Hydroxyapatite Stones Research Articles

Prediction of chemical components of urinary stones through colour Doppler ultrasound twinkling artefacts under optimized space composite algorithm

AbstractThe study focused on the application value of the space compounding algorithm‐based colour Doppler ultrasound twinkling artefacts in predicting chemical components of urinary tract stones. Specifically, the minimum variance method was used to optimize the space‐compounding algorithm to improve the quality of colour Doppler ultrasound artefacts. Then, the urinary system stone model was built to quantitatively analyse the influence of stone components on colour Doppler twinkling artefacts. The results showed that no notable differences were noted in the twinkling artefact intensity (TAI), the width of twinkling artefact (TAW), and the length of twinkling artefact (TAL) between the oxalic acid monohydrate, hydroxyapatite, uric acid, and cystine stone models (p < 0.01). The area under the curve (AUC) of the TAI for the diagnosis of calcium‐free calculus models was 0.978, that of TAW was 0.9462, and that of TAL was 0.9315. The diagnostic sensitivity and specificity of TAI were 89% and 96%, respectively, the diagnostic sensitivity and specificity of TAW were 86% and 80%, respectively, and the diagnostic sensitivity and specificity of TAL were 78% and 97%, respectively. The ability of TAL (AUC of 0.953) to distinguish between hydroxyapatite stone model and cystine stone was better than TAI (AUC of 0.702) and TAW (AUC of 0.657) (p < 0.01); and TAL and TAW were positively correlated with TAI (R2 was 0.79 and 0.68, respectively, p < 0.01). In conclusion, the space compounding algorithm based on minimum variance method can improve the quality of colour Doppler ultrasound twinkling artefacts, and colour Doppler ultrasound twinkling artefacts can predict the chemical components of urinary stones, which can be used as a criterion for clinical diagnosis.

Dual-Energy Multidetector Computed Tomography: A Highly Accurate Non-Invasive Tool for in Vivo Determination of Chemical Composition of Renal Calculi

Introduction. Computed tomography is more accurate than excretory urography in evaluation of renal stones due to its high sensitivity and temporal resolution; it permits sub-millimetric evaluation of the size and site of calculi but cannot evaluate their chemical composition. Dual-energy computed tomography allows evaluating the chemical composition of urinary calculi using simultaneous image acquisition at two different energy levels.
 The objective of the research was to determine renal stone composition using dual-energy multidetector computed tomography, and its correlation with post-extraction chemical analysis of stones.
 Materials and Methods. This prospective study was conducted in the Department of Radiodiagnosis and Imaging from September 2017 to March 2019. A total of 50 patients with urolithiasis at the age of 18-70 years were included in the study. Dual-energy computed tomography ratios of various stones were noted, and preoperative composition of calculi was given based on their colour and dual-energy computed tomography ratio. These results were compared with the post-extraction chemical analysis of stones (using Fourier infrared transform spectroscopy as the standard comparative method.)
 Results. The most common type of calculi in our study population was calcium oxalate stones (78%) followed by uric acid stones (12%), cystine stones (6%) and hydroxyapatite stones (4%). The dual-energy ratio of calcium oxalate, uric acid, cystine and hydroxyapatite stones ranged from 1.38-1.59, 0.94-1.08, and 1.20-1.28 and 1.52-1.57, respectively, with the mean dual-energy ratio of 1.43, 1.01, 1.25 and 1.55, respectively. Dual-energy computed tomography was found to be 100% sensitive and specific for differentiating uric acid stones from non‑uric acid stones. The sensitivity and specificity in differentiating calcium oxalate calculus from non‑calcium oxalate calculus was 97.5% and 90.9%, respectively, with 96% accuracy and kappa value of 0.883 suggesting strong agreement.
 Conclusions. Dual-energy computed tomography is highly sensitive and accurate in distinguishing between various types of renal calculi. It has vital role in management as uric acid calculi are amenable to drug treatment, while most of non-uric acid calculi require surgical intervention.

