Shereen S. Azer

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.

Effect of substrate shades on the color of ceramic laminate veneers

STATEMENT OF PROBLEM Ceramic laminate veneers are generally fabricated with varying thicknesses ranging from 0.3 to 1 mm, depending on the need to mask discolored teeth or slightly correct the contour of malpositioned teeth. Clinical color reproduction poses a challenge because of color interaction with the underlying substrate, whether tooth structure or esthetic restorative material. PURPOSE The purpose of this in vitro investigation was to measure the effect of color change resulting from applying 2 shades of ceramic material, translucent (T1) and opaque (O2), to 2 shades of composite resin substrate material, light (A3) and dark (C4), on the overall color of ceramic laminates. MATERIAL AND METHODS Forty disks were fabricated. Twenty disks (15 × 0.5 mm) were cut from pressed ceramic, 10 disks for each shade (translucent and opaque). Additionally, 20 disks (15 × 4.0 mm) were fabricated from light-polymerized composite resin material, 10 disks for each shade (light and dark). The ceramic disks were bonded to the composite resin disks with clear resin cement. The specimen combinations were divided into 4 groups (n=5). Color measurements were done with a colorimeter (Minolta Chroma Meter CR-200b) configured with diffuse illumination/0-degree viewing geometry. Mean CIE lightness (L*), chroma (C*(ab)), and hue angle (h(ab)) values were obtained. A 2-way analysis of variance (ANOVA) was used to compare the means and standard deviations between the different color combinations (α=.05), followed by Tukeys HSD post hoc test for significant interactions. RESULTS The 2-way ANOVA showed significant differences (P<.001) in L*, C*(ab), and h(ab) for a change in the composite resin substrate, regardless of the ceramic material shade. There was significant color change from dark to light substrate (P=.044). The mean h(ab) (SD) of dark substrate/opaque veneer was 89.62 (1.5), while the mean h(ab) of light substrate/translucent veneer was 81.23 (1.7). CONCLUSIONS Within the limitations of this study, the selected color of a 0.5 mm ceramic laminate veneer was significantly affected by the change in color of the supporting substrate.

Effect of home bleaching systems on enamel nanohardness and elastic modulus

OBJECTIVES The purpose of this study was to evaluate the nanohardness and elastic modulus of human enamel after treatment with tray and strip bleaching systems. METHODS Fifty-five human enamel samples were exposed to five different bleaching agents. Nanoindentations were made before and after bleaching treatments following the manufacturers directions using a Nanoindenter XP (MTS Systems Corporation, Oak Ridge, TN, USA). Nanohardness and elastic modulus measurements were obtained and the results were statistically analyzed using a repeated measures analysis of variance with a post-hoc Tukey-Kramer multiple comparison test. RESULTS Nanohardness and elastic modulus measurements showed decrease of mean values for each group except the control which remained the same. There were significant differences due to time (before and after treatment) and material effects in nanohardness (P<0.0001) and elastic modulus (P=0.0241). Measurements after treatment showed significant decrease in nanohardness between all groups and the control group. There was a significant difference in hardness between CP and TO after treatment. Additionally, there were significant differences in elastic modulus between the control group when compared to OB and TO after treatment. While there were significant changes in the elastic modulus due to treatment for both CP and TO, there were no significant differences between any of the groups after treatment. CONCLUSIONS Nanohardness and elastic modulus of human enamel were significantly decreased after the application of home-bleaching systems.

Accuracy of Kubelka–Munk reflectance theory for dental resin composite material☆

OBJECTIVE The objective of this study is to determine the effect of interfacial reflection correction (IRC) on the accuracy of this reflectance model for contemporary dental resin composite materials. METHODS Visible reflectance spectra were obtained for varying thicknesses (∼0.3-1.2mm) of five shades of each of two brands (Herculite Ultra and Kalore) of dental resin composite materials on black, gray and white backings. For each shade and brand, K-M theory was fit (SAS non-linear fit) for each of three IRC methods: (1) no IRC (No), (2) an IRC method which uses a theoretical value of the internal reflection for translucent materials (Tr), and (3) an IRC method which uses a derived value of the internal reflection for opaque materials (Op). The errors were subjected to repeated measures analysis of variance and Bonferroni corrections were applied to selected pairwise comparisons. RESULTS The Op method had a statistically lower error than the No method at wavelengths from 460 to 560nm, and the Tr method had this lower error at wavelengths from 440 to 780nm. SIGNIFICANCE Corrected K-M reflectance theory may be used to accurately quantify the optical K-M absorption and scattering coefficients for contemporary dental resin composite materials, and this theory may be used to calculate accurately the reflectance spectrum for a clinically relevant thickness value and for a backing that is low, mid-range or high in lightness. Both color and translucency information of resin composite materials may be accurately predicted using corrected Kubelka-Munk reflectance model.

