Influence of framework design on the cervical color of metal ceramic crowns
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Influence of framework design on the cervical color of metal ceramic crowns

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Statement of problem. The replication of natural teeth, especially for single tooth restorations in patients with high ...

Statement of problem. The replication of natural teeth, especially for single tooth restorations in patients with high
esthetic needs, represents a challenge.
Purpose. The purpose of the study was to analyze the color of the cervical portion of single metal ceramic crowns
fabricated with different metal framework designs.
Material and methods. The color, as measured on the CIELAB color scale, of 3 different groups of restorations
(n=10) fabricated with a high noble metal alloy (V-Deltaloy) and feldspathic porcelain (Noritake Super Porcelain) was
analyzed with a colorimeter. Conventional metal ceramic crowns with metal facial margins were compared to metal
ceramic crowns with porcelain facial margins and a horizontal reduction of the metal framework (1.0 mm reduction)
or an additional vertical reduction (1.0 mm reduction). In all specimens, the finish line was positioned at a subgingival
or equigingival level. The 6 groups obtained by the combination of the levels of the 2 factors (framework extension
and finish line location) were examined with an ANOVA Fisher’s F-test and a post hoc Tukey’s HSD test (􀁟=.05).
Results. The mean color difference for all the groups was clinically acceptable (!􀁌<3.7). Conventional metal ceramic
crowns showed higher differences in relation to finish line location (!􀁌=2.34), while a vertical reduction of the framework
was related to lower values (!􀁌=0.96). Mean Lab* values were reported for all the groups of crowns. Statistically
significant differences were present for L*, a*, and b* values when related to framework extension. Considering each
value in relation to the interaction between framework extension and finish line location factors, significant differences
were present only for L* and a* values.
Conclusions. No significant differences in base shade were present among the investigated crowns. Nevertheless metal
ceramic crowns with vertical cut-back and porcelain facial margins presented more consistent results that tended to
be closer to those of natural teeth. (J Prosthet Dent 2011;106:310-318)

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Influence of framework design on the cervical color of metal ceramic crowns Document Transcript

  • 1. cervical color of metal ceramic crowns Gianluca Paniz, DDS, MS,a Yongjeong Kim, DDS, DMD, MS,b Haythem Abualsaud, BDT, MS,c and Hiroshi Hirayama, DDS, DMD, MSd School of Dental Medicine, Tufts University, Boston, Mass; University of Padova, Padova, Italy; College of Dentistry, King Saud University, Riyadh, Saudi ArabiaStatement of problem. The replication of natural teeth, especially for single tooth restorations in patients with highesthetic needs, represents a challenge.Purpose. The purpose of the study was to analyze the color of the cervical portion of single metal ceramic crownsfabricated with different metal framework designs.Material and methods. The color, as measured on the CIELAB color scale, of 3 different groups of restorations(n=10) fabricated with a high noble metal alloy (V-Deltaloy) and feldspathic porcelain (Noritake Super Porcelain) wasanalyzed with a colorimeter. Conventional metal ceramic crowns with metal facial margins were compared to metalceramic crowns with porcelain facial margins and a horizontal reduction of the metal framework (1.0 mm reduction)or an additional vertical reduction (1.0 mm reduction). In all specimens, the finish line was positioned at a subgingi-val or equigingival level. The 6 groups obtained by the combination of the levels of the 2 factors (framework extensionand finish line location) were examined with an ANOVA Fisher’s F-test and a post hoc Tukey’s HSD test ( =.05).Results. The mean color difference for all the groups was clinically acceptable (∆ <3.7). Conventional metal ceramiccrowns showed higher differences in relation to finish line location (∆ =2.34), while a vertical reduction of the frame-work was related to lower values (∆ =0.96). Mean Lab* values were reported for all the groups of