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.

Intraoral voice recording-towards a new smartphone-based method for vocal rehabilitation

After laryngectomy, a new voice is needed. We present the first steps in the development of a smartphone-based method. A microphone is placed in the mouth to record the pseudo-whispering voice of laryngectomized patients. This recording is analyzed by voice recognition software followed by voice synthesis. Eventually, this will be performed on a smartphone. We placed a microphone at 10 different places inside and outside the mouth (two in front of the mouth (at 2 and 20 cm), five on the palate and three on the lower jaw) and made voice recordings in eight healthy men. These recordings were analyzed by voice recognition software. The text generated by the software was compared with the original text. Over all positions, the correct detection of words recorded in the mouth was 19.3% vs. 75.2% (p = 0.01) outside the mouth. In the mouth, recording taken on the maxilla (22.8%) was much better than on the mandible (13.5%) (p = 0.01). The optimum position for a microphone on the maxilla was at the highest point of the palate with 31.9% correct word identification there (p = 0.028). Further investigations have to be undertaken with forthcoming development of smartphone processing power and with development of a smartphone-based voice recognition application.

Dimensional stability in composite cone beam computed tomography

An automated increase in the field of view (FOV) for multipurpose cone beam CT (CBCT) by "stitching" (joining) up to three component volumes to yield a larger composite volume must still ensure dimensional stability, especially if the image is to form the basis for a surgical splint. Dimensional stability, image discrepancies and the influence of movement artefacts between exposures were evaluated. The first consumer installation of the Kodak 9000 three-dimensional (3D) extraoral imaging system with stitching software was used for the evaluation of a human mandible with three endodontic instruments as markers. The distances between several reproducible points were measured directly and the results compared with the values measured on screen. Displacements of the mandible along all axes between exposures as well as angular displacements were conducted to test the capability of the system. The standard deviations (SD) of the results for the vertical distances varied between 0.212 mm and 0.409 mm (approximately 1-2 voxels; range, 0.6-1.3 mm) and may be considered the systematic error. The SD of the results for the horizontal and diagonal distances varied between 0.195 mm and 0.571 mm (approximately 1-3 voxels; range, 0.6-1.7 mm) if the group with overall horizontal angulations of 10° and a central rotation of 20° was omitted. In conclusion, the evaluated stitching software is a useful tool to expand the options of combined CBCT with an initial small FOV by allowing a merger of up to three component volumes to yield a larger FOV of about 80 × 80 × 37 mm. The dimensional stability was acceptable when seen in relation to the induced disturbance. Further evaluation of this composite CBCT/digital imaging and communications in medicine system for subsequent splint fabrication may yield promising results.

Fracture characteristics of carbon fibre, ceramic and non-palladium endodontic post systems at monotonously increasing loads

A carbon fibre post system, three non-palladium and one palladium metal post systems, two ceramic post systems, and a metal post system with a ceramic core were studied in vitro. The control group consisted of root-filled test teeth without posts. The test teeth were identical artificial roots of an upper central incisor made from a posterior composite whose module of elasticity was similar to that of natural dentine. All posts were cemented in the roots using Panavia 21 TC. Subsequently, standardized full crowns were cemented onto all roots. On a universal testing machine, the test teeth were loaded palatally at monotonously increasing loads until root fracture. The highest mean fracture loads were found for the carbon fibre post system (312.5 +/- 58.8 N). The fracture load of non-palladium metal posts (242.3-300.4 N) did not differ significantly from that of the Perma-dor post (265.9 N), which does contain palladium. Values of 300.3 +/- 89.3 N (aluminium oxide ceramics) and 193.5 +/-57.0 N (zirconia ceramics) were found for the ceramic posts. The control group exhibited a fracture load of 228.8 +/- 35.7 N. The mean distance between the vestibular end of the fracture gap and the point of force application was between 10.1 +/- 2.3 and 14.7 +/- 1.2 mm.

Laboratory strength of glass ionomer and zinc phosphate cements

PURPOSE

The present in vitro study examined 3 mechanical properties, namely compressive, flexural, and diametral tensile strength, of various commercially available cements and core materials as a function of time after mixing.

MATERIALS AND METHODS

The examined materials were 2 cermet cements (Ketac Silver [ESPE, Seefeld, Germany] and Chelon Silver [ESPE]), 1 metal-reinforced glass ionomer cement (Miracle Mix [GC Dental Industrial Corp, Tokyo, Japan]), 2 conventional glass ionomer cements (Ketac Bond [ESPE] and Ketac Cem [ESPE]), 1 standard cure zinc phosphate cement (Harvard Cement [Richter and Hoffmann, Berlin, Germany]), and 1 zinc phosphate cement with the addition of 30% silver amalgam alloy powder (Harvard Cement 70% with Dispersalloy 30% [Richter and Hoffmann/Johnson and Johnson, East Windsor, NJ]). Properties were measured using a universal testing machine at 15 minutes, 1 hour, and 24 hours after first mixing.

RESULTS

Compressive strengths varied widely between the 3 times of measurement from 5.8 +/- 6.6 MPa for Ketac Cem to 144.3 +/- 10.2 MPa for Ketac Silver. Twenty-four hours after mixing, the Bonferroni test showed significant (p <or= .01) differences between Ketac Silver and all other materials tested. Diametral tensile strengths ranged widely from 4.4 +/- 0.9 MPa for Ketac Cem to 11.5 +/- 2.2 MPa for Chelon Silver. At 15 minutes, 1 hour, and 24 hours after first mixing, the analysis of variance did not show any significant differences between Ketac Silver, Chelon Silver, and Miracle Mix. The 3-point flexural strength of Ketac Silver showed, at 15 minutes with 13.5 +/- 3.9 MPa and at 24 hours with 27.2 +/- 7.4 MPa, the highest values.

