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Marginal Discrepancies (marginal + discrepancy)
Selected AbstractsEffects of Tooth Preparation Burs and Luting Cement Types on the Marginal Fit of Extracoronal RestorationsJOURNAL OF PROSTHODONTICS, Issue 2 2009Mohamed F. Ayad BDS Abstract Purpose: Although surface roughness of axial walls could contribute to precision of a cast restoration, it is unclear how the roughness of tooth preparation affects marginal fit of the restoration in clinical practice. The purpose of this study was to describe the morphologic features of dentin surfaces prepared by common rotary instruments of similar shapes and to determine their effects on the marginal fit for complete cast crowns. Materials and Methods: Ninety crowns were cast for standardized complete crown tooth preparations. Diamond, tungsten carbide finishing, and crosscut carbide burs of similar shape were used (N = 30). The crowns in each group were subdivided into three groups (n = 10) for use with different luting cements: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia 21). Marginal fit was measured with a light microscope in a plane parallel to the tooth surface before and after cementation between four pairs of index indentations placed at equal distances around the circumference of each specimen. Difference among groups was tested for statistical significance with analysis of variance (ANOVA) followed by Ryan-Einot-Gabriel-Welsch Multiple Range Test (,= 0.05). Results: Analysis of measurements disclosed a statistically significant difference for burs used to finish tooth preparations (p < 0.001); however, luting cement measurements were not significantly different (p= 0.152). Also, the interaction effect was not significantly different (p= 0.685). For zinc phosphate cement, the highest marginal discrepancy value (100 ± 106 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (36 ± 30 ,m) was for tooth preparations refined with finishing burs. For glass ionomer cement, the highest marginal discrepancy value (61 ± 47 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (33 ± 40 ,m) was for tooth preparations refined with finishing burs. For adhesive resin cement, the highest marginal discrepancy value (88 ± 81 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (19 ± 17 ,m) was for tooth preparations refined with finishing burs. Conclusions: Marginal fit of complete cast crowns is influenced by tooth preparation surface characteristics, regardless of the type of luting agent used for cementation. Tooth preparations refined with finishing burs may favor the placement of restorations with the smallest marginal discrepancies, regardless of the type of cement used. [source] Marginal Adaptation of Cerec 3 CAD/CAM Composite Crowns Using Two Different Finish Line Preparation DesignsJOURNAL OF PROSTHODONTICS, Issue 3 2006Jaber Hussain Akbar DDS Purpose: The purpose of this study was to compare marginal discrepancies of Cerec 3 CAD/CAM composite crowns, fabricated on human prepared teeth with two different finish line designs, chamfer and shoulder. Materials and Methods: Sixteen human molar teeth were used to prepare full crowns. Eight teeth were prepared with a 1-mm-wide chamfer finish line and the other eight with a 1.2- to 1.5-mm circumferential shoulder. Cerec 3 crowns were fabricated from optical impressions using Paradigm MZ100 composite polymer. Marginal adaptation was evaluated in two ways: (1) using modified United States Public Health Service (USPHS) criteria to evaluate eight preselected sites on each crown margin, and (2) using scanning electron microscopy (SEM) to measure marginal gaps on all four axial walls with 15 measurements on each wall (60 measurements per crown). An evaluation of the number of acceptable crowns, determined by having all measured sites per tooth with margin gap size less than 100 ,m, as a function of finish line design was also conducted. Results: In both chamfer and shoulder groups, there were only two crowns (out of eight) with clinically acceptable ratings for all eight measurement sites according to USPHS criteria. Fisher's chi-square analysis showed that there was no statistically significant difference in marginal adaptability as a function of finish line design ( p > 0.05). With SEM imaging, overall mean marginal gaps for the chamfer group were 65.9 ± 38.7 ,m (range 35.0 to 130.0 ,m), and for the shoulder group were 46.0 ± 9.2 ,m (range 26.3 to 55.6 ,m); this difference was not found to be statistically significant ( p > 0.05). While crown assessment based on mean marginal discrepancy measurements indicated that both the chamfer and shoulder groups were considered clinically acceptable (<100 ,m); crown acceptability based on all measurement sites being less than 100 ,m indicated that in the chamfer and shoulder groups there were four and three acceptable crowns out of eight, respectively. The Fisher's chi-square test indicated no statistically significant difference between the groups ( p > 0.05). An agreement rate of 81.2% was calculated between the two evaluation methods, modified USPHS criteria and SEM measurements. Conclusions: Based on mean marginal discrepancy measurements, the typical marginal assessment technique, Cerec 3 Paradigm MZ100 crown restorations appear to have acceptable