It is a basic prerequisite for the successful completion of endodontic treatment to thoroughly understand the root canal space anatomy. With the development of dental devices in dentistry, the root canal morphology of the mandibular first premolars can be presented in more detail. Before conducting root canal therapy on the mandibular first premolar with complex root canal morphology, it should be necessary to evaluate the potential difficulties and risks for making an appropriate treatment plan. The present paper reviews the research progress on the diversities of root canal morphology in mandibular first premolars in recent years, and then makes technologic recommendations based on the morphology diversities.
Humans ; Dental Pulp Cavity/diagnostic imaging* ; Bicuspid/anatomy & histology* ; Mandible ; Tooth Root/anatomy & histology* ; Root Canal Therapy

OBJECTIVE: To explore an efficient and automatic method for determining the anatomical landmarks of three-dimensional(3D) mandibular data, and to preliminarily evaluate the performance of the method. METHODS: The CT data of 40 patients with normal craniofacial morphology were collected (among them, 30 cases were used to establish the 3D mandibular average model, and 10 cases were used as test datasets to validate the performance of this method in determining the mandibular landmarks), and the 3D mandibular data were reconstructed in Mimics software. Among the 40 cases of mandibular data after the 3D reconstruction, 30 cases that were more similar to the mean value of Chinese mandibular features were selected, and the size of the mandibular data of 30 cases was normalized based on the Procrustes analysis algorithm in MATLAB software. Then, in the Geomagic Wrap software, the 3D mandibular average shape model of the above 30 mandibular data was constructed. Through symmetry processing, curvature sampling, index marking and other processing procedures, a 3D mandible structured template with 18 996 semi-landmarks and 19 indexed mandibular anatomical landmarks were constructed. The open source non-rigid registration algorithm program Meshmonk was used to match the 3D mandible template constructed above with the tested patient's 3D mandible data through non-rigid deformation, and 19 anatomical landmark positions of the patient's 3D mandible data were obtained. The accuracy of the research method was evaluated by comparing the distance error of the landmarks manually marked by stomatological experts with the landmarks marked by the method of this research. RESULTS: The method of this study was applied to the data of 10 patients with normal mandibular morphology. The average distance error of 19 landmarks was 1.42 mm, of which the minimum errors were the apex of the coracoid process [right: (1.01±0.44) mm; left: (0.56±0.14) mm] and maximum errors were the anterior edge of the lowest point of anterior ramus [right: (2.52±0.95) mm; left: (2.57±1.10) mm], the average distance error of the midline landmarks was (1.15±0.60) mm, and the average distance error of the bilateral landmarks was (1.51±0.67) mm. CONCLUSION The automatic determination method of 3D mandibular anatomical landmarks based on 3D mandibular average shape model and non-rigid registration algorithm established in this study can effectively improve the efficiency of automatic labeling of 3D mandibular data features. The automatic determination of anatomical landmarks can basically meet the needs of oral clinical applications, and the labeling effect of deformed mandible data needs to be further tested.
Humans ; Imaging, Three-Dimensional/methods* ; Mandible/diagnostic imaging* ; Software ; Algorithms ; Anatomic Landmarks/anatomy & histology*

OBJECTIVETo investigate an ideal modeling method of designing 3D mesh scaffold substitutes based on tissue engineering to restore mandibular bone defects. By analyzing the theoretical model from titanium scaffolds fabricated by 3D printing, the feasibility and effectiveness of the proposed methodology were verified.

METHODSBased on the CT scanned data of a subject, the Mimics 15.0 and Geomagic studio 12.0 reverse engineering software were adopted to generate surface model of mandibular bone and the defect area was separated from the 3D model of bone. Then prosthesis was designed via mirror algorithm, in which outer shape was used as the external shape of scaffold. Unigraphics software NX 8.5 was applied on Boolean calculation of subtraction between prosthesis and regular microstructure structure and ANSYS 14.0 software was used to design the inner construction of 3D mesh scaffolds. The topological structure and the geometrical parameters of 3D mesh titanium scaffolds were adjusted according to the aim of optimized structure and maximal strength with minimal weight. The 3D mesh scaffolds solid model through two kinds of computer-aided methods was input into 3D printing equipment to fabricate titanium scaffolds.

RESULTSIndividual scaffolds were designed successfully by two modeling methods. The finite element optimization made 10% decrease of the stress peak and volume decrease of 43%, and the porosity increased to 76.32%. This modeling method was validated by 3D printing titanium scaffold to be feasible and effective.

CONCLUSIONS3D printing technology combined with finite element topology optimization to obtain the ideal mandibular 3D mesh scaffold is feasible and effective.

