David G. Gratton

An In Vitro Comparison of Vertical Marginal Gaps of CAD/CAM Titanium and Conventional Cast Restorations

PURPOSE To determine if there was a significant difference between the vertical marginal openings of cast restorations, computer-aided design, and computer-aided machining restorations. MATERIALS AND METHODS Ten working dies were created from a single master die and used to fabricate ten restorations in each of the following groups: computer-aided design/computer-assisted machining (CAD/CAM), WAX/CAM, and WAX/CAST. The CAD/CAM titanium restorations were fabricated using the scanning and crown design modules of the KaVo Everest system. The WAX/CAM titanium restorations were fabricated using the double scan technique with the KaVo Everest system. The WAX/CAST high noble copings were fabricated using the conventional lost wax casting technique. The restorations were seated on the master die, and high-resolution digital photographs were made of the marginal area on all four sides. The vertical marginal opening was then measured using a calibrated digital software program. One-way ANOVA and Tukeys post hoc tests were used to determine the presence of statistically significant differences. RESULTS The vertical margin openings were CAD/CAM: 79.43 +/- 25.46 microm; WAX/CAM: 73.12 +/- 24.15 microm; WAX/CAST: 23.91 +/- 9.80 microm. There was a statistically significant difference between the WAX/CAST group and the remaining groups. CONCLUSIONS There was no difference between the vertical marginal gaps of the CAD/CAM and WAX/CAM. The WAX/CAST technique resulted in smaller vertical marginal gaps than either CAD/CAM or WAX/CAM.

3D and 2D Marginal Fit of Pressed and CAD/CAM Lithium Disilicate Crowns Made from Digital and Conventional Impressions

PURPOSE This in vitro study evaluated the 3D and 2D marginal fit of pressed and computer-aided-designed/computer-aided-manufactured (CAD/CAM) all-ceramic crowns made from digital and conventional impressions. MATERIALS AND METHODS A dentoform tooth (#30) was prepared for an all-ceramic crown (master die). Thirty type IV definitive casts were made from 30 polyvinyl siloxane (PVS) impressions. Thirty resin models were produced from thirty Lava Chairside Oral Scanner impressions. Thirty crowns were pressed in lithium disilicate (IPS e.max Press; 15/impression technique). Thirty crowns were milled from lithium disilicate blocks (IPS e.max CAD; 15/impression technique) using the E4D scanner and milling engine. The master die and the intaglio of the crowns were digitized using a 3D laser coordinate measurement machine with accuracy of ±0.00898 mm. For each specimen a separate data set was created for the Qualify 2012 software. The digital master die and the digital intaglio of each crown were merged using best-fitting alignment. An area above the margin with 0.75 mm occlusal-gingival width circumferentially was defined. The 3D marginal fit of each specimen was an average of all 3D gap values on that area. For the 2D measurements, the marginal gap was measured at two standardized points (on the margin and at 0.75 mm above the margin), from standardized facial-lingual and mesial-distal digitized sections. One-way ANOVA with post hoc Tukeys honestly significant difference and two-way ANOVA tests were used, separately, for statistical analysis of the 3D and 2D marginal data (alpha = 0.05). RESULTS One-way ANOVA revealed that both 3D and 2D mean marginal gap for group A: PVS impression/IPS e.max Press (0.048 mm ± 0.009 and 0.040 mm ± 0.009) were significantly smaller than those obtained from the other three groups (p < 0.0001), while no significant differences were found among groups B: PVS impression/IPS e.max CAD (0.088 mm ± 0.024 and 0.076 mm ± 0.023), C: digital impression/IPS e.max Press (0.089 mm ± 0.020 and 0.075 mm ± 0.015) and D: digital impression/IPS e.max CAD (0.084 mm ± 0.021 and 0.074 mm ± 0.026). The results of two-way ANOVA revealed a significant interaction between impression techniques and crown fabrication methods for both 3D and 2D measurements. CONCLUSIONS The combination of PVS impression method and press fabrication technique produced the most accurate 3D and 2D marginal fits.