crowns. Statisticallysignificant differences were present for L*, a*, and b* values when related to framework extension. Considering eachvalue in relation to the interaction between framework extension and finish line location factors, significant differ-ences were present only for L* and a* values.Conclusions. No significant differences in base shade were present among the investigated crowns. Nevertheless metalceramic crowns with vertical cut-back and porcelain facial margins presented more consistent results that tended tobe closer to those of natural teeth. (J Prosthet Dent 2011;106:310-318) If metal ceramic is selected as the restorative material for a crown in the esthetic zone, a vertical cut-back of approximately 1 mm is recommended on the facial metal framework/ porcelain facial margin to achieve an adequate esthetic result. If a conventional metal frame- work design is selected, deep subgingival margins might reduce the color impairment.Presented as a poster at the Greater New York Academy of Prosthodontics Annual Meeting, December 2006, New York, NY.a Adjunct Assistant Professor, Graduate & Postgraduate Prosthodontics, Department of Prosthodontics and Operative Dentistry,Tufts University; Adjunct Professor, Department of Prosthodontics, University of Padova, Dental School.b Associate Professor, Graduate and Postgraduate Prosthodontics, Department of Prosthodontics and Operative Dentistry.c Senior Specialist, College of Dentistry, King Saud University.d Professor, Division Head of Postgraduate Prosthodontics, Director of Graduate and Postgraduate Prosthodontics, Director ofAdvanced Education in Esthetic Dentistry, and Director of Advanced Dental Technology and Research program, Tufts University,School of Dental Medicine.The Journal of Prosthetic Dentistry Paniz et al
  • 2. November 2011 311 The replication of natural teeth metal framework reduction of 2 mm timate goal in achieving an accuratewith single tooth restorations in pa- coronally from the buccocervical line color match is to achieve the smallesttients with high esthetic needs and angle. With this design, metal was not possible ∆E value.34 The correlationexpectations represents a challenging visible at the external crown surface, between ∆E and clinical observationtask in restorative dentistry.1-4 An im- light transmission was increased, and was analyzed in an in vivo study ofportant consideration is color repro- the opaquing effect of metal and subjects treated with composite resinduction in the cervical portion, where opaque porcelain was eliminated in veneers. Within the limitation of thea thinner layer of restorative material the cervical region. Recent studies study, 3.7 was the average color dif-must be used to prevent harm to the have confirmed that the metal frame- ference among teeth rated as a matchpulpal tissue or interference with the work should be cut back a minimum in the oral environment.44 When ana-proper emergence profile.5-7 of 2 mm away from the shoulder to lyzing metal ceramic crowns, different Different materials and techniques avoid a color mismatch.33 However, results were obtained. Thresholds forhave been proposed to achieve an others show similar esthetic results acceptability were reduced to ∆E=1.7,improved esthetic result. The metal with less reduction of the metal while perceptibility was reduced toceramic crown is one of the most framework, which also provides im- ∆E=0.4. In addition, observers werepopular restorations since it com- proved porcelain support.27 more sensitive to and critical ofbines good esthetics with adequate One of the objective methods crowns whose color differed in red-strength, accurate fit, and long-term for evaluating color in dentistry is ness (∆a*) than crowns whose colorsurvival.8 Esthetic problems with this through colorimetric or spectropho- differed to the same extent in yellow-type of restoration are related to the tometric analysis.34-40 These instru- ness (∆b*).45 More recently, differentopaque porcelain layer used to mask ments use the CIELAB color scale, thresholds for perceptibility (∆E<2.6)the dark color of the underlying met- which identifies tooth color through and acceptability (∆E<5.5) of shadeal framework. Acting as a barrier to the black/white (L* value), green/red mismatch have been described in alight transmission, this opaque layer (a* value) and yellow/blue