Comparing Zirconium Crown Marginal Adaptation in Preparations with Two Different Occlusal Reductions.

This study aimed to assess and contrast the effects on the vertical marginal fit of full contour CAD/CAM-generated monolithic zirconia crowns at pre- and post-cementation levels with various occlusal reduction schemes (planar and flat) and cements. Forty sound human maxillary first premolars were sampled for this study. The samples were divided into two main groups with twenty samples in each group according to the occlusal reduction scheme as follows: Group A included a chamfer finishing line design with a planar occlusal reduction scheme and Group B included a chamfer finishing line design with a flat occlusal reduction scheme. Each group was sampled into two subgroups (n = 10) based on the type of cement as follows: resin-modified glass ionomer cement (Fuji Plus) for subgroups A1 and B1, and a universal adhesive system (Duo Estecem II) for subgroups A2 and B2. Marginal gaps were tested in four indentations using a Dino light stereomicroscope (230×). Paired T-tests and Student's t-tests were used to analyze the data. Before cementation, subgroup A1 scored the lowest mean of vertical marginal gap values, while subgroup B2 scored the highest mean; following cementation, subgroup A1 scored the lowest mean of vertical marginal gap values, and subgroup B2 scored the highest mean of vertical marginal gap values. A chamfer finishing line design with a planar occlusal reduction scheme could be a preferable occlusal reduction scheme.

Distribution patterns of occlusal contact areas on natural posterior teeth - Evaluations of a cross-sectional population-based study with the Greifswald Digital Analyzing System (GEDAS).

AIM: The aim of our investigations is to optimize the anatomical basis for the design of a sufficient occlusal relationship, especially in view of the innovative technologies by analyzing the occlusal contact point patterns at cusp structures according to A-, B-, C- localization tooth by tooth on the individual occlusal surfaces in the posterior region in static habitual occlusal position. MATERIALS AND METHODS: In 3300 subjects of the population-based Study of Health in Pomerania (SHIP 1) the interocclusal registration in habitual intercuspation using silicone registration was used and analyzed by using the special evaluation software Greifswald Digital Analyzing System (GEDAS II). Chi square test was used to investigate whether the distribution of contact areas differed in the group of premolars or molars - each considered separately for maxilla and mandible - on the basis of the probability of error p < 0.05. RESULTS: In 709 subjects (446 male with a mean age of 48.9 ± 13.04 years; 283 female with a mean age of 52.4 ± 14.23 years) the antagonistic situation was specifically considered on natural posterior teeth without conservative or restorative-prosthetic interventions, i.e. without caries, fillings, crowns or other restorations. On the basis of these subjects, the silicone registrations were analyzed using GEDAS II. For the first and second upper molars, the ABC contact distribution was the most frequent: 20.4 % for the first and 15.3 % for the second molar. The second most frequent contact area for maxillary molars was area 0. The upper molars had contact areas only at the maxillary palatal cusp (B-/C-contacts). This contact relationship was most frequent in the maxillary premolar (18.1-18.6 %). In mandibular premolars, with the buccal cusps areas A and B were frequently involved (15.4-16.7 %). Mandibular molars showed a frequent contact pattern involving all A-, B-, C- and 0- contact areas (13.3-24.2 %). To capture the possible influence of the antagonistic dentition situation, the antagonistic situation was specifically considered and except for the mandibular premolars (p < 0.05) the contact distribution did not differ for molars and maxillary premolars regarding the dental status of the antagonistic teeth. Natural posterior teeth without occlusal contacts were observed from 20.0 % in the second lower molars to 9.7 % in the first upper molars. CONCLUSION: Our results suggest a clinically relevant due to the fact, that this study is the first population-based epidemiological study to analyze the occlusal contact point patterns at cusp structures according to A-, B-, C- localization tooth by tooth on the individual occlusal surfaces in the posterior region in static habitual occlusal position in order to optimize the anatomical basis for the design of a sufficient occlusal relationship.

