Equine Odontoclastic Tooth Resorption and Hypercementosis: Histopathologic Features.

Equine odontoclastic tooth resorption and hypercementosis (EOTRH) is a painful progressive condition of older horses that involves multiple teeth, including canines and incisors. EOTRH is uncommonly recognized by veterinary pathologists and in some cases may be misdiagnosed as cementoblastoma. The cause is unknown. The goals of this study were to describe the histopathologic features of EOTRH in 17 affected horses from the United States and to increase awareness of this condition. Samples ranged from affected tooth to the entire rostral mandible and maxilla. Affected teeth exhibited cemental hyperplasia and lysis. The marked proliferation of cementum in severe cases caused bulbous enlargement of the intra-alveolar portions of affected teeth. Several teeth contained necrotic debris, bacteria, and plant material in the regions of cemental lysis. All horses exhibited dentinal lysis in at least affected tooth, and several contained necrotic debris in these regions. Endodontic disease was often present with inflammation, lysis, necrotic debris, fibrosis, and/or a thin rim of atubular mineralized tissue in the pulp cavity. Periodontal disease was a common feature that was primarily characterized by moderate lymphoplasmacytic inflammation. Resorption with secondary hypercementosis appears to begin on the external surface of the teeth rather than within the pulp cavity. Distinguishing EOTRH from other diseases requires a complete history that includes the number and location of affected teeth, a gross description of regional hard/soft tissue health, and radiographic findings.

Change in creep rate and microstructure in an aged, low-copper amalgam.

Low-copper amalgams aged at 37 degrees C, 50 degrees C, 60 degrees C, 70 degrees C, and 80 degrees C for periods of 7 and 30 days were examined using a scanning electron microscope and an x-ray diffractometer. Gamma-one Ag-Hg grain size and gamma 2 Sn-Hg volume fraction, and surface area were determined by quantitative metallography. At 60 degrees C and below, gamma 1 was the predominant matrix phase. Little beta 1 Ag-Hg was found. In this temperature range, both gamma 1 grain size and ADA creep were found to obey an Arrhenius law. A linear relationship was found between the log of the mean ADA creep and the mean gamma 1 grain size. Above 60 degrees C, the gamma 1 phases and the majority of the gamma Ag-Sn particles disappeared. In their place, beta 1 appeared. Gamma-two volume fraction increased during aging at temperatures over 60 degrees C, but a coarsening of gamma 2, reflected in a decrease in gamma 2 surface area per unit volume, also took place. Aging for 30 days or less resulted in decreases in ADA creep. At 60 degrees C and below, the decrease was caused by increases in gamma 1 grain size. Above 60 degrees C, the decrease in ADA creep was caused by several factors, one of which was the appearance of large beta 1 grains.