Radiodensity of base, liner and luting dental materials

The aim of this study was to determine the radiodensity of base, liner and luting dental materials and to compare them with human enamel and dentin. Four classes of materials were examined: conventional glass ionomers (CG)—Vitro Cem, Ketac Bond, Vidrion F, Vidrion C; resin-modified glass ionomers (RMGI)—Fuji II LC, Vitrebond; resinous cement (RC)—Rely-X ARC; and zinc phosphate cement (ZP)—Cimento LS. Five 2-mm-thick standard samples of each material and five 2-mm-thick enamel and dentin samples were produced. An aluminum step wedge served as control. Samples were positioned over a phosphor plate of Digora digital system, exposed to X-ray, and the radiodensity obtained in the software Digora for Windows 2.0. Data were submitted to Kruskal–Wallis and Dunnett multiple comparisons test (α=0.05). According to statistical analysis, the following sequence in degree of radiodensity could be seen among the groups: Cimento LS (ZP) > Vitro Cem (CG) = Fuji II LC (RMGI) = Rely-X ARC (RC) = Vitrebond (RMGI) > Ketac Bond (CG) > enamel = Vidrion F (CG) > Vidrion C (CG) = dentin. The presence of radiopaque fillers such as zinc, strontium, zirconium, barium, and lanthanium rather than material type seems to be the most important factor when analyzing material radiodensity. Almost all investigated materials presented an accepted radiodensity.     

Effect of software version and parameter settings on the marginal and internal adaptation of crowns fabricated with the CAD/CAM system

Objective

This study investigated the marginal and internal adaptation of individual dental crowns fabricated using a CAD/CAM system (Sirona’s BlueCam), also evaluating the effect of the software version used, and the specific parameter settings in the adaptation of crowns.

Material and Methods

Forty digital impressions of a master model previously prepared were acquired using an intraoral scanner and divided into four groups based on the software version and on the spacer settings used. The versions 3.8 and 4.2 of the software were used, and the spacer parameter was set at either 40 μm or 80 μm. The marginal and internal fit of the crowns were measured using the replica technique, which uses a low viscosity silicone material that simulates the thickness of the cement layer. The data were analyzed using a Friedman two-way analysis of variance (ANOVA) and paired t-tests with significance level set at p<0.05.

Results

The two-way ANOVA analysis showed the software version (p<0.05) and the spacer parameter (p<0.05) significantly affected the crown adaptation. The crowns designed with the version 4.2 of the software showed a better fit than those designed with the version 3.8, particularly in the axial wall and in the inner margin. The spacer parameter was more accurately represented in the version 4.2 of the software than in the version 3.8. In addition, the use of the version 4.2 of the software combined with the spacer parameter set at 80 μm showed the least variation. On the other hand, the outer margin was not affected by the variables.

Conclusion

Compared to the version 3.8 of the software, the version 4.2 can be recommended for the fabrication of well-fitting crown restorations, and for the appropriate regulation of the spacer parameter.     

INFLUENCE OF APPLICATION SITE OF PROVISIONAL CEMENT ON THE MARGINAL ADAPTATION OF PROVISIONAL CROWNS

Introduction: Marginal discrepancies may lead to cement washout and marginal leakage, damaging periodontal and pulp tissues or causing premature loss of the restoration. Purpose: This study evaluated the influence of application site of provisional cement on the marginal adaptation of provisional crowns. Material and Methods: Four different application sites of provisional cement (Temp Bond NE, Kerr Corporation) were used for cementation of provisional crowns on phantom teeth prepared for full crown restorations, performing 4 experimental groups (n=10): cement applied to all internal surfaces of the crown (CAO); cement applied to all internal surfaces of the crown, except for the occlusal surface (CA); cement applied to the cervical crown margin (CM); and cement applied to the cervical tooth margin (TM). A comparison microscope (Mitutoyo America Corporation) was used to measure the distances between the internal tangents of two circular marks, one made on the provisional crown and one made apical to the tooth preparation margin, in areas corresponding to buccal, lingual, mesial and distal surfaces. Marginal adaptation was determined before and after cementation, with 0.0001-mm accuracy. Data were analyzed statistically by ANOVA and Tukey''s test at 5% significance level. Results: Mean values of marginal opening obtained for each group were: CAO: 145 μm; CA: 67 μm; CM: 46 μm; TM: 34 μm. CA, CM and TM presented significantly lower marginal openings than CAO (p<0.05). Conclusion: complete filling of the crown with provisional cement, including the occlusal surface, provided grater marginal discrepancies when compared to the other methods evaluated.     