Number and localization of occlusal contact areas on natural posterior teeth without dental findings - evaluations of the regional baseline study (SHIP-1) with the Greifswald Digital Analyzing System (GEDAS).

Sufficient occlusion is a basic prerequisite for the functional efficiency of the occlusal surfaces. Exactly where and in what number the occlusal contacts in the posterior region should be present for this purpose is controversial. The present study investigated the number and location of occlusal contacts on posterior teeth without dental findings, ie, without caries or restorative restorations such as fillings, crowns, etc. Such natural posterior teeth were present in 709 subjects (males (m) = 446: 48.9 ± 13.04 years, females (f) = 283: 52.4 ± 14.23 years) of a subject collective of 1223 subjects (m = 648, f = 575) of the regional baseline study 'Study of Health in Pomerania 1' (SHIP-1). Silicone bite registrations in habitual intercuspation (IP) were evaluated, whereby the test persons were asked to fix the bite block with biting force without biting firmly. The registrations were scanned with a document scanner in incident and transmitted light; a calibration strip was used to determine the transparency threshold of a layer thickness of 20 µm, below and equal to which the transparent zone was considered as a contact or contact area. The Greifswald Digital Analyzing System 2 (GEDAS 2) software was used to determine the number and location of occlusal contact areas tooth by tooth. To define the localization of the contacts, a cross with two concentric circles symmetric to the longitudinal fissure was superimposed on the occlusal surface; this resulted in four inner and four outer quadrants. Thus, the number of pixels in occlusal contact areas per inner and outer quadrant could be determined. The image resolution was 300 dpi. On average (median), the premolars had two occlusal contacts each, the posterior teeth had four to five, and tooth 46 had six contacts. The right and left teeth did not differ in the frequency of occlusal contacts in the Mann-Whitney U test for independent samples. In the maxillary premolars, frequent contact areas were primarily located mesially on the inner and outer slopes of the palatal cusp. In the maxillary molars, the palatal slope of the distopalatal cusp and the inner slopes of the mesiopalatal and distopalatal cusps were frequently affected. On the mandibular premolars, the inner slopes of the buccal cusps and the buccal slope of the distobuccal cusp were particularly frequently addressed; in teeth 35 and 45, the buccal slope of the mesiobuccal cusp was also somewhat more frequently addressed. Teeth 36 and 46 frequently had contact areas on the buccal slope of the distobuccal cusp as well as on the inner slopes of the distal cusps (distobuccal and distolingual), whereas teeth 37 and 47 tended to behave similarly. Epidemiologically, the focus of the frequent contact areas on the respective supporting cusps of the maxillary and mandibular posterior teeth and a distribution of contacts stabilizing the tooth in its position in the dental arch through the interlocking were confirmed. It makes sense to take this into account when designing occlusal surfaces in the posterior region.

Validation of digital analysis of occlusion in primary and mixed dentition using GEDAS.

AIM: The present prospective clinical study aimed to validate the Greifswald Digital Analyzing System (GEDAS) as a method for digital assessment of the occlusion in primary and mixed dentition. MATERIALS AND METHODS: The reproducibility of GEDAS in primary and mixed dentition was assessed using the intraclass correlation coefficient (ICC). In addition, the acceptability of the method to the dentist, the child, and the parent/caregiver was assessed using a modified visual analog scale of faces, the Frankl behavior scale, and the 10-point Likert scale. In total, 20 participants aged between 3 and 9 years (mean age: 6; standard deviation: ± 1.74) with primary (n = 10) and mixed (n = 10) dentition were recruited. RESULTS: The ICC for the number of contact points in all teeth was 0.94 and for the area of contact points was 0.97, indicating good to excellent reproducibility. The average total number of contacts per bite registration per arch in the primary and mixed dentition was 36.5 (17 to 66) and 37.9 (9 to 74), respectively. The average of the total area of interocclusal contact area in the primary and mixed dentition was 25.55 mm2 (5.39 to 70.20) and 29.59 mm2 (2.80 to 78.53), respectively. During the procedure, the majority of dentists reported the child's behavior to be positive (85%) and found the procedure easy to perform (80%), short (6.0 min), and tolerable (80%). CONCLUSION: GEDAS is an occlusal analysis tool with good acceptability and reproducibility in children and could be considered for the planning and assessment of restorative and orthodontic treatment in the intermediate stages.

