New Concept of Polymethyl Methacrylate (PMMA) and Polyethylene Terephthalate (PET) Surface Coating by Chitosan.

Chitosan is known for its hemostatic and antimicrobial properties and might be useful for temporary coating of removable dentures or intraoral splints to control bleeding after oral surgery or as a supportive treatment in denture stomatitis. This study investigated a new method to adhere chitosan to polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET). There were 70 cylindrical specimens made from PMMA and 70 from PET (13 mm diameter, 6 mm thickness). The materials with ten specimens each were sandblasted at 2.8 or 4.0 bar with aluminum oxide 110 µm or/and aluminum oxide coated with silica. After sandblasting, all specimens were coated with a 2% or 4% acetic chitosan solution with a thickness of 1 mm. Then the specimens were dried for 120 min at 45 °C. The precipitated chitosan was neutralized with 1 mol NaOH. After neutralization, all specimens underwent abrasion tests using the tooth-brushing simulator with soft brushes (load 2N, 2 cycles/s, 32 °C, 3000 and 30,000 cycles). After each run, the specimen surfaces were analyzed for areas of remaining chitosan by digital planimetry under a light microscope. The best chitosan adhesion was found after sandblasting with aluminum oxide coated with silica (U-Test, p < 0.05) in both the PMMA and the PET groups. Hence, with relatively simple technology, a reliable bond of chitosan to PMMA and PET could be achieved.

Effect of thermocycling on the shear bond strength of different resins bonded to thermoplastic foil applied in occlusal splint therapy.

PURPOSE: Temporomandibular disorders are a group of symptoms related to the impaired function of the temporomandibular joints and associated muscles. Occlusal splint therapy is a common treatment in the aforementioned syndrome. One of the methods of manufacturing occlusal splints is to place a polymer on thermoplastic foil. The aim of this study was to evaluate the shear bond strength of light- and self-cured resins bonded to thermoplastic foil dependent on artificial aging. MATERIALS AND METHODS: Thirty cylinders composed of light-cured resin and 30 cylinders made of self-cured resin were attached to 60 rectangular thermoplastic plates. All specimens were divided into six groups. A control study was conducted for groups 1 and 2. The other preparation groups were subjected to thermocycling by setting appropriately 1000 cycles for groups 3 and 4 and 3000 cycles for groups 5 and 6 in distilled water. Bond strength was measured in a universal testing machine. The results were subjected to statistical analysis using the Mann-Whitney U test (p ≤ 0.05). RESULTS: The statistics revealed that the values of the shear bond strength for specimens composed of self-cured resin after 1000 and 3000 thermocycles were significantly higher than on those made of light-cured resin (p = 0.003 and p = 0.002). CONCLUSION: The shear bond strength between the self-cured resin and the thermoplastic foil was higher and more resistant to aging than the shear bond strength between the light-cured resin and the thermoplastic foil.

Experimental study on the use of spacer foils in two-step putty and wash impression procedures using silicone impression materials.

STATEMENT OF PROBLEM: The 2-step putty and wash impression technique is commonly used in fixed prosthodontics. However, cutting sluiceways to allow the light-body material to drain is time-consuming. A solution might be the use of a spacer foil. PURPOSE: The purpose of this study was to evaluate the influence of spacer foil on the margin reproduction and dimensional accuracy of 2-step putty and wash impressions. MATERIAL AND METHODS: Two methods of creating space for the wash material in a 2-step putty and wash impression were compared: the traditional cutout technique and a spacer foil. Eleven commercially available combinations of silicone impression materials were included in the study. The impressions and the cast production were carried out under standardized conditions. All casts were measured with a 3-dimensional (3D) coordinate measuring machine. Preparation margin reproduction and the diameters and spacing of the stone cast dies were measured (α=.05). RESULTS: The 2 methods showed significant differences (P<.05) in the reproduction of the preparation margins (complete reproduction cutout, 90% to 98%; foil, 74% to 91%). The use of a foil resulted in greater dimensional accuracy of the cast dies compared to the cutout technique. Cast dies from the cutout technique were significantly smaller than the metallic original cast (cutout median, 4.55 mm to 4.61 mm; foil median, 4.61 to 4.64). Spacing between the dies revealed only a few additional significant differences between the techniques. CONCLUSIONS: When spacer foils were used, dies were obtained that better corresponded to the original tooth.

Physical properties of polyamide-12 versus PMMA denture base material.

