Flexural strength of experimentally filled resins made of electron beam irradiated silica fillers.

This study investigated the influence of different silica fillers on the flexural strength of experimentally filled resins. Hydrophilic (non-silanated) silica, hydrophobic silica modified by organofunctional silane, and silica modified by organofunctional silane that additionally contains polymerizable carbon double bonds were assigned into further subgroups: the first subgroup was electron beam irradiated with 10 kGy (dose rate) and the second with 30 kGy, whereas the third constituted the non-irradiated control group. In total, nine experimentally filled resin blends were mixed. Rectangular specimens were constructed, and a flexural strength test was performed. Regardless of the type of silica, specimens constructed of blends containing non-irradiated fillers showed the lowest flexural strength in comparison to their corresponding irradiated groups. With increasing dose rates from 10 to 30 kGy, filler irradiation prior to blend mixing resulted in slightly increased flexural strength values for hydrophilic as well as for organofunctional silanated silica. Specimens constructed of blends with fillers that were not only modified by silane containing polymerizable carbon double bonds but were additionally irradiated showed the highest flexural strength. The results of this study indicate that the flexural strength of filled resins could be enhanced by advance preparation of silica fillers with silane coupling agents followed by electron beam irradiation.

Naturalistic changes in the readiness of postpartum women to quit smoking.

BACKGROUND: This study involves a long-term examination of the natural behavioral changes in postpartum women undergoing smoking cessation. The analysis was based on the readiness to quit smoking as assessed using the Transtheoretical Model of intentional behavioral change. This is a secondary data analysis of a randomized controlled trial. METHODS: Between May 2002 and March 2003, all women in the maternity wards of six hospitals in the German state of Mecklenburg-West Pomerania were screened for smoking before or during pregnancy. Of the women who answered in the affirmative, 871 (77%) participated in the study.We utilized a questionnaire to classify 345 women into stages of progress regarding their motivation to change their smoking behavior 4­6 weeks postpartum (T0). Participants were followed-up after 6 (T1), 12 (T2), and 18 months(T3). In addition to the descriptive analysis, latent transition analysis was applied as a statistical method to test models of patterns of change and to evaluate transitions in the stages of change over time. RESULTS: During the time interval between consecutive follow-up surveys, 59.1% (T0/T1), 72.3% (T1/T2), and 67.9% (T2/T3) of women remained at the same stage of motivation to change. Most relapses into earlier stages occurred 6 months postpartum (T1) (31.5% of the stage transition). The patterns of change across the first three time points were best described by a model that includes stability, one-stage progressions,and one-to-four-stage regressions. CONCLUSIONS: Readiness to quit smoking in study participants did not substantially change over the span of 18 months postpartum.

Marginal adaptation of three self-adhesive resin cements vs. a well-tried adhesive luting agent.

This in vitro study compared the marginal adaptation of three self-adhesive composite cements with the clinically well-tried dentin adhesive system Panavia F 2.0. A total of 32 Empress 2 all-ceramic MOD-inlays (eight in each group) were luted using the self-adhesive composite cements Maxcem, Multilink Sprint, and RelyX Unicem Clicker; Panavia F 2.0 served as a clinically well-tried control. Each luted inlay underwent long-term water storage of 90 days as well as additional mechanical and thermal loading to simulate oral service. Marginal integrity was evaluated in both dentin and enamel finishing lines using scanning electron microscopy (SEM) and dye penetration tests. Dye penetration was lowest for Panavia followed by RelyX Unicem. Maxcem and Multilink showed a considerable dye penetration of up to 60%. After aging, SEM analysis revealed a reduction of "perfect margin" areas for Multilink Sprint and RelyX Unicem in enamel and for Maxcem and Multilink in dentin. Compared with the well-tried system Panavia--which was assumed as the golden standard of adhesive luting systems--only the self-adhesive luting agent RelyX Unicem showed similar results of marginal adaptation after long-term water storage.

The impact of cement mixing and storage errors on the risk of failure of glass-ceramic crowns.