MO118ROLE OF DUAL ENERGY COMPUTED TOMOGRAPHY IN PREDICTING THE CHEMICAL COMPOSITION OF STONES

Abstract Background and Aims Dual-energy CT (DECT) has shown excellent outcomes in differentiating the chemical composition of the urinary stones with a great accuracy. A reliable determination of the chemical type of the stone help the clinician to better satisfy treatment options for the patient- medical versus surgery We used the DECT in our study to assess the accuracy of non-invasive differentiation of renal stones using the 3rd generation dual-source computed tomography (CT) scanner in determining the chemical composition of renal stones and to determine appropriate management based on DECT determined chemical composition of stones. Method This prospective study was conducted in the Department of surgery and radiodiagnosis and Imaging, Era Medical College and RML institute of Medical Sciences , Lucknow over the study period, i.e., November 2016 to May 2018 . The patients were those referred for non-contrast/contrast CT for the diagnosis/evaluation of urolithiasis from the department of Surgery admitted for PCNL/ESWL/therapeutic ureterorenoscopy. DECT ratios of the various stones were noted and compared with the post extraction analysis of stones for composition. A total of 100 patients were included in the study, and their DECT results were compared with the post-extraction analysis (by infrared spectroscopy as the standard comparative method). Results Mean age of patients was 41.15+/- 10.08 years with 64% being males. DECT was highly sensitive and specific in the diagnosis of various types of calculi based on their dual-energy ratio. It was found to be 100% sensitivity and 97.2% specificity for differentiating UA stones with level of agreement between chemical and DECT was almost perfect (k= .951) .However for hydroxyapatite stones was substantial (k=.889). Most of the stones belonged to non-UA category (72%), and only 28% were UA calculi. The sensitivity and specificity in differentiating a calcium oxalate from non-calcium oxalate calculus was 94.1% and 95.5%, respectively. Conclusion DECT highly sensitive and effective in characterizing chemical composition of the urinary stones and can help in determining the management plan and reduce the unnecessary burden of surgical interventions.

MP03-05 URINARY CITRATE WASTING AMONG NEPHROLITHIASIS PATIENTS ASSOCIATES WITH OBESITY AND DIABETES MELLITUS

INTRODUCTION AND OBJECTIVE: Urinary citrate is thought to decrease calcium stone formation through direct inhibition of crystallization and by complexing with calcium. A subset of nephrolithiasis patients excrete very high amounts of citrate with unclear clinical implications. Here we sought to profile nephrolithiasis patients with urinary citrate wasting. METHODS: We identified 2,257 consecutive patients who underwent 24-hour urine studies performed at our institution from 2001 to 2017. We identified patients with 1st time urine testing with citrate wasting, defined as >1500 mg/day. Patients were excluded if on any alkali therapy. After applying these selection criteria, a total of 55 citrate wasters were identified and randomly matched 1:3 by age and sex to other stone formers for a final comparative cohort of n = 165. Univariate analyses with chi-square and t-tests were used to assess differences in demographic, clinical, stone and 24-hour urine characteristics. RESULTS: Citrate wasters had significantly higher mean ± SD BMI (35.0 ± 7.3 vs 29.9 ± 7.9 kg/m2, p < 0.001) and a higher prevalence of diabetics (61.8 vs 20.6%, p < 0.001). Calcium oxalate monohydrate (COM) and uric acid stones were the two most common stones the citrate wasting group (70% and 15% respectively), while COM and hydroxyapatite stones were most common in the control group (58% and 20% respectively). Uric acid stones were more commonly observed among citrate wasters (15% vs 7%, p = 0.096). On 24-hour urine analysis, the citrate wasting group showed higher urine values of calcium, oxalate, uric acid, and sodium (all p<0.001; see Figure). Notably, urine pH showed no difference between groups. These results were largely unchanged when examining differences by sex. CONCLUSIONS: Nephrolithiasis patients who excrete > 1500mg of urinary citrate per day are more likely to be obese and diabetic, with generally worse urinary analytes overall relating to stone recurrence risk. Further investigation is needed on the etiologic and clinical implications of these findings.Source of Funding: None

Effect of sample time on urinary lithogenic risk indexes in healthy and stone-forming adults and children

