The adverse effects of tungsten carbide grinding on the strength of dental zirconia.

OBJECTIVES: This study investigated the effects of tungsten-carbide grinding on the surface characteristics and mechanical strength of dental 3 mol% yttria-stabilized zirconia (3Y-TZP). METHODS: Two types of tungsten-carbide burs (TC), 6-blade (TC1) and 8-blade (TC2) were used to grind 3Y-TZP, in a dental air-turbine handpiece with water-cooling and were also subjected to air-particle abrasion (APA): TC1 + APA and TC2 + APA; and rubber polishing (RP): TC1 + RP and TC2 + RP; one group received only rubber-polishing RP. The control group received no treatment. Surface characterization was examined by surface roughness (Ra) and atomic force microscopy. Specimens were also observed with scanning electron microscopy (SEM) and X-ray-diffraction (XRD) for microstructure and crystalline phases. A piston-on-three-balls biaxial-flexural strength (BFS) test was performed with 15 samples-per-group and the broken specimen were observed under SEM to investigate the fracture origin pattern. One-way ANOVA, Kruskal-Wallis test and Weibull analysis were performed at α = 0.05. RESULTS: Groups TC1 and TC2 had the lowest mean BFS (p < 0.05) with up to 74 % reduction in strength. APA and RP both significantly increased the mean BFS after tungsten-carbide grinding but was still less than the control (p < 0.05). Compared to the control, the mean BFS was significantly reduced for all groups except for the RP group (p < 0.05). APA and rubber-polishing following TC2 grinding had significant higher mean BFS than those following TC1 grinding respectively (p < 0.05). SEM revealed distinct micro-cracks after tungsten-carbide grinding. SIGNIFICANCE: Tungsten-carbide burs (6- and 8-blade) are not recommended for zirconia grinding due to the significant reduction of biaxial-flexural strength and observed micro-structural surface and subsurface damage.

A clinical technique for virtual articulator mounting with natural head position by using calibrated stereophotogrammetry.

Accurate articulator-mounted casts are essential for occlusion analysis and for fabrication of dental prostheses. Although the axis orbital plane has been commonly used as the reference horizontal plane, some clinicians prefer to register the horizontal plane with a spirit level when the patient is in the natural head position (NHP) to avoid anatomic landmark variations. This article presents a digital workflow for registering the patient's horizontal plane in NHP on a virtual articulator. An orientation reference board is used to calibrate a stereophotogrammetry device and a 3-dimensional facial photograph with the patient in NHP. The horizontal plane can then be automatically registered to the patient's virtual model and aligned to the virtual articulator at the transverse horizontal axis level. This technique showed good repeatability with positional differences of less than 1 degree and 1 mm in 5 repeated measurements in 1 patient.

A 2-part facebow for CAD-CAM dentistry.

Converting the patient's clinical information into the virtual world is a prerequisite for the computer-aided design and computer-aided manufacturing (CAD-CAM) of dental restorations. This article describes a modified facebow which facilitates the radiation-free registration of the maxillary teeth to a 3-dimensional face image for transfer to a virtual articulator. This facebow can be easily fabricated with minimal materials and adjusted to fit different patients; its error in tooth registration was demonstrated to be less than 1 mm.

Effect of burn-out temperature on magnetic keepers in cast noble metal alloy posts.

STATEMENT OF PROBLEM: Early loss of magnetic keepers in cast gold posts is seen in clinical practice. PURPOSE: The purpose of this vitro study was to investigate the effect of burn-out temperature on the retention of magnetic keepers in cast gold alloy and on the thickness of the oxide layer at the keeper-alloy interface. MATERIAL AND METHODS: One hundred and five keepers (Magfit EX) were cast with gold alloy (Protor 3) at 3 different burn-out temperatures: 500 degrees C, 600 degrees C, or 700 degrees C (n=35). To test for retention of keepers, 60 specimens (n=20) were tested to failure in tension mode in a universal testing machine (UTM); 45 specimens (n=15) were sectioned, and the interface was evaluated under a scanning electron microscope (SEM). Tensile force data were analyzed with 1-way ANOVA, and SEM data were analyzed with 1-way repeated measures ANOVA. Bonferroni multiple comparisons were performed for post hoc analysis (alpha=.05). RESULTS: Retention of the keepers was significantly higher at lower burn-out temperatures (P<.001). The retention of the keepers became unpredictable and immediate failures were observed at a burn-out temperature of 700 degrees C. Oxide formation at the keeper-alloy interface was significantly less at lower burn-out temperatures (P<.001). CONCLUSIONS: A burn-out temperature of 500 degrees C for casting the Magfit EX keeper with type IV high-strength gold alloy is recommended.