This study evaluated the impact of different mixing ratios and wrongly stored blends of dual-curing composite cements on Empress2 glass-ceramic crowns by means of a flexural strength test and a fracture resistance test. Thermally damaged blends and fresh blends were mixed using different mixing ratios of dual-curing Panavia F and Variolink II composite cement (2:1; 1:1; 1:1.5; 1:1.75; base/catalyst). Sixteen groups of rectangular beams of both cements (two blends, four ratios, chemical-curing, light-curing) were constructed. Their flexural strength was determined in a three-point bending test. Furthermore, 64 Empress2 all-ceramic crowns were luted onto human molars, again using fresh and thermally damaged blends as well as different mixing ratios of the luting agents. After aging, fracture resistance was investigated. The flexural strength of dual-curing composite cements was influenced to a statistically significant extent by mixing ratios and storage conditions. In particular, the chemical curing mode of these cements was affected by the thermal damage of the blends. However, this study could not demonstrate a significant impact on the fracture resistance of Empress2 glass-ceramic crowns when different mixing ratios or wrongly stored cements were used. Dual-curing composite luting agents seem to tolerate a wide range of mixing errors, but their chemical curing mode may be affected by storage errors.

Concepts for the treatment of adolescent patients with missing permanent teeth.

INTRODUCTION: Missing permanent teeth is observed with syndromes or is frequently hereditarily propagated in families. The treatment of these patients is a multi-task of specialists of oral surgery, orthodontics and prosthodontics. DISCUSSION: Despite functional and aesthetic considerations, the main problem of all treatment is that it had to be performed in a growing child. This article discusses the conventional and implant-driven concepts to treat patients from childhood to adolescence with selective or multiple missing permanent teeth.

Influence of core material on fracture resistance and marginal adaptation of restored root filled teeth.

AIM: To investigate ex vivo the influence of direct placement core materials on the fracture strength and marginal adaptation of root filled maxillary central incisors restored with glass fibre-reinforced posts, various core materials and all-ceramic crowns. METHODOLOGY: Forty-eight human maxillary incisors were root filled. Posts were placed and teeth restored with composite cores and crowns (n = 8). Six core materials were examined after thermal cyclic and mechanical loading (TCML). Fracture force was determined under static loading. The marginal adaptation at the interfaces between cement-tooth and cement-crown were categorized as 'intact margin' or 'marginal gap' using scanning electron microscopy. Statistical analysis was undertaken with the Mann-Whitney U-test (alpha = P < or = 0.05). RESULTS: Median fracture strength varied between 204 N (low viscous experimental core) and 1094 N (Multicore). No difference in fracture resistance was found with varying viscosity of the core material. The layering technique improved the fracture performance (P = 0.059) to a minor degree. Crowns with dedicated core materials (Rebilda 1063 N; Multicore 1094 N) had a significantly higher fracture resistance than crowns with a conventional restorative material (Tetric Ceram 509 N). Significantly poorer marginal adaptation before TCML was found for the layering technique at the tooth-cement interface and for all experimental cores after TCML. At the crown-cement interface significant differences in marginal adaptation could be determined between Multicore-layered core (P = 0.002) and Multicore-Rebilda (P = 0.001) after TCML. CONCLUSIONS: The fracture strength of post and core restorations was dependent on the core material and bonding system. Marginal adaptation was influenced by the method of application of the core material and by TCML.

Experimental composites made of electron beam irradiated reinforced fillers.

This study investigated the influence of electron beam irradiated reinforced fillers on the three body wear and flexural strength of experimental composite blends. Three formulations of reinforced fillers were investigated: (A) high loaded inorganic filler composite with 60 wt.% SiO2, (B) low loaded inorganic filler composite with 40 wt.% SiO2, (C) organic filler composite (precipitated Bis-phenol-A-di-methacrylate). The fillers were assigned to two subgroups of unswollen (A, B, C) and monomer swollen (As, Bs, Cs) fillers. The experimental blends (matrix: Urethane-dimethacrylate) were mixed using un-treated, annealed (90 degrees C), or electron beam irradiated fillers with 30 and 90 kGy, respectively. All specimens were heat-cured for 20 min at 140 degrees C. Three-body abrasion and flexural strength tests were performed. The highest flexural strength was evaluated for composites made of the 30 kGy irradiated type Bs filler. The comparison with annealed fillers showed that the effect was independent of increasing temperatures during the radiation process. Blends with a SiO2 content of 60 wt.% (type A, As) had significantly less wear than blends with 40 wt.% (type B, Bs) or blends with organic fillers (type C, Cs). The flexural strength of the composite could be improved by using pre-irradiated reinforced fillers. However, wear was not affected using this procedure.

