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Biomedical subjects

J Mah

Publications and source records attributed to J Mah.

17 recordsLinked to original sources
PubMed2007

Contact damage in an yttria stabilized zirconia: implications.

This paper presents the results of a combined experimental and computational study of contact damage in a 3 mole% yttria partially stabilized zirconia (3-YSZ) that is relevant to hip implants and dental restorations. Contact-induced loading in real applications is idealized using Hertzian contact model to explain plasticity phenomena and failure mechanisms observed under monotonic and cyclic loading. Under monotonic loading, the elastic moduli increase with increasing loading levels. Under cyclic loading, the ceramic specimens fail with progressive cone cracking. X-ray analyses reveal that stress-induced phase transformation (from tetragonal to monoclinic phases) occurs under cyclic contact loading above the critical load levels (approximately 8.5 kN). Furthermore, when the cyclic loading level (5.0 kN) is less than a critical load levels (7.5 kN) that is required to induce surface cone cracks, significant plastic damage is observed in the subsurface zone underneath the contact area. These suggest that the cyclic contact loading induce both plastic damage and tetragonalto-monoclinic phase transformation in the 3-YSZ, leading to significant degradation in long-term strength. The implications of the results are discussed for the design of zirconia femoral heads in total hip replacements and zirconia crowns in dental restoration.

Biocompatible Materials↗
PubMed2003

Current status and future needs in craniofacial imaging.

Imaging is a keystone in understanding and delivery of craniofacial health care. Recent developments in imaging have brought forth many diverse technologies and approaches. This review provides the current status of methods in craniofacial imaging and discusses future needs and directions. New developments in three-dimensional dental and skeletal imaging, as well as three-dimensional facial image acquisition and animation of jaw movement and facial expression are reviewed. Visualization and convergence of the data from these technologies for construction of patient-specific models is described. Insights on how these technologies and approaches could impact research, education as well as the future of craniofacial health care will be discussed.

Computer Simulation↗
PubMed2003

Three-dimensional visualization of the craniofacial patient: volume segmentation, data integration and animation.

The research goal at the Craniofacial Virtual Reality Laboratory of the School of Dentistry in conjunction with the Integrated Media Systems Center, School of Engineering, University of Southern California, is to develop computer methods to accurately visualize patients in three dimensions using advanced imaging and data acquisition devices such as cone-beam computerized tomography (CT) and mandibular motion capture. Data from these devices were integrated for three-dimensional (3D) patient-specific visualization, modeling and animation. Generic methods are in development that can be used with common CT image format (DICOM), mesh format (STL) and motion data (3D position over time). This paper presents preliminary descriptive studies on: 1) segmentation of the lower and upper jaws with two types of CT data--(a) traditional whole head CT data and (b) the new dental Newtom CT; 2) manual integration of accurate 3D tooth crowns with the segmented lower jaw 3D model; 3) realistic patient-specific 3D animation of the lower jaw.

Cineradiography↗
PubMed2001

Assessment of pacemaker chronotropic response: implementation of the Wilkoff mathematical model.

There are few practical guidelines for proper adjustment of rate responsive pacemaker sensor parameters. This study describes the application of the chronotropic assessment exercise protocol (CAEP) and the Wilkoff model of chronotropic response to assess the adjustment of pacemaker sensor parameters. In 31 patients implanted 1 month previously with a dual sensor pacemaker, pacemaker sensor parameters were adjusted to yield a peak sensor rate of 100 beats/min on a simple 6-minute walk (low intensity treadmill exercise [LITE] protocol); the maximum sensor rate was set to the age predicted maximum heart rate (220-age). The rate response behavior of the pacemaker was then assessed using the slope of metabolic-chronotropic relation (MCR) during CAEP exercise. After adjustments based on the LITE protocol, CAEP exercise yielded MCR slopes of 0.92 +/- 0.25 for the entire study group, which compares well with the predicted normal slope of 1. However, 7 of the 31 patients had sensor MCR slopes during CAEP exercise that were 2 SD or more below expected. To test the sensitivity of this approach to suboptimal pacemaker programming or suboptimal exercise, simulations were performed with the maximum sensor rate programmed below age-predicted maximum heart rate or with exercise truncated before maximum exertion; with these conditions, MCR slopes were sharply lower for the entire group. The authors conclude that a simple treadmill walk (LITE) allowed for optimum programming of sensor parameters in most patients, but in a minority the chronotropic behavior was underresponsive. Failure to appropriately adjust pacemaker maximum sensor rate or failure to achieve peak exercise sharply limits the accuracy of this methodology.