marginal adaptability (mean discrepancies <100 ,m). Thus, the evidence from this investigation would suggest that the finish line preparation design had no effect on marginal adaptation for Cerec 3 composite crowns. [source] Determination of the dynamics of restored teeth by 3D electronic speckle pattern interferometry,LASERS IN SURGERY AND MEDICINE, Issue 4 2004H. Lang Abstract Background and Objectives The difficulties typically encountered in studying the effects of restorations on tooth reinforcement are often due to the 3-dimensional (3D) nature of deformation. Therefore, electronic 3D-Speckle-Interferometry (3D-ESPI) was used to assess the impact of different restorative materials on the deformation of teeth. Study Design/Materials and Methods Small and large MOD-preparations in extracted premolars were restored with gold inlays, ceramic inlays, composite resin inlays, amalgam, or composite resin. The restorations and cusps were loaded (90 N) and the deformation was assessed by 3D-ESPI. Results Teeth with small restorations were deformed only slightly and the differences between the materials were minimal (P>0.05). In contrast, teeth with large restorations displayed material-specific deformation patterns: (a) all materials led to decreased deformation as compared with unfilled teeth, (b) elastic materials caused only local deformation, (c) non-adhesive materials resulted in translation of the restoration and marginal discrepancies, (d) adhesive inlays brought about increased deformation of the luting resin composite, (e) loading of the cusps caused higher deformation than loading of the restorations, and (f) bonded restorations stabilized the cusps. Conclusions The results show that the deformation pattern of restored teeth is material-specific but the extent of deformation is primarily limited by the remaining tooth substance. Lasers Surg. Med. 34:300,309, 2004. © 2004 Wiley-Liss, Inc. [source] Effect of preparation convergence on retention and seating discrepancy of complete veneer crownsJOURNAL OF ORAL REHABILITATION, Issue 10 2004D. C. N. Chan summary, The purpose of this study was to evaluate the retention and marginal seating discrepancy of complete veneer crown cemented with zinc phosphate using various preparation convergence designs. The method employed was that of cementing cast metal crowns onto 46 metal dies fabricated as complete veneer crown preparations with various convergence angles ranging from 0° to 70° and a shoulder finish line. The marginal discrepancy was calculated by measuring the change in crown height before and after cementation using an optical measuring microscope. The force required to remove the crowns from the dies in a vertical direction was determined using an Instron universal testing machine and recorded as retention. The increase in preparation convergence exhibited a wide variation of seating discrepancy between specimens, ranging from 4·58 ± 1·13 to 73·13 ± 78·32 ,m. Significant tilting of crown was observed as the convergence angle of preparation increased. The retention values ranged from 4·03 ± 0·61 to 12·12 ± 0·33 MPa. The Pearson analysis revealed statistically significant correlations between preparation convergence and marginal discrepancy (r = +0·62), and retention (r = ,0·91). Complete veneer crown retention and marginal discrepancy were influenced by the preparation convergence design. [source] Differing Expansion Contributions of Three Investment Materials Used for Casting TitaniumJOURNAL OF PROSTHODONTICS, Issue 5 2009Danny Low BDS, MScDent, MScMed Abstract Purpose: This laboratory study aimed at investigating the effect of setting expansion (SE), which could enlarge a wax pattern by concurrent exothermic reaction. Materials and Methods: Two phosphate-bonded investment materials (Rematitan Plus, T-invest C & B) and alumina-magnesia-based investment material (Titavest CB) were subjected to setting temperature and SE measurements (n = 10). Full-crown wax patterns were prepared from metal dies having the same design. Crown castings (n = 6) were made using a one-chamber high-pressure casting machine. Commercially pure titanium ingot (Japanese Industrial Standard Class II) was used for each casting. Dimensional accuracy of the cast crowns was expressed by marginal discrepancy for a pair of wax pattern and casting prepared from the same die. All results were then subjected to regression analysis. Results: Rematitan Plus gave the highest setting temperature (about 70°C) and the highest SE (1.16 ± 0.01%) almost concurrently. The result was that Rematitan Plus produced oversized crowns from the lowest thermal expansion (TE) value (0.53 ± 0.05%) reducing the linear correlation to 0.80 (p < 0.05). No significant linear relationship was found between SE of investment material and crown-casting accuracy. Conclusions: The almost concurrent occurrence of high SE and high setting temperature generation in Rematitan Plus enlarged the wax pattern and effectively supplemented its low TE to produce oversized crowns. Despite this adverse effect, the correlation between TE and crown accuracy was still high. It is generally expected that the TE values given by manufacturers predict crown accuracy, when uniform TE, small SE, and minimum heat generation during setting are assured. [source] | ||||||||||