Mandible Model Research Articles

Evaluation of the Auto Surfacing methods to create a surface body of the mandible model

Designing an anatomical structure for a surgical procedure is not a simple task. It is especially true of the craniofacial area, which consists of bone tissues with very complex geometry. CAD modelers need appropriate knowledge and skills in medicine and technical sciences to fully use the currently available tools in related processes with the reconstruction of the craniofacial areas. The presented preliminary studies are based on four patients treated at the Department of Maxillofacial Surgery. The segmentation process of the mandible model was performed in the ITK SNAP software. The process of generating surface body models was performed in the Auto Surfacing module in Geomagic software using two different methods: organic and mechanical. Then compare both methods for the accuracy of generating a CAD model of the mandible based on a triangle mesh structure in the Focus Inspection and the GOM Inspect software.

Accuracy of two different registration methods of dynamic navigation system for dental implant placement

Objective: To compare cusp and U-tube registration methods of dynamic navigation system in dental implant placement. Methods: Twenty resin mandible models and 40 implants were utilized, with implants being placed by a single researcher using one of the two registration methods selected at random. Accuracy was measured through the superimposition of the final and planned implant positions. Angular deviation, three-dimensional (3D) entry deviation, and 3D apex deviation were analyzed. Results: The 3D entry deviation, and 3D apex deviation and angular deviation of cusp group and U-tube group were (1.07±0.46) and (0.93±0.54) mm, (1.16±0.55) and (1.03±0.53) mm, 2.06°±0.98°and 1.62°±0.97°. No significant differences (t=0.91, P=0.368; t=0.79, P=0.436; t=1.42, P=0.164) were observed when comparing these two registration methods. Conclusions: Both the cusp and U-tube registration methods are highly accurate when implemented in vitro. The cusp registration technique can also overcome several of the limitations of the U-tube approach, and it is convenient for clinic.

Application of the Homologous Modeling Technique for Precision Medicine in the Field of Oral and Maxillofacial Surgery

In the field of oral and maxillofacial surgery, establishment of a new method for predicting morphology is desirable. Therefore, the purpose of the present study was to establish a new method for predicting the original shape of a mandibular defect site using the homologous modeling technique. This study used data from 44 patients who underwent computed tomography in the Department of Oral Surgery at Osaka Medical College. Two types of homologous models were constructed: total mandible (TM) and half mandible (HM). Principal component analysis (PCA) was performed using point cloud data of the homologous model M and homologous model HM, and a multiple regression equation was created using the PC value of TM as the object variable and PC value of HM as the explanatory variable. The predicted PC (M) was created from PC (HM) using a regression formula, back-calculated from point cloud data from PC (M), to create the predicted mandible model. Finally, the original image (TC-M) and estimated mandible were superposed and examined. The mean absolute error between the predicted mandible and actual mandible was 1.04 ± 1.35 mm. We believe that this method will be applicable in actual clinical practice.

Biomechanical Performance of PEEK and Graphene-Modified PMMA as Telescopic Removable Partial Denture Materials: A Nonlinear 3D Finite Element Analysis.

To assess stress and deformation in telescopic removable partial denture (RPD) frameworks manufactured with polyether ether ketone (PEEK) or graphene-modified polymethyl methacrylate (PMMA), as well as the stress of the underlying mucosa, via nonlinear 3D finite element analysis. The 3D model of a full mandible was merged with a 3D-scanned Kennedy Class I model with bilaterally missing molars. The tissues, the telescopic crowns, and the RPD framework were designed and created using dental CAD software. The model was duplicated, and two materials-PEEK and graphene-modified PMMA-were assigned to the telescopic crowns and their frameworks. A force of 200 N was applied perpendicularly to the molars, and constraints were placed in the mandibular ramus and the inferior border. The generated von Mises stress and deformation of the frameworks, as well as the stresses of the telescopic crowns and mucosa, were also assessed. Statistical analysis of the differences between the tested materials was conducted via an independent samples t test at (α = .05). The von Mises stresses of the telescopic crowns and their frameworks in the graphene-modified PMMA model were significantly higher than in the PEEK model. In contrast, the deformation of the telescopic RPD framework of the PEEK model was significantly higher than the graphene-modified PMMA model. The stresses of the mucosa in both models showed an insignificant difference. PEEK material showed better biomechanical performance than the graphene-modified PMMA in telescopic RPDs.

