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Abstracts of the December 2007 Issue

 

Working time of elastomeric impression materials:

Relevance of rheological tests

 

Markus Balkenhol, dds , Masafumi Kanehira, dds , phd, Werner J. Finger, dds , phd  &  Bernd Wöstmann, dds

 

Abstract: Purpose: To study possible relationships between rheological parameters of elastomeric impression materials and their dimensional accuracy at different stages during setting within the manufacturers’ recommended working time. Methods: Four chemically different impression material-types were tested. Impressions were taken of a master cone at 30-second intervals after mixing and up to 30 seconds beyond the recommended working time. Impression accuracy (Dd) was determined as the dimensional deviation of stone dies from the master cone. The phase angle d(t) and storage modulus G’(t) were measured and the working time determined according to ISO 4823. Three operators assessed the latest point in time for uncompromised impression taking. Correlation analysis was performed using Spearman’s Rho (P= 0.05). Results: For most materials investigated, Dd(t) was constant within the manufacturers’ recommended working time whereas d(t) and G’(t) changed significantly. There was no correlation (P> 0.05) between Dd(t) versus d(t) and G’(t), respectively. When determined according to ISO 4823, working time was longer than operator-assessed working time for all materials investigated. (Am J Dent 2007;20:347-351).

 

Clinical significance: Dentists should preferably take impressions reasonably early within the manufacturers’ recommended working time in order to avoid inaccuracy when approaching the very end of the working time. Rheological tests, including the procedure described in the ISO 4823, are unsuitable for identifying the latest point in time at which impression taking is still possible with consistent accuracy using the impression materials tested.

 

*: Dr. Markus Balkenhol, Schlangenzahl 14, 35392 Giessen, Germany.  

E-*:   markus.balkenhol@dentist.med.uni-giessen.de

 

Post-endodontic restorations with adhesively luted fiber-reinforced

composite post systems: A review

 

Kerstin  Bitter, dr med dent    &  Andrej  M.  Kielbassa, dr med dent

 

Abstract: Purpose: To review the literature on adhesive luting of fiber-reinforced composite posts ( FRC ) to provide evidence for the clinical procedure of restoring endodontically treated teeth using FRC posts. Methods: Data focusing on bonding behavior between root canal dentin, luting agent, and FRC post in vitro as well as in vivo performance of teeth restored with FRC posts were reported. These data were identified by searches of “PubMed”, “Scopus”, and “Cochrane Library” databases with the terms “post-endodontic restoration”, “fiber post”, “adhesive luting”, “root canal dentin”, “clinical study”, and “pre-treatment fiber post”. Papers published up to September 2007 were selected, and most relevant references were chosen. Cross-referencing of significant papers identified additional relevant articles. Results: FRC posts seem to have become increasingly popular for the restoration of endodontically treated teeth. Compared to metal posts, FRC posts revealed reduced fracture resistance in vitro, along with a usually restorable failure mode. Bonding behavior among FRC post, luting agents, and root canal dentin demonstrated varying results. Bond strengths between FRC posts and resin cements can be enhanced by using various pre-treatment procedures; however, bonding to root canal dentin still seems to be challenging. Most clinical studies investigating survival rates of teeth restored with FRC posts revealed promising results, but risk factors (e.g., the loss of coronal tooth structure) have not been studied intensively. In addition, randomized controlled clinical long term trials are scarce. (Am J Dent 2007;20:353-360).

 

Clinical significance: Evidence-based recommendations are still not possible, and further research using standardized protocols is warranted.

 

*: Dr. Kerstin Bitter , Department of Operative Dentistry and Periodontology, Charité Centrum 3 for Dental Medicine, Charité - Universitätsmedizin Berlin, Aßmannshauser Straße 4-6, D - 14197 Berlin, Germany. E-*: kerstin.bitter@charite.de

 

Five-year clinical evaluation of  One-Up Bond F in non-carious

cervical lesions

 

Michael  F.  Burrow, mds , phd, med    &   Martin  J.  Tyas, bds , phd ddsc   

 

