PubMed Health⌕ Search

Biomedical subjects

M D Rohrer

Publications and source records attributed to M D Rohrer.

46 records · Page 3Linked to original sources
PubMedDate not supplied

Fluorosis in a wild cotton rat (Sigmodon hispidus) population inhabiting a petrochemical waste site.

We have developed an in situ mammalian model for evaluating environmental contamination using wild cotton rats. In a series of experiments, 200 male cotton rats were captured during 4 collection periods (spring 1991 = 35; fall 1991 = 60; spring 1992 = 53; fall 1992 = 52). A total of 103 of these cotton rats were captured from control sites, and the remaining 97 were captured from an abandoned oil refinery. All sites were located in the vicinity of Cyril, Oklahoma. There were alterations in the incisors of cotton rats captured from the refinery site. Normal color of cotton rat incisors is deep yellow-orange, which is imparted by a pigment normally produced by ameloblasts. Grossly, the upper incisors of 37 of 97 rats and lower incisors of 54 of 97 rats were affected. The affected incisors were white, chalky, and thin with striations and erosions of the enamel. Microscopic examination revealed that there were dysplastic and necrotic changes in the ameloblasts. The bone fluoride levels were significantly higher in rats captured from the refinery as compared to the rats captured from the control sites.

Animals↗
PubMedDate not supplied

Evaluation of titanium implants placed into simulated extraction sockets: a study in dogs.

The purpose of this study was to evaluate the effect of gap width on bone healing around implants placed into simulated extraction socket defects of varying widths in 10 mongrel dogs. All premolars were removed and the alveolar ridges were reduced to a width of 7 mm. Nine weeks later, a total of 80 implants, 10 mm long by 3.3 mm wide, were placed into osteotomy sites prepared to 3 different diameters in the coronal half, simulating extraction sockets. Three experimental sites, with gap sizes of 0.5 mm, 1.0 mm, and 1.4 mm, were created; the control sites had no gap. The depth of each defect was measured at the time of implant placement. All implants were stable at the time of placement. The dogs were euthanized 12 weeks after implant placement, and blocks containing the implants and adjacent bone were submitted for histologic evaluation. Clinically, all control and test sites healed, with complete bone fill in the defect. Percentages of bone-to-implant contact were measured histologically. As the gap widened, the amount of bone-to-implant contact decreased, and the point of the highest bone-to-implant contact shifted apically. These changes were statistically significant (P < .001). No statistically significant differences in bone-to-implant contact were found between the sites when the apical 4 mm of implants were compared. Within the limits of this study, the simulated extraction socket defects healed clinically, with complete bone fill, regardless of the initial gap size. However, the width of the gap at the time of implant placement had a significant impact on the histologic percentage and the height of bone-to-implant contact.

Analysis of Variance↗
PubMedDate not supplied

Postmortem histologic evaluation of mandibular titanium and maxillary hydroxyapatite-coated implants from 1 patient.

Postmortem examination of human specimens is an extremely important aspect of evaluating the relative compatibility and long-term success of endosseous implant surfaces. The bone-implant interface of 5 commercially pure titanium screw-type mandibular implants after 85 months of service and 2 hydroxyapatite- (HA) coated maxillary implants after 38 months of service were examined. All implants were stable at the time of the patient's death. The mandibular implants had an average of 65% contact with bone and the maxillary implants had an average of 47% contact. The HA coating had separated from the maxillary implants in some areas and was free within surrounding connective tissue or surrounded by invaginating sulcular epithelium. The arrangement and pattern of bone contact appeared different between HA-coated and titanium implant surfaces.

Aged↗
PubMedDate not supplied

Histologic evaluation of hydroxyapatite-coated root-form implant retrieved after 7 years in function: a case report.