BackgroundThe diagnosis and follow-up of stone forming patients is usually performed by analysis of 24-h urine samples. However, crystallization risk varies throughout the day, being higher at night. The main objective of this study is to evaluate the urinary crystallization risk in adults and children by calculating risk indexes based on different collection periods.MethodsThe study included 149 adults (82 healthy and 67 stone-formers) and 108 children (87 healthy and 21 stone-formers). 24-h urine was collected, divided into 12-h daytime sample (8 am to 8 pm), and 12-h overnight sample (8 pm to 8 am next morning). Solute concentrations, the calcium to citrate ratio (Ca/Cit), and the ion activity product of calcium oxalate (AP[CaOx]) and calcium phosphate (AP[CaP]) were calculated in each 12-h sample and in overall 24-h urine. Assessments were also related to stone type.ResultsCa/Cit and AP(CaOx) were significantly higher in stone forming patients than in healthy subjects. The 12-h overnight samples had the highest values for both risk indexes, confirming a greater risk for crystallization at night. The AP(CaP) index was significantly higher in patients with pure hydroxyapatite stones than healthy controls, but was not significantly different between stone-formers overall and healthy controls.ConclusionsThe calculation of risk indexes is a simple method that clinicians can use to estimate crystallization risk. For this purpose, the use of 12-h overnight urine may be a reliable alternative to 24-h collections.

Characterization of Urinary Tract Stones with Dual Energy Computed Tomography

Introduction. Dual Energy Computed Tomography (DECT) scan can provides simple and reliable differentiation between uric acid and non-uric acid stones. The characterization of various stones was based on the dual energy ratio and x-ray attenuation or HU. Methodology. A prospective study was conducted among 101 adult patients in Tribhuvan University Teaching Hospital (TUTH), Nepal. Informed written consent was obtained from all the participants. The standard low doses CT KUB were performed in multi-slice CT scanner (Siemens Somatom Definition AS+ 128 slice) at 120 kVp and 250 mAs. When stones were detected, second dual energy scans using 80 kVp and 140 kVp were obtained focusing only on the region of stones for their characterization. After post processing and graphical analysis at Syngo Via work station, the components of the stones were identified. Statistical analysis was performed in SPSS v21.0 software.Results. Out of 101 patients, 49 (48.5%) had calcium oxalate stones, 17 (16.87%) had uric acid stones, 16 (15.8%) had hydroxyapatite, 15 (14.9%) had cystine and 4 (4%) had mixed type of stones. Dual energy ratios were ranged from 0.55-1.11 for uric acid stone, 1.12-1.24 for cystine and more than 1.24 for calcium oxalate and hydroxyapatite stones. The mean HU noted in our study were; for uric acid stones (461.12 ± 119 HU at 80 kV, 449 ± 98.5 HU at 140 kV), for cystine (870.79 ± 386 at 80 kV, 743 ± 341 at 140 kV), for calcium oxalate (1246 ± 448 at 80 kV, 915 ± 316 at 140 kV) for hydroxyapatite (1301 ± 387 at 80 kV, 896 ± 315 at 140 kV) and mixed stone had (779.25 ± 269 HU at 80 kV, 665.5 ± 252 HU at 140 kV).

Stone Composition Among First-Time Symptomatic Kidney Stone Formers in the Community