OBJECTIVES: Polyamide-12 (PA) is a flexible material suited for denture bases and clasping. This study investigated its potential aging effects with a focus on surface roughness, color stability, and elasticity. METHODS: PA specimens (Valplast) of 40×10×2 mm and equally measuring PMMA specimens (Palapress) as control were fabricated. Color changes after storage in air, water, coffee, and red wine (n=10) were measured using the CIE L*a*b* color specification. Elasticity after thermocycling (1000, 3000, and 7000 cycles, n=15) was measured by three-point bending testing. Mean surface roughness (Ra) was determined after storage in the liquids mentioned above and thermocycling (n=10). RESULTS: Tukey's HSD test (P<0.05) revealed statistically significant color changes of PA in red wine (ΔE=4.27 after 12 days, ΔE=6.90 after 12 days) and coffee (ΔE=3.93 after 36 days) but no color changes in PMMA. Elastic modulus of PA was 845 MPa and not affected by thermocycling (Tukey's HSD test, P>0.81). Dry specimens showed significantly decreased elasticity (P<0.001). Mean surface roughness (PA 0.20 µ m, PMMA 0.28 µ m) did not change significantly after thermocycling or storage (Mann-Whitney U-test, 0.16

The use of light-cured resin as an alternative method of occlusal splints manufacturing--in vitro study.

BACKGROUND: Temporomandibular disorders are very common nowadays. One of the methods to treat these problems is occlusal splint therapy. Modern materials should be introduced to this treatment. OBJECTIVES: The aim of this paper was to evaluate the properties of light-activated urethane dimethacrylate and the quality of the bonds it creates with thermoforming foils. MATERIAL AND METHODS: Thermoforming foils were covered with light-cured resin. A bond was formed between the materials using an adhesive. A coating lacquer was used on the resin as a final preparatory step. Three laboratory tests were run: dye penetrant inspection, a Vickers microhardness test and a linear polymerization shrinkage test. The materials were layered and then cured with a polymerizing lamp emitting light of a wavelength of 400 Nm, according to the manufacturer's instructions. All the occlusal splints were fitted to upper dental arch. The devices had been made in an articulator on specially prepared gypsum models. The results were analyzed statistically using a one-sided binomial test, Spearman's rank-order correlation coefficient and the Friedman ANOVA (p=0.05). RESULTS: In the dye penetrant inspection, only one sample out of sixty showed the effects of color penetration to the adhesive connection. The dye only penetrated the layer of lacquer coating the resin. The average value of the Vickers microhardness test with a load of F=50 g applied to the material surface for 30 s was HV0.05=7.43 N/mm2. The average linear shrinkage of the resin observed after polymerization was 1.175%. CONCLUSIONS: Light-cured resin and an adhesive connection between the resin and thermoforming foil do not show susceptibility even to strong dye. The maximum polymerization shrinkage occurs immediately after curing. The light-cured resin that was tested seems to be a good alternative method for occlusal splints manufacturing.

Preparation of chitin-silica composites by in vitro silicification of two-dimensional Ianthella basta demosponge chitinous scaffolds under modified Stöber conditions.

Chitin is a biopolymer found in cell walls of various fungi and skeletal structures of numerous invertebrates. The occurrence of chitin within calcium- and silica-containing biominerals has inspired development of chitin-based hybrids and composites in vitro with specific physico-chemical and material properties. We show here for the first time that the two-dimensional α-chitin scaffolds isolated from the skeletons of marine demosponge Ianthella basta can be effectively silicified by the two-step method with the use of Stöber silica micro- and nanodispersions under Extreme Biomimetic conditions. The chitin-silica composites obtained at 120 °C were characterized by the presence of spherical SiO2 particles homogeneously distributed over the chitin fibers, which probably follows from the compatibility of Si-OH groups to the hydroxyl groups of chitin. The biocomposites obtained were characterized by various analytical techniques such as energy dispersive spectrometry, scanning electron microscopy, thermogravimetric/differential thermal analyses as well as X-ray photoelectron spectroscopy, Fourier transform infrared and Raman spectroscopy to determine possible interactions between silica and chitin molecule. The results presented proved that the character and course of the in vitro chitin silicification in Stöber dispersions depended considerably on the degree of hydrolysis of the SiO2 precursor.

Clinical test of masticatory efficacy in patients with maxillary/mandibular defects due to tumors.