dimen- clinical setting and used in experimen-causes an impairment of color and sions (b* value).41 In an analysis of tal research.46,47translucency, which is more evident the color of natural, maxillary central The purpose of this study was toin the cervical portion, where the por- incisor teeth, Hasegawa et al42 found compare, through spectrophotomet-celain is thinner.2, 9-11 Furthermore, the significant variations in Lab* values ric digital technology, the color ofpresence of a facial, marginal metal along the axis of the surface of the the cervical portion of single metalcollar thick enough to support the teeth: L* was higher in the center; a* ceramic crowns fabricated with dif-overlying layers of porcelain and resist was higher in the cervical region and ferent metal framework designs. Con-metal deformation during porcelain significantly lower when approaching ventional metal ceramic crowns withfiring12,13 often becomes an esthetic the incisal edge; and b* was higher in metal margins (metal extended to theissue.14 To fulfill the esthetic require- the cervical area but with gradual and finish line) were compared with col-ments, collarless metal ceramic resto- significant reduction toward the in- larless metal ceramic crowns fabri-rations have been suggested, limiting cisal area. Older subjects had darker cated with different metal extensions.the extension of the metal framework and more yellowish color at the cen- Subgingival and equigingival marginto a certain distance from the margin ter of the natural tooth. Both reddish positions were evaluated. The null hy-of the preparation. Several techniques and yellowish colors of natural teeth pothesis was that there would be nohave been proposed to fabricate col- tended to increase from the incisal to color differences present in the cer-larless metal ceramic restorations, in- the cervical area, whereas translucen- vical portion of single metal ceramiccluding platinum foil techniques,14,15 cy decreased. In an in vitro study, the crowns fabricated with different met-the direct-lift technique,16 and the distribution of color was identified for al framework design and tested withwax technique.17-20 Research has con- 3 regions with respective mean Lab* equigingival and subgingival marginfirmed adequate marginal adapta- values of 71.4, 0.9, and 12.8 for the placement.tion21-24 and fracture resistance25-31 for incisal portion, 72.4, 1.2, and 16.2this type of restoration. In particular, for the middle portion, and 72.6, 1.5, MATERIAL AND METHODSto achieve adequate strength, a deep and 18.4 for the gingival portion.43chamfer preparation and no more The most commonly used method The color of 3 different marginthan 1 mm of unsupported ceramic for evaluating color differences among design groups of restorations (n=10)are recommended.27 specimens is through ∆L*, ∆a*, and fabricated with high noble metal alloy Analyzing the esthetic effect of ∆b*. Their combination is described (V-Deltaloy; Metalor Dental AG, Biel-metal ceramic restorations through as color difference (∆E), which is de- Bienne, Switzerland) and feldspathictransillumination and photography, termined by the following equation: porcelain, (Noritake Super Porcelain;Geller and Kwiatkowski32 proposed a ∆E = (∆L*2+ ∆a*2+∆b*2)1/2.34 The ul- Noritake Dental Supply Co, Nagoya,Paniz et al
  • 3. 312 Japan) was measured with a color- imeter (ShadeVision System; X-Rite, Inc, Grand Rapids, Mich). The sam- ple size was arbitrary as no a priori power analysis was performed, and no reliable estimate of within-group standard deviation for the population could be obtained. The conventional metal ceramic crowns with metal margins (group C) were compared with metal ceramic crowns with 2 different designs of porcelain facial margin. One group had a horizontal reduction of the metal framework 1 Different designs of metal framework tested. Conventional metal (group H: 1.0 mm reduction), and ceramic crowns (Cmc), metal ceramic crowns with horizontal re- the second had an additional vertical duction of metal framework (Hmc), and metal ceramic crowns with reduction (group V: 1.0 mm vertical additional vertical reduction of metal framework (Vmc). reduction) (Fig. 1). One extracted, intact, human Type and thickness of materials used for crowns maxillary central incisor was prepared to receive the crowns. The facial re- Materials Cervical