Feasibility Studies ; Humans ; Mandible ; anatomy & histology ; Porosity ; Printing, Three-Dimensional ; Tissue Engineering ; methods ; Tissue Scaffolds ; Titanium

To review the recent progress about the anatomical and radiographical studies of bifid mandibular canal (BMC) in English literature recorded in PubMed from 2006 to 2015 to deepen our understanding of BMC. A BMC is an anatomical variation of the mandibular canal; its occurrence might be a result of the incomplete fusion of mandibular canal during prenatal development. The four types of BMC have been classified according to anatomical location and configuration. Characteristic radiographic features and identifying methods of BMC on panoramic radiography and cone beam computed tomography (CBCT) were described; the visibility of BMC on panoramic radiographs and CBCT images was compared. Clinical value of identifying the location as well as the configuration of BMC for surgical procedures that involve the mandible was discussed.
Cone-Beam Computed Tomography ; Humans ; Mandible ; abnormalities ; anatomy & histology ; diagnostic imaging ; surgery ; Radiography, Panoramic

OBJECTIVEThis study aims to identify the effects of corticotomy-assisted orthodontic premolar intrusion andevaluate the changes of root resorption and the alveolar bone.

METHODSBoth sides of the mandible of eight male Beagle dogswere randomly assigned into experimental and control groups. The third (P3) and fourth (P4) premolars were intruded withboth mini-screw implant anchorage (MIA) and corticotomy on the experimental side. By contrast, P3 and P4 were intrudedwith MIA alone on the control side. During pre-operation and after 2, 4, 8, and 12 weeks of orthodontic force applications,cone beam computed tomography was performed on every dog. The distance of tooth intrusion and root resorption of furcation, as well as the apex and height changes of the alveolar bone were measured and analyzed.

RESULTSThe intrusion distanceof premolars on the experimental side was greater than that on the control side (P < 0.05). The root of furcation and apex onboth sides occurred in root resorption, and the root resorption of the apex on the experimental side was lighter than that onthe control side after 12 weeks of force application (P < 0.05). The alveolar bone height decreased, and the height reductiondistance on the experimental side was greater than that on the control side after 8 and 12 weeks of force application (P < 0.05).

CONCLUSIONCorticotomy accelerates orthodontic molarintrusion and reduces root resorption.

Animals ; Bicuspid ; anatomy & histology ; Bone Screws ; Cone-Beam Computed Tomography ; Dogs ; Male ; Mandible ; Root Resorption ; Tooth Movement Techniques ; Tooth Root

OBJECTIVEThis research aimed to analyze the three-dimensional position of mandibular canal (MC) and man of MC and its relationship with the surrounding structures dibular morphology of normal young males and females by using data from cone beam computed tomography (CBCT), as well as to provide an anatomical basis for clinical surgery of the mandible.

METHODSNormal occlusion and CBCT scans of 29 normal young people were conducted. InVivo 5 software was used to reconstruct the mandible, anchor the points, and measure the jaw shape and three-dimensional course of MC. All measurements were analyzed with SSPS 17.0 software.

RESULTSThe MC lingual bone cortex was thinner than the MC buccal bone cortex, and the distance of the MC to the buccal bone cortex gradually increased. However, the distance of the MC to the tongue bone cortex and alveolar crest gradually decreased from proximal to distal. In addition, the distance of the MC to the mandibular lower margin was minimal at the first molar and reached the maximum at the second premolar. No significant difference was observed among the heights, widths, and thicknesses of the left and right sides of the cortical bone of the mandibular body cross sections. From the midline to the farthest point, the height and lower one-third thickness of the lingual cortical bone of the mandibular body cross sections gradually decreased, whereas the width of the upper cross section and upper one-third thickness of the buccal cortical bone gradually increased. Significant difference was observed in some measured values.

CONCLUSIONAfter MC enter into the mandibular foramen, it moved away from the lingual to the buccal bone but gradually returned to the lingual bone; its general course is closer to the lingual bone. The mandibles of males are thicker than those of females. CBCT can accurately display the course of MC and its relationship with the surrounding structures.

Alveolar Process ; Bicuspid ; Cone-Beam Computed Tomography ; methods ; Dental Pulp Cavity ; Female ; Humans ; Hyoid Bone ; Male ; Mandible ; anatomy & histology ; diagnostic imaging ; Molar ; Software ; Surveys and Questionnaires ; Tongue ; Zygoma

It has recently been reported that long-standing post-traumatic open bite can be successfully corrected with botulinum toxin type A (BTX-A) injection into the anterior belly of the digastric muscle (ABDM). The report documented an individual with bilaterally symmetrical and otherwise unremarkable anterior digastric musculature. However, the existence of variant anterior digastric musculature is common and may complicate the management of anterior open bite with BTX-A injection. Screening for variant ABDM can be accomplished via ultrasound, computed tomography, and magnetic resonance imaging. Screening for variant ABDM should be performed prior to BTX-A injection in order to account for musculature that may exert undesired forces, such as inferolateral deviation, on the anterior mandible in patients with anterior open bite.
Anatomy, Regional ; Botulinum Toxins, Type A* ; Humans ; Magnetic Resonance Imaging ; Malocclusion ; Mandible ; Mandibular Injuries ; Mass Screening* ; Nerve Block ; Open Bite* ; Orthognathic Surgery ; Ultrasonography

OBJECTIVETo explore the effect of intervention with unilateral mastication on masseter muscle asymmetry.

