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Biomedical subjects

P E Larsen

Publications and source records attributed to P E Larsen.

At least 19 recordsLinked to original sources
PubMed2001

Vertical ramus osteotomy allows exposure of the distal internal carotid artery to the base of the skull.

Exposure of the distal internal carotid artery (ICA) above the level of the second cervical vertebra can be difficult and often require maneuvers such as division of the digastric muscle or mandibular subluxation. These techniques increase exposure but may not provide adequate access. We report a series of eight cases in which vertical division of the mandibular ramus provided access of the ICA up to the base of the skull. Over the last 10 years, eight patients underwent vertical ramus osteotomy (VRO) to aid in distal ICA exposure. Preoperative arteriography revealed ICA lesions within 1.5 cm of the skull base. Indications for surgery were compelling and included gunshot wounds to zone III of the neck (n = 2), transient ischemic attack (n = 2), and preocclusive stenosis (n = 4). VRO was performed through a standard vertical neck incision and was created from the depth of the sigmoid notch to the angle of the mandible after elevating the masseter muscle from the bone. Miniature titanium plates were used to reapproximate the mandible after endarterectomy (n = 5), bypass (n = 2), or arterial repair (n = 1). We found that VRO provides reliable exposure of the distal ICA up to the base of the skull. Unlike mandibular subluxation, it requires no pre-incision preparation, thus mandibulotomy can be performed after carotid artery dissection has begun, and may even be avoided. VRO is especially useful when carotid artery pathology unexpectedly extends beyond the usual field of exposure. Work on the carotid artery at the skull base is associated with significant complications and should be reserved for compelling indications.

Adult↗
PubMed2001

Histomorphometric comparison of implant anchorage for two types of dental implants after 3 and 6 months' healing in baboon jaws.

STATEMENT OF PROBLEM: A complete understanding of dental implant prognosis requires better knowledge of the bone anatomy after implant healing. Such baseline data are necessary to compare against load-induced changes in anatomy. PURPOSE: The purpose of this article is to describe and compare measures of implant support (percentage [%] integration and percentage [%] bone area) for various implants in baboon jaws after healing times of 3 and 6 months. MATERIAL AND METHODS: Commercially pure titanium (cpTi) and titanium alloy (Ti-alloy) screw-shaped implants were placed in the posterior jaws of 9 female baboons after 2 months of postextraction healing. Specimens were harvested after 3 months (5 baboons: 8 cpTi, 7 Ti-alloy) and after 6 months (4 baboons: 8 cpTi, 8 Ti-alloy). Each implant provided 6 polished horizontal sections for data collection, which was accomplished from digitized images with the IMAGE analysis system (reliability at 1.6%). Three- and six-month data for each parameter were compared with the use of ANOVA (P<.01). RESULTS: The results revealed a significant increase in the % integration (cpTi 39.1 to 56.2; Ti-alloy 40.0 to 55.2) and the % bone area (cpTi 38.8 to 47.9; Ti-alloy 38.9 to 49.2) from 3 to 6 months for both implants. This significant increase was also true for comparisons by jaw for each implant material (P<.01 for overall and by jaw comparisons). CONCLUSION: A time-dependent increase in jawbone anchorage was measured in this nonhuman primate population, and it was shown that the 6-month maxillary data were comparable to the 3-month mandibular data. These results lend support to the clinical strategy of waiting longer to load implants in the maxilla.

Alloys↗
PubMed1998

Distraction osteogenesis of the mandible with a modified intraoral appliance: a pilot study in miniature pigs.