Human Perception of Dental Porcelain Translucency Correlated to Spectrophotometric Measurements

PURPOSE This study evaluated the relationship between instrumental measurements and subjective visual assessment of differences in dental porcelain translucency. MATERIALS AND METHODS Unshaded feldspathic porcelain was used with controlled amounts of tin oxide to create two groups of 12-mm diameter disks with incremental changes in opacity. Contrast ratio (CR = Yb/Yw) was determined with a spectrophotometer, and used as a measure of porcelain translucency (Group A = 0.20 to 0.40; Group B = 0.6-0.8). Within each group, there were 14 specimens with 11 CRs. Three observer groups (first year dental students, residents, faculty with >10 years of shade matching experience) were recruited to assess the translucency between porcelain disks under two lighting conditions (reflected light, transmitted light). Each subjects ability to distinguish between specimens of differing translucency was determined. Descriptive statistics and three-way ANOVA followed by a post-hoc Tukey-Kramer test were used to evaluate the translucency perception threshold (TPT) of subjects (alpha= 0.05). RESULTS The overall mean TPT (DeltaC) was 0.07, while 50% of the subjects could perceive a 0.06 CR difference between porcelain specimens. Three-way ANOVA revealed a significant difference in translucency perception among the observer groups (p < 0.0001), whereas the main effects for porcelain opacity (p= 0.3038) and lighting condition (p= 0.0645) were not significant, and no significant interactions were found. Post-hoc Tukey-Kramer test indicated that the mean TPT observed in the faculty group (DeltaC = 0.04) was significantly lower than those observed in student (DeltaC = 0.09) and resident groups (DeltaC = 0.08), while there was no significant difference between students and residents. CONCLUSIONS The overall mean TPT of all subjects was 0.07, and 50% of the study population perceived a 0.06 CR difference in translucency. Increased shade matching experience (> or =10 years) significantly improved the ability to perceive differences in translucency; however, neither the viewing condition nor porcelain opacity affected the perceived translucency threshold.

Ceramic materials for porcelain veneers: Part II. Effect of material, shade, and thickness on translucency

STATEMENT OF PROBLEM Information regarding the differences in translucency among new ceramic systems is lacking. PURPOSE The purpose of this study was to compare the relative translucency of the different types of ceramic systems indicated for porcelain veneers and to evaluate the effect of shade and thickness on translucency. MATERIAL AND METHODS Disk specimens 13 mm in diameter and 0.7-mm thick were fabricated for the following 9 materials (n=5): VITA VM9, IPS Empress Esthetic, VITA PM9, Vitablocks Mark II, Kavo Everest G-Blank, IPS Empress CAD, IPS e.max CAD, IPS e.maxPress, and Lava Zirconia. VITA VM9 served as the positive control and Lava as the negative control. The disks were fabricated with the shade that corresponds to A1. For IPS e.maxPress, additional disks were made with different shades (BL2, BL4, A1, B1, O1, O2, V1, V2, V3), thickness (0.3 mm), and translucencies (high translucency, low translucency). Color coordinates (CIE L∗ a∗ b∗) were measured with a tristimulus colorimeter. The translucency parameter was calculated from the color difference of the material on a black versus a white background. One-way ANOVA, the post hoc Tukey honestly significant difference, and the Ryan-Einot-Gabriel-Welsch multiple range tests were used to analyze the data (α=.05). RESULTS Statistically significant differences in the translucency parameter were found among porcelains (P<.001) according to the following rank: VM9>PM9, Empress Esthetic>Empress CAD>Mark II, Everest, e.max CAD>e.max Press>Lava. Significant differences also were noted when different shades and thickness were compared (P<.001). CONCLUSIONS Different ceramic systems designed for porcelain veneers present varying degrees of translucency. The thickness and shade of lithium disilicate ceramic affect its translucency. Shade affects translucency parameter less than thickness.

Ceramic materials for porcelain veneers. Part I: Correlation between translucency parameters and contrast ratio.

STATEMENT OF PROBLEM Different parameters are used in the literature to describe translucency, making it difficult for clinicians to find clear information on ceramic translucency and compare studies. PURPOSE The purpose of this study was to assess the correlation between the contrast ratio (CR) and translucency parameter (TP) when the translucency of different types of ceramic systems is compared. MATERIAL AND METHODS Disks 13 mm in diameter and 0.7 mm thick were fabricated for the following materials (n=5): VITA VM9, VITA PM9, IPS Empress CAD, IPS e.max CAD, IPS e.maxPress, and Lava Zirconia. VITA VM9 served as positive control, while Lava Zirconia served as negative control. The luminous reflectance (Y) and color coordinates (CIE L* a* b*) of the specimens were measured with a tristimulus colorimeter. The CR (CR=Yb/Yw) was calculated from the reflectance of the light of the material on a black backing (Yb) to the reflectance on a white backing (Yw). The TP (TP=[(Lb*Lw*)(2+)(ab*-aw*)(2+)(bb*-bw*)(2) ](1/2)) was calculated from the color difference of the material on a black versus a white background. One-way ANOVA based on ranked data and the Pearson and Spearman rank correlation tests were used to analyze the data (α=.05). RESULTS A significant correlation between CR and TP was found when all specimens were included (P<.001). The coefficient of -0.99 indicated a strong decreasing relationship between the 2 variables. CONCLUSIONS Either CR or TP can be used to evaluate the relative translucency of ceramic systems.

