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The Effect of Ceramic Thickness and Resin Cement Shades on the Color Matching of Ceramic Veneers in Discolored Teeth

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  ORIGINAL ARTICLE The effect of ceramic thickness and resin cement shadeson the color matching of ceramic veneers in discolored teeth Wenzhong Xing 1 ã Xiaodong Chen 1 ã Dafei Ren 1 ã Kangru Zhan 1 ã Yining Wang 2 Received: 11 May 2016/Accepted: 18 November 2016   The Society of The Nippon Dental University 2017 Abstract  The objective of this study was to analyze theeffects of ceramic material thickness and resin cementshade on the color matching of ceramic veneers at the graytooth structures. Seventy-two artificial maxillary rightcentral incisor teeth (C2 shade) were prepared according toveneer tooth preparation in practice. Ceramic materials(LT, A2 shade, IPS e.max Press) were selected to fabricatethe 0.50- and 0.75-mm thick veneers at the body region.The ceramic veneer specimens were bonded to the artificialteeth by the 6 shades of resin cements (Variolink Veneer:shades of HV ? 3, LV-2, LV-3; and RelyX TM Veneer:shades of WO, TR, A3). A clinical spectrophotometer(Crystaleye, Olympus) was used to measure the colorparameters. The color differences ( D E   values) of ceramicveneers and A2 shade tab (Vitapan Classical, Vita) and C  * ab  values were calculated. The results of three-wayANOVA indicated that the  D E   values of ceramic veneerand A2 shade tab were significantly different in thethickness of ceramic materials, shades of resin cements,and measuring regions (  p \ 0.001). There were significantdifferences in 0.50-mm-thick ceramic veneers that exhib-ited higher  D E   values compared with veneers that were0.75-mm thick. Tukey’s HSD test showed that the average D E   values in body region were significantly smaller thanthat in cervical and incisal regions. The color matching of ceramic veneers was significantly influenced not only bythe ceramic thickness and the resin cement shades but alsothe tooth regions. Keywords  Ceramic veneer    Thickness    Resin cement   Color difference Introduction The popularity of porcelain veneers has been attributed totheir superior optical property, increased translucency, andimprovedesthetics[1].Asaconservativetechnique,patientsand clinician prefer these restorations due to minimal toothreduction compared to other full coverage restorations [2].The preparations of ceramic veneers are mostly limited totheenamellayer,inordertoobtainadurablebondinginterfaceand achieve greater clinical longevity [3]. Accordingly, thethicknessofceramicmaterialswasrestrictedbytheamountof toothreduction.Ideally,athintranslucentceramicbondedtoanon-discolored tooth provides an esthetically pleasing cera-micveneerrestoration[4].Ifaceramicveneerwasplacedonagrayunderlyingtoothstructure,itmightresultindiscolorationand shadowing of the veneer restorations [5, 6]. Therefore, clinicians should take care to achieve a good color matchingforceramicveneersduetothematerial’slimitedthicknessandhigh translucency [7].Color matching in dentistry has traditionally been per-formed with shade guides according to the color of healthyadjacent natural tooth [8]. Because the desirable color of ceramic veneers and the color of underlying tooth structurecannot always be chosen by the clinicians, the shades andthickness of ceramic materials and the shades of resincements become important variables in manipulating thefinal color of ceramic veneers [7, 9]. In practice, the cor- responding try-in pastes in the resin cement system can be &  Yining 1 Department of Prosthetics, Dalian Stomatological Hospital,Dalian 116021, China 2 Key Laboratory for Oral Biomedical Engineering, Ministryof Education, School and Hospital of Stomatology, WuhanUniversity, 237 Luoyu Road, Wuhan 430079, China  1 3 OdontologyDOI 10.1007/s10266-016-0287-9  used to evaluate the color matching of veneers and predictthe final esthetic effects of veneers [10]. When the resultantcolor of the ceramic veneers does not match the expectedcolor, the different shades of resin cements could beexpected to modify the final color of ceramic veneer toachieve the good color matching [5, 7, 9, 11]. The purpose of this study was to analyze the effect of the thickness of ceramic materials and resin cement shadeson the color matching of ceramic veneers at the gray toothstructures. The null hypothesis was that the final color of ceramic veneers would not be affected by ceramic thick-ness