Alma Dozic

The influence of porcelain layer thickness on the final shade of ceramic restorations

STATEMENT OF PROBLEM Ceramic restorations should be made of porcelain layers of different opacity, shade, and thickness in order to provide a natural appearance. By means of CAD/CAM layering technology such as CICERO, it is feasible to produce all-ceramic crowns with porcelain layers of predetermined thickness. However, it is not yet known whether changes in thickness of these porcelain layers within the clinically available space can perceivably influence the overall shade of the restoration. PURPOSE The purpose of this study was to determine, quantitatively, the effect of different thickness ratios of opaque porcelain (OP) and translucent porcelain (TP) layers on the overall shade of all-ceramic specimens. MATERIAL AND METHODS The CIELAB values of 5 assembled specimens, each consisting of 2 or 3 discs (CORE 0.70 mm/OP--0, 0.25, 0.50, 0.75, or 1.00 mm/TP 1.00, 0.75, 0.50, 0.25, or 0 mm) were determined with a spectrophotometer for the Vita shades A1, A2, and A3. Distilled water was used to attain optical contact between the layers. Black or white backgrounds were used to assess the influence of the background on the final shade. Color differences (DeltaE) between layered specimens were determined. Correlation between the thickness ratio and the L*, a*, and b* values was calculated by 2-tailed Spearman correlation analysis. RESULTS The results indicated that small changes in OP/TP thickness ratio can perceivably influence the final shade of the layered specimens (DeltaE>1). Redness a* and yellowness b* increased with the thickness of OP for all shades. Redness a* (P<.01 for all shades) correlated more strongly with thickness than yellowness b* (P<.01 for A1 and A3; P<.05 for A2). The lightness (L*) was shade dependent. The correlation (r) between OP/TP thickness and L* was 0.975 (P<.01) for shade A1, 0.700 (not statistically significant) for shade A2, and 0.900 (P<.05) for shade A3. CONCLUSION Small changes in thickness and shade of opaque and translucent porcelain layers can influence the final shade of the layered porcelain specimen.

Perceptibility and acceptability thresholds for colour differences in dentistry

INTRODUCTION Data on acceptability (AT) and perceptibility thresholds (PT) for colour differences vary in dental literature. There is consensus that the determination of ΔE* is appropriate to define AT and PT, however there is no consensus regarding the values that should be used. The aim of this clinical review was to provide a systematic approach to the topic of colour science of high clinical relevance to dental research. MATERIALS AND METHODS MEDLINE/PubMed, WoS and EBSCO databases were searched up to January 7, 2013; the outcome was restricted to English, and to clinical studies were spectrophotometers were used for measurement. RESULTS Forty-eight studies were eligible and met the inclusion criteria. Of the 48 studies there appeared to be a trend in their source references: 44% referred to the same study for the PT (ΔE*=1); and 35% referred to the same article for the AT (ΔE*=3.7). CONCLUSIONS More than half the studies defined PT as ΔE*=1, and one third of the studies referred to ΔE*=3.7 as the threshold at which 50% of observers accepted the colour difference. Most clinical studies refer to the same few in vitro literature that have attempted to determine PT and AT from decades ago.

Color coverage of a newly developed system for color determination and reproduction in dentistry

OBJECTIVES A newly developed system for color determination and reproduction is logically arranged and systematically combines a few components to acquire its broad color range. The objective was to evaluate color coverage of human teeth with the range of the new system and to compare it with other existing systems. METHODS The systems for color determination used in this study were: New system Standard (NS), New system Expanded (NE), Vita Classical (VC) and Vita 3D-Master (V3D) (Vita Zahnfabriek, Germany), Vintage Halo (VH) (Shofu, Japan), Chromascope (CH) (Ivoclar Vivadent, Lichtenstein). The tabs of all systems were measured with digital spectrophotometer, SpectroShade-Micro (MHT, Italy), and their L*a*b* values were compared with the L*a*b* values of 198 teeth (mean age=30.10; SD=13.15) to obtain their coverage errors. The ΔE≤1.6 was established as threshold for perceptibility. RESULTS Wilcoxon-signed rank test showed that the coverage of the teeth with the NE range was the best, as indicated by the lowest mean minimal ΔE value, followed by the NS range. Both ranges had statistically significant lower mean minimal ΔE values than all the other systems (p>0.01). The percentage of ΔE≤1.6 was significantly higher for NS and NE range than for the other systems (p>0.01). CONCLUSIONS The newly developed color determination and color reproduction system could cover the range of human teeth, used in this study, below the level of perceptibility (ΔE≤1.6) better than four other available contemporary systems.

Data Comparison Between Two Dental Spectrophotometers

OBJECTIVES The objective of this study was to clinically test whether the data from two different spectrophotometers, based on spot and surface measurements, can be compared. METHODS Under standardized clinical conditions two devices (Vita Easyshade and Spectro Shade-Micro) were used to record the color of three areas (cervical, middle, and incisal) per tooth for three upper maxillary anterior teeth in 102 participants. Each position was measured three times to attain an average for the CIE L*a*b* coordinates and to attain the corresponding Vita Classical shade tab integrated in the software of both devices. Vita tabs were also described as L*a*b* values using earlier published translations so that color differences (ΔE) could be calculated between them. RESULTS The regression analysis between the two devices showed that the independent correlation coefficients of the L*a*b* values are low. Yet when the suggested shade codes are compared with Vita colors instead of L*a*b*, 40% of the cases were equal and 51% were clinically acceptable. SIGNIFICANCE According to this study the two devices do not give a comparable shade selection output, and thus the exchange of L*a*b* values between the two spectrophotometers cannot be recommended.