duction was 1.5 mm following the Crown Layers (Manufacturer) Thickness depth of a rounded shoulder finishing line. The margin was positioned at the Metal framework High noble metal alloy 0.3 mm (V-Delta Alloy, Metalor) level of the cement-enamel junction and 2.0 mm of incisal reduction was Opaque layer Porcelain opaque 0.1 mm performed. Throughout the study, the (POA1, Noritake Porcelain) tooth was stored in a 0.05 % thymol and distilled water solution. The pre- Dentin porcelain Feldspathic porcelain 1.0 mm pared tooth was duplicated with a (A1B, Noritake Porcelain) vinyl polysiloxane impression mate- rial (CapSil, Aquatrols Corporation of Enamel porcelain Feldspathic porcelain 0.1 mm America, Paulsboro, NJ). Type IV den- (A1B, Noritake Porcelain) tal stone (New Fuji-Rock, GC Corp, Porcelain for Feldspathic porcelain Minimal Tokyo, Japan) was used to fabricate butt margin (MA1, Noritake Porcelain) achievable the 30 dies, each corresponding to a single crown. Cement medium Translucent cement Thin layer A standardized framework was (Variolink II, trial-base, cast for each die in a high noble metal Ivoclar Vivadent AG) alloy (V-Delta; Metalor Dental AG). After the heat treatment process, lingual side of the crown. For group applications of margin porcelain were the intaglio surfaces were finished to V crowns, an additional 1.0 mm was applied to achieve adequate marginal a uniform facial and interproximal added to the vertical reduction of the integrity. The thickness of the margin thickness of 0.3 mm. For the conven- metal framework. porcelain was reduced as much as tional margin design, group C, the Dental porcelain (Noritake Super possible. Two layers of dentin porce- metal framework remained extended Porcelain; Noritake Dental Supply lain were applied to all 3 groups to to the preparation finish line (Fig. Co) was applied to all groups with achieve proper contour and reduced 1). For group H crowns, the cervi- a brush-on technique according to to a cervical thickness of 1.4 mm. cal margin of the metal framework the manufacturer’s recommenda- Enamel porcelain was then applied was reduced at the axiocervical line tions and fired under vacuum in a over the dentin porcelain to achieve a angle at a distance of 1.5 mm from porcelain furnace (Programat P300; proper final crown contour with a 1.5 the preparation finishing line; this re- Ivoclar Vivadent AG, Schaan, Liech- mm thickness at the cervical area. All duction was made on the facial and tenstein). Three layers of opaque por- specimens were autoglazed according interproximal margin, leaving 150 de- celain were applied to all of the metal to the manufacturer’s recommenda- grees of metal collar exposure on the frameworks. For groups V and H, 2 tions. A caliper (Iwanson Decimal The Journal of Prosthetic Dentistry Paniz et al
  • 4. November 2011 313 conditions for each of the experimen- tal margins. Six experimental groups were evaluated in the study. On the computer screen, the cervi- cal portion of the teeth was selected by using a transparent custom-made plastic template, which was fabricat- ed to fit the computer screen to better identify the different tooth portions. A 4 mm length was considered enough to represent the cervical portion since 2 Selected cervical portion in equigingival (left) and subgingival the initial length of the tooth before (right) groups of metal ceramic crowns. Note that subgingival preparation was approximately 12 crowns have margin positioned 0.5 mm apical to gingival level. mm, and a standardized area, extend- ing 2 mm from the gingival level, was Groups analyzed. Variables included framework extension (3 selected in the cervical portion (Fig.groups of specimens) and finish line location (total 6 study groups) 2). The measurements were recorded in CIELAB coordinates. Groups of Framework The color difference among the Specimens Extension Study Finish Line experimental groups was determined (n=30) (C, H, V) Groups Location (S, E) with the equation: ∆E= [(∆L*)2 + Cmc Finish line CST (∆a*)2 + (∆b*)2]1/2,33,34 calculated from the mean values of L*, a*, and Hmc 1.5 mm horizontal reduction, HST b*. To determine clinical significance, Subgingival the ∆E values were related to those (buccocervical line angle) (0.5mm) present in the literature, which range Vmc 1 mm additional vertical VST from 1.7 to 3.7. 