Intrauterine temporomandibular joint dislocation: prenatal sonographic evaluation

Single-cell RNA sequencing analysis of the temporomandibular joint condyle in 3 and 4-month-old human embryos

BACKGROUND

The temporomandibular joint (TMJ) is a complex joint consisting of the condyle, the temporal articular surface, and the articular disc. Functions such as mastication, swallowing and articulation are accomplished by the movements of the TMJ. To date, the TMJ has been studied more extensively, but the types of TMJ cells, their differentiation, and their interrelationship during growth and development are still unclear and the study of the TMJ is limited. The aim of this study was to establish a molecular cellular atlas of the human embryonic temporomandibular joint condyle (TMJC) by single-cell RNA sequencing, which will contribute to understanding and solving clinical problems.

RESULTS

Human embryos at 3 and 4 months of age are an important stage of TMJC development. We performed a comprehensive transcriptome analysis of TMJC tissue from human embryos at 3 and 4 months of age using single-cell RNA sequencing. A total of 16,624 cells were captured and the gene expression profiles of 15 cell clusters in human embryonic TMJC were determined, including 14 known cell types and one previously unknown cell type, "transition state cells (TSCs)". Immunofluorescence assays confirmed that TSCs are not the same cell cluster as mesenchymal stem cells (MSCs). Pseudotime trajectory and RNA velocity analysis revealed that MSCs transformed into TSCs, which further differentiated into osteoblasts, hypertrophic chondrocytes and tenocytes. In addition, chondrocytes (CYTL1^high + THBS1^high) from secondary cartilage were detected only in 4-month-old human embryonic TMJC.

CONCLUSIONS

Our study provides an atlas of differentiation stages of human embryonic TMJC tissue cells, which will contribute to an in-depth understanding of the pathophysiology of the TMJC tissue repair process and ultimately help to solve clinical problems.

Neonatal Temporomandibular Joint Dislocation: A Case Report and Literature Review

Neonatal temporomandibular joint (TMJ) dislocation is rare. The purpose of this study is to describe a case of neonatal TMJ dysfunction and to review the literature on this topic. A six-day-old female was seen with both parents for evaluation of a dislocating jaw. Her mother had been breastfeeding successfully but noticed that there was a noticeable click every time the baby swallowed. Her jaw came out and down as she fed and then returned to the normal position. Over the last few days, her mother felt that only one side was involved as her jaw movement seemed asymmetrical. Her primary care physician had witnessed the click during the sucking reflex. The patient had a normal appearance and was otherwise healthy. The pediatric otolaryngologist observed deviation of the jaw toward the left with a palpable click upon mouth opening and spontaneous reduction with mouth closing. The symptoms resolved over the following month. The literature review showed few cases of TMJ dislocation in infants, most of which described fixed dislocation related to vomiting or crying. Due to the development of the TMJ in infancy characterized by joint laxity and a flat mandibular fossa, malfunctioning of the hinge joint mechanism could be expected to be more common early in life.

Hemifacial microsomia (oculo-auriculo-vertebral spectrum) in an individual from the Teramo Sant'Anna archaeological site (7th-12th centuries of the Common Era, Italy)

BACKGROUND

This study is based in an analysis of the skeletal remains of an adult male from the Teramo Sant'Anna archaeological site (7th-12th centuries of the Common Era, Teramo, Italy).

RESULTS AND DISCUSSION

The individual shows distinct abnormalities that principally involve asymmetric hypoplasia and dysmorphogenesis of the facial skeleton. The combination of these findings and the absence of abnormalities of the spine strongly suggest diagnosis of the congenital malformation known as hemifacial microsomia. This very heterogeneous syndrome affects primarily aural, ocular, oral and mandibular development. Despite the lack of clinical information and the absence of soft tissue, it was possible to perform a differential diagnosis for this palaeopathological case. Mastication was probably altered considering that the mandible is extremely asymmetric and lacks true condyles. The temporomandibular joints are present, but the right one is hypoplastic and abnormal in shape. There is evidence of bilateral dislocation, and the facial muscles are hypertrophic.

CONCLUSIONS

This case represents an important contribution to the palaeopathological literature because this is an uncommon condition that has not been widely documented in ancient skeletal remains.