Non-contacting Laser Profilometer Research Articles

SURFACE ROUGHNESS OF POLYAMIDE KNITTED FABRICS

Fabrics are never ideally smooth. Their texture varies between fine and coarse, quantified through the surface’s vertical deviation. Fabric roughness, or its opposite smoothness, is employed as measure of the surface texture of fabrics. In general, texture depends upon fiber properties, yarn count, yarn twist, and fabric structure and fabric design). This research aims to determine the limitations in visual perception of surface roughness in comparison to objective surface roughness measurements of low weight polyamide fabrics. Subjective evaluation is used for the visual assessment, while instrumental measurement of the properties was conducted using a noncontact laser profilometer. Subjective evaluation was conducted by a panel of forty untrained evaluators on a sample of seven polyamide knitted fabrics with different yarn count and composition. The roughness profile parameters were measured using Talysurf CLI 500 according to ISO 4827. Although the surface roughness measured as arithmetic mean deviation (Ra) and roughness through visual inspection of the fabric are correlated, instrumental measurements of roughness are more precise. Differences in the surface roughness arising from significantly different yarn structures will be observed, while those due to the knitted fabric structure are negligible in visual inspection.

Effect of surface treatments on biaxial flexural strength, fatigue resistance, and fracture toughness of high versus low translucency zirconia

BackgroundMechanical surface treatments can deteriorate the mechanical properties of zirconia. This study evaluated and compared the biaxial flexural strength, fracture toughness, and fatigue resistance of high translucency (HT) to low translucency (LT) zirconia after various mechanical surface treatments.MethodsFour hundred eighty zirconia discs were prepared by milling and sintering two HT (Katana and BruxZir) and LT (Cercon and Lava) zirconia blocks at targeted dimensions of 12 mm diameter × 1.2 mm thickness. Sintered zirconia discs received one of the following surface treatments: low-pressure airborne particle abrasion (APA) using 50 µm alumina particles, grinding using 400 grit silicon carbide paper, while as-sintered specimens served as control. Internal structure and surface roughness were evaluated by scanning electron microscope (SEM) and a non-contact laser profilometer, respectively. Half of the discs were tested for initial biaxial flexural strength, while the rest was subjected to 106 cyclic fatigue loadings, followed by measuring the residual biaxial flexural strength. Fractured surfaces were examined for critical size defects (c) using SEM to calculate the fracture toughness (KIC). The effect of surface treatments, zirconia type, and cyclic fatigue on the biaxial flexural strength was statistically analyzed using three-way analysis of variance (ANOVA) and Tukey HSD post hoc tests (α = 0.05). Weibull analysis was done to evaluate the reliability of the flexural strength for different materials.ResultsThe initial biaxial flexural strength of LT zirconia was significantly higher (p < 0.001) than that of HT zirconia in all groups. While low APA significantly increased the biaxial flexural strength of LT zirconia, no significant change was observed for HT zirconia except for Katana. Surface grinding and cyclic fatigue significantly reduced the flexural strength of all groups. High translucency zirconia reported higher fracture toughness, yet with lower Weibull moduli, compared to LT zirconia.ConclusionLT zirconia has higher biaxial flexural strength, yet with lower fracture toughness and fatigue resistance, compared to HT zirconia. Low-pressure APA has significantly increased the biaxial flexural strength in all zirconia groups except BruxZir. Grinding was deteriorating to biaxial flexural strength and fracture toughness in all zirconia types. Cyclic fatigue has significantly decreased the biaxial flexural strength and reliability of HT and LT zirconia.

APPLICATION OF NON-CONTACT PROFILOMETER IN AUTOMATED PRODUCTION

The main thesis of this paper was to briefly describe the measurement technique using a non-contact laser profilometer. This paper is divided into several parts, where in the introduction, in the theoretical analysis, we described the necessity of using control mechanisms in automation. Then, in the second chapter, we have developed the technology of measurement with a profilometer and its application in scientific work and in practice. In the experimental part, we have defined the application of a profilometer in laboratory conditions on an automated line in the measurement of a part printed with a 3D printer. Finally, we evaluated the advantages and disadvantages of this device compared to mechanical measuring devices.

