Clinical evaluation of zirconia crowns cemented with two different resin cements: A retrospective study.

BACKGROUND: Self-adhesive resin cement has been used extensively with zirconia crowns. Several in vitro studies showed that adhesive resin cementation may increase zirconia crowns' retention and their fatigue resistance. OBJECTIVES: This retrospective study aimed to evaluate the clinical performance, survival and success rates and complications encountered with zirconia crowns cemented with two different self-adhesive resin cements. METHODS: A total of 112 patients who received 176 monolithic zirconia crowns were evaluated. Crowns were cemented with RelyX Unicem 2 (n = 74) and Panavia SA (n = 102) self-adhesive resin cements. Clinical assessments of the crowns and supporting periodontal structures were performed following the modified California Dental Association (CDA) criteria. Intraoral photographs and periapical and bitewing radiographs were obtained for further assessment by two evaluators. Descriptive statistics, McNemar, t-test, log rank (Mantel-Cox) tests and Kaplan-Meier survival analyses were performed (a = .05). RESULTS: The 5-year survival and success rates were 100% and 96.4%, respectively. The complications encountered were recurrent caries (2.2%) and the need for endodontic treatment (0.5%). No technical complications, such as fracture or loss of retention, were observed. The type of cement and patient-related factors did not influence the survival and success rates of the crowns. CONCLUSIONS: Survival rate of zirconia crowns cemented with two different self-adhesive resin cements was 100% after 5 years.

Clinical performance of CAD-CAM crowns provided by predoctoral students at the University of Toronto.

STATEMENT OF PROBLEM: The clinical success of monolithic lithium disilicate glass-ceramic (LDGC) crowns manufactured with computer-aided design and computer-aided manufacturing (CAD-CAM) technology provided by predoctoral students has not been fully investigated. PURPOSE: The purpose of this retrospective clinical study was to evaluate the performance of laboratory-fabricated monolithic posterior LDGC CAD-CAM crowns provided by predoctoral students at the University of Toronto. Specific patient- and provider-related factors were also investigated. MATERIAL AND METHODS: A sample of posterior LDGC CAD-CAM crowns (IPS e.max) provided by predoctoral students was evaluated. Crown preparations were made according to specific criteria, and crowns were milled in an in-house laboratory by using the CEREC Bluecam system. The crowns were cemented with Rely-X Unicem (3M ESPE) and Calibra Universal (Dentsply Sirona) resin cements. Clinical assessments of the crowns and supporting periodontal structures were performed following the modified California Dental Association (CDA) criteria. Intraoral photographs and periapical and bitewing radiographs were obtained for further assessment by 2 evaluators. Descriptive statistics, McNemar, t test, log rank (Mantel-Cox) tests, Pearson chi-squared tests, simple logistic regression, odds ratios, and Kaplan Meier survival analyses were performed (α=.05). RESULTS: A total of 189 patients receiving 210 crowns (108 premolar and 102 molar) were examined with a follow-up period of up to 6 years. Altogether, 28 complications were observed (12 technical, 11 biological, and 5 esthetic). No significant association was found between patient age, sex, periodontal condition, tooth type, tooth vitality, cement type, and crown longevity. However, significantly lower survival and success rates were found for mandibular crowns than for maxillary crowns (P=.029). The provider's experience had no significant effect on the clinical performance of LDGC CAD-CAM crowns. The 6-year cumulative survival rate was 93.0%, and the success rate was 86.4%. CONCLUSIONS: The ease of use of the CAD-CAM system and clinical performance of LDGC suggest that this technology should be used in the dental school setting by predoctoral students.

Radiant-exposure attenuation through Class-2 proximal slots.