Equipment Design↗
PubMed1999

Evaluation of 3-hour ambulation post cardiac catheterization.

There is much variation in the length of immobilization for patients post cardiac catheterization. While it is generally agreed that a period of time on bedrest is necessary to prevent post procedural complications, the optimal duration remains unknown. The purpose of this study was to evaluate the effects of 3-hour ambulation post cardiac catheterization with a 7 french (F) arterial catheter on bleeding, hematoma formation, and vascular complications. Retrospective chart data were gathered for a period of 8 months for patients who were on the traditional 5-hour ambulation protocol, and prospective data were gathered for a period of 7 months for patients who received the 3-hour protocol. A total of 880 patients were included in the study, with 472 in the 5-hour ambulation group and 408 in the 3-hour ambulation group. The overall incidence of delayed bleeding and hematoma formation for the 15 month study period was 19.1%, with no occurrence of vascular complications in either group. Patients who received the 3-hour ambulation protocol experienced a significantly lower rate of bleeding and hematoma formation (13%) than patients who received the 5-hour ambulation protocol (24.4%) (p < 0.001). Ambulating patients 3 hours post cardiac catheterization with a 7F catheter was found to be safe, and thus has the potential to decrease hospital length of stay, as well as increase patient comfort.

Adolescent↗
PubMed1998

Expression of bone microsomal casein kinase II, bone sialoprotein, and osteopontin during the repair of calvarial defects.

The temporal expression of bone microsomal casein kinase II, osteopontin, bone sialoprotein, alkaline phosphatase, and the accumulation of a solid calcium-inorganic orthophosphate mineral phase, have been charted from day 2 to day 21 during the repair of calvarial defects in rats induced by the implantation of decalcified rat bone matrix. Unlike the sequence of events that occur when the same decalcified bone matrix is implanted subcutaneously or intramuscularly, in which cases the first tissue to form in response to the implant is cartilage that subsequently calcifies and is later resorbed and replaced by bone, the repair of cranial defects is quite different. In the latter case, the first cells induced are undifferentiated mesenchymal cells and early fibroblasts followed by osteoblastic direct bone formation. Somewhat later a few small islands of cartilage are formed, widely separated and spatially distinct from the newly formed bone matrix. All of the cartilage and most of the implanted decalcified bone matrix are later resorbed and replaced by new bone by day 21. This in vivo model of the repair of a bone defect by direct bone formation has provided an excellent system to follow specific biochemical and physicochemical events. The total accumulation and rate of accumulation of the mineral and the two noncollagenous phosphoproteins (bone sialoprotein and osteopontin), as well as the activities of alkaline phosphatase, and for the first time either in vivo or in cell culture, the activity of microsomal casein kinase II, the major enzyme that phosphorylates the bone phosphoproteins, have been determined as a function of healing time in vivo. The overall general pattern of accumulation of the phosphoproteins and calcium-phosphate mineral phase and their relationships are similar to those reported in osteoblast cell cultures also monitored as a function of time.

Alkaline Phosphatase↗
PubMed1996

The catalysis of redox cycling by pyrroloquinoline quinone (PQQ), PQQ derivatives, and isomers and the specificity of inhibitors.

Pyrroloquinoline quinone (PQQ) is a widely distributed redox-active cofactor and essential nutrient. For its detection in protein-free ultrafiltrates or dialysates, a highly sensitive amplification assay was developed on the basis of PQQ's ability to catalyze redox cycling at pH 10 in the presence of excess glycine, oxygen, and nitro blue tetrazolium. Herein, we examine the propensities of PQQ, PQQ triester, and its various isomers, and certain PQQ triester derivatives, to catalyze glycine-fueled redox cycling and show that PQQ is the most capable of catalyzing redox cycling. Furthermore, PQQ has a unique pattern of inhibition induced by a series of PQQ antagonists of different potencies. The data indicate that putative PQQ from a biological sample, separated by HPLC and detected by the glycine-fueled redox-cycling assay, can be further identified as PQQ based on the profile of inhibition it displays with the antagonists such as those employed in this study. The methodology presented here should facilitate the specific detection of PQQ in biological samples.

Animals↗
PubMed1996

Clinicopathologic correlation of DNA flow cytometric content analysis (DFCA), surgical staging, and estrogen/progesterone receptor status in endometrial adenocarcinoma.

