International Journal of Computerized Dentistry, 01/2018

Occlusion is a central aspect of all prosthetic restorations, including complete dentures. Within the follow-up (SHIP 1) of the regional population-based "Study of Health in Pomerania" (SHIP), a number of 3300 study participants were examined concerning the occlusion of artificial teeth in purely mucosa and non-implant-borne complete dentures. These subjects were representative of the population. Therefore, occlusal bite registrations obtained in habitual intercuspation (IP) were made and were digitally evaluated with the Greifswald Digital Analyzing System (GEDAS) software based on transparent contact areas. A total of 495 subjects wore such complete dentures, of whom 438 wore maxillary dentures (217 men, 71.3 ± 9.2 years; 221 women, 68.9 ± 9.1 years), and 278 wore mandibular dentures (141 men, 70.4 ± 8.5 years; 137 women, 70.4 ± 8.5 years). The mean number of denture teeth was 13.4 ± 0.89 in the maxilla (of which 6.8 ± 2.77 were in occlusal contact), and 13.3 ± 0.91 in the mandible (of which 6.8 ± 2.97 were in occlusal contact). In general, the premolars (maxilla: 2.8 ± 1.31; mandible: 2.6 ± 1.29 teeth) had more occlusal contact than the molars (maxilla: 2.2 ± 1.24; mandible: 2.3 ± 1.23 teeth). The differences were highly significant, with P 0.01 in the Wilcoxon test for paired samples. Furthermore, there were distinctions between both sides, with the right side having more posterior teeth in contact than the left side (maxillary right: 2.6 ± 1.18; maxillary left: 2.5 ± 1.14; mandibular right: 2.5 ± 1.13; mandibular left: 2.4 ± 1.13), each significant for the maxilla at P = 0.022 (Wilcoxon test). Here, the number of denture teeth played a role. In dentures with exactly 14 denture teeth (maxillary: n = 301; mandibular: n = 179), there were significantly more molars than premolars in contact in the mandible (premolars: 2.4 ± 1.37; molars: 2.7 ± 1.27; P = 0.026), whereas in the maxilla the ratio of premolars to molars in contact was reversed (premolars: 2.8 ± 1.36; molars: 2.6 ± 1.25); however, the latter difference proved barely significant at just P = 0.099. Women tended to have slightly fewer contact-bearing teeth than men (posteriors in men: 5.1 ± 2.04; in women: 4.9 ± 2.03); the differences were not significant. Nor were there any significant differences between the groups 70 years (maxillary: n = 189; mandibular: n = 101), and ≥ 70 years (maxillary: n = 249; mandibular: n = 177). The presence of dysfunction of the masticatory system was determined using the Helkimo Index (HI). A value of HI ≥ 2 was regarded as dysfunctional. The groups with and without dysfunctions differed significantly for the number of posterior teeth on the right side of the maxilla (HI ≥ 2: 2.2 ± 1.34; HI 2: 2.6 ± 1.6; P = 0.041) in the Mann-Whitney U test. The difference in the groups according to HI was found to be slightly significant regarding the number of posteriors (HI ≥ 2: 4.5 ± 2.28; HI 2: 5.1 ± 2.00; P = 0.063) and molars (HI ≥ 2: 1.9 ± 1.34; HI 2: 2.3 ± 1.22; P = 0.092) with occlusal contacts. The differences for the mandibular premolars and for the maxillary left posterior teeth were not significant. Conclusion: With regard to masticatory system dysfunctions, it makes sense to ensure that there are molar contacts, especially in the maxilla. A tendency to "premolarize" contacts should be counteracted by appropriate measures. Keywords: occlusion, complete denture, artificial teeth, population-based analysis

The aim of this study was to analyze the effect of occlusal modifications on the muscular activity of the masseter and anterior temporalis muscles. The study included 41 healthy dentate subjects who were examined in relation to the muscle activity of the masseter and anterior temporalis muscles recorded by surface electromyography (EMG) bilaterally in two different sessions. Occlusal plastic strips (thickness: 0.4 or 0.8 mm) were placed on different mandibular teeth to simulate different bite constellations (unilateral, bilateral transversal, and bilateral diagonal). Controlled by visual feedback, the subjects performed submaximum occlusion at 10% and 35% of maximum voluntary contraction (MVC). The activity ratios of the muscles were analyzed by two-way repeated measurement analysis of variance (ANOVA), and the reliability of muscle activity data was determined by intraclass correlation coefficient (ICC) analysis. The activity ratios of the masseter muscles were not significantly different under various biting conditions. In contrast, the anterior temporalis muscles showed significant differences (P 0.001) between unilateral configurations and the other biting conditions (bilateral transversal or diagonal), in particular during biting at 10% MVC. In general, ICC values revealed low to moderate reliability of the measurements of muscle activity. Under controlled submaximum occlusal loading, the activity behavior of the masseter muscles remained stable, whereas the anterior temporalis muscles reacted differently to distinct occlusal biting configurations. The results support the assumption that the anterior temporalis muscles might operate as fine-tuning muscles when asymmetric bite force distributions occur, for instance during chewing, caused by food fragments between the teeth. Keywords: activity ratio, clenching, electromyography (EMG), masticatory muscles, occlusal interference, occlusal modification, visual feedback

