The fatigue life of a cobalt-chromium alloy after laser welding

The aim of this study was to investigate the fatigue life of laser welded joints in a commercially available cast cobalt-chromium alloy. Twenty rod shaped specimens (40 mm x 1.5 mm) were cast and sand blasted. Ten specimens were used as controls and the remaining ten were sectioned and repaired using a pulsed Nd: YAG laser welder. All specimens were subjected to fatigue testing (30N - 2Hz) in a controlled environment. A statistically significant difference in median fatigue life was found between as-cast and laser welded specimens (p < 0.001). Consequently, the technique may not be appropriate for repairing cobalt chromium clasps on removable partial dentures. Scanning electron microscopy indicated the presence of cracks, pores and constriction of the outer surface in the welded specimens despite 70% penetration of the weld.     

Gingival squamous cell carcinoma: diagnostic delay or rapid invasion?

BACKGROUND: The similarity between gingival squamous cell carcinoma (GSCC) and more common periodontal lesions may lead to a delay in diagnosis or misdiagnosis. Neoplastic lesions of gingival tissues are frequently diagnosed at an advanced stage. METHODS: To assess the relative time from when patients first become aware of the problem to histopathologic diagnosis (total diagnostic time), 59 consecutive oral cancer cases were examined in this study. The following variables were considered: age, gender, smoking habits, tumor stage at diagnosis, and total diagnostic time. The median of the patients' total diagnostic time (1.5 months) was used as a cutoff point to distinguish between delayed and non-delayed cases. Analysis of the variables was undertaken using the Student t test and chi2 test, with a 95% confidence interval (CI). RESULTS: The total diagnostic time was <1.5 months for 75% of gingival carcinomas, 50% of tongue carcinomas, and 78% of floor-of-the-mouth carcinomas. It was >1.5 months for 25% of gingival carcinomas, 50% of tongue carcinomas, and 21% of floor-of-the-mouth carcinomas. No significant differences in time before diagnosis were found when gingival cancers were compared to other oral tumors (chi2=0.21; 95% CI=-0.40 to 0.26). However, by the time of diagnosis, gingival cancers had invaded adjacent structures more frequently than other oral cancers (chi2=13.51; 95% CI=0.18 to 0.85). CONCLUSIONS: The gingival location of oral squamous cell carcinoma (OSCC) was associated with advanced stages at the time of diagnosis, due to early invasion of contiguous bone tissue (T4-primary tumor). This would indicate that even earlier referral and diagnosis are necessary.     

Improving esthetically objectionable human enamel fluorosis with a simple microabrasion technique

Mild-to-moderately severe enamel fluorosis (EF) is an unsightly maturation-phase dental disorder. Despite extensive epidemiological studies on EF, little is known about individual treatment options. This study was carried out to determine whether a simple microabrasion technique is effective in improving the esthetics of EF . Patients with a variety of severities were treated using a water-cooled fine diamond polishing bur at high speed to remove the surface enamel layers. Photographs of the affected teeth before and after treatment were shown by computer to a panel of three judges (two lay and one experienced), who rated the appearance of the teeth using a newly developed visual analog scale. The severity of EF was rated randomly and blind for 52 individual teeth (26 before and 26 after treatment). Reteated-measures analysis of variance was used to analyze the results. The lay judges rated the appearance of the teeth with EF as significantly more objectionable before treatment. All judges found a significant improvement in the severity of EF after treatment. Using a newly developed visual analog scale, our study indicates that EF of an objectionable nature can be significantly improved with a simple microabrasion technique, thus conserving tooth structure and minimizing the cost of treating EF.     

Ethanol wet-bonding challenges current anti-degradation strategy

The long-term effectiveness of chlorhexidine as a matrix metalloproteinase (MMP) inhibitor may be compromised when water is incompletely removed during dentin bonding. This study challenged this anti-bond degradation strategy by testing the null hypothesis that wet-bonding with water or ethanol has no effect on the effectiveness of chlorhexidine in preventing hybrid layer degradation over an 18-month period. Acid-etched dentin was bonded under pulpal pressure simulation with Scotchbond MP and Single Bond 2, with water wet-bonding or with a hydrophobic adhesive with ethanol wet-bonding, with or without pre-treatment with chlorhexidine diacetate (CHD). Resin-dentin beams were prepared for bond strength and TEM evaluation after 24 hrs and after aging in artificial saliva for 9 and 18 mos. Bonds made to ethanol-saturated dentin did not change over time with preservation of hybrid layer integrity. Bonds made to CHD pre-treated acid-etched dentin with commercial adhesives with water wet-bonding were preserved after 9 mos but not after 18 mos, with severe hybrid layer degradation. The results led to rejection of the null hypothesis and highlight the concept of biomimetic water replacement from the collagen intrafibrillar compartments as the ultimate goal in extending the longevity of resin-dentin bonds.     

Providing support for the pontic of natural tooth adhesive bridges: a clinical report

Resin bonded bridges have become established as a treatment option for replacing missing teeth. Their development can be traced to the work of Rochette who used a macro mechanically bonded metal framework to stabilize mobile teeth. Adaptations of Rochette's concept, using natural teeth as pontics, have been presented. The use of a natural tooth has aesthetic and psychological advantages for the patient. The high failure rate of natural tooth pontics may be explained by a lack of support for the tooth on the metal framework. A clinical report is presented to illustrate a previously unreported technique to improve pontic support.     

A comparison of four epidemiological methods of assessing periodontal disease

An epidemiological study of periodontal disease, using four methods of assessment of severity of periodontal disease, was conducted on a representative sample of 1,976 New Mexicans aged 18 to 44 years. Periodontal disease was assessed using PI and PDI and radiographic and mobility assessments. One objective of the study was to assess whether radiographic scores and measurements of clinical mobility added significantly to the precision of discrimination between the severity of periodontal disease in populations when using the PI and PDI. Findings indicated that the PI discriminated between population groups as efficiently as the PDI plus radiographic and mobility scores. In this study females had less severe periodontal disease than males; Anglos had less severe disease than Spanish-Americans, Mexicans, American-Indians, and Negroes; persons with a greater number of years of schooling and persons in the higher socioeconimic groups had less severe periodontal disease than persons with fewer years of schooling and in the lower socio-economic groups respectively; urban and rural persons had a similar severity.     

Anterior tooth positions in prosthodontics

The problems associated with positioning anterior health teeth in prosthetic treatment procedures are discussed and some recent work reviewed. Useful guides for establishing the artificial anterior dental relationship have been described and an application of these guides has been illustrated.