserve further investigations, with high sample size, well-defined diagnostic criteria, and rigorous scientific methodologies. Finally, long-term controlled studies are needed to identify posterior crossbite as a possible risk factor for TMDs.