Reinhold Lang

Flexural properties of fiber reinforced composite using a vacuum/pressure or a manual adaptation manufacturing process

PURPOSE This study investigated the influence of fiber content and water storage on the flexural strength of beams made of two fiber-reinforced composites (FRC), the Vectris and the FibreKor system. MATERIAL AND METHODS A manual adaptation method (FibreKor, n=30) and a vacuum/pressure process (Vectris, n=30) were compared using 25x4x2mm(3) beams. One group of the Vectris (n=10) and the FibreKor beams (n=10) was stored in water for 24h, a further group was thermal-cycled (TC) 6000x5 degrees C/55 degrees C, and a third group was stored in water for 30days at 37 degrees C. All beams were then loaded to failure using a three-point bending test and the flexural strength was calculated. Finally, the fiber volume percent (vol%) was determined. RESULTS Generally, the flexural strength decreased significantly with increasing storage time independent of the investigated fiber- and/or manufacturing system. With the parameters 24h/TC/30days, the mean of flexural strength for the Vectris beams was 618/579/545N/mm(2), and for FibreKor 585/534/499N/mm(2). A fiber content of 28.1+/-0.4vol% was assessed for the Vectris beams and 12.8+/-0.6vol% for the FibreKor beams. After 24h storage in water, the Vectris and the FibreKor beams demonstrated a statistically significant higher flexural strength than after 30days storage in water. CONCLUSIONS A vacuum/pressure manufacturing process in contrast to manual adaptation, resulted in a markedly higher fiber content, but did not necessarily lead to significantly higher flexural strength. Not only the fiber content, but also matrix composition as well as the bond between fibers and matrix determined the properties of FRC.

In vitro examination of the fracture strength of 3 different fiber‐reinforced composite and 1 all‐ceramic posterior inlay fixed partial denture systems

PURPOSE This in vitro study was carried out to examine the fracture strength of metal- free posterior inlay fixed partial dentures (IFPDs). The 3-unit IFPDs were made of either a polyethylene fiber-reinforced composite, 3 glass fiber-reinforced composites, or an all-ceramic material. MATERIALS AND METHODS Eight IFPDs were fabricated of each material in accordance with the manufacturers instructions and luted to extracted human molars with a dual-cure adhesive system. The molars were positioned in PMMA resin 10 mm apart mesiodistally. Inlay cavity preparations with enamel finishing lines were used. After thermal cycling and mechanical loading in an artificial oral environment, the cemented IFPDs were mechanically loaded until failure. Visual and radiologic examinations were done out to discern the different forms of fracture. Median and 25%/75% percentile values were calculated. Statistical analysis was performed using the Mann-Whitney U test and the Kruskal-Wallis test (p< or =0.05). RESULTS With a median (and 25%/75% percentile) fracture strength of 368 N (234 N/424 N), the FibreKor/Conquest Sculpture showed significantly lower values than the Connect/BelleGlass [898 N (736 N/1033 N)], Vectris/Targis [723 N (692 N/806 N)], Everstick/Sinfony [634 N (532 N/673 N)], and Empress2 [520 N (385 N/706 N)]. CONCLUSIONS Assuming maximum chewing forces of > or =500N in posterior areas, all systems showed sufficient fracture strength in most cases and warrant further investigation for potential clinical use.

Self-adhesive resin cement versus zinc phosphate luting material: A prospective clinical trial begun 2003

OBJECTIVES The literature demonstrates that conventional luting of metal-based restorations using zinc phosphate cements is clinically successful over 20 years. This study compared the clinical outcomes of metal-based fixed partial dentures luted conventionally with zinc phosphate and self-adhesive resin cement. METHODS Forty-nine patients (mean age 54+/-13 years) received 49 metal-based fixed partial dentures randomly luted using zinc phosphate (Richter & Hoffmann, Berlin, Germany) or self-adhesive resin cement (RelyX Unicem Aplicap, 3M ESPE, Germany) at the University Medical Center Regensburg. The core build-up material was highly viscous glass ionomer; the finishing line was in dentin. The study included 42 posterior, 5 anterior crowns and two onlays. Forty-seven restorations were made of precious alloys, 2 of non-precious alloys. The restorations were clinically examined every year. The clinical performance was checked for plaque (0-5; PI, Quigley-Hein), bleeding (0-4; PBI; Mühlemann) and attachment scores. The examination included pulp vitality and percussion tests. STATISTICS Means of scores, standard deviation, cumulative survival and complication rates were calculated using life tables. RESULTS The mean observation time was 3.16+/-0.6 years (min: 2.0; max: 4.5 years). During that time no restoration was lost, no recementation became necessary. One endodontic treatment was performed in the self-adhesive composite group after 2.9 years. At study end bleeding (1.44 RelyX Unicem vs. 1.25 zinc phosphate) and plaque (1.64 RelyX Unicem vs. 1.0 zinc phosphate) scores showed no statistically significant difference. SIGNIFICANCE The self-adhesive resin cement performed clinically as well and can be used as easily as zinc phosphate cement to retain metal-based restorations over a 38-month observation period.

