A cone-beam CT based technique to augment the 3D virtual skull model with a detailed dental surface

Cone-beam computed tomography (CBCT) is used for maxillofacial imaging. 3D virtual planning of orthognathic and facial orthomorphic surgery requires detailed visualisation of the interocclusal relationship. This study aimed to introduce and evaluate the use of a double CBCT scan procedure with a modified wax bite wafer to augment the 3D virtual skull model with a detailed dental surface. The impressions of the dental arches and the wax bite wafer were scanned for ten patient separately using a high resolution standardized CBCT scanning protocol. Surface-based rigid registration using ICP (iterative closest points) was used to fit the virtual models on the wax bite wafer. Automatic rigid point-based registration of the wax bite wafer on the patient scan was performed to implement the digital virtual dental arches into the patient's skull model. Probability error histograms showed errors of ≤0.22 mm (25% percentile), ≤0.44 mm (50% percentile) and ≤1.09 mm (90% percentile) for ICP surface matching. The mean registration error for automatic point-based rigid registration was 0.18 ± 0.10 mm (range 0.13–0.26 mm). The results show the potential for a double CBCT scan procedure with a modified wax bite wafer to set-up a 3D virtual augmented model of the skull with detailed dental surface.     

Relationship between occlusal curvatures and bite force in humans

PurposeIt is clinically believed that humans with a broad and rounded dental arch accompanied by a shallow curve of Spee have good masticatory function. However, the relationship between them has not been elucidated fully. The purpose of this study was to quantitatively examine the relationship between occlusal curvatures and bite force.Materials and methodsBite force was measured and analyzed in 20 young adults with healthy permanent dentition and normal stomatognathic function using a bite force recording system. Study models of the mandibular dental arch were scanned with CCD cameras, and X, Y and Z coordinates of the cusp tips of the molars were recorded. Their occlusal curvatures were analyzed using a three-dimensional measurement system.ResultsBite force showed significant positive correlations (0.52 < R < 0.57) with the radius of the anteroposterior occlusal arc of the molar region and the radii of the translateral occlusal arcs in the second premolar, first molar and second molar regions, and showed significant positive correlation (R = 0.71) with the radius of the occlusal sphere of the molar region.ConclusionsIt was suggested that occlusal curvatures is related with the magnitude of bite force, and that the three dimensional spherical analysis of occlusal curvatures is useful predictor of the masticatory function.     

Digital replacement of the distorted dentition acquired by cone beam computed tomography (CBCT): a pilot study

During cone beam computed tomography (CBCT) scanning, intra-oral metallic objects may produce streak artefacts, which impair the occlusal surface of the teeth. This study aimed to determine the accuracy of replacement of the CBCT dentition with a more accurate dentition and to determine the clinical feasibility of the method. Impressions of the teeth of six cadaveric skulls with unrestored dentitions were taken and acrylic base plates constructed incorporating radiopaque registration markers. Each appliance was fitted to the skull and a CBCT performed. Impressions were taken of the dentition with the devices in situ and dental models were produced. These were CBCT-scanned and the images of the skulls and models imported into computer-aided design/computer-aided manufacturing (CAD/CAM) software and aligned on the registration markers. The occlusal surfaces of each dentition were then replaced with the occlusal image of the corresponding model. The absolute mean distance between the registration markers in the skulls and the dental models was 0.09 ± 0.02 mm, and for the dentition was 0.24 ± 0.09 mm. When the method was applied to patients, the distance between markers was 0.12 ± 0.04 mm for the maxilla and 0.16 ± 0.02 mm for the mandible. It is possible to replace the inaccurate dentition on a CBCT scan using this method and to create a composite skull which is clinically acceptable.     