DNA flow cytometric content analysis (DFCA) and estrogen (ER) and progesterone (PR) receptor levels are reported to be prognostic with regard to the malignant potential of endometrial adenocarcinoma. We retrospectively reviewed the records of 50 patients presenting with endometrial adenocarcinoma between July 1990 and December 1992, to determine the extent of any pathologic features reported at the time of hysterectomy. Patients whose tumors were nondiploid (aneuploid) by flow cytometry generally presented with a higher pathologic stage, higher grade, and more frequent lymph node involvement. In addition, the majority of clear cell and uterine papillary serous (UPS) adenocarcinoma were also nondiploid. Fourteen of 21 ER-positive tumors aneuploid, as were 18 of 37 PR-positive tumors. We also found DNA-A (DNA content aneuploid) patterns frequently associated with tumor characteristics implicated by other authors as related to aggressiveness. Further studies comparing the molecular biology of tumors to their clinicopathologic features and behavior are needed to fully understand the ultimate malignant potential.

Adenocarcinoma↗
PubMed1995

Longitudinal compliance with annual screening for fecal occult blood. Minnesota Colon Cancer Control Study.

In a randomized, controlled trial of fecal occult blood screening for colorectal cancer, the Minnesota Colon Cancer Control Study carried out 11 annual mail screens in two phases between 1976 and 1992. This long-term compliance record of 15,476 individuals is summarized and related to demographic characteristics as well as to the screening experience of the participants. There was a strong and consistent effect of age, with peak compliance among participants about 70 years old, and lower compliance among the youngest (< or = 55 years) and oldest (> or = 80 years) participants. There was a significantly higher rate of screen compliance among participants who lived with other participants, compared with households where only one individual participated in the study. Finally, participants who underwent a diagnostic colorectal examination with negative results had significantly lower odds of compliance.

Aged↗
PubMed1994

Flow cytometric DNA content analysis of paraffin-embedded tissue derived from cervical carcinoma.

PURPOSE: Flow cytometric deoxyribonucleic acid (DNA) content analysis has been shown to be of prognostic importance in some cancers. There have been recent reports of a prognostic importance for DNA content analysis in cervical carcinoma. METHODS AND MATERIALS: We retrospectively reviewed the hospital and radiation oncology records of cervical carcinoma patients who presented between 1984-1990. RESULTS: A total of 101 archival paraffin-embedded blocks were processed, of which 77 were of technical quality for analysis. Thirty-five percent were found to be DNA content aneuploid (DNA-A) and 65% DNA content diploid (DNA-D). No statistical difference was found between the two groups in age at diagnosis, % S-phase, coefficient of variation (CV), or proliferative index (PI). A statistical difference was noted in the G2M phase between the two groups (p = 0.004). The median % S-phase was 8.4% in the DNA-D group. A statistical difference (p = 0.017) in survival was noted between the low and high % S-phase DNA-D groups. In patients who received radiation alone, high-PI patients had improved survival compared to low-PI patients. No statistical difference in survival was noted in the high % S-phase DNA-D group and DNA-A group (p = 0.28). Proportional Hazard (Cox) Regression found clinical stage the only independent prognostic indicator for survival. CONCLUSION: Flow cytometric DNA content analysis is being used more frequently in the management of different malignant tumors. Our study shows that DNA content analysis is useful in determining the prognosis and survival outcomes in cervical carcinomas and may aid in predicting outcome to certain types of treatment regimens.

Aneuploidy↗
PubMed1993

Characterization of the glycine-dependent redox-cycling activity in animal fluids and tissues using specific inhibitors and activators: evidence for presence of PQQ.

Pyrroloquinoline quinone, a redox cofactor first isolated from bacteria, efficiently catalyzes the nonenzymatic oxidation of glycine in the presence of nitroblue tetrazolium. We report that certain metallic cations and heterocyclic aromatic cations, like the N-methyl phenazonium cation and aryl-iodonium compounds, strongly and specifically inhibit this redoxcycling activity. The inhibition by metal cations is reversed by Tiron and that of the aromatic cations by Tiron and thyroxine. These inhibitors and activators affect authentic PQQ and the redox-activity of putative PQQ isolated from biological sources in a similar manner. This indicates that pyrroloquinoline quinone occurs naturally in animal tissues and fluids.

Animals↗
PubMed1991

The foot in Apert syndrome.