Optical characteristics of contemporary dental composite resin materials

OBJECTIVES Optical and physical properties of dental restorative composite materials are affected by composition. Basic optical absorption and scattering properties have been derived through the use of a corrected reflectance model, but practical and important optical properties are not easily derived from these basic spectral characteristics. The purposes of this study are to derive and compare colour and translucency characteristics of two cured contemporary nanohybrid composites being marketed as universal composites, and to evaluate colour difference between each composite material and published shade guide data. METHODS Previously derived optical scattering and absorption coefficients for five diverse shades of these composite materials were used to calculate the CIE colour parameters of L*, a* and b* at infinite thickness under various illuminants and to derive ideal translucency parameters at various thicknesses using two colour difference formulae. RESULTS Differences were found in the inherent colour parameters and in the translucency parameters between the brands for some of the shades studied. The colour differences of the inherent colours from published shade guide data were always higher than the perceptibility limit, and often higher than the acceptability limit. CONCLUSIONS Inherent colours and ideal translucency parameters may be calculated from optical coefficients for a variety of illuminants. Different inherent colour parameters of composite materials marked for the same shade indicate the influence of compositional differences between these materials. CLINICAL SIGNIFICANCE Since patients are seen under various illuminations, the ability to assess appearance matching characteristics under diverse illuminants will help assure an optimum match for the patient.

Effect of pH on tooth discoloration from food colorant in vitro.

OBJECTIVES The purpose of this study was to evaluate the effect of acidic, neutral and alkaline food colorant media (FCM) on tooth discoloration in vitro. METHODS Treatment (n=24) and control (n=24) sterile, hydrated human molars were prepared in individual, impervious holders and their color measured (pretest) using a non-contact spectroradiometer system. Specimens were randomly assigned to and immersed in one of the three buffer solutions (pH 2, pH 7 or pH 12). Red food color (Red 40) was added to the treatment buffer solutions at 0.025%. Immersed specimens were incubated for 4h at 37°C. Color was also measured after immersion/incubation (posttest) and again after subsequent 2-min of polish using plain-pumice slurry with a slow-speed handpiece (post-polish). Differences in CIE a* (redness parameter) were analyzed by repeated measures ANOVA with Bonferroni-corrected t-tests for the pairwise comparisons of interest. RESULTS Tooth discoloration was measured as total stain (mean difference in a* between posttest minus pretest), extrinsic stain (mean difference in a* post-polish minus posttest) and intrinsic stain (mean difference in a* post-polish minus pretest). No significant change in color was observed between the control and treatment groups for neutral and alkaline FCM. However, acidic FCM caused reddish tooth discoloration posttest minus pretest, post-polish minus pretest and post-polish minus posttest compared to neutral and alkaline treatment and control groups. CONCLUSIONS The degree and type of tooth discoloration are influenced by both the low pH and food color rather than the dietary pigment alone.

Effect of bleaching on tooth discolouration from food colourant in vitro.

OBJECTIVES The purpose of this study was to evaluate the effect of bleaching on tooth discolouration from neutral food colourant media (NFCM). METHODS Freshly extracted human molar teeth (n = 32) were divided into four groups (n = 8): non-bleached treatment-NBT, non-bleached control-NBC, bleached treatment-BT and bleached control-BC. Bleached teeth specimens were subjected to 20% carbamide peroxide bleaching agent for 10h. Colour measurements (pre-test) were done using a non-contact spectroradiometer. The teeth specimens were immersed in a neutral buffer solution. NBT and BT groups had 0.025% red food colour (Red 40) added to the buffer solution. The immersed specimens were incubated for 4h at 37°C. Colour was again measured after immersion/incubation (post-test) and after subsequent polishing using plain-pumice slurry (post-polish). Differences in CIE a* (redness parameter) were analysed by repeated measures ANOVA with Bonferroni-corrected t-tests for the pairwise comparisons of interest. RESULTS Tooth discolouration was measured as total stain (mean difference in a* between post-test minus pre-test), extrinsic stain (mean difference in a* post-polish minus post-test) and intrinsic stain (mean difference in a* post-polish minus pre-test) A statistically significant difference in the mean Δa* was observed (P = 0.009) between staining treatment for bleached and non-bleached teeth. Also, a statistically significant difference (P < 0.001) was noted between control and treatment groups of bleached teeth that were subjected to staining. CONCLUSIONS Bleaching resulted in total and extrinsic tooth discolouration by the NFCM. CLINICAL SIGNIFICANCE It might be beneficial to avoid highly pigmented foods immediately following bleaching in order to optimize the effects of tooth whitening.