METHODSForty-three subjects (19 males and 24 females, mean age 20.0∓0.5 years) with unilateral chewing were divided into group A0 with motivation and without intervention, group A1 with motivation and intervention, group B0 without motivation or intervention, and group B1 without motivation but with intervention. In groups A0 and A1, the motivation was removed and groups A1 and group B1 received interventions. Surface electromyography was recorded using surface electromyography in all the subjects in mandible postural position (MPP), with maximum clenching in intercuspal position (ICP) and during chewing. The sEMG of the left and right masseter muscle were separately recorded to assess the asymmetry index of the masseter muscles (ASMM) and its changes after intervention.

RESULTSIn groupA0, the ASMM at MPP, during maximum clenching and chewing had no obvious changes after removal of the motivation. In group A1, the ASMM at MPP, during maximum clenching and chewing were obviously decreased after intervention. In group B0, the ASMM at MPP and during maximum clenching showed no obvious changes but ASMM during chewing significantly increased after removal of the motivation. In group B1, the ASMM at MPP, during maximum clenching and chewing all decreased obviously after intervention.

CONCLUSIONInterventions can significantly improve the bilateral symmetry of the masseter muscles in subjects with unilateral chewing, and the motivation for unilateral chewing should be removed before intervention.

Electromyography ; Female ; Humans ; Male ; Mandible ; Masseter Muscle ; anatomy & histology ; Mastication ; Young Adult

BACKGROUNDThe thickness of the alveolar mucosa influences the probability of the occurrence of denture-induced irritations. Thick denture-supporting tissues offer relief from mucosal tenderness and ulcers; however, the uniformity of the thickness across the entire mandibular alveolar mucosa cannot be accurately determined in edentulous patients. This study aimed to assess the mucosal thickness of the denture-bearing area in the edentulous mandible.

METHODSTwenty-seven edentulous patients underwent cone-beam computed tomography scanning, wherein the patients wore a record base to retract soft tissues away from the alveolar mucosa. The measured regions were the central incisor (IC), lateral incisor (IL), canine (Ca), first premolar (P1), second premolar (P2), first molar (M1), and second molar (M2) regions. The thickness was measured in the alveolar ridge crest (T), buccal (B1-B4), and lingual (L1-L4) alveolar ridge mucosa. The average thickness of the mucosa at buccal sides (B) and lingual sides (L) were also assessed.

RESULTSThe differences in the mucosal thickness between the left and right sides were not significant. In the Ca-M2 regions, T was the thickest, and L3 was the thinnest of all the measured points in the same regions. L was significantly less than B in posterior regions (P < 0.01). On the other hand, M2 at L4 was thinnest of all the measured regions from Ca to M2 (P < 0.01), and was thicker than IC, IL, P1, and P2 at B2.

CONCLUSIONSSince the mucosal thickness of denture-bearing area in the edentulous mandible is not uniform; the tissue surface of the denture base or custom tray should be selectively relieved, which may reduce the risk of denture-induced irritations.

Aged ; Aged, 80 and over ; Alveolar Process ; anatomy & histology ; Dentures ; Female ; Humans ; Jaw, Edentulous ; Male ; Mandible ; anatomy & histology ; cytology ; Middle Aged ; Mucous Membrane ; cytology ; Retrospective Studies

OBJECTIVETo investigate the accurate and individual treatment of temporomandibular joint(TMJ) injury based on 3D digital technology.

METHODSMaxillo-mandibular model was made using rapid prototyping technology based on the pre-operation 3D CT results. According to the 3D digital measurement results, TMJ concepts were ordered and the prosthesis was used to simulate the replacement surgery on the model. Then the joint replacement surgery was performed afterward.

RESULTS(1)After total replacement of TMJ, no pain happened and mouth open was not limited. Three months later, the joint position was normal and stable. The month open width was 4 cm. (2)After condyle replacement, primary healing was achieved with complete survival of bone graft. No edema was seen. Symmetric facial appearance was satisfactory.

CONCLUSIONSBilateral individual prosthesis for total TMJ or condyle replacement is an ideal method for TMJ injury.

Arthroplasty, Replacement ; methods ; Bone Transplantation ; Computer-Aided Design ; Humans ; Imaging, Three-Dimensional ; methods ; Joint Prosthesis ; Mandible ; Prosthesis Design ; methods ; Range of Motion, Articular ; Temporomandibular Joint ; anatomy & histology ; injuries