The measurement threshold and limitations of an intra-oral scanner on polished human enamel

ObjectiveTo investigate the measurement threshold of an intra-oral scanner (IOS) on polished human enamel. MethodsThe optical performance of an IOS was compared to a gold-standard non contacting laser profilometer (NCLP), on a painted microscope slide, compared to increasing particle size of silicon-carbide papers (21.8–269.0 μm) and separately on polished human enamel with increasing step-heights. The enamel samples were randomised (n = 80) and scanned using the IOS and NCLP at increasing step-height depths (μm) (1.87–86.46 μm) and quantified according to ISO:5436-1. The measurement threshold of the IOS was determined using a custom designed automated lesion localisation algorithm, corroborated by Gaussian skewness (Ssk) and kurtosis (Sku) analysis, to assess the minimum step-height measured on each enamel sample. ResultsThe NCLP showed statistically increased Sq surface roughness for all silicon carbide particle sizes compared to the microscope slide, whereas, the IOS Sq roughness discriminated silicon-carbide particles above 68.0 μm compared to the glass slide (p ≤ 0.02). On polished enamel, the automated minimum detectable step-height measurable on each sample was 44 μm. No statistically significantly different step-height enamel lesion measurements were observed between NCLP and IOS above this threshold (p > 0.05). SignificanceThis study revealed the fundamental optical metrological parameters for the IOS, was step-heights above 44 μm and this reflects the data acquisition of the system. These results highlight the limitations of IOS used in this study, mandating further research to optimise the performance of other IOS systems, for measuring wear of materials or tooth wear on human unpolished natural enamel surfaces.

The Effects of Various Polishing Procedures on Surface Topography of CAD/CAM Resin Restoratives.

To investigate the effects of different polishing procedures on surface properties of CAD/CAM resin blocks. In this study, three different CAD/CAM restorative materials (Cerasmart, Lava Ultimate and Shofu Block HC) were used. CAD/CAM blocks were cut in 3-mm-thick slabs and divided into 5 groups. Group-1: Glaze; Group-2: Two-step Diamond Polisher; Group-3: One-step Diamond Polisher; Group-4: Three-step Diamond Polisher; Group-5: Polishing Discs+Diamond Paste. After polishing, top surfaces of the samples were prepared to screen by noncontact laser profilometer (Nanovea) for measurements. Data were analyzed using two-way analysis of variance (ANOVA). The arithmetical mean deviation of the profile was defined as Ra. The extension of Ra (a line's arithmetical mean height) to a surface was defined as Sa. Compared to the arithmetical mean of the surface, Sa expresses the difference in terms of each point's height as an absolute value. Sa was commonly used to assess surface roughness. The highest surface roughness (Ra) values in this study were 0.313 ± 0.05 for Cerasmart, 0.433 ± 0.10 for Lava Ultimate and 0.320 ± 0.05 for Shofu Block HC. The specimens in Group-4 displayed higher Ra values than other groups for each CAD/CAM material. According to surface topography (Sa) values, highest values were 2.936 ± 1.25 for Cerasmart, 2.633 ± 1.28 for Lava Ultimate and 3.489 ± 0.57 for Shofu Block HC. For Cerasmart, LAVA Ultimate and Shofu blocks, Group-1 exhibited significantly higher Sa values than other groups (p < 0.001). Optiglaze Color, Sof-Lex Diamond and Identoflex Diamond Ceramic Polisher create smooth CAD/CAM resin surfaces. However, surface roughness values of Cosmedent Nano/Microhybrid Diamond and Diapolisher Paste applied specimens were high. According to Sa values, highest roughness values belong to Optiglaze Color.