Abstract: Purpose: To evaluate the retention and marginal staining of restorations placed in non-carious cervical lesions using the all-in-one self-etching system, One-Up Bond F and Palfique Estelite resin composite. Methods: Fifty-one non-undercut non-carious cervical lesions received restorations with One-Up Bond F and Palfique Estelite in 15 subjects (mean age 57.7 years) by one operator. Teeth were cleaned with pumice and water, restored following the manufacturer's instructions and evaluated at 6 months, 1, 2, 4 and 5 years for retention and presence of marginal staining. Results: At 1 year, 42 restorations were evaluated, and all were intact with three restorations showing slight marginal staining. At 2 years, 37 restorations were evaluated from 11 subjects, and all were intact. Marginal staining was observed around nine restorations. At 4 years, 27 restorations and at 5 years, 24 restorations could be evaluated. Marginal staining showed a significant increase at the enamel and cervical margins over the 5 years of the study, with two restorations showing severe, nine mild and 13 no staining. Although a number of restorations could not be evaluated, the retention rate of 92% at 5 years showed One-Up Bond F/Palfique Estelite resin composite for the restoration of non-carious cervical lesions produced an excellent outcome. Marginal staining was limited to a small number of subjects and is unlikely to be a problem if margins are refurbished at recall visits. (Am J Dent 2007;20:361-364)

 

 

Clinical significance: The all-in-one adhesive, One-Up Bond F, with Palfique Estelite resin composite is an effective adhesive for restorations in non-carious cervical lesions.

 

 

*: Dr. Michael F. Burrow, School of Dental Science, 720 Swanston Street , Melbourne 3010, Victoria , Australia .  E-*: mfburrow@unimelb.edu.au

 

 

Susceptibility of a polycaprolactone-based root canal filling material to degradation. Evidence of biodegradation from a simulated field test

 

Franklin R. Tay, bdsc (hons), phd,  David H. Pashley, dmd, phd,  Robert J. Loushine, dds , Sergio Kuttler, dds , Franklin García-Godoy, dds , ms,  Nigel M. King, bds , ms, phd   & Marco Ferrari, md, dds , phd

 

Abstract: Purpose: To examine if Resilon, a polycaprolactone-based root filling material, was susceptible to microbial biodegradation by using a simulated field test that consisted of incubating the material in wet dental sludge under mesophilic and aerobic conditions. Methods: Pressed disks prepared from Resilon, polycaprolactone (positive control) and gutta-percha (negative control) were incubated in wet dental sludge for up to 4 months and examined for topographical changes using scanning electron microscopy. Results: Gutta-percha exhibited minimal changes in surface integrity, while polycaprolactone and Resilon exhibited severe surface pitting and erosion. In the latter, disappearance of the polymer matrix was accompanied by exposure of mineral and bioactive glass fillers. Bacteria and hyphae-like structures were present on the disk surfaces. (Am J Dent 2007;20:365-369).  

 

Clinical significance:  The incorporation of polycaprolactone in the Resilon polymer/filler blend did not prevent its microbial biodegradation in a simulated field study. Thus, the potential for clinical biodegradation of Resilon in root canals should be further investigated in long term clinical trials using methodologies other than radiographic examination alone, as fillers do not undergo biodegradation and will appear radiopaque on radiographs even after the degradation of a radiolucent polymeric component.

   

*: Dr. Franklin Tay, Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta , GA , 30912-1129 , USA .  E-*:  tayfranklin7@gmail.com

 

 

The effect of direct and indirect water storage on the microtensile dentin bond strength of a total-etch and two self-etching adhesives

 

Ali I.  Abdalla, dds , phd, Magda El Eraki, dds , phd  &   Albert J. Feilzer, dds , phd

 