In vitro evaluation of the marginal and internal discrepancies of different esthetic restorations

Objective

This study examined the fit of two types of all-ceramic single crowns and indirect composite resin full coverage crowns.

Material and Methods

Thirty intact human mandibular first premolars were selected for this study and prepared using a machine to standardize the dimensions and randomly divided into 3 groups. Slip cast (IC) (In-Ceram Zirconia, Vita Zahnfabrik), copy-milled zirconia (CM) (ICE, Zirkonzahn) and indirect composite resin crowns (NECO, HeraeusKulzer, Hanau, Germany), (N=30, 10 per group) were fabricated according to each manufacturer''s recommendations. Before cementation, discrepancies were measured at the marginal zone in each crown. Crowns were then cemented with G-Cem capsule self-adhesive luting cement (GC Corporation, Tokyo, Japan). Four positions were marked for each zone (mid-facial, mid-mesial, mid-distal, and mid-lingual) and three measurements were made at each of the four positions yielding to a total of 12 measurements per crown before and after cementation. The measurements were performed at a different magnification using a stereo microscope (SZ11, Olympus, Japan). Marginal, axial and occlusal zone discrepancies (µm) were evaluated after cementation. The data were statistically analyzed using two-way ANOVA and Tukey''s test.

Results

Before cementation, significantly less marginal discrepancies were noted compared with after cementation in all groups (p<0.05). No significant differences were found within each zone (Marginal= IC: 84.2, NECO: 95.22, CM: 84.22; Axial= IC: 54.22, NECO: 64.2, CM: 55.22; Occlusal= IC: 119.97, NECO: 129.18, CM: 121.15) in the three crown systems (p>0.05). Occlusal zone discrepancies were significantly higher than those of the marginal and axial zones in all groups (p<0.05).

Conclusions

Slip cast and copy-milled zirconia crowns showed comparable fit to composite resin crowns in all marginal, axial and occlusal areas.     

Microleakage of core materials for complete cast gold crowns

This study evaluated the microleakage patterns of complete cast-gold crowns cemented onto teeth rebuilt with pin-retained cores made from cast gold, amalgam, composite resin, and silver-reinforced glass ionomer by using three different cements (zinc phosphate, glass ionomer, and resin cement). Crowns cemented onto unrebuilt tooth preparations with zinc phosphate cement served as controls. The cemented specimens were thermocycled between 4 degrees and 50 degrees C in waterbaths. They were then embedded in epoxy resin and sectioned. The extent of marginal microleakage was evaluated with a stereomicroscope and scored. The findings indicated that the type of luting agent used appeared to affect microleakage more than the core material. No significant differences in the degree of microleakage were found under crowns cemented onto teeth rebuilt with the four core materials when cemented with the same luting cement.     

EFFECT OF CAST RECTIFIERS ON THE MARGINAL FIT OF UCLA ABUTMENTS

Objectives:

This study assessed the effect of cast rectifiers on the marginal misfit of cast UCLA abutments compared to premachined UCLA abutments. The influence of casting and porcelain baking on the marginal misfit of these components was also investigated.

Methods:

Two groups were analyzed: test group – 10 cast UCLA abutments, finished with cast rectifier and submitted to ceramic application; control group – 10 premachined UCLA abutments, cast with noble metal alloy and submitted to ceramic application. Vertical misfit measurements were performed under light microscopy. In the test group, measurements were performed before and after the use of cast rectifiers, and after ceramic application. In the control group, measurements were performed before and after casting, and after ceramic application. Data were submitted to statistical analysis by ANOVA and Tukey''s test (α= 5%).

Results:

The use of cast rectifiers significantly reduced the marginal misfit of cast UCLA abutments (from 25.68μm to 14.83μm; p<0.05). After ceramic application, the rectified cylinders presented misfit values (16.18μm) similar to those of premachined components (14.3 μm). Casting of the premachined UCLA abutments altered the marginal misfit of these components (from 9.63 μm to 14.6 μm; p<0.05). There were no significant changes after porcelain baking, in both groups.