Effect of airborne-particle abrasion of a titanium base abutment on the stability of the bonded interface and retention forces of crowns after artificial aging

Statement of problemPublished data have shown that a mechanical surface treatment of titanium surfaces increases bonding potential. However, most of the studies are based on shear or tensile tests performed on flat-surfaced specimens and do not take into consideration the retention given by the titanium base (ti-base) axial walls and the thermomechanical loading seen in a clinical setting. PurposeThe purpose of this in vitro study was to evaluate the influence of different airborne-particle abrasion (APA) methods of the ti-base surface on the stability of the bonded interface and retention forces between these titanium bases and lithium disilicate crowns after thermomechanical aging. Material and methodsSixty internal connection implants (Conelog) were restored with lithium disilicate crowns and bonded to the corresponding ti-bases (Conelog). The ti-bases were divided into 4 groups (n=15), 3 experimental groups applying different APA methods, 30-μm silica-modified Al2O3 particles (CoJet) (30-SiO-AlO), 50-μm Al2O3 (Cobra Aluoxyd) (50-AlO), 110-μm silica-modified Al2O3 particles (Rocatec Plus) (110-SiO-AlO), and 1 control group (NoT). Ti-bases were airborne-particle abraded (10 seconds, 0.25 MPa at a 10-mm distance) under standardized conditions in a custom-made APA device. All crowns were cemented with a resin cement (Multilink Hybrid Abutment). After aging (1 200 000 cycles, 49 N, 1.67 Hz; 5 °C-55 °C, 120 seconds), all specimens were assessed for the presence of bond failures by optical microscopy (×50). The retention forces (N) were tested by using a pull-off test (0.5mm/min). Modes of failure were classified (Type 1, 2, or 3). An additional ti-base representing each group was prepared for surface roughness (μm) calculation (Ra, Rc, Rz) with a noncontact laser profilometer, and representative scanning electron microscope (SEM) images were recorded (×1000). Chi-squared tests were performed to analyze the bonded interface failure and modes of failure, and a Kruskal-Wallis test was selected to evaluate retention force values (α=.05). ResultsThe percentages of bonding failure after aging were 73.3% (NoT), 40% (30-SiO-AlO), 6.7% (50-AlO), and 40% (110-SiO-AlO). The stability of the bonded interface was influenced by the APA method applied (P<.05). Mean ±standard deviation retention force values varied from 206.3 ±86.3 N (NoT) to 420 ±139.5 N (50-AlO), and the differences between these 2 groups were significant (P<.05). Modes of failure were predominantly Type 2 (30-SiO-AlO; 50-AlO; 110-SiO-AlO) and Type 3 (NoT). ConclusionsAirborne-particle abrasion of the titanium surface increased the bond stability and retention forces between the ti-base and the respective crown. The use of 50-μm Al2O3 provided the most stable bonded interface among the different treatments.

Effects of Lasers and Their Delivery Characteristics on Machined and Micro-Roughened Titanium Dental Implant Surfaces.

The aim of the study was to investigate the effects of neodymium: yttrium aluminium garnet (Nd:YAG) (1064 nm) and erbium: yttrium aluminium garnet (Er:YAG) (2940 nm) laser energy on titanium when delivered with conventional optics (focusing handpieces or plain ended optical fibres) or with a conical tip. Machined and micro-roughened implant discs were subjected to laser irradiation under a variety of energy settings either dry (without water) or wet (with water). Samples were scanned using a 3D non-contact laser profilometer and analysed for surface roughness, volume of peaks and the maximum diameter of the ablated area. Conical tip designs when used with both lasers showed no surface effect at any power setting on both machined and micro-roughened implant surfaces, regardless of the irrigation condition. When used with conventional delivery systems, laser effects on titanium were dose related, and were more profound with the Nd:YAG than with the Er:YAG laser. High laser pulse energies caused surface fusion which reduced the roughness of micro-roughened titanium surfaces. Likewise, repeated pulses and higher power densities also caused greater surface modifications. The presence of water reduced the influence of laser irradiation on titanium. It may be concluded that conical fibres can reduce unwanted surface modification, and this may be relevant to clinical protocols for debridement or disinfection of titanium dental implants.