Abstract: Purpose: To evaluate the effect of direct and indirect water storage on the microtensile dentin bond strength of one total-etch and two self-etching adhesives. Methods: The adhesive materials were: one total-etch adhesive; Admira Bond and two self-etch adhesives; Clearfil SE Bond and Hybrid Bond. Freshly extracted human third molar teeth were used. In each tooth, a Class I cavity (4 x 4 mm) was prepared in the occlusal surface with the pulpal floor extending approximately 1 mm into dentin. The teeth were divided into three groups (n=12). Each group was restored with the resin composite Clearfil APX using one of the tested adhesives. For each experimental group three test procedures (n=10) were carried out: Procedure A: the teeth were stored in water for 24 hours, then sectioned longitudinally, buccolingually and mesiodistally to get rectangular slabs of 1.0 – 1.2 mm thickness on which a microtensile test was carried out; Procedure B: the teeth were also sectioned, however the slabs were stored in water at 37°C for 1 year before microtensile testing; Procedure C: the teeth were kept in water at 37°C for 1 year before sectioning and microtensile testing. During microtensile testing the slabs were placed in a universal testing machine and load was applied at a cross-head speed of 0.5 mm/minute. Results: For the 24-hour water storage groups there was no significant difference in bond strength between the three adhesives. After 1 year of indirect water storage, the bond strength decreased but the reduction was not significantly different from those of 24 hours. After 1 year of direct water storage, the mean bond strengths of Admira Bond and Hybrid Bond were significantly reduced compared to their 24-hour results. In contrast the average value of Clearfil SE Bond was not significantly affected. (Am J Dent 2007;20:370-374).

 

Clinical significance: All the tested adhesives showed no reduction in bond strength after indirect water exposure for 1 year. After 1 year direct water exposure, the bond produced by two-step self-etch adhesive was stable. In contrast, the two-step total-etch and all-in-one self-etch adhesive were unable to resist deterioration.

 

*: Dr. Ali I. Abdalla, Department of Restorative Dentistry, Faculty of Dentistry, University of Tanta , Tanta , Egypt .  E-*: Aliebraheem01@yahoo.com

 

Surface treatments on quartz fiber post: Influence on adhesion

and flexural properties

 

Nicolas  Cheleux, dds ,  Patrick  Sharrock, phd   &   Michel  Degrange, dds , phd

 

Abstract: Purpose: To evaluate (1) the effect of various surface treatments to optimize post adhesion, and (2) if these surface treatments had any adverse effect on the overall mechanical and chemical properties of the posts. Methods: Six experimental batches were set according to the nature of the surface treatments which were followed or not by post silani-zation. Post surface treatments were: control, chloroform (CHCl3) and sandblasting (sand) with Al2O3 50 µm. The silane (sil) used was Silane Coupling Agent Calibra. In all cases, a dual-cure bonding agent was applied Prime&Bond NT + Self Cure Activator. The Groups were: 1 (control), 2 (sil), 3 (CHCl3), 4 (CHCl3 + sil), 5 (sand), 6 (sand + sil). Following surface treatments, the posts were embedded in resin composite and the composite-post interfacial strength was investigated with a push-out test. Flexural and fatigue tests were performed to control the mechanical performances of the treated posts. Push-out data were analyzed using two-way ANOVA and Scheffé’s multiple means comparisons test (α= 0.05). SEM observations revealed the topographical modifications induced by sandblasting and the solvent. Results: Sandblasting or surface treatment with chloroform increased the bond strength (P< 0.001). The best values were obtained with the combination of sandblasting followed by post silanization. The flexural properties were not modified by the surface treatments (P= 0.072) and all the posts reached 3,000,000 cycles without breaking. (Am J Dent 2007:20:375-379).  

 

Clinical significance: A combination of sandblasting followed by silane and bonding agent application can be used in daily practice for increasing post retention to the composite core without modifying the mechanical resistance of the quartz fiber post. 

   

*: Dr. Nicolas  Cheleux, Faculty of Odontology, Paul Sabatier University, 3 chemin des Maraîchers, 31062 Toulouse, France . E-*:  cheleux@club-internet.fr

 

 

Marginal accuracy of press-ceramic veneers influenced by preparation design and fatigue

 

Christian  F.J.  Stappert, dds , ms, dr med dent ,  Ummuhan  Ozden, dds , dr med dent ,  Wael  Att, dds , dr med dent , Thomas Gerds, dipl- math , dr rerr nat   &   Joerg  R.  Strub, dds , dr med dent , phd

 