Conclusion:

The use of cast rectifiers reduced the vertical misfit of cast UCLA abutments. Even with carefully performed laboratory steps, changes at the implant interface of premachined UCLA abutments occurred. Ceramic application did not alter the marginal misfit values of UCLA abutments.     

不同粘固剂对 IPS-Empress 2后牙全瓷冠边缘适合性的影响

目的 :探讨不同粘固剂粘固的IPS Empress 2后牙全瓷冠的边缘适合性。方法 :采用印模复制和扫描电镜技术 ,测量磷酸锌粘固剂、PanaviaF树脂粘结系统和Dyracteompomer粘结剂粘固的IPS Empress 2后牙全瓷冠咀嚼模拟试验前后的边缘粘固剂厚度 ,并观察粘固剂表面状态。结果 :3种粘固剂粘固的全瓷冠边缘粘固剂厚度无显著性差异 (P >0 .0 5 ) ;磷酸锌粘固剂粘固的全瓷冠边缘粘固层有明显缺损 ,且咀嚼模拟试验后缺损增多 ,而另两种树脂类粘固剂未见明显缺损。结论 :PanaviaF树脂粘结系统和Dyractcompomer粘结剂粘固的IPS Empress 2后牙全瓷冠具有良好而稳定的边缘适合性     

In vitro study of fracture incidence and compressive fracture load of all-ceramic crowns cemented with resin-modified glass ionomer and other luting agents

Statement of problem. Anecdotal reports based on clinical observation have recently linked resin-modified glass ionomer luting agents with postcementation fracture of all-ceramic crowns. Purpose.This study evaluated the fracture incidence of In-Ceram and VitaDur Alpha porcelain jacket all-ceramic crowns cemented with 5 luting agents (Fuji I, Fuji Plus, Vitremer, Advance, and Panavia 21) during 2 months storage in 0.8% NaCl solution. Material and methods. Fifty human maxillary premolar teeth were prepared for each ceramic system and divided into 5 subgroups of 10 teeth to be cemented with 5 luting cements. Specimens were observed for fracture lines and crack initiation at storage times up to 2 months. Incidence of fracture was analyzed with Fisher’s Exact test. Specimens that did not fracture during storage were loaded in compression to failure. Failure loads were analyzed by analysis of variance and multiple pairwise comparisons. Results. Only all-ceramic crowns cemented with Advance cement fractured during the 2-month observation period, and porcelain jacket crowns were found to fracture earlier and more frequently than In-Ceram crowns. Cracks initiated at the crown margin, and multiple crack lines were found as the time of storage increased. In-Ceram crowns were significantly stronger (140 ± 21.5 kg) than porcelain jacket crowns (98.6 ± 17.8 kg) at P <.05. For In-Ceram crowns, cement type did not influence failure load while for porcelain jacket crowns, Fuji I (110.5 kg) was significantly higher than Vitremer (86.6 kg) at P <.05. Conclusions. For the cements studied, only crowns cemented with Advance cement demonstrated fracture during 2-month storage. Results for the true resin-modified glass ionomer cements do not support anecdotal reports of fracture of all-ceramic crowns cemented with these materials. (J Prosthet Dent 1998;80:699-707.)     

EFFECT OF DIFFERENT PROPHYLAXIS METHODS ON SOUND AND DEMINERALIZED ENAMEL

Considering the importance of professional plaque control for caries prevention, this study comprised an in vitro evaluation of wear by two prophylaxis methods (sodium bicarbonate jet – Profident and pumice and brush) on sound bovine enamel and with artificial carious lesions. Sixty enamel fragments were employed (4x4mm), which were divided into 4 groups: GI – 15 sound blocks treated with pumice and brush; GII – 15 sound blocks treated with Profident; GIII – 15 demineralized blocks treated with pumice and brush, and GIV – 15 demineralized blocks treated with Profident. In the fragments of Groups III and IV, artificial carious lesions were simulated by immersion in 0.05M acetic acid solution 50% saturated with bovine enamel powder at 37^oC for 16h. The specimens were submitted to the prophylactic treatments for 10 seconds. Wear analysis was performed by profilometer and revealed the following results: 0.91μm – GI; 0.42μm – GII; 1.6μm – GIII, and 0.94μm – GIV. The two-way ANOVA and Tukey''s test (p<0.05) revealed significant difference between all groups. Scanning electron microscopy images were employed to illustrate the wear pattern, with observation of larger alteration on the demineralized enamel surface (GIII; GIV), round-shaped wear on GI and GIII and blasted aspect on GII and GIV. The study indicated that the demineralized enamel presented more wear than the sound enamel, and the brush led to larger wear when compared to Profident.     