Gray Matter Brain Alterations in Temporomandibular Disorder Tested in a Population Cohort and Three Clinical Samples.

Temporomandibular pain (TMD) is a frequent symptom comprising pain around the mandibular jaw with a high dependence on stressors. Chronic pain has been associated with changes of the brains gray matter volume (GMV), but previous studies on GMV alterations associated with TMD have yielded contradictory results. This might be caused by divergent samples and study methods. We here tested GMV alterations using voxel based morphometry in three clinical samples (summing up to 47 TMD patients) and a population sample with 57 participants who indicated facial pain for the last 6 months. The GMV of pain patients was compared against age-matched and gender-matched participants without chronic pain (60 for the clinical sample comparison and 381 for the cohort sample comparison) who underwent the same assessments as the patient group (MRI measurements and data evaluation using CAT12). In a region of interest analysis, only the clinical samples showed an effect of decreased GMV in the anterior medial cingulate cortex reaching into the medial prefrontal cortex, known to be especially vulnerable for chronic pain gray matter volume reduction. The analysis of the population-based sample did not reveal relevant GMV differences. Overall, an important question remains as to whether most inconsistent results from voxel based morphometry-studies in chronic pain are related to chance results facilitated by small sample size and selection of patient samples. PERSPECTIVE: Using voxel based morphometry 2 samples with chronic temperomandibular pain were compared to controls investigating the brains GMV. Only the clinical sample showed a decrease in anterior cingulate GMV. Contradicting results on GMV loss in temperomandibular pain might be based on small samples in prior studies.

The rotation vs translation behavior during habitual opening and closing movements of the mandible and the relationship to movement paths of condylar points.

When recording condylar movement paths with the aid of electronic measuring systems, it is often found that, especially in jaw opening and closing movements, excursive and incursive paths of movement are not congruent but run separately, independently of one another to a greater or lesser degree. The objective of the study was to investigate this phenomenon in the context of rotation vs translation behavior, also taking into consideration additional side-specific condylar movement patterns. For this purpose, the electronic movement records of habitual jaw opening of 259 participants of the associated project of the population-representative basic study SHIP 0 were evaluated. The condylar movement path (condylar tracing, ConTrac) at the arbitrary axis point, the excursion vs incursion behavior in the condylar tracing grid (ExInGrid), and the rotation vs translation behavior (RotTrans) were classified, and the translational condylar path and the maximum angle of rotation were determined metrically. Relationships between the parameters ConTrac, ExInGrid, and RotTrans were statistically analyzed using cross tabulations and Spearman's correlation coefficient. Only about 18% of ConTrac showed congruence of excursive and incursive movement path components, while 39% demonstrated noncongruent paths, and 43% showed further conspicuous features in the movement path. For the parameter ExInGrid, recognizable to highly pronounced loop formation patterns to a degree of 89% were observed in the condylar tracing grid. An average of 12.5 mm (min 2.1 mm, max 21.7 mm) was determined for the purely translational component of the condylar movement path, and 32.1 degrees (min 12 degrees, max 45 degrees) for the maximum angle of rotation. Concerning the rotation vs translation behavior, the linear basic pattern occurred at around 9%; the sigmoidal pattern at 28%; and the hysteretic, loopy or irregular pattern at 63%. The parameters RotTrans and ExInGrid showed a strong correlation, whereas the strength of the correlation for ConTrac and ExInGrid or RotTrans and ConTrac was evaluated as weak or very weak. The rotation vs translation behavior influences condylar movement paths in the positional relationship of excursive and incursive components. The visualization of several condylar movement paths in the form of a condylar tracing grid helps to capture complex rotational and translational motion components of the real condyles more effectively than the assessment of a single condylar movement path.

