State-of-the-art technologies provide new insights linking skin and blood vessel abnormalities in SSc-related disorders.

OBJECTIVE: A key unanswered question in systemic sclerosis (SSc) is how microvascular abnormality and fibrosis inter-relate. Our aim was to use state-of-the-art non-invasive imaging methods to gain new insights into pathophysiology, comparing patients with different subtypes of SSc, including early dcSSc, not only to healthy controls but also to patients with causes of Raynaud's phenomenon not progressing to fibrosis. METHODS: Laser Doppler imaging, nailfold capillaroscopy, spectroscopy, and ultrasound measured (respectively) perfusion, microvascular structure, oxygenation/oxidative stress, and skin thickening in the hands of 265 subjects: 31 patients with primary Raynaud's phenomenon (PRP), 35 with undifferentiated connective tissue disease (UCTD), 93 with limited cutaneous SSc (lcSSc), 46 with diffuse cutaneous SSc (dcSSc, including 27 'early') and 60 healthy controls. RESULTS: Mean perfusion was reduced in SSc groups compared to controls (lcSSc 172 perfusion units [standard deviation 157], late-dcSSc 90 [145], early-dcSSc 68 [137] vs. controls 211 [146]; p = 0.0002) as was finger-oxygenation (lcSSc 12.1 [13.6] arbitrary units [AU], late-dcSSc 12.2 [8.4], early-dcSSc 11.1 [11.3] vs controls 14.9 [10.5]; p = 0.0049). Oxidative stress was increased at the hand-dorsum in SSc groups (p = 0.0007). Perfusion positively correlated with oxygenation (r = 0.23, p < 0.001), and capillary density negatively with skin thickness (r = -0.26, p < 0.001). CONCLUSION: Our findings lend support to the hypothesis that in SSc, particularly early dcSSc, (but not in PRP or UCTD), reduced perfusion (together with structural microvascular abnormality) associates with reduced oxygenation, with oxidative stress and with skin thickening/fibrosis, most likely driving a vicious cycle which ultimately results in irreversible tissue injury. Findings in skin may mirror alterations in internal organs.

Microvascular Response in Patients with Complex Regional Pain Syndrome as Measured by Laser Doppler Imaging.

OBJECTIVES: Our aim was to investigate the hypothesis that microvascular dysfunction occurs in patients with CRPS. Specifically, whether there were functional differences in either deeper cutaneous blood vessels or more superficial nutritive vessels between the affected and unaffected limb in patients with CRPS, and between CRPS patients and healthy control subjects. METHODS: Twenty-two patients with CRPS (five male; mean age 45 years; eight upper limb involvement, 14 lower limb) and 23 healthy control subjects (one male; 43 years) were recruited. Microvascular flow at affected and unaffected contralateral sites was measured, following local heating, using laser Doppler imaging (red/green wavelengths). Corresponding sites were imaged in healthy controls. Maximum flux level and area under the curve (first 20 scans, AUC20) were measured. RESULTS: Vasodilator responses to heat were similar in affected and unaffected limbs, and in healthy controls. For example, median (IQR) "red" AUC20 in CRPS was 138.6 (120.0-152.9)% change from baseline in affected limb and 135.0 (120.7-166.8)% in unaffected limb, and (in healthy controls) 133.1 (117.2-145.9)% and 139.1% (126.0-162.1) in limb 1 and 2. CONCLUSIONS: We found no impairment of vasodilation in cutaneous microvessels in CRPS. The vasomotor changes in CRPS may relate to larger vessel dysfunction.

Pilot study assessing pathophysiology and healing of digital ulcers in patients with systemic sclerosis using laser Doppler imaging and thermography.

OBJECTIVES: Systemic sclerosis (SSc)-related digital ulcers (DU) cause significant pain and disability and are often a primary endpoint in clinical trials. However, their pathophysiology has been little studied. The objectives of this prospective study were to determine whether laser Doppler imaging (LDI) and thermography can identify ischaemic components in both fingertip and extensor surface DU and assess ulcer healing. METHODS: Patients prospectively reported new DU over a year. Patients' DU underwent imaging until the ulcer had healed. Ischaemia was defined as lower blood flow or skin temperature (and inflammation as higher) within the ulcer, compared to a non-affected site. RESULTS: 53 ulcers (19 fingertip, 18 extensor, 16 'other' sites) in 17 patients were imaged (53 with LDI, 52 with thermography). For LDI data 32 (60%) ulcers were ischaemic; median perfusion ulcer/unaffected area; 0.79 (range 0.11-2.9). For thermography data 35 (66%) were ischaemic; 0.98 (0.89 to 1.1). Inflammation in the surrounding area was identified for all ulcers by LDI but not thermography. In the 36 ulcers with repeat imaging, LDI showed trends (with healing) towards increased ulcer perfusion (p=0.23) and decreased hyperaemia in adjacent areas (p=0.59). Skin temperature at the ulcer site showed no significant change (p=0.13) but adjacent area showed decreased temperature (p=0.04 signifying decreased blood flow). CONCLUSIONS: LDI and thermography are sufficiently sensitive to measure ischaemia in both fingertip and extensor ulcers. LDI was better suited to monitoring change in perfusion with healing (due to higher imaging resolution, or vascular changes occurring in more superficial skin layers).

