PubMed Health⌕ Search

Biomedical subjects

M D Rohrer

Publications and source records attributed to M D Rohrer.

At least 19 recordsLinked to original sources
PubMed1995

Interlayer formation and its effect on debonding polycrystalline alumina orthodontic brackets.

During the debonding of ceramic orthodontic brackets, there is a risk of causing fractures, cracks, or flaking of enamel or of the bracket itself. Preliminary work on the resin-enamel interface under bonded brackets with the indirect (modified Thomas) or the thermal-cured indirect bonding techniques revealed an interlayer of unfilled resin formed between the filled resin and the enamel surface. The direct bonding technique, on the other hand, showed no such layer. This study was designed to determine the effect of the interlayer on conventional debonding techniques for polycrystalline ceramic orthodontic brackets. Variables examined were bracket failure or fracture (BF), amount of remnant adhesive (ARI), and enamel damage. Brackets were bonded to 90 fresh bovine teeth. These were divided into three groups of 30 each, based on three methods of bonding, i.e., direct, indirect (modified Thomas), and an indirect technique that used a thermal-cured resin. Each bonding group was further divided into three groups of 10 each, based on the type of debonding technique used, i.e., lift off, delamination, and twisting. Brackets bonded by the indirect (modified Thomas, BF mean = 0.27, ARI mean = 0.93) and the indirect technique that used a thermal-cured resin (BF mean = 0.03, ARI mean = 0.43) resulted in an overall significantly lower failure (p < 0.01) and ARI score on debonding (p < 0.0001) compared with those bonded by the direct technique (BF mean = 1.03, ARI mean = 1.97). Specimens evaluated under the stereomicroscope revealed that the brackets bonded with the indirect techniques debonded at the filled-unfilled resin interface or within the interlayer of unfilled resin.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Oxide↗
PubMed1993

Effects of holmium:YAG laser on equine articular cartilage and subchondral bone adjacent to traumatic lesions: a histopathological assessment.

This study was performed to investigate the effects of holmium:yttrium-aluminum-garnet (Ho:YAG) laser energy on articular cartilage and subchondral bone adjacent to traumatically created cartilage lesions in a continuous weight-bearing model. The 2.1-microns wavelength was delivered efficiently and precisely in hand-controlled contact and near-contact hard tissue arthroscopic surgery in a saline medium. Bilateral arthroscopy was performed on normal antebrachiocarpal and intercarpal joints of four adult horses. One hundred twenty traumatic lesions were created on three weight-bearing articular surfaces with a knife, curet, or motorized burr. Depths of the lesions were partial and full thickness. Configurations of the lesions were lacerations, scrapes, and craters. Left limbs were used as controls. Right limb lesions were treated with various intensities of laser energy: 0.1. 0.16, and 0.2 J. Animals were killed at intervals of 1, 3, and 8 weeks. Gross microscopic anatomy was documented, and tissue sections were subjected to blind review by a pathologist. Mankin grading for cellularity and proteoglycan content was used to qualitatively evaluate cartilage response. Cartilage adjacent to all lesions exposed to laser energy had better cellularity and proteoglycan content (p < 0.05) than did corresponding controls by Mankin grading. Mankin grades for levels of 0.16 and 0.2 J were lower (p < 0.05) than were those of controls or lesions exposed to 0.1 J. There was loss of cellularity and necrosis in subchondral bone at higher energy levels (0.16 and 0.2 J). This study examined the effects of Ho:YAG laser on articular cartilage and subchondral bone in terms of depth of damage and healing response over time in a weight-bearing model. Additional research to define dose-response curves for Ho:YAG laser treatment of cartilage and subchondral bone are indicated.

Animals↗
PubMed1993

Use of bovine-derived hydroxyapatite in the treatment of edentulous ridge defects: a human clinical and histologic case report.

The advent of AIDS has created patients fears regarding human tissue transfers, including bone grafts in dental surgery. In the face of these fears, alternative allograft materials are of increasing interest to clinicians. One such alternative is naturally derived xenogeneic hydroxyapatite (HA). In this study, two patients with edentulous ridge defects received bovine-derived HA grafts in conjunction with a dental implant treatment plan. The results were evaluated histologically. Both patients showed excellent clinical results with histological confirmation of osseous formation. The outcomes suggest that further consideration of the use of bovine-derived HA is merited as a means of remediating edentulous ridge defects.

Aged↗
PubMed1992

The cutting-grinding technique for histologic preparation of undecalcified bone and bone-anchored implants. Improvements in instrumentation and procedures.

An improved technique for histologic sectioning of hard tissues is described. Thin sections (5 to 15 microns) of undecalcified tissues such as bones with ceramic and metallic implants as well as teeth with enamel and fillings can be produced. Implant-tissue and hard tissue-soft tissue interfaces are well preserved. Because of the development of equipment and materials designed specifically for this technique, consistently good results are obtained. Most stains used in the paraffin technique may also be used in these sections.

Animals↗
PubMed1987

A histologic evaluation of a mandibular cross section one year after augmentation with hydroxyapatite particles.