This case report presents a clinical, radiographic, and histologic evaluation of 2 non-adjacent, hydroxyapatite-coated, root-form implants retrieved from the maxillary canine area of a patient after 7 years in function. Clinical examination revealed immobile implants with no sign of pathosis. Radiographic examination indicated close proximity of the bone to the implant surface without evidence of radiolucency. Histologically, the 2 implants appeared to be well integrated with the surrounding bone; 84% of the surface of the first implant and 79% of the surface of the second implant had close bone apposition at the interface. There was no evidence of dissolution of the hydroxyapatite coating. The bone appeared to be in immediate contact with the coating. These observations suggest that a particular hydroxyapatite coating on root-form implants can resist degradation during long-term function.

Aged↗
PubMedDate not supplied

Maxillary and mandibular titanium implants 1 year after surgery: histologic examination in a cadaver.

Nondecalcified histologic sections (from a cadaver) of 12 IMTEC implants in four jaw quadrants 1 year after surgery showed significant osseointegration. Microscopically, no apparent difference was observed in new bone growth and osseointegration in those implants placed in the maxilla or mandible, or between titanium plasma-spray-coated (TPS) implants and TPS-treated implants coated with hydroxyapatite. Areas in which implants were placed through the bony floor of the maxillary sinus showed new bone growth above the normal level of the floor of the sinus around the implants and into mechanical retention holes. Small penetrations of the maxillary sinus membrane or the lingual plate of the mandible did not affect the function of the implants, nor did they cause any symptoms. A vertical component of soft tissue around the cervical part of the osseointegrated implants, noted in histologic sections to be as much as 5 mm below the crest of the alveolar bone in at least one area, was not discernible radiographically even when 5-mm-thick sections of bone containing the implants were radiographed.

Aged↗
PubMedDate not supplied

Changes in the rabbit temporomandibular joint associated with posterior displacement of the mandible.

The purpose of this investigation was to study the changes in temporomandibular joint tissues, in particular the disc and its attachments, associated with muscle-powered continuous posterior displacement of the mandible for 33 days. After measurement of incisal relationships, food and water consumption, histologic and morphometric analysis, and radiologic data, it was determined that spatial relationships of joint tissues were altered. Mandibular retrusion leads to alteration in disc morphology and induces anterior positioning of the disc relative to the condylar head. Nutritional intake was disrupted by distal displacement crowns placed on the maxillary incisor teeth.

Analysis of Variance↗
PubMedDate not supplied

Bone formation and reosseointegration in peri-implantitis defects following surgical implantation of rhBMP-2.

This study was designed to evaluate bone formation and reosseointegration following surgical implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in peri-implantitis defects. Hydroxyapatite-coated dental implants were placed bilaterally in the mandibular and maxillary premolar area in four rhesus monkeys and were allowed to osseointegrate for 1 year. Cotton ligatures were then placed around the healing abutments, and plaque was allowed to accumulate for 11 months. Resulting circumferential peri-implantitis defects exhibited a large intrabony and horizontal component. At reconstructive surgery, peri-implantitis defects in contralateral jaw quadrants were randomly assigned to receive rhBMP-2 (0.43 mg/mL implant volume) in an absorbable collagen sponge carrier or a carrier control. The animals were sacrificed 4 months postsurgery, and block sections were prepared for histometric analysis. Summary statistics included means calculated per animal. Paired t tests were used to evaluate differences between experimental conditions (n = 4). Defect depth amounted to 3.4 +/- 0.9 mm and 3.2 +/- 0.9 mm for rhBMP-2 and control defects, respectively. Vertical bone gain in rhBMP-2 defects (2.6 +/- 1.2 mm) was significantly greater than in controls (0.8 +/- 0.8 mm; P < .01). Reosseointegration within the confines of the defect for rhBMP-2 defects (29.0 +/- 10.5%) differed significantly from that in the control (3.5 +/- 2.5%; P < .01). Reosseointegration within the extent of newly formed bone averaged 40.0 +/- 11.0% in rhBMP-2 defects as compared to 8.9 +/- 7.8% in the control (P < .01). Osseointegration in resident bone amounted to 69.5 +/- 6.9% and 72.6 +/- 8.0% for rhBMP-2 and control defects, respectively. There is significant evidence that rhBMP-2 has potential to promote bone formation and reosseointegration in advanced peri-implantitis defects in a demanding nonhuman primate model.

