ABSTRACT
STATEMENT OF PROBLEM: Zirconia can be used either monolithically or veneered with porcelain. However, whether veneering zirconia affects marginal fit is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the marginal fit of the monolithic and layered zirconia prostheses using 2 different assessment methods. MATERIAL AND METHODS: An ideal complete crown with a chamfer finish line was prepared on an extracted maxillary central incisor. Two prosthesis designs, a framework and a monolithic design, and 2 marginal fit evaluation methods, the silicone replica and the triple scanning techniques, were used. In the first group, 10 crowns were fabricated with the framework design followed by porcelain veneering, and 10 crowns were fabricated monolithically in the second group. The marginal gap in each group was evaluated with both the silicone replica and triple scan methods. Data were statistically analyzed with a 2-way repeated measures ANOVA (α=.05). RESULTS: A significant difference was found in the mean marginal gap by design type (P=.003), with the monolithic prostheses having lower mean marginal gaps (31.0 and 84.0 µm). However, both groups showed clinically acceptable marginal fit. No significant difference was found between the assessment methods (P=.092). CONCLUSIONS: Monolithic zirconia crowns had a better marginal fit than veneered zirconia frameworks. Both the replica and triple scan techniques for marginal gap assessment yielded similar results.
Subject(s)
Dental Porcelain , Dental Prosthesis Design , Dental Prosthesis Design/methods , Computer-Aided Design , Dental Marginal Adaptation , Crowns , ZirconiumABSTRACT
Background. This study aimed to evaluate the effect of different pouring times and spacer thicknesses on the three-dimensional accuracy of casts made of 3D-printed custom trays. Methods. A partial edentulous maxillary model was scanned for fabricating custom acrylic trays. Twenty custom trays were created using a CAD/CAM system and divided into two groups in terms of their spacer thicknesses (2 mm and 4 mm). All the trays were designed with 2-mm thickness, multiple retentive holes measuring 2 mm in diameter, and three interior seating stops (two on the edentulous ridge and one on the incisal edge of the central incisors). Impressions were made using monophasic polyvinyl siloxane and poured in two different times (one hour and 24 hours after removal) with type IV dental stone. All the casts were scanned to measure three distances (inter-buccal cusps, inter-palatal cusps, and inter-fossa distances) between the two first premolars. The data were analyzed with two-way ANOVA and Bonferroni test at a significance level of 0.05. Results. There was no significant difference between the 3D accuracy of casts made using two different spacer thicknesses poured at 1-hour and 24-hour intervals. However, there was a difference between casts made after 1 hour and 24 hours when using custom trays with 2 mm of spacer thickness in terms of inter-buccal distance. Conclusion. There was no significant difference between the accuracy of casts made using custom trays with either 2 or 4 mm of spacer thickness, which were poured 1 hour or 24 hours after tray removal.
ABSTRACT
OBJECTIVE: The main goal of this study was to evaluate differences in stress distribution relevant to the number of implants under an anterior bridge when combined with a removable partial denture in the posterior region. MATERIALS AND METHODS: Four three-dimensional finite element models (3D FEM) were designed from a mandible containing an implant-supported bridge extending between canines, and a bilateral distal extension removable partial denture. A nonrigid connection was selected as the attachment method between the partial denture and the anterior implant-supported fixed prosthesis; 2, 3, 4 and 5 implants supporting the bridge all with 10mm length and 3.8 mm diameter were assessed. With the aid of the finite element program ANSYS 8.0, the models were loaded and von Mises stresses were evaluated. RESULTS: In spongy bone, stress forces showed a decrease from 2 implants to 4 implants but showed an increase in the 5-implant model. Stresses on cortical bone of terminal implants were in similar range in the 2-, 3- and 4-implant models. While, in the 5-implant model the amount of stresses on terminal implants increased dramatically. The stresses on implants were nearly similar in all models, with the greatest amount on terminal implants. CONCLUSION: Within the limitations of this study, 2-, 3- and 4-implant models showed less stress on cortical and spongy bone in comparison with the 5-implant model. The stresses transferred to implants were nearly similar.
ABSTRACT
BACKGROUND AND AIMS: Temporomandibular disorders (TMD) account for the most common orofacial pains rising from musculoskeletal origin. The aim of this study was to investigate the level of knowledge, attitudes and practice of dental practitioners regarding TMD in Tehran, Iran. MATERIALS AND METHODS: A questionnaire, containing 29 questions on etiology, signs and symptoms, diagnosis and treatment of TMD, was given to 200 randomly selected general dental practitioners and specialists as well as 11 TMD ex-perts. RESULTS: An overall response rate of 97% was achieved among participants (mean age: 39 ± 8.2 years old; mean years in practice: 11.5 ± 7.4). The mean score of knowledge of TMD was found to be 10.85± 2.54 (of a total of 23). TMD specialists were significantly more knowledgeable than general dental practitioners (p<0.05). With respect to attitude, there was a significant difference among various age groups, and by increasing age and years in practice, the attitude towards TMD had weakened. However, no significant difference was recorded between general dental practitioners' attitude and that of TMD experts towards TMD. There was a positive correlation between subjects' knowledge and attitude (P= 0.007, r=0.138). CONCLUSION: According to the results, the level of knowledge and attitude of general dental practitioners of Tehran regarding TMD is not desirable. The majority are not willing to admit and treat TMD patients.