Non-invasive Imaging of Localised Scleroderma for Assessment of Skin Blood Flow and Structure.

Extensive morphoea causes major morbidity, disability and disfigurement; pathophysiology is poorly understood. The aim of this study was to investigate, with non-invasive imaging, the relationship between localised abnormalities of skin structure and perfusion, which characterise morphoea. Thirty-two patients with morphoea underwent imaging at affected and unaffected sites. Skin thickness was imaged with optical coherence tomography (OCT) and high-frequency ultrasound (HFUS). Perfusion was imaged with dual-wavelength laser Doppler imaging (LDI) and thermography. Epidermal thickness showed a small increase from affected to unaffected site (OCT, active and inactive plaques [p = 0.005 and p = 0.004], HFUS active plaques only [p = 0.03]). Deeper perfusion was higher within affected than unaffected sites (LDI p < 0.001, thermography p < 0.0001, active and inactive plaques). Epidermal thickness was inversely related to superficial (but not deeper) perfusion. This novel study of OCT, HFUS, LDI and thermography confirms loss of epidermal thickness and increased deeper perfusion in morphea plaques.

A double-blind, randomized, placebo-controlled crossover trial of the α2C-adrenoceptor antagonist ORM-12741 for prevention of cold-induced vasospasm in patients with systemic sclerosis.

OBJECTIVES: Our primary purpose was to evaluate the efficacy of the high-potency α2C-adrenoceptor antagonist ORM-12741 in the attenuation of a cold-induced reduction in finger blood flow and temperature in patients with RP secondary to SSc. Secondary objectives were to assess safety and tolerability. METHODS: This was a phase IIa, randomized, double-blind, crossover, single-dose, placebo-controlled, single-centre study. Patients attended five times: initial screening, treatment visits 1-3 (each at least 1 week apart) and 1-2 weeks after the last treatment. At each treatment visit, each subject received a single oral dose of 30 mg or 100 mg of ORM-12741 or placebo. Thirty minutes later the subject underwent a cold challenge. Blood flow to the fingers was assessed by three methods [temperature by probe, laser Doppler imaging (LDI) and infrared thermography] performed before, during and after the cold challenge. RESULTS: Twelve patients (10 female, mean age 58 years) were included. The area under the rewarming curve (LDI) of the right index finger (arbitrary flux units × time) was lower for both 30 mg (P = 0.043) and 100 mg (P = 0.025) of ORM-12741 compared with placebo, indicating delayed reperfusion. The time to 70% temperature recovery (middle finger probe) was longer with active than placebo treatment: mean (s.d.) values for placebo, 30 mg of ORM-12741 and 100 mg of ORM-12741 were 21.4 min (12.4), 25.7 min (12.2) and 26.9 min (13.9), respectively. Overall ORM-12741 was well tolerated. CONCLUSION: ORM-12741 did not expedite recovery from a cold challenge in the fingers of patients with SSc. TRIAL REGISTRATION: https://www.clinicaltrialsregister.eu/; no. 2010-024005-13.

The influence of measurement location on reliability of quantitative nailfold videocapillaroscopy in patients with SSc.

