Accuracy and Precision of Occlusal Contacts of Stereolithographic Casts Mounted by Digital Interocclusal Registrations

Statement of problem Little peer-reviewed information is available regarding the accuracy and precision of the occlusal contact reproduction of digitally mounted stereolithographic casts. Purpose The purpose of this in vitro study was to evaluate the accuracy and precision of occlusal contacts among stereolithographic casts mounted by digital occlusal registrations. Material and methods Four complete anatomic dentoforms were arbitrarily mounted on a semi-adjustable articulator in maximal intercuspal position and served as the 4 different simulated patients (SP). A total of 60 digital impressions and digital interocclusal registrations were made with a digital intraoral scanner to fabricate 15 sets of mounted stereolithographic (SLA) definitive casts for each dentoform. After receiving a total of 60 SLA casts, polyvinyl siloxane (PVS) interocclusal records were made for each set. The occlusal contacts for each set of SLA casts were measured by recording the amount of light transmitted through the interocclusal records. To evaluate the accuracy between the SP and their respective SLA casts, the areas of actual contact (AC) and near contact (NC) were calculated. For precision analysis, the coefficient of variation (CoV) was used. The data was analyzed with t tests for accuracy and the McKay and Vangel test for precision (α=.05). Results The accuracy analysis showed a statistically significant difference between the SP and the SLA cast of each dentoform (PPP Conclusions For the accuracy evaluation, statistically significant differences were found between the occlusal contacts of all digitally mounted SLA casts groups, with an increase in AC values and a decrease in NC values. For the precision assessment, the CoV values of the AC and NC showed the digitally articulated cast’s inability to reproduce the uniform occlusal contacts

Preliminary Study on the Analysis of Infantile Occlusion : 1st Report : Application of T-Scan

In the present study, the relationship of items for T-Scan measurement with masticatory ability value, maximum occlusal force and masticatory area was analyzed in adults, as a preliminary measure to examining the applicability of the T-Scan system to infants. The following conclusions were obtained; 1. Correlation coefficients between occlusal contact area and masticatory ability and between maximum occlusal force and masticatory ability were r = 0.755 and r = 0.792, respectively, both being significant to 5%. 2. Correlation coefficients between occlusal contact point number and maximum occlusal. force and between occlusal contact point number and occlusal contact area were r = 0.835 and r = 0.813, respectively, both being significant to 5%. 3. In terms of the factor (T-Scan) in occlusal contact time, correlation coefficients between total front-back (TFB) and right front-back (RFB) and between primary front -back (PFB) and RFB were r = 0.844 and r = 0.862, respectively, both being significant to 5%. The correlation coefficient between TRB and left front-back (LFB) was r = 0. 899, significant to 1%. 4. In terms of the factor (T-Scan) in occlusal contact force, correlation coefficient between right force (RF) and left force (LF) was r = 0.907, significant to 1%

The combined effects of salivas and occlusal indicators on occlusal contact forces

Background Some occlusal detection products are designed for use on dry teeth, but this is not always achieved. Others are suited for dry and wet applications. Objective The objective of this study is to assess the combined effects, on occlusal contact forces, of two previously studied affecting variables—occlusal detection products and saliva. Methods We used a full‐arch dentiform with three occlusal detection products (an articulating film, an articulation paper and T‐Scan) in combination with human (HS) and an artificial saliva. The maxillary arch assembly, weighing ~54 N (the maximum bite force), was lowered onto (occlusion) and lifted off (disclusion) of the mandibular arch through 10 cycles by a mechanical testing machine. The forces and moments acting on the mandibular arch were continuously recorded by a load cell that supported it. Results The maximum values of Flateral (the in‐occlusal plane component of the occlusal contact force) were analysed by occlusion/disclusion separately using one‐way ANOVA, with factor for group type to identify the significant effect of salivas on products, effect of products, effect of salivas with products, effect of human saliva. A difference in occlusion and/or in disclusion was considered different. Statistical differences (P < 0.0001) in Flateral were found in: dry product vs product + HS, dry product vs product + artificial saliva (with articulating film and T‐Scan) and HS vs product + HS (with articulation paper and T‐Scan). Conclusion All products were affected by the salivas, except articulation paper by artificial saliva

Clinical Effectiveness of Using Aesthetic Fixed Prosthetic Appliances with Combined Occlusal Surface