CONCLUSIONS

Setting time influences the mechanical properties of the materials tested in this study. Ketac Silver, a glass ionomer cement reinforced with sintered glass-silver particles, showed the highest mechanical properties of the examined materials.

Organotypic cultures of gingival cells: an epithelial model to assess putative local effects of orthodontic plate and occlusal splint materials under more tissue-like conditions

This article explores whether organotypic cultures of immortalized gingival keratinocytes constitute a suitable model for assessing the epithelial cell compatibility of two groups of dental resins, each of them representing one group used in orthodontics and temporo-mandibular disorders (TMD) therapy under conditions more closely resembling the actual tissue situation. The resins were tested with the agar diffusion assay (ADA) in conventional monolayer and organotypic cultures. Compared to the control exhibiting a neutral red destaining index of 3, the index of 4 obtained after exposure of monolayers to one soft permanent resin (Durabase) indicated the presence of a non-lytic but physiologically active substance. In contrast, the adaptation of the ADA to organotypic cultures revealed no apparent lesions at the epithelial surface by performing scanning electron microscopy, while histoarchitecture indicated the development of stratified surface epithelia. This was substantiated by undamaged cells in the uppermost cell layers and by the preservation of cell-to-cell contacts. Furthermore, indirect immunofluorescence for Ki-67 and the cytokeratins ck 14 and ck4 revealed that cell proliferation and epithelial structure were maintained, while differentiation was enhanced, possibly increasing epithelial resistance. The results obtained from the organotypic cultures suggest that (i) cell-affecting effects of materials visible in monolayer cultures may not be seen in epithelia resembling that in vivo and that (ii) enhanced differentiation may be associated with increased stability of the epithelial cells. Thus, organotypic cultures of gingival cells constitute a tissue model allowing short-term tissue compatibility studies of dental materials and rendering a potential candidate also for long-term studies.

The Procera AllCeram system

The Procera AllCeram system is indicated for manufacturing all-ceramic crowns for single-tooth restorations in the anterior and posterior regions. In addition, it is possible to create metal-free superstructures on CeraOne abutments from the Brånemark implant system or crowns on individually prepared aluminum oxide abutments (CerAdapt). The Procera copings, which are manufactured using computer-aided design/manufacturing technology, are characterized by very good mechanical properties. Ceramic veneers tailored to the copings offer excellent esthetics, favorable abrasion behavior, and an ideal surface structure for non-inflammatory apposition of the periodontal or periimplant tissues. The present article offers an overview of previous scientific studies, describes clinical and laboratory procedures, and presents case reports.

Success rates for two different types of post-and-cores

The objective of our follow-up study was to evaluate the success of two different types of partially prefabricated post-and-core systems following crown placement. Two hundred and thirty-seven Permador posts and 49 Radix posts were evaluated clinically. Radiological follow-up was performed for 230 Permador posts and 47 Radix posts. The restorations had been in situ for an average of 3.9 years (Permador posts) and 2.3 years (Radix posts), respectively. Root canal fillings were evaluated as to their length, their homogeneity and their flushness with the walls of the root canal. The post-and-cores were evaluated for their orientation in the root canal and for the length of the inserted post relative to the length of the root. The position of the post was classified as centric in 78.0% of the restorations followed, and eccentric in 19.5%, while 2.5% showed a root perforation. The minimal requirement that the length of the post-and-core should at least be equal to the length of the clinical crown was met in 85% of the cases. Eighteen (6.3%) of the 286 teeth examined had to be extracted. There were significant correlations between insertion periods, horizontal bone loss, length of the root canal filling, and position of the post on one hand and tooth loss on the other.

Temperature response in the pulpal chamber during ultrahigh-speed tooth preparation with diamond burs of different grit

STATEMENT OF PROBLEM

Ultrahigh-speed tooth preparation can traumatize the hard dental tissues and the dental pulp.

PURPOSE

This in vitro study examined the relationship between different grits of diamond burs on the temperature response within a pulpal chamber during tooth preparation with a turbine.

MATERIAL AND METHODS

Newly extracted, undamaged third molars were secured by a rapid-tensioning device mounted on an air-supported slide. NiCrNi thermocouples were inserted apically and used to determine the temperature within a pulpal chamber. The grinding tests used cylindrical fine, coarse, and ultracoarse diamond burs.

RESULTS

The maximal temperature elevation within the pulp was 3.2 degrees C, and the most pronounced rise in temperature occurred with ultracoarse burs. Temperature increases in the pulpal chambers and grinding times or temperatures of the cooling water were approximately proportional. Residual dentinal thickness was inversely proportional to temperature elevation within the pulpal chamber.

CONCLUSIONS

This study demonstrated that coarse diamond burs resulted in more pronounced temperature increases within the pulpal chamber during tooth preparation. In addition, the benefit of short intervals between grinding steps and a cooling water temperature between 30 degrees C and 32 degrees C was confirmed. A cooling temperature of 38 degrees C to 43 degrees C did not afford actual cooling.