44,45 A 2-way ANOVA was calculated reduction for each CIELAB coordinate (L*, a*, and b* values) to show which of the 2 Cmc Finish line CET factors (framework extension or finish Hmc 1.5 mm horizontal reduction, HET line location) had a significant impact Equigingival on the values of each coordinate. A (buccocervical line angle) post hoc Tukey’s Honestly Significant Difference (HSD) test was performed Vmc 1 mm additional vertical VET to determine statistically significant reduction differences among the group means.Caliper; Asa Dental s.p.a., Lucca, cally (Fig. 2). To achieve repeatability RESULTSItaly) with an accuracy of 0.05 mm of measurements, the position of thewas used to measure and adjust the tooth and of the measuring instru- The mean L*, a*, and b* valuesfinal thicknesses, which are reported ment was standardized for all the are presented in Table III. When con-in Table I. measurements with custom-position- sidering L* values through the analy- The color of the cervical region of ing indices. Each measurement was sis of variance (2-way ANOVA), therethe crowns, fitted on a prepared max- performed 5 times to reduce mea- were significant differences (P=.012)illary central incisor, was measured surement error. Since natural teeth among the different groups of crowns,with a colorimeter (ShadeVision Sys- are usually observed in a wet environ- with framework extension having thetem; X-Rite, Inc). The measurements ment, all measurements were made main effect (Table IV). The mean L*were made in a dental mannequin with the specimens in a slightly moist value for the Vmc group (78.8) was(KaVo Dental, Biberach/Riss, Germa- condition. All the crowns were mea- significantly lower (P=.027) thanny) with the margin of the restoration sured with the application of trans- the mean value for the Cmc grouppositioned either 0.5 mm subgingi- parent cement medium try-in paste (79.4) and also significantly lowervally (subgroup S) or at the gingival (Variolink II; Ivoclar Vivadent AG). Ta- (P=.023) than the value for the Hmclevel (subgroup E) by moving the pre- bles I and II summarize the porcelain group (79.4) (Fig. 3). Considering L*pared tooth 0.5 mm more or less api- layer thicknesses and measurement values in relation to framework ex-Paniz et al
  • 5. 314 Mean L* values, a* values, and b* values for each single group of crowns (n=6) L* a* b* Mean Mean Mean Group Values SD Values SD Values SD CST 78.48 0.93 3.77 0.34 12.26 0.65 HST 79.96 0.81 3.06 0.47 11.87 1.00 VST 78.89 0.55 3.64 0.07 13.33 0.60 CET 80.37 0.84 2.53 0.27 11.65 0.58 HET 78.92 0.68 2.31 0.23 11.78 1.15 VET 78.71 0.57 2.69 0.25 13.30 0.82 Two-way ANOVA table for L* value (main effects and interaction term) Sum of Mean Source Squares df Square F P Framework extension 5.39 2 2.69 4.81 .12 Finish line location 0.74 1 0.74 1.33 .25 Framework extension × 22.5 2 11.25 20.07 <.001 Finish line location Error 30.3 54 0.56 Framework Extension; LS Means Framework Extension* Finishing Line; LS Means Current effect: (F2, 54) = 4.82, P=.012 Current effect: (F2, 54) = 20.0, P<.001 80.0 81.5 79.8 81.0 Sub-gingival 79.6 Equi-gingival 80.5 79.4 80.0 79.2 L* L* 79.5 79.0 79.0 78.8 78.6 78.5 78.4 78.0 78.2 77.5 Cmc Hmc Vmc Cmc Hmc Vmc Framework Extension Framework Extension 3 L* values in relation to framework extension factor. 4 L* values in relation to framework extension and fin- ishing line location factors. The Journal of Prosthetic Dentistry Paniz et al
  • 6. November 2011tension and finish line location fac- with framework extension having the measured subgingivally and 2.7 whentors, significant differences (P<.001) main effect (Table V). Hmc crowns measured equigingivally (Fig. 6).were present (Table IV). The post showed lower a* values (2.69) than When considering b* values, therehoc Tukey test revealed no significant Cmc crowns (3.17) and Vmc crowns were significant differences (P<.001)differences (P=.95) between subgin- (3.17) (Fig. 5). Considering a* values among the different groups of crowns,gival (78.9) and equigingival (78.7) in relation to framework extension with framework extension having themeasurements within the Vmc group. and finish line location factors, signif- main effect (Table VI). Vmc crownsHowever, significant differences were icant differences (P=.043) were pres- show higher values (13.3) than Cmcpresent within the Cmc (P<.001) and ent (Table V). The post hoc