PURPOSE: To determine the extent of radiant exposure (RE) attenuation of three LED light-polymerization units (LPUs), and their beam-profile, at the bottom of the Class-2 slot, using MARC-PS. METHODS: 10 seconds RE was delivered to MARC-PS' anterior sensor by Bluephase-Style, Demi-Plus, and Deep-Cure-S. Two ivorine lower first-molars received Class-2 proximal box preparations: (3×2×4 mm and 4×4×4 mm) and were sectioned horizontally above the cementoenamel junction. Tofflemire matrix-retainer was placed around each tooth and secured with a low-fusing compound. Each LPU tested delivered 10 seconds RE to MARC-PS through proximal slots. Mean RE of three readings per group was obtained. Data were analyzed using Pearson correlation, mixed ANOVAs with a pre-set alpha of 0.05. RESULTS: RE attenuation ratio calculated from the baseline to 4× 4×4/3×2×4 Class-2 boxes were: 58.25/80.03 Bluephase-Style; 49.36/80.25 Demi-Plus; 32.8/77.43 Deep-Cure-S. A significant and strong correlation (r= 0.86, P< 0.001) between the reduction in aperture size and RE was found. The beam profile of LED-LPUs tested decreased RE values at the bottom of a proximal box. More than 80% RE value reduction from the baseline to the smallest Class-2 cavity 3×2×4 aperture was observed. CLINICAL SIGNIFICANCE: Polymerization of resin-composites at the bottom of the Class-2 box is challenging due to the small aperture size, depth, and hard-to-reach location. Inadequate polymerization at the bottom of the Class-2 proximal box is a causative factor for secondary caries and, ultimately, restoration failure.

Clinical performance of chairside monolithic lithium disilicate glass-ceramic CAD-CAM crowns.

OBJECTIVES: To evaluate the clinical performance and the effect of various patient and provider-related factors on the longevity of chairside monolithic posterior lithium disilicate glass-ceramic (LDGC) computer-aided design (CAD)-computer-aided manufacturing (CAM) crowns provided by predoctoral students. MATERIALS AND METHODS: A sample of posterior LDGC CAD-CAM crowns was evaluated. Crown preparations were milled chairside using the CEREC Omnicam system and cemented with Rely-X Unicem or Calibra Universal resin cements. Clinical assessment of the crowns and supporting periodontal structures was performed using the modified California Dental Association (CDA) criteria. Intraoral photographs as well as radiographs were taken for further assessment by two evaluators. Kaplan-Meier survival analysis was performed. RESULTS: A total of 40 crowns were inserted in 32 patients and evaluated for 4 years. Three complications were observed (two-technical and one-biological). No chipping or fracture of crowns was observed. No significant association was found between age, sex, periodontal condition, tooth type, tooth vitality, cement type, and longevity. The 4-year cumulative survival and success rates were 95.0 and 92.3%, respectively. CONCLUSION: Chairside LDGC CAD-CAM crowns exhibited a high survival rate after 4 years in function and were shown to be a viable and reliable treatment option for posterior teeth. CLINICAL SIGNIFICANCE: The high survival rate of chairside CAD-CAM crowns observed in this study suggests the likelihood of predictable performance in the predoctoral setup.

Radiopacity of Resin Cements Using Digital Radiography.

STATEMENT OF PROBLEM: Monitoring performance of glass-ceramic based indirect restorations using radiographic imaging might be difficult due to their low radiopacity. Therefore, materials used for their cementation must possess adequate radiopacity. PURPOSE: This study determined radiopacity of a group of resin-cements used for adhesive-cementation of glass-ceramic-based restorations using digital radiography. METHODS: Two specimens were prepared from a group of resin cements (VariolinkII-opaque, VariolinkII-opaque (base), VariolinkII-Transparent, VariolinkII-Transparent (base), Nexus, RelyX Unicem, RelyX ultimate, Duolink, Monocem and Resinomer) and longitudinal sections of same thickness were obtained from molar and premolar. Specimens were assigned to two groups one had molar section with 10 specimens whereas other had premolar with remaining 10 specimens. Each group was placed on digital radiograph sensor (Schick CDR, size 2) together with aluminum step-wedge. Sensor was exposed to X-ray using standard technique. Two images were obtained for each group. Pixel measurements were made using NIH Image-J software. Mean pixel measurements were converted into aluminum thickness equivalents. Data were statistically-analyzed using one-way ANOVA and Tukey's tests. RESULTS: ANOVA revealed significant difference in mean pixel values among cements (p < 0.001). VariolinkII-opaque showed highest mean aluminum equivalent (4.6 mm Al/1 mm) followed by VariolinkII-opaque-Base (4.5 mm Al/1 mm), VariolinkII-transparent (4.45 mm Al/1 mm), VariolinkII-transparent-Base (4.45 mm Al/1 mm), Nexus (2.95 mm Al/1 mm), Duolink (2.7 mm Al/1 mm), RelyX Unicem (2.2 mm Al/1 mm) and finally RelyX ultimate (2 mm Al/1 mm). All cements had mean radiopacity values higher than that of enamel whereas Monocem (1.25 mm Al/1 mm) and Resinomer (1.2 mm Al/1 mm) had means between those of enamel and dentin. CONCLUSIONS: All tested resin-cements showed radiopacity values higher than that of dentin which is adequate for diagnostic purposes according to ISO recommendation. CLINICAL SIGNIFICANCE: The use of resin cement with adequate radiopacity for adhesive cementation of glass-ceramic based restorations enables their radiographic monitoring. (J Esthet Restor Dent 29:215-221, 2017).

