Abfraction: separating fact from fiction

Non-carious cervical lesions involve loss of hard tissue and, in some instances, restorative material at the cervical third of the crown and subjacent root surface, through processes unrelated to caries. These non-carious processes may include abrasion, corrosion and possibly abfraction, acting alone or in combination. Abfraction is thought to take place when excessive cyclic, non-axial tooth loading leads to cusp flexure and stress concentration in the vulnerable cervical region of teeth. Such stress is then believed to directly or indirectly contribute to the loss of cervical tooth substance. This article critically reviews the literature for and against the concept of abfraction.
Although there is theoretical evidence in support of abfraction, predominantly from finite element analysis studies, caution is advised when interpreting results of these studies because of their limitations. In fact, there is only a small amount of experimental evidence for abfraction. Clinical studies have shown associations between abfraction lesions, bruxism and occlusal factors, such as premature contacts and wear facets, but these investigations do not confirm causal relationships. Importantly, abfraction lesions have not been reported in pre-contemporary populations.
It is important that oral health professionals understand that abfraction is still a theoretical concept, as it is not backed up by appropriate clinical evidence. It is recommended that destructive, irreversible treatments aimed at treating so-called abfraction lesions, such as occlusal adjustment, be avoided.     

High-dose intravenous immunoglobulin modifies complement-mediated in vivo clearance

The mechanism of effect of high-dose intravenous immunoglobulin (IVIG) therapy in immune cytopenias is incompletely known. One of the leading theories ascribes the short-term effects of IVIG to the competition of infused IVIG for Fc receptors, thereby inhibiting IgG-mediated clearance. Using a system independent of IgG-Fc receptor interactions, we examined another potential mechanism of IVIG action. Guinea pigs were infused with a human IVIG preparation at 600 mg/kg/day for two consecutive days. Parallel groups of animals were treated with the same volume and/or concentration of saline and albumin. Clearance of IgM- sensitized guinea pig erythrocytes, which is wholly complement dependent, was significantly retarded in animals treated with high-dose IVIG. The effect was specific for IVIG, since human albumin (as a second foreign protein) failed to change the clearance of IgM- sensitized guinea pig erythrocytes. Experiments in which IVIG-treated animals were subjected to pre- and posttreatment clearance studies revealed heterogeneity among individual animals in respect to their response to IVIG infusions. Decrease of available plasma complement components did not account for the effect, since both C3 and CH50 values remained unchanged after IVIG treatment, despite rising levels of IVIG in sera of treated animals. The results of in vitro C3 uptake studies and the effect of IVIG on clearance of preopsonized cells suggest that IVIG produces a kinetic depression of C3 uptake and modifies the process of complement fragment deposition on erythrocytes. A generalized effect on mononuclear phagocytes is less likely but cannot be wholly ruled out. These studies establish another potential mechanism of IVIG action and suggest extension of its use to other complement-mediated diseases.     

Studies on protamine mRNA in epididymal sperm of adenine-induced infertile rats

Objective: To investigate the protamine and protamine mRNA in the epididymal sperm of normal and infertile rats. Methods: Rats were made infertile by adenine treatment. The total nuclear basic protein (TNBP) of epididymal sperm was extracted and analyzed by gel electrophoresis. The total RNA was isolated and the relative amount of protamne mRNA was determined by means of RT-PCR techniques. Results: The content of protamine in the epididymal sperm was much less in the infertile than that in the normal rats. The same results were obtained with protamine mRNA analysis. Conclusion: The relative amount of protamine mRNA in the sperm could reflect the content of sperm protamine. The results may provide a new approach toward the genetic diagnosis for male infertility.     