Microleakage of all-ceramic crowns using self-etching resin luting agents

Self-etching adhesive systems are a new generation of materials that possess acidic methacrylates that can generate self-adhesion. There is limited data reported on the marginal leakage of ceramic restorations bonded with self-etching adhesive materials. This study assessed and compared the amount of microleakage of bonded ceramic crowns using three different types of self-etching adhesive systems with and without a die spacer. Eighteen human molars were prepared for all-ceramic IPS Empress crowns and the teeth were randomly assigned to each experimental group. The buccal side had the preparation finish line 1.5 mm below the CEJ, and the lingual finish line was 1.5 mm above the CEJ, creating margins in enamel and dentin. Two die-spacing techniques were used (three layers or no layer of die spacer). Each crown restoration was cemented with one of three self-etching resin luting agents (Panavia F 2.0, Multilink and RelyX Unicem). The specimens were thermally cycled for 1000 cycles, then immersed in a 5% methylene blue dye solution for 24 hours. The teeth were then rinsed, embedded in clear epoxy resin and sectioned. A total of 60 sections were evaluated for each type of resin luting agent using digital image analysis at 70x magnification. A novel formula, using mean percentage of microleakage, was developed by dividing the extent of dye penetration along the tooth/resin luting cement interphase and the total perimeter of the tooth crown surface. The data were analyzed using three-way analysis of variance at the 0.05 level of significance. Fisher's PLSD intervals were calculated for comparing significant means. Panavia F 2.0 showed a lower degree of microleakage than RelyX Unicem and Multilink at both the enamel and dentin margins. Interactions of the main effects (cement, margin and die spacer technique) were all highly significant (p< or =0.004). The degree of microleakage was higher on the dentin margins than on the enamel margins (p<0.0001). The degree of microleakage for the die spacer group was not significantly different from the group with no die spacer technique (p>0.1). Overall, Panavia F 2.0 showed the least microleakage, followed by RelyX Unicem and Multilink, respectively.     

不同粘固剂对全瓷冠边缘完整性影响的研究

目的研究不同粘固剂粘固的全瓷冠边缘完整性。方法全瓷冠修复24颗离体上颌第三磨牙,随机分成3组,每组8个,分别用自酸蚀树脂粘接系统、Compomer粘固剂和磷酸锌粘固剂粘固,用扫描电镜观测标本牙疲劳试验前后边缘完整性及粘固剂表面质量。结果自酸蚀树脂粘接组试验前后完整边缘率均高于95%,Compomer组和磷酸锌粘固剂粘固组完整边缘率分别为16%~19%和5%,组间均有显著性差异（P〈0.001）;自酸蚀树脂粘接组边缘区粘固剂缺损显著小于其它两组（P〈0.05）。结论用自酸蚀树脂粘接系统粘固全瓷冠有优良的边缘完整性和边缘区表面质量。     

Effect of abutment neck taper and cement types on the amount of remnant cement in cement-retained implant restorations: an in vitro study

PURPOSEThe present study aims to analyze the effect of abutment neck taper and types of cement on the amount of undetected remnant cement of cement-retained implant prostheses.MATERIALS AND METHODSThree neck taper angles (53°, 65°, 77°) and three types of cement (RMGI: resin-modified glass ionomer, ZPC: zinc phosphate cement, ZOE: zinc oxide eugenol cement) were used. For each group, the surface percentage was measured using digital image and graphic editing software. The weight of before and after removing remnant cement from the abutment-crown assembly was measured using an electronic scale. Two-way ANOVA and Duncan & Scheffe’s test were used to compare the calculated surface percentage and weight of remnant cement (α = .05).RESULTSThere were significant differences in remnant cement surface percentage and weight according to neck taper angles (P < .05). However, there were no significant differences in remnant cement surface percentage and weight on types of cement. No interaction was found between neck taper angles and types of luting cement (P > .05). The wide abutment with a small neck taper angle showed the most significant amount of remnant cement. And the types of luting cement did not influence the amount of residual cement.CONCLUSIONTo remove excess cement better, the emergence profile of the crown should be straight to the neck taper of the abutment in cement-retained implant restoration.     