Experimental design of FPD made of all-ceramics and fibre-reinforced composite.

OBJECTIVES This study was carried out to combine flexural properties of FRC materials with aesthetic values of ceramics. METHODS The bonding strength of fibre-reinforced composite to ceramic was determined. Afterwards, 8 three unit and 8 four unit FPDs (fixed partial dentures) were manufactured based on the experimental design and were then adhesively luted onto human molars. After thermal cycling and mechanical loading in an artificial environment, the fracture strength and marginal adaptation was determined. FPDs made of FRC (fibre-reinforced composite) materials were used as a control. RESULTS The most reliable bonding strength of ceramic to FRC material was achieved using acid etching in combination with adhesive luting techniques. Median fracture strength values of 575 N for three unit FPD and 876 N for four unit FPD were established. More than 85% of the experimental FPDs showed a perfect margin while less than 15% revealed a marginal gap, even after thermal cycling and mechanical loading (TCML). The strongest influence of TCML on the marginal adaptation of the experimental design FPD was determined within the four unit system showing approximately a 10% change in marginal gap and perfect margin. SIGNIFICANCE Assuming an improvement in adhesive bonding between the ceramic and the FRC material and, in addition, an enhancement of the contact surface between pontic and abutment, the hybrid technique could represent an interesting procedure for further investigations and, eventually, clinical implication.

Comparison of failure rates of adhesive-fixed partial dentures for in vivo and in vitro studies

Abstract The objective was to investigate associations between the results of an in vitro and an in vivo study using an artificial mouth and a study of adhesive fixed partial dentures (AFPD) begun in 1985 [1]. Twenty extracted human molars and 20 human upper incisors were inserted into PMMA resin, 6 mm apart to represent a gap. Two preparation methods (identical to those in in vivo conditions) were used: a retentive preparation technique (posterior) and a non-retentive preparation technique (anterior). The frameworks of the bridges consisted of CoCr-alloy with a ceramic veneered pontic to replace the missing tooth. The bonding surfaces of the posterior AFPDs were conditioned with a tribochemical system, while the anterior AFPDs were sandblasted. All AFPDs were inserted using a dual curing composite cement. During thermal-cycling and mechanical loading (TCML: 6000×5°C/55°C, 1.2×106×50 N, 1.66 Hz) in an artificial environment, the frequency and type of failures were observed. The above mentioned loading parameters were hypothesized to represent a period of 5 years under oral conditions. The results were compared to those of similar bridge-types in the in vivo study. The Kaplan-Meier estimations showed similar graphs for in vivo and in vitro with both types of AFPDs. In vivo and in vitro, the retentively prepared AFPDs were markedly more successful. With regard to the failure types, the simulation-parameters seemed to represent a loading stress that was comparable to in vivo conditions.

Technical failure rates of double crown-retained removable partial dentures

Abstract Removable partial dentures (RPD) can be retained using conical crowns or parallel-sided telescopic double crowns. The purpose of this study was to evaluate and compare the technical failure rate of the two retainer systems. One hundred seventeen dentures made by dentists of the medical school were included. Seventy-four RPD were retained with parallel-sided crowns (n=251) and 43 with conical crowns (n=160). Following the medical report follow-ups from January 1992 to December 1998, technical RPD failures were noted and analyzed. Technical problems occurred during the observation time in 48.8% of the conical retained dentures and 34.2% of the parallel-sided retained dentures. In both cases, loss of cementation was most frequently noted, while loss of the facings occurred only with conical crowns. Other technical failures did not depend on the type of retainer system used. These were most frequently problems with the denture base, e.g., fracture of artificial teeth or the metal framework. We conclude that there were different technical failures of both double crown retainer systems. These problems were not insignificant in number but treatable.