Augmented reality guided in reconstruction of mandibular defect with fibular flap: A cadaver study

BackgroundAugmented reality (AR) navigation has been developed in recent years and can overcome some limitations of existing technologies. This study aimed to investigate a novel method of fibula free flap (FFF) osteotomy based on AR technology through a cadaver study. MethodsOne mandible, seven fibulas, and seven lower limb specimens underwent computed tomography (CT) examination. We used the professional software Proplan CMF 3.0 to design a defective mandible model and created fourteen virtual reconstruction plans using the fibulas and lower limb specimens. The AR-based intraoperative guidance software prototype was developed using the Unity Real-Time Development Platform, and virtual plans were transferred into this software prototype. We used AR-based surgical navigation to guide the FFF osteotomy and used these fibular segments to reconstruct the defective mandible model. After reconstruction, all segments were scanned by CT. Osteotomy accuracy was evaluated by measuring the length and angular deviation between the virtual plan and the final result. The reconstruction precision was reflected by the volume overlap rate and average surface distance between the planned and obtained reconstruction. ResultsThe length difference, angular deviation, volume overlap rate and average surface distance of the in vitro group were 1.03±0.68 mm, 5.04±2.61°, 95.35±1.81%, and 1.02±0.27 mm, respectively. Those of the in vivo group were 1.18±0.84 mm, 5.45±1.47°, 95.31±2.09%, and 1.22±0.12 mm. ConclusionsDue to the ideal result of cadaver experiments, an AR-based FFF osteotomy guided system may become a novel approach to assist FFF osteotomy for the reconstruction of defective mandibles.

ECFC-derived exosomal THBS1 mediates angiogenesis and osteogenesis in distraction osteogenesis via the PI3K/AKT/ERK pathway.

BackgroundDistraction osteogenesis (DO) is a widely used bone regenerative technique. However, the DO process is slow, and the consolidation phase is long. Therefore, it is of great clinical significance to explore the mechanism of DO, and shorten its duration. Recent studies reported that stem cell exosomes may play an important role in promoting angiogenesis related to DO, but the mechanism remains unclear.MethodsCanine endothelial colony-forming cells (ECFCs) were isolated and cultured, and the expression of THBS1 in canine ECFCs were inhibited using a lentiviral vector. The exosomes secreted by canine ECFCs were isolated and extracted, and the effect of exosomes on the angiogenic activity of Human umbilical vein endothelial cells (HUVECs) was detected by proliferation, migration, and tube formation experiments. WB and qRT-PCR were used to explore the effects and mechanisms of THBS1-mediated ECFC-Exos on HUVECs angiogenesis. Then, a mandibular distraction osteogenesis (MDO) model was established in adult male beagles, and exosomes were injected into the canine peripheral blood. Micro-CT, H&E, Masson, and IHC staining were used to explore the effects and mechanisms of THBS1-mediated ECFC-Exos on angiogenesis and osteogenesis in the DO area.ResultsECFC-Exo accelerated HUVECs proliferation, migration and tube formation, and this ability was enhanced by inhibiting the expression of THBS1 in ECFC-Exo. Using Western blot-mediated detection, we demonstrated that inhibiting THBS1 expression in ECFCs-Exo activated PI3K, AKT, and ERK phosphorylation levels in HUVECs, which promoted VEGF and bFGF expressions. In the DO model of the canine mandible, ECFCs-Exo injected into the peripheral blood aggregated into the DO gap, thus promoting angiogenesis and bone formation in the DO tissue by reducing THBS1 expression in ECFC-Exo.ConclusionOur findings suggested that ECFC-Exos markedly enhances angiogenesis of endothelial cells, and promotes bone healing in canine MDO. Thus, THBS1 plays a crucial role in the ECFC-Exos-mediated regulation of canine MDO angiogenesis and bone remodeling.The translational potential of this articleThis study reveals that the angiogenic promotion via THBS1 suppression in ECFC-Exos may be a promising strategy for shortening the DO duration.

CGF-HLC-I repaired the bone defect repair of the rabbits mandible through tight junction pathway.