Peel bond strength between 3D printing tray materials and elastomeric impression/adhesive systems: A laboratory study

ObjectivesThe present study aimed to evaluate the bonding between three 3D printed custom tray materials and three elastomeric impression/adhesive systems using the peel test.MethodsTest blocks were 3D printed by three different technologies using Dental LT, FREEPRINT tray, and polylactide (PLA) tray materials. The reference test blocks were conventionally fabricated with Zeta Tray LC, a light-curing resin. The surface topographies of the four tray materials were investigated by scanning electron microscopy (SEM) analyses and roughness measurements. The peel bond strength between the four tray materials and three impression/adhesive systems, vinylsiloxanether (VSXE), vinyl polysiloxane (VPS), and polyether (PE), was measured (n = 12 per group). The peeling failure modes and rupture sites were identified microscopically.ResultsThe four tray materials featured different surface topographies. The peel bond strength was not significantly different with VSXE and PE, but PLA and the reference showed higher peel bond strength with VPS than the Dental LT and FREEPRINT tray (p < 0.05). The rupture site of adhesive failure in all groups was partly at the adhesive-impression material interface and partly within the adhesive but never at the adhesive-tray material interface.SignificanceThe 3D printed tray materials can achieve satisfactory chemical compatibility with the adhesives of VSXE, VPS, and PE. Surface topographies generated by the 3D printing technologies may affect bonding. Generally, 3D printed tray materials can provide clinically adequate bond strength with the elastomeric impression/adhesive systems. PLA is recommended for bonding with VPS when severe impression removal resistance is detected.     

Two-year follow-up of changes in bite force and occlusal contact area after intraoral vertical ramus osteotomy with and without Le Fort I osteotomy

This study was performed to examine the longitudinal changes in bite force and occlusal contact area after mandibular setback surgery via intraoral vertical ramus osteotomy (IVRO). Patients with mandibular prognathism who underwent IVRO (surgical group: 39 men and 39 women) were compared with subjects with class I skeletal and dental relationships (control group; 32 men and 35 women). The surgical group was divided into two subgroups: 1-jaw surgery (n = 30) and 2-jaw surgery (n = 48). Bite force and contact area were measured in maximum intercuspation with the Dental Prescale System before treatment, within 1 month before surgery, and at 1, 3, 6, 9, 12, and 24 months postsurgery. A linear mixed model was used to investigate the time-dependent changes and associated factors. Bite force and contact area decreased during presurgical orthodontic treatment, were minimal at 1 month postsurgery, and increased gradually thereafter. The 1-jaw and 2-jaw subgroups showed no significant differences in bite force. The time-dependent changes in bite force were significantly different according to the contact area (P < 0.05). The results of this study suggest that bite force and occlusal contact area gradually increase throughout the postsurgical evaluation period. Increasing the occlusal contact area may be essential for improving bite force after surgery.     

Surface roughness of impression materials and dental stones scanned by non-contacting laser profilometry

ObjectiveTo analyze differences in the way dental materials digitize on a non-contacting laser profilometer (NCLP).MethodsThree Type IV dental stones and 15 impression materials were mixed according to the manufacturer's instructions and expressed against a glass block to record its surface characteristics. From each material an area of 6 × 40 mm was scanned on the NCLP and the Ra, Rq and Rt roughness values measured from 20 randomly selected transverse profiles. The surface of the impression materials was subsequently poured in Moonstone? (Bracon Ltd., Etchingham, England) dental stone and the same roughness values obtained from these casts. Differences in roughness values from the dental materials were compared using ANOVA and differences in roughness between impression materials and the Moonstone? casts compared using paired t-tests.ResultsThere were significant differences in roughness values between individual materials within each type (impression material or dental stone) (p < 0.05). The roughness of the dental stones varied between Ra = 0.87 and 0.99 μm, Rq = 1.09 and 1.23 μm, and Rt = 5.70 and 6.51 μm. The roughness values of the impression materials varied between Ra = 0.75 and 4.56 μm; Rq = 0.95 and 6.27 μm and Rt = 4.70 and 39.31 μm. Darker materials showed higher roughness values compared to lighter materials (p < 0.05). The roughness of the Moonstone? casts varied between Ra = 0.80 and 0.98 μm; Rq = 1.01 and 1.22 μm, and Rt = 5.04 and 6.38 μm. Roughness values of some impression materials were statistically significantly lower when the surface was reproduced in Moonstone? (p < 0.01).SignificanceDigitization of dental materials on optical profilometers was affected by color and transparency.     

