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Background/Objectives: To assess the incidence of and risk factors for black triangles between the central incisors after orthodontic treatment; Methods: Ninety-seven post-treatment patients (29 men and 68 women; mean age, 22.7 years) were retrospectively divided into two groups based on the presence or absence of black triangles, using intraoral photographs. Based on the Jemt Index, the black triangle occurrence group was further classified into mild, moderate, and severe groups. Parameters from periapical radio graphs, lateral cephalograms, and study models were compared between the occurrence and the non-occurrence groups by using independent t-tests. Logistic regression analysis was performed to identify the risk factors for black triangles; Results: The incidence of black triangles between the central incisors was 51% and 64% in the maxilla and in the mandible, respectively. The factors significantly associated with the occurrence of black triangles were age, treatment duration, the lingual inclination of the maxillary incisors in the maxilla, and age in the mandible (p < 0.05); Conclusions: This study showed the diverse risk factors associated with black triangles between central incisors after orthodontic treatment and revealed that the formation of black triangles is relatively common. Considering these risk factors during orthodontic diagnosis and treatment planning can help minimize the occurrence of black triangles.

Abstract Background Retinoblastoma is an intraocular cancer of infancy and childhood, which has been treated with radiation therapy and chemotherapy. Radiation on growing patients can cause deterioration in maxillofacial growth and development that leads to severe skeletal discrepancies between the maxilla and mandible, and dental problems such as crossbite, openbite, and hypodontia. Case presentation We present the case of a 19-year-old Korean man with chewing disability and dentofacial deformities. He had undergone enucleation of the right eye and radiation therapy of the left eye due to retinoblastoma 100 days after birth. Subsequently, he received cancer therapy for the secondary nasopharyngeal cancer at the age of 11 years. He was diagnosed with severe skeletal deformity including sagittal, transverse, and vertical growth deficiency of the maxilla and midface, and with class III malocclusion, severe anterior and posterior crossbite, posterior openbite, multiple missing upper incisors, right premolars, and second molars, and impaction of the lower right second molars. To restore impaired functions and esthetics of the jaw and dentition, the orthodontic treatment combined with two jaw surgery was performed. At the end of surgical orthodontics, dental implants were placed for prosthetic treatment of missing teeth. Additional plastic surgery for zygoma elevation was done with calvarial bone graft followed by fat graft. Facial esthetics and occlusal functions of patient were favorably enhanced with the improvement of skeletal discrepancy and the rehabilitation of maxillary dentition by prosthetic work. At the 2-year follow-up, the skeletal and dental relationships and implant prosthetics were well maintained. Conclusion In an adult patient with dentofacial deformities caused by early cancer therapy in the head and neck area, interdisciplinary interventions including additional plastic surgery of zygoma depression and prosthetic work of missing teeth as well as surgical–orthodontic treatment could establish favorable facial esthetics and oral rehabilitation.

Organic/inorganic halide perovskite materials have attracted substantial attention in solar cells, and they have achieved significant improvements in recent years. In perovskite solar cells (PSCs), the engineering of interfacial properties between multilayers is an important determinant of performance and stability. Here, we designed a bilayer structure of hole transporting layer by inserting poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), which can improve the interfacial properties between the perovskite and the nickel oxide (NiO) hole transport layer in p-i-n planar PSCs. We observed that the hole transporting PTAA/NiO bilayer leads to higher performance by optimizing the energy level and accelerating the extraction of charges from the interface. The power conversion efficiency of the PSC was improved from 17.29% to 19.05% when the PTAA/NiO bilayer was introduced instead of the NiO monolayer. Ultimately, we confirmed that this interface engineering provides thermal and air stability of PSCs.