The influence of electron beam irradiation on the shear bond strength of glass-reinforced frameworks and veneer composites.

The bond between glass fibre framework and veneer composite can be achieved by silane coupling agents or by monomers that penetrate into a polymer network. However, it has been clinically demonstrated that his bond can fail. This study investigated whether electron beam irradiation improved the bond strength of fibre-frameworks and veneer composite with and without additional coupling agents.

The influence of electron beam irradiation on fibre-reinforced composite specimens.

This study investigated whether glass fibre-reinforced composite (FRC) specimens can benefit from post-curing using electron beam irradiation. Twenty-four frameworks of the Vectris and 24 of the Stick glass fibre-reinforced system were veneered with their correspondent veneer materials. Eight specimens of both systems were post-cured using electron beam irradiation (3 x 33 kGy, 10 MeV). The specimens were fixed in a restrained-end apparatus and inserted in an artificial mouth. With the exception of controls (n = 8 each) all other groups were thermally cycled and mechanically loaded (TCML). Finally, all samples were loaded to fracture using a universal testing machine. In two of eight non-irradiated Vectris/Targis specimens facing fracture occurred during TCML. Irradiation avoided these failures. No Stick/Sinfony facing fractured. However, Stick frameworks showed considerable torsions. Post-curing with electron beam irradiation made Stick frameworks stiffer. The fracture load of irradiated Stick/Sinfony specimens reached 520 +/- 31 N; control (without TCML and irradiation) 396 +/- 14 N, TCML-group without irradiation 362 +/- 41 N. Irradiated Vectris/Targis had a fracture resistance of 575 +/- 57 N; the control 556 +/- 36 N and the TCML group without irradiation 383 +/- 51 N. This investigation demonstrated that different types of FRC systems could considerably benefit from electron beam irradiation. The reconstructions became stiffer and resisted higher load.

Influence of stress simulation parameters on the fracture strength of all-ceramic fixed-partial dentures.

OBJECTIVES: This in vitro study tested the influence of diverse stress simulation parameters on the fracture strength of all-ceramic three-unit fixed partial dentures (FPDs). METHODS: All-ceramic FPDs made of Empress 2 (Ivoclar-Vivadent, FL) were exposed to thermal cycling and mechanical loading (TCML) with varying loading parameters such as chewing force (amount, frequency), thermal loading, lateral jaw motion, abutment material, artificial periodontium or antagonistic denture. To investigate the influence of the abutment material, human teeth, polymer abutments and alloy abutments were used. Two different TCML devices with pneumatic or weight loading were compared. FPDs without aging were used as a control. RESULTS AND SIGNIFICANCE: Combined thermal and mechanical loading significantly reduced the FPD fracture resistance from 1832N to 410N. Duplication of chewing frequency, phase load increase or additional lateral movement did not effect the results. Increasing chewing force, artificial periodontium, and antagonist or abutment material reduced the fracture resistance of the tested FPDs. Different devices with weight or pneumatic loading had no significant influence on the loading capacity of the FPDs. Artificial aging should be performed combining thermal cycling with mechanical loading. Simulation of the artificial periodontium, human antagonists and abutments should be included to achieve a significant aging.

Composite veneering of metal based fixed partial dentures.

The aim of this in vitro study was to determine the thermal mechanical properties of veneering composites after polymerization with the appropriate polymerization device. Fracture tests were performed to investigate the effect on fixed partial dentures (FPDs). Dynamic mechanical thermal analysis was used to determine the temperature-dependent mechanical properties. To approximate the clinical situation, the fracture resistance of three-unit metal-based FPDs with different composite veneering was investigated after a simulated 5-year oral wearing period. The restorations were made of a high gold alloy and veneered with three different composites. To determine the influence of fabrication, one composite was used in a light-polymerizing and a heat/pressure-curing version and, in addition, a newly developed heat protection paste was used. After a 5-year simulation period, the fracture resistance was determined. The storage modulus varied between 14268 N mm(-2) (Belleglass) and 6616 N mm(-2) (Sinfony). Adoro showed no significant differences between light curing (9155 N mm(-2)) and heat curing (8184 N mm(-2)) variations. The Adoro-veneering with the heat protection paste showed the highest median fracture strength (1700 N), followed by Adoro LC (1555 N), Belleglass (1051 N), Adoro HP (1150 N) and Sinfony (909 N). The most common failure type occurring in all FPDs was a cracking of the composite, exposing the metal framework. All FPDs showed stress cracking of the composite. The heat protection paste seemed to reduce the crack formation after fabrication and increased the fracture resistance of the composite veneering. Stress cracking after thermal cycling and mechanical loading affected all composites, but all veneered three-unit alloy FPDs showed a fracture resistance sufficient for posterior application.