Accuracy of implant position when placed using static computer-assisted implant surgical guides manufactured with two different optical scanning techniques: a randomized clinical trial

Data from cone beam computed tomography (CBCT) and optical scans (intraoral or model scanner) are required for computer-assisted implant surgery (CAIS). This study compared the accuracy of implant position when placed with CAIS guides produced by intraoral and extraoral (model) scanning. Forty-seven patients received 60 single implants by means of CAIS. Each implant was randomly assigned to either the intraoral group (n = 30) (Trios Scanner, 3Shape) or extraoral group (n = 30), in which stereolithographic surgical guides were manufactured after conventional impression and extraoral scanning of the stone model (D900L Lab Scanner, 3Shape). CBCT and surface scan data were imported into coDiagnostiX software for virtual implant position planning and surgical guide design. Postoperative CBCT scans were obtained. Software was used to compare the deviation between the planned and final positions. Average deviation for the intraoral vs. model scan groups was 2.42° ± 1.47° vs. 3.23° ± 2.09° for implant angle, 0.87 ± 0.49 mm vs. 1.01 ± 0.56 mm for implant platform, and 1.10 ± 0.53 mm vs. 1.38 ± 0.68 mm for implant apex; there was no statistically significant difference between the groups (P > 0.05). CAIS conducted with stereolithographic guides manufactured by means of intraoral or extraoral scans appears to result in equal accuracy of implant positioning.     

The virtual human face: Superimposing the simultaneously captured 3D photorealistic skin surface of the face on the untextured skin image of the CBCT scan

The aim of this study was to evaluate the impact of simultaneous capture of the three-dimensional (3D) surface of the face and cone beam computed tomography (CBCT) scan of the skull on the accuracy of their registration and superimposition. 3D facial images were acquired in 14 patients using the Di3d (Dimensional Imaging, UK) imaging system and i-CAT CBCT scanner. One stereophotogrammetry image was captured at the same time as the CBCT and another 1 h later. The two stereophotographs were individually superimposed over the CBCT using VRmesh. Seven patches were isolated on the final merged surfaces. For the whole face and each individual patch: maximum and minimum range of deviation between surfaces; absolute average distance between surfaces; and standard deviation for the 90th percentile of the distance errors were calculated. The superimposition errors of the whole face for both captures revealed statistically significant differences (P = 0.00081). The absolute average distances in both separate and simultaneous captures were 0.47 and 0.27 mm, respectively. The level of superimposition accuracy in patches from separate captures was 0.3–0.9 mm, while that of simultaneous captures was 0.4 mm. Simultaneous capture of Di3d and CBCT images significantly improved the accuracy of superimposition of these image modalities.     

Novel stress increases hypothalamic-pituitary-adrenal activity in mice with a raised bite

Background and objectiveIn humans, occlusal disharmony may cause various physical complaints, including head and neck ache, stiffness in the shoulder and neck, and arthrosis of the temporomandibular joints. Occlusal disharmony induced by raising the bite in rodents, increases plasma corticosterone levels, which leads to morphologic changes in the hippocampus and altered hippocampus-related behavior. The paraventricular nucleus (PVN) of the hypothalamus regulates the hypothalamic-pituitary-adrenal system. Chronically stressed animals exposed to a novel stress exhibit higher adrenocorticotropic hormone levels than naive control animals. We hypothesized that there would be different response of the corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) to a novel acute stress with occlusal disharmony.DesignIn order to investigate how exposure of mice with occlusal disharmony to a novel acute stress (restraint stress) affects the PVN, we induced occlusal disharmony by raising the vertical dimension of the bite (bite-raised condition) and examined the expression of corticotrophin releasing hormone (CRH) mRNA and arginine vasopressin (AVP) mRNA in mouse PVN.ResultsCRH mRNA expression was increased in the PVN of the bite-raised group 90 min after the bite-raising procedure, but the expression was recovered to the control level at 14 days. AVP mRNA expression in the PVN was normal at 90 min, and increased significantly 14 days after the bite-raising procedure. Exposure to restraint stress in the bite-raised mice induced a significant increase in CRH mRNA expression in the PVN.ConclusionsThe bite-raising procedure induced a rapid CRH mRNA response and a slower AVP mRNA response in the parvocellular PVN of the hypothalamus. Exposure to a novel stress following the bite-raising procedure further reinforced the CRH stress response. Thus, occlusal disharmony, such as that induced by raising the bite, may be a risk factor for hypersensitivity to a novel stress.     