Influence of marginal fit and cement types on microleakage of all-ceramic crown systems

The purpose of this study was to evaluate the effects of both marginal fit and cementing with different luting agents on the microleakage of all-ceramic crown systems. Thirty-six extracted upper central incisors were prepared for full-coverage crowns and were divided into three groups. Group 1: CAD/CAM-fabricated ZrO2, Group 2: Heat-pressed lithium-disilicate, and Group 3: Cast Cr-Co copings as the control group. Copings were made following standard techniques, and groups were assigned cementation with either self-adhesive resin cement (A) or glass-ionomer luting cement (B). The specimens were subjected to thermocycling, immersed in basic fuchsin solution, sectioned mesiodistally and buccolingually. The surface of each section was digitally photographed under a stereomicroscope. Microleakage was scored using a five-point scale, and the marginal gap was measured using image analysis software. Data were statistically analyzed using 2-way ANOVA, Kruskal-Wallis, and Mann-Whitney U tests (α: 0.05). The marginal discrepancy of each group was 82.7 ± 7 μm, 92.6 ± 4 μm and 96.5 ± 7 μm respectively. Group 1 showed significantly smaller gaps than Group 3 (P = 0.042). Self-adhesive resin cement (A) showed a lower level of microleakage than glass-ionomer luting cement (B) in all groups (P = 0.029). Microleakage scores of '0' were 83% for 1A, 50% for 1B, 50% for 2A, 16% for 2B, 33% for 3A and none for 3B. Marginal discrepancy and cement type both had significant effects on microleakage. Lower levels of microleakage were recorded with self-adhesive resin cement, while CAD/CAM-fabricated ZrO2 copings showed smaller marginal discrepancy and less microleakage in comparison to cast Cr-Co.     

Microleakage--full crowns and the dental pulp.

Recent studies have described microleakage under full crowns cemented with several different cements. This study tested three different types of crown margin preparations--a chamfer, a shoulder, and a shoulder plus a bevel to determine whether or not the margin preparation could affect microleakage. All crowns were cemented with zinc phosphate cement. The crowns were tested for leakage in thermocycled dye. All crowns demonstrated significant leakage following the path of the dentinal tubules into the pulp. This could possibly be one of the causes of pulpal inflammation and even pulpal death under full crowns.     

Evaluation of marginal fit and internal adaptation of zirconia copings fabricated by two CAD - CAM systems: An in vitro study

Statement of Problem:

Three main factors which determine the success of an All-ceramic restoration are esthetic value, resistance to fracture and third being the marginal fit. Marginal fit and internal adaptation are crucial factors in increasing the longevity of the restoration. Newer and economical CAD CAM systems have been introduced claiming better marginal fit and adaptation of All ceramic crowns. CAD CAM systems involves scanning of the die or the tooth preparation and milling of the restoration, which may have variations among the systems available.

Aim of the Study:

Our study intended to check the marginal fit and internal adaptation of commonly used CAD CAM systems namely CERAMILL and CEREC -In Lab MC XL.

Materials and Methods:

Two groups of typodont teeth (n = 10) were prepared using a standardized protocol to receive All ceramic copings. 10 samples of Group A were used for fabrication of copings using CERAMILL system and 10 samples of Group B were used for fabrication of copings using CEREC -In Lab MC XL system. They were then luted with glass ionomer cement under mild finger pressure. Samples were embedded in resin and sliced longitudinally. They were then viewed under stereomicroscope and readings were measured along 15 points using ImageScope software. The P value was set at 0.05 at 95% confidence interval with 80% power. The data were checked for normality and unpaired t-test was used to evaluate the results of the two groups.

Results:

The overall internal adaptation was 61.5 ± 5.2 μm for CERAMILL and 56.9 ± 5.7 μm for CEREC -In Lab MC XL (P < 0.05). The marginal fit for CERAMILL was 83 μm and for CEREC -In Lab MC XL was 68 μm (P < 0.05).

