Design of removable partial dentures: a survey of dental laboratories in Greece

The aim of this study was to compare data on design and fabrication methods of removable partial dentures (RPDs) in two major cities in Greece. A questionnaire was sent to 150 randomly selected dental technicians. The participation rate was 79.3%. The anterior palatal strap, the lingual bar, and the Roach-type clasp arm designs were preferred. Half of the RPDs fabricated were retained using precision attachments. Differences between the two cities were observed in types of major maxillary connectors used, types of attachments and impression materials used, as well as the design of distal-extension RPDs. Postdoctoral education was found to have an impact on RPD fabrication. Despite the differences observed, design and fabrication of RPDs followed commonly used principles.

Within-subject comparison of two rigid bar designs connecting two interforaminal implants: patients' satisfaction and prosthetic results

BACKGROUND: There is evidence for the superiority of two-implant overdentures over complete dentures in the mandible. Various anchorage devices were used to provide stability to overdentures. The aim of the present study was to compare two designs of a rigid bar connecting two mandibular implants. MATERIALS AND METHODS: Completely edentulous patients received a new denture in the maxilla and an implant-supported overdenture in the mandible. They were randomly allocated to two groups (A or B) with regard to the bar design. A standard U-shaped bar (Dolder bar) was used connecting the two implants in a straight line. For comparison, precision attachments were soldered distal to the bar copings. Group A started the study with the standard bar (S-bar), while group B started with the attachment-bar (A-bar). After 3 months, they had to answer a questionnaire (visual analogue scale [VAS]); then the bar design was changed in both groups. After a period of another 3 months, the patients had to answer the same questions; then they had the choice to keep their preferred bar. Now the study period was extended to another year of observation, and the patients answered again the same questionnaire. In vivo force measurements were carried out with both bar types at the end of the test periods. The prosthetic maintenance service carried out during the 6-month period was recorded for both bar types in both groups. Statistical analysis as performed with the SPSS statistical package (SPSS Inc., Chicago, IL, USA). RESULTS: Satisfaction was high in both groups. Group B, who had entered the study with the attachment bar, gave slightly better ratings to this type for four items, while in group A, no differences were found. At the end of the 6-month comparison period, all but one patient wished to continue to wear the attachment bar. Prosthetic service was equal in groups A and B, but the total number of interventions is significantly higher in the attachment bar. Force patterns of maximum biting were similar in both bar designs, but exhibited significantly higher axial forces in the attachment bar. CONCLUSIONS: Both bar designs provide good retention and functional comfort. High stability appears to be an important factor for the patients' satisfaction and oral comfort. Rigid retention results in a higher force impact and appears to evoke the need for the retightening of occlusal screws, resulting in more maintenance service.

Influence of the lubricant and the alloy on the wear behaviour of attachments

Wear of attachments leads to a loss of retention and reduces the function of overdentures. This study evaluated the retention force changes of an attachment system for overdentures. The influence of the lubricant and the alloy on wear constancy was examined.

Precision of endodontic working length measurements: a pilot investigation comparing cone-beam computed tomography scanning with standard measurement techniques

The objective of this pilot investigation was to evaluate the utility and precision of already existing limited cone-beam computed tomography (CBCT) scans in measuring the endodontic working length, and to compare it with standard clinical procedures.

A sublimation technique for high-precision measurements of d13CO2 and mixing ratios of CO2 and N2O from air trapped in ice cores

In order to provide high precision stable carbon isotope ratios (δ13CO2 or δ13C of CO2) from small bubbly, partially and fully clathrated ice core samples we developed a new method based on sublimation coupled to gas chromatography-isotope ratio mass spectrometry (GC-IRMS). In a first step the trapped air is quantitatively released from ~30 g of ice and CO2 together with N2O are separated from the bulk air components and stored in a miniature glass tube. In an off-line step, the extracted sample is introduced into a helium carrier flow using a minimised tube cracker device. Prior to measurement, N2O and organic sample contaminants are gas chromatographically separated from CO2. Pulses of a CO2/N2O mixture are admitted to the tube cracker and follow the path of the sample through the system. This allows an identical treatment and comparison of sample and standard peaks. The ability of the method to reproduce δ13C from bubble and clathrate ice is verified on different ice cores. We achieve reproducibilities for bubble ice between 0.05 ‰ and 0.07 ‰ and for clathrate ice between 0.05 ‰ and 0.09 ‰ (dependent on the ice core used). A comparison of our data with measurements on bubble ice from the same ice core but using a mechanical extraction device shows no significant systematic offset. In addition to δ13C, the CO2 and N2O mixing ratios can be volumetrically derived with a precision of 2 ppmv and 8 ppbv, respectively.

Impact of measurement errors on the determination of the linear modulus of human meniscal attachments

For the development of meniscal substitutes and related finite element models it is necessary to know the mechanical properties of the meniscus and its attachments. Measurement errors can falsify the determination of material properties. Therefore the impact of metrological and geometrical measurement errors on the determination of the linear modulus of human meniscal attachments was investigated. After total differentiation the error of the force (+0.10%), attachment deformation (−0.16%), and fibre length (+0.11%) measurements almost annulled each other. The error of the cross-sectional area determination ranged from 0.00%, gathered from histological slides, up to 14.22%, obtained from digital calliper measurements. Hence, total measurement error ranged from +0.05% to −14.17%, predominantly affected by the cross-sectional area determination error. Further investigations revealed that the entire cross-section was significantly larger compared to the load-carrying collagen fibre area. This overestimation of the cross-section area led to an underestimation of the linear modulus of up to −36.7%. Additionally, the cross-sections of the collagen-fibre area of the attachments significantly varied up to +90% along their longitudinal axis. The resultant ratio between the collagen fibre area and the histologically determined cross-sectional area ranged between 0.61 for the posterolateral and 0.69 for the posteromedial ligament. The linear modulus of human meniscal attachments can be significantly underestimated due to the use of different methods and locations of cross-sectional area determination. Hence, it is suggested to assess the load carrying collagen fibre area histologically, or, alternatively, to use the correction factors proposed in this study.