Effect of alloy type and casting technique on the fracture strengthof implant-cemented structures

Objectives: To evaluate the influence of alloy type and casting procedure on the fracture strength (FS) of metallicframeworks for implant-supported fixed prostheses.Study design: Thirty three-unit structures for lower posterior bridges were waxed-up and randomly assigned totwo groups (n=15) according to alloy type and casting technique: Group 1 (C): cobalt-chromium cast in a centrifugalmachine (TS1, Degussa–Hüls); Group 2 (T): titanium cast in a pressure-differential device (Cyclarc II,Morita). Each structure was cemented onto two prefabricated abutments under a constant seating pressure. After6 months of water aging, samples were loaded in a static universal testing machine (EFH/5/FR, Microtest) untilfracture. Axial compressive loads were applied at the central fossa of the pontics. FS data were recorded and surfacetopography of the fractured connectors was SEM-analyzed. A Chi-Square test was performed to assess thedependence of pores on the alloy type and casting procedure. ANOVA and Student–Newman–Keuls (SNK) testswere run for FS comparisons (p<0.05).Results: One third of the C structures showed pores inside the fractured connectors. T frameworks demonstratedhigher FS than that of C specimens exhibiting pores (p=0.025). C samples containing no pores recorded the greatestmean FS (p<0.001).Conclusions: Fracture strength of metallic frameworks depended on the alloy type and casting procedure. Cobaltchromiumcasts often registered pores inside the connectors, which strongly decreased the fracture resistance.An accurate casting of titanium with a pressure-differential system may result in the most predictable techniqueunder the tested experimental conditions (AU)

Effect of alloy type and casting technique on the fracture strength of implant-cemented structures.

OBJECTIVES: To evaluate the influence of alloy type and casting procedure on the fracture strength (FS) of metallic frameworks for implant-supported fixed prostheses. STUDY DESIGN: Thirty three-unit structures for lower posterior bridges were waxed-up and randomly assigned to two groups (n=15) according to alloy type and casting technique: Group 1 (C): cobalt-chromium cast in a centrifugal machine (TS1, Degussa-Hüls); Group 2 (T): titanium cast in a pressure-differential device (Cyclarc II, Morita). Each structure was cemented onto two prefabricated abutments under a constant seating pressure. After 6 months of water aging, samples were loaded in a static universal testing machine (EFH/5/FR, Microtest) until fracture. Axial compressive loads were applied at the central fossa of the pontics. FS data were recorded and surface topography of the fractured connectors was SEM-analyzed. A Chi-Square test was performed to assess the dependence of pores on the alloy type and casting procedure. ANOVA and Student-Newman-Keuls (SNK) tests were run for FS comparisons (p <0.05). RESULTS: One third of the C structures showed pores inside the fractured connectors. T frameworks demonstrated higher FS than that of C specimens exhibiting pores (p=0.025). C samples containing no pores recorded the greatest mean FS (p <0.001). CONCLUSIONS: Fracture strength of metallic frameworks depended on the alloy type and casting procedure. Cobalt-chromium casts often registered pores inside the connectors, which strongly decreased the fracture resistance. An accurate casting of titanium with a pressure-differential system may result in the most predictable technique under the tested experimental conditions.

Magnifying loupes in modern dental practice: an update.

UNLABELLED: There are three principal reasons for adopting magnifying loupes for operative dentistry: to enhance visualization of fine detail, to compensate for the loss of near vision (presbyopia) and to ensure maintenance of correct posture. The wearing of loupes is becoming an accepted norm amongst qualified practitioners and increasingly in the undergraduate population. However, further research is required before evidence-based recommendations can be made about their effectiveness in achieving the three principles. Compared to the medical literature, there is a paucity of studies on the use of loupes in dentistry. This article presents an overview of the well-documented (but under-researched) optical and ergonomic benefits of wearing loupes and highlights special circumstances where the use of loupes would be inadvisable. The article concludes with a review of the small number of studies on magnifying loupes specifically for restorative dentistry. CLINICAL RELEVANCE: The reader should consider the information in this article prior to the purchase of magnifying loupes.

Placement of posterior composite restorations in United Kingdom dental practices: techniques, problems, and attitudes.

OBJECTIVE: To investigate the range of techniques used by U.K. general dental practitioners when placing posterior composites, their attitudes and opinions and problems encountered. METHODS: A pre-piloted questionnaire was distributed to 500 UK GDPs selected at random from the U.K. Dentists Register requesting specific information on attitudes, use and problems encountered in relation to posterior composite placement. RESULTS: 254 useable replies were returned (response rate= 51%). Over 95% of respondents would consider placing posterior composites, but only 33% (n=84) would regularly or often place composite in the occlusal surface of a molar tooth. 62% of respondents (n=157) are influenced by articles in peer-reviewed journals when deciding to place a posterior composite, while 95% (n=241) reported that they are not influenced by advertising. Techniques for managing operatively exposed dentine vary, and are related to the depth of the dentine cavity: 79% (n=201) use a 'dentine-bonding' technique (i.e., no base/liner) approach for shallow cavities, while only 9% (n=23) would consider this approach for a deep dentine cavity. Only 10% of respondents (n=25) use a sectional metal matrix system for restoring occlusoproximal cavities, while 29% (n=74) use transparent matrix systems, and 61% (n=155) use a circumferential metal matrix system. More than one-half (52%, n=132) of practitioners reported they experienced problems with food packing in more than one in four posterior composites placed. CONCLUSIONS: Despite having been previously discouraged by financial guidelines and with probable limited exposure to posterior composite instruction at dental school, U.K. GDPs are placing posterior composites with reasonable reference to current best available evidence. Diverse opinions exist on the management of certain clinical scenarios, such as of operatively exposed dentine.