Tukey’s (12, P<.001) and Hmc (11.9, P<.001)Hmc (P=.035) groups. Conventional test showed that, for all of the groups crowns (Fig. 7). Considering b* val-metal ceramic crowns had an L* value of crowns, mean values were signifi- ues in relation to framework exten-of 78.4 when measured subgingivally cantly higher when measured subgin- sion and finish line location factors,and 80.4 when measured equigingi- givally. Cmc crowns (P<.001) showed no significant differences (P=.488)vally. Specimens from the Hmc group a value of 3.78 when measured sub- were present (Table VI and Fig. 8).had a mean L* value of 80 when mea- gingivally and 2.54 when measured The ∆E values among the groupssured subgingivally and 78.9 when equigingivally. Hmc crowns (P<.001) of crowns are represented in Tablemeasured equigingivally (Fig. 4). showed a value of 3.06 when mea- VII. Evaluating subgingival groups of When considering a* values, there sured subgingivally and 2.31 when crowns, the base shade comparisonwere significant differences (P<.001) measured equigingivally. Vmc crowns between Cmc crowns (CST) and Vmcamong the different groups of crowns, (P<.001) showed a value of 3.65 when crowns (VST) showed ∆ =1.15. The Table V. Two-way ANOVA table for a* value (main effects and interaction term) Sum of Mean Source Squares df Square F P Framework extension 3.03 2 1.51 16.85 <.001 Finish line location 14.4 1 14.4 159.4 <.001 Framework extension × 0.60 2 0.30 3.34 .04 Finish line location Error 4.86 54 0.09 Framework Extension; LS Means Framework Extension* Finishing Line; LS Means Current effect: (F2, 54) = 16.9 P<.001 Current effect: (F2, 54) = 3.3, P=.043 3.4 4.2 3.3 4.0 3.8 3.2 3.6 3.1 3.4 3.0 3.2 Sub-gingivalb* 2.9 L* 3.0 Equi-gingival 2.8 2.8 2.6 2.7 2.4 2.6 2.2 2.5 2.0 2.4 1.8 Cmc Hmc Vmc Cmc Hmc Vmc Framework Extension Framework Extension5 a* values in relation to framework extension factor. 6 a* values in relation to framework extension and fin- ishing line location factors.Paniz et al
  • 7. 316 Two-way ANOVA for b* value (main effects and interaction term) Sum of Mean Source Squares df Square F P Framework extension 27.1 2 13.6 19.53 <.001 Finish line location 0.89 1 0.89 1.28 .26 Framework extension × 1.01 2 0.50 0.72 .48 Finish line location Error 37.5 54 0.69 Framework Extension; LS Means Framework Extension* Finishing Line; LS Means Current effect: (F2, 54) = 19.5 P<.001 Current effect: (F2, 54) = 0.73, P=.488 14.0 14.5 14.0 Sub-gingival 13.5 13.5 Equi-gingival 13.0 13.0 b* b* 12.5 12.5 12.0 12.0 11.5 11.5 11.0 11.0 10.5 Cmc Hmc Vmc Cmc Hmc Vmc Framework Extension Framework Extension 7 b* values in relation to framework extension factor. 8 b* values in relation to framework extension and fin- ishing line location factors. ∆E values among different groups of crowns --- CST HST VST CET HET VET CST --- 1.68 1.15 2.34 1.59 1.51 HST 1.68 --- 1.90 0.70 1.28 1.93 VST 1.15 1.90 --- 2.49 2.04 0.96 CET 2.34 0.70 2.49 --- 1.47 2.34 HET 1.59 1.28 2.04 1.47 --- 1.58 VET 1.51 1.93 0.96 2.34 1.58 --- The Journal of Prosthetic Dentistry Paniz et al
  • 8. November 2011 317same comparison performed equig- strated ∆E to be lower than 1.7 (Table crowns (Hmc) showed lower values,ingivally (CET vs. VET), found higher VII). Evaluating subgingival groups of indicating a color closer to that ofmean values (∆ =2.34). Consider- crowns, excluding the first 0.5 mm natural teeth.43ing the color of each specific group coronal to the finish line (Fig. 2), the Considering b* values, equigingivalof specimens, Vmc crowns showed base shade comparison between Cmc and subgingival crowns showed simi-∆ =0.96 when comparing equigin- crowns (CST) and Vmc crowns (VST) lar b* values, except for the analysis ofgival and subgingival groups, Hmc showed clinically acceptable results Cmc crowns, which showed lower val-crowns showed ∆ =1.28, and Cmc (∆ =1.15). The same comparison ues when equigingival (Figs. 7, 8). Incrowns showed ∆ =2.34 (Table VII). performed equigingivally, including general, vertical cut-back crowns (Vmc) the most apical 0.5 mm (CET vs VET), showed higher values, indicating a color DISCUSSION found mean values above the limit closer to that of natural teeth.43 of acceptability (∆ =2.34). This re- The use of a dental mannequin This study was designed to achieve sult suggests that, when the shade of with a plastic gingival substitute al-a standardized