Cuspal Deflection of Premolars Restored with Bulk-Fill Composite Resins.

OBJECTIVE: This in vitro study compared cuspal deflection of premolars restored with three bulk-fill composite resins to that of incrementally-restored ones with a low-shrinkage silorane-based restorative material. MATERIALS AND METHODS: Forty freshly-extracted intact human upper premolars were used. Reference points at buccal and palatal cusp tips were acid-etched and composite rods were horizontally bonded to them (TPH-Spectra-HV, Dentsply). Two acrylic resin guiding paths were made for each premolar to guide beaks of a digital micrometer used for cuspal deflection measurements. Standardized MOD cavities, 3 mm wide bucco-lingually and 3.5 mm deep, were prepared on each premolar. Prepared teeth were then equally divided into four groups (n = 10) and each group was assigned to one of four composite resin (QuiXX, Dentsply; X-tra fil, Voco; Tetric EvoCeram Bulk Fill, Ivoclar Vivadent; low-shrinkage Filtek LS, 3M/ESPE). Adper Single Bond-Plus, 3M/ESPE was used with all bulk-fill restoratives. LS-System Adhesive, 3M/ESPE was used with Filtek LS. For each prepared premolar, cuspal deflection was measured in microns as the difference between two readings between reference points before and after restoration completion. Means and SDs were calculated and data statistically-analyzed using One-way ANOVA and Tukey's test. RESULTS: Filtek LS showed the lowest mean cuspal deflection value 6.4(0.84)µm followed by Tetric EvoCeram Bulk Fill 10.1(1.2) µm and X-tra fil 12.4(1.35)µm, while QuiXX showed the highest mean 13(1.05)µm. ANOVA indicated significant difference among mean values of groups (p < 0.001). Tukey's test indicated no significant difference in mean values between QuiXX and X-tra fil (p = 0.637). CONCLUSIONS: Tetric EvoCeram Bulk Fill had significantly lower mean cuspal deflection compared with the two other bulk-fill composite resins tested. Filtek LS had the lowest significant mean cuspal deflection in comparison to all tested bulk-fill restoratives. CLINICAL SIGNIFICANCE: The use of Tetric EvoCeram Bulk fill composite resin restorative for class II MOD cavities resulted in reduced cuspal deflection in comparison to the two other bulk-fill composite resins tested. The silorane-based Filtek LS restorative resulted in the least cuspal deflection in comparison to all tested bulk-fill composite restoratives.

The Effect of Self-adhesive and Self-etching Resin Cements on the Bond Strength of Nonmetallic Posts in Different Root Thirds.

