Strength in bending was determined for inter. dental fixation apparatuses applied to hemimandibles obtained from 24 canine cadavers. Hemimandibles were osteotomized perpendicular to the long axis between the third and fourth premolars, and segments were stabilized with 1 of 5 interdental fixation apparatuses: Erich arch bar (EAB, n = 6); Stout loop (SL, n = 6); acrylic A, n = 6); Stout loop and acrylic (SLA, n = 24); and Erich arch bar and acrylic (EABA, n = 6). Ultimate strengths (mean +/- SEM) of EAB, SL, A, SLA, and EABA were 395 +/- 48; 523 t 57; 1,106 +/- 102; 1,306 +/- 156; and 2,707 +/- 504 N.m, respectively. Stiffness (mean +/- SEM) of EAB, SL, A, SLA, and EABA were 2,944 t 357; 6,322 +/- 2,201; 16,010 +/- 5,017; 15,777 +/- 1,026; and 27,079 +/- 5,576 N.m/ radian, respectively. Yield strengths (mean +/- SEM) Of EAB, SL, A, SIA, and EABA were 66 +/- 6; 264 +/- 19; 911 +/- 126; 1,114 +/- 159; and 1,855 +/- 401 N.m, respectively. There were no significant differences in acrylic weight, cross-sectional area of the acrylic, or area moment of inertia of acrylic at the osteotomy site among A, SIA, and EABA; and there were no significant differences in osteotomy surface area and area moment of inertia at the osteotomy site among all apparatuses (P > 0.05). The EABA apparatus had significantly higher mean ultimate strength, mean stiffness, and mean yield strength compared to other interdental fixation apparatuses. There were no significant differences in the mean ultimate strength, mean stiffness, or mean yield strength between EAB and SL (P > 0.05). Apparatuses that combine acrylic with metal reinforcement (SLA, EABA) were significantly stronger and stiffer than those that used metal alone (EAB, SL) or acrylic alone (A).

Microscopic examination of the nasal mucosa of clinically normal specific-pathogen-free pigs and of toxicogenic type-D Pasteurella multocida toxin challenge-exposed specific-pathogen-free pigs indicated that the surface epithelium in pigs of both groups was microscopically normal; erosions or appreciable inflammatory changes were not evident. In pigs of both groups and in aU 3 regions of the nasal cavity, the endothelial lining of all blood vessels appeared normal without detectable changes to the walls at postinoculation day 10. Vascular injury in the cartilage or the bone was not discernible in control or challenge-exposed pigs. There were marked differences in the osseous structures of the conchae when the 2 groups were compared. In control pigs, active bone formation and remodeling were observed, and the septal cartilage was normal. In toxin challenge-exposed pigs, there likewise was normal bone formation and remodeling in the vestibular region, and the septal cartilage was normal. In marked contrast, conspicuous changes were observed in the osseous core of the conchae of the respiratory and, sometimes, the olfactory regions. These changes consisted of bone necrosis and resorption by large numbers of osteoclasts with variable replacement by dense mesenchymal stroma, which resulted in conchal atrophy. In the absence of any discernible damage or injury (angiopathy) to the nasal vessels, it appears that the action of the dermonecrotoxin of P multocida serotype D is on the most active osteoblasts and the associated organic matrix of the bone, with subsequent disruption of normal bone formation and remodeling of the nasal conchae.

Microscopic examination of the nasal mucosa of clinically normal specific-pathogen-free pigs and of toxicogenic type-D Pasteurella multocida toxin challenge-exposed specific-pathogen-free pigs indicated that the surface epithelium in pigs of both groups was microscopically normal; erosions or appreciable inflammatory changes were not evident. In pigs of both groups and in aU 3 regions of the nasal cavity, the endothelial lining of all blood vessels appeared normal without detectable changes to the walls at postinoculation day 10. Vascular injury in the cartilage or the bone was not discernible in control or challenge-exposed pigs. There were marked differences in the osseous structures of the conchae when the 2 groups were compared. In control pigs, active bone formation and remodeling were observed, and the septal cartilage was normal. In toxin challenge-exposed pigs, there likewise was normal bone formation and remodeling in the vestibular region, and the septal cartilage was normal. In marked contrast, conspicuous changes were observed in the osseous core of the conchae of the respiratory and, sometimes, the olfactory regions. These changes consisted of bone necrosis and resorption by large numbers of osteoclasts with variable replacement by dense mesenchymal stroma, which resulted in conchal atrophy. In the absence of any discernible damage or injury (angiopathy) to the nasal vessels, it appears that the action of the dermonecrotoxin of P multocida serotype D is on the most active osteoblasts and the associated organic matrix of the bone, with subsequent disruption of normal bone formation and remodeling of the nasal conchae.

Brain stem auditory evoked potential (BAEP) testing with air-conducted click stimuli can be used to diagnose sensorineural deafness in dogs if conductive deafness can be ruled out. Detection of conductive deafness can be performed by recording BAEP elicited by a vibratory stimulus transducer placed against the skull. Air- and bone-conducted BAEP were compared in dogs, varying bone stimulator placement, click polarity, and stimulus intensity. Optimal bone stimulator placement was determined to be over the mastoid process, followed by the mandible and the zygomatic arch. Condensation polarity clicks gave responses preferable to those elicited by rarefaction or alternating polarity. Bone-conducted BAEP peak latencies were significantly longer than air-conducted latencies after correction of the latencies for the air conduction time accompanying air-conducted stimuli. Significant differences between stimulus modalities were not seen for BAEP peak amplitudes or interpeak latencies. Latency-intensity and amplitude-intensity regressions had similar effects for both modalities: latencies decreased and amplitudes increased as stimulus intensity increased.