Electron beam irradiation of denture base materials.

UNLABELLED: Electron beam irradiation can be used to influence the properties of polymers. It was the aim of this study to investigate whether PMMA denture base materials can benefit from irradiation in order to have increased fracture toughness, work of fracture or hardness. Rectangular specimens of heat-and auto-curing denture base materials were electron beam irradiated (post-cured) with 25, 100 and 200 kGy using an electron acceleration of 10 MeV or 4.5 MeV respectively. Fracture toughness, work of fracture, Vickers hardness and colour changes were measured and compared with not-irradiated specimens. The toughness, work of fracture and hardness increased using 10 MeV with a dose of 25 kGy and with 100 kGy using 4.5 MeV. However, the clinical use may not benefit from the observed small changes. Higher dosage (200 kGy) decreased the values significantly. The colour changes reached a level which was found to be not clinically acceptable. CONCLUSION: PMMA denture base materials do not benefit from post-curing with electron beam irradiation.

In vitro fracture resistance and marginal adaptation of metallic and tooth-coloured post systems.

The aim of this in vitro study was to compare the fracture resistance and marginal adaptation of all-ceramic incisor crowns with all-ceramic posts, glass-fibre-reinforced posts and titanium posts as well as a control without any post. Three groups of eight maxillary incisors were restored with an all-ceramic post, a fibre-reinforced composite (FRC) post, a titanium post and a further group was restored without posts. Composite cores were provided and all-ceramic crowns were adhesively luted. After artificial ageing, the fracture resistance of the restored teeth was determined. The marginal adaptation of the restorations at the interfaces between cement-tooth and cement-crown was evaluated with scanning electron microscopy using replica specimen before and after ageing. The restored teeth without posts [270N (235/335)] showed no significantly different fracture strength compared with teeth with the titanium system [340N (310/445)]. The all-ceramic posts [580N (425/820)] and the FRC posts [505N (500/610)] both provided a significant higher fracture resistance than the teeth without posts. Prior to ageing, all materials showed <5% separation at the margins cement-tooth or cement-crown ('marginal gap'). After ageing, the interfaces of all systems deteriorated to values between 6 and 14% marginal gap. The greatest marginal gap was found with the titanium system (14%) at the interface cement-crown and with the all-ceramic posts (12%) at the transition between cement-tooth. Regarding fracture resistance and the marginal adaptation, the all-ceramic and FRC posts may be considered as an alternative to the commonly used titanium post restorations.

Marginal adaptation in dentin of a self-adhesive universal resin cement compared with well-tried systems.

OBJECTIVES: This study compares the marginal adaptation of a new self-adhesive universal resin cement with only one application step, to the marginal adaptation of established cements and their corresponding adhesive systems. METHODS: All-ceramic crowns were inserted on human molars using a new self-adhesive universal resin cement without and with one pre-treatment step, a resin cement with a smear-layer removing and a compomer cement with a smear-layer dissolving adhesive system. After simulation of five years oral stress, the marginal adaptation was evaluated by dye penetration and scanning electronic microscope analysis using the replica technique. RESULTS: Scanning electron microscopy: all investigated luting agents showed comparable amounts of 'perfect margin' ranging between 88-98% (median). Dye penetration: the self-adhesive system had significantly lower dye penetration (18-25%, median). SIGNIFICANCE: The results indicate that a self-adhesive universal resin cement without pre-treatment can provide a marginal adaptation at dentin which is comparable to established luting agents.

Fixed partial dentures: all-ceramics, fibre-reinforced composites and experimental systems.