Effect of occlusal splint therapy on maximum bite force in individuals with moderate to severe attrition of teeth

ObjectiveThe purpose of the pilot study was to determine the effect of restoring lost occlusal vertical dimension (OVD) due to attrition on maximum bite force in humans.MethodologyA total of 124 subjects in age range of 25–40 years, with moderate to severe attrition, having full complement of teeth were screened according to inclusion and exclusion criteria. After consent, occlusal vertical dimension was assessed by employing mechanical and physiological methods in the experimental group and a maxillary canine guided hard splint was fabricated for each subjects fulfilling inclusion criteria and with positive consent (78). Bite force in experimental group was measured before, immediately after delivery of splint and subsequently at an interval of four, eight, and twelve weeks. Due loss during follow up, only 50 subjects could be available for bite force recording till 12 weeks. Bite force of age, gender, height and weight matched controls with no signs of attrition was also measured for comparison.ResultsBite force of the experimental group was found to be significantly less than the matched controls (P = 0.000) initially. After delivery of splint, bite force values increased progressively till twelve weeks. However comparison of bite force values of experimental group with control group showed no significant difference at end of eight (P = 0.008) and twelve weeks (P = 0.162).ConclusionIt was concluded that maximum bite force increases with restoration of lost vertical using splint therapy. A time period of 8–12 weeks is required to restore the maximum bite force value approximately similar to matched controls.     

Does pain in the masseter and anterior temporal muscles influence maximal bite force?

ObjectiveThe aim of this study was to evaluate changes in pain and muscle force, and the relationship between them, in patients with muscle pain and bruxism, prior to and after treatment.MethodsThirty women with bruxism and myofascial pain (Ia) were included in this study. Sleep bruxism diagnosis was made based on clinical diagnostic criteria, and awake bruxism diagnosis was made by patient questionnaires and the presence of tooth wear. The diagnosis of myofascial pain was established according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC-TMD). Dentulous or partially edentulous patients (rehabilitated with conventional fixed prostheses) were included in the study according to the inclusion and exclusion criteria. The pain treatment protocol included occlusal splints, patient education, and physiotherapy for 30 days. Bite force was measured using a dynamometer at the central incisor and the first molar regions on both sides. The exams were performed at baseline, after 7 days, and 30 days after treatment. The Wilcoxon test was used to compare patient pain level response among the periods analyzed in the study. Bite force data were submitted to two-way repeated-measures ANOVA, followed by the Tukey HSD test (p < 0.05). A simple regression analysis was performed to verify the relation between pain level and bite force.ResultsResults revealed that there was a statistical difference in pain level over time for both muscles and sides (p < 0.01). In the molar region, the bite force exhibited significantly higher values after 30 days of treatment, when compared with the baseline (p < 0.001). There was a correlation between pain level and bite force only for the temporal muscle in all periods analyzed (p < 0.05). There was no strong correlation in the response level points to support the association of pain and bite force.ConclusionsPain level decreased and bite force increased in the molar region after treatment. No strong correlation or dispersion in the relationship between pain levels and bite force was seen in women with myofascial pain and bruxism.     