A Simplified Technique for Creating a Customized Gingival Emergence Profile for Implant‐Supported Crowns

A successful implant restoration is one that will allow adequate function and esthetics. Soft-tissue management around implant-supported restorations continues to present a considerable challenge for the restoring dentist as well as the laboratory technician while fabricating the final prosthesis. This article presents a simplified and economical technique to direct gingival tissue healing, as well as create a removable gingival replica of the customized gingival emergence profile. The created profile can then be used in the dental laboratory to achieve a superior and predictable esthetic outcome for implant-supported fixed restorations.

Effect of mixing methods on the physical properties of dental stones

OBJECTIVES This in vitro comparative study evaluated the effect of different stone mixing methods on material properties of four dental stones. Two ADA type IV stones (Silky-Rock and Snap-Stone), one type V high expansion stone (Die Keen), and one recently introduced type V specialty stone (HandiMix) were chosen for this study. METHODS Forty cylindrical specimens (25 mm x 12.5 mm) were cast for each of the nine stone sub-groups and bench dried at 23+/-2 degrees C for 1 and 24h. Specimens were then tested in an Instron in tensile and compression modes at crosshead speeds of 0.5 and 1.0 mm/min, respectively. Four rectangular-shaped specimens (30 mm x 15 mm x 15 mm) of each stone type were cast and bench dried for 48 h. Knoop microhardness measurements were obtained from defined areas on each specimen for surface hardness testing using 200 g load and 20s dwell time. A 12.6 mm(2) area was then delimited in the center of two sides of each specimen and photographed under low power magnification (40x). The average pore number per area was then determined for each specimen for surface porosity testing. The setting time and setting expansion for each stone type was recorded as well. RESULTS ANOVA (P<0.001) and Ryan-Einot-Gabriel-Welsh test (P<0.05) showed significant differences between diametral tensile strengths and pore numbers for both stone types and mixing methods. CONCLUSION Within the limitations of this study, the newly introduced mixing method did not appear to have an effect on the physical properties of HandiMix stone.

Mandibular function after Myorelaxation Therapy in temporomandibular disorders

PURPOSE The aim of this study was to analyze the efficacy of Myorelaxation Therapy in temporomandibular disorders on the basis of mandibular movement measurements, reported functional impairment and clinical findings. MATERIAL/METHODS To ascertain the mandibular movements 78 women were investigated. The first group consisted of 32 consecutive patients (23.3±4.8 years) suffering from muscle disorder and disk displacement with a reduction serving as a treated group. The second group was formed from 46 volunteers, as a healthy group (20.1±1.3 years). Jaw-tracking records (K7, Myotronics-Noromed Inc.) were performed including the measurements of opening, lateral and protrusive movement range, maximal and average velocity of opening/closing. Reported impairment and clinical data were collected. The treatment involved nocturnally applied a non-occluding sublingual relaxation splint combined with daily performed stretching exercises. Measurements were taken before treatment, after 4 weeks with no interventions (control period) and after 3 weeks, 3 and 6 months. RESULTS After the treatment mandibular opening range increased by 8mm (19%, p<0.05), lateral movement by 2.1mm (36%, p<0.05) while protrusive movement decreased by 0.5mm (p>0.05). Maximal and average velocity parameters significantly increased (p>0.05). These results were supported by the decrease in reported impairment and clinical pain occurrence (p<0.05). Only joint clicking change was non-significant (p>0.05). CONCLUSIONS Myorelaxation Therapy was effective in the treatment of our group of patients. A significant improvement in the opening and lateral movement range, as well as opening/closing velocity was obtained after 6 months of treatment. This method can be easily managed by general practitioner, especially in muscles-related TMD types.