BACKGROUND: The goal of the study was to evaluate the masticatory efficacy in patients who had been provided with resection prostheses after tumor removal in the maxillary/ mandibular region. These patients complained of impairment of masticatory function. PATIENTS AND METHODS: 3 groups of patients were compared under clinical-experimental conditions. A uniform chewing material was masticated by the participants under standardized conditions. A sieving procedure was used to evaluate the masticatory efficacy. Analysis of the particle sizes and particle masses obtained was performed with the aid of computers. RESULTS: The results showed that the masticatory efficacy of the patients with resection prostheses was the lowest of the 3 groups compared. The number of existing supporting zones and the location of the defect were found to be important influencing factors. Recording of the dietary habits of all patients was performed using a standardized dietary questionnaire. These data were analyzed using the corresponding software of the German Nutrition Society. With regard to the patients with resection prostheses, it was revealed that they often switched to food that did not require mastication. CONCLUSIONS: A nutritional guideline for patients with resection prostheses was developed, which is available for downloading free of charge on the Internet.

Simple method for preparation of nanostructurally organized spines of sand dollar Scaphechinus mirabilis (Agassiz, 1863).

Unique skeletal formations of marine invertebrates, including representatives of Echinodermata, have the unique potential to serve as templates for bio-inspired materials chemistry, biomimetics, and materials science. The sand dollar Scaphechinus mirabilis (Agassiz, 1983) is widely distributed in the northwest of the Pacific Ocean from southern Japan to the Aleutian Islands. This animal is the main source of naphtochinone-based substances. These compounds have recently drawn medical attention for their use as cardiological and ophthalmological drugs. Unfortunately, after extraction of the naphtochinones, the residual skeletons and spines of the sand dollars were usually discarded. Here, we report the first method for the preparation of nanostructurally organized spines of S. mirabilis, using a simple enzymatic and hydrogen peroxide-based treatment. Application of this method opens the way for development of non-wasteful environmentally clean technology of sand dollars as well-known industrial marine invertebrates.

Four-year clinical performance and marginal analysis of pressed glass ceramic inlays luted with ormocer restorative vs. conventional luting composite.

OBJECTIVES: The aim of the present study was to evaluate the ormocer Definite (Degudent, Hanau, Germany) as resin luting cement. METHODS: In a controlled prospective clinical study, 57 Cergogold (Degudent) all-ceramic inlays were placed in 24 patients by four dentists. The restorations were luted with two different systems (MD=Definite Multibond+Definite; SV=Syntac+Variolink Ultra, Ivoclar Vivadent, Liechtenstein) without lining. At baseline, after 12, 24, and 48 months, restorations were examined according to modified USPHS scores and criteria. RESULTS: One patient including three restorations missed the 4 years recall (dropout). After 48 months of clinical service, four restorations in four patients (three luted with Definite, one with Variolink) failed due to inlay fracture (n=3) and tooth fracture (n=1), all other fillings were clinically acceptable (survival rate 93.3% for Definite vs. 95.2% for Variolink; Kaplan-Meier algorithm). Except for the rate of hypersensitivity at baseline (MD: 27%; SV 0%; p<0.05), no differences were evident between the luting cements at any recalls (Mann-Whitney U-test; p>0.05). Between the four recalls, a statistically significant deterioration was detected for both groups regarding the criteria marginal adaptation, filling integrity (cracks/chippings/fractures), and tooth integrity (Friedman test; p<0.001). After 4 years, mainly distinct deterioration with marginal fractures or chippings in proximal and marginal areas of the inlays were observed. No differences were found for surface roughness, color matching, and proximal contact (p>0.05). CONCLUSIONS: For luting of ceramic inlays, only slight differences between the two luting systems were detectable.

Nanohybrid vs. fine hybrid composite in Class II cavities: clinical results and margin analysis after four years.

OBJECTIVES: This controlled prospective split-mouth study evaluated the clinical behavior of two different resin composites in extended Class II cavities over a period of four years. METHODS: Thirty patients received 68 direct resin composite restorations (Grandio bonded with Solobond M: n=36, Tetric Ceram bonded with Syntac: n=32) by one dentist in a private practice. All restorations were replacement fillings, 24 cavities (35%) revealed no enamel at the bottom of the proximal box, in 33 cavities (48%) the proximal enamel width was less than 0.5mm. The restorations were examined according to modified USPHS criteria at baseline, and after six months, one, two, and four years. At each recall, impressions were taken for replica preparation. Replicas of 44 select subjects were assessed for marginal quality under a stereo light microscope (SLM) at 130x and 22 replicas were assessed under a scanning electron microscope (SEM) at 200x. RESULTS: Both recall rate and survival rate were 100% after four years of clinical service. No significant difference was found between the restorative materials (p>0.05; Mann-Whitney U-test). Hypersensitivities were significantly reduced over time (p<0.05; Friedman test). A significant deterioration over time was found for the criteria marginal integrity (66% bravo after four years), tooth integrity (15% bravo), filling integrity (73% bravo) and proximal contact (p<0.05; Friedman test). SLM and SEM analysis of restoration margins revealed differences in the amount of perfect margins, in favor of Tetric Ceram (p<0.05). SIGNIFICANCES: Both materials performed satisfactorily over the four-year observation period. Due to the extension of the restorations, wear was clearly visible after four years of clinical service with 50% bravo ratings.

