Tuncer Burak Özçelik

Colorimetric analysis of opaque porcelain fired to different base metal alloys used in metal ceramic restorations

STATEMENT OF PROBLEM The popularity of base metal alloys has considerably increased in recent years because of their superior mechanical properties as well as the high cost of noble alloys. However, there is disagreement about their effect on the opaque porcelain color and the color differences among base metal alloys. PURPOSE The purpose of this in vitro study was to determine and compare the influence of various commercially available base metal alloys (excluding titanium-based systems) on the resulting color of opaque porcelain with the use of a colorimetric device. MATERIAL AND METHODS Fourteen different types of Ni-Cr and 3 different types of Co-Cr porcelain bonding alloys were selected with a Au-Pd alloy (V-Delta SF) as the control group for colorimetric measurements and determination of color shift after opaque application. Shade B1 of an opaque porcelain (IPS d.SIGN Opaquer) was applied (0.1 mm) to all specimens (16 mm x 1 mm). The color coordinates of each specimen were measured with a chromameter. The data were displayed in L*, a*, and b* values according to the CIELAB system, and the color differences (DeltaE) between base metal alloys and the control group were calculated. Data were statistically analyzed with 1-way ANOVA (alpha=.05). The ANOVA was followed by Dunnetts multiple comparison test for comparisons with the control group to determine specifically which groups were significantly different from the control group. RESULTS The L* value of only 1 base metal alloy was significantly different from the control group (P<.001). All base metal alloy groups except 3 had a* values which were significantly different from the control group a* value (P=.001 for Rexillium III, P=.008 for Heracles N, and P<.001 for the remaining 12 alloys), whereas only 3 base metal alloys were not statistically significantly different from the control group in the means of b* values (P<.001). All base metal alloys to which opaque porcelain was applied had significantly different DeltaE values in comparison with the control group (P<.001). CONCLUSIONS The data of the study indicated that a 0.1-mm-thick layer of opaque porcelain applied on the Ni-Cr and Co-Cr alloys did not reliably reproduce the color of opaque porcelain. However, within the limitations of this study, the color differences of base metal alloys measured according to the control group are within clinically acceptable limits (DeltaE<3.5).

Management of chronic unilateral temporomandibular joint dislocation with a mandibular guidance prosthesis: A clinical report

Recurrent or chronic dislocation of the temporomandibular joint is relatively rare and often results in facial asymmetry, impairment of function, and discomfort. Although manual reduction is the primary choice of treatment, patients presenting with recurrent or prolonged dislocations require conservative and surgical methods to limit forward movement of the mandibular condyle. This clinical report presents a 75-year-old woman with severe mandibular deviation and subsequent facial asymmetry caused by a chronic unilateral temporomandibular joint dislocation that was treated with a mandibular guidance prosthesis combined with physical therapy.

Evaluation of marginal fit of CAD/CAM restorations fabricated through cone beam computerized tomography and laboratory scanner data

STATEMENT OF PROBLEM Whether cone beam computed tomography (CBCT) images can be used for the fabrication of computer-aided design/computer-aided manufacturing (CAD/CAM) restorations is unknown. PURPOSE The purpose of this in vitro study was to evaluate the marginal fit of CAD/CAM restorations fabricated by using data from CBCT scans with 3 different voxels and laser scanner images. MATERIAL AND METHODS A crown preparation was made on an extracted premolar tooth according to ceramic crown preparation guidelines. The prepared tooth was scanned with a 3-dimensional (3D) extraoral laser scanner (D900; 3Shape), and CBCT scans were also made with an i-CAT cone beam 3D imaging system at 3 different voxel resolution settings: 0.125 mm, 0.20 mm, and 0.30 mm. The 3D images obtained from the laser scanner and CBCT scans were sent to CAD software, and a crown design was completed. Information was sent to CAM software to mill the crowns from poly(methyl methacrylate) (PMMA) blocks (n=9 from the laser scanner and 27 from 3 different CBCT scans). A total of 144 images (4 groups, 9 crowns per group, 4 sites per crown) were measured for vertical marginal discrepancy under a stereoscopic zoom microscope. One-way analysis of variance (ANOVA) was used to analyze the data. According to the assumption of homogeneity of variance, the post hoc Tukey multiple comparison test was performed (α=.05). RESULTS The marginal gap values of crowns fabricated with an extraoral laser scanner were significantly lower than those of crowns fabricated with 0.3-, 0.2-, and 0.125-voxel CBCT images (P<.001). The marginal gap was greater when 0.3- and 0.2-voxel CBCT images were used than when 0.125-voxel CBCT images were used (P<.001). CONCLUSIONS Crowns fabricated with the laser scanner images had lower and clinically acceptable marginal discrepancies than crowns fabricated with CBCT images in 3 different voxels. Of all the CBCT scans, only images with 0.125 voxel produced crowns with clinically acceptable marginal discrepancy.

