Comparative study of stress characteristics around the adjacent teeth tissues during insertion of mini-screws with different insertion angles: A three-dimensional finite element study.

With a limited alveolar bone position, there is a high risk that mini-screws (MS) implants could cause damage to the adjacent teeth. To reduce this damage, the position and tilt angle of the MS must be optimized. The aim of this study was to assess the effect of MS implantation angle on the stress exerted on adjacent periodontal membrane and roots. A three-dimensional finite element model containing dentition, periodontal ligament, jaw and MS were established based on the CBCT images and MS scanning data. The MS was first inserted perpendicular to the surface of the bone at specific locations and then tilted at an angle of 10° and 20° to the mesial and distal teeth, respectively. The stress distribution in the periodontal tissue of the adjacent teeth was analyzed after MS implantation at different angles.The stress on the adjacent tooth root and periodontal ligament was most uniformly distributed when the MS was inserted vertically. It changed 9.4-97.7% when the axis of MS was tilted at 10-degree and 20-degree angles from the point of vertical insertion. The stresses experienced by the periodontal ligament and the root are similar. When the horizontal angle of the MS insertion was changed, the MS was closer to the adjacent tooth, resulting in greater stress near the PDL and root. It was recommended to insert the MS vertically into the alveolar bone surface to avoid root damage due to excessive stress.

Effect of a digital guide on the positional accuracy of intermaxillary fixation screw implantation in orthognathic surgery.

BACKGROUND: Intermaxillary fixation screw (IMFS) implantation is a common procedure in orthognathic surgery (OGS) performed to the temporary maxillary-mandibular fixation and stable bite relationships. The study aims to assess the accuracy of IMFS implantation with a digital guide to reduce the occurrence of root damage. METHODS: This prospective study involved 40 patients undergoing OGS at the Affiliated Hospital of Qingdao University from August 2017 to May 2021. The patients were randomly divided into two groups according to whether the IMFS implantation was with or without digital guide (20 patients in the experimental group and 20 controls). The digital guides used in the experimental group were designed according to a virtual implantation plan and printed using stereolithography. In the control group, IMFSs were directly implanted by a surgeon based on clinical experience. Postoperatively, cone-beam computed tomography was performed to compare root proximity of IMFSs between the two groups and verify the accuracy of IMFS placement. RESULTS: In the experimental group, there was no case of root damage, the incidence of the periodontal ligament (PDL) injured was 22.1%, and 77.9% IMFSs were placed without contacting adjacent anatomic structures. In the control group, the incidence of root damage had been up to 20.8%, 31.7% IMFSs injured the PDL, and only 47.5% IMFSs were placed between the roots (P < 0.001). CONCLUSION: IMFSs can be placed more accurately with surgical guides, reducing the incidence of root and PDL damages.

Identification and characterization of glnA promoter and its corresponding trans-regulatory protein GlnR in the rifamycin SV producing actinomycete, Amycolatopsis mediterranei U32.

The genetic requirements for the transcription of glnA, encoding the major glutamine synthetase in a rifamycin SV-producing Amycolatopsis mediterranei strain, U32, were investigated. Primer extension experiments showed that the promoter of U32 glnA (pglnA) was likely to have two transcription initiation sites: P(1) and P(2), located 157 and 45 nucleotides (nt) upstream of the translational start codon, respectively. Gel mobility shift and DNase I footprinting analyses revealed a 30 bp cis-element located at 45 to 75 nt downstream of P1, or 38 to 68 nt upstream of P(2). The sequence of the cis-element displayed high similarity to the corresponding regions of pglnA from Streptomyces coelicolor and S. roseosporus. With xylE as a reporter gene, the expression levels of U32 pglnA and its deletion derivatives under different nitrogen-source conditions were analyzed by detecting the catechol dioxygenase activities in S. lividans TK54, S. coelicolor J508 and S. coelicolor FS10 (glnR mutant). These in vivo studies showed that the activation of U32 pglnA in S. coelicolor required GlnR, and its binding to the U32 pglnA was further confirmed by the gel mobility shift assay. Cloning and heterologous expression of the U32 glnR allowed us to detect the in vitro interaction between the U32 GlnR and the corresponding pglnA cis-element. Further evidence shown by in vivo glnR inactivation and complementation indicated that GlnR is essential for the active transcription of glnA in U32.