The aim of this in vitro study was to compare the fracture strength of three-unit FPDs (fixed partial dentures) and three-unit inlay FPDs after a simulated 5-year oral wearing period. The restorations were made of a pressable all-ceramic (Empress 2) and two specially designed, experimentally fixed partial dentures combining ceramics with dental composite. Three-unit FPDs and inlay FPDs were manufactured and were adhesively luted onto human molars. After thermal cycling and mechanical loading in an artificial environment, the fracture strength was determined. Zircon-based milled ceramic (Lava) three-unit FPDs were used as a control. The zircon ceramic and the fibre-based ceramic three-unit FPDs showed median fracture values between 1000 and 1400 N. For composite veneered zircon FPDs a fracture strength of about 800 N and for all-ceramic Empress 2 of about 350 N could be determined. The results for the inlay FPDs were between 1300 N and 1400 N for FRC/ceramic, 1000 N for zircon/composite and 500 N for all-ceramic restorations. The all-ceramic showed higher fracture resistance applied as inlay FPDs. The described hybrid techniques combining ceramics and composites could represent an interesting procedure for further investigations and, eventually, clinical implication.

Marginal adaptation and fracture resistance of adhesively luted glass fibre-composite reinforced molar crowns with different inner crown surfaces.

OBJECTIVES: This study compared the influence of different inner crown surfaces on the fracture resistance and marginal adaptation of adhesively fixed glass fibre-reinforced molar crowns. MATERIALS AND METHODS: Vectris/Targis crowns were constructed with an inner framework of glass fibres (directly on the tooth) or an inner veneering composite layer between the fibre-framework and the tooth-substance. Both groups were sandblasted inside using Al(2)O(3); 50 microm grain size (200 kPa, 20 s) and silane coated. A control group had the inner fibre framework, but was neither sandblasted nor silane coated. The crowns were adhesively cemented on extracted human teeth, and thermally cycled and mechanically loaded (TCML: 6000 x 5 degrees C/55 degrees C; 1.2 x 10(6) x 50 N, 1.66 Hz). The marginal adaptation before and after TCML was evaluated and the fracture resistance was investigated using a Zwick universal testing machine. RESULTS: After TCML the proportion of 'perfect margin' of the control group decreased significantly at the interface crown/cement. For the variations with an inner fibre framework or inner composite layer the marginal adaptation or fracture resistance did not decrease significantly after ageing. The fracture resistance values were control: 1509N+/-486; inner fibre framework: 1896N+/-342; inner composite layer: 1754N+/-340. CONCLUSIONS: In the case of the investigated fibre framework and veneering composite, the inner surface of glass fibre-reinforced molar crowns can be covered with a composite layer or with a glass fibre framework. Both methods achieve comparable high fracture strengths and reliable marginal adaptation.

Fracture resistance of fiber-reinforced vs. non-fiber-reinforced composite molar crowns.

UNLABELLED: This study compared fracture resistance of fiber-reinforced and non-fiber-reinforced composite molar crowns under simulated oral stress conditions. Three groups of fiber-reinforced composite crowns were constructed using one polyethylene fiber (belleGlass/Connect) and two glass fiber reinforcement systems (Sculpture/FiberKor, Targis/Vectris). The non-fiber-reinforced crowns based on the facing material alone: Sculpture, Targis or belleGlass. Additionally, crowns were made of the non-reinforced composite Artglass. Each group consisted of eight crowns. All crowns were luted to human molars and exposed to thermal cycling and mechanical loading (6000 x 5 degrees C/55 degrees C; 1.2 x 10(6x)50 N; 1.66 Hz). The fracture resistance was measured using a Zwick universal testing machine. RESULTS: The non-reinforced Artglass crowns demonstrated the highest fracture resistance, significantly higher than the resistance shown with belleGlass, belleGlass/Connect or Targis. Artglass showed an extremely wide distribution of values, however. No statistically significant differences were found between the reinforced and non-reinforced composite crowns of Vectris/Targis, FiberKor/Sculpture or Connect/belleGlass although the reinforced crowns showed a tendency towards higher values. The fracture resistance values scattered markedly more for the reinforced crowns, and their lowest fracture values also reached the level of the lowest non-reinforced crowns. The small distribution of fracture values for the non-reinforced crowns indicates that they will be less susceptible for manufacturing faults and more reliable under clinical conditions. CONCLUSIONS: RESULTS of this study suggest that single molar composite crowns (tested in this study) do not benefit from fiber-reinforcement.