Experimental investigations for mechanical joint strength following ultrasonically welded pin osteosynthesis.

The purpose of this study was to determine whether fixation of cranial bone segments using ultrasonically welded pin osteosynthesis showed differences in mechanical stability as compared to fixation of cranial bone segments using screw osteosynthesis. Right and left cranial bone segments from each of 16 young sheep were obtained by craniotomy and re-fixed: on the right with a mesh plate and pins, and on the left with a mesh plate and screws. All osteosynthesis materials consisted of PDLLA, fully amorphous polyactid. A total of 167 cranial bone / mesh plate segments from 16 animals were investigated; 84 segments were pin-fixed and 83 segments were screw-fixed. The implantation time of the re-fixed segments ranged from 1 day to 196 days. The mechanical methods chosen for simulation of stress on the bone segment bonds were two bending tests (horizontal and vertical directions) and a tensile test. The values obtained in the mechanical tests indicate differences in the bond strength between the pin- and screw- fixation methods over the length of in vivo implantation time. The mechanical stability of the ultrasonically welded pin osteosynthesis bonds over the screw osteosynthesis bonds proved to be statistically significant. The implication of these findings should also be relevant in the field of medicine.

Comparative PRKAR1A genotype-phenotype analyses in humans with Carney complex and prkar1a haploinsufficient mice.

Carney complex (CNC) is a familial multiple neoplasia syndrome characterized by cardiac and extracardiac myxomas in the setting of spotty skin pigmentation and endocrinopathy. We previously identified PRKAR1A (regulatory subunit 1alpha of protein kinase A) mutations in CNC. Mutational analyses of the PRKAR1A gene in 51 unrelated CNC probands now detect mutations in 65%. All mutations, except for one unique missense mutation, lead to PRKAR1A haploinsufficiency. Therefore, we studied the consequences of prkar1a haploinsufficiency in mice. Although we did not observe cardiac myxomas or altered pigmentation in prkar1a(+/-) mice, we did observe some phenotypes similar to CNC, including altered heart rate variability. Moreover, prkar1a(+/-) mice exhibited a marked propensity for extracardiac tumorigenesis. They developed sarcomas and hepatocellular carcinomas. Sarcomas were frequently associated with myxomatous differentiation. Tumors from prkar1a(+/-) mice did not exhibit prkar1a loss of heterozygosity. Thus, we conclude that although PRKAR1A haploinsufficiency does predispose to tumorigenesis, distinct secondary genetic events are required for tumor formation.

[Restoration of Class V cavities with the Ormocer-based filling system Admira]. / Die Versorgung von Klasse-V-Kavitäten mit dem Ormocer-basierenden Füllungssystem Admira.

The aim of this study was to evaluate the clinical effectiveness of an Ormocer-based restorative system for treatment of mixed carious and non-carious class V cavities. 70 restorations in 25 patients were placed with the condensable material Admira (group 1). In a second group of eight patients, the treatment of 25 cavities took place with the flowable material Admira Flow in combination with composite-bonded to-flowable technique or with the flowable material alone. The clinical evaluation was carried out using a modified clinical criteria system (Böhm et al. 1991) after Lutz et al. (1977) and Ryge (1980). Restorations of group 1 reached the two-year-level, those of group 2 the one-year-level. Good results were obtained with both condensable material and flowable material despite the small number of failures in the various clinical criteria. The retention rate of the flowable composite was 100% after six and twelve months and was the only parameter superior to those of the condensable material (98.6% resp. 93.9%). After two years, group 1 showed significant differences to base line with respect to volume behaviour and surface texture. No significant differences were determined with respect to of colour match, bond zone morphology and clinical acceptance. A SEM evaluation of replicas confirmed clinical results but also revealed clinically invisible failures of bond zone morphology.

Dimensional changes of one-piece frameworks cast from titanium, base metal, or noble metal alloys and supported on telescopic crowns.