Investigation of erosive wear behaviors of AA6082-T6 aluminum alloy

AA6082-T6 aluminum alloys are widely used in various applications in automotive and aircraft industries. They offer an attractive combination of surface properties, strength and corrosion resistance. The structural components manufactured by AA6082-T6 aluminum alloys can be exposed to impingement of solid particles throughout their service life. In this study, erosive wear behaviors of AA6082-T6 aluminum alloy were investigated. For the evaluation of erosive wear induced by solid particle impacts, a detailed study was conducted on AA6082-T6 aluminum alloy by using aluminum oxide (Al2O3) erodent particles. Two different particles were used in solid particle erosion tests, which are 60 mesh (212–300 µm) and 120 mesh (90–125 µm), respectively. Also, the aluminum alloy samples were tested under two different air pressures (1.5 bar and 3 bar). The erosive wear tests were carried out according to ASTM G76 standard at six various impact angles (15°, 30°, 45°, 60°, 75°, 90°). The surface roughness and morphology of worn samples were analyzed by using a non-contact laser profilometer. It was found that erodent particle size affected the surface erosion damage, erosion rate, crater morphology and roughness. The eroded surfaces of specimens were analyzed by SEM. The surfaces of specimens were also investigated by using EDS in SEM studies.

Solid Particle Erosion Behavior of Carbon Fiber - Metal Wire Hybrid Reinforced Polymer Composites

Carbon fiber reinforced composite materials (CFRP) are being widely used in aircraft parts and unmanned air vehicle (UAV) airframe production due to their high specific stiffness and strength. Besides their superior characteristics, they have a disadvantage of poor electrical conductivity when used in UAV airframes which subjected to lightning strike during their service life. In order to protect UAV airframe from lightning strike damage, adding a metal wire to CFRP composite is an alternative method. Moreover, UAV and aircraft airframe materials subjected to solid particle erosion damage during their service life also.Surface damage induced by solid particle erosion cause aerodynamic losses and result with increase in specific fuel consumption or shortening of maximum air vehicle range. Also worn body could be lost its lightning strike residence. It is evident that there is no much literature study about CFRP - metal wire hybrid reinforced composites solid particle erosion behavior. The aim of this study is to characterize the solid particle erosion behavior of CFRP - metal wire hybrid reinforced composite and analyze the post wear damage induced in the surface of the samples. Solid particle tests were performed according to ASTM G 76 standard in a specially designed test rig.Mass loss and erosion rate measurements after tests were done and damage mechanisms were discussed. Surface roughness analysis of specimens before and after solid particle erosion tests were performed by using 3D non-contact laser profilometer.

An in-situ pilot study to investigate the native clinical resistance of enamel to erosion

ObjectivesTo investigate the differences in susceptibility of the surface of native and polished enamel to dietary erosion using an in-situ model. MethodsThirty healthy volunteers (n = 10 per group) wore mandibular appliances containing 2 native and 2 polished enamel samples for 30 min after which, the samples were exposed to either an ex-vivo or in-vivo immersion in orange juice for 5, 10 or 15 min and the cycle repeated twice with an hour’s interval between them. Samples were scanned with a non-contacting laser profilometer and surface roughness was extracted from the data, together with step height and microhardness change on the polished enamel samples. ResultsAll volunteers completed the study. For native enamel there were no statistical difference between baseline roughness values versus post erosion. Polished enamel significantly increased mean (SD) Sa roughness from baseline for each group resulting in roughness change of 0.04 (0.03), 0.06 (0.04), 0.04 (0.03), 0.06 (0.03), 0.08 (0.05) and 0.09 (0.05) μm respectively. With statistical differences between roughness change 45 min in-vivo versus 45 min ex-vivo (p < 0.05). Microhardness significantly decreased for each polished group, with statistical differences in hardness change between 30 min in-vivo versus 30 min ex-vivo (p < 0.05), 45 min in-vivo versus 30 min ex-vivo (p < 0.01), 45 min in-vivo versus 45 min ex-vivo (p < 0.01). ConclusionsThe native resistance to erosion provided clinically is a combination of the ultrastructure of outer enamel, protection from the salivary pellicle and the overall effects of the oral environment. ClinicalTrials.gov identifierNCT03178968. Clinical significanceThis study demonstrates that outer enamel is innately more resistant to erosion which is clinically relevant as once there has been structural breakdown at this level the effects of erosive wear will be accelerated.