Computerized occlusal analysis - innovative approaches for a practice-oriented procedure.

A hands-on method for instrument-based occlusal analysis with digital technology is presented using a patient case example. The method is based on new software for digital occlusal analysis that includes a new measuring system for recording mandibular function (Jaw Motion Analyser Optic System/oJMA). With the new system, occlusal contact patterns in the real movement function of the mandible are captured and analyzed digitally with regard to occlusal interferences or a suitable therapeutic position of the mandible. For this purpose, scans of both jaws are brought together with the movement recordings by means of a special coupling tray and then visualized together as one complete image. Since the movement paths of the temporomandibular joints (TMJs) are also captured, the new system makes it possible to define a suitable therapeutic position specifically aimed at relieving the TMJs, and a therapeutic change in the jaw relation can be adjusted, for instance, by using an occlusal splint. Dedicated software modules provide a layer-by-layer analysis of the intercuspation relationship and the generation of 'envelopes' for occlusal gliding movements. This system is used to gain a deeper and more comprehensive understanding of the relationship between the structure and function of the occlusion. Interfaces to CAD software have also been established.

Effects of centric mandibular splint therapy on orofacial pain and cerebral activation patterns.

OBJECTIVES: To investigate the effects on pain, movement kinematics, and cerebral representation by a 3-month mandibular splint therapy. MATERIAL AND METHODS: Thirteen patients with temporo-mandibular joint disease (TMD) and moderate pain intensity were investigated before (PRE), within (after 2 weeks, POST1) and after a period of 12 weeks (POST2) using functional magnetic resonance imaging (fMRI) of representation of occlusal movements on natural teeth and on an individually fitted mandibular splint. In addition, kinematic investigations of jaw movements, muscle electromyography and pain ratings using a pain diary (VAS-scale 0-100) were measured. RESULTS: Although the patient's pain ratings decreased about 60%, kinematic and electromyographic characteristics over therapy were not significantly altered. Over therapy, we observed a decrease of fMRI activation magnitude in the primary somatosensory cortex (S1) and secondary somatosensory cortex (S2) and insular cortex during occlusion. Left hemispheric anterior insula and the cerebellar fMRI activation decrease were associated with decrease in pain over time. CONCLUSIONS: Within the limitations of this pilot study, a reduction in both discriminative (primary and secondary somatosensory cortex) and affective (anterior insula) areas for pain processing suggest that altered pain anticipation is critical for the therapeutic effects of mandibular splint therapy after TMD. CLINICAL RELEVANCE: A 3-month mandibular splint therapy moderately decreases pain and anticipatory anterior insular activation.

Standard and limit values for the symmetry of articulation parameters in the temporomandibular joint area - evaluations of the associated project of the SHIP study.

