Biomechanical impact of different isthmus positions in mandibular first molar root canals: a finite element analysis.

OBJECTIVE: This study used image-based finite element analysis (FEA) to assess the biomechanical changes in mandibular first molars resulting from alterations in the position of the root canal isthmus. METHODS: A healthy mandibular first molar, characterized by two intact root canals and a cavity-free surface, was selected as the subject. A three-dimensional model for the molar was established using scanned images of the patient's mandibular teeth. Subsequently, four distinct finite element models were created, each representing varied root canal morphologies: non-isthmus (Group A), isthmus located at the upper 1/3 of the root (Group B), middle 1/3 of the root (Group C), and lower 1/3 of the root (Group D). A static load of 200 N was applied along the tooth's longitudinal axis on the occlusal surface to simulate regular chewing forces. The biomechanical assessment was conducted regarding the mechanical stress profile within the root dentin. The equivalent stress (Von Mises stress) was used to assess the biomechanical features of mandibular teeth under mechanical loading. RESULTS: In Group A (without an isthmus), the maximum stress was 22.2 MPa, while experimental groups with an isthmus exhibited higher stresses, reaching up to 29.4 MPa. All maximum stresses were concentrated near the apical foramen. The presence of the isthmus modified the stress distribution in the dentin wall of the tooth canal. Notably, dentin stresses at specific locations demonstrated differences: at 8 mm from the root tip, Group B: 13.6 MPa vs. Group A: 11.4 MPa; at 3 mm from the root tip, Group C: 14.2 MPa vs. Group A: 4.5 MPa; at 1 mm from the root tip, Group D: 25.1 MPa vs. Group A: 10.3 MPa. The maximum stress in the root canal dentin within the isthmus region was located either at the top or bottom of the isthmus. CONCLUSION: A root canal isthmus modifies the stress profile within the dentin. The maximum stress occurs near the apical foramen and significantly increases when the isthmus is located closer to the apical foramina.

Minimally invasive surgical removal of bilateral impacted mandibular supernumerary teeth using 3D surgical guide template: a case report.

Impacted supernumerary teeth are defined as the presence of one or more teeth in a patient's upper and lower jaws in addition to the normal number of teeth in the dental arch. It has an incidence rate of approximately 1%-14% and more frequently occurs in males than females, may be single or multiple, unilateral or bilateral, erupted or impacted. In this article, we describe the case of a patient with two supernumerary teeth between the roots of the mandibular second premolar and the first molar, which influenced the effectiveness of the first orthodontic treatment. The special anatomical position of the complex supernumerary teeth made tooth extraction challenging. Given the higher risk status of surgery, we implemented a novel tooth extracting technique for this patient. Thus, in this study, we describe a case of minimally invasive extraction of bilateral mandibular impacted supernumerary teeth using a digital 3D positioning guide plate.

Acoustic features of the plosives of Uyghur speakers with velopharyngeal insufficiency / 中华物理医学与康复杂志

Objective To analyze the acoustic features of plosive consonants in Uyghur as spoken by persons with post-palatoplasty velopharyngeal insufficiency.Methods Thirty-one Uyghur-speaking children without a speech disorder were selected as a control group,while 28 others with velopharyngeal insufficiency (VPI) formed the VPI group.All were recorded speaking 9 Uyghur words which contain the plosive consonants/b/,/d/and/g/.The consonants' duration (CD),amplitude (CA),their first formants (VF1),second formants (VF2),third formants (VF3) and fourth formants (VF4) as voiced as well as the voice onset time (VOT) were measured and analyzed using the PRAAT software for the two groups.Results The VF1,VF3 and VF4 of the plosive consonant /b/ were significantly lower for those in the VPI group than among the controls,and the CD of/b/was significantlylonger.There were also significant differences between the two groups in terms of the VF1s,VF3s and CDs of the other plosive consonants.The VOTs of the consonant/b/,/d/ and/g/ were (0.12±0.05)s,(0.10±0.03)s and (0.09±0.03) s,respectively,with an occurrence rate of up to 100％ in the control group,significantly different from those in the VPI group (P＜0.05).Conclusion The acoustic features of the three plosive consonants/b/,/d/ and /g/ can distinguish Uyghur-speaking children with velopharyngeal insufficiency from those with normal speech.

Repairing of peri-implant bone defects with dental pulp stem cells / 国际生物医学工程杂志

Objective To establish an animal experimental model of immediately peri-implant bone defects in rabbit mandibular anterior teeth,and to investigate the osteogenetic capability of dental pulp stem cells (DPSCs) on bone defects around implant.Methods Eight rabbits were involved,whose bilateral mandibular anterior teeth were removed to form the bone defects with 2 mm × 3 mm area on the buccal side of tooth extraction sockets,and then the implants were implanted immediately.The rabbits were divided into two groups.The implants were Bio-oss with DPSCs and Bio-oss with phosphate buffer saline respectively for the experimental group and the control group.The bone regeneration in the defect region was evaluated by general observation,hematoxylin-eosin (HE) staining and Goldner trichrome staining and scanning electron microscope (SEM) at 4 weeks after implantation.Results The implantations were successfully conducted,and the implants were stable.There was no significant difference between the implants.The results of the HE staining and the trichrome staining showed that in the experimental group,new bone tissue and partial woven bone formed,and the properties of the newly formed bone cells were large,abundant,well differentiation,and arranging in woven pattern.While in the control group,the new bone-like tissue formation was less,and the mature cell differentiation was ordinary.The SEM results showed that there was a higher osteointegration between the new bone and the implant in the experimental group comparing with the control group.Conclusions The capability of Bio-oss with DPSCs is relatively superior to single Bio-oss in osteogenesis and osseointegration.