Conclusion:

The marginal adaptation of CEREC -In Lab MC XL (68 μm) was found to be superior to CERAMILL (83 μm) (P < 0.05). Both the CEREC -In Lab MC XL and CERAMILL copings demonstrated internal adaptation and marginal fit within acceptable discrepancy range. When corroborating both the internal adaptation and marginal fit, CEREC -In Lab MC XL was found to be better than CERAMILL.     

Influence of luting agent on the microleakage of all-ceramic crowns

PURPOSE: In this in-vitro study, microleakage of all-ceramic crowns was evaluated at enamel and dentin margins. MATERIALS AND METHODS: Forty maxillary central incisors were randomly divided into 4 groups (n = 10). While buccal and palatal margins were placed on enamel, mesial and distal margins were placed below the cementoenamel junction. In groups 1 to 3, IPS Empress 2 crowns were luted with Variolink 2/Syntac Classic (group 1), Bifix DC/Solobond Plus (group 2) and Calibra/Prime & Bond NT combinations (group 3), respectively. In the control group (group 4), porcelain-fused-to-metal crowns were luted with a zinc-phosphate cement. All specimens were subjected to 5000 thermocycles (at 5 degrees C to 55 degrees C; 30-s dwell time). After immersion in India ink for 48 h at 37 degrees C, the specimens were sectioned both buccolingually and mesiodistally. Each section was evaluated for microleakage under a stereomicroscope at 24X magnification. RESULTS: According to the Krukal-Wallis test, in all groups, there were significant differences in microleakage at the enamel margins (p = 0.001). Nevertheless, the margins finished in dentin showed no significant differences (p = 0.163). According to the Mann-Whitney U-test, statistically significant differences were observed in microleakage between groups 1 and 3 (p = 0.049), groups 1 and 4 (p = 0.001), groups 2 and 4 (p = 0.002), and between groups 3 and 4 (p = 0.045) at the enamel margin. In group 1, significantly greater microleakage was observed at the dentin margin compared to the enamel margin (p = 0.007). CONCLUSION: The adhesive luting technique demonstrated an excellent ability to minimize microleakage of all-ceramic crowns at the enamel margins. Water-based dentin bonding systems showed less microleakage than the water-free acetone-based dentin bonding system at the enamel margin.     

Combined effects of thermocycling and load-cycling on microleakage of computer-aided design/computer-assisted manufacture molar crowns

This study evaluated the combined effects of thermocycling and compressive load-cycling on microleakage of computer-aided design/computer-assisted manufacture molar crowns. Sixteen ceramic (Vita Mark-II) and 16 composite resin (Paradigm MZ-100) crowns were milled using the CEREC 3D system. Eight crowns of each group were cemented to prepared molars using Panavia F 2.0, and 8 were cemented using RelyX Unicem Clicker. Specimens were thermocycled for 500 cycles and subjected to load-cycling for 1,000,000 cycles (60 to 600 N). Specimens were then tested for microleakage. Data were analyzed statistically using the Tukey post hoc test. All composite resin crowns survived load and thermal fatigue, while 6 ceramic crowns developed cracks. There were no statistically significant differences among groups regarding microleakage scores. Paradigm MZ-100 crowns were more crack-resistant to combined load and thermal fatigue than those composed to Vita Mark-II. However, microleakage scores of both types of crowns were similar. Int J Prosthodont 2011;24:376-378.     

Effect of a fluoride varnish on the margin leakage and retention of luted provisional crowns