The purpose of this study was to evaluate an intraoral, nontooth-borne, submucosal distraction appliance in the pig mandible from a clinical, radiographic, and histologic perspective. Intraoral distraction appliances were fabricated, tested for strength, and then adapted and rigidly fixated to the mandibles of three growing miniature Yucatan pigs. A bicortical osteotomy was performed on the right side of the mandible, and a buccal and lingual corticotomy on the left. Two amalgam markers were placed on each side of the osteotomy/corticotomy sites as references. Measurements were taken to evaluate the length and vector of the distraction site, and radiographs were obtained perioperatively. After a latency period of 5 days, distraction was commenced and continued for 13 days at a rate of 1 mm/day. Clinical evidence of distraction was apparent in all cases, with resulting Class III skeletal deformities. Distraction progressed further for the corticotomy sides than the osteotomy sides because of distraction device failure. Radiographic examination revealed increased bone density at the periphery of the distracted callus, with less density apparent centrally. Histologic examination showed fibrous connective tissue in the center of the callus, with cartilage and osteoid formation at the periphery. Bone formation was parallel to the vectors of distraction in all cases. This study confirms that the use of a modified intraoral appliance for distraction osteogenesis is feasible. Use of this device overcomes many of the problems associated with extraoral devices and may have clinical applications.

Animals↗
PubMed1997

Isolation of isoflavones from soy-based fermentations of the erythromycin-producing bacterium Saccharopolyspora erythraea.

A search for an abundant and economical source of isoflavones, particularly genistein, led to the discovery that the erythromycin-producing organism Saccharopolyspora erythraea also produces this promising new cancer-prevention agent. Erythromycin fermentation is a large-scale, soybean-based process used world-wide for the commercial production of this medically important antibiotic. Results from this study indicate that genistin (the glucoside form of genistein), which is added to the fermentation in the soybean media, was converted to genistein through the action of a beta-glucosidase produced by the organism. Genistein was co-extracted with erythromycin from the fermentation broth, then separated from erythromycin during the second step of the purification process for the production of erythromycin.

Chromatography, High Pressure Liquid↗
PubMed1997

Effect of prosthetic superstructure accuracy on the osteointegrated implant bone interface.

OBJECTIVE: This study evaluated the biologic result of forces induced by a misfitting prosthetic superstructure on implants placed in a New Zealand white rabbit tibia model. STUDY DESIGN: Nine rabbits had two dental implants placed in both right and left proximal tibias. After 6 weeks, one animal was sacrificed for baseline integration data, and the remaining animals had fitting or misfitting prosthetic superstructures attached to the implants for 12 weeks. Implants were evaluated clinically, radiographically, and histomorphometrically at the scanning electron microscopic level. RESULTS: No clinical, radiographic, or histomorphometric evidence exists of integration failure with implants subjected to superstructure strain, although bone remodeling is noted. CONCLUSIONS: Given the limitations of sample size, animal model used, duration of prosthetic superstructure attachment, and loading confounders possible, the study of prosthetic framework misfit must be evaluated with another animal model, such as an intraoral primate model, to determine the relationship between clinical performance and histologic findings.

Adaptation, Physiological↗
PubMed1996

The response of bone in primates around unloaded dental implants supporting prostheses with different levels of fit.

Implant failure as a consequence of prosthetic loading following clinical determination of successful stage I healing is poorly understood. A basic premise of accepted prosthetic protocol is passive connection of multiunit prostheses to the implant support. To better understand mechanical factors related to implant failure, this basic passivity premise was experimentally tested prior to study of functional loading research. The purpose of this preliminary study was to measure the bone response around implants placed in the mandible of baboons that supported prostheses exhibiting two levels of fit and not loaded occlusally. Screw-retained prostheses that exhibited a mean linear distortion of 38 microns and 345 microns made up the fit and misfit groups respectively. The results failed to distinguish a difference in bone response between the two levels of prosthetic fit. Although the finding can be argued as a sample size limitation, the data strongly suggest an opposite response than is clinically expected and, consequently, does not warrant the use of additional animals in this initial study. Because the design of this study does not mimic the clinical application of misfitting prostheses (where dynamic functional loads are superimposed with misfit loads), it cannot be inferred that, in clinical application, fit does not alter the osseointegrated interface. Ongoing investigation of failure due to nonpassive connections under dynamic loading conditions of mastication will help clarify the clinical significance of passivity.