OBJECTIVES: Nailfold videocapillaroscopy is being increasingly used as a marker of SSc-related microvascular disease, including in response to treatment. However, it requires further validation. Our aim was to assess the inter-observer, intra-observer and test-retest variability of semi-automated measurement of capillary features as well as of a manual density measurement. METHODS: All capillary apexes in images from 58 patients with SSc were marked up independently by two trained observers (inter-observer variability). The first observer then re-marked the images (intra-observer variability), and finally, the first observer marked up a second image of the same nailfold (test-retest). Mark-up of capillaries was carried out on cropped mosaic images (cropped independently by the observers to a fixed width, to allow the same length of nail bed to be studied for each patient) and on whole mosaic images (examining the whole nail bed). RESULTS: Reproducibility of independently cropped mosaic images was poor and was due to the variation in the positioning of the cropped area. However, quantification of whole mosaic images was highly reproducible, e.g. for inter-capillary distance, the intra-class correlation coefficient for inter-observer, intra-observer and test-retest reliability was 0.95, 0.98 and 0.90 (compared with 0.88, 0.79 and 0.89 for cropped mosaic images), respectively. Intra-observer limits of agreement for whole mosaic images were better than inter-observer reproducibility. CONCLUSION: Quantitative assessment of SSc-related change in nailfold capillaries is unreliable if examination of the same set of capillaries cannot be guaranteed. Conversely a wide-field, high-magnification system that allows visualization of the whole nail bed offers a highly reproducible approach for quantitative assessment and therefore has potential as an outcome measure.

Photoacoustic imaging is a novel tool to measure finger artery structure and oxygenation in patients with SSc.

Systemic sclerosis (SSc)-related digital ischaemia is a major cause of morbidity, resulting from a combination of microvascular and digital artery disease. Photoacoustic imaging offers a newly available, non-invasive method of imaging digital artery structure and oxygenation. The aim of this study was to establish whether photoacoustic imaging could detect and measure vasculopathy in digital arteries, including the level of oxygenation, in patients with SSc and healthy controls. 22 patients with SSc and 32 healthy controls (HC) underwent photoacoustic imaging of the fingers. Vascular volume and oxygenation were assessed across eight fingers at the middle phalanx. In addition, oxygenation change during finger occlusion was measured at the non-dominant ring finger and the vascular network was imaged along the length of one finger for qualitative assessment. There was no statistically significant difference in vascular volume between patients with SSc and HC (mean of eight fingers; SSc, median 118.6 IQR [95.0-130.5] vs. HC 115.6 [97.8-158.9]) mm3. However, baseline oxygenation (mean 8 fingers) was lower in SSc vs. HC (0.373 [0.361-0.381] vs. 0.381 [0.373-0.385] arbitrary sO2 units respectively; p = 0.03). Hyperaemic oxygenation response following occlusion release was significantly lower in SSc compared to HC (0.379 [0.376-0.381] vs. 0.382 [0.377-0.385]; p = 0.03). Whilst vascular volume was similar between groups, digital artery oxygenation was decreased in patients with SSc as compared to HC, indicative of functional deficit. Photoacoustic imaging offers an exciting new method to image the vascular network in patients with SSc and the possibility to capture oxygenation as a functional measure.

Feasibility study of mobile phone photography as a possible outcome measure of systemic sclerosis-related digital lesions.

Objective: Clinical trials assessing systemic sclerosis (SSc)-related digital ulcers have been hampered by a lack of reliable outcome measures of healing. Our objective was to assess the feasibility of patients collecting high-quality mobile phone images of their digital lesions as a first step in developing a smartphone-based outcome measure. Methods: Patients with SSc-related digital (finger) lesions photographed one or more lesions each day for 30 days using their smartphone and uploaded the images to a secure Dropbox folder. Image quality was assessed using six criteria: blurriness, shadow, uniformity of lighting, dot location, dot angle and central positioning of the lesion. Patients completed a feedback questionnaire. Results: Twelve patients returned 332 photographs of 18 lesions. Each patient sent a median of 29.5 photographs [interquartile range (IQR) 15-33.5], with a median of 15 photographs per lesion (IQR 6-32). Twenty-two photographs were duplicates. Of the remaining 310 images, 256 (77%) were sufficiently in focus; 268 (81%) had some shadow; lighting was even in 56 (17%); dot location was acceptable in 233 (70%); dot angle was ideal in 107 (32%); and the lesion was centred in 255 (77%). Patient feedback suggested that 6 of 10 would be willing to record images daily in future studies, and 9 of 10 at least one to three times per week. Conclusion: Taking smartphone photographs of digital lesions was feasible for most patients, with most lesions in focus and central in the image. These promising results will inform the next research phase (to develop a smartphone monitoring application incorporating photographs and symptom tracking).

Preliminary clinical evaluation of semi-automated nailfold capillaroscopy in the assessment of patients with Raynaud's phenomenon.