A quality assessment of the casting process on magnetic keepers.

PURPOSE: The objective of this study was to qualitatively investigate the effect of the burn-out (mold) temperature, investment material, and casting alloy on the surface integrity of the Magfit EX keeper. MATERIALS AND METHODS: Forty-two Magfit EX keepers were waxed-up, invested in five investment materials (Beauty-Cast, Cristobalite, CM-10, Cera-Fina, Castorit-super), and subjected to burn-out temperatures ranging from 450 to 700 degrees C at intervals of 50 degrees C. The keeper samples were then cast into copings with three alloys (Castwell, Protor 3, Optimum) under standard conditions. The keeper surfaces were then examined under a microscope, and the compositions were assessed by an X-ray micro-analyzer in a scanning electron microscope (SEM). A new keeper served as control. RESULTS: At a burn-out temperature of 550 degrees C, the keeper surface started to disintegrate. X-ray micro-analysis showed an increase in oxygen content with increasing temperature. At 700 degrees C, the keeper surface disintegrated, and the composition differed markedly from that of the new keeper. The keeper surfaces were intact with all investments except those with Beauty-Cast. The keeper surfaces were found to be damaged when the casting alloy was Optimum. CONCLUSIONS: Beauty-Cast investment with a burn-out temperature of 700 degrees C is unsuitable for casting the Magfit EX keeper-coping unit. Also, high fusing alloys are not recommended for casting Magfit EX keepers.

Comparison of the retentive characteristics of cobalt-chromium and commercially pure titanium clasps using a novel method.

This study aimed to compare the retentive forces of cast cobalt-chromium (Co-Cr) and commercially pure titanium (cpTi) clasps. A clasp assembly comprising a pair of symmetrical clasps was made to fit the opposite halves of a hardened stainless-steel sphere. This twin clasp was designed to counterbalance the tipping forces when the clasp assembly was drawn from the sphere. A total of 120 clasp assemblies were fabricated in cast Co-Cr and cpTi and placed at undercut depths of 0.25 mm, 0.50 mm, and 0.75 mm (n = 20 for each). For Co-Cr clasps, the retentive forces at these undercuts depths were 2.34 +/- 0.23 N, 4.65 +/- 0.35 N, and 7.56 +/- 0.50 N, respectively. The corresponding retentive forces for cpTi clasps were 1.24 +/- 0.13 N, 2.34 +/- 0.23 N, and 3.70 +/- 0.27 N. The retentive force of cpTi clasps was approximately half that of Co-Cr clasps for the same undercut depth.

A preliminary report on patient acceptance of a novel intra-oral lubricating device for the management of radiotherapy-related xerostomia.

Management of radiotherapy-related xerostomia is difficult. Saliva substitutes are helpful but the effects are short-lived. The purpose of the study was to develop a prototype intra-oral lubricating device for the management of radiotherapy-related xerostomia and to evaluate patient acceptance. An intra-oral lubricating device was fabricated that incorporated a reservoir in the palatal vault and permitted slow release of saliva substitute by the patient. Preliminary clinical testing was done in five patients with radiotherapy-related xerostomia. A measure incorporating seven questions was used to explore patient acceptance. The device was simple to fabricate using materials available in a technical laboratory. All patients were able to wear the device for at least 4 h per day throughout the test period. The device was considered easy to use and clean. Some impairment of speech and chewing was noted although this appeared to be related to the bulkiness of the reservoir. General oral comfort was improved due to the lubricating effect. The bulk of the reservoir was reduced as a consequence of patient feedback. The design addressed key problems associated with previous lubricating systems. Patient reports on oral functioning with the device in situ provided pivotal information on the device's utility.

Tympanometry measures in native and non-native Hawaiian children.