Background: The human-like collagen I (HLC-I) combined concentrated growth factors was used to construct CGF-HLC-I composite biomaterials to repair the critical bone defect disease model of rabbit mandible. This study aimed to research the repair mechanism of CGF-HLC-I/Bio-Oss in rabbit mandibular critical bone defect, to provide a new treatment direction for clinical bone defect repair. Methods: The optimal concentration of HLC-I (0.75%) was selected in this study. Nine New Zealand white rabbits were randomly divided into 3 groups, normal control group, Bio-Gide/Bio-Oss and CGF-0.75%HLC-I/Bio-Oss group (n = 3, each group). CGF-0.75%HLC-I/Bio-Oss and Bio-Gide/Bio-Oss were implanted into rabbit mandibles, then X-ray, Micro-CT, HE and Masson staining, immunohistochemical staining and biomechanical testing were performed with the bone continuity or maturity at 4, 8 and 12 weeks after surgery. The repair mechanism was studied by bioinformatics experiments. Results: As the material degraded, the rate of new bone formation in the CGF-0.75% HLC-I/Bio-Oss group was better than that the control group by micro-CT. The biomechanical test showed that the compressive strength and elastic modulus of the CGF-0.75%HLC-I/Bio-Oss group were higher than those of the control group. HE and Masson staining showed that the bone continuity or maturity of the CGF-0.75%HLC-I/Bio-Oss group was better than that of the control group. Immunohistochemical staining showed significantly higher bone morphogenetic protein 2 (BMP2) and Runt-related transcription factor 2 (RUNX2) in the CGF-0.75%HLC-I/Bio-Oss group than the control group at 8 and 12 W and the difference gradually decreased with time. There were 131 differentially expressed proteins (DEPs) in the Bio-Gide/Bio-Oss and CGF-0.75%HLC-I/Bio-Oss groups, containing 95 up-regulated proteins and 36 down-regulated proteins. KEGG database enrichment analysis showed actinin alpha 1 (ACTN1) and myosin heavy-Chain 9 (MYH9) are the main potential differential proteins related to osteogenesis, and they are enriched in the TJs pathway. Conclusion: CGF-0.75%HLC-I/Bio-Oss materials are good biomaterials for bone regeneration which have strong osteoinductive activity. CGF-0.75%HLC-I/Bio-Oss materials can promote new bone formation, providing new ideas for the application of bone tissue engineering scaffold materials in oral clinics.

Modified internal curvilinear distraction device with a pre-embedding guide rail, drive screw, and universal joint for curvilinear lengthening of the mandible: A finite element analysis and animal experiment

ObjectivesThe semiburied design of the traditional internal distractor has a relatively high risk of infection and aesthetic problems. To reduce these potential risks, a modified internal distractor with design of pre-embedding curvilinear rail, drive screw, and universal joint was invented. Its stress distribution characteristics and the effect on curvilinear distraction osteogenesis (DO) in vivo were further tested. Materials and methodsFinite element analysis (FEA) was performed on a model of the human mandible and distraction device to measure the stress distribution during curvilinear DO. Six beagles underwent curvilinear DO and consolidation using the new device. Radiological and histological examinations were performed on the new bone. ResultsOn FEA, the stress was concentrated in the condyle (128.6 MPa) and curved guide rails (324.8 MPa). Four of the six animals completed the DO period and were consolidated for 12 weeks. Secondary infections were not observed. Radiography showed that a new fan-shaped bone—15.5 ± 5.5 mm in length and 4.6 ± 1.6 mm in height—was formed in the bone gap. Micro-computed tomography and histological examinations of specimens indicated that the structure of the new bone was similar to that of the normal bone. ConclusionsThe modified internal curvilinear distraction device meets the mechanical strength requirement and achieve curvilinear DO in animal experiments.

Timing selection for loosened tooth fixation based on degree of alveolar bone resorption: a finite element analysis

ObjectiveThis study aimed to evaluate timing of fixation to retard bone absorption using finite element analysis(FEA).MethodsVolunteer CT images were used to construct four models of mandibles with varying degrees of alveolar bone resorption. By simulating occlusal force loading, biomechanical analysis was made on the periodontal membrane, tooth root and surrounding bone (both cancellous and cortical) of mandibular dentition.ResultsThe von Mises stress value of the periodontal structures was positively related with the degree of alveolar bone resorption, and the von Mises stress at the interface between the periodontal membrane and tooth root was increased significantly in moderate to severe periodontitis models. The von Mises stress at the interface between the periodontal cortical bone and cancellous bone was increased significantly in the severe periodontitis model. And the von Mises stress value with oblique loading showed significantly higher than vertical loading.ConclusionTeeth with moderate to severe periodontitis, loosened tooth fixation can be used to retard bone absorption.