Physically accurate deformable models based on the finite element method (FEM) are being used for a wide range of applications, from entertainment to medicine. This article describes how we applied this method in the CAD/CAM area that is concerned with reconstructing 3D models of teeth. We simulated the process of mastication by employing a deformable model that represented the substrate, and a rigid model that represented the teeth. We extended a recent approach for substrate deformation by also modelling the fracture of the substrate by the mastication process. Although including fracturing into the process allowed us to assess a mastication result, it posed new technical challenges such as defining the start of fracturing, propagating fracture through the substrate, detecting collisions between substrate pieces after fracturing, and resolving such collisions. We developed an approach that solved these challenges. The resulting simulation allowed us to compare the functionality of different occlusal designs in a mastication process. We are convinced that these simulations are an interesting tool that could be used to improve occlusal performance, especially in complete dentures, which are nowadays being more and more digitally designed. Keywords: occlusion, masticatory performance, CAD/CAM, complete dentures, chewing simulation, substrate

Purpose: The objectives of this in vitro study were to evaluate the flexural strength (FS), surface roughness (Ra), and hydrophobicity of polymethylmethacrylate (PMMA)-based computer-aided design/computer-aided manufacturing (CAD/CAM) polymers and to compare the properties of different CAD/CAM PMMA-based polymers with conventional heat-polymerized PMMA following thermal cycling. Materials and methods: Twenty rectangular-shaped specimens (64 × 10 × 3.3 mm) were fabricated from three CAD/CAM PMMA-based polymers (M-PM Disc [M], AvaDent Puck Disc [A], and Pink CAD/CAM Disc Polident [P], and one conventional heat-polymerized PMMA (Promolux [C]), according to ISO 20795-1:2013 standards. The specimens were divided into two subgroups (n = 10), a control and a thermocycled group. The specimens in the thermocycled group were subjected to 5000 thermal cycling procedures (5 to 55°C; 30 s dwell times). The Ra value was measured using a profilometer. Contact angle (CA) was assessed using the sessile drop method to evaluate surface hydrophobicity. In addition, the FS of the specimens was tested in a universal testing machine at a crosshead speed of 1.0 mm/min. Surface texture of the materials was assessed using scanning electron microscope (SEM). The data were analyzed using two-way analysis of variance (ANOVA), followed by Tukey's HSD post-hoc test (α 0.05). Results: CAD/CAM PMMA-based polymers showed significantly higher FS than conventional heat-polymerized PMMA for each group (P 0.001). CAD/CAM PMMA-based polymer [P] showed the highest FS, whereas conventional PMMA [C] showed the lowest FS before and after thermal cycling (P 0.001). There were no significant differences among the Ra values of the tested denture base polymers in the control group (P > 0.05). In the thermocycled group, the lowest Ra value was observed for CAD/CAM PMMA-based polymer [M] (P 0.001), whereas CAD/CAM PMMA-based polymers [A] and [P], and conventional PMMA [C] had similar Ra values (P > 0.05). Conventional PMMA [C] had a significantly lower CA and consequently lower hydrophobicity compared to the CAD/CAM polymers in the control group (P 0.001). In the thermocycled group, CAD/CAM PMMA-based polymer [A] and conventional PMMA [C] had significantly higher CA, and consequently higher hydrophobicity when compared to CAD/CAM polymers [M] and [P] (P 0.001). However, no significant differences were found among the other materials (P > 0.05). Conclusions: The FS and hydrophobicity of the CAD/CAM PMMA-based polymers were higher than the conventional heat-polymerized PMMA, whereas the CAD/CAM PMMA-based polymers had similar Ra values to the conventional PMMA. Thermocycling had a significant effect on FS and hydrophobicity except for the Ra of denture base materials. Keywords: CAD/CAM, digital complete dentures, flexural strength (FS), hydrophobicity, PMMA, surface roughness (Ra)

The rehabilitation of the edentulous patient with complete dentures is still an essential aspect of dental prosthetics. Modern digital manufacturing technologies have made it possible to produce even complete dentures digitally. This has several advantages, especially regarding the properties of the denture material. In addition, the use of digital technology facilitates new treatment concepts and procedures that reduce the number of appointments needed at the dental office. Keywords: CAD/CAM, high-performance polymers, additive manufacturing, virtual wax try-in, innovative treatment concepts, complete denture, digital dentistry

When determined by conventional jaw relation recording methods, the real position of the condyle remains largely unclear because the geometric relationship between the reference point and the position of the condyle is unknown. Sicat Function combines cone beam computed tomography (CBCT) data with digital jaw motion tracking (JMT) data and digital intraoral surface data. It is thus capable of measuring and visualizing patient-specific jaw movements. The corresponding patient-specific treatment position can be defined and integrated in various therapeutic appliances, eg, repositioning splints designed to increase the vertical dimension of occlusion (VDO). Keywords: CAD/CAM, cone beam computed tomography (CBCT), jaw motion tracking (JMT), jaw relation recording, mandibular movement