PURPOSE: The purpose of this study was to evaluate the effect of self-adhesive and self-etching resin cements on the bond strength of nonmetallic posts in different root regions. MATERIALS AND METHODS: Sixty single-rooted human teeth were decoronated, endodontically treated, post-space prepared, and divided into six groups. Glass-fiber (GF) posts (Exacto, Angelus) and fiber-reinforced composite (FRC) posts (EverStick, StickTeck) were cemented with self-adhesive resin cement (Breeze) (SA) (Pentral Clinical) and self-etching resin cement (Panavia-F) (SE) (Kuraray). Six 1-mm-thick rods were obtained from the cervical (C), middle (M), and apical (A) regions of the roots. The specimens were then subjected to microtensile testing in a special machine (BISCO; Schaumburg, IL, USA) at a crosshead speed of 0.5 mm/min. Microtensile bond strength data were analyzed with two-way ANOVA and Tukey's tests. RESULTS: Means (and SD) of the MPa were: GF/SA/C: 14.32 (2.84), GF/SA/M: 10.69 (2.72), GF/SA/A: 6.77 (2.17), GF/SE/C: 11.56 (4.13), GF/SE/M: 6.49 (2.54), GF/SE/A: 3.60 (1.29), FRC/SA/C: 16.89 (2.66), FRC/SA/M: 13.18 (2.19), FRC/SA/A: 8.45 (1.77), FRC/SE/C: 13.69 (3.26), FRC/SE/M: 9.58 (2.23), FRC/SE/A: 5.62 (2.12). The difference among the regions was statistically significant for all groups (p < 0.05). The self-adhesive resin cement showed better results than the self-etching resin cement when compared to each post (p < 0.05). No statistically significant differences in bond strengths of the resin cements when comparable to each post (p > 0.05). CONCLUSION: The bond strength values were significantly affected by the resin cement and the highest values were found for self-adhesive resin cement.

Overview of CEREC CAD/CAM chairside system.

This article describes CAD/CAM technology used in dentistry and different restorative materials used in conjunction with adhesive cementation with particular attention given to the evolution of the CEREC system, as well as various ceramics developed for this system. Advantages and limitations of materials and technique are also discussed.

Gingival microleakage of class V composite restorations with fiber inserts.

AIM: This study investigated the effect of different fiber inserts (glass and polyethylene), bonding agents, and resin composites on the gingival margin microleakage of class V composite restorations. MATERIALS AND METHODS: Sixty premolars were sterilized and mounted in acrylic resin bases. Class V cavities were prepared buccally and lingually, 1 mm below the cementoenamel junction, comprising 12 groups (n = 10). In the experimental groups fiber inserts were cut and placed at the gingival seat, while the control groups had no inserts. Combinations of two composite materials, Filtek-Z250 and Filtek-LS (3M-ESPE), and four bonding agents, Clearfil SE bond (Kuraray) (C), Scotch Bond Multipurpose (3M-ESPE) (SB), Prime and Bond NT (Dentsply) (PB), and Filtek-LS (3M-ESPE) (LS) were used. Restorations were incrementally inserted and polymerized for 40s. Specimens were then stored in distilled water for 7 days and thermocycled for 500 cycles. Teeth surfaces were sealed with nail polish except for 1 mm around restoration margins and immersed in 2% red procion dye. Teeth were then sectioned buccolingually and dye penetration was assessed with five-point scale. Data were statistically-analyzed by Kruskal-Wallis, ANOVA and Tukey's tests (α = 5%). RESULTS: Mean microleakage scores varied from 0.40 (Groups C, C with polyethylene, LS, LS with polyethylene) to 1.50 (SB). CONCLUSION: Different bonding agents led to differences in microleakage scores where C and LS showed significantly lower microleakage than PB. SB had highest mean microleakage score, however, incorporation of fibers resulted in significant reduction in microleakage. CLINICAL SIGNIFICANCE: Class V resin composite restorations bonded with a total-etch adhesive had a significant reduction in mean microleakage scores when glass or polyethylene fibers were placed at the gingival cavo-surface margin. In contrast, for two self-etch adhesive systems, the incorporation of fibers had no significant effect on mean microleakage scores.

Six-year clinical performance of lithium disilicate glass-ceramic CAD-CAM versus metal-ceramic crowns.