Foot deformity in Apert syndrome is very characteristic and predictable. Progressive synostosis occurs on what is presumably an unsegmented cartilaginous mass. The first ray shortens with medial deviation of the great toe, secondary to growth abnormality and a delta phalanx. The two phalanx digits characteristically go on to fusion, with maintenance of minimal motion at the metatarsal phalangeal joints. The midfoot and hindfoot progress to characteristic fusion in a supinated position. There is prominence of the fifth metatarsal with callosities under the fifth and third metatarsal heads in all patients. Orthotic and surgical management of these conditions is necessary to ensure maximal function in the symptomatic Apert patient.

Acrocephalosyndactylia↗
PubMed1985

The effect of repeated mating at short intervals on reproductive performance of gilts.

Three trials involving 87 gilts were completed to investigate the role of additional sexual stimulation on various reproductive parameters. Forty-five gilts were mated twice at 12-h intervals at second pubertal estrus with intact boars beginning 12 h after detection of sexual receptivity (control group). Forty-two gilts were exposed to a vasectomized boar 15 min following each fertile mating to provide additional copulatory stimulus (treatment group). This additional exposure improved (P less than .01) conception rate (100 vs 84%). No statistical differences were observed in number of corpora lutea (CL), number of viable embryos (VE) or number of total embryos (TE) at d 30. These results suggest that additional mating stimuli may have a beneficial effect on conception rate. While the use of additional males resulted in more pregnant females, it likely did not have an effect on litter size.

Animals↗
PubMed1983

The effect of intrauterine infusions of prostaglandin E2 on luteal function in nonpregnant gilts.

Two trials were conducted to study the effects of intrauterine infusions of prostaglandin E2 (PGE2) on luteal function in nonpregnant gilts. Cannulae were surgically implanted on day 9 postestrus into the lumen of each horn with a cephalic vein cannula inserted for collection of peripheral blood. Intrauterine infusions of 0, 25, 75 or 200 microg of PGE2 were initiated at 0900 h on day 12 and administered thereafter every 12 hr until estrus or day 22 in the first trial. The second trial protocol included an increase in the dose of PGE2 administered as well as the frequency of infusion. Infusion of 0, 200, 300 or 400 microg PGE2 was begun at 0300 h on day 12 and continued every 6 hr until estrus or day 22. Cephalic plasma samples for progesterone analysis were collected every six hours from 0300 h on day 11 to 2100 h on day 26 in both trials. In Trial 1 mean plasma progesterone concentrations for all treatments were not different (P>0.05) from the controls on any given day of the estrous cycle. Interestrous interval was unaffected by intrauterine infusion of PGE2. The mean plasma progesterone concentrations for all treatments were not different (P>0.05) from the controls on days 11-18 of the estrous cycle in Trial 2. However, plasma progesterone concentrations for the 200-microg and 300-microg PGE2 groups appeared to be greater than the controls on days 14 and 15, indicating a possible delay in the decline of progesterone for these groups. The mean plasma progesterone concentrations for the treatment groups were lower (P<0.05) than the controls on days 20-26 of the cycle. treatment cycle length did not differ (P>0.05) from previous cycle length; thus treatment with PGE2 had no effect on interestrous interval. PGE2 may have retarded the decline of progesterone secretion by the corpus luteum in some cases, but at these dosages and frequencies of administration PGE2 was ineffective in prolonging luteal maintenance.

Journal Article↗
PubMedDate not supplied

Intramedullary nailing versus plate fixation for unstable forearm fractures in children.

The purpose of this study was to compare the clinical and radiographic results of plate and screw fixation with intramedullary nailing for unstable fractures of the radius and ulna in children. We proposed that there was a statistically significant difference in the functional outcome and rate of complications between the two groups of patients. A retrospective analysis of 23 patients who were treated with plate-and-screw fixation and 18 who were treated with intramedullary nailing was performed. The average age was 10 years (range, 5-15). Indications for operative treatment included open fractures, irreducible fractures, and unstable fractures. Excellent results were obtained in 78% of patients in both groups at an average of 12 months after surgery. The functional results, rate of union, and rate of complications were statistically similar for the two groups. Intramedullary fixation allows short operative time, excellent cosmesis, minimal soft-tissue dissection, ease of hardware removal, and early motion after nail removal. Intramedullary fixation may provide a useful alternative for treatment of unstable fractures of the radius and ulna.

Adolescent↗