Design of patient specific basal dental implant using Finite Element method and Artificial Neural Network technique.

The bone conditions of mandibular bone vary from patient to patient, and as a result, a patient-specific dental implant needs to be designed. The basal dental implant is implanted in the cortical region of the bone since the top surface of the bone narrows down because of aging. Taguchi designs of experiments technique are used in which 25 optimum solid models of basal dental implants are modeled with variable geometrical parameters, viz. thread length, diameter, and pitch. In the solid models the implants are placed in the cortical part of the 3D models of cadaveric mandibles, that are prepared from CT data using image processing software. Patient-specific bone conditions are varied according to the strong, weak, and normal basal bone. A compressive force of 200 N is applied on the top surface of these implants and using finite element analysis software, the microstrain on the peri-implant bone ranges from 1000 to 4000 depending on the various bone conditions. According to the finite element data, it can be concluded that weak bone microstrain is comparatively high compared with normal and strong bone conditions. A surrogate artificial neural network model is prepared from the finite element analysis data. Surrogate model assisted genetic algorithm is used to find the optimum patient-specific basal dental implant for a better osseointegration-friendly mechanical environment.

P-68027784-328 - 'Jaw-in-a-Day' simultaneous jaw reconstruction with intraoral implant surgery.

<h3>Purpose</h3> Composite defects including teeth-soft tissue-bone are caused after tumor ablation in oral and maxillofacial area and makes severe problems in diet and phonation. There have been some trials to reconstruct occlusion immediately after tumor ablation. Max et al. reported fibula reconstruction with CAD/CAM reconstruction plates and dental implants. They reported a fibula cutting guide which has holes for dental implant position. Yadranko et al. reported a 3d printed mandible model to simulated fibula segment fixation and dental implant installation. Here we report a technique using a teeth supported dental implant guide to reconstruct proper occlusion immediately. <h3>Methods</h3> Previous reported articles were reviewed. Comparison between installing implants several years after reconstruction was done. According to reports of Max et al., there were 3.3mm centerpoint deviation and 13.0 degree angular deviation of implant with their Methods. <h3>Results</h3> Reconstructing occlusion simultaneously with bone has several advantages. It dramatically shortens period of dentition loss. Soft tissue management can be done simply. In result, when installing dental implants outside the oral cavity, error due to bone positioning is inevitable. Intraoral implant surgery after fixation of bone segment is thought to reduce these errors. <h3>Conclusions</h3> Our final goal for reconstruction of oral and maxillofacial defect is not positioning bone segment properly but reconstructing proper occlusion. Even though the bone segment is positioned in a slightly different position from the planned position, intraoral implant guide using other teeth as a reference will make it possible to install implant in planned position.

Introducing surface-to-surface matching technique to evaluate mandibular symmetry: A retrospective study

