Quintessence International, 10/1999

Objective: Finite-element method was used to explore the stress distribution of incisors restored with porcelain veneers. The design of the incisal palatal finish line was analyzed as a function of incisal overlap and initial tooth substance loss (coronal fractures). Method and materials: The treatment of intact and fractured incisors was investigated using 8 different designs of porcelain veneer. The palatal finish line varied from butt margins to extended chamfers. The stress distribution was assessed in a 2-dimensional finite-element model, reproducing a buccolingual cross section of an incisor. A palatal 50-N horizontal force was applied to the incisal edge to simulate an extreme functional load. The palatal surface tangential stresses were calculated. Results: Considerable differences were detected in the stresses at the level of the incisal-palatal restoration margin. The margins of restorations with limited incisal overlap (butt margin or minichamfer) showed low tensile stresses or even compressive stresses. Restorations with a long chamfer extending into the palatal concavity were subjected to the highest tensile stresses. In the presence of moderate crown fractures (incisal one third) or severe wear, butt margins limited the palatal extension of ceramic, thus reducing the amount of stress at the restoration interface. In the presence of severe crown fractures (incisal two thirds), the margins (either butt or chamfered) were subjected to low tensile forces when located in the smooth convex area of the cingulum. Conclusion: Because of the geometry and natural elastic modulus of mineralized tooth structures, a concentration of tensile stresses is formed at the palatal concavity of teeth restored with porcelain veneers. Long chamfers extending into the palatal concavity are unfavorable because thin extensions of ceramic are generated in an area of maximum tensile stresses. Minichamfers or butt margins are generally recommended, especially in the presence of moderate crown fractures or severe wear.

Objective: Eight amalgam alloys, 6 high-copper and 2 low-copper, were assessed for expansion via photoelastic resin. Method and materials: The photoelastic resin sheet was sectioned into 20 x 25-mm blocks, and two 4 x 8-mm holes were drilled into the resin. The amalgam alloys were hand condensed into the prepared holes. Test conditions for each alloy were (1) uncontaminated, (2) contaminated with 5 µL of Ringer's solution, and (3) contaminated with 5 µL of cell culture medium. Results: Contaminated high-copper amalgam alloys may exhibit expansion to varying degrees but do not show the classic delayed expansion. One spherical, nonzinc high-copper alloy showed no expansion, whether it was uncontaminated or contaminated, and 3 high-copper alloys with different amounts of zinc (0% to 1%) showed slight expansion when contaminated. One low-copper alloy displayed delayed expansion; within 17 days after initial expansion in the photoelastic resin, it had exceeded the greatest stress observed in any contaminated, high-copper zinc-containing alloy at 3 months. Conclusion: Contamination of dental amalgam is to be avoided, but a zinc-containing high-copper amalgam will not exhibit classic delayed expansion even if contaminated.

Linear enamel hypoplasia is a developmental disturbance of enamel resulting in clinically visible horizontal defects in enamel that are present on eruption of the tooth. Nondevelopmental lesions of the hard tissues of the tooth, including carious, abrasion, erosion, attrition, and abfraction lesions, require varying amounts of time after tooth eruption to develop. Because linear enamel hypoplasia lesions are present on eruption and are exposed to the factors responsible for abrasion, erosion, and abfraction, nondevelopmental lesions could occur within them in any combination. This report describes a patient with multiple teeth with linear enamel hypoplasia lesions containing nondevelopmental defects as well as nondevelopmental defects that occurred separately. Severe pain and a unique lesion morphology were associated with the linear enamel hypoplasia defects. Affected teeth were extracted because of advanced periodontitis and were sectioned to determine the nature of the enamel and dentin lesions.

Sjögren's syndrome (SS) is a progressive autoimmune rheumatic disorder. Its precise etiology is unknown, although several contributing factors have been identified. One theory is that the condition results from complications related to infection with the Epstein-Barr virus. Primary exposure to or reactivation of Epstein-Barr virus elicits expression of the human leukocyte antigen complex. This is recognized by T lymphocytes (CD 4+) resulting in the release of cytokines (tumor necrosis factor, interleukin-2, interferon-gamma, and others). A genetic marker specific for Sjögren's syndrome, HLA-DR4, has been identified. According to the World Health Organization, the prevalence of Sjögren's syndrome is unknown. A recent epidemiologic study in Sweden estimated the prevalence in the adult population to be 2.7%. In the United States, 10 years ago, the number of patients with Sjögren's syndrome was thought to be fewer than 100,000. This number today is estimated to be more than 1 million. Sjögren's syndrome has been reported in nearly every major country of the world, and the geographic distribution of cases appears to be relatively uniform. Sjögren's syndrome typically affects women (90%) during the fourth or fifth decade of life. Isolated cases of Sjögren's syndrome in children have been reported.

Objective: The purpose of this study was to examine the effect of salivary flow rate on the levels of antimicrobial salivary proteins in 24 patients with Sjögren's syndrome and 22 age- and race-matched healthy control subjects. Method and materials: Parameters examined included stimulated salivary flow rate, total salivary protein, lactoferrin, lysozyme, amylase, and secretory immunoglobulin A. Results: The mean total salivary protein and the mean salivary amylase were significantly greater in patients than in controls. However, no significant difference was observed in the mean stimulated salivary flow rates or the levels of lactoferrin, lysozyme, or secretory immunoglobulin A of patients and controls. To examine the effect of salivary flow rate on the levels of salivary antimicrobial protein, the levels of these proteins in patients with salivary flow rate of = 0.3 mL/min per gland were compared to those in healthy controls with salivary flow rate = 0.4 mL/min per gland. Analyses showed the levels of lactoferrin to be significantly higher among patients than among controls. Conclusion: The levels of salivary amylase and lactoferrin may be influenced by the levels of salivary output in patients with Sjögren's syndrome. The relationship between salivary flow rate and the levels of amylase and lactoferrin is not clear at the present time.

The endodontic treatment of an atypical maxillary lateral incisor that contained a C-shaped root canal is described. The unusual anatomic configuration of this particular tooth and the advantage of using image magnification to facilitate endodontic treatment are discussed.

Objective: A microleakage study and a scanning electron microscopic investigation were conducted to test whether etching of enamel would improve adhesion of glass-ionomer cement sealants to fissure enamel. Method and materials: Forty-eight extracted human molars and premolars were divided into 2 equal groups, and their crowns were cleaned with pumice. In group 1 enamel was etched for 45 seconds with 37% phosphoric acid. In group 2, enamel was not etched. Glass-ionomer sealant was applied to all 48 teeth. Twenty teeth from each group were thermocycled in water (120 cycles between 0°C and 56°C) and stained with 0.5% methylene blue solution. The remaining 4 teeth from each group served as a control for the scanning electron microscopic evaluation. Twelve teeth from each group were cut into 5 sections, and 12 were cleaved into 3 sections in a buccolingual direction. Results: Statistically significant differences in amounts of microleakage were found between group 1 and group 2. Minimal microleakage was detected in 90% of the etched teeth, whereas extensive microleakage was observed in 85% of nonetched teeth. The scanning electron microscopic evaluation correlated positively with the microleakage observations. The etched teeth revealed a cohesive failure within the sealant material, while the nonetched teeth demonstrated an adhesive failure at the sealant-enamel interface. Observation of the nonthermocycled teeth confirmed those findings. Conclusion: Results suggested that etching prior to application enhances the bonding of glass-ionomer sealant to fissure enamel.