PURPOSE: To assess the clinical performance of monolithic CAD-CAM lithium disilicate glass-ceramic (LDGC) crowns and metal-ceramic (MC) crowns provided by predoctoral students. This study also assessed the effects of patient and provider-related factors on their clinical performance as well as patient preference for these types of crowns. MATERIALS AND METHODS: Twenty-five patients who received 50 crowns (25 LDGC CAD-CAM and 25 MC) provided by predoctoral students were retrospectively examined. LDGC CAD-CAM crowns were milled in-house using the CEREC Bluecam system and cemented with either RelyX Unicem or Calibra Esthetic resin cements. MC crowns were cemented with RelyX Unicem cement. Clinical assessment of the crowns and the supporting periodontal structures were performed following the modified California Dental Association (CDA) criteria. Patients' preference was recorded using a visual analog scale (VAS). The results were statistically analyzed using log-rank test, Pearson Chi-squared test and Kaplan-Meier survival analysis. RESULTS: Twelve complications were observed in the MC crown group (9-esthetic, 2-technical and 1-biological). In comparison, 2 complications in the LDGC CAD-CAM crown group were observed (1-technical and 1-esthetic). The 6-year cumulative survival rates for MC crowns and LDGC CAD-CAM were 90.8% and 96%, respectively, whereas the success rates were 83.4% and 96%, respectively. Overall, patients preferred the esthetic outcomes of LDGC CAD-CAM crowns over MC crowns. CONCLUSION: The high survival and success rates, low number of complications, and the high level of patients' acceptance of monolithic LDGC CAD-CAM crowns lend them well as predictable and viable alternatives to the "gold standard" MC crowns.

Stress Distribution of Monolithic and Veneered 3-unit Zirconia FDPs - Finite Element Analysis.

PURPOSE: To evaluate the effect of restoration design on fracture resistance and stress distribution of veneered and monolithic 3-unit zirconia fixed partial dentures (FDPs) using finite element analysis (FEA). MATERIALS AND METHODS: Identical epoxy resin replicas of mandibular second premolar and second molar (to serve as abutment for the 3-unit bridge) were divided into four groups (n = 10): monolithic zirconia (MZ) restorations; conventional layering veneering technique (ZL), heat-pressed technique (ZP), or CAD/CAM lithium disilicate glass ceramic (CAD-on). Specimens were subjected to compressive cyclic loading on the mesio-buccal cusp of the pontic (load range 50 to 600 N; aqueous environment; 500,000 cycles) in a universal testing machine. Data were statistically analyzed at 5% significance level with Fisher exact test and Kaplan-Meier survival analysis. 3D models were constructed in accordance with experimental groups. The stress distribution in each model was analyzed and evaluated according to the location and magnitude of the maximum principal stresses (MPS) using ANSYS software. RESULTS: Specimens from ZL and ZP groups failed at different stages of the 500,000 cycles fatigue, while CAD-on and MZ restorations survived fatigue test. Statistically, there was a significant difference between the groups (P < .001). The MPS were located under the mesial connector in both monolithic and bilayered 3-unit zirconia FDPs. These stresses were found to be higher in monolithic geometries compared to bilayered zirconia FDPs. CONCLUSION: Monolithic 3-unit zirconia and CAD-on zirconia frameworks resulted in superior fracture resistance. Restoration design significantly affected the stress distribution of 3-unit zirconia FDPs.

Fatigue resistance and microleakage of CAD/CAM ceramic and composite molar crowns.

PURPOSE: The aim of this study was to determine effect of compressive cyclic loading on fatigue resistance and microleakage of monolithic CAD/CAM molar ceramic and composite crowns. MATERIALS AND METHODS: Thirty-two extracted molars were prepared to receive CEREC crowns according to manufacturer's guidelines using a special paralleling device (Parallel-A-Prep). Sixteen feldspathic ceramic crowns (VITABLOCS Mark II) (VMII) and 16 resin-composite crowns (Paradigm-MZ100 blocks) (PMZ) were milled using a CEREC-3D machine. Eight crowns of each group were cemented to their respective teeth using self-etching resin cement (Panavia-F-2.0) (PAN), and eight were cemented using self-adhesive resin cement (RelyX-Unicem-Clicker) (RXU). Following storage for 1 week in water, specimens were subjected to uniaxial compressive cyclic loading in an Instron testing machine at 12 Hz for 1,000,000 cycles. Load was applied at the central fossa, and the cycle range was 60-600 N. Specimens were then subjected to microleakage testing. Data were statistically analyzed using factorial ANOVA and Post Hoc (Tukey HSD) tests. RESULTS: All composite crowns survived compressive cyclic loading without fracture, while three ceramic crowns from the subgroup cemented with RXU developed surface cracks at the center of occlusal surfaces, extending laterally. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other three subgroups (p < 0.05). CONCLUSIONS: After 1,000,000 cycles of compressive cyclic loading, PMZ composite molar crowns were more fatigue-resistant than VMII ceramic crowns. Cement type had a significant effect on fatigue resistance of the ceramic crowns but not the composite ones. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other subgroups (p < 0.05).