ObjectivesThis study introduced a three-dimensional (3D) surface-to-surface matching technique to evaluate the mandibular symmetry of teenagers and adults with unilateral second molar scissor bite. MethodsThe targets came from 73 cone-beam computed tomography (CBCT) images with unilateral second molar scissor bite, including teenagers (n = 30) and adults (n = 43). 73 images without scissor bite and matched in sex and age were selected as controls. The scans were developed into 3D mandible models and seven mandibular functional unit models, including condylar process (Co), coronoid process (Cr), mandibular ramus (Ra), mandibular angle (Ma), alveolar process (Ap), mandibular body (Mb) and chin process (Ch). The surface-to-surface matching technique was introduced. 3D deviation analysis and matching percentages calculation were performed and compared to evaluate the symmetry of the mandible. ResultsComparisons were made between the study samples and control samples. For teenagers, the matching percentages of the entire mandible (55.31 ± 7.24%), Mb (69.04 ± 9.22%) and Co (65.19 ± 10.67%) in the study group were lower than that of the entire mandible (60.87 ± 6.38%) (P <0.01), Mb (75.0 ± 8.71%) (P <0.05) and Co (70.25 ± 8.20%) (P <0.05) in the control group. While Ap, Ra, Ch, Cr and Ma showed no statistically significant differences (P >0.05). For adults, the matching percentages of the entire mandible (48.88 ± 9.77%), Ap (65.83 ± 11.21%), Mb (64.43 ± 12.03%), Ch (79.17 ± 10.29%), Ra (64.11 ± 9.84%) and Co (61.08 ± 11.64%) in the study group were lower than the entire mandible (59.28 ± 5.49%) (P <0.01), Ap (73.65 ± 9.10%) (P <0.01), Mb (71.66 ± 8.40%) (P <0.01), Ch (83.86 ± 5.59%) (P <0.05), Ra (68.54 ± 7.87%) (P <0.05) and Co (66.20 ± 10.62%) (P <0.05) of the control group. Only Cr and Ma showed no statistically significant differences (P >0.05). ConclusionMandibular asymmetry was observed in both teenagers and adults with unilateral second molar scissor bite. Moreover, compared with teenagers, more mandibular units of adult patients were affected. Clinical significanceBased on the surface-to-surface matching technique, the symmetric and morphological information of the mandible can be converted into visual color maps and quantitative descriptions. This method can bring convenience to the study of the growth of mandible, orthodontic treatment and orthognathic surgery design.

A Non-Linear Osteometric Modeling Method for Three-Dimensional Mandibular Morphological Changes During Growth: One-Year Monitoring of Miniature Pigs Using Cone-Beam Computed Tomography.

Knowledge of mandibular growth and development is essential for diagnosis of malformation and early interception. A previous method of quantifying mandibular growth using the distances between selected anatomical landmarks over the growth period does not provide a complete, quantitative description of the continuous growth patterns. The current study aimed to bridge the gap by measuring the 3D continuous growth of the mandible in miniature pigs using cone-beam computerized tomography (CBCT). The mandibles of the pigs were CBCT-scanned monthly over 12 months, and the 3D mandibular models were reconstructed. A new non-linear, time-dependent osteometric modeling approach was developed to register two consecutive mandible models by searching for the corresponding points with the highest likelihood of matching the anatomical and morphological features so that the morphological changes patterns for each month could be described using color maps on the models. The morphological changes of the mandible were found to decrease anteriorly, with the condyle region and the posterior part of the ramus growing faster than the rest of the mandible. The condyle region showed the fastest growth rate and the posterior ramus the second during the growth period, while the middle and anterior corpus regions showed the slowest growth rates. In conclusion, the current results revealed the non-linear patterns and rates of morphological changes in different growth regions and the whole mandible. The new approach may also be useful for future studies on the growth of the mandible in other animals.

Statistical shape modelling of the human mandible: 3D shape predictions based on external morphometric features

One of the main limitations in subject-centred design approach is represented by getting 3D models of the region of interest. Indeed, 3D reconstruction from imaging data (i.e., computed tomography scans) is expensive and exposes the subject to high radiation doses. Statistical Shape Models (SSMs) are mathematical models able to describe the variability associated to a population and allow predicting new shapes tuning model parameters. These parameters almost never have a physical meaning and so they cannot be directly related to morphometric features. In this study a gender-combined SSM model of the human mandible was setup, using Generalised Procrustes Analysis and Principal Component Analysis on a dataset of fifty mandibles. Twelve morphometric features, able to characterise the mandibular bone and readily collectable during external examinations, were recorded and correlated to SSM parameters by a multiple linear regression approach. Then a cross-validation procedure was performed on a control set to determine the combination of features able to minimise the average deviation between real and predicted shapes. Compactness of the SSM and main modes of deformations have been investigated and results consistent with previous works involving a higher number of shapes were found. A combination of five features was proved to characterise predicted shapes minimising the average error. As completion of the work, a male SSM was developed and performances compared with those of the combined SSM. The features-based model here proposed could represent a useful and easy-to-use tool for the generation of 3D customised models within a virtual interactive design environment.