BACKGROUND: Ethnicity has been readily accepted as a variable affecting the incidence of otitis media, with certain indigenous groups having an increased risk of middle ear dysfunction. Tympanometry provides objective information on middle ear status, and findings obtained from this procedure have often served as a criterion for medical referral. OBJECTIVE: To extend previous research and to facilitate use of normative tympanometry measures obtained from children with native Hawaiian ancestry. METHODS: Data were collected from 718 ears of 359 children in academic levels ranging from preschool to third grade. Subjects were matched across groups (182 native Hawaiian; 177 non-native Hawaiian) for academic level and gender. Variables included physical ear-canal volume (Vec), tympanometric peak compliance (peak Y, also known as static admittance), tympanometric width (TW), and tympanometric peak pressure (TPP). RESULTS: Significantly higher TW (F1,714=8.82, P=0.008) and TPP (F1,714=9.98, P=0.002) values occurred in ears of native Hawaiian children. Statistical interaction between gender and age was not significant. CONCLUSION: Differences in tympanometric findings between groups suggest differences in middle ear function, and these findings continue to underscore the importance of including tympanometry within a hearing screening protocol for early identification of possible hearing impairment.

Threshold contrast ratio and masking ability of porcelain veneers with high-density alumina cores.

PURPOSE: The purposes of this study were to: (1) investigate the correlation between the color difference of bilayer porcelain veneers over white and black backgrounds (deltaE1) and their opacity (contrast ratios); (2) determine whether there is a recommendable threshold contrast ratio above which the color difference is clinically acceptable (when deltaE < or = 5); and (3) compare the ability of porcelain veneers to mask a color change from white to black backgrounds (deltaE1) and their ability to mask a color change from white to clinically discolored teeth (deltaE2). MATERIALS AND METHODS: Forty-four maxillary anterior teeth of eight patients with severe tetracycline discoloration were prepared for bilayer porcelain veneers in shade A2 porcelain. The cores were 0.25 mm thick. The color (CIE L*a*b*) and reflectance (Y) of the midbuccal region of each veneer were measured over white and black backgrounds using a colorimeter under artificial daylight. The veneers were bonded to discolored teeth, and their color was measured after 1 week. RESULTS: The mean color difference deltaE1 was 10.6 (SD 2.6). The mean contrast ratio was 0.75 (SD 0.1). There was a close and statistically significant correlation between deltaE1 and contrast ratio. The determined threshold contrast ratio was 0.91. The mean color difference deltaE2 was 11.6 (SD 5.5). A paired t test showed no difference between deltaE1 and deltaE2. CONCLUSION: There was a significant correlation between the masking ability of veneers (deltaE1) and their opacity (contrast ratio). There was no significant difference in the ability of the porcelain veneers in masking a color change from white to black backgrounds compared to their ability to mask the color change from white to the discolored teeth.

A double casting technique to minimize distortion when constructing fixed partial dentures on implants.

The casting of extensive implant superstructures that have a good passive fit may be technically demanding. A simple, 2-stage casting technique is presented that avoids common problems associated with the casting of large superstructures. The fabrication of a 7-unit metal-ceramic screw-retained fixed partial denture supported by 5 implants is used to illustrate this technique.

Precision surgical template for implant placement: a new systematic approach.

The importance of a precise surgical template for implant placement cannot be overstated. The radiographic template carries both clinical and radiographic information for the planning of fixture angulation and location. This article describes a systematic approach to the fabrication of a dual-purpose radiographic surgical template. The simple steps result in the accurate transfer of radiographic information to the surgical template with no need for complex equipment or maneuvers. key words: dental implants, implant placement, radiographic template, surgical template

Preliminary guidelines for the evaluation and management of dyslipidemia in adults infected with human immunodeficiency virus and receiving antiretroviral therapy: Recommendations of the Adult AIDS Clinical Trial Group Cardiovascular Disease Focus Group.

Dyslipidemia is a prevalent condition that affects patients infected with human immunodeficiency virus (HIV) who are receiving antiretroviral therapy. These preliminary recommendations summarize the current understanding in this area and propose guidelines for management. Existing guidelines for the management of dyslipidemia in the general population formed the general basis for our recommendations. Data on the prevalence and treatment of dyslipidemia of HIV-infected patients, implications of treatment-related dyslipidemia in other chronically ill populations, and pharmacokinetic profiles for the available hypolipidemic agents in non-HIV populations were considered. Although the implications of dyslipidemia in this population are not fully known, the frequency, type, and magnitude of lipid alterations in HIV-infected people are expected to result in increased cardiovascular morbidity. We propose that these patients undergo evaluation and treatment on the basis of existing guidelines for dyslipidemia, with the caveat that avoidance of interactions with antiretroviral agents is paramount.