and resin cement shades. Materials and methods One heat-pressed glass-ceramic material and six shades of resin cements were evaluated in this study. Theflowchart of experimental design is in Fig. 1. Fabrication of ceramic veneers Seventy-two artificial maxillary right central incisor teeth(C2 shade, Yamahachi, Yamahachi Dental Mfg. Co.,Japan) were used to simulate the natural discolored teeth.The root section of artificial tooth was fabricated with self-curing acrylic resin (Shanghai Medical Equipment Co.,LTD., China) to position the artificial tooth in standardmaxillary model (Nisshin Corporation, Japan). These arti-ficial teeth were prepared using a veneer teeth preparatorykit (NTI-Set 1752, NTI-Kahla GmbH, Germany) accordingto the clinical procedure. The tooth reductions wereachieved to 0.3, 0.5, and 0.7 mm at the cervical, body, andincisal regions, respectively. Preparation depth was evalu-ated by relining a silicone index (Silagum putty soft, DMG,Hamburg, Germany) of uncut tooth structure. The incisalfinish line of artificial tooth was prepared for a windowdesign and the cervical margin was placed at the crown partof the cemento-enamel junction about 1.0 mm.The ceramic veneer samples were of the same mor-phology and curve on the buccal surface using the methodof impression duplicating wax patterns. The buccal surfacemorphology of the artificial teeth and root was duplicatedwith impression materials (Honigum and Silagum, DMG,Hamburg, Germany) (Impression I). After the teethpreparation, the molten wax was put into impression I, andthe prepared artificial tooth was inserted into the impres-sion. The artificial tooth and duplicating wax pattern weretaken out together after the wax solidified. The wax pat-terns were checked with the loupe (Shanghai optical Fig. 1  Flowchart of experiment designOdontology  1 3  instrument factory, China) and repaired when the edgeswere defective. The wax patterns were then imbedded andpressed with ceramic ingots (IPS e.Max, LT, A2 shade,Ivoclar, Vivadent, Liechtenstein) according to the manu-facturer’s instructions. The ceramic veneer samples werethe specimens of the 0.50-mm-thick group.A ceramic veneer sample of the 0.50-mm-thick groupwas selected and fixed on the prepared resin abutment toothwith 0.25-mm-thick double-faced adhesive tape. The edgesof ceramic veneer and resin abutment were sealed with thewax. Then, the buccal surface impression of the combi-nation ceramic veneer with resin teeth and the root sectionwas taken with impression materials (Honigum and Sila-gum, DMG, Hamburg, Germany) (Impression II). The waxpatterns of 0.75-mm-thick group were fabricated usingImpression II and imbedded and pressed using the abovemethods.The ceramic veneer specimen was adjusted to seat on itscorresponding artificial teeth. All ceramic specimens werecleaned using the ultrasonic in distilled water for 10 min.The buccal surfaces of ceramic veneers were glazed withcolorless glaze liquid (Ivoclar Vivadent, Liechtenstein)according to the manufacturer’s instructions. The thicknessof ceramic veneers in the cervical, body, and incisal areawas measured by the thickness gauge with accuracy0.01 mm (Weihai measuring implement factory co., LTD,China). The bonding of ceramic veneer Thirty-six ceramic veneer samples in each thickness cate-gory were randomly divided into six groups ( n  =  6)according to the color parameters of ceramic veneersbefore cementation. Six resin cement shades were selectedfrom two resin cement systems, corresponding to shadesLV-3, LV-2, HV ? 3 (Variolink Veneer, Ivoclar Vivadent,Liechtenstein) and WO, TR, A3 (RelyX TM Veneer, 3MESPE, USA). The bonding process of each resin cementsystem was undertaken according to the manufacturer’sinstructions. The resin cement was placed on the bondingsurface of the ceramic veneers and gently pressed onto theresin artificial teeth. A light-polymerizing unit (MiniLED TM , Satelec, France) was used to cure for 5 s. Theexcess resin cements were removed and then curing con-tinued for 40 s. The bonded specimens were stored inphysiological saline for 24 h at 37   C to ensure completepolymerization. Color measurement The right maxillary lateral incisor and left maxillary centralincisor in the maxillary standard model (Nisshin Corpora-tion, Japan) were replaced by resin artificial teeth (A2shade, Yamahachi, Yamahachi dental Mfg., co. Japan). Tosimulate the clinical situation, the maxillary standardmodel with ceramic veneer samples was mounted in ablack inspection box (Crystaleye, Olympus, Japan) thatsimulates the dark background of the oral cavity. A dentalspectrophotometer (Crystaleye, Olympus, Japan) was usedto measure the color parameters of specimens in the cer-vical, body, and incisal regions: (1) the prepared resinartificial teeth, (2) the ceramic veneer specimens before thebonding treatment, and (3) the ceramic veneer specimensafter cementation. Calculation of color difference The color differences were calculated using the followingformula:  D E  *  =  [(  L  * 1  -  L  * A2 ) 2 ?  ( a * 1  -  a * A2 ) 2 ?  (- b * 1  -  b * A2 ) 2 ] 1/2 ; the chroma of the ceramic veneer spec-imens were calculated by the following formula: C  * ab  =  ( a * 2 ?  b * 2 ) 1/2 .In order to determine the color effect of resin cement onthe ceramic veneers, the  D E   value of 3.3 was consideredthe clinically unacceptable threshold in this study [12–14]. Statistical analysis The three-way ANOVA was used to analyze the maineffect of the thickness of ceramic materials, the shade of resin cements, and the measuring regions on the colordifferences ( D E   values) of ceramic veneers and A2 shadetab (Vita Classical Shade Guide, Vita Zahnfabrik, Ger-many). Tukey’s HSD test was used to evaluate within-group effects of the cement shades and the color measuringregions on the  D E   values at each ceramic thickness( a  =  0.05). Results The average thickness of ceramic veneers in 0.50-mm-thick group is 0.34, 0.51, and 0.73 mm in cervical, body,and incisal region, respectively (Table 1). The thickness of the 0.75-mm-thick specimens was about more than0.20 mm in three regions compared with 0.50-mm-thick group. The  L  *,  a *, and  b * values of the seventy-two pre-pared artificial teeth were smaller standard deviations and95% confidence intervals in Table 2. The color parametersof the shade guide for the A2 shade tab in the Crystaleyesoftware (Crystaleye Application Ver. 1.4, Olympus,Japan) are as follows: cervical  L  *71.9,  a *1.4,  b *18.5; body  L  *72.7,  a *1.0,  b *18.8; incisal  L  *68.2,  a *0.3,  b *14.5.Distributions of the  L  * and  C  * ab  values of 0.50- and0.75-mm-thick specimens are presented in Figs. 2, 3. The color parameters of ceramic veneers cemented with LV-3, Odontology  1 3  LV-2 or TR shade resin cements have similar distributionof   L  * and  C  * ab  values. The color parameters of ceramicveneers cemented with WO shade resin cement werelocated in the high  L  * value or low  C  * ab  value region. The  L  * and  C  * ab  values of the ceramic veneers cemented byHV ? 3 shade resin cement were close to the values of A2shade tab in body region. The  D E   values between ceramicveneers and A2 shade tab are presented in Table 3. Thesevalues ranged from 1.9 to 6.5 for the 0.5 mm-thick ceramicveneer specimens and from 1.0 to 5.9 for the 0.75-mm-thick specimens. The highest D E   value was observed in thecervical regions of 0.50-mm-thick cemented with LV-3shade, whereas the 0.75-mm-thick ceramic veneerscemented with the WO shade exhibited the lowest D E   value in the body regions.The results of three-way ANOVA showed that the D E   values were influenced by ceramic thickness, shade of resin cements, and measuring regions, as well as theinteraction terms of these three variables (  p \ 0.001). The Table 1  The means, standarddeviations, and 95% confidenceintervals of the thickness of ceramic veneer specimens (mm)Group Region Thickness 95% confidence intervalsMean (sd) Lower bound Upper bound0.50-mm-thick Cervical 0.34 (0.03) 0.34 0.35Body 0.51 (0.01) 0.50 0.51Incisal 0.73 (0.03) 0.72 0.740.75-mm-thick Cervical 0.51 (0.03) 0.50 0.52Body 0.73 (0.05) 0.72 0.75Incisal 0.93 (0.04) 0.91 0.94 Table 2  The means, standard deviations, and 95% confidence intervals of   L  *,  a *, and  b * color parameters of resin tooth after preparationCervical Body IncisalMean (sd) 95% confidence intervals Mean (sd) 95% confidence intervals Mean (sd) 95% confidence intervalsLower bound Upper bound Lower bound Upper bound Lower bound Upper bound  L  * 64.2 (0.8) 64.0 64.4 67.9 (0.7) 67.7 68.1 66.5(0.6) 66.3 66.6 a * 3.5 (0.2) 3.5 3.6 2.3 (0.3) 2.2 2.4 1.2 (0.3) 1.1 1.3 b * 20.7 (0.9) 20.4 20.9 22.1 (0.6) 21.9 22.2 19.0 (1.2) 18.7 19.3 Fig. 2  The distribution of   L  * and  C  * ab  of 0.50-mm-thick ceramicspecimens in the cervical, body, and incisal regions  Fig. 3  The distribution of   L  * and  C  * ab  of 0.75-mm-thick ceramicspecimens in the cervical, body, and incisal regionsOdontology  1 3
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