OBJECTIVES: Nailfold capillaroscopy is well established in screening patients with Raynaud's phenomenon for underlying SSc-spectrum disorders, by identifying abnormal capillaries. Our aim was to compare semi-automatic feature measurement from newly developed software with manual measurements, and determine the degree to which semi-automated data allows disease group classification. METHODS: Images from 46 healthy controls, 21 patients with PRP and 49 with SSc were preprocessed, and semi-automated measurements of intercapillary distance and capillary width, tortuosity, and derangement were performed. These were compared with manual measurements. Features were used to classify images into the three subject groups. RESULTS: Comparison of automatic and manual measures for distance, width, tortuosity, and derangement had correlations of r=0.583, 0.624, 0.495 (p<0.001), and 0.195 (p=0.040). For automatic measures, correlations were found between width and intercapillary distance, r=0.374, and width and tortuosity, r=0.573 (p<0.001). Significant differences between subject groups were found for all features (p<0.002). Overall, 75% of images correctly matched clinical classification using semi-automated features, compared with 71% for manual measurements. CONCLUSIONS: Semi-automatic and manual measurements of distance, width, and tortuosity showed moderate (but statistically significant) correlations. Correlation for derangement was weaker. Semi-automatic measurements are faster than manual measurements. Semi-automatic parameters identify differences between groups, and are as good as manual measurements for between-group classification.

Reliability of dermoscopy in the assessment of patients with Raynaud's phenomenon.

OBJECTIVE: Few rheumatologists have access to wide field or video capillaroscopy (abnormal capillaries being highly predictive of CTD), and a key question is whether they should, therefore, purchase a dermatoscope. The aim of this study was to estimate the inter- and intra-observer variability of dermoscopy (magnification 10x) among rheumatologists with little or no experience of the technique. Good reliability is a necessary prerequisite for a test to be a valid clinical or research tool. METHODS: Dermoscopy was performed in all 10 nail folds from 16 subjects with a range of capillary normality/abnormality. The 160 nail fold images thus acquired were made into two PowerPoint presentations, each of 80 images with 16 duplicate slides. Each participating rheumatologist graded one of the sets of 96 images, grading scale (0-3): normal, mildly abnormal/'suspicious', definitely abnormal, grossly abnormal capillaries or 'unclassifiable' when capillaries could not be adequately identified. Data from both presentations were pooled for analysis. RESULTS: Twenty-eight rheumatologists participated in the study. For the decision as to whether an image could be classified or not, the inter- and intra-observer kappa-coefficients were 0.59 (95% CI 0.51, 0.67) and 0.63 (95% CI 0.45, 0.74), respectively. Conditional on being able to classify, the intra-class correlation coefficient for inter- and intra-observer reliability was 0.72 (95% CI 0.66, 0.77) and 0.85 (95% CI 0.82, 0.92), respectively. CONCLUSIONS: Inter- and intra-observer reliability were good, suggesting that with little training, dermoscopy is likely to be a useful technique to identify capillary distortions/underlying CTD.

Quantitative nailfold video capillaroscopy in patients with idiopathic inflammatory myopathy.

OBJECTIVES: To quantify nailfold capillary density and dimensions in patients with idiopathic inflammatory myopathy (IIM) and compare them with those in healthy controls; to look for associations with microvascular disease in IIM; and to determine whether nailfold capillary density and dimensions change over time. METHODS: Nailfold video microscopy (x300 magnification) was performed on 24 patients with IIM and 35 healthy controls. Capillary density and dimensions (total width and apical width) were quantified. Patients were clinically assessed and disease activity recorded using the Myositis Disease Activity Assessment Tool. Disease severity and physical function were assessed using the myositis damage index and Stanford HAQ, respectively. Findings were analysed using linear and logistic regression, adjusted for age and sex. In a subgroup of 16 patients with IIM and 27 controls, the process was repeated 6-12 months later and the results were analysed using Student's t-test. RESULTS: Capillary density was lower and dimensions were higher in patients with IIM compared with healthy controls (P < 0.001 for all). Anti-Jo-1 antibody was associated with reduced capillary density. In the longitudinal cohort, the mean change in capillary density was -1.4 in patients vs -0.4 in controls (P = 0.07). Mean change in capillary dimensions did not differ between patients and controls, but some patients demonstrated pronounced changes in capillary morphology over time. CONCLUSIONS: Reduced capillary density and increased dimensions in patients with IIM can be quantified using nailfold capillaroscopy, suggesting that nailfold capillaroscopy may be useful as an outcome measure of microvascular disease in studies of IIM.