A study in vitro to compare home and surgery vital bleaching techniques.

The aim of this study was to compare the effectiveness of three different types of commonly used bleaching techniques using an in-vitro model. Five groups of 10 tooth specimens were prepared and allocated randomly to treatment groups. The four treatment groups tested were a home tray bleaching product, an 'in surgery' tray bleaching product and an 'in surgery power bleaching' product for use with an activating light. The bleaching agent in the latter group was also tested without light activation to assess the additional benefit of the bleaching lamp. A placebo group treated with water was also included. Colour change was assessed using a Vita shade guide and an electronic chromometer. The mean change in shade guide units ranged from 10.9 to 13.2 units, with the 'in surgery' tray bleaching system producing the largest change. For the chromometer readings the mean change in tooth colour ranged from 3.6 to 25.6 units, with the night guard vital bleaching product producing the largest change. This study has demonstrated in vitro that all the different bleaching systems tested produced comparable changes in tooth colour.

The erosive potential of some flavoured waters.

OBJECTIVES: To assess the erosive potential of a number of readily available flavoured waters in the laboratory. METHODS: The erosive potential was assessed by measuring the pH, neutralisable acidity and ability to erode enamel. These were compared to an orange juice positive control. RESULTS: The pH of the flavoured waters ranged from 2.64-3.24 with their neutralisable acidity ranging from 4.16-16.30 mls of 0.1M NaOH. The amount of enamel removed following 1-hour immersion in the drinks ranged from 1.18-6.86 microns. In comparison, the orange juice control had a pH of 3.68, a neutralisable acidity of 19.68 mls of 0.1 M NaOH and removed 3.24 microns of enamel. CONCLUSIONS: Many of the flavoured waters tested were found to be as erosive as orange juice. This information will be of use to clinicians when counselling patients with tooth surface loss. (Eur J Dent 2007;1:5-9).

Does low acid orange juice equal low erosion?

UNLABELLED: This paper compares the erosive potential of standard Tropicana smooth orange juice with a new low acid orange juice. Three parameters are compared in the laboratory; pH, neutralizable acidity and the ability to erode enamel. The pH of the standard orange juice is 3.88 compared with the low acid orange juice which has a pH of 4.18. The neutralizable acidity of the low acid juice is lower (16.96 ml of 0.1 M NaOH) than the standard juice (28.46 ml of 0.1 M NaOH). The low acid orange juice produces less enamel erosion (2.49 microm) than the standard juice (5.23 pm). Ideally, these laboratory findings need to be confirmed in a randomized controlled clinical trial before this product could be recommended unreservedly for patients that are clinically susceptible to erosion. CLINICAL RELEVANCE: As dietary advice forms a cornerstone in the clinical management of erosion, the introduction of a commercially available low acid orange is most welcome.

Relationship between S. mutans and the autofluorescence of carious dentin.

PURPOSE: To investigate the relationship between the presence of S. mutans and the autofluorescent signal detected in carious dentin, using confocal laser-scanning microscopy. METHODS: Experiment 1:15 visually caries-free freshly extracted premolars were coated with varnish except for two 2 mm x 2 mm windows; five were subjected to a 15-day bacterial artificial caries system using Streptococcus mutans while 10 underwent a 7-day controlled, lactic acid (0.5 M, pH 2.7) demineralization protocol. At the end of both periods, all teeth were longitudinally sectioned and the 20 bacterial and 40 acid-induced artificial lesions were examined by confocal laser-scanning microscopy. The media containing the S. mutans was also examined for autofluorescence. Experiment 2: 20 750 microm-thick caries-free coronal dentin disks were prepared from 10 healthy premolars. Ten underwent a demineralization protocol using 0.1 M EDTA (pH 4.8) for 21 days. All 20 were finally subjected to the same artificial bacterial caries system as above for 15 days and then examined for autofluorescence using confocal laser-scanning microscopy. RESULTS: Experiment 1 results showed that acid-demineralized lesions did not generate any autofluorescence. Lesions created by the bacterial system did exhibit autofluorescence. The media with or without S. mutans did not exhibit autofluorescence. Experiment 2: bacteria-induced lesions on dentin that had previously been acid-demineralized generated a visibly stronger autofluorescence signal than those lesions grown on sound dentin. It is hypothesized that dentin demineralization during the carious process exposes more matrix to a bacteria-matrix interaction, thus generating or refining the matrix chromophore responsible for the autofluorescence signal detected in carious dentin.