HIV RNA quantitation: marker of HIV infection.

Assessment of the status and prognosis of an HIV-infected individual traditionally has been difficult for the clinician. The use of markers of disease progression such as CD4+ has been found to not be a complete indicator of the status of an HIV-infected individual. As a result, determining appropriate therapy for the treatment of this viral infection has been both unpredictable and challenging. Recent development of a laboratory assay has brought a new tool in the management of HIV. The assay is a quantitation of the amount of detectable HIV RNA and estimates the amount of HIV viral load or HIV viral burden present in the blood. Since the development of this assay, HIV RNA quantitation has rapidly become an important surrogate marker of HIV infection. In addition, this quantitation is used to determine the effectiveness of anti-HIV therapies. Understanding the differences and results of quantitative assays is imperative in the management of HIV-infected patients. This article summarizes the events leading to the creation of quantitative assays, explanations and comparisons of the current quantitative assays, and nursing considerations for the implications and uses of viral load markers.

Effect of foscarnet on quantities of cytomegalovirus and human immunodeficiency virus in blood of persons with AIDS.

Four intravenous dosages of foscarnet given for 10 days were compared with no therapy in persons with AIDS who had asymptomatic cytomegalovirus (CMV) viremia. CMV viremia was quantitated by endpoint cell dilution microcultures, pp65 antigenemia assay, and measurement of CMV DNA in peripheral blood leukocytes by a quantitative-competitive PCR. Human immunodeficiency virus type 1 (HIV-1) viremia was quantitated by endpoint cell dilution microculture, serum p24 antigen assay, and PCR for HIV-1 RNA in plasma. Twenty-seven subjects who had received a median of 22 months of nucleoside antiretroviral therapy were enrolled. Twenty-two subjects received foscarnet, which was well tolerated and decreased the CMV burden, as reflected by all three indicator assays. During the 10 days of dosing, the level of CMV viremia, as measured by 50 percent tissue culture infective doses, decreased from 117.5 to 12.7 (P = 0.001), the amount of CMV DNA decreased from 20,328 copies to 622 copies per 150,000 leukocytes (P = 0.02), and the level of CMV pp65 antigenemia decreased from 14.9 to 1.6 positive peripheral blood mononuclear cells per 50,000 leukocytes (P = 0.008). A significant pharmacodynamic relationship was found between the peak foscarnet concentration and a decrease in the level of CMV antigenemia (P < 0.05). Foscarnet had no effect on quantitative HIV-1 microcultures during the 10 days of treatment, but the HIV-1 p24 antigen level in serum decreased significantly, from 454 to 305 pg/ml (P = 0.01). Also, a significant pharmacodynamic relationship was seen between plasma HIV-1 RNA concentrations and both peak foscarnet concentration (P < 0.01) and the area under the foscarnet time-concentration curve (P < 0.05). Reductions in the levels of CMV and HIV-1 viremia correlated quantitatively with systemic exposure to foscarnet, whereas control subjects actually experienced an increase in CMV and HIV-1 burdens. The dual antiviral activity of foscarnet shown in this trial encourages investigation of its use in combination with other antiretroviral therapies for persons with AIDS.

A trial comparing nucleoside monotherapy with combination therapy in HIV-infected adults with CD4 cell counts from 200 to 500 per cubic millimeter. AIDS Clinical Trials Group Study 175 Study Team.