Bone quality effect on short implants in the edentulous mandible: a finite element study

IntroductionThe aim of this study was to verify whether the use of short implants could optimize stress distribution of bone surrounding implants in atrophic mandibles with different bone qualities.MethodsA three-dimensional model of the atrophic mandible with three levels of bone quality was made using computer software. Short implants (6 mm) and standard implants (10 mm) were used in four designs: Design 1 "All-On four", Design 2 "All-On-four" with two short implants, Design 3 four vertical implants with two short implants, and Design 4 six short implants. The distal short implants were placed at the first molar position. All twelve models were imported into finite element analysis software, and 110 N oblique force was loaded on the left second premolar. Maximum principal stress values of peri-implant bone and the volumes of bone with over 3000 microstrians (overload)were analyzed.ResultStress values and volumes of overload bone increased in all four groups with the decline of bone quality. The highest stress values were found in the cortical bone surrounding the Design 1 inclined implant in two lower bone quality mandibles, and the lowest in Design 3. However, Design 1 had less overload bone tissue than all three designs with short implants.ConclusionShort implants placed posteriorly helped decrease stress values in peri-implant bone, while bone surrounding short implants had a high resorption risk in low bone quality mandible.

Growth patterns and shape development of the paediatric mandible – A 3D statistical model

Background/aimTo develop a 3D morphable model of the normal paediatric mandible to analyse shape development and growth patterns for males and females. MethodsComputed tomography (CT) data was collected for 242 healthy children referred for CT scan between 2011 and 2018 aged between 0 and 47 months (mean, 20.6 ± 13.4 months, 59.9% male). Thresholding techniques were used to segment the mandible from the CT scans. All mandible meshes were annotated using a defined set of 52 landmarks and processed such that all meshes followed a consistent triangulation. Following this, the mandible meshes were rigidly aligned to remove translation and rotation effects, while size effects were retained. Principal component analysis (PCA) was applied to the processed meshes to construct a generative 3D morphable model. Partial least squares (PLS) regression was also applied to the processed data to extract the shape modes with which to evaluate shape differences for age and sex. Growth curves were constructed for anthropometric measurements. ResultsA 3D morphable model of the paediatric mandible was constructed and validated with good generalisation, compactness, and specificity. Growth curves of the assessed anthropometric measurements were plotted without significant differences between male and female subjects. The first principal component was dominated by size effects and is highly correlated with age at time of scan (Spearman's r = 0.94, p < 0.01). As with PCA, the first extracted PLS mode captures much of the size variation within the dataset and is highly correlated with age (Spearman's r = −0.94, p < 0.01). Little correlation was observed between extracted shape modes and sex with either PCA or PLS for this study population. ConclusionThe presented 3D morphable model of the paediatric mandible enables an understanding of mandibular shape development and variation by age and sex. It allowed for the construction of growth curves, which contains valuable information that can be used to enhance our understanding of various disorders that affect the mandibular development. Knowledge of shape changes in the growing mandible has potential to improve diagnostic accuracy for craniofacial conditions that impact the mandibular morphology, objective evaluation, surgical planning, and patient follow-up.

Biomechanical analysis of inclined and cantilever design with different implant framework materials in mandibular complete-arch implant restorations

Statement of problemInclined distal implants with posterior framework cantilevers are an alternative to straight implants for the treatment of edentulous jaws, avoiding grafting procedures and utilizing pre-existing bone. However, little is known about the implant, framework, and peri-implant bone stresses exerted by this design. PurposeThe purpose of this finite element analysis study was to assess the biomechanical properties of the inclined versus straight design, with different implant framework material to generate implant-supported complete-arch fixed mandibular prostheses. Material and methodsA finite element model of the edentulous mandible was generated by using 4 implants in 2 distinct configurations: the inclined design and the straight design. Different framework materials were tested: pure titanium, cobalt-chromium alloy, type IV gold alloy, zirconia, polyetheretherketone (PEEK), and carbon fiber–reinforced polyetheretherketone (CFR-PEEK). A 300-N load at a 75-degree angle was applied to the occlusal plane from the lingual side of the buccal cusps of the 2 premolars and the first molar teeth. Subsequently, stresses on the implant, surrounding bone, and framework were measured and analyzed quantitatively and qualitatively. ResultsIn terms of implant configurations, the inclined design demonstrated less stress on the posterior cortical bone, implants, and framework than the straight design. Comparing the framework materials, zirconia and metal exhibited reduced cortical bone and implants stresses but elevated framework stress when compared with the polymeric frameworks. ConclusionsFrom a biomechanical viewpoint, in edentulous patients with excessive posterior alveolar bone resorption, the inclined design exhibited more favorable stress distribution around the posterior implants than the straight design. In implant-supported complete-arch fixed mandibular prostheses, zirconia and metal, particularly cobalt-chromium alloy, distributed the stresses more effectively to the implants and supporting bone than polymeric materials.