Comparison of the accuracy for three dental impression techniques and index: An in vitro study

ObjectivesThis in vitro study compared the dimensional accuracy of stone index (I) and three impression techniques: tapered impression copings (T), squared impression copings (S) and modified squared impression copings (MS) for implant-supported prostheses.MethodsA master cast, with four parallel implant abutment analogs and a passive framework, were fabricated. Vinyl polysiloxane impression material was used for all impressions with two metal stock trays (open and closed tray). Four groups (I, T, S and MS) were tested (n = 5). A metallic framework was seated on each of the casts, one abutment screw was tightened, and the gap between the analog of implant and the framework was measured with a stereomicroscope. The groups’ measurements (80 gap values) were analyzed using software (LeicaQWin – Leica Imaging Systems Ltd.) that received the images of a video camera coupled to a Leica stereomicroscope at 100× magnification. The results were statistically analyzed with Kruskal–Wallis One Way ANOVA on Ranks test followed by Dunn's Method, 0.05.ResultsThe mean values of abutment/framework interface gaps were: Master Cast = 32 μm (SD 2); Group I = 45 μm (SD 3); Group T = 78 μm (SD 25); Group S = 134 μm (SD 30); Group MS = 143 μm (SD 27). No significant difference was detected among Index and Master Cast (P = .05).ConclusionUnder the limitations of this study, it could be suggested that a more accurate working cast is possible using tapered impression copings techniques and stone index.     

Can an entry-level 3D printer create high-quality anatomical models? Accuracy assessment of mandibular models printed by a desktop 3D printer and a professional device

This study was performed to determine whether an in-house printed mandible model is sufficiently accurate for daily clinical practice. Ten example mandible models were produced with a desktop 3D printer (fused filament fabrication, FFF) and compared with 10 equivalent mandible models fabricated using a professional-grade 3D printer (selective laser sintering, SLS). To determine the precision of the printed models, each model was scanned with an optical scanner. Subsequently, every model was compared to its original standard tessellation language (STL) file and to its corresponding analogue. Mean ± standard deviation and median (interquartile range) differences were calculated. Overall these were −0.019 ± 0.219 mm and −0.007 (−0.129 to 0.107) mm for all 10 pairs. Furthermore, correlation of all printed models to their original STL files showed a high level of accuracy. Comparison of the SLS models with their STL files revealed a mean difference of −0.036 ± 0.114 mm and median difference of −0.028 (−0.093 to 0.030) mm. Comparison of the FFF models with their STL files yielded a mean difference of −0.055 ± 0.227 mm and median difference of −0.022 (−0.153 to 0.065) mm. The study findings confirm that in-house 3D printed mandible models are economically favourable as well as suitable substitutes for professional-grade models, in particular considering the geometric aspects.     

Denture flask fabrication using fused deposition modeling three-dimensional printing

PurposeThis paper describes a method for making a customized denture flask using fused deposition modeling (FDM) by three-dimensional (3D) printing. We have proposed a new digital dental prosthesis using conventional dental base materials and artificial teeth.MethodsUsing the universal development system software, a denture-designed Standard Tessellation Language (STL) file and a denture flask STL file were superimposed, and the denture region was set as an empty space. After setting the offset value to 200 μm between the denture base and teeth for artificial tooth positioning, the flask was created by FDM 3D printing. Conventional artificial teeth were inserted into the 3D-printed flask, and resin packing, finishing, and polishing were performed using the conventional method for fabricating the complete denture.ConclusionsThe 3D printing materials used to make digital dental prostheses have not yet been fully validated. Therefore, the production of a 3D-printed denture flask, which can use conventional complete denture materials, presents a new alternative to the digital fabrication of dentures.     

Airway space changes after maxillomandibular counterclockwise rotation and mandibular advancement with TMJ Concepts® total joint prostheses: three-dimensional assessment