In vitro study of fracture strength and marginal adaptation of polyethylene-fibre-reinforced-composite versus glass-fibre-reinforced-composite fixed partial dentures.

This in vitro study was carried out in order to estimate the clinical usability of adhesively luted three-unit posterior fixed partial dentures (FPD) made of a polyethylene-fibre-reinforced-composite system (PFRC) in comparison with a glass-fibre-reinforced-composite system (GFRC). Therefore the fracture strength and marginal adaptation were examined. A total of 16 FPDs of each material combination were manufactured and adhesively luted to human molars. Before and after an artificial ageing process by thermal cycling and mechanical loading (TCML) the quality of the marginal adaptation was examined by evaluating epoxy replicas in a scanning electron microscope (SEM). After TCML the fracture strength of eight FPDs of each series was tested by mechanical loading them to failure. With the remaining eight FPDs the quality of deeper layers of the luting was examined with a dye penetration technique. The calculated median fracture strength values (25/75% percentiles) were 830 N (643/982) for the PFRC and 884 N (684/1,113) for the GFRC. The SEM analysis showed at least 80% of perfect marginal areas for both material combinations in dentine as well as in enamel before and after TCML. Looking at the cement-tooth interfaces the dye penetration technique showed statistically significant better results for the enamel finishing lines than for those in dentine. With finishing lines in dentine the two material combinations showed statistically significant differences for this interface. Fracture force results as well as marginal quality encourage further clinical investigations on both systems although the GFRC performed slightly better than the PFRC.

Frequency and costs of technical failures of clasp- and double crown-retained removable partial dentures.

OBJECTIVES: The aim of this study was to evaluate the frequency of technical failure rates and the maintenance costs of clasp- or double crown-retained removable partial dentures (RPDs) (parallel-sided and conical double crowns). MATERIAL AND METHODS: According to three different retainer systems used between January 1992 to December 1998, three subgroups were randomly assigned from a group of 181 patients consisting of forty cases each. The average observation time was 4.2+/-1.7 years, with a minimum of 1.0 years and a maximum of 6.9 years. Technical complications such as fractures of the artificial teeth, loss of cementation, loss of facings as well as fractures of the metal framework and the soldering were recorded due to the medical reports. RESULTS: Twenty percent of all clasp-retained dentures showed technical complications during the observation period, whereas 50% of conical crown-retained (CC) and 32.5% of the parallel-sided retained dentures (PS) required repair. Most often reported was loss of cementation for double crowns (n=13, 32.5% PS; n=8, 20% CC) and fractures of the clasps (n=5). Although clasp-retained dentures had a markedly lower frequency of failures (n=8) than double crown systems (n=31), the calculated repair costs per event during the observation time were more than twice as high for clasp-retained dentures (172.5 Euro) than for double crown systems (8-78 Euro). The hypothesis that the maintenance costs of the more sophisticated double crown system are higher must be rejected.

Glass-fibre-reinforced-composite fixed partial dentures on dental implants.

UNLABELLED: The objective was to investigate the fracture strength and marginal fit of implant suprastructures made of fibre-reinforced composite which were fixed onto the implants using cementation or screws. A sample (n=8) of 4-unit bridges, made of the fibre-reinforced composite Vectris/Targis, were adhesively cemented onto titanium conical implant abutments. The second sample consisted of eight screwable Vectris/Targis bridges which were based on prototypes of titanium crown bases. After a 5 year simulation of thermal cycling and mechanical loading (TCML), all specimen were loaded to fracture. Marginal fit was investigated using a semiquantitative SEM analysis. The cemented 4-unit bridges showed a fracture strength of 1553 N (Q1=1498 N, Q3=1825 N) and the screw-fixed bridges had a median of 1457 N (Q1=1223 N, Q3= 1781 N). The analysis of the marginal adaptation showed similar results of cemented and screwed bridges. The bond between the Targis facing-material and the composite cement was significantly deteriorated after TCML. CONCLUSION: Suprastructures made of glass-fibre-reinforced composite could become an alternative to reconstructions with a metal-framework. Both, fixation onto the implants with screws or cementation, are possible.