Effect of crown stiffness and prosthetic screw absence on the stress distribution in implant-supported restoration: A 3D finite element analysis.

This in-silico investigation evaluated the mechanical impact of Morse tape implant-abutment interface and retention system (with and without screw) and restorative materials (composite block and monolithic zirconia) by means of a three-dimensional finite element analysis (3D-FEA). Four 3D models were designed for the lower first molar. A dental implant (4.5 × 10 mm B&B Dental Implant Company) was digitized (micro CT) and exported to computer-aided design (CAD) software. Non-uniform rational B-spline surfaces were reconstructed, generating a 3D volumetric model. Four different models were generated with the same Morse-type connection, but with a different locking system (with and without active screw) and a different crown material made of composite block and zirconia. The D2 bone type, which contains cortical and trabecular tissues, was designed using data from the database. The implants were juxtaposed inside the model after Boolean subtraction. Implant placement depth was simulated for the implant model precisely at crestal bone level. Each acquired model was then imported into the finite element analysis (FEA) software as STEP files. The Von Mises equivalent strains were calculated for the peri-implant bone and the Von Mises stress for the prosthetic structures. The highest strain values in bone tissue occurred in the peri-implant bone interface and were comparable in the four implant models (8.2918e-004-8.6622e-004 mm/mm). The stress peak in the zirconia crown (64.4 MPa) was higher than in the composite crown (52.2 MPa) regardless of the presence of the prosthetic screw. The abutment showed the lowest stress peaks (99.71-92.28 MPa) when the screw was present (126.63-114.25 MPa). Based on this linear analysis, it is suggested that the absence of prosthetic screw increases the stress inside the abutment and implant, without effect on the crown and around the bone tissue. Stiffer crowns concentrate more stress on its structure, reducing the amount of stress on the abutment.

The Influence of Custom-Milled Framework Design for an Implant-Supported Full-Arch Fixed Dental Prosthesis: 3D-FEA Sudy.

The current study aimed to evaluate the mechanical behavior of two different maxillary prosthetic rehabilitations according to the framework design using the Finite Element Analysis. An implant-supported full-arch fixed dental prosthesis was developed using a modeling software. Two conditions were modeled: a conventional casted framework and an experimental prosthesis with customized milled framework. The geometries of bone, prostheses, implants and abutments were modeled. The mechanical properties and friction coefficient for each isotropic and homogeneous material were simulated. A load of 100 N load was applied on the external surface of the prosthesis at 30° and the results were analyzed in terms of von Mises stress, microstrains and displacements. In the experimental design, a decrease of prosthesis displacement, bone strain and stresses in the metallic structures was observed, except for the abutment screw that showed a stress increase of 19.01%. The conventional design exhibited the highest stress values located on the prosthesis framework (29.65 MPa) between the anterior implants, in comparison with the experimental design (13.27 MPa in the same region). An alternative design of a stronger framework with lower stress concentration was reported. The current study represents an important step in the design and analysis of implant-supported full-arch fixed dental prosthesis with limited occlusal vertical dimension.

Evaluation of Satisfaction Perceived by Prosthetic Patients Compared to Clinical and Technical Variables.

OBJECTIVES: The purpose of this study is to relate the clinical quality of the complete denture and specific anamnestic factors to the level of satisfaction perceived by patients. Also identifying possible prognostic parameters that could be predictive of future satisfaction. MATERIALS AND METHODS: On the basis of a substantial existing literature, the most appropriate parameters to determine the prosthetic quality have been determined to evaluate the satisfaction perceived by patients about their denture; a completely new questionnaire has been drawn up. Ninety-eight patients have been included in the research, they have undergone a clinical examination, and they have filled out the questionnaire anonymously. The ANOVA test and Pearson correlation test have been employed to relate clinical and anamnestic factors to the overall satisfaction score. RESULTS: The average level of patients' satisfaction was between "quite satisfied" and "very satisfied." There is no significant variability of satisfaction related to the type of prosthesis. The ANOVA test did not verify relationships between the overall satisfaction score and the anamnestic data examined. Pearson linear correlation coefficient between the overall prosthetic quality and the general satisfaction perceived by patients is 0.493 (P < 0.01). Extension of the prosthetic body (r = 0.478; P < 0.01) and retention (r = 0305; P < 0.05) are in correlation with the overall patients' satisfaction. CONCLUSION: there is a moderately strong relationship between the overall prosthetic quality and the general satisfaction perceived by patients. Particularly, the retention and the adequate extension of the prosthetic body appear to be factors that are most associated with satisfaction. Instead, the anamnestic factors are not related to overall satisfaction score.

Dynamometric assessment of the mechanical resistance of porcelain veneers related to tooth preparation: a comparison between two techniques.