The objective of the research was to evaluate the clinical effectiveness of using aesthetic fixed prosthetic appliances with combined occlusal surface.Materials and methods. The study included 30 patients who were divided into 2 groups: Group I included 20 patients with combined occlusal surface of the crowns; Group II included 22 patients with ceramic occlusal surface of the crowns. The patients were observed 3, 6 and 12 months after prosthetic repair.Results. 6 months after prosthetic repair, the occlusal contact surface area in Group I increased by 0.79%, while in Group II, it increased by 1.4%.12 months after prosthetic repair, the occlusal contact surface area in Group I and Group II increased by 2.37% and 5%, respectively.The aforementioned data indicated that the occlusal contact surface area increased as the period of ceramic fixed prosthetic appliance wearing increased.When combining the occlusal surface in dental prostheses, the occlusal contact surface area increased approximately 2 times slower. The study demonstrated convincingly that crowns burnt on a zirconium dioxide frame were a better choice as compared to cast framework made of nickel-cobalt-chrome alloy. In case of cast frameworks, the indicators of crown margin discrepancy were worse than in case of milled frameworks - 15% versus 5%, respectively. In addition, one cast framework crown (5%) in Group II was remodeled and one crown (5%) was recemented.Conclusions. Aesthetic fixed prosthetic appliances with combined occlusal surface demonstrated high functional and aesthetic characteristics. The use of the USHPS system showed a decisive advantage of milled frameworks and combined occlusal surface over traditional cast ceramic frameworks.The combination of high mechanical, strength and tribological properties of zirconium dioxide and high biological as well as aesthetic properties of ceramic materials helped reveal high clinical characteristics of aesthetic appliances with combined occlusal surface.

A Hemispherical Contact Model for Simplifying 3D Occlusal Surfaces

Statement of problem Currently, dental articulators can recreate mandibular movements and occlusal contacts. However, whether virtual articulators can also provide information about occluding dental surfaces, functional movements, and the mandibular condyles is unclear. Purpose The purpose of this in vitro study was to evaluate the occluding surfaces on dental casts obtained from a patient and approximate them to a hemispherical contact model. Both models were tested by digitizing the Dentatus ARL dental articulator. Material and methods A combination of photogrammetry and structure from motion methods were used to scan a Dentatus ARL articulator and representative dental casts. Using computer-aided engineering and finite element analysis, contact points and action vectors to the forces on occluding surfaces and condyles were obtained for cast and hemispherical models. This experiment was performed using centric occlusion and 3 different condylar inclinations. The Kruskal-Wallis 1-way analysis of variance on ranks test was used to allow all pairwise comparisons between condylar inclination and mechanical action vector values in each location (α=.05). Results Action vectors from the cast model and each location of the hemispherical model were calculated to show the mechanical consequences and the similarity among models. Overall, no significant differences were observed for action vectors (A20 versus A40 versus A60) at each location (dental cast/hemisphere, right condylar, and left condylar) in the analysis of dental casts and the hemisphere model (.382≤P≤.999). Conclusions This study provided graphical information that may assist the dental professional in determining which occlusal contacts should be modified to attain condylar and balanced centric occlusion

Studies on the Analysis of Infantile Occlusion : 2nd Report: Application of T-scan

In the present study, relationships among measuring items of T-scan system, masticatory force value and masticatory surface were analyzed (according to the Black Silicon Method). The following results were obtained: 1. Correlation between occlusal contact surface and masticatory force value: The above corrlation showed r=0.755, which was significant at 5%. 2. Correlation between maximum occlusal force and masticatory force value: The above correlation showed r=0.792, which was significant at 5%. 3. Correlation between occlusal contact point number and maximum occlusal force: The above correlation form T-scan showed r=0.835, which was significant at 5%