The articulation parameters, especially the horizontal condylar inclination angle (HCI), the Bennett angle (BA), and the immediate side shift (ISS) were determined in 259 subjects (100 males; 159 females) of the associated project with reference to the population-representative baseline study (Study of Health in Pomerania, SHIP 0). The evaluations were based on a clinical functional status and electronic motion recording with the ultrasonic measuring system Jaw Motion Analyser (JMA, Zebris, Isny, Germany). The reference plane, to which all measured values were represented and the HCI calculated, was the hinge axis infraorbital plane (HA-IOP). The HCI was determined after an excursive movement with a length of 4 mm to the HA-IOP in the sagittal view and the BA after a mediotrusive excursion movement of 6 mm in the horizontal view to the midsagittal plane. For the standard and limit values, the average value in addition to the standard deviation and the 10th and 90th percentile value (10th percentile value, 90th percentile value) were determined: HCI right 52.1 ± 10.14 degrees (39.4 degrees, 64.0 degrees), HCI left 53.1 ± 9.67 degrees (42.3 degrees, 67.0 degrees), BA right 15.2 ± 7.53 degrees (6.7 degrees, 25.0 degrees), BA left 14.2 ± 7.84 degrees (5.4 degrees, 24.1 degrees). The HCI was approximately 2 to 3 degrees larger in females (males: right 50.5 ± 9.47 degrees, left 51.9 ± 8.99 degrees; females: right 53.1 ± 10.42 degrees, left 53.8 ± 10.03 degrees). Likewise, the BA in the age group ≥ 40 years (males: right 14.4 ± 6.62 degrees, left 13.1 ± 7.14 degrees; females: right 17.0 ± 9.02 degrees, left 16.9 ± 8.72 degrees). The latter proved to be statistically significant in the t test for independent samples, assuming variance equivalence on the right, with P = 0.009, and with rejection of the variant equivalence on the left, with P = 0.002. The right and left HCI and BA joint values showed highly significant linear dependence at P < 0.001, but rather low, however, for the HCI with r2 = 0.175 for the HCI and r2 = 0.228 for the BA. In 46% of cases, the right and left HCI values differed up to 5 degrees only; a further 20.9% were in an interval difference of between 5 and 10 degrees. The following results were shown for the differences in the BA: 56.4% of the cases were between 0 and 5 degrees, and 26.2% were in the interval ranges of 5 to 10 degrees. ISS occurred in 18.1% of cases on the right side of the joint, and in 27.8% of cases on the left side. On both sides of the joint it was significantly more frequent in the age group ≥ 40 years with assumed variance equality than in the age group < 40 years (P = 0.002 right, P = 0.003 left). The groups relating to the Helkimo index (HI) did not differ significantly in all function-specific parameters. If it is assumed that there is no significant influence on the occlusion if the HCI values differ by 7 to 8 degrees from the average value, only approximately one third of all cases (35.1%) were characterized by a purely average value setting in the articulator. In 41.7% of cases, one joint value was situated outside the average value range; in 23.2% of the cases both values were outside the average value range. Without a measurement of the condylar path inclination, however, it is impossible to decide to what extent the HCI deviates from the average value, and which joint side is larger or smaller than the other and to what extent. These results suggest that in extensive and complex cases, the articulator should be adjusted according to individual, function-specific joint values.

Digital workflow for TMD diagnostics and bite alteration: description of a case treated using Sicat Function.

A patient with arthrogenic temporomandibular dysfunction (TMD) complaints presented. In addition to a clinical diagnosis, an instrumental one with Sicat Function (Sicat) was performed. For this purpose, movements of the mandibular function were recorded with an ultrasonic-based measuring system (JMT+) and correlated with cone beam computed tomography (CBCT) image data. A reference tray (FusionBite) ensured spatial agreement. In addition, full-arch scans taken with the Cerec Omnicam intraoral scanner (Dentsply Sirona) were matched to the CBCT data. From the movement data, a biomechanically optimized joint position was determined, for which an occlusal splint was milled. Subsequently, the functional result achieved was retained with computer-aided design/computer-aided manufacturing (CAD/CAM) temporary restorations and tabletops and was monitored with Sicat Function until delivery of the final rehabilitation. To this end, the movements were tracked with the JMT+ after each treatment step. The reference tray was successively adapted and augmented so that the original jaw relation in the FusionBite could be maintained, which guaranteed comparability with the initial situation without the need for an additional CBCT image. Sicat Function has proven to be an excellent system supporting a digital workflow in situations where controlled bite-position changes are indicated in patients with arthrogenic TMD complaints.

Fully digital workflow for presurgical orthodontic plate in cleft lip and palate patients.