This study focused on three-dimensional (3D) airway space changes and stability following simultaneous maxillomandibular counterclockwise rotation, mandibular advancement, and temporomandibular joint (TMJ) reconstruction with custom-made total joint prostheses (TMJ Concepts^®). Cone beam computed tomography (CBCT) scans of 30 consecutive female patients with irreversibly compromised TMJs were obtained at the following intervals: T1, presurgery; T2, immediately after surgery; and T3, at least 6 months after surgery. The CBCT volumetric datasets were analysed with Dolphin Imaging^® software to evaluate surgical and postsurgical changes to oropharyngeal airway parameters. The average changes in airway surface area (SA), volume (VOL), and minimum axial area (MAA) were, 179.50 mm², 6302.60 mm³, and 92.23 mm², respectively, at the longest follow-up (T3 ? T1) (P ≤ 0.001). Significant correlations between the amount of mandibular advancement and counterclockwise rotation of the occlusal plane and 3D airway changes were also found (P ≤ 0.01). The results of this investigation showed a significant immediate 3D airway space increase after maxillomandibular counterclockwise rotation and mandibular advancement with TMJ Concepts total joint prostheses, which remained stable over the follow-up period.     

Monolithic crowns fracture analysis: The effect of material properties,cusp angle and crown thickness

ObjectivesThis study aimed to investigate the collective influence of material properties and design parameters on the fracture behavior of monolithic dental crowns.MethodsThree-dimensional (3D) models (N = 90) with different combinations of design parameters (thickness, cusp angle and occlusal notch geometry) and material type (lithium disilicate, feldspar ceramic, zirconia, hybrid resin ceramic and hybrid polymer-infiltrated ceramic) were developed for the failure analysis using extended finite element method (XFEM) to identify the stress distribution, crack initiation load, fracture surface area and fracture pattern. Analytical formulation, in vitro fracture tests and fractographic analysis of dedicated models were also performed to validate the findings of the XFEM simulation.ResultsFor all material types considered, crowns with a sharp occlusal notch design had a significantly lower fracture resistance against occlusal loading. In most of the models, greater crown thickness and cusp angle resulted in a higher crack initiation load. However, the effect of cusp angle was dominant when the angle was in the low range of 50° for which increasing thickness did not enhance the crack initiation load.SignificanceComparing the critical load of crack initiation for different models with the maximum biting force revealed that for the studied monolithic materials excluding zirconia, a design with a rounded occlusal notch, 70° cusp angle and medium thickness (1.5 mm occlusal) is an optimum combination of design parameters in terms of tooth conservation and fracture resistance. Zirconia crowns exhibited sufficient strength for a more conservative design with less thickness (1.05 mm occlusal) and sharper cusp angle (60°).     

Soft tissue-based registration of intraoral scan with cone beam computed tomography scan

The aim of this study was to evaluate a novel soft tissue-based method to register an intraoral scan (IOS) with a cone beam computed tomography (CBCT) scan. IOS and CBCT data were obtained from eight dentate patients (mean age 21 ± 2 years; three male, five female) and 14 fully edentulous patients (mean age 56 ± 9 years; eight male, six female). An algorithm was developed to create a soft tissue model of the CBCT scan, which allowed a soft tissue-based registration to be performed with the IOS. First, validation was performed on dentate jaws with registration of the palatal mucosal surface and accuracy evaluation at the level of the teeth. Second, fully edentulous jaws were registered using both the palatal and alveolar crest mucosal surfaces. Distance maps were created to measure the method accuracy. The mean registration error was 0.49 ± 0.26 mm for the dentate jaws. Registration of the fully edentulous jaws had a mean error of 0.16 ± 0.08 mm at the palate and 0.16 ± 0.05 mm at the alveolar crest. In conclusion, the high accuracy of this registration method may allow the digital workflow to be optimized when no teeth are available to perform a regular registration procedure.     

Skeletal,dental and facial aesthetic changes following anterior maxillary segmental distraction by tooth-borne device in patients with cleft lip and palate