Clinical Aspects of Combination of Ceramic and Acrylic Occlusal Surfaces

The objective of the research was to develop and substantiate the methods of constructing the occlusal surfaces when manufacturing aesthetic fixed restorations through the combination of different materials.Materials and methods. The study included 65 patients with ceramic and acrylic occlusal surfaces of aesthetic fixed dental prostheses. Group I included 21 patients with a combination of ceramic and acrylic occlusal surfaces. Group II included 22 patients with a combination of ceramic occlusal surfaces. Group III included 22 patients with a combination of acrylic occlusal surfaces. The patients were observed 3, 6 and 12 months after prosthetic repair.Results. The greatest increase in the occlusal contact surface area of fixed restorations was observed in Group I, that is, when combining dental prostheses with ceramic and acrylic occlusal surfaces. Considering uneven abrasion of the occlusal surfaces, we do not recommend to combine different materials when veneering the occlusal surface of the antagonistic teeth.Conclusions. This study demonstrated the important role of the correct combination of materials when veneering the occlusal surfaces. Physical and chemical properties of materials, namely the abrasion resistance play a significant role in the long-term denture functioning.The smallest increase in the occlusal contact surface area was observed in Group II when combining ceramic occlusal surfaces. It was due to a good abrasion resistance of ceramics as compared to acrylic resin as well as the presence of the glazed layer which prevents the premature abrasion of the occlusal surfaces of the antagonistic teeth due to lower surface roughness.The combination of acrylic resin and ceramics when constructing the occlusal surfaces of fixed restorations in Group I demonstrated the highest rate of the increase in the occlusal contact surface area – 9.93%. It was due to a low hardness of acrylic resin and its high surface roughness. In addition, there was observed an uneven abrasion of the occlusal surfaces resulting in periodontal tissue overload, thereby negatively affecting denture functioning

Unravelling the functional biomechanics of dental features and tooth wear

Most of the morphological features recognized in hominin teeth, particularly the topography of the occlusal surface, are generally interpreted as an evolutionary functional adaptation for mechanical food processing. In this respect, we can also expect that the general architecture of a tooth reflects a response to withstand the high stresses produced during masticatory loadings. Here we use an engineering approach, finite element analysis (FEA), with an advanced loading concept derived from individual occlusal wear information to evaluate whether some dental traits usually found in hominin and extant great ape molars, such as the trigonid crest, the entoconid-hypoconulid crest and the protostylid have important biomechanical implications. For this purpose, FEA was applied to 3D digital models of three Gorilla gorilla lower second molars (M2) differing in wear stages. Our results show that in unworn and slightly worn M2s tensile stresses concentrate in the grooves of the occlusal surface. In such condition, the trigonid and the entoconid-hypoconulid crests act to reinforce the crown locally against stresses produced along the mesiodistal groove. Similarly, the protostylid is shaped like a buttress to suffer the high tensile stresses concentrated in the deep buccal groove. These dental traits are less functional in the worn M2, because tensile stresses decrease physiologically in the crown with progressing wear due to the enlargement of antagonistic contact areas and changes in loading direction from oblique to nearly parallel direction to the dental axis. This suggests that the wear process might have a crucial influence in the evolution and structural adaptation of molars enabling to endure bite stresses and reduce tooth failure throughout the lifetime of an individual

Digital evaluation of occlusal forces: comparison between healthy subjects and TMD patients

ABSTRACT Aim: Continuous technological innovation has provided the clinicians to access to a computerized device that can analyse the different characteristics of occlusal contacts. The purpose of this research was to use this device to study the occlusal forces comparing healthy subjects and TMD patients. Materials and Methods: The study was conducted by following specific criteria to select participants, the sample was divided into two homogeneous groups: control group (CG) comprising healthy subjects, and dysfunctional group (DG) comprising TMD patients. The occlusal force analysis was performed using the computerized system T-Scan III V 5.20 T. The data were analysed with statistical methods. Results: The most significant differences emerged between the groups in the average occlusal load distribution and in the location of the centre of occlusal forces (COF). In particular, compared with the CG and the functional standard, reductions in the molar field forces on the second and first molars of 27% and 6.9%, respectively, were observed in the DG. The COF was located in the most forward position in TMD patients compared with healthy subjects. Conclusions: Although the differences in the distribution of the occlusal forces and the location of the occlusal centre of gravity were significant, the relationship between occlusal contacts and TMD remains to be fully clarified. Further research is needed to investigate whether studying occlusal force distributions in both healthy subjects and TMD patients

An overview of selected orthodontic treatment need indices

Orthodontics is a fast developing science as well as the field of medicine in general. The attempt of this book is to propose new possibilities and new ways of thinking about Orthodontics beside the ones presented in established and outstanding publications available elsewhere. Some of the presented chapters transmit basic information, other clinical experiences and further offer even a window to the future. In the hands of the reader this book could provide an useful tool for the exploration of the application of information, knowledge and belief to some orthodontic topics and questions