Nail-fold capillary abnormalities are associated with anti-centromere antibody and severity of digital ischaemia.

OBJECTIVES: Advances in nail-fold capillaroscopy allow capillary abnormalities to be quantified. Our aim was to investigate, in patients with SSc, the relationships between the degree of nail-fold capillary abnormality and disease subtypes (lcSSc and dcSSc), duration of RP and the presence of (i) severe digital ischaemia (as defined by previous i.v. vasodilators, debridements or amputations), (ii) a positive ACA, (iii) clinically evident calcinosis, (iv) pulmonary arterial hypertension and (v) telangiectases. METHODS: This was a retrospective study of 176 patients. Six capillary measurements (four semi-automated and two manual) were calculated (automated width, distance between capillaries, tortuosity and derangement, and manual distance and density). Relationships between these measurements and the different clinical features of SSc were examined using multiple linear regressions (adjusted for age, sex and smoking status). RESULTS: One hundred and forty-two patients had lcSSc and 34 had dcSSc. Sixty-eight (39%) had a history of severe digital ischaemia, 66 (38%) were anti-centromere positive, 53 (30%) had clinically evident calcinosis and 26 (15%) had an estimated pulmonary artery pressure of >30 mmHg. Positive associations were found between both automated and manually measured distance between capillaries and (i) presence of severe digital ischaemia and (ii) positive ACA, and reduced density was also associated with positive anti-centromere. Patients with moderate/severe telangiectases had wider capillaries compared with those with 'mild' lesions. CONCLUSIONS: Both severe digital ischaemia and positive ACA are associated with measurable nail-fold capillaroscopic change, which has the potential of being an outcome measure for the structural microvascular disease associated with SSc-spectrum disorders.

Three-dimensional optoacoustic imaging of nailfold capillaries in systemic sclerosis and its potential for disease differentiation using deep learning.

The autoimmune disease systemic sclerosis (SSc) causes microvascular changes that can be easily observed cutaneously at the finger nailfold. Optoacoustic imaging (OAI), a combination of optical and ultrasound imaging, specifically raster-scanning optoacoustic mesoscopy (RSOM), offers a non-invasive high-resolution 3D visualization of capillaries allowing for a better view of microvascular changes and an extraction of volumetric measures. In this study, nailfold capillaries of patients with SSc and healthy controls are imaged and compared with each other for the first time using OAI. The nailfolds of 23 patients with SSc and 19 controls were imaged using RSOM. The acquired images were qualitatively compared to images from state-of-the-art imaging tools for SSc, dermoscopy and high magnification capillaroscopy. The vascular volume in the nailfold capillaries were computed from the RSOM images. The vascular volumes differ significantly between both cohorts (0.216 ± 0.085 mm3 and 0.337 ± 0.110 mm3; p < 0.0005). In addition, an artificial neural network was trained to automatically differentiate nailfold images from both cohorts to further assess whether OAI is sensitive enough to visualize anatomical differences in the capillaries between the two cohorts. Using transfer learning, the model classifies images with an area under the ROC curve of 0.897, and a sensitivity of 0.783 and specificity of 0.895. In conclusion, this study demonstrates the capabilities of RSOM as an imaging tool for SSc and establishes it as a modality that facilitates more in-depth studies into the disease mechanisms and progression.

A Multicenter Study of the Validity and Reliability of Responses to Hand Cold Challenge as Measured by Laser Speckle Contrast Imaging and Thermography: Outcome Measures for Systemic Sclerosis-Related Raynaud's Phenomenon.