Abstract: Purpose: To investigate the influence of preparation design and mouth motion fatigue on the marginal accuracy of press-ceramic veneers bonded to human maxillary central incisors. Methods: Forty-eight extracted human maxillary central incisors divided in three groups of 16 specimens each, received veneer preparations. In Group WP a window preparation (WP) was performed. Specimens in Group IOP were prepared with an incisal overlap (IOP) of 2 mm without palatal chamfer. For Group CVP, specimens received a complete-veneer preparation (CVP) of 3 mm incisal reduction and 2 mm palatal extension. Veneers were fabricated with IPS Empress and bonded adhesively with dual polymerizing composite Variolink II. The discrepancies of marginal fit were examined on epoxy replicas before and after mouth motion fatigue at x200 magnification. Results: The mean (geometrical) (95% confidence limits) marginal accuracy after cementation was recorded as follows: WP-46 (43-49) µm, IOP-46 (44-49) µm and CVP-54 (51-58) µm. Fatigue led to a significant decrease of marginal accuracy in all groups (P< 0.036) [WP-47 (44-50) µm, IOP-51 (48-53) µm and CVP-63 (59-67) µm]. Group CVP demonstrated significantly higher marginal gap values than groups WP and IOP, before and after fatigue (P< 0.004). No significant differences were found between groups WP and IOP. (Am J Dent 2007;20:380-384).

 

Clinical significance: Examined preparation designs and luting method demonstrated a high marginal accuracy of press-ceramic veneers in vitro. The observed increase of marginal discrepancy for complete press-ceramic veneers was considered to be acceptable also for clinical application.

 

*: Dr. Christian Stappert, Department of Biomaterials and Biomimetics, New York University College of Dentistry, Arnold and Marie Schwartz Hall of Dental Sciences, 345 East 24th Street (Rm. 846S), New York , 10010 NY, USA .  E-*:  christian.stappert@nyu.edu

 

 

Remineralization of artificial interproximal carious lesions

using a fluoride mouthrinse

 

Markus  Jörg  Altenburger, dds ,  Jörg Fabian  Schirrmeister, dds ,  Karl-Thomas  Wrbas, dds & Elmar Hellwig, dds , phd

 

Abstract: Purpose: To evaluate remineralization and fluoride uptake of demineralized enamel specimens in artificial interproximal spaces using a 250 ppm fluoride mouthrinse (100 ppm amine fluoride and 150 ppm sodium fluoride) compared to a placebo-mouthrinse. Methods: This was a two-way, double-blind, in situ study. 24 volunteers wore intraoral appliances in the lower jaw with mounted demineralized enamel specimens forming an artificial interproximal space. The volunteers rinsed their mouths for 28 days, twice a day with the respective mouthrinse and brushed their teeth at least twice a day with a fluoride-free dentifrice. The specimens were cleaned once a day to simulate the use of dental floss. For analysis methods transversal microradiography, fluoride content measurement and quantitative light-induced fluorescence were used. Results: Mineral gain was significantly higher after the use of the fluoride mouthrinse: 571.88 Vol.%∙µm (±79.33 Vol.%∙µm SEM ) compared to the placebo treatment 51.14 Vol.%∙µm (±72.14 Vol.%∙µm SEM ). Significantly more fluoride uptake was observed after using the fluoride mouthrinse: 3666.39 µg/cmł (±513.50 µg/cmł SEM ) than after the placebo mouthrinse: 516.95 µg/cmł (±75.83 µg/cmł SEM ). The quantitative light-induced fluorescence showed a significant remineralizing effect after the fluoride treatment: -388.47 %∙mm˛ (± 18.76%∙mm˛ SEM ) compared to the placebo treatment -27.88%∙mm˛ (±20.19%∙mm˛ SEM ). (Am J Dent 2007;20:385-389).

 

Clinical significance: The results demonstrated a clear remineralizing effect of the fluoride mouthrinse tested and might be recommended for caries prevention and during therapeutic phases to support remineralization especially in difficult-to-reach areas.

 

*: Dr. Markus Jörg Altenburger, Department of Operative Dentistry and Periodontology, Dental School and Hospital, Albert-Ludwigs University Freiburg, Hugstetter Str. 49, 79095 Freiburg, Germany.  E-*: markus.altenburger@uniklinik-freiburg.de

 

Influence of three different sealants on root dentin demineralization in situ

 

Christian  Ralf  Gernhardt, dr med dent ,  Katrin  Bekes, dr med dent , dds &  Hans -Guenter  Schaller, dr med dent , dds

 