OBJECTIVE: In most cases, according to our treatment concept, a presurgical orthodontic treatment (POT) is performed on patients with cleft lip and palate (CLP). The aim of this case report is to demonstrate a completely digital workflow for the production of a palate plate. MATERIALS AND METHODS: For the assessment of the maxillary arch, a digital impression of the jaw was made on two patients with an intraoral scanner (Cerec Omnicam Ortho). After reconstruction of a virtual model from the scan data, appropriate areas of the jaw could be blocked out and a plate constructed. This was printed with a DLP three-dimensional (3D) printer (SHERA EcoPrint D30) with class IIa biocompatible material. After minor surface finishing, the plates could be incorporated in the patients' mouths. RESULTS: The scans could be performed in a short time without affecting the very young patients. All clinically relevant areas for the production and digital measurement of the models could be recorded. The plates showed an extremely good fit, and there were no differences in wear compared with a conventionally manufactured plate. CONCLUSION: For the first time, a risk-free digital impression of the edentulous jaw in CLP babies with a subsequently completely digitally constructed and 3D-printed palatal plate could be shown.

Effects of occlusal modifications on the muscular activity of the masseter and anterior temporalis muscles.

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.

Occlusion of artificial teeth in complete dentures: population-based analysis.

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.

Testing occlusal performance by using chewing simulation with virtually designed substrate.

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.

Does a face-bow lead to better occlusion in complete dentures? A randomized controlled trial: part I.

OBJECTIVES: In a double-blinded randomized controlled clinical trial, the impact of face-bow registration for remounting complete dentures (CDs) on the occlusal parameters (part I) was evaluated. MATERIALS AND METHODS: New CDs of 32 patients were duplicated and mounted after intraoral pin registration according to mean settings (group 1) and (group 2) using a face-bow (arbitrary hinge axis). The vertical dimension was reduced to the first occlusal contact point, and a bite record was fabricated in the articulator. The number of contacts and the number of teeth in contact were evaluated by a computer program (laboratory result). After randomization, half of the CDs were adjusted according to protocol of group 1 and group 2 and delivered to the patients. After 3 days (T1) and 84 days (T2), clinical static contact points and teeth in contact were counted. Contact points and teeth in contact of both groups (laboratory results) and at different moments (clinical results) were analyzed statistically with the F test and bootstrapping. RESULTS: Laboratory: No. 2 (face-bow) showed more occlusal contact points than no. 1 (mean setting), p > 0.05. The number of teeth with at least one occlusal contact was significantly higher in no. 2 (p = 0.027). Clinic: The mean number of teeth with at least one clinical contact point was significantly higher in no. 1 (no. 1 = 7.13, no. 2 = 5.31; p = 0.042). Extent of the vertical shift poorly correlated with number of laboratory occlusal contact points (R 2 = 0.017). CONCLUSIONS: Considering the complex multistep study design, a limited number of participants, and referring to one specific arbitrary face-bow, the following conclusion could be drawn: no substantial difference by the use of the arbitrary face-bow compared to a mean setting could be determined, when changing the vertical dimension in the articulator within a remounting procedure of complete dentures. CLINICAL RELEVANCE: Further research is necessary to determine the effects of different arbitrary face-bows on the fabrication and adaptation of removable dentures.

A completely CAD/CAM individual transmission device for electronic mandible movement registration.

The connection of a device for the registration of mandibular movements depends on the coupling of the teeth with a paraocclusal adapter. This is normally done by individualizing a prefabricated metal support, either directly on the patient or in the dental laboratory. The goal was to create an individual paraocclusal adapter by means of additive computer-assisted design/computer-assisted manufacturing (CAD/CAM) procedures, and to test it clinically. Starting from intraoral scans of the maxillary and mandibular teeth, an individual paraocclusal adapter was constructed by combining an adapter piece adapted to the tooth and jaw shape with a prefabricated standard part. This article describes step by step the design using the 3D CAD software, up until production by means of 3D printing. Initial clinical experience is also discussed.