Distribution of spermidine and spermine in blood from cystic fibrosis patients and control subjects

Previous studies have shown an abnormality of the spermidine-to- spermine (Spd/Spm) ratio in whole blood of cystic fibrosis homo-and heterozygotes. To investigate Spd and Spm distribution amoung blood components as a possible cause of the abnormality, blood was fractionated using Rabinowitz's glass bead technique and Boyum's Ficoll- Hypaque method. Free (unconjugated) polyamines were extracted with perchloric acid and quantitated on an amino acid analyzer. In controls, mean +/- SEM concentrations in nmoles/10(9) cells of Spd and Spm, respectively, were 1.02 +/- 0.08 and 0.894 +/- 0.28 for erythrocytes; 126 +/- 31 and 357 +/- 105 for lymphocytes; 36 +/- 16 and 240 +/- 33 for granulocytes; and less than 0.5 and less than 0.5 nmoles/ml for plasma. When converted to the concentration in whole blood, it was found that greater than 90% of Spd and over 70% of Spm was associated with erythrocytes. While the higher cellular concentration in leukocytes was not unexpected, the fact that Spd and Spm in whole blood were primarily associated with erythrocytes was a new finding. Comparison with controls revealed that the Spd/Spm ratio in both whole blood and erythrocytes was significantly higher in the group of cystic fibrosis patients.     

Decreased actin content of lymphocytes from patients with chronic lymphocytic leukemia

Actin, a major cytoskeletal protein, was quantitated in normal and chronic lymphocytic leukemia lymphocytes. The actin content of normal human blood lymphocytes was 2.2 +/- 0.4 mg/10(9) cells and represented 6.6% +/- 1.8% of the total cellular protein. A significant decrease (p less than 0.001) was noted in chronic lymphocytic leukemia lymphocytes that contained 1.4 +/- 0.3 mg actin/10(9) cells, constituting 4.3% +/- 1.1% of the total protein. Normal T and B cells did not differ in actin content. Reduced actin levels were found in the T as well as in the B lymphocytes of "B-cell" chronic lymphocytic leukemia. The possible importance of the decreased actin level in the anomalous capping response and motility of chronic lymphocytic leukemia lymphocytes is discussed.     

Increased heat sensitivity of red blood cells in hereditary elliptocytosis with acquired cobalamin (vitamin B12) deficiency

Structural membrane proteins were studied from erythrocytes (RBC) of a patient with a nonhemolytic form of hereditary elliptocytosis (HE) who developed a microcytic anemia with fragmented RBC while cobalamin (B12) deficient. Evidence is presented for qualitative changes in the patient's RBC membranes not related to a loss of structural proteins. Sensitivity of RBC to heat treatment was studied as well as quantitative changes in proteins by densitometry of 1% SDS--10% PAGE gels. Fractions of RBC of various sizes from the patient while B12 deficient all possessed a marked degree of heat sensitivity when compared to RBC from the patient after B12 repletion, normal family members, HE controls, B12-deficient controls, anemic controls, and normal controls. Because loss of spectrin (bands 1 + 2) from heat- sensitive RBC membranes in hereditary pyropoikilocytosis has been reported, the amount of spectrin relative to band 3 was measured. No decrease in the ratio of bands (1 + 2)/3 was found. In addition, no chromatographically abnormal membrane proteins were found by SDS-PAGE of the patient's RBC while B12 deficient. Our findings indicate that B12 deficiency results in an abnormal membrane with enhanced instability in some forms of HE. Since protein loss was not found, we conclude that an alteration in membrane protein interaction may be involved.     

Red cell antibody problems in 1000 liver transplants

Liver transplant patients frequently require large amounts of blood. The frequency and nature of their red cell (RBC) antibody problems were examined. Records were reviewed in 496 adults and 286 children undergoing 1000 consecutive transplants. Twenty-two percent of adults and 14 percent of children had RBC alloantibodies. Antibodies of potential clinical significance were found before transplant in 6.3 percent of adults and 1.0 percent of children; despite immunosuppression, they appeared 1 to 5 weeks after transplant in an additional 7.5 and 5.2 percent respectively. These antibodies probably represented secondary immune responses. Of 58 transplant patients with prior potentially significant antibodies, 8 required 7 to 110 units of antigen-untyped blood after 8 to 28 units of antigen-negative blood; of these patients, one had subsequent hemolysis. Positive direct antiglobulin tests in 24 percent of adults and 10 percent of children were most often thought to be due to nonspecific adsorption of IgG. Anti-recipient ABO antibodies developed in 22 of 60 (37%) evaluable ABO-unmatched grafts; 13 cases had associated hemolysis. In all, 36 percent of adults and 20 percent of children had diverse RBC antibody problems. Resolution of these problems is an important part of the laboratory support necessary for a liver transplantation program.