Abstract: Purpose: To evaluate in situ the onset of initial demineralization in human dentin pretreated either with two different dentin bonding agents or a desensitizer. Methods: 28 freshly extracted human molars were included in this study. The root surfaces were thoroughly cleaned, thereby removing the cementum. From each tooth four root dentin specimens were prepared. The specimens were distributed among the following experimental groups: C: control group (untreated), S: Syntac Classic, X: Xeno III , and H: Hyposen. For each subject, one dentin specimen of each group was inserted into both buccal aspects of a bilateral intraoral mandibular appliance. The appliances were worn by 14 subjects for 5 weeks day and night. One side was brushed daily with fluoride-containing toothpaste (Aronal) (B). On the other side, plaque was allowed to grow (NB). Individual oral hygiene techniques were performed without any fluorides. During meals, the appliance was stored in 10% sucrose solution. After the in situ period, slabs (150 µm) were ground and studied using polarized light microscopy. Results: For lesion depth, ANOVA revealed significant differences between brushed and unbrushed specimens. In the brushed groups, the  following lesion depths were evaluated (mean values and standard deviation in microns): Group B-C: 74.1 (±18.5), Group B-S: 27.6 (±9.6); Group B-X: 28.7 (±9.6), and Group B-H: 34.3 (±20.6). The non-brushed specimens showed following lesion depths: Group NB-C: 101.7 (±23.9), Group NB-S: 59.9 (± 13.1), Group NB-X: 52.5 (± 12.1), and Group NB-H: 72.9 (± 19.9). Compared to the non-brushed groups, lesion depths in the brushed group were significantly decreased (P< 0.05, Tukey’s test). The reduction of lesion depths after application of the three agents was significant in both cases (brushed and non-brushed groups). Within the limitations of an in situ study it can be concluded that the demineralization of the root surface can be inhibited by application of dentin adhesives and desensitizers under different oral hygiene conditions. (Am J Dent 2007;20:390-393).

 

Clinical significance: The application of clinically proven dentin bonding agents and desensitizing agents might have a caries-protective effect on exposed root surfaces.

 

*: Dr. Christian Ralf Gernhardt, Department of Operative Dentistry and Periodontology, University School of Dental Medicine, Martin-Luther-University Halle-Wittenberg, Grosse Steinstrasse 19, 06108 Halle, Germany. E-*: christian.gernhardt@medizin.uni-halle.de

 

 

In vitro wear of primary and permanent enamel.

Simultaneous erosion and abrasion

 

Gisele  Maria  Correr, dds , ms,  Roberta  Caroline  Bruschi  Alonso, dds , ms,  Simonides  Consani, dds , ms, phd, Regina  Maria  Puppin-Rontani, dds , ms, phd  &  Jack  L.  Ferracane, phd

 

Abstract: Purpose: To evaluate the wear differences between primary and permanent enamel caused by the association of abrasion and erosion. Methods: Fragments of 40 human teeth (20 primary and 20 permanent) were cast in acrylic rings, polished to expose a flat enamel area, and evaluated with a 3D profiler. Antagonists were made from primary and permanent molars. The specimens were distributed into four groups (n=10) according to type of substrate and slurry (neutral and acidic), and cycled 100,000 times in the OHSU oral wear simulator. Specimens were cleaned and re-profiled. Volume loss and maximum depth were determined on the polished specimens. Data were submitted to ANOVA and Tukey’s test. The area of the wear facet on the antagonist was measured. Results: Primary enamel showed more wear than permanent enamel, regardless of the slurry type. The acidic environment increased the wear rate compared to the neutral slurry. The association of abrasion and erosion increased the wear rate for the primary teeth only. There was no significant difference among groups for cusp wear and no correlation between cusp wear and the enamel wear. (Am J Dent 2007;20:394-399).

 

Clinical significance: Primary teeth are more susceptible to wear than permanent teeth, especially in an acidic environment, and limited exposure to acidic food and drink should be recommended to prevent accelerated tooth wear in children.

 

*: Dr. Gisele Maria Correr, Department of Restorative Dentistry, Dental Material Area, Piracicaba Dental School, UNICAMP, Av. Limeira, 901, CEP 13414-018, Piracicaba, SP, Brazil. 