Surface Changes of PathFile after Glide Path Preparation: An Ex Vivo and In Vivo Study

IntroductionThe aim of this study was to evaluate the changes in the surface profile of rotary nickel-titanium (NiTi) files designed to prepare a glide path and conventional stainless steel (SS) hand files when used in extremely narrow canals both in clinical and experimental conditions. MethodsThis ex vivo/in vivo study used either SS #10 K hand files or the PathFile system (Dentsply Maillefer, Ballaigues, Switzerland) to establish a glide path in maxillary molars with narrow root canals (defined as canals that bound a #8 K-file at the working length). After treatment, all files were cleaned and scanned using a noncontact laser profilometer. Changes to the surface profile (Ra cutting edge waviness = RaCEW) and roughness (Ra cutting edge roughness = RaCER) of the cutting edges and the surface roughness of the flute area (Sa flute roughness = SaFR) were analyzed. Results#10 K-files had significant increases in all types of measurements (RaCEW, RaCEW, and SaFR) after the preparation of second mesiobuccal canals compared with the control group (P < .05) in both studies. In the ex vivo study, the PathFile (P1) had no significant changes in the surface profile from baseline but had a significant increase in the surface roughness of the flute (SaFR) (P < .05). PathFiles that were used 3 times in vivo had a significant increase in roughness (flute and cutting edge) values across all PathFile sizes compared with control values. ConclusionsThis study showed that PathFiles had significantly less surface defects compared with SS files after the preparation of narrow canals, indicating their possible benefits when establishing a glide path in extremely narrow canals.

Effect of Helium on Irradiation Creep Behavior of B-Doped F82H Irradiated in HFIR

The diameter of pressurized tubes of F82H and B-doped F82H irradiated up to ~6 dpa have been measured by a non-contacting laser profilometer. The irradiation creep strains of F82H irradiated at 573 and 673K were almost linearly dependent on the effective stress level for stresses below 260 MPa and 170 MPa, respectively. The creep strain of 10BN-F82H was similar to that of F82H IEA at each effective stress level except 294 MPa at 573K irradiation. For 673K irradiation, the creep strain of some 10BN-F82H tubes was larger than that of F82H tubes. However, the generation of ∼300 appm He did not cause a large difference in the irradiation creep behavior at 6 dpa.

FIRÇALAMANIN VE BEYAZLATICILI DİŞ MACUNLARIN KOMPOZİTLERİN YÜZEY ÖZELLİKLERİNE ETKİSİ

Purpose: Purpose of this in vitro study is to compare the effect of brushing and two different whitening toothpaste brushing on surface roughness and microhardness of four different type of composites (hybrid, nanohybrid, nanofilledand silorane based composites). Material and Methods: 80 composite samples were prepared. Samples were classified into 4 main groups (n=20): Control,Colgate Motion Whitening Toothbrush (CWT),Opalescence Whitening Toothpaste (OWT) and Beyond Pearl White Toothpaste (BPW). Control group was stored in distilled water for 14 day, as baseline. CWT brushing were applied 2 minutes a day with distilled water or OWT or BPW for 14 days. After 14 days, surface roughness (Sa) was measured by noncontact 3D laser profilometer and surface hardness (VHN) were measured by Vickers tester. SEM Evaluation was done under x750. Kruskal Wallis, post Hoc Dunn’s multiple comparison, Mann Whitney U tests were used in the comparison of groups. Statistical significance level was established at p<0.05. Result: Although roughness’s of the hybrid and nano filled composites were significantly increased (p<0.05), there are no significant changes were measured in surface hardness of CWT brushed composite specimens (p≥0.05). Hybrid composite showed the most roughness surface after brushing with BPW (32.62±6.17). No structural changes were detected on SEM micrographs of all groups after brushing. Conclusion: There is no significant differences between micro hardness of microhybrid composites which are neither methacrylate nor silorane based composites. Roughness and hardness of nano composites showed no significant difference after brushing with toothbrush and whitening toothpastes