A pathologic mandibular fracture in a 35-year-old woman 1 year after the attempted filling of a bone defect with particulate, dense hydroxyapatite resulted in a partial mandibular resection, allowing observation of cross sections of the mandible and associated soft tissue. Thin tissue sections were examined without decalcification. This permitted excellent observation of the hydroxyapatite particles, the bone, and the soft tissue. Osseointegration had occurred only in the areas closely associated with the bone. The immobility of the particles was a prerequisite for involvement with new bone formation. Hydroxyapatite particles in areas that allowed any mobility were surrounded by connective tissue with no bone formation evident. Heterogeneous particles were observed, indicating the possibility of a lack of purity in the hydroxyapatite ceramic, which may have contributed to the resorption of the particles. These findings, as well as other clinical and experimental findings, lead us to question the concept of hydroxyapatite as a bioactive ceramic that induces osteogenesis or osteoconductivity.

Adult↗
PubMed1986

Microwave sterilization of hydrophilic contact lenses.

We used standard 2,450-MHz microwave irradiation to achieve sterilization of hydrophilic contact lenses contaminated with a variety of bacterial, fungal, and viral corneal pathogens. A three-dimensional rotisserie was used to overcome the problem of "cold spots" within the microwave oven. The contact lenses became dehydrated in approximately two minutes. Rehydration with normal saline restored their shape and appearance. The time necessary to prohibit all growth of the bacterial and fungal organisms studied ranged from 45 seconds to eight minutes. All viral contaminants were completely inactivated after four minutes of microwave exposure. Refractive properties were unaffected after 101 exposures to microwaves for ten minutes. Slit-lamp examination and scanning electron microscopy disclosed minute particles on the surface of these contact lenses but no damage to the lens matrix from irradiation.

Bacteria↗
PubMed1985

Microwave sterilization of nitrous oxide nasal hoods contaminated with virus.

Although there exists a desire to eliminate the possibility of cross-infection from microbial contaminated nitrous oxide nasal hoods, effective and practical methods of sterilization in a dental office are unsatisfactory. Microwaves have been used to sterilize certain contaminated dental instruments without damage. In this study nasal hoods contaminated with rhinovirus, parainfluenza virus, adenovirus, and herpes simplex virus were sterilized in a modified microwave oven. Ninety-five percent of the virus activity was destroyed after 1 minute of exposure of the contaminated nasal hoods to microwaves. By the end of 4 minutes, complete inactivation of all four viruses was found. Repeated exposure of the nasal hoods to microwaves resulted in no damage to their texture and flexibility. Microwave sterilization may potentially provide a simple and practical method of sterilizing nitrous oxide anesthesia equipment in a dental or medical practice.

Adenoviruses, Human↗
PubMed1985

Comparison of meclofenamate sodium with buffered aspirin and placebo in the treatment of postsurgical dental pain.

The efficacy of meclofenamate sodium (Meclomen) at two different doses was compared with that of buffered aspirin and placebo in the control of postsurgical pain in a double-blind, randomized study of 205 patients. Meclofenamate sodium, 200 mg, was significantly better than meclofenamate sodium, 100 mg, in some efficacy parameters. Both doses of meclofenamate sodium were superior to buffered aspirin in most parameters of efficacy, and more effective than placebo in every parameter.

Acetaminophen↗
PubMed1985

Microwave sterilization.

This study has shown that representative fungi, viruses, and aerobic and anaerobic bacteria, including spore formers, can easily be killed in a conventional microwave oven with proper modifications. Metal instruments, including air turbine handpieces and burs, and acrylic dentures can be sterilized in short periods. Consistent sterilization can be accomplished only if the items to be sterilized are rotated in a three-dimensional manner throughout the microwave cavity. Arcing back to the magnetron and damage to the microwave oven are prevented by placing a radar absorbent material within the oven and with proper insulation of the item to be sterilized.

Bacteriological Techniques↗
PubMed1982

Histopathology of mixed anaerobic intraabdominal infection in mice.

This study characterized acute peritonitis and chronic abscess formation resulting from experimental mixed anaerobic infection with Bacteroides melaninogenicus and Fusobacterium necrophorum. At intervals after infection liver and spleen samples were obtained, fixed, and processed for histological examination. An acute to chronic infection progressed in mice infected with this mixture of anaerobic bacteria, whereas, no infection resulted when either organism was injected alone. Acute inflammatory cell infiltrates were noted in tissue samples at 12 h postinfection. Small, discrete areas of liver cell necrosis with neutrophilic infiltrates were observed as early as 24 h. By 48 h after infection the liver parenchyma was infiltrated with both acute and chronic inflammatory cells, with moderate to severe hepatocyte degeneration recognized at 72 h. Large intrahepatic abscesses were present in the subphrenic (upper lobe) area 2 to 6 weeks after experimental infection.

Animals↗
PubMed1982

Congenital epulis (gingival granular cell tumor): ultrastructural evidence of origin from pericytes.

The congenital epulis (gingival granular cell tumor) is a rare lesion of unknown origin found only in newborn infants. Remarkable similarities are noted between this lesion and the adult granular cell tumor (myoblastoma) by both light and electron microscopy. An electron microscopic study of a lesion from the anterior mandibular ridge in a newborn male infant was performed. No Schwann cells, axon fibers, odontogenic elements, or any muscle cells could be found. Cytoplasmic features were similar to those in adult granular cell tumors. Cells which appeared to be in a transitional state, not yet true granular cells, were found juxtaposed to the vessels in the position of pericytes. Fine-structure details of these cells were consistent with pericytes. Cells of this type found farther from the vessels appeared more like the typical granular cells. The cells were filled with structures of the autophagic type devoid of normal cell organelles. These findings support the theory that these are nonneoplastic, degenerative, or reactive lesions arising from a mesenchymal cell, possibly the pericyte.

Cytoplasmic Granules↗