E-*: giselefop@yahoo.com

 

Cytotoxic effects of different concentrations of chlorhexidine

                                  

Lorena  Brito de Souza, dds ,  Sabrina  García de Aquino, dds ,  Pedro  Paulo  Chaves de Souza, dds , ms, phd, Josimeri  Hebling, dds , ms , phd   &   Carlos Alberto de Souza Costa, dds , ms , phd

 

Abstract: Purpose: To evaluate the cytotoxic effects of different concentrations of Chlorhexidine (Chx) to the odontoblast cell line MDPC-23. Methods: The odontoblast-like cells were seeded (30,000 cells/cm2) in 60 wells of 24-well dishes and then incubated in contact with the following experimental and control solutions: Group 1: 0.0024% Chx; Group 2: 0.004% Chx; Group 3: 0.02% Chx; Group 4: Phosphate buffer saline solution (PBS, negative control); and Group 5: 0.06% H2O2 (positive control). Cell metabolic activity was measured by MTT assay and the cell morphology was analyzed by SEM . Results: The cytotoxic effects of Chx are dose-dependent. The reduction in the cell metabolism for Groups 1, 2, and 3 was 24.8%, 29.9% and 70.8%, respectively. No statistical difference was observed between the Groups 1 and 2 in which no significant cell morphology changes occurred. Consequently, it was concluded that 0.02% Chx solution presents high cytotoxicity to the odontoblast-like cells MDPC-23. On the other hand, 0.0024% and 0.004% Chx causes slight cytopathic effects to the cultured cells. (Am J Dent 2007;20:400-404). 

 

Clinical significance: Chlorhexidine (Chx) solutions do not interfere with the bonding mechanism during adhesive restoration and inhibit further degradation of the resin/dentin interface. In addition, low concentrations of Chx, such as 0.0024% and 0.004% do not cause significant toxic effects to the pulp cells and can be regarded as a potential chemical agent to be used as a cavity cleanser.

 

*: Dr. Carlos Alberto de Souza Costa, University of Săo Paulo State / UNESP, Rua Humaitá 1680, CEP: 14.801-903, CP: 331 – Centro, Araraquara, SP, Brazil .  E-*: casouzac@foar.unesp.br

 

 

 

Fracture load of fixed partial dentures anchored by composite inlays

 

Brigitte  M.  Ohlmann, dr med dent ,  Marc  Schmitter, pd, dr med dent ,  Olaf  Gabbert, dr med dent & Peter  Rammelsberg, prof, dr med dent

 

Abstract: Purpose: To evaluate in vitro the fracture load of fixed partial dentures (FPDs) anchored by use of composite inlays. The effects of span length, silica-coating, mechanical loading and framework material were also tested. Methods: Defined box inlay cavities were made on a mandibular molar and a premolar. Fifty-six FPDs were manufactured using a polymer composite material and received an industrial prefabricated polymethylmethacrylate (PMMA) frame for stabilization. All FPDs underwent thermal cycling. The FPDs were divided into test groups simulating the effect of different span length (7 or 12 mm), tribochemically silicoating (yes or no) and mechanical loading (yes or no). The load to fracture was measured and fracture sites were evaluated. As a control group for the PMMA frame, a metal alloy frame was used, and evaluated under the most unfavorable conditions. The Mann-Whitney U-test followed by the Bonferroni correction was used for statistical analysis. Results: The span length significantly affected the fracture load. Values ranged from 413 N for the 12 mm span length to 706 N for the 7 mm span length. Thermal cycling and mechanical loading significantly reduced fracture load values for FPDs with the 12 mm span length, but there were no significant effects for FPDs with 7 mm span length. Silicoating pretreatment of the metal abutments significantly reduced fracture load values. Replacement of the PMMA frame with a metal frame increased fracture load values up to 1,075 N. (Am J Dent 2007;20:405-410.)

 

Clinical significance: Short span, inlay-retained composite FPDs with PMMA frames showed acceptable fracture load values, but they cannot yet be unreservedly recommended for clinical use.

 

*: Dr. Brigitte Ohlmann, Department of Prosthodontics MZK II, University of Heidelberg, Im Neuenheimer Feld 400, 69120  Heidelberg, Germany. 