Maxillary skeletal deficiency secondary to cleft lip and palate (CLP) remains a significant challenge. The aim of this study was to present the comprehensive skeletal, dental and facial aesthetic outcomes of anterior maxillary segmental distraction osteogenesis (AMSDO) for treatment of maxillary hypoplasia in patients with CLP. Twelve patients with maxillary hypoplasia treated with AMSDO by a customized tooth-borne distractor were included. Three-dimensional changes of anterior maxillary segment, upper incisor and pharyngeal space were measured by three-dimensional reconstruction derived from cone beam computed tomography (CBCT) data. Length and width of dental arch during distraction were determined in dental casts. Nasolabial angle, soft-tissue convexity and patient’s subjective satisfaction were assessed to evaluate facial aesthetic improvements. Nasopharyngoscopic evaluation and speech assessment were also performed before and after distraction. All patients successfully received AMSDO without serious complications. Following AMSDO, the anterior maxillary segments moved forward 5.56 ± 0.28 mm and slightly upward 1.15 ± 0.13 mm. AMSDO significantly lengthened maxillary dental arch, generated new bone to relieve dental crowding and improved patients’ facial aesthetic without worsening velopharyngeal closure and speech quality. AMSDO by tooth-borne distractor is an effective surgical alternative for the advancement in patients with cleft maxillary hypoplasia.     

Making three-dimensional Monson's sphere using virtual dental models

ObjectivesThe Monson's sphere and curve of Wilson can be used as reference for prosthetic reconstructions or orthodontic treatments. This study aimed to generate and measure the three-dimensional (3-D) Monson's sphere and curve of Wilson using virtual dental models and custom software.MethodsMandibular dental casts from 79 young adults of Korean descent were scanned and rendered as virtual dental models using a 3-D digitizing scanner. 26 landmarks were digitized on the virtual dental models using a custom made software program. The Monson's sphere was estimated by fitting a sphere to the cusp tips using a least-squares method. Two curves of Wilson were generated by finding the intersecting circle between the Monson's sphere and two vertical planes orthogonal to a virtual occlusal plane. Non-parametric Mann–Whitney and Kruskal–Wallis tests were performed to test for difference between sex and in cusp number within tooth position.ResultsThe mean radius of Monson's sphere was 110.89 ± 25.75 mm. There were significant differences between males and females in all measurements taken (p < 0.01), within 16.87–17.27 mm. Furthermore, morphological variation derived from variability in cusp number in the second premolar and second molar were not found to influence occlusal curvature (p > 0.05).ConclusionsThis study describes a best-fit algorithm for generating 3-D Monson's sphere using occlusal curves quantified from virtual dental models. The radius of Monson's sphere in Korean subjects was greater than the original four-inch value suggested by Monson.Clinical significanceThe Monson's sphere and curve of Wilson can be used as a reference for prosthetic reconstruction and orthodontic treatment. The data found in this study may be applied to improve dental treatment results.     

Three-body wear of 3D printed temporary materials

ObjectiveThe aim of this study was to investigate the three-body wear of different additively manufactured temporary materials, one temporary PMMA material for CAD/CAM milling and one resin-based composite for direct restorations as a control group by using an ACTA machine.MethodsSpecimens (n = 8) of the 3D printing materials 3Delta temp, NextDent C&B, Freeprint temp were additively manufactured by DLP 3D printer. Postprocessing was carried out according to the manufacturer's specifications. Telio CAD were cut out of blocks, Tetric EvoCeram was applied directly and light cured. Three-body wear was simulated with an ACTA machine. Data were statistically analysed (ANOVA, post hoc test: Tukey, p < 0.05). The worn surfaces of the specimens were examined with a FE-SEM.ResultsThe average mean wear was 50 ± 15 μm for Tetric EvoCeram < 62 ± 4 μm for 3Delta temp < 236 ± 31 μm for Telio CAD < 255 ± 13 μm for NextDent C&B < 257 ± 24 μm for Freeprint temp. After 200,000 cycles, the wear and wear rates for Tetric EvoCeram and 3Delta temp were significantly lower than those for the other materials. SEM revealed that 3Delta temp has a higher filler proportion than the other 3D printing materials but less than Tetric EvoCeram.SignificanceThe filler content influences the wear behaviour of additively manufactured materials as well as dental restorative composite materials. While most 3D printing materials have a low inorganic filler load, which qualifies the materials for temporary use only, one 3D printing material has an optimized composition that would qualify the material for longer clinical service time if wear is considered as the outcome variable.