Short-Segment Drilling Guides for the Management Comminuted Mandibular Fractures.

Treatment of a severely comminuted mandibular fracture is challenging. This technical note describes a novel office-based workflow, combining virtual surgery planning with short-segment drilling guides. The authors reduced the comminuted mandibular fractures via virtual surgery planning. Then, the reconstructed mandible model was printed using an in-house 3D printer. Next, the reconstruction plate was preformed according to the shape of the mandibular model surface, and the position of the screw hole in the mandibular surface was determined. Finally, hand-made short-segment drilling guides for screw position transfer were fabricated with temporary resin. During the operation, the authors reset the guides for the drill to make screw holes as planned. After the hole was drilled, the pre-bent plate was applied to the mandible. The fracture was expected to be reduced, when tightening the screws. in our workflow, by using short and simple operative procedures, the authors were able to achieve precise reduction and reduce the operation time.

Assessment of Dental Arch Parameters in Turkish Twins.

The aim of this study is to investigate the relative contributions of genetic and environmental factors to variations in dental dimensions in a sample of Turkish twins, and to estimate heritability using dental casts. The study samples were selected from the twin children between 3-15 years old who referred for their first dental examination. Fifty nine monozygotic and one hundred and forty three dizygotic twin pairs were examined in the study. The alginate impression material used to create the plaster model of maxilla and mandible. Anterior arch width, posterior arch width, arch length and arch circumference were measured on models prepared from measurements taken for both maxilla and mandible with digital caliper. The similarities and differences of the measurements were compared between pairs of twins and zygocytes. Morever, the effects of bad oral habits, bruxism, a result of psychosocial factors on measurements were examined. Statistical analysis was performed using Paired T Test, Wilcoxon Test and Mann Whitney U test. A total of 404 dental models of 118 (29.2%) monozygotic and 286 (70.8%) dizygotic twins were evaluated. There was no statistical difference between sibling pairs in both monozygotic and dizygotic twins. The measurement similarity between twin siblings differed according to zygosity in all measurements (p<0.05). It has been observed that the finger sucking and mouth breathing affect the dental arch measurements (p<0.05). These results indicate that the differences in dental arch dimensions between monozygotic twin pairs are less than the difference between dizygotic twin pairs.

In Silico Biomechanical Evaluation of WE43 Magnesium Plates for Mandibular Fracture Fixation.

Titanium fixation devices are the gold standard for the treatment of mandibular fractures; however, they present serious limitations, such as non-degradability and generation of imaging artifacts. As an alternative, biodegradable magnesium alloys have lately drawn attention due to their biodegradability and biocompatibility. In addition, magnesium alloys offer a relatively high modulus of elasticity in comparison to biodegradable polymers, being a potential option to substitute titanium in highly loaded anatomical areas, such as the mandible. This study aimed to evaluate the biomechanical competence of magnesium alloy WE43 plates for mandibular fracture fixation in comparison to the clinical standard or even softer polymer solutions. A 3D finite element model of the human mandible was developed, and four different fracture scenarios were simulated, together with physiological post-operative loading and boundary conditions. In a systematic comparison, the material properties of titanium alloy Ti-6Al-4V, magnesium alloy WE43, and polylactic acid (PLA) were assigned to the fixation devices, and two different plate thicknesses were tested. No failure was predicted in the fixation devices for any of the tested materials. Moreover, the magnesium and titanium fixation devices induced a similar amount of strain within the healing regions. On the other hand, the PLA devices led to higher mechanical strains within the healing region. Plate thickness only slightly influenced the primary fixation stability. Therefore, magnesium alloy WE43 fixation devices seem to provide a suitable biomechanical environment to support mandibular fracture healing in the early stages of bone healing. Magnesium WE43 showed a biomechanical performance similar to clinically used titanium devices with the added advantages of biodegradability and radiopacity, and at the same time it showed a remarkably higher primary stability compared to PLA fixation devices, which appear to be too unstable, especially in the posterior and more loaded mandibular fracture cases.