ObjectiveTo determine the variation in kidney stone composition and its association with risk factors and recurrence among first-time stone formers in the general population. Patients and MethodsMedical records were manually reviewed and validated for symptomatic kidney stone episodes among Olmsted County, Minnesota, residents from January 1, 1984, through December 31, 2012. Clinical and laboratory characteristics and the risk of symptomatic recurrence were compared between stone compositions. ResultsThere were 2961 validated first-time symptomatic kidney stone formers. Stone composition analysis was obtained in 1508 (51%) at the first episode. Stone formers were divided into the following mutually exclusive groups: any brushite (0.9%), any struvite (0.9%), any uric acid (4.8%), and majority calcium oxalate (76%) or majority hydroxyapatite (18%). Stone composition varied with clinical characteristics. A multivariable model had a 69% probability of correctly estimating stone composition but assuming calcium oxalate monohydrate stone was correct 65% of the time. Symptomatic recurrence at 10 years was approximately 50% for brushite, struvite, and uric acid but approximately 30% for calcium oxalate and hydroxyapatite stones (P<.001). Recurrence was similar across different proportions of calcium oxalate and hydroxyapatite (P for trend=.10). However, among calcium oxalate stones, 10-year recurrence rate ranged from 38% for 100% calcium oxalate dihydrate to 26% for 100% calcium oxalate monohydrate (P for trend=.007). ConclusionCalcium stones are more common (93.5% of stone formers) than has been previously reported. Although clinical and laboratory factors associate with the stone composition, they are of limited utility for estimating stone composition. Rarer stone compositions are more likely to recur.

MP33-07 CLINICAL AND METABOLIC RISK FACTORS FOR PLUG FORMATION AMONG IDIOPATHIC CALCIUM OXALATE STONE FORMERS

INTRODUCTION AND OBJECTIVES: Collecting duct plugs could provide a nidus for stone formation within the kidney. However, their role in idiopathic calcium oxalate (iCaOx) calculogenesis remains poorly defined. Thus, we evaluated factors associated with endoscopically detected plugs in a cohort of iCaOx stone formers. METHODS: Data was collected from a prospective cohort of patients undergoing percutaneous nephrolithotomy (PCNL) between 2009-2014. After stone removal, accessible renal papillae were endoscopically videotaped, biopsied, and analyzed to quantify the percent surface area (SA) occupied by plaque and plug. Stone composition was determined by micro-CT, and all patients underwent metabolic evaluation with 24 hour urine collections. RESULTS: Data were available for 89 iCaOx formers. Plugs were detected in 33 (37%), with a mean % plug SA of 1.4 (median1⁄41.0, IQR1⁄40.2-1.6). Patients with plugs had a higher mean % plaque SA than those with no plugs (5.3% versus 2.3%, p1⁄40.02); moreover, a moderately strong correlation was found between % plaque and % plug (Spearman r1⁄40.25, p-value1⁄4.016). Patients with a higher % mean SA plugging (>1%) were more likely to have a higher urinary pH (mean 6.3 vs 6.0, p1⁄40.03). Neither urinary hydroxyapatite supersaturation (SS) or percentage apatite significantly differed between the high and low plug group (mean 4.7 vs 3.5 D.G.; p1⁄40.08 and 20.7 vs 10.9; p1⁄40.40, respectively). CONCLUSIONS: Within a cohort of iCaOx stone formers, plaque and plugs often coexist and are positively correlated. Those with greater amounts of plugs also tended to have higher levels of urinary pH. Gender, hydroxyapatite SS and hydroxyapatite stone content were similar across high and low plug group. Intraluminal features known to favor calcium phosphate crystallization, namely higher pH, may play a role in plug formation. However, the pathogenic significance of these plugs in the iCaOx population remains to be established.

Diagnostic value of color Doppler twinkling artifact and in urinary calcium stones: an in vitro experiment

Objective To investigate the diagnostic value of twinkling artifact in urinary calcium stones. Methods Calcium oxalate monohydrate, hydroxyapatite and whitlockite stone phantoms were prepared and embedded in porcine kidneys for ultrasound scanning. The length and width of twinkling artifact were measured. The intensity of twinkling artifact and the contrast-to-noise ratio (C/N ratio) of acoustic shadowing were recorded and all the data was analyzed statistically. Results All the stone phantoms generated twinkling artifact and acoustic shadowing. The difference of the intensity, length and width of twinkling artifact and the C/N ratio of acoustic shadowing had statistically significant each composition (P<0.01). There was no overlap between 95% confidence interval of the intensity of twinkling artifact for any two compositions, and any two compositions of stones could be differentiated by the intensity of twinkling artifact (P<0.05). The C/N ratio of acoustic shadowing of calcium oxalate monohydrate and whitlockite stone phantoms were higher than those of hydroxyapatite ones (P<0.05). The receiver operating characteristic (ROC) curve displayed that the cutoff value of 1 127 of the intensity of twinkling artifact could be used to diagnose hydroxyapatite stones. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and area under the curve (AUC) were 74%, 68%, 69.8%, 72.3% and 0.743 respectively. Conclusions Twinkling artifact could be used to differentiate the calcium stones, which will be helpful for clinical treatment. Key words: Ultrasonography; Kidney calculi; Twinkling artifact

Stone composition as a function of age and sex.