Biomechanical Evaluation of Tooth- and Implant-Supported Fixed Dental Prostheses with Various Nonrigid Connector Positions: A Finite Element Analysis

PURPOSE In the tooth- and implant-supported fixed dental prosthesis (FDP), rigid and nonrigid connector (NRC) designs have been preferred by clinicians for many years. The aim of this study was to analyze the stress distribution on the connecting areas of the superstructure and supporting structure of the tooth- and implant-supported FDP designs under both static vertical and oblique occlusal loads. MATERIALS AND METHODS Four 2D finite element analysis (FEA) models were prepared presuming that the first and second molars were missing, and that the implant (3.80-mm diameter × 13-mm length) was placed in the second molar NRC design and patrix-matrix position supported by teeth/implants. Nonlinear contact elements were used to simulate a realistic interface fixation within the implant system and the sliding function of the NRC. Supporting periodontal ligament and alveolar bone (cortical and trabecular) were also modeled. Linear static analysis was performed on the prepared 2D solid models with a total masticatory force of 250 N (50 N for premolar, 100 N for first molar, 100 N for second molar), 0° (at a right angle) and 30° to the long axis of the supports. The maximum equivalent Von Mises (VM(Max)) was analyzed around the supporting teeth/implant and connector areas on tooth- and implant-supported FDP. RESULTS The simulated results indicated that the highest level of VM(Max) (400.377 MPa) was observed on the NRC with the matrix positioned on the implant site of tooth- and implant-supported FDP under vertical occlusal load. The highest level of VM(Max) (392.8 MPa) under oblique occlusal load was also observed on the same model; however, the lowest VM(Max) value around implants was observed with the NRC when the patrix was positioned on the implant site of the FDP. Under vertical occlusal loads, in designs where the NRC was placed on the implant site, the stress formed around the implant decreased when compared to the designs where the NRCs were positioned on the tooth site. CONCLUSIONS The efficiency of the NRC exhibited varying behavior depending on the direction of the load applied. The use of the patrix part of the NRC on the implant site may be more efficient in reducing the stress formation around the implant.

Digital evaluation of the accuracy of impression techniques and materials in angulated implants

OBJECTIVES The aim of this study was to investigate the accuracy of 2 different impression techniques and 3 different impression materials in models simulating parallel and angulated implants. METHODS Three master models simulating partial edentulous mandible with 2 implants at the sites of second premolars (parallel) and second molars with different angulations (parallel, 10° or 20° angulated) were fabricated. Two different impression techniques [splinted direct (D), indirect (I)] and 3 different monophase impression materials [polyether (PE), vinyl polysiloxane (VPS), vinyl polyether silicone (VPES)] were used for each master model and a total of 180 impressions were made (n=10). Master model and casts were scanned by a modified laser scanner and data were transferred to VRMesh software. Master model and duplicate cast scans were digitally aligned observing the superposition of anatomic markers. Angular and coronal deviations between master and duplicated copings were calculated and data were statistically analyzed. RESULTS Mean angular and coronal deviations were in a range of 0.205-0.359° and 22.56-33.33μm, respectively. Statistical analysis revealed that the angulation of implant affected both coronal and angular deviations of the impression copings (P<0.05). According to statistical analyses, for parallel implants, the accuracy of impression materials and techniques were ranging as VPS-D=PE-D>VPS-I=PE-I>VPES-D>VPES-I from most accurate to the least. For 10° and 20° angulated implants the most accurate material and technique was VPS-D whereas the least accurate combination was VPES-I (P<0.05). CONCLUSION Angulation, impression technique and material were found to be effective on the accuracy of implant impressions. CLINICAL SIGNIFICANCE Clinicians may prefer VPS impression material and splinted direct technique for impressions of both parallel and up to 20° angulated implants.

A surgical guide for craniofacial implant placement for an implant-retained auricular prosthesis

Craniofacial implants provide excellent stability and retention for auricular prosthetic rehabilitation. Accurate location of implants is important to achieve optimal prosthetic results. This article describes an alternative procedure for fabricating an acrylic resin surgical template for craniofacial implant placement with the assistance of a 6-inch contour duplication gauge.

Salvaging an angled implant abutment with damaged internal threads: A clinical report

This clinical report describes a technique to fit an existing fixed detachable implant-supported prosthesis to a zygomatic implant abutment with stripped internal threads. The threads of the abutment were retapped and a wide diameter/wide head retaining screw was used to secure the existing prosthesis on the abutment. Care is needed in the retrieval of broken screws so as not to damage the internal threads of the implants, which might lead to irreversible complications.