Analysis of Variance↗
PubMed1994

Treatment of Class II division 2 malocclusion with combined bilateral sagittal split osteotomy and total subapical osteotomy.

This paper describes a modification of the combined bilateral sagittal split osteotomy and total subapical osteotomy procedure; a representative case treated with this approach is presented. In addition, diagnostic and treatment planning considerations for the comprehensive surgical-orthodontic therapy of individuals presenting with differential sagittal discrepancy between the mandibular corpus and symphysis are discussed, along with limitations of diagnostic criteria commonly used in cephalometric appraisal of the facial soft tissue outline.

Adult↗
PubMed1993

Osteointegration of implants in radiated bone with and without adjunctive hyperbaric oxygen.

A study was undertaken to evaluate the integration of endosseous implants in rabbit tibias that had received a tumoricidal dose of radiation. The effect of hyperbaric oxygen on integration in this compromised situation was also evaluated. Despite clinical and radiographic evidence of success of all implants, there was a significant decrease in amount of histologic bony integration of implants placed in the tibias that had received radiation therapy when compared to contralateral control implants. Adjunctive hyperbaric oxygen therapy significantly improved the amount of histologic integration of implants placed within the radiated tibias evaluated at 10 and 16 weeks after placement. Hyperbaric oxygen was also associated with better soft tissue wound healing in the radiated surgical site. Increased integration time significantly improved the amount of histologic integration in the animals that did not receive hyperbaric oxygen.

Animals↗
PubMed1993

A systematic approach to management of high-flow vascular malformations of the mandible.

High-flow vascular malformations of the mandible are associated with significant morbidity and mortality. As these lesions are rare, the experience that a clinician has with treatment may be limited. To facilitate understanding and treatment of such lesions in a controlled and efficient manner, a treatment protocol is presented that includes careful preoperative planning, embolization, and surgery.

Arteriovenous Malformations↗
PubMed1993

Etiology of implant complications: anecdotal reports vs prospective clinical trials.

The dental profession has in the past overreacted to anecdotal reports of both positive and negative outcomes involving implants. Because implant complications usually involve multiple variables, it is necessary to isolate these variables as much as possible when structuring a study to assess implant success vs failure. The methodology used in a study of Omniloc implants is reported, including detailed criteria for patient exclusion, patient demographics, statistical method, measurement indices, control procedures, and success criteria.

Adolescent↗
PubMed1992

Alveolar osteitis after surgical removal of impacted mandibular third molars. Identification of the patient at risk.

One hundred thirty-eight impacted mandibular third molars were surgically removed. A prospective study of risk factors associated with the development of alveolar osteitis (dry socket) postoperatively was undertaken. Two surgeons, one experienced and one inexperienced, removed the teeth. Patients were controlled for age, sex, use of oral contraceptives, radiographic difficulty of the extraction, and tobacco use. Patients treated by the inexperienced surgeon and those using tobacco had a significantly greater incidence of alveolar osteitis. Previously identified risk factors of increased age, female sex, oral contraceptive use, and increased surgical time were not associated with an increased incidence of dry socket. Recommendations are made regarding prevention of alveolar osteitis in those patients identified as being at high risk.

Adolescent↗
PubMed1991

The effect of a chlorhexidine rinse on the incidence of alveolar osteitis following the surgical removal of impacted mandibular third molars.

A prospective randomized double-blind placebo-controlled study was conducted with 139 patients (278 bilaterally impacted mandibular third molars) to determine the effect of a perioperative 0.12% chlorhexidine gluconate rinse on the incidence of alveolar osteitis following surgical removal of impacted mandibular third molars. A statistically significant 60% reduction in the incidence of alveolar osteitis was obtained in the chlorhexidine group compared with the placebo group. In most subgroups analyzed, chlorhexidine was associated with at least a 50% reduction in alveolar osteitis compared with control groups.

Adolescent↗