Kidney stones are heterogeneous but often grouped together. The potential effects of patient demographics and calendar month (season) on stone composition are not widely appreciated. The first stone submitted by patients for analysis to the Mayo Clinic Metals Laboratory during 2010 was studied (n=43,545). Stones were classified in the following order: any struvite, any cystine, any uric acid, any brushite, majority (≥50%) calcium oxalate, or majority (≥50%) hydroxyapatite. Calcium oxalate (67%) was the most common followed by hydroxyapatite (16%), uric acid (8%), struvite (3%), brushite (0.9%), and cystine (0.35%). Men accounted for more stone submissions (58%) than women. However, women submitted more stones than men between the ages of 10-19 (63%) and 20-29 (62%) years. Women submitted the majority of hydroxyapatite (65%) and struvite (65%) stones, whereas men submitted the majority of calcium oxalate (64%) and uric acid (72%) stones (P<0.001). Although calcium oxalate stones were the most common type of stone overall, hydroxyapatite stones were the second most common before age 55 years, whereas uric acid stones were the second most common after age 55 years. More calcium oxalate and uric acid stones were submitted in the summer months (July and August; P<0.001), whereas the season did not influence other stone types. It is well known that calcium oxalate stones are the most common stone type. However, age and sex have a marked influence on the type of stone formed. The higher number of stones submitted by women compared with men between the ages of 10 and 29 years old and the change in composition among the elderly favoring uric acid have not been widely appreciated. These data also suggest increases in stone risk during the summer, although this is restricted to calcium oxalate and uric acid stones.

Correlation between urinary stones and urinary tract infections

To explore the correlation of urinary stones and urinary tract infections. 300 cases with urinary tract stones received in our hospital from Feb. 2010 to Oct. 2013 were chosen as study samples. Urine routine index, situation of urine positivity and urinary tract infection after surgery were analyzed while, intraoperative cotton swabs were tested after being dipped in liquid near stones. Main components of stones in non-infected and infected stone group were analyzed and compared. Data on urolithiasis was collected. 96 infected stones were found in 300 patients, accounting for 32%, which including 35 cases of E. coli (36.5%), 28 cases of Staphylococcus epidermidis (29.2%), and 15 cases of Proteus mirabilis (15.6%). Numbers of urine abnormalities, urine positivities, positive intraoperative cotton swabs and urinary tract infections in patients in the group with infected stones, were significantly higher than in the group without infected stones and the differences were statistically significant (χ² = 8.203, 73.99, 178.9, 24.26, P < 0.05). The incidence rates of hexahydrate magnesium ammonium phosphate, carbonate apatite and hydroxyapatite stones in the group with infected stones were significantly higher than those in the non-infected-rock group while the incidence rates of calcium oxalate and uric acid stones were found significantly lower than those in the non-infected-stone group, with differences statistically significant (χ² = 167.6, 21.00, 8.586, 73.17, 48.79, P < 0.05). Bacteria could cause urinary tract stones, and infected stones were always associated with urinary tract infections. Bacteria detection in patients with urinary calculi was particularly important to avoid the urinary tract infections.