Ultimate tensile strength of five interchangeable prosthetic retaining screws

Implant prosthetic retaining screws have been reported to serve as built-in safety factors to protect against overload in the implants “vertical stack,” although loosening and fracture of retaining screws are often considered complications. Manufacturers have responded by introducing interchangeable prosthetic retaining screws, which can give the clinician the impression that interchanging screws will not have an adverse effect on the remainder of the implant complex and for the integration of the implant itself. The objective of this investigation was to measure the ultimate tensile strength of four retaining screws from three manufacturers and two alloy types (gold and titanium) using the Nobelpharma gold prosthetic retaining screw as a standard for the comparisons. Five screws of each type were loaded in tension in an Instron Universal Testing Machine until fracture occurred. A Tukey-Kramer Test (significance level =.05) analysis of the data showed that all of the interchangeable prosthetic retaining screws were significantly different from the control screws in respect to ultimate tensile strength. The data suggest that interchanging prosthetic retaining screws will influence their built-in safety feature.

Biomechanical study of SonicWeld Rx pin in cortical bone graft layering technique.

PURPOSE The purpose of this in vitro study was to determine the biomechanical values of the SonicWeld Rx pin system in comparison with titanium screws for use in onlay cortical bone grafting. MATERIALS AND METHODS In this study, 2.1-mm SonicWeld Rx pins and 1.5-mm titanium screws, measuring 7 mm in length, were used. Sawbone blocks were positioned to simulate an onlay bone graft, and the pins and screws were used to replicate bicortical fixation. Four groups were designated for vertical load application, and failure of the fixation was determined when stability was compromised. Study groups consisted of fixation material types and number of fixation appliances. A Bose Electroforce 3300 system was used to deliver the force and to obtain data. RESULTS Comparison of SonicWeld Rx 1-pin fixation with titanium 1-screw fixation showed similar peak resistance loads. Average peak loading resistance for SonicWeld Rx 1-pin fixation was 65.54 N and that for titanium 1-screw fixation was 59.37 N, with no significant difference (P = .9698). Average peak strength of SonicWeld Rx 2-pin and titanium 2-screw fixations was 110.24 and 97.3 N, respectively, with no significant difference (P = .1041). CONCLUSION Based on the measured biomechanical values, SonicWeld Rx fixation can withstand similar peak load forces compared with that of titanium screw fixation. The SonicWeld Rx fixation can be an alternative method of fixation for onlay bone grafting in dentoalveolar ridge augmentation.

Critical Thinking Theory to Practice: Using the Expert’s Thought Process as Guide for Learning and Assessment

Critical thinking skills are essential for the successful dentist, yet few explicit skillsets in critical thinking have been developed and published in peer-reviewed literature. The aims of this article are to 1) offer an assessable critical thinking teaching model with the experts thought process as the outcome, learning guide, and assessment instrument and 2) offer three critical thinking skillsets following this model: for geriatric risk assessment, technology decision making, and situation analysis/reflections. For the objective component, the student demonstrates delivery of each step in the thought process. For the subjective component, the student is judged to have grasped the principles as applied to the patient or case. This article describes the framework and the results of pilot tests in which students in one year at this school used the model in the three areas, earning scores of 90% or above on the assessments. The model was thus judged to be successful for students to demonstrate critical thinking skillsets in the course settings. Students consistently delivered each step of the thought process and were nearly as consistent in grasping the principles behind each step. As more critical thinking skillsets are implemented, a reinforcing network develops.

Patterns of morphological integration in the dental arches of individuals with malocclusion

In humans, there is a large range of variation in the form of the maxillary and mandibular dental arches. This variation can manifest as either prognathism or retrognathism in either or both arches, which can cause malocclusion and lead to abnormal masticatory function. This study aims to identify aspects of variation and morphological integration existing in the dental arches of individuals with different types of malocclusion.