In vivo Measurements of Tooth Wear over 12 Months

The aim of this study was to measure the progression of tooth wear in a cohort of 63 patients, 43 males and 20 females with a mean age of 39.1 years. Recruitment followed referral from general practice to Guy’s Hospital for advice/management of tooth wear. Addition silicone impressions were taken at 6-month intervals for a total of 12 months; impressions were subsequently poured in type IV gypsum. Casts were scanned using a non-contacting laser profilometer and then superimposed using Geomagic® Qualify 11. Wear was measured in µm by tooth per time interval. A questionnaire highlighting dietary, parafunctional and gastric risk factors was obtained from each participant. Clustered multiple regression analysis was used to determine the relationship between tooth wear progression and risk factors. Maximum follow-up times were 6 months for 63 participants and 12 months for 30 participants. The measurement error was 15 µm. At the tooth level, 72.2% of 1,078 teeth wore <15 µm over a 6-month period. At the subject level, 77.7% of 63 participants showed median wear <15 µm over a 6-month period. There was a statistical trend towards tooth wear progression being associated with gastric risk factors (p < 0.05). The lower molars and the upper anterior teeth were the most commonly affected teeth; the lower molars and the upper central incisors were the most severely affected teeth. Tooth wear progression was slow in this cohort, suggesting that tooth wear may be cyclical and inactive in the majority of participants.

A method to evaluate profilometric tooth wear measurements

ObjectivesTo test the accuracy of measurements of tooth wear using a non-contacting laser profilometer (NCLP) and surface matching software. MethodsThe accuracy and repeatability of the NCLP and software in measuring length was assessed by repeatedly scanning a calibrated 25mm engineering steel gage block. Volumetric measurements were assessed after scanning commercially pure titanium frustums of varying volume. The accuracy and repeatability of the systems in measuring step height and volume after surface matching were assessed using a custom built model with cemented engineering slip gages and cemented onlays of super-plastically formed titanium. The overall effect on the uncertainty of measurement of repeated superimpositions of the same cast, repeated impressions of the same patient and using step-over distances smaller than the laser spot size were also quantified. ResultsThe accuracy and repeatability were 1.3μm and 1.6μm in measuring length. The system was accurate for volumetric measurement with coefficients of variation <5%. Measurements using the model with cemented engineering slip gages and cemented super-plastically formed titanium onlays varied slightly (23.07μm and 1.6mm3). Scanning and superimposing the same model introduced mean error of 2.7μm (SD=0.7). Scanning and superimposing separate casts from repeated impressions of a patient introduced mean error of 14.8μm (SD=2.8). Decreasing step-over distances reduced measurement error (p<0.05). SignificanceThe methodologies described here served to assess sources of error in tribology studies using surface mapping and surface matching technologies. The results optimized data interpretation. Study supported by Guy's and St. Thomas’ Charity and the Royal College of Surgeons of England.

The dimensional stability of impression materials and its effect on in vitro tooth wear studies

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 24 h, 2, 4, 8 and 12 weeks. The impression materials tested were [1] Aquasil ®, [2] Aquasil ® DECA, [3] Affinis ®, [4] Express ®, [5] Extrude ®, [6] Impregum ®, [7] President ® and [8] Take 1 ®. Results Seven addition silicones and one polyether [6] were tested. [2] and [6] 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 [1] expanded over time (+31.5 μm) ( p < 0.05). The results from the custom block showed that all materials contracted compared to direct measurements of the block. [4] and [7] expanded over time (+62 μm and +63.8 μm respectively). [8] contracted over time (−54.7 μm) ( 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.