Contrasting Histopathology and Crystal Deposits in Kidneys of Idiopathic Stone Formers Who Produce Hydroxy Apatite, Brushite, or Calcium Oxalate Stones

Our previous work has shown that stone formers who form calcium phosphate (CaP) stones that contain any brushite (BRSF) have a distinctive renal histopathology and surgical anatomy when compared with idiopathic calcium oxalate stone formers (ICSF). Here we report on another group of idiopathic CaP stone formers, those forming stone containing primarily hydroxyapatite, in order to clarify in what ways their pathology differs from BRSF and ICSF. Eleven hydroxyapatite stone formers (HASF) (2 males, 9 females) were studied using intra-operative digital photography and biopsy of papillary and cortical regions to measure tissue changes associated with stone formation. Our main finding is that HASF and BRSF differ significantly from each other and that both differ greatly from ICSF. Both BRSF and ICSF patients have significant levels of Randall's plaque compared with HASF. Intra-tubular deposit number is greater in HASF than BRSF and nonexistent in ICSF while deposit size is smaller in HASF than BRSF. Cortical pathology is distinctly greater in BRSF than HASF. Four attached stones were observed in HASF, three in 25 BRSF and 5-10 per ICSF patient. HASF and BRSF differ clinically in that both have higher average urine pH, supersaturation of CaP, and calcium excretion than ICSF. Our work suggests that HASF and BRSF are two distinct and separate diseases and both differ greatly from ICSF.

Differentiating Calcium Oxalate and Hydroxyapatite Stones In Vivo Using Dual-Energy CT and Urine Supersaturation and pH Values

Knowledge of urinary stone composition can guide therapeutic intervention for patients with calcium oxalate (CaOx) or hydroxyapatite (HA) stones. In this study, we determined the accuracy of noninvasive differentiation of these two stone types using dual-energy CT (DECT) and urine supersaturation (SS) and pH values. Patients who underwent clinically indicated DECT scanning for stone disease and subsequent surgical intervention were enrolled. Stone composition was determined using infrared spectroscopy. DECT images were processed using custom-developed software that evaluated the ratio of CT numbers between low- and high-energy images. Clinical information, including patient age, gender, and urine pH and supersaturation profile, was obtained from electronic medical records. Simple and multiple logistic regressions were used to determine if the ratio of CT numbers could discriminate CaOx from HA stones alone or in conjunction with urine supersaturation and pH. Urinary stones (CaOx n = 43, HA n = 18) from 61 patients were included in this study. In a univariate model, DECT data, urine SS-HA, and urine pH had an area under the receiver operating characteristic curve of 0.78 (95% confidence interval [CI] 0.66-0.91, P = .016), 0.76 (95% CI 0.61-0.91, P = .003), and 0.60 (95% CI 0.44-0.75, P = .20), respectively, for predicting stone composition. The combination of CT data and the urinary SS-HA had an area under the receiver operating characteristic curve of 0.79 (95% CI 0.66-0.92, P = .007) for correctly differentiating these two stone types. DECT differentiated between CaOx and HA stones similarly to SS-HA, whereas pH was a poor discriminator. The combination of DECT and urine SS or pH data did not improve this performance.

Biochemical and Physicochemical Presentations of Patients With Brushite Stones

We determined whether the biochemical and physicochemical backgrounds of patients with brushite stones differ from those with hydroxyapatite and calcium oxalate stones. From a computer data base of patients completing ambulatory evaluation 19 with brushite stones, 24 with hydroxyapatite stones and 762 with calcium oxalate stones were identified with the specified composition in greater than 70% of stones. Absorptive hypercalciuria type I was present in 63% of patients with brushite, 17% with hydroxyapatite and 30% with calcium oxalate stones. Distal renal tubular acidosis was noted in 32% of patients with brushite, 42% with hydroxyapatite and 3% with calcium oxalate stones. Mean urinary calcium in the brushite group was significantly higher than in the hydroxyapatite and calcium oxalate groups (265 +/- 125 vs 186 +/- 103 and 187 +/- 95 mg daily, respectively). Urinary pH in the brushite group was slightly but significantly higher than in the calcium oxalate group (6.15 +/- 0.30 vs 5.91 +/- 0.42). The brushite relative saturation ratio in the brushite group was marginally higher than in the hydroxyapatite group and significantly higher than in the calcium oxalate group (3.25 +/- 2.03 vs 2.34 +/- 1.51 and 1.83 +/- 1.66, respectively). Patients with predominantly brushite stones could be distinguished from those with predominantly hydroxyapatite and calcium oxalate stones by higher urinary saturation with respect to brushite due mainly to hypercalciuria from absorptive hypercalciuria.

