Burak Yilmaz

Fabricating complete dentures with CAD/CAM technology

Conventional complete denture prosthetics require several appointments to register the maxillomandibular relationship and evaluate the esthetics. The fabrication of milled complete dental prostheses with digital scanning technology may decrease the number of appointments. The step-by-step method necessary to obtain impressions, maxillomandibular relation records, and anterior tooth position with an anatomic measuring device is described. The technique allows the generation of a virtual denture, which is milled to exact specifications without the use of conventional stone casts, flasking, or processing techniques.

Porcelain thickness and cement shade effects on the colour and translucency of porcelain veneering materials

OBJECTIVE Purposes of this in vitro study include evaluating colour changes in combinations of feldspathic porcelain and cement resulting from different thicknesses of porcelain and different shades of composite luting agent, and evaluating relative translucency parameter (RTP) values. MATERIALS AND METHODS Porcelain discs of shade A1 at nominal thicknesses of 0.5 and 1.0mm were bonded to cements of three shades in a factorial design. Colours were calculated for CIE D65 Illuminant and Standard Human Observer on black, grey and white backings. A colour difference (CD) was calculated of each possible pair of different porcelain thickness values for the same cement shade and each possible pair of different cement shades for the same porcelain thickness. RTP was analyzed by ANOVA and selected pairwise comparisons. RESULTS All mean CDs studied were perceptible and most were at or greater than the clinical acceptability threshold, with the notable exception that the mean CDs and their confidence limits were below the clinical acceptability threshold for a change in porcelain thickness when utilizing the Clear cement shade. Variation in the shade of the resin luting cement will result in CDs which are near or beyond clinical acceptability. A decrease in porcelain thickness did significantly increase RTP when bonded to the resin cement shades studied. CONCLUSION Changes in porcelain thickness or cement shade may adversely affect basic aesthetic properties of these materials. Development of methods for analyzing aesthetic effects over greater ranges of thickness for these materials would improve the prognosis for using these materials.

Color Stability of Denture Acrylic Resins and a Soft Lining Material Against Tea, Coffee, and Nicotine

PURPOSE The purpose of this study was to investigate the effect of four solutions [saliva (control group), saliva+tea, saliva+coffee, saliva+nicotine] on the color of different denture base acrylic resins (heat-polymerized, injection-molded, autopolymerized) and a soft denture liner. MATERIALS AND METHODS Twenty specimens from each type of test material were prepared (2.5 mm diameter, 2 mm thickness). Five specimens from each test material (heat-polymerized, chemically polymerized, injection-molded acrylic resin, soft denture reliner) were stored in each solution in 37 degrees C in a dark environment. Colorimetric measurements were done on the 1st, 7th, and 30th days. Color differences among specimens immersed in saliva (control group), and staining solutions were evaluated over time. Data were statistically analyzed with one-way analysis of variance (ANOVA) (alpha= 0.05). ANOVA was followed by Tukey test to find which groups differed from each other. RESULTS Significant color shifts occurred in heat-polymerized and injection-molded acrylic resins in coffee and in soft liner in nicotine over time (p < 0.05) (DeltaE > 1). The color shift of soft liner in nicotine was significantly different than that of the remainder of the test materials in nicotine (p < 0.05). The color shift magnitudes of each test material in coffee and tea were not significantly different when compared among the test material groups (p > 0.05). CONCLUSIONS The effect of staining solutions on the color of each test material in each session was perceivable by the human eye (DeltaE > 1); however, the color shifts of all test materials were clinically acceptable (DeltaE < 3.7) except for soft liner in nicotine, which was not clinically acceptable over time. Therefore, minimizing drinking of such beverages and use of tobacco, particularly when soft liner is applied, may be advantageous for denture wearers for long-term color stability.

Load to failure of different zirconia abutments for an internal hexagon implant

STATEMENT OF PROBLEM Various zirconia abutment designs are available to restore implant systems. Fracture resistance is one of the criteria involved in selecting among these options. PURPOSE The purpose of this in vitro study was to measure and compare load to failure for 5 zirconia abutments for an internally hexagon implant. MATERIAL AND METHODS Five 4.1×11.5-mm Zimmer tapered screw-vent implants were individually secured in a loading apparatus, and 3 specimens of each of the 5 different abutments (Zimmer Contour with a Ti ring, anatomic-contour Atlantis-Zr, anatomic-contour Inclusive-Zr, anatomic-contour Astra Tech ZirDesign, Legacy Straight Contoured abutment with Ti core) (N=15) were loaded at a 30-degree angle until the implant abutment complex failed. Data for load to failure were compared with analysis of variance and a Tukey-Kramer post hoc test (α=.05). RESULTS The custom anatomic-contour abutment (Inclusive) showed the lowest load to fracture, and the stock anatomic-contour (AstraTech ZirDesign) the second lowest load to fracture. These were significantly lower than all other abutments (P<.05). The highest overall fracture strength was of a zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured), which was significantly greater than all other abutments (P<.05). Anatomic-contour zirconia abutments fractured at an average of 275 N compared with the average fracture load of 842 N for zirconia abutments with titanium component (P<.05). CONCLUSION The stock zirconia abutment with a titanium ring and the zirconia abutment with a titanium core-hexagon (Legacy Straight Contoured) had significantly greater fracture resistance than that of any of the 1-piece anatomic-contour zirconia abutments tested.