STATEMENT OF PROBLEM: The dimensional accuracy of 1-piece frameworks cast from commercially pure titanium and used to accommodate supporting telescopic crowns has not been demonstrated. PURPOSE: To compare dimensional changes incurred in frameworks cast from commercially pure titanium, a cobalt-chromium alloy, and a noble metal (gold) alloy. MATERIAL AND METHODS: This study was based on 2 different models, both prepared to receive telescopic crowns: 1 with 4 dies, designed to measure dimensional changes of the castings in the horizontal plane; and another with 2 dies, designed to measure dimensional changes in the vertical plane. As variables for the 2-die models, the palatal shape (16- and 20-mm radius) as well as the palatal depth (20-mm radius with the smallest palatal depth of 8 mm, 16-mm radius with flat palate and palatal depth of 10 mm, 16-mm radius with greatest palatal depth of 16 mm) were studied. Ten specimens each were fabricated from a commercially pure titanium, a cobalt-chromium alloy, and a gold alloy. All castings were fabricated under standardized conditions. All measurements were taken with a computer-controlled measuring microscope at the margins of the simulated telescopic crowns; these served to calculate the ideal midpoint from which the distances between the telescopic crowns were measured. The positional relation of the telescopic crowns was determined in horizontal and vertical directions. The measurements of the cast models were compared with measurements of the original model. The distances between the dies and the angles of the chosen telescopic crowns were calculated in fractions of millimeters and the angles were measured in degrees. The Kruskal-Wallis test and the Mann-Whitney U test were used for statistical analysis. The level of significance was alpha=5%. RESULTS: With the following exceptions, none of the 3 alloy types showed significantly different results. With the 4-die model, all 3 alloys showed significant variations from the original model for chosen lengths (P=.001). For those lengths, the dimensional accuracy of the noble metal alloy was approximately 99.9% of the length of the original; for the 2 other alloys, an average value of 99.4% was determined. With the 2-die models the calculated angle was significantly different from the original model for all alloys (P=.001 or.000), independent from the palatal vault and depth. Significant differences from the original model were also found for the distance between the 2 telescopic crowns with all alloys for the 2-die model with a 16-mm depth palatal vault and a 16-mm radius (P=.001,.006, or.009). CONCLUSIONS: Within the limitations of this study, the significant different dimensional changes both for the 4-die models and the 2-die models did not depend on the type of alloy. The 2-die models demonstrated significant dimensional changes resulting from the palatal geometry of the corresponding test models; the 4-die models demonstrated a tendency to contract toward the geometric center.

Torque capacity of metal and plastic brackets with reference to materials, application, technology and biomechanics.

AIM: The aim of the present study was to investigate slot deformation and the equivalent torque capacity of plastic brackets in comparison with those of a metal bracket in vitro and to simulate them under clinical conditions. MATERIAL AND METHOD: For this purpose the expansion characteristics of the brackets and their resistance to extraoral mechanical loading were compared in in-vitro activating experiments. In a further investigation, the labial crown torque of an upper central incisor was measured in a simulated intraoral clinical situation, using the Orthodontic Measuring and Simulation System (OMSS). Four types of bracket manufactured by Forstadent, Pforzheim, Germany, were tested: the plastic brackets Aesthetik-Line and Brillant, the latter from a previous series (Brillant-old) and from a modified series (Brillant-new), and the metal bracket MINI-MONO. For testing purposes the brackets were torqued with 0.016" x 0.022" (0.41 x 0.56 mm) and 0.018" x 0.022" (0.46 x 0.56 mm) ideal steel archwires (Remanium, Dentaurum, Ispringen, Germany). RESULTS: In the activating experiments, significantly higher torque losses and lower torquing moments were registered with both rectangular archwires with the plastic brackets than with the metal bracket. In the simulation tests, significantly higher torquing moments were registered with the metal bracket than with the plastic brackets. The OMSS model approximates the clinical situation, with the torque loss being notably higher than in the in-vitro activating experiments. This is due to the adjacent teeth giving the archwire additional play. In addition, the torquing process of the rectangular wire may deform the archwire, resulting in subsidiary forces. CONCLUSION: On the basis of the present results, the Brillant and Aesthetik-Line plastic brackets and the MINI-MONO metal bracket can be recommended for torquing. In view of the high torque losses, however, the torques programmed in the straight wire technique must be seen as questionable. It would be helpful to the practitioner if data were provided by the manufacturer on the flexing to be expected in plastic brackets, which has to be offset by additional torque or the possible renunciation of bracket torque.