Determination of trace amounts of oxalate in renal calculi and related samples by gas chromatography-mass spectrometry

A GC-MS method has been developed for determination of trace amounts of oxalate in renal stones. The steps involved are: solubilisation of the oxalate in renal stones with HCl, elimination of cationic species by use of a cation-exchange resin, evaporation of water, reconstitution with ethyl acetate, and formation of trimethylsilyl esters of oxalic acid with chlorotrimethylsilane. Trichlorocacetic acid was used as internal standard. With appropriate sample treatment the method has also been applied to urine and food. The main analytical features of the method were: linear range 0.2–5.0 mg oxalate L1, limit of detection 0.06 mg oxalate L1 (concentrations in the solution chromatographed), coefficient of variation of the method 1.3%. Twenty-seven renal stones were analysed by the method. The average oxalic acid content of uric acid calculi was 0.11 mg g1 (SD=0.08,n=13). A larger amount of oxalate was found in struvite calculi (mean value 0.2 mg oxalic acid g1,SD=0.13,n=8). Hydroxyapatite stones can be classified according to their oxalate content: samples with very low oxalate content (below theLOD of the method) and samples with large amounts of oxalate (0.431 and 0.801 mg oxalic acid g1).

Bond strength of fiber-reinforced composite bars for orthodontic attachment.

Long fiber-reinforced composites (FRC) have been shown to have enhanced mechanical properties that allow their use in orthodontic appliances as bars that join teeth to form either anchorage or active units. This study was designed to determine if the bonding of an orthodontic attachment has sufficient strength to withstand loading during clinical use. The experimental model consisted of a hydroxyapatite stone that simulated enamel, FRC bars, and a bonded metal hook. Three specimen types were compared: (1) a metal hook-pad (the control), (2) a woven FRC with a hook-pad, and (3) a unidirectional FRC with a hook-pad. Loads were applied both parallel and at 90 degrees to the tooth surface. Under no condition was the FRC pad combination weaker than the control pad. Under some loading conditions, the loads before failure were as much as 3 times greater than those for the control. The lowest strength was found with loads at 90 degrees to the tooth surface for all 3 types. Failure normally occurred in the FRC and rarely at the bracket or tooth interface. The excellent bonding of the orthodontic attachment to the FRC and the high strengths of the FRC attachment combination demonstrate the ability to form connecting bars between teeth for either anchorage or active segmental movements. These bars offer advantages in simplicity in treatment by reducing the need for some bands, attachments, or wires.

Five Years Experience in Experimental Laser Lithotripsy

In the first part of our experience approximately 300 stones of different composition have been treated in vitro with three different laser sources: Nd-YAG laser (1,064 nm), dye laser (504 nm) and alexandrite laser (755 nm). Calcium oxalate monohydrate and brushite stones appeared to be the most resistant to lithotripsy. Highest fragmentation rates were obtained for calcium oxalate dihydrate stones followed by struvite, uric acid and hydroxyapatite stones. The Nd-YAG laser did not appear to be ideal for lithotripsy since early damage to the fiber tip was observed when this source was used. Both the dye and the alexandrite lasers were almost always effective in fragmenting the various types of stones. We subsequently treated some cystine stones while immersed in water or in solutions of carmine indigo (2%), methylene blue (5%), rifamycin (0.6 and 6%) and rifampicin (0.8 and 0.3%) with the dye or the alexandrite laser. The spectra of these solutions, previously analyzed with the spectrophotometer, showed that rifamycin and rifampicin absorbed large amounts of light radiation at the wave length of the dye laser (504 nm). Successful fragmentation occurred only when the dye laser was used to treat stones immersed in the more concentrated solutions of these two substances. The quantity of fragmented material after treating a 10-cm3 cystine stone previously immersed in the more concentrated solutions of rifamycin and rifampicin (30 and 10 mm3, respectively) confirmed previous results.(ABSTRACT TRUNCATED AT 250 WORDS)