Microtensile bond strength of glass fiber posts cemented with self-adhesive and self-etching resin cements.

PURPOSE: To evaluate the bond strength of glass fiber posts to intraradicular dentin when cemented with self-etching and self-adhesive resin cements. MATERIALS AND METHODS: Forty-eight single-rooted human teeth were decoronated, endodontically treated, post-space prepared and divided into 8 groups (n = 6). The glass fiber posts used were: Exacto (EA) (Angelus) and everStick (ES) (StichTeck), which were cemented with two self-adhesive resin cements: BisCem (BIS) (Bisco) and Rely-X Unicem (UNI) (3M/ESPE), and two self-etching resin cements: Esthetic Cementing System NAC100 (NAC) (Kuraray) and Panavia-F (PAN) (Kuraray). Specimens were thermocycled between 5°C and 55 °C for 1000 cycles and stored in water at 37°C for 1 month. Four 1-mm-thick (in cross section) rods were obtained from the cervical region of the roots. Specimens were then subjected to microtensile testing in a special machine (BISCO; Schaumburg, IL, USA) or a crosshead speed of 0.5 mm/min. Microtensile bond strength (µTBS) data were analyzed with two-way ANOVA and Tukey's tests. RESULTS: Means (and SD) of µTBS (MPa) were: EA/PAN: 10.3 (4.1), EA/NAC: 14 (5.1) EA/BIS: 16.4 (4.8), EA/UNI: 19.8 (5.1), ES/PAN: 25.9 (6.1), ES/NAC: 29.1 (7), ES/BIS: 28.9 (6), ES/UNI: 30.5 (6.6). ANOVA indicated significant differences among the groups (p < 0.001). Mean µTBS values obtained with ES post were significantly higher than those obtained with EA (p < 0.001). For EA, Tukey's test indicated that higher µTBS means were obtained with the self-adhesive resin cements (BIS and UNI), which were statistically significantly different (p < 0.05) from values obtained with the self-etching resin cements (PAN and NAC). Different cements had no significant effects on the bond strength values of ES post (p > 0.05). µTBS values obtained with ES post were significantly higher than those obtained with EA post irrespective of the resin cement used. CONCLUSION: everStick posts resulted in the highest mean µTBS values with all cements. Self-adhesive cements performed well in terms of bond strength.

Diametral tensile strength of composite core material with cured and uncured fiber posts.

The aim of this study was to determine the influence of different types of posts and post head designs on the fracture resistance of a composite resin core material using the diametral tensile strength (DTS ). Seventy-five disc specimens were prepared using a composite core and prefabricated glass fiber posts and were divided into four test groups and one control group (n=15). The use of fiber posts reduced the DTS of the composite core material; the DTS value of the control material was significantly higher (p=0.05) than all of the test groups.

Hardness of Resin Cements Polymerized through Glass-Ceramic Veneers.

