Influence of artificial aging: mechanical and physicochemical properties of dental composites under static and dynamic compression.

OBJECTIVE: The aim of the study was to evaluate the influence of filler content, degradation media and time on the mechanical properties of different dental composites after in vitro aging. MATERIALS AND METHODS: Specimens (1 mm3) of three commercially available composites (GrandioSO®, Arabesk Top®, Arabesk Flow®) with respect to their filler content were stored in artificial aging media: artificial saliva, ethanol (60%), lactic acid (pH 5) and citric acid (pH 5). Parameters (Vickers microhardness, compressive strength, elastic modulus, water sorption and solubility) were determined in their initial state (control group, n = 3 for microhardness, n = 5 for the other parameters) and after 14, 30, 90 and 180 days (n = 3 for microhardness, n = 5 for the other parameters for each composite group, time point and media). Specimens were also characterized with dynamic-mechanical-thermal analysis (compression tests, F = ± 7 N; f = 0.5 Hz, 1 Hz and 3.3 Hz; t = 0-170 °C). RESULTS: Incorporation of fillers with more than 80 w% leads to significantly better mechanical properties under static and dynamic compression tests and a better water sorption behavior, even after chemical degradation. The influence of degradation media and time is of subordinate importance for chemical degradation. CONCLUSION: Although the investigated composites have a similar matrix, they showed different degradation behavior. Since dentine and enamel occur only in small layer thickness, a test specimen geometry with very small dimensions is recommended for direct comparison. Moreover, the use of compression tests to determine the mechanical parameters for the development of structure-compatible and functionally adapted composites makes sense as an additional standard. Clinical relevance Preferential use of highly filled composites for occlusal fillings is recommended.

Peri-implantitis cleaning instrumentation influences the integrity of photoactive nanocoatings.

OBJECTIVE: To determine in vitro the loss of integrity caused on photocatalytic anatase coated implant surfaces by clinical instrumentation through changes in surface topography and loss of functionality. METHODS: Anatase-coated titanium discs were treated with diamond burs, polishers, plastic and metal hand instruments, air scaler and air flow devices. The pressure exerted through instrumentation was measured online. Surface topography was evaluated through scanning electron microscopy and contact profilometry, surface function through hydrophilization capacity upon UV-A activation. RESULTS: Treatment with diamond burs and instruments with metal tips resulted in an increase of roughness. Use of silicone polishers led to smoothening, which was more pronounced on the anatase surface. Plastic instruments, the air abrasive system and rubber cups left the surfaces intact. Functionality was partially lost on surfaces subjected to hand instruments and completely lost upon diamond burs and silicone polishers. SIGNIFICANCE: The integrity of functional nanocoatings depends on the applied instrumentation. Air flow device, rubber cup with polishing paste and plastic tipped instruments prevent damage on these nanosurfaces and may be preferably used when decontaminating anatase and other nanocoatings in a clinical setting.

[Failure analysis as basis for quality assurance strategies in implant technology]. / Schadensanalyse als Basis für Qualitätssicherungsstrategien in der Implantattechnologie.

BACKGROUND: Implant safety is a topic gaining more and more public interest. Implants are safety relevant medical devices which in the case of failure can lead to life-threatening situations. OBJECTIVES: A well-founded failure analysis requires expert knowledge not only of materials and implant design but also a qualified explantation procedure and storage conditions. METHODS: A selective literature search was carried out putting the main emphasis on implant failure analysis supplemented with own investigations. RESULTS: The reasons for implant breakdown are mostly failures of materials and in the manufacturing process. In some cases false material combinations can lead to tribocorrosion effects under cyclic loading. CONCLUSION: The increased level of knowledge gained from complex analyses of failed implants produces valuable evidence for better quality management.

Dental implants and immediate loading: multivariate analysis of success factors.

OBJECTIVES: The authors had for aim to examine factors potentially influencing the success of immediate implant placement and loading. MATERIALS AND METHODS: One hundred and ninety-five consecutive patients (16.5 to 80.4 years of age) were provided with 310 prostheses supported by 896 immediately loaded implants. The mean follow-up was 27.5 months. Univariate and multivariate Cox regression was performed to analyze potential modifiers of implant success. RESULTS: The overall implant success rate was 96.7%. The statistically significant modifiers of success on multivariate analysis (P<0.05) were duration of functional use (P<0.001), type of superstructure (P<0.001), implant-abutment connection (P<0.001), and maxilla versus mandible (P=0.026). None of the other investigated factors (age, gender, implant location/design/length) were statistically significant modifiers of success. DISCUSSION: Our study results demonstrate high success rates for immediately loaded implants whatever types and superstructure used. Prosthetic designs and their implementation have a significant effect on the success rate of implant-supported restoration, with adjusted hazard ratios of up to 51. Maxilla versus mandible was the only significant non-external modifier when using an adjusted hazard ratio of 2.75.

Scaling of polymers in aligned rods.

We study the behavior of self-avoiding polymers in a background of infinitely long vertically aligned rods that are either frozen in random positions or free to move horizontally. We find that in both cases the polymer chains are highly elongated, with vertical and horizontal size exponents that differ by a factor of 3. Though these results are different than previous predictions, our results are confirmed by detailed computer simulations.

Intermittent androgen suppression for prostate cancer: Canadian Prospective Trial and related observations.

The Canadian Prospective Trial of intermittent androgen suppression was a prototype therapeutic initiative started in 1995 for the management of patients in biochemical relapse after radiation for localized prostate cancer. An interim analysis has yielded several observations on the relations between baseline serum prostate specific antigen (PSA), nadir serum PSA, Gleason score, and time off-treatment. In a typical androgen-dependent tumor, the response of serum PSA to androgen withdrawal is biphasic, but with early tumor progression, plateauing of serum PSA is observed. Ligand-independent activation of the androgen receptor, a mechanism subserving the initiation of androgen independence, can be counteracted experimentally with decoy molecules and clinically with nonsteroidal antiandrogens. In some patients, it is possible to lengthen the off-treatment interval by inhibiting the enzyme 5 alpha-reductase, an effect that can be reinforced by lowering serum testosterone with an antigonadotropin. Serial measurements of serum PSA indicate that intermittent androgen suppression engenders a more diverse range of hormone-related responses than previously appreciated. These include: (1) repeated differentiation of tumor with recovery of apoptotic potential; (2) inhibition of tumor growth by rapid restoration of serum testosterone; and (3) restraint of tumor growth by subnormal levels of serum testosterone. These responses are aspects of regulation that should be taken into account when planning long-term treatment of prostate cancer with intermittent androgen suppression.