STATEMENT OF PROBLEM: There is little agreement regarding a palatal extension of the preparation for porcelain veneers, as it represents a more invasive technique than a preparation limited to the facial surface of a tooth. PURPOSE: The purpose of this study was to detect the stress in maxillary anterior teeth restored with porcelain veneers and compare the resistance to fracture of porcelain veneers prepared using different preparation designs. MATERIAL AND METHODS: Forty-five maxillary anterior teeth were restored with porcelain veneers and divided into 9 groups as follows: Ca, canines with no preparation; Ca-Ch, canines with palatal chamfer preparation; Ca-W, canines with window preparation; LI, lateral incisors with no preparation; LI-Ch, lateral incisors with palatal chamfer preparation; LI-W, lateral incisors with window preparation; CI, central incisors with no preparation; CI-Ch, central incisors with palatal chamfer preparation; CI-W, central incisors with window preparation. Shear-flexural fracture tests were performed. The fractured specimens were subjected to scanning electron microscope (SEM) analysis. Data were statistically analyzed with univariate analysis of variance and the Tukey post hoc test for multiple comparisons (alpha=.05). RESULTS: The following mean fracture load values (N) were recorded: Ca, 395 +/- 6; Ca-Ch, 310 +/- 8; Ca-W, 322 +/- 8; LI, 309 +/- 8; LI-Ch, 242 +/- 6; LI-W, 225 +/- 8; CI, 298 +/- 8; CI-Ch, 255 +/- 8; CI-W, 221 +/- 6. The SEM analysis showed that both adhesive and cohesive fractures were primarily concentrated at the cervical region. Statistical analysis showed that both the type of tooth and the design of the preparation significantly influenced the resistance to fracture of the restored teeth (P<.001). CONCLUSION: The chamfer preparation is recommended for central incisors, whereas the window preparation showed better results for canines. Both preparations can be adopted in the restoration of lateral incisors.

Rapid prototyping: a new method of preparing trays for indirect bonding.

This article describes a new method of preparing trays for indirect bracket bonding. Computer-aided technology is used to design the individualized trays, which are then produced with a rapid prototyping procedure. Application in clinical practice and the advantages of time savings and accurate bracket placement are discussed.

Evaluation of cervical posture of children in skeletal class I, II, and III.

Previous studies on the relationship between morphological structure of the face and cervical posture have predominantly focused on vertical dimensions of the face. The aim of this study was to investigate whether there are significant differences in cervical posture in subjects with a different sagittal morphology of the face, i.e., a different skeletal class. One hundred twenty (120) children (60 males and 60 females, average age 9.5 yrs., SD+/-0.5) were admitted for orthodontic treatment. Selection criteria was: European ethnic origin, date of birth, considerable skeletal growth potential remaining and an absence of temporomandibular joint dysfunction (TMD). Lateral skull radiographs were taken in mirror position. Subjects were divided into three groups based on their skeletal class. The cephalometric tracings included postural variables. The most interesting findings were: 1. children in skeletal class III showed a significantly lower cervical lordosis angle (p<0.001) than the children in skeletal class I and skeletal class II; 2. children in skeletal class II showed a significantly higher extension of the head upon the spinal column compared to children in skeletal class I and skeletal class III (p<0.001 and p<0.01, respectively). This is probably because the lower part of their spinal column was straighter than those of subjects in skeletal class I and II (p<0.01 and p<0.001, respectively). Significant differences among the three groups were also observed in the inclination of maxillary and mandibular bases to the spinal column. The posture of the neck seems to be strongly associated with the sagittal as well as the vertical structure of the face.

Treatment of joint pain and joint noises associated with a recent TMJ internal derangement: a comparison of an anterior repositioning splint, a full-arch maxillary stabilization splint, and an untreated control group.

Pain and joint noises associated with temporomandibular joint (TMJ) internal derangement are often treated by using an intra-oral splint. This study evaluated whether an anterior repositioning splint (AR splint) could be more effective in the treatment of these symptoms than a full-arch maxillary stabilization splint (FAMS splint), because of its capability to re-establish immediately the normal condyle/disk relationship. The authors treated 40 patients (average age 16.8; range 8.0-24.0) with confirmed internal derangement, joint pain, and joint noises in at least one TMJ for at least two months, with AR splint (20 subjects) or FAMS splint (20 subjects); 10 untreated patients comprised the control group. Joint noise, joint pain, and the intensity of pain were assessed using a visual analogic scale (VAS), and the pain was characterized (i.e., constant or chewing/biting pain) and evaluated monthly for eight months. Significantly fewer AR splint patients experienced pain after four months of treatment. A significantly lower intensity of pain was experienced by the AR splint patients after two months of treatment. Significantly fewer AR splint patients experienced chewing/biting pain after eight months of treatment. The frequency of joint noises decreased over time, with no significant differences between the groups. In conclusion, the AR splint seems to be more effective in decreasing pain, but it seems to make no difference in the treatment of joint noises.

Cervical lordosis angle measured on lateral cephalograms; findings in skeletal class II female subjects with and without TMD: a cross sectional study.

The literature reports evidence of various types of correlations between cervical alterations and cervical pain, and the existence of cervical pain in subjects with temporomandibular joint internal derangement (TMD). The hypothesis of this study is that cervical lordosis angle (CVT/EVT angle) alteration on cephalometrics could be correlated to the presence of TMD. The cephalometric records of 50 females with documented TMD were compared with those of a control group of 50 females. The subjects in the sample were 25-35 years of age, average 28.9 years (SD, 3.2). Radiographs were taken in mirror position, and seventeen variables, including the CVT/EVT angle, were traced. Double measurements were made to evaluate method error using Dahlberg's formula. Pearson's correlation coefficient and Mann-Whitney's t-test were used to evaluate the data. Intra-group analysis showed significant correlations between the CVT/EVT angle and mandibular length (p<0.01), mandibular position (p<0.05), mandibular divergence (p<0.01), and overjet (p<0.01) in both groups. Between groups, the analysis showed significant differences in CVT/EVT angle (p<0.05), maxillary protrusion (p<0.01), mandibular protrusion (p<0.01), mandibular length (p<0.01), mandibular divergence (p<0.05), and overbite (p<0.05).