Using digitally coded healing abutments and an intraoral scanner to fabricate implant-supported, cement-retained restorations

The accuracy of conventional impression materials and stone dies has been a consistent challenge for clinicians. As an alternative, intraoral scanning technology has the potential to resolve this problem. This clinical report describes the step-by-step technique necessary to scan digitally coded healing abutments with an intraoral scanner and generate implant abutments and cement-retained restorations without the use of impression materials, dental stone, or implant impression copings and analogs.

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.

Influence of recasting different types of dental alloys on gingival fibroblast cytotoxicity

STATEMENT OF PROBLEM Surplus alloy from the initial casting is commonly reused with the addition of new alloy. This recasting procedure could affect the cytotoxicity of dental alloys. PURPOSE The purpose of this in vitro study was to evaluate the effect of repeated casting of high-noble and base metal alloys on gingival fibroblast cytotoxicity. MATERIAL AND METHODS Disk-shaped specimens (5 × 2 mm, n=60) of a high-noble (Au-Pt) and 2 base metal (Ni-Cr and Cr-Co, n=20) alloys were prepared with 100% new alloy and 50%, 65%, and 100% once recast alloy. The elemental composition of specimens was analyzed with X-ray energy-dispersive spectroscopy. Five specimens from each group were conditioned in saline with 3% fetal bovine serum albumin. The conditioning media were analyzed for elemental release with atomic absorption spectroscopy. Cytotoxic effects were assessed on human gingival fibroblast with a 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyl tetrazolium bromide (MTT) colorimetric assay. The data were analyzed with 1-way and 2-way ANOVA and Tukeys HSD multiple comparison test (α-=.05). RESULTS Elemental compositions of Co-Cr and Au-Pt alloys were significantly different among casting protocols. Elemental release of Co-Cr and Ni-Cr alloys was significantly different between new and recast specimens (P<.001). Nickel release increased with recast alloy addition. The 2-way ANOVA showed a significant effect of the casting procedure (P<.001) alloy group (P<.001) and their interaction for cytotoxicity (P<.001). The Ni-Cr alloy groups with 65% and 100% recast alloy had lower cellular activity than all other specimens (P<.001). CONCLUSIONS The results of this study indicated that alloys containing nickel have increased cytotoxic effects and that composition of the alloys affected the cytotoxicity. Furthermore, recasting nickel-containing alloys with 65% surplus metal addition significantly increased the cytotoxic activity.

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.

In vitro evaluation of color replication of metal ceramic specimens using visual and instrumental color determinations

STATEMENT OF PROBLEM It remains unclear whether or not the performance of intraoral colorimetric devices is accurate. PURPOSE The purpose of this study was to evaluate the color replication of metal ceramics using an intraoral colorimeter and visual shade determination. MATERIAL AND METHODS Twenty-five metal ceramic specimens were prepared to match 5 different shades (A1, B1, C3, D3, A3.5) of the Vitapan Classical shade guide. Five clinicians determined the shades of the specimens using the same shade guide. The shade determination was based on the agreement of at least 3 of the 5 observers. Instrumental shade determinations were made with an intraoral colorimeter (ShadeEye NCC) to obtain results in terms of the Vitapan Classical shade guide. Based on these shade determinations, 50 additional metal ceramic specimens (25 visually determined and 25 instrumentally determined) were prepared. The master (initial) and definitive (additional) specimens were analyzed with a spectrophotometer. L*, a*, b* values of each specimen were measured, and the color difference between the master and definitive specimens was calculated. The Wilcoxon signed rank test was used to analyze the color difference (ΔE) values (α=.05). RESULTS Visual shade determination produced lower ΔE values than instrumental shade determination. The differences between ΔE values of different shade determination methods were significant for master specimens of the shades B1 and A3.5 (P=.02). The ΔE value calculated from the result of instrumental determination of shade B1 (ΔE=2.97) was within the clinically acceptable limit (ΔE=3.5), whereas the ΔE value for A3.5 (4.03) exceeded the limit for clinical acceptability. The ΔE values for C3 exceeded the acceptable limit for both shade determination methods (ΔE>3.5). CONCLUSIONS Color replication of metal ceramic specimens using visual shade determination was more accurate compared to instrumental shade determination. The replication of the high-value shades (A₁-B₁) was observed to be reliable with both shade determination methods.

Effects of shade tab arrangement on the repeatability and accuracy of shade selection

STATEMENT OF PROBLEM Appropriate and repeatable shade matching using visual shade selection remains a challenge for the restorative dentist. PURPOSE The purpose of this study was to evaluate the effect of different arrangements of a shade guide on the repeatability and accuracy of visual shade selection by restorative dentists. MATERIAL AND METHODS Three Vitapan Classical shade guides were used for shade selection. Seven shade tabs from one shade guide were used as target shades for the testing (A1, A4, B2, B3, C2, C4, and D3); the other 2 guides were used for shade selection by the subjects. One shade guide was arranged according to hue and chroma and the second was arranged according to value. Thirteen male and 22 female restorative dentists were asked to match the target shades using shade guide tabs arranged in the 2 different orders. The sessions were performed twice with each guide in a viewing booth. Collected data were analyzed with Fishers exact test to compare the accuracy and repeatability of the shade selection (α=.05). RESULTS There were no significant differences observed in the accuracy or repeatability of the shade selection results obtained with the 2 different arrangements. When the hue/chroma-ordered shade guide was used, 58% of the shade selections were accurate. This ratio was 57.6% when the value-ordered shade guide was used. The observers repeated 55.5% of the selections accurately with the hue/chroma-ordered shade guide and 54.3% with the value-ordered shade guide. CONCLUSIONS The accuracy and repeatability of shade selections by restorative dentists were similar when different arrangements (hue/chroma-ordered and value-ordered) of the Vitapan Classical shade guide were used.