STATEMENT OF PROBLEM: Provisional crowns cemented with provisional luting agents are susceptible to washout, margin leakage, and secondary caries when placed for a prolonged period. PURPOSE: This study was conducted to determine the effect of combining a varnish containing 2.26% NaF with 2 provisional luting agents on the margin leakage and retention of provisional crowns. MATERIAL AND METHODS: Acrylic resin provisional crowns were fabricated for 8 shoulder-prepared molars. The eight provisional (N=24) crowns were luted individually with Temp-Bond (TB), Freegenol (FG), or Duraphat (DU). Specimens were thermocycled 500 times (5 degrees and 60 degrees C) with a 1-minute dwell time, stored in 100% relative humidity at 37 degrees C for 6 days, and then immersed in a 0.5% Gentian violet solution for 24 hours. Seven days after cementation, a removal test of the crowns (shear retention test) was conducted with a universal testing machine at a crosshead speed of 5 mm/min. Retention was determined as the maximum recorded force needed for crown dislodgment. DU varnish was applied to the inner surface of the dislodged crowns with no removal of the cement layer TB, FG (N=16). The crowns were relined with a 0.5-mm layer of acrylic resin and luted with a combination of luting agent and DU (TB, FG) N=16. No luting agent (NC) served as the control (N=8). Results were analyzed with the Wilcoxon matched-pairs signed-ranks test. Leakage at the margins was assessed with a 4-level dye penetration scale, and statistical differences were identified with a chi(2) test. All hypothesis testing was conducted at the 95% level of confidence. RESULTS: The mean 7-day retention forces were as follows: 44.5 N (Temp-Bond), 51.6 N (Freegenol), and 35.9 N (Duraphat). There were no significant differences among these values. Duraphat combined with Freegenol decreased the retention of provisional crowns, but Duraphat combined with Temp-Bond increased the retention of provisional crowns by 69-145%. Duraphat alone and in combination with both provisional luting agents significantly reduced margin leakage (P<.05). The least margin leakage was evident when the provisional crowns were luted with Duraphat alone. CONCLUSION: With regard to retention and margin leakage, the results of this study suggest that Duraphat varnish can be successfully used as provisional luting agent for single provisional crowns.     

Effect of luting cement on dental biofilm composition and secondary caries around metallic restorations in situ

Since the importance of luting cement on secondary caries in enamel and dentin is unknown, an in situ crossover study was conducted in three phases over 21 days using a fluoride-containing toothpaste. One hundred and twenty-six metallic restorations were cemented into the dentinoenamel junction of slabs of human teeth with zinc phosphate (ZP), resin-modified glass ionomer (GI) or resinous cement (RC). The slabs were inserted onto flanges of the removable partial acrylic dentures of 14 volunteers and covered with gauze to enhance dental plaque accumulation. The volunteers used fluoride toothpaste (1.100 microg F/g, w/w). After 21 days, the biofilm that formed on the slabs was collected for biochemical and microbiological analyses, and the demineralization in enamel-dentin around the restorations was evaluated. The fluoride concentration of biofilm in the GI group was higher (p<0.05) than the ZP and RC groups. Also, the concentration of Zinc in biofilm formed on the slabs cemented with ZP was higher (p<0.05) than the other groups. However, the effect of the luting material on enamel or dentin demineralization was not statistically significant (p>0.05). The data suggest that when fluoride toothpaste is used, the anticariogenic property of the luting cement may not be relevant to the reduction of secondary caries.     

EFFECT OF STORAGE PERIOD ON THE ACCURACY OF ELASTOMERIC IMPRESSIONS

Aims:

To investigate the effect of the storage period on the accuracy of recently developed elastomeric materials.

Methods:

Simultaneous impressions of a steel die were taken using a polyether (I: Impregum Soft Heavy and Light body, 3M ESPE) and vinyl polysiloxane (P: Perfectim Blue Velvet and Flexi-Velvet, J.Morita). The trays were loaded with the heavy-bodied impression materials while the light-bodied impression materials were simultaneously spread on the steel die. The impressions were poured after 2 hours, 24 hours, and 7 days. Impressions were stored at approximately 55% relative humidity and room temperature. Ten replicas were produced for each experimental condition (n=60). Accuracy of the stone dies was assessed with a depth-measuring microscope. The difference in height between the surface of the stone die and a standard metallic ring was recorded in micrometers at four demarcated points, by two independent examiners. Dxata were submitted to two-way ANOVA and Tukey test (α = 0.05).

Results:

Significant differences were found among the groups. Smaller discrepancies were observed when pouring was performed up to 24 hours (I-2h= 65.0 ± 15.68 μm; I-24h= 81.6 ± 11.13 μm) for the polyether, and up to 7 days for the vinyl polysiloxane (P-2h= 79.1 ± 13.82 μm; P-24h= 96.8 ± 6.02 μm; P-7d= 81.4 ± 4.3 μm). Significant dimensional discrepancies, however, were observed when polyether was stored for 7 days (I-7d= 295.3 ± 17.4 μm).

Conclusion:

Storage may significantly affect the dimensional accuracy of impressions and, thus, a maximum period and storage condition should be specified for the recently developed materials.