(1) Background: The aim of this study is to evaluate the hardness of resin cements polymerized through ceramic disks under different process factors (ceramic type and thickness, light-polymerization units and polymerization time); (2) Method: Three types of ceramic blocks were used (IPS e.max CAD; Celtra Duo; VITABLOCS). Ceramic disks measuring 0.5 mm, 1.0 mm and 1.5 mm were cut from commercial blocks. Two resin cements (Rely X Veneer and Variolink Esthetic) were polymerized through the ceramic specimens using distinct light-polymerization units (Deep-cure; Blue-phase) and time intervals (10 and 20 s). Hardness of cement specimens was measured using microhardness tester with a Knoop indenter. Data were statistically analyzed using factorial ANOVA (α = 5%); (3) Results: Mean microhardness of Rely X Veneer cement was significantly higher than that of Variolink Esthetic. Deep-cure resulted in higher mean microhardness values compared to Blue-phase at 0.5- and 1-mm specimen thicknesses. Moreover, a direct correlation was found between polymerization time and hardness of resin cement; (4) Conclusions: Surface hardness was affected by resin cement type and ceramic thickness, and not affected by ceramic types, within evaluated conditions. Increasing light-polymerization time significantly increased the hardness of the cement.

Microleakage of posterior composite restorations lined with self-adhesive resin cements.

PURPOSE: This study determined the microleakage of Class II composite restorations lined with self-adhesive resin-cements as bonding agents. METHODS: Forty-five caries-free extracted molars were sterilized, mounted in acrylic bases and divided into five equal groups according to the adhesive used: RXU (RelyX-Unicem, self-adhesive resin-cement, 3M ESPE), BRZ (Breeze, self-adhesive resin-cement, Pentron Clinical Technologies), MON (Monocem, self-adhesive resin-cement, Shofu), PAN (Panavia-F-2.0, resin-cement with self-etch primer, Kuraray) and SBMP (Scotchbond Multi-Purpose, total-etch three-step adhesive, 3M ESPE). Class II MOD cavities were prepared with gingival floors located on dentin at one side and on enamel on the other. The bonding agent SBMP, used according to the manufacturer's directions, or a thin layer of resin cement, was applied on all cavity walls and cavosurface margins. Filtek Z250 (3M ESPE) was used to restore cavities in all groups. The specimens were subjected to 1,000 thermocycles between 5 degrees C and 55 degrees C. All tooth surfaces were sealed with nail-varnish to within 1 mm from the restoration margins. The specimens were immersed in 2% fuchsine red solution for 24 hours at 37 degrees C. The teeth were then sectioned mesiodistally and dye penetration was assessed according to a five-point scale. Data were statistically analyzed with the Chi-square test (p < 0.05). RESULTS: Microleakage scores revealed that, on enamel margins, the SBMP group had significantly less microleakage than the RXU and BRZ groups, which, in turn, had significantly less microleakage than the MON and PAN groups; whereas on dentin margins, the RXU and BRZ groups had significantly less microleakage than the SBMP, MON and PAN groups. CONCLUSIONS: This in-vitro study showed that, when two self-adhesive resin-cements (RXU & BRZ) were used as liners in Class II composite restorations, they resulted in low microleakage scores as compared to the two other cements at both the enamel and dentin cavosurface margins.

Bond strength of orthodontic brackets with new self-adhesive resin cements.

INTRODUCTION: In this investigation, we determined the shear bond strength (SBS) of metallic and ceramic orthodontic brackets with new self-adhesive cements. METHODS: One hundred extracted premolars were used. They were sterilized and their roots embedded in stone bases, with the facial surfaces perpendicular to the bottom of the bases. The teeth were divided into 2 main groups, to receive metallic or ceramic brackets (Victory series 3M Unitek, Monrovia, Calif). In each group, the specimens were further divided into 5 subgroups according to the cement used: an etch-and-rinse control, Transbond-XT (3M Unitek); a resin cement with self-etch primer, Esthetic Cement system NC-100, (Kuraray, Okayama, Japan); and 3 self-adhesive resin cements: Rely-X Unicem (3M ESPE, Seefeld, Germany), Biscem DC (Bisco, Schaumburg, Ill), and Breeze (Pentron, Wallingford, Conn). Ten brackets were cemented in each subgroup. The specimens were stored in distilled water at 37 degrees C for 7 days and subjected to 3000 thermocycles between 5 degrees C and 55 degrees C. The brackets were then debonded in shear with a testing machine. RESULTS: Mean values for the metallic brackets cemented with Transbond XT, Esthetic Cement system, Rely-X Unicem, Biscem DC, and Breeze were 18.6, 6.0, 6.0, 2.2, and 8.4 MPa, respectively. For the ceramic brackets, the values were 22.7, 17, 7.7, 1.6, and 9.5 MPa, respectively. Analysis of variance (ANOVA) showed significant differences among the subgroups (P <0.05) for both bracket types. For the ceramic brackets, the Tukey test showed no statistical difference in mean SBS between Transbond XT and Esthetic Cement system. CONCLUSIONS: The SBS values of brackets cemented with etch-and-rinse cement were significantly higher than those of the 3 self-adhesive cements. However, when the self-etch adhesive, Esthetic Cement system, was used with ceramic brackets, no significant difference was found in the SBS compared with Transbond XT (P = 0.052).