Trial of protective effect of fissure sealants, in vivo, on the palatal surfaces of anterior teeth, in patients suffering from erosion

Objectives Previous work has shown protection to eroded teeth offered by a resin-based adhesive lasted up to three months. The hypothesis investigated in this study was whether application of a fissure sealant would offer longer protection. Methods Seventeen adult patients with palatal tooth wear were recruited and written consent obtained. Metal discs were cemented on the palatal surfaces of all upper anterior teeth following previously published techniques. Alternate teeth within each subject were randomly chosen and coated with a clear fissure sealant using previously published methods. The uncoated teeth were used as controls. Accurate impressions were taken in custom made trays and repeated at 3, 6, 9, 12 and 20 months and scanned using a non-contacting laser profilometer. Results The mean (standard deviation) thickness of the fissure sealant was 290 μm (500) at the start and after 3 months a mean thickness of 120 μm (260) remained. At this point the control surfaces showed a mean 70 μm (113) of tooth wear. At 6 and 9 months the mean wear for control teeth was higher at 120 μm (114) and 110 μm (114) than sealed teeth at 50 μm (260) and 60 μm (440), respectively. A comparison of paired sites within subjects at their final visit indicated a statistically significant difference in wear between the sealed and control teeth ( p = 0.016). Conclusions The use of fissure sealant to protect palatal dentine surfaces may have a role in prevention of tooth wear for up to a period of nine months.

Surface roughness of impression materials and dental stones scanned by non-contacting laser profilometry

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 × 40 mm 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 0.99 μm, Rq = 1.09 and 1.23 μm, and Rt = 5.70 and 6.51 μm. The roughness values of the impression materials varied between Ra = 0.75 and 4.56 μm; Rq = 0.95 and 6.27 μm and Rt = 4.70 and 39.31 μm. 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 0.98 μm; Rq = 1.01 and 1.22 μm, and Rt = 5.04 and 6.38 μm. 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.

Effect of resin coating on dentine compared to repeated topical applications of fluoride mouthwash after an abrasion and erosion wear regime

Objectives The role of fluoride in preventing erosion and abrasion on dentine remains unclear. The aim of this study was to investigate the effect of repeated applications of a 0.05% fluoride mouthwash and an adhesive on wear of dentine using stainless steel discs reference points and a laser profilometer. Methods Small stainless steel discs were bonded to 60 caries free extracted molars which had previously been sectioned horizontally. The teeth were equally divided and subjected to four modalities in an erosion and abrasion laboratory model. Step heights were measured from the metal discs using a non-contacting laser profilometer at 100, 500, 1000, 2500 and 5000 cycles. Results The results after 5000 cycles showed that dentine coated with a dentine adhesive (0.015 μm, S.D. 0.090) had statistically less wear than fluoride (0.127 μm, S.D. 0.150), abrasion and erosion (0.182 μm, S.D. 0.150) or abrasion only (0.096 μm, S.D. 0.090) ( p < 0.001). Conclusion In conclusion dentine surfaces coated with a resin-based adhesive provided more protection against erosion and abrasion than a fluoride mouthrinse. There were no statistical differences between the modalities for cycles less than 5000.

The application of non-contact laser profilometry to the determination of permanent structural changes induced by compaction of pellets

Pellets of different mechanical properties were produced by extrusion and spheronisation process based on various composition (microcrystalline cellulose (MCC), lactose, glyceryl monostearate (GMS), water, ethanol and glycerol). Six hundred milligrams of these pellets were compacted at two different pressures (86.7 and 130MPa) to form flat-faced tablets and stored for 48h in ambient temperature and humidity after which their permanent structural change (plastic deformation) was investigated in terms of surface roughness parameters of both faces of the tablets, using a non-contact laser profilometer. The results were compared with the deformability values obtained from the force/displacement curve as well as the phase angle values obtained from the dynamic scan of a dynamic mechanical analyser. The increase in deformability of the pellets with the increase in porosity, increase in the contents of GMS, lactose or ethanol in the formulations and increase in compaction pressure was illustrated by the reduction of the surface roughness parameters. Analysis of variance identified the significant difference in the mean rugosity values of the tablets from the various formulations, tablet faces and compaction pressures. The deformability values obtained were reasonably comparable to those plasticity values obtained in terms of phase angle from the dynamic scan of the DMA and the force/displacement curves. The laser profilometry technique in conjunction with scanning electro-microscopy (SEM) demonstrated the low and broad based wavelike structure of the pellets after compaction rather than spiky sharp protrusions. This confirms the capability of determining the plastic deformability of the pellets from the surface roughness parameters obtained from non-contact laser profilometry.