BACKGROUND: This double-blind study evaluated treatment with either a single nucleoside or two nucleosides in adults infected with human immunodeficiency virus type 1 (HIV-1) whose CD4 cell counts were from 200 to 500 per cubic millimeter. METHODS: We randomly assigned 2467 HIV-1--infected patients (43 percent without prior antiretroviral treatment) to one of four daily regimens: 600 mg of zidovudine; 600 mg of zidovudine plus 400 mg of didanosine; 600 mg of zidovudine plus 2.25 mg of zalcitabine; or 400 mg of didanosine. The primary end point was a > or = 50 percent decline in the CD4 cell count, development of the acquired immunodeficiency syndrome (AIDS), or death. RESULTS: Progression to the primary end point was more frequent with zidovudine alone (32 percent) than with zidovudine plus didanosine (18 percent; relative hazard ratio, 0.50; P<0.001), zidovudine plus zalcitabine (20 percent; relative hazard ratio, 0.54; P<0.001), or didanosine alone (22 percent; relative hazard ratio, 0.61; P<0.001). The relative hazard ratios for progression to an AIDS-defining event or death were 0.64 (P=0.005) for zidovudine plus didanosine, as compared with zidovudine alone, 0.77 (P=0.085) for zidovudine plus zalcitabine, and 0.69 (P=0.019) for didanosine alone. The relative hazard ratios for death were 0.55 (P=0.008), 0.71 (P=0.10), and 0.51 (P=0.003), respectively. For zidovudine plus zalcitabine, the benefits were limited to those without previous treatment. CONCLUSIONS: Treatment with zidovudine plus didanosine, zidovudine plus zalcitabine, or didanosine alone slows the progression of HIV disease and is superior to treatment with zidovudine alone. Antiretroviral therapy can improve survival in patients with 200 to 500 CD4 cells per cubic millimeter.

Strategies for control of zidovudine concentrations in serum.

There are several clinical scenarios in which knowledge of zidovudine disposition may be important. This study evaluated the clinical utility of pharmacokinetic parameters for zidovudine derived from sparse serum concentration data obtained in an outpatient setting. Twelve human immunodeficiency virus-infected participants had two serum zidovudine concentrations determinations obtained on two different clinic visits, 2 to 38 days apart. Zidovudine concentrations were measured by radioimmunoassay. A one-compartment oral absorption model was used to describe zidovudine disposition. Three different approaches were used to estimate pharmacokinetic parameters: Bayesian estimation with one or two concentrations and least squares with one concentration. The ability of these parameters to predict concentrations measured during the second clinic visit was assessed by calculation of precision and bias and compared with predictions using standard fixed or weight-adjusted parameters. Estimated pharmacokinetic parameters for zidovudine were consistent with literature values; there was no statistically significant difference among the parameters calculated with the three estimation strategies. Absorptive phase concentrations were poorly predicted by all methods (mean percent bias, 157 to 249%; mean percent precision, 389 to 537%). Predictive ability for concentrations obtained in the elimination phase was strikingly improved: mean percent bias, -17 to 70%; mean percent precision, 40 to 95%. Bayesian and least-squares estimated parameters were statistically better than fixed-parameter values for predicting concentrations in the elimination phase. These observations provide a modeling framework to determine pharmacokinetic disposition of zidovudine in an individual, screen for the existence of a drug interaction, and conduct concentration-controlled clinical trials.

The effect of cimetidine and ranitidine administration with zidovudine.

STUDY OBJECTIVE: To evaluate the possibility of a drug interaction with zidovudine and histamine2-receptor antagonists in individuals infected with the human immunodeficiency virus. DESIGN: Randomized crossover study. SETTING: University-affiliated research center. PATIENTS: Six HIV-infected individuals. INTERVENTIONS: The subjects received 7-day regimens of zidovudine 600 mg/day alone, zidovudine with cimetidine 1200 mg/day, and zidovudine with ranitidine 300 mg/day. MEASUREMENTS AND MAIN RESULTS: The renal clearance of zidovudine when given alone was 0.41 L/kg/hour, and was reduced to 0.18 L/kg/hour (p = 0.002) when given with cimetidine. In the presence of cimetidine the urinary excretion of zidovudine decreased from 89.5 to 53.7 microM (p = 0.01), the urinary ratio of metabolite to parent increased from 5.16 to 9.96 (p = 0.0001), and the fraction of zidovudine converted to metabolite increased from 0.86 to 0.92 (p = 0.0025). CONCLUSION: Cimetidine presumably inhibits the renal clearance of zidovudine by competing for tubular secretion. Based on the observation that neither cimetidine nor ranitidine had a significant effect on serum concentrations of zidovudine or zidovudine glucuronide, a change in the dosage of zidovudine is not warranted.

Essential HIV/AIDS facts. What you need to know in 1992.

The fast pace of HIV/AIDS research and the wide spectrum of issues involved can be intimidating for busy primary care physicians who see HIV-infected patients infrequently. The information covered in this article is intended to form a core that should be a part of all physicians' medical knowledge today.