Microleakage of porcelain and composite machined crowns cemented with self-adhesive or conventional resin cement.

PURPOSE: Resistance of machined crowns to microleakage when cemented with new self-adhesive cements has not been fully investigated. This study evaluated microleakage of machined crowns milled from porcelain and composite blocks and bonded to teeth with self-adhesive and conventional resin cement. MATERIALS AND METHODS: Thirty-two freshly extracted premolars of similar shape and size were sterilized and mounted in resin blocks. Teeth received standard crown preparations with 1-mm circumferential shoulder finish line, flat occlusal surface reduced by 2 mm, and ideal angle of convergence. Prepared teeth were divided into two equal groups and assigned to either porcelain (Vita Mark II, Vident) or composite (Paradigm MZ100, 3M ESPE) blocks for crown fabrication. Optical impressions were captured for each tooth with the intraoral camera of a CEREC 3D machine. Crowns were designed and milled from both materials. Each group was then subdivided into two subgroups (n = 8) according to cement used (self-adhesive resin cement, RelyX Unicem, 3M ESPE or resin cement with self-etching adhesive, Panavia F 2.0, Kuraray). Following seating, a 5-kg weight was applied on the occlusal surface of the crown for 5 minutes. Specimens were then stored in water at 37°C for 24 hours. Specimens were thermocycled for 3000 cycles between 5°C and 55°C, then coated with nail varnish and immersed in a 2.0% basic red fuchsine dye solution for 24 hours. Teeth were then rinsed and sectioned mesiodistally and assessed under magnification for microleakage. A five-point scale was used to score degree of microleakage. Data were statistically analyzed with 2-way ANOVA and Kruskal-Wallis nonparametric test. RESULTS: Crown material had no significant effect on microleakage (p= 0.67); however, cement type had a significant effect (p < 0.0001), with Panavia F 2.0 resulting in lower microleakage scores than RelyX Unicem. CONCLUSIONS: Compared to the self-adhesive cement, the resin cement with separate primer/bonding agent resulted in significantly lower microleakage scores, irrespective of crown material.

Convergence Angle of Preparations for Lithium Disilicate Glass-Ceramic Crowns by Dental Students and Its Effect on Crown Retention.

The aims of this study were to determine the convergence angles of posterior teeth prepared by dental students at the University of Toronto for lithium disilicate glass-ceramic (LDGC) CAD/CAM crowns and to investigate their effect on loss of retention rate. A total of 280 preparations for posterior monolithic LDGC CAD/CAM crowns were performed on 270 patients (169 women and 101 men). Crowns were cemented with RelyX Unicem and Calibra Universal resin cements. Mesial, distal, and angle of convergence were measured on the bitewing radiographs. Cemented crowns were followed for up to six years. Data were analyzed for tooth type and location and for operator experience. The results showed the majority of convergence angles were greater than the recommended guidelines but fell within a clinically acceptable range (20 to 24 degrees). However, angles of convergence for mandibular molar preparations were highest (28.06±5.50 degrees), while maxillary premolars exhibited the lowest values (24.72±6.59 degrees). No significant difference was found between the results of dental students and foreign-trained dentists. Over a six-year observation period, only two crowns lost retention. The findings of this study indicated that ideal taper angles were impractical and difficult to achieve in clinical education settings.