Alveolar Bone Loss↗
PubMedDate not supplied

Effect of allogeneic, freeze-dried, demineralized bone matrix on guided bone regeneration in supra-alveolar peri-implant defects in dogs.

This randomized, split-mouth design study evaluated the adjunctive effect of allogeneic, freeze-dried, demineralized bone matrix on guided bone regeneration in a critical-size, supra-alveolar, peri-implant defect model. Contralateral supra-alveolar peri-implant defects, 5 mm in height, each including two titanium implants, were surgically created in five beagle dogs. Demineralized bone matrix in autologous blood was placed over the implants in one randomly selected mandibular jaw quadrant. A space-making expanded-polytetrafluoroethylene membrane was used to provide guided bone regeneration bilaterally. Following a 16-week healing interval, tissue blocks were harvested and prepared for histometric analysis. Differences between experimental conditions (guided bone regeneration sites with and without demineralized bone) were evaluated using paired t tests (n = 4). Demineralized bone particles were discernible, with limited signs of resorption. The bone matrix particles appeared to be solidified within a dense connective tissue matrix and in close contact with the implants. Limited matrix remineralization was apparent adjacent to the alveolar crest. No statistically significant differences were found between experimental conditions for any parameter examined. Peri-implant defect height averaged 5.0 +/- 0.2 mm and 4.9 +/- 0.4 mm, vertical bone regeneration 1.5 +/- 0.9 mm and 1.1 +/- 0.4 mm, osseointegration within the extent of the defect 10.0 +/- 3.9% and 15.3 +/- 5.3%, osseointegration within the extent of regenerated bone 30.4 +/- 13.7% and 52.1 +/- 17.9%, and osseointegration within the alveolar base 68.8 +/- 13.1% and 74.4 +/- 7.1% for guided bone sites with and without demineralized bone, respectively (P > .05). The results suggest that freeze-dried demineralized bone has no adjunctive effect on guided bone regeneration in supra-alveolar peri-implant defects, that guided bone regeneration has a limited potential to enhance alveolar regeneration in this defect model, and that a 16-week healing interval appears insufficient for turnover and maturation of demineralized bone under provisions for guided bone regeneration.

Alveolar Bone Loss↗
PubMedDate not supplied

Bone formation and osseointegration stimulated by rhBMP-2 following subantral augmentation procedures in nonhuman primates.

The purpose of this study was to evaluate bone formation and osseointegration using titanium dental implants in the subantral space following surgical implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2). In each of four cynomolgus monkeys, one subantral site was treated with rhBMP-2 (0.19 mg per implant) in an absorbable collagen sponge (ACS). The contralateral site was treated with vehicle in ACS (control). Three months later, two screw-type titanium dental implants were placed into each augmented sinus, and one additional implant was placed immediately anterior to the sinus. Thus, each animal had three experimental sites: rhBMP-2, control, and nonsinus. Animals were sacrificed after an additional 3 months, and block sections were harvested and prepared for histometric analysis. Analysis of variance and t tests were used to evaluate differences between experimental conditions. Mean (+/- SD) vertical bone gain was significantly greater in rhBMP-2 than in control sites (6.0 +/- 0.3 versus 2.6 +/- 0.3 mm; P < .002). Bone density in rhBMP-2 sites averaged 14.4 +/- 2.9% versus 13.9 +/- 4.6% and 14.1 +/- 3.6% for control and nonsinus sites, respectively, without significant differences between experimental conditions. Bone-implant contact in rhBMP-2 sites (41.4 +/- 7.7%) was not significantly different from that in control (38.9 +/- 12.4%) and nonsinus sites (46.8 +/- 10.6%). The present study provides evidence for considerable vertical bone gain in the subantral space following surgical implantation of rhBMP-2, thus allowing placement of dental implants. The newly formed bone appears to be of similar quality and to be as suitable for osseointegration as the residual bone in this nonhuman primate model. Thus, surgical implantation of rhBMP-2 appears to have clinical utility and may provide a realistic alternative to autogenous bone grafts for subantral augmentation procedures.

Analysis of Variance↗