E-*:  Brigitte_Ohlmann@med.uni-heidelberg.de

 

 

Effect of denture cleansers on the hardness of heat- or auto-cured

acrylic- or silicone-based soft denture liner s

 

Ayşe Meşe, dds , phd

 

Abstract: Purpose: To investigate the effect of short (24 hours) and long term (6 months) exposure to a variety of commercially available denture cleanser solutions on the hardness of a variety of acrylic- and silicone-based resilient liners that were either heat- or auto-cured. Methods: The denture liners investigated were an acrylic-based heat-cured (Vertex Soft), acrylic-based auto-cured (Coe-Soft), a silicon-based heat-cured (Molloplast-B) and silicon-based auto-cured (Mollosil Plus) resilient liners. Cylindirical specimens (20 mm diameter, 12 mm high) were made of each material, using 10 replications for each test condition. Immersion solutions consisted of distilled water (control), and those based on alcohol, chlorhexidine, or an alkaline peroxide (Dermacol, aqueous chlorhexidine, Steradent) as a major active component. Specimens were fabricated according to manufacturer directions. Shore-A durameter hardness readings were taken on all specimens at each time interval and then compared statistically using four-way ANOVA and Tukey HSD (α= 0.05). Results: The results of this study indicated that, compared with distilled water, significant effect on the hardness of the specimens were found after immersion in all of the denture cleanser solutions at 24 hours and at 6 months. Specimens immersed in chlorhexidine showed higher and significant hardness changes than those immersed in other cleanser solutions. Also, it was determined that hardness of resilient liner materials increased with time and significantly higher hardness was recorded at 6 months for the auto-cured specimens compared with their heat-cured counterparts. (Am J Dent 2007;20:411-415).

 

Clinical significance: The increasing hardness was greatest in acrylic resin-based, auto-cured resilient liner in all cleansers especially in chlorhexidine, which suggests that the use of this resilient liner may not provide long-term clinical success.

 

*: Dr. Ayşe Meşe, Department of Prosthodontics, Dental Faculty, The University of Dicle Diyarbakır , Turkey . E-*: amese@dicle.edu.tr

 

 

Resistance to thermo-mechanical stress of different coupling agents

used as intermediate layer in resin-fiber post bonds

 

Francesca Monticelli, dds , msc , phd, Raquel  Osorio, dds , phd, Franklin  R.   Tay , bdsc (hons), phd, Fernanda  T.  Sadek, dds , msc , phd, Marco  Ferrari, md, dds , phd  &  Manuel  Toledano, md, dds , phd

 

Abstract: Purpose: To evaluate the microtensile bond strength (MTBS) of different coupling agents used in fiber post-composite bonds to withstand different in vitro challenging procedures. Methods: 63 fiber posts (DT Light Post) etched with 10% hydrogen peroxide were divided into three groups according to the silane/adhesive system applied: (1) Porcelain Bond Activator (PBA) + Clearfil SE Bond; (2) PBA + Clearfil Tri S Bond; (3) Monobond-S. A composite build-up (Clearfil AP-X) was performed around the post producing cylindrical specimens that were divided into three subgroups according to the different aging protocol: (1) 24-hour storage at room temperature; (2) Thermocycling (5000 cycles, 5°/55°C dwell time: 30 seconds); (3) Cyclic loading (45° angle, 20,000 cycles, load 5-50 N at 3.0 Hz). Samples were then cut obtaining sticks that were loaded in tension until failure. Bond strength values were statistically analyzed with two-way ANOVA and Tukey test (α = 0.05). Failure mode was recorded and the morphologic aspect of post/core interface after aging was evaluated under SEM . Results: Both post superficial treatment, thermocycling and cyclic loading influenced bond strength. After 24 hours, samples treated with silane/adhesive couplings attained higher MTBS than those bonded with conventional silane. No significant differences in the microtensile bond strength at the post/core interface were recorded between the different silane/adhesive couplings. After challenging, no differences were found between the tested groups. (Am J Dent 2007;20: 416-420).

 

Clinical significance: The application of a pre-activated single-bottle MPS silane solution formed relatively stable composite-fiber post bonds, reducing time required for the clinical procedure. Alternative coupling strategies may be desirable allowing a more stable bonding mechanism.

 

*: Dr. Francesca Monticelli, Department of Restorative Dentistry and Dental Materials. Policlinico Le Scotte, University of Siena , Viale Bracci , 53100 Siena , Italy .  E-*: francescamonti@hotmail.it

 

 

 

 


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