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Objectives To assess the effect of implant angulation on the retention of two different attachment systems for implant-supported overdentures after a simulated fatigue period of 5.5 years. Material and Methods Two test set-ups were constructed. A two-implant mandibular implant-supported overdenture design was simulated using acrylic resin blocks to support implant replicas (Model 1 and Model 2). The replicas were set up in the canine regions (22-mm inter-implant distance). In Model 1, the implants were parallel (0° to the vertical axis) and in Model 2 they were divergent (20° to the vertical axis). The Locator and the ball attachment systems were tested at both set-ups. A simulated fatigue period of 5.5 years that equated to 10,000 cycles of insertion and removal of the denture was used. Retention values for each attachment system at each angulation set-up were measured at baseline, every 500 cycles until 4000 cycles and then every 1000 cycles. Results After simulated fatigue, the retention for both systems at both set-ups reduced. The Locator system reduced from 108.9 to 20.2 N in the parallel set-up and from 82.3 to 17.3 N in the divergent set-up. For the ball system, the retention reduced from 56.2 to 46 N when parallel and from 45.7 to 40.7 N when divergent. Conclusion Both attachment systems showed a significant reduction in retention after simulated fatigue at both parallel and divergent set-ups. The change in implant angulation caused a significant reduction in retention for the ball attachment system only, although this was still higher at the end of testing than the Locator attachment system. The Locators also had a significantly faster rate of loss of retention at both set-ups. Clinically, this may indicate that the ball attachments may perform better with divergent implants. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To assess the dimensional stability of 8 impression materials over 12 weeks relevant to in vitro tribology studies. Methods: Ten impressions from eight impression materials were taken of a metal block (ADA block) conforming to the American Dental Association specification for impression materials and of another metal block (custom block) which allowed measurements over a larger surface area. The impressions and blocks were scanned on a non-contacting laser profilometer (Taicaan® – Southampton, UK) and using surface metrology software Boddies® (Taicaan® – Southampton, UK) measurements were made at 24h, 2, 4, 8 and 12 weeks. The impression materials tested were Aquasil®, Aquasil® DECA, Affinis®, Express®, Extrude®, Impregum®, President® and Take 1®. Results: Seven addition silicones and one polyether were tested. and were monophasic, the rest were putty-wash. The results from impressions of the ADA block showed that all materials contracted compared to measurements obtained directly from the block expanded over time (+31.5μm) (p <0.05). The results from the custom block showed that all materials contracted compared to direct measurements of the block. and expanded over time (+62μm and +63.8μm respectively). contracted over time (−54.7μm) (p <0.05). Significance: No material showed linear changes >1.5% and were stable for 12 weeks. Nevertheless, the range of changes would affect tribology studies were cut-offs lesser than the reported changes are selected. All impressions should be processed after similar time delays to reduce the errors introduced by dimensional changes. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of this research was to compare two-dimensional (2D) and three-dimensional (3D) tooth measuring techniques after subjecting enamel samples to tooth wear in vitro on an erosion–abrasion model. Method: 80 polished mid-coronal enamel sections were subjected to 10 wear cycles. Each cycle consisted of remineralization for 2h in artificial saliva, followed by 10min immersion in one of four acidic fruit drinks or distilled water and finally toothbrush abrasion with a non-fluoridated tooth paste. The resulting wear scars were measured using 2D and 3D techniques using surface matching software. Results: The 2D step heights measurements from the exposure to the four acidic drinks showed no statistically significant differences (median wear range=22.4–32.5μm) between them (p =0.99) but there were differences with distilled water (median wear=10.0μm) (p =0.01). The 3D measurements showed that two drinks produced more wear compared to the others and water when the whole surface and volume exposed to wear was accounted for (p =0.01). Significance: The difference in data from the two techniques showed that 3D measurements gave a more accurate assessment of the impact of the wear regime. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To compare three instruments for their ability to quantify enamel loss after acid erosion. Methods: 6 randomized parallel groups of bovine enamel samples were subjected to citric acid (higher acidity) or orange juice (lower acidity) erosion and remineralisation in a cycling model. Two protected shoulders were created on each of the samples using tape, to serve as reference for analysis. The time of exposure to each acid was varied, along with presence or absence of agitation. After treatment, samples were measured on 3 instruments capable of measuring step height: a contact profilometer (CP); a non-contact profilometer (NCP); and a confocal laser scanning microscope (CLSM) by three different examiners. Additionally, 3D (volume) step height was also measured using the CLSM. Results: Increasing acid concentration and exposure time resulted in greater erosion, as did agitation of samples while in acid solution. All instruments/methods identified the same statistically significant (p <0.05) pair-wise differences between the treatments groups. Further, all four methods exhibited strong agreement (Intra-class correlation≥0.96) in erosion level and were highly correlated, with correlations of 0.99 or higher in all cases. Significance: All instruments/methods used in this study produced very similar conclusions with regard to ranking of enamel loss, with data showing very high agreement between instruments. All instruments were found to be equally suited to the measurement of enamel erosion. [Copyright &y& Elsevier]