OBJECTIVE: Reliable and objective outcome measures to facilitate clinical trials of novel treatments for systemic sclerosis (SSc)-related Raynaud's phenomenon (RP) are badly needed. Laser speckle contrast imaging (LSCI) and thermography are noninvasive measures of perfusion that have shown excellent potential. This multicenter study was undertaken to determine the reliability and validity of a hand cold challenge protocol using LSCI, standard thermography, and low-cost cell phone/mobile phone thermography (henceforth referred to as mobile thermography) in patients with SSc-related RP. METHODS: Patients with RP secondary to SSc were recruited from 6 UK tertiary care centers. The patients underwent cold challenge on 2 consecutive days. Changes in cutaneous blood flow/skin temperature at each visit were imaged simultaneously using LSCI, standard thermography, and mobile thermography. Measurements included area under the curve (AUC) for reperfusion/rewarming and maximum blood flow rate/skin temperature after rewarming (MAX). Test-retest reliability was assessed using intraclass correlation coefficients (ICCs). Estimated latent correlations (estimated from multilevel models, taking values between -1 and 1; denoted as rho values) were used to assess the convergent validity of LSCI and thermography. RESULTS: In total, 159 patients (77% with limited cutaneous SSc) were recruited (84% female, median age 63.3 years). LSCI and standard thermography both had substantial reliability, with ICCs for the reperfusion/rewarming AUC of 0.67 (95% confidence interval [95% CI] 0.54, 0.76) and 0.68 (95% CI 0.58, 0.80), respectively, and ICCs for the MAX of 0.64 (95% CI 0.52, 0.75) and 0.72 (95% CI 0.64, 0.81), respectively. Very high latent correlations were present for the AUCs of LSCI and thermography (ρ = 0.94; 95% CI 0.87, 1.00) and for the AUCs of standard and mobile thermography (ρ = 0.98; 95% CI 0.94, 1.00). CONCLUSION: This is the first multicenter study to examine the reliability and validity of cold challenge using LSCI and thermography in patients with SSc-related RP. LSCI and thermography both demonstrated good potential as outcome measures. LSCI, standard thermography, and mobile thermography had very high convergent validity.

The effects of XeCl laser etching of Ni-Cr alloy on bond strengths to composite resin: a comparison with sandblasting procedures.

OBJECTIVES: The aim of this study was to determine the effect of laser surface treatment of Ni-Cr alloy on the tensile bond strength of a proprietary composite resin (Panavia 21) in comparison with a conventional sandblasting technique. METHODS: Eighty cylinders of Ni-Cr were randomly allocated into the following groups: Group I-sandblasting only; Group II-low laser fluence (3.0 J/cm(2)); Group III-medium laser fluence (4.0 J/cm(2)); Group IV-high laser fluence (4.9 J/cm(2)); Group V-sandblasting in combination with medium laser fluence (4.0 J/cm(2)). Specimens within groups were bonded into pairs with resin cement as per manufacturer's instructions. They were then de-bonded using a tensile test. RESULTS: The mean de-bond strengths (SD) were: Group I-13.1 (4.2)MPa; Group II-17.6 (5.8)MPa; Group III-25.7 (11.8)MPa; Group IV-22.6 (6.6)MPa; Group V-41.8 (13.2)MPa. A statistically significant improvement (Bonferroni, p<0.05) in bond strength was found for the specimens which had been both lased and sandblasted (Group V) compared to all other groups, including those which were only sandblasted. SIGNIFICANCE: Laser pre-treatment of Ni-Cr alloy increases bond strength to composite resin compared with sandblasting; laser pre-treatment in combination with sandblasting further increases the de-bond strengths.

Qualitative assessment of surface topography of XeCl laser etched Ni-Cr alloy.

OBJECTIVES: The aims of this study were to compare the mode of debonding (adhesive or cohesive) of laser-etched Ni-Cr alloy (Wiron 99) to a standard sandblasting technique, and to a combination of sandblasting and laser etching. The etched surfaces were examined using optical and electron microscopy techniques. METHODS: Five groups of randomly allocated Ni-Cr cylinders were prepared: Group I-sandblasted; Groups II-IV-laser etched at three fluences (3.0, 4.0 and 4.9 J/cm2), Group V-combination sandblasting and laser etching (4.0 J/cm2). Within groups specimens were bonded into pairs (N=8) with composite luting cement (Panavia 21) prior to tensile debonding. Optical and scanning electron microscopy were performed both prior to and following debonding. RESULTS: An oxide layer was observed on sample surfaces before surface preparation by lasing or abrasion. Sandblasting removed the oxidation layer, which low and medium laser fluences alone failed to fully ablate. The highest (4.9 J/cm2) laser fluence melted the surface of the Ni-Cr alloy, covering the oxidation layer. A combination of sandblasting and lasing at 4.0 J/cm2 allowed full removal of the surface oxidation layer due to abrasion, followed by roughening of the surface with the laser. This resulted in greater mean tensile debonding strengths [Murray, A, Attrill, D, Dickinson, M. Dent Mater, 2004, In press] and a tendency for cohesive rather than adhesive interface failures. Groups I-IV underwent partial adhesive failure at both surfaces. Group V, in the main, underwent cohesive failure with a layer of adhesive remaining on both surfaces. SIGNIFICANCE: Laser etching of Ni-Cr alloy in combination with sandblasting optimises bonding to composite luting agents, resulting in a high proportion of cohesive failures when compared to sandblasting or lasing alone.