evaluation of 3 differ- conventional metal ceramic crowns is lowed exclusion of portions of theent metal framework designs for the analyzed, there is significant color im- crowns, creating 2 different groups ofcolor of the cervical area of metal pairment in the most apical 0.5 mm specimens, subgingival (S) and equig-ceramic restorations. The goal was of the restoration. Furthermore, the ingival (E). However, the plastic gingi-to understand whether the technical color of the cervical portion of Vmc va did not replicate a clinical situationchallenges of fabricating and man- crowns is most consistent between since it eliminated the impact of theaging a collarless metal ceramic res- the equigingival and subgingival crown on the soft tissue, whose colortoration19, 21-24, 26-32 were justified to groups (∆ =0.96), while that of the influences the final esthetic outcome.achieve an improved esthetic result. Hmc crowns is moderate (∆ =1.28), Similarly, this study did not considerThe data support rejecting the null and that of the Cmc crowns is the the possibility of short-term or long-hypothesis that no color differences worst (∆ =2.34) (Table VII). The pos- term tissue recession. The use of a dif-would be present in the cervical por- sible positive esthetic implication of ferent gingival substitute could helption of single metal ceramic crowns the use of an additional millimeter of overcome these shortcomings in pos-fabricated with different metal frame- metal framework reduction was not sible future research. Furthermore,work designs. tested in this study because of the in- considering the development of ce- In analyzing tooth color, the pri- creased fracture risk present with this ramic restorations, a similar studymary concern was to obtain clinically type of restoration.25,27,28 design could be used to evaluate corerelevant results, and for this reason, Through the analysis of Lab* val- ceramic restorations.the data obtained through the colo- ues, a deeper understanding of therimetric measurement were related to color differences and of influenc- CONCLUSIONthe values reported in the literature. ing factors can be drawn (Figs. 3-8).A natural tooth was not selected as a Considering L* values, Cmc crowns Within the limitations of thisstandard since previously completed showed the highest value when equi- study, the following conclusions werein vitro research clearly showed signif- gingival (CET), the lowest when sub- drawn:icant color differences when compar- gingival (CST), and the highest differ- 1. No significant differences ining tooth structure to a metal ceramic ence of values between equigingival base shade were present among therestoration. 33 According to Johnston and subgingival specimens (Figs. 3, investigated crowns.and Kao,44 a ∆E > 3.7 indicates vi- 4). As discussed in the ∆E analysis, 2. Vertical cut-back crowns (Vmc)sually perceivable color differences this confirmed that significant color had a cervical shade which was morewhich are clinically unacceptable. By impairment occurs in the most apical consistent and appeared to be moreusing this threshold and comparing 0.5 mm of the ceramic of metal ce- similar to that of a natural tooth.the groups with the most clinical rel- ramic crowns. In contrast, when ana- 3. Conventional metal ceramicevance, no clinical differences were lyzing Vmc crowns, the results were crowns (Cmc) were characterized bynoted (Table VII). A similar compari- more consistent and the color also significant color impairment in theson can be made to other recent clini- closer to that of natural teeth.43 most apical 0.5 mm of the ceramic.cal references.47 Even if Johnston and Considering a* values, consis- 4. Vertical cut-back crowns (Vmc)Kao44 is often cited in the literature, tent differences were present be- tended to have mean L* and b* valuesother values were considered for this tween equigingival (E) and subgingival closer to those of natural teeth, whilein vitro study. According to Douglas (S) crowns. In general, equigingival horizontal cut-back crowns (Hmc)and Brewer,45 the threshold for accept- crowns demonstrated lower values tended to have closer mean a* values.ability is ∆E=1.7 and for perceptibil- (Figs. 5 and 6). Among the differentity, 0.4. Several comparisons demon- types of design, horizontal cutbackPaniz et al
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