Abstract: Objective: To analyze differences in the way dental materials digitize on a non-contacting laser profilometer (NCLP). Methods: Three Type IV dental stones and 15 impression materials were mixed according to the manufacturer''s instructions and expressed against a glass block to record its surface characteristics. From each material an area of 6×40mm was scanned on the NCLP and the Ra, Rq and Rt roughness values measured from 20 randomly selected transverse profiles. The surface of the impression materials was subsequently poured in Moonstone™ (Bracon Ltd., Etchingham, England) dental stone and the same roughness values obtained from these casts. Differences in roughness values from the dental materials were compared using ANOVA and differences in roughness between impression materials and the Moonstone™ casts compared using paired t-tests. Results: There were significant differences in roughness values between individual materials within each type (impression material or dental stone) (p <0.05). The roughness of the dental stones varied between Ra=0.87 and 0.99μm, Rq=1.09 and 1.23μm, and Rt=5.70 and 6.51μm. The roughness values of the impression materials varied between Ra=0.75 and 4.56μm; Rq=0.95 and 6.27μm and Rt=4.70 and 39.31μm. Darker materials showed higher roughness values compared to lighter materials (p <0.05). The roughness of the Moonstone™ casts varied between Ra=0.80 and 0.98μm; Rq=1.01 and 1.22μm, and Rt=5.04 and 6.38μm. Roughness values of some impression materials were statistically significantly lower when the surface was reproduced in Moonstone™ (p <0.01). Significance: Digitization of dental materials on optical profilometers was affected by color and transparency. [Copyright &y& Elsevier]

Objectives: To determine if Sa roughness data from measuring one central location of unpolished and polished enamel were representative of the overall surfaces before and after erosion. Methods: Twenty human enamel sections (4x4 mm) were embedded in bis-acryl composite and randomised to either a native or polishing enamel preparation protocol. Enamel samples were subjected to an acid challenge (15 minutes 100 mL orange juice, pH 3.2, titratable acidity 41.3mmol OH/L, 62.5 rpm agitation, repeated for three cycles). Median (IQR) surface roughness [Sa] was measured at baseline and after erosion from both a centralised cluster and four peripheral clusters. Within each cluster, five smaller areas (0.04 mm2) provided the Sa roughness data. Results: For both unpolished and polished enamel samples there were no significant differences between measuring one central cluster or four peripheral clusters, before and after erosion. For unpolished enamel the single central cluster had a median (IQR) Sa roughness of 1.45 (2.58) μm and the four peripheral clusters had a median (IQR) of 1.32 (4.86) μm before erosion; after erosion there were statistically significant reductions to 0.38 (0.35) μm and 0.34 (0.49) μm respectively (p<0.0001). Polished enamel had a median (IQR) Sa roughness 0.04 (0.17) μm for the single central cluster and 0.05 (0.15) μm for the four peripheral clusters which statistically significantly increased after erosion to 0.27 (0.08) μm for both (p<0.0001). Conclusion: Measuring one central cluster of unpolished and polished enamel was representative of the overall enamel surface roughness, before and after erosion. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of tooth type (molar/premolar), tooth surface (buccal/lingual), smear layer or no smear layer, storage of specimens in deionised water, mode and speed of agitation, and rinsing method between cycles on mean step height loss and Knoop microhardness (KHN) change. Polished human enamel specimens embedded in acrylic resin were prepared from sound permanent molar and premolar tooth surfaces. A 0.3% (pH 3.2) solution of citric acid was used to erode the specimens, in a cycling procedure, consisting of 10 min immersion followed by rinsing in deionised water for 30 s with a spray bottle, for 5 cycles. The specimens were analysed with a non-contact white light profilometer and KHN. Molar teeth (148.99±24.49 KHN) and buccal surfaces (155.62±30.35 KHN) produced significantly less microhardness change compared to premolar (186.40±20.74 KHN) and lingual surfaces (179.76±23.21 KHN; p<0001). The effect of storage and rinsing showed little difference in mean step height loss (<1 µm) and microhardness change. With no smear layer a significantly lower mean step height loss and microhardness change (p<0.001) was observed. Agitation was performed with Orbital, Gyro and See-Saw rockers at 30, 40, 60, and 70 rpm. The mean step height loss was largest for See-Saw at 70 rpm (11.73±0.91 μm) and lowest for Orbital at 30 rpm (2.76±1.12 μm). A statistical difference was found between all types of agitation and speeds (p<0.001). In conclusion, this study has shown that the variables investigated here have a significant impact on the measurable outcome, highlighting the importance of accurate and detailed method sections. [ABSTRACT FROM AUTHOR]