Effect of alloy recasting on the color of opaque porcelain applied on different dental alloy systems

STATEMENT OF PROBLEM The effect of different proportions of recast dental alloys on the color of overlying opaque porcelain (OP) is unknown. PURPOSE The purpose of this study was to compare the color of OP applied on 2 different proportions (50% and 100%) of recast alloys with the color of commercially available shade tabs of OP. MATERIAL AND METHODS Six different metal alloy systems (2 base: Metalloy CC, Cr-Co [B-MCC]; Heraenium NA, Ni-Cr [B-HNA]; 3 noble: Cerapall 2, Pd-Au [N-CP2]; Triumph, Pd-Ag [N-T]; V-Deltaloy, Au-Pd [N-VD]; and 1 high-noble: V-Gnathos Plus, Au-Pt [HN-GP]) were selected for the fabrication of disk-shaped specimens (10 mm in diameter, 1 mm in thickness). Each alloy was divided into 2 subgroups: 50% new alloy with 50% recast alloy (n=3) and 100% recast alloy (n=3). OP (B1) was applied (0.1 mm) to all specimens. The color coordinates (L*, a*, b*) of each specimen and the corresponding commercially available OP shade tab (control) were measured with a spectroradiometer, and color differences between specimens and control group were calculated. Data were statistically analyzed (2-way ANOVA, Ryan-Einot-Gabriel-Welsch multiple range test, α=.05). RESULTS For each alloy, ΔL*(L(control)(-)L(recastalloy)) values for the 2 subgroups were not statistically different from each other. The Δa* and Δb* of different proportions of N-CP2, B-HNA, N-VD, and HN-GP were not statistically different within the alloys. However, the a* values of 100% recast N-T and B-MCC were significantly closer to the a* values of the control group, and the b* values of 50% recast B-MCC were significantly closer to the b* values of the control group (P<.05). Delta E(control-recast) alloy values for different proportions of alloys were not statistically different. However, color differences did not meet the criterion of clinical acceptability (ΔE=3.46). CONCLUSIONS According to the results of this study, the different proportions (50% and 100%) of recast alloys used have similar effects on the color of OP. Differences between the final color of OP on the recast alloys used and the color of OP shade guide tabs did not meet the criterion of clinical acceptability considered in this study.

Effect of fabrication stages and cementation on the marginal fit of CAD-CAM monolithic zirconia crowns

Statement of problem Monolithic zirconia crowns fabricated using computer‐aided design and computer‐aided manufacturing (CAD‐CAM) technology have recently become an alternative dental prosthetic treatment. The marginal fit of monolithic zirconia crown may be affected by different stages of the fabrication procedures in the laboratory and cementation. Information regarding the accuracy of fit of monolithic zirconia crowns at different stages of fabrication and cementation is limited. Purpose The purpose of this in vitro study was to evaluate the effect of different stages of fabrication and cementation on the vertical marginal discrepancy (VMD) of CAD‐CAM fabricated monolithic zirconia crowns. Material and methods Six ivorine right maxillary first molar typodont teeth with standardized anatomic preparations for complete coverage ceramic crowns were scanned with a 3‐dimensional laboratory scanner. Crowns were designed using CAD software and milled from presintered monolithic zirconia blocks in a 5‐axis dental milling machine. A cement space of 25 &mgr;m for the margins and a 50‐&mgr;m space starting 1 mm above the finish lines of the teeth were virtually set in the CAD software. A total of 144 measurements were performed on 6 specimens with 8 measurement locations in 3 different stages using stereoscopic zoom microscopy; after initial production of the crowns (post‐sintering group), after glazing (post‐glazing group), and after cementation (post‐cementation group). The VMD values were statistically analyzed with 1‐way repeated measures ANOVA and the Holm‐Sidak method (&agr;=.05). Results Different stages of fabrication and cementation significantly affected the VMD of tested crowns (P=.003). The mean VMD was 38 &mgr;m for post‐sintering group, 38 &mgr;m for post‐glazing group, and 60 &mgr;m for post‐cementation group, with statistical differences between the post‐sintering group, the post‐cementation group (P<.002), and the post‐glazing group and post‐cementation group (P<.003); there were no statistical differences between the post‐sintering group and the post‐glazing group (P=.966). Conclusions Within the limitations of this in vitro study, glazing did not significantly change the VMD of CAD‐CAM monolithic zirconia crowns. Cementation significantly increased the VMD values.

The Effect of Different Polishing Sequences on the Adhesion of Streptococcus mutans to Feldspathic Porcelain

The aim of this research was to determine whether extra-oral surface treatments on feldspathic porcelain surfaces influence initial adhesion of Streptococcus mutans. Ninety-six porcelain specimen discs were fabricated and divided into six equal groups according to surface treatment: fine-grit diamond polishing (Group 1); self-glazing (Group 2); overglazing (Group 3); overglazing followed by a finishing procedure and then overglazing (Group 4); Pearl Surface polishing (Group 5); and Diamond Twist SCLTM polishing (Group 6). Surface roughness and hydrophobicity were assessed. An S. mutans suspension was incubated on each specimen group and evaluated. A one-way analysis of variance, post-hoc Tukey honestly significantly different test, Friedman test, and t-test were used for statistical analysis. Group 1 showed the highest surface roughness (p < 0.001) and bacterial adhesion (p < 0.05). Groups 5 and 6 specimen surfaces presented significantly higher contact angles (p < 0.05). Group 1 had the highest S. mutans adhesion, followed by Groups 3, 5, 6, 2, and 4 (p < 0.05). Reglazing after grinding may therefore decrease bacterial adhesion beneficially.