The influence of varying layer thicknesses on the color predictability of two different composite layering concepts

OBJECTIVE Optical properties of teeth are mimicked by composite layering techniques by combining a relatively opaque layer (dentin) with more translucent layers (enamel). However, the replacing material cannot always optically imitate the tooth when applied in the same thickness as that of the natural tissues. The natural layering composite system is available in 2 concepts: (1) dentin (D) and enamel (E) have the same shade but with different translucencies; (2) D and E have different shades where E is always the same high translucent shade. The objective was to evaluate the influence of varying thicknesses of E and D composites on the overall color and on the translucency for both concepts. METHODS For each concept three composite brands were tested; Concept 1: Clearfil Photo Bright (Kuraray), Herculite XRV Ultra (Kerr), Venus Diamond (Heraeus Kulzer); Concept 2: Amaris (VOCO), CeramX Duo (DENTSPLY) and Point4 (Kerr). Two specimens of each shade (A1-A3) per composite were made of standardized thicknesses with a poly-acrylic mold and Teflon cover, making 36 specimens of wedge-like dimension. The L*a*b* values were measured three times against a white and black background (n=216). Students t-tests revealed significant levels between the average ΔE* values of the 3 areas for each composite. RESULTS Statistically significant differences (p<0.05) were found for all thicknesses and for all shades between the concepts. Concept 2 showed greater variations in ΔE* with increased thicknesses. SIGNIFICANCE Concept 2 composites are more sensitive to layer thickness changes, which implicates less predictability in a daily clinical routine.

De directe composietveneerbrug na extractie op jeugdige leeftijd

Zolang kinderen en adolescenten nog geen 20 jaar zijn, ligt het niet voor de hand om ‘permanente’ kronen en bruggen te plaatsen. Voorzover traditioneel kroon- en brugwerk permanent genoemd kan worden althans. Zolang de groei nog doorgaat, is het beter om zogenoemde semipermanente restauraties te vervaardigen. De directe composietveneerbrug is daar een voorbeeld van.

De definitieve keramische brug in de onderkaak

SamenvattingIn het vorige artikel (TP-Exkies, augustus 2009) beschreven we het computerondersteund ontwerpen (of CAD) en het computerondersteund produceren (of CAM) van geprefabriceerde tijdelijke kunststofbruggen. Deze tijdelijke bruggen worden uiteraard vervangen door meer permanente. Daarover gaat dit vervolgartikel.

I De tijdelijke kunststof brug

SamenvattingDoor de computer is er een tendens dat niet de tandarts in de mond, maar de tandtechnicus op het studiemodel het CAD-ontwerp voor de tijdelijke brug maakt en deze ook met behulp van de computer slijpt uit een blok of schijf kunststof1. In het eerste deel van deze serie over geprefabriceerde CADCAM-bruggen gaat het over het inLab-systeem van Cerec en het ZENO Tec-systeem van Wieland. Het tandtechnisch deel van deze beide systemen wordt getoond aan de hand van het vervaardigen van een achtdelige geprefabriceerde, tijdelijke CADCAM-brug in de onderkaak en van eenzelfde zesdelige brug in de bovenkaak.

De CAD/CAM-brug door de tandarts geoptimaliseerd door de porseleintechnicus (3)

SamenvattingIn voorgaande bijdragen beschreven we onderzoek waarbij de tandarts zelf door het maken van een extra tijdelijke brug, een bouwmodel (mock-up) kan verkrijgen voor een computerbrug. De anatomische mock-up brug wordt gescand met behulp van een laserstraal waardoor een digitaal model van de brug wordt gecreëerd. Vervolgens wordt het digitale bouwmodel van de brug computerondersteund verder ontworpen (CAD) en geproduceerd (CAM). De CAD/CAM-brug wordt daarna gefreesd uit een blok monochromatisch keramiek. (Afbeeldingen 1-5)

De CAD/CAM-brug door de tandarts (2)

SamenvattingEen CAD/CAM-brug is een restauratie die computerondersteund wordt ontworpen (CAD: computer-aided design) en computerondersteund geproduceerd (CAM: computer-aided manufacturing). Voor de CADprocedure is het nodig dat de tandarts een conventionele afdruk van de geprepareerde pijlerelementen maakt. De afdruk wordt naar het laboratorium gestuurd waar de afdruk wordt uitgegoten in gips. Het gipsmodel wordt vervolgens gescand, wat resulteert in een driedimensionale tekening van de pijlerelementen.Op deze digitale tekening ontwerpt de computer het bouwmodel van de pijlerkronen en het brugdeel. Dit digitale bouwmodel wordt naar de freesmachine gestuurd die de brug produceert (CAM) uit een blok keramiek.