Biofilm formation on the surface of modern implant abutment materials

OBJECTIVE To investigate the formation of biofilms on the surface of materials applied for the fabrication of implant abutments. MATERIAL AND METHODS Specimens were prepared from the implant abutment materials titanium, zirconia, and polyetheretherketone (PEEK); specimens made from polymethylmethacrylate (PMMA) were used for reference. All specimens were polished to high gloss using silicon carbide paper; surface roughness was determined using profilometry, and surface free energy was calculated from contact angle measurements. After the simulation of salivary pellicle formation, multispecies biofilm formation was initiated by exposing the specimens to a suspension of Streptococcus gordonii, Streptococcus mutans, Actinomyces naeslundii, and Candida albicans for either 20 or 44 h. Viable microbial biomass adherent to the specimens (n = 10 per material and incubation time) and the percentage of dead microorganisms in the different biofilms (n = 5, accordingly) were determined. RESULTS Significantly lower surface roughness was identified for PEEK and PMMA than for zirconia and titanium (P < 0.001); surface free energy was significantly lower for zirconia than for PEEK (P = 0.038). Significantly higher viable biomass and a significantly higher percentage of dead microorganisms were identified after 44 h than after 20 h of biofilm formation (P < 0.001, respectively); after 20 h, PEEK surfaces harbored significantly lower viable biomass than the surfaces of the other materials (P < 0.0125). After 44 h, significant differences were identified in the percentage of dead microorganisms organized in the biofilms on the different materials (P = 0.012). CONCLUSIONS Within the limitations of a laboratory study, the results suggest that biofilm formation on the surface of PEEK is equal or lower than on the surface of conventionally applied abutment materials such as zirconia and titanium. However, clinical studies are necessary to corroborate these preliminary results.

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.

Candida albicans biofilm formation on soft denture liners and efficacy of cleaning protocols

OBJECTIVE The aim of this study was to investigate Candida albicans biofilm formation on denture liners and to analyse the efficacy of cleaning protocols. MATERIAL AND METHODS Specimens were prepared from four silicone-based soft denture liners. After artificial ageing and surface free energy determination, specimens were incubated with saliva (2 h) and Candida albicans ATCC 10231 for either short- (2.5 h) or long-term (24 h) biofilm formation. Adherent cells were determined either after incubation of specimens with Candida albicans or after treatment with different denture cleaning protocols. Statistical analysis was performed using one-way anova and the Games-Howell test (α = 0.05). RESULTS For both short- and long-term biofilm formation, similar amounts of Candida albicans cells were found on the surface of the different liners (p = 0.295 and 0.178, respectively). For both short- and long-term biofilm formation, the highest cleaning efficacy was observed for sodium hypochlorite (NaOCl; p < 0.01). The efficacy of the chemical denture cleaner in removing long-term Candida albicans biofilms was significantly lower than the efficacy of removal by brushing (p < 0.001). CONCLUSION Different silicone-based soft denture liners yield similar Candida albicans biofilm formation on their surface. The highest efficacy for the removal of Candida albicans biofilms was identified for NaOCl. Chemical denture cleaners appear to have rather low efficacy to remove mature Candida albicans biofilms.

Biofilm formation and Candida albicans morphology on the surface of denture base materials

Fungal biofilms may contribute to the occurrence of denture stomatitis. The objective of the study was to investigate the biofilm formation and morphology of Candida albicans in biofilms on the surface of denture base materials. Specimens were prepared from different denture base materials. After determination of surface properties and salivary pellicle formation, mono‐ and multispecies biofilm formation including Candida albicans ATCC 10231 was initiated. Relative amounts of adherent cells were determined after 20, 44, 68 and 188 h; C. albicans morphology was analysed employing selective fluorescence microscopic analysis. Significant differences were identified in the relative amount of cells adherent to the denture base materials. Highest blastospore/hyphae index suggesting an increased percentage of hyphae was observed in mono‐ and multispecies biofilms on the soft denture liner, which did not necessarily respond to the highest relative amount of adherent cells. For both biofilm models, lowest relative amount of adherent cells was identified on the methacrylate‐based denture base material, which did not necessarily relate to a significantly lower blastospore/hyphae index. The results indicate that there are significant differences in both biofilm formation as well as the morphology of C. albicans cells in biofilms on the surface of different denture base materials.