Application of neural networks to the prediction of lymph node metastasis in oral cancer

Neural networks are a new type of computing algorithm. They are especially useful in pattern recognition. In this study we applied neural networks to the prediction of lymph node metastasis of patients with oral cancer. A data set of 1,116 lymph nodes verified histopathologically was used to train and evaluate the neural networks. Various three-layer feed-forward networks with a back-propagation algorithm were employed in this study. Performance of the neural networks was compared with that of radiologists and discriminant analysis (Quantification theory type II). Neural networks had a sensitivity of 80.6% and a specificity of 94.6%. Diagnostic accuracy of the neural networks was 93.6%, which was comparable to those of discriminant analysis and clinical radiologists.     

Pulp response in primary teeth with deep residual caries treated with silver fluoride and glass ionomer cement ('atraumatic' technique)

A bstract — Histological assessment of the dental pulps of 55 carious primary teeth was carried out 3 to 56 months after treatment by the 'atraumatic' technique involving application of 40 per cent silver fluoride to residual caries followed by restoration with glass ionomer cement. Fifty of the 55 teeth examined showed a favourable pulpal response, including presence of abundant reparative dentine and a wide odontoblast layer. Histological comparisons were made between these teeth and others not treated with silver fluoride but restored with glass ionomer cement, amalgam or zinc oxide and eugenol.
Possible mechanisms of the action of silver fluoride in arresting residual caries are discussed. The question of whether or not treatment of carious dentine with silver fluoride represents a biologically acceptable clinical procedure cannot be answered on the basis of pulpal histology alone. The very high concentration of fluoride in commercial preparations of silver fluoride raises several questions concerning its clinical safety.     

A Survey of U.S. Prosthodontists and Dental Schools on the Current Materials and Methods for Final Impressions for Complete Denture Prosthodontics

PURPOSE: The purpose of this study was to survey members of The American College of Prosthodontists (ACP) to evaluate current materials and methods for final impressions for complete denture prosthodontics in the United States. In addition, those methods were compared with methods and materials taught in U.S. dental schools via a second survey sent to the chairpersons of prosthodontic/restorative departments. MATERIALS AND METHODS: An anonymous questionnaire was mailed to all 1762 active ACP members in the United States in 2003. A slightly modified questionnaire was also distributed to chairpersons of prosthodontic/restorative departments in the 54 U.S. dental schools. Data analysis was performed via frequency distribution and chi-square statistics. RESULTS: Nine hundred and forty-five questionnaires were returned by members of the ACP (54% return rate) and 42 questionnaires were returned by the U.S. dental schools (78% return rate). The majority of the reporting prosthodontists (88%) and dental schools (98%) use a border-molded custom tray for final impressions for complete denture prosthodontics. The most popular material for border molding was plastic modeling compound (67% of reporting ACP members, and 95% of the responding dental schools). Variability of the materials used for final impressions was observed, with the most popular materials being polyvinylsiloxane for the ACP members (36%) and polysulfide for the dental schools (64%). Statistically significant differences were found in the materials used for border molding by prosthodontists based on the time elapsed since completion of prosthodontic training. No differences were found in the materials used for impression of edentulous arches based on years of experience. Geographic location did not influence the materials and methods used by prosthodontists for complete denture final impressions. CONCLUSIONS: There was variability of the materials and techniques used for final impressions by ACP members and dental schools; however, overall there was an agreement on the materials and techniques used by prosthodontists and dental schools. Distinct trends for increasing use of polyvinylsiloxane and polyether for border molding procedures and impressions of edentulous arches were observed both in members of the ACP and in the U.S. dental schools.     

University of North Carolina Caries Risk Assessment Study. III. Multiple Factors in Caries Prevalence

The baseline caries experienced of approximately 5,000 children in South Carolina and Maine was used as the dependent variable in caries risk assessment analyses. Clinical, microbiologic, and demographic factors served as independent variables in a multivariate relationship to caries through regression and discriminant function analyses. Four factors--number of dental visits by the child in the past year, presence of white spot lesions, and both the urgency of need for restorative care and the future caries increment predicted by the examiner--associated significantly and consistently with caries prevalence in primary and permanent teeth of first and fifth graders at both study sites. Several factors associated significantly with caries prevalence at only one site or grade within a site, suggesting that wide applicability of a specific caries risk assessment model may be limited. In these analyses, sensitivity ranged from .60 to .72 and specificity varied from .86 to .91 in the four grade-site groups. The ultimate goal of this longitudinal study is to identify highly caries-prone children in time to prevent the occurrence of a future caries increment. Although the lack of consistent association of many variables, including microbiologic factors, with baseline caries prevalence was unexpected, it is expected that some of these variables will contribute predictive power in the prospective study.     

Effect of Heat Treatment on Joint Properties of Laser-Welded Ag-Au-Cu-Pd and Co-Cr Alloys

PURPOSE: This study investigated the effect of heat treatment on the strengths of laser-welded cast Ag-Au-Cu-Pd and Co-Cr alloys. MATERIALS AND METHODS: Cast plates of Ag-Au-Cu-Pd (Ag) and Co-Cr (Co) alloys were prepared. After polishing the surfaces to be welded, the plates were matched and butted Ag to Ag (Ag/Ag), Co to Co (Co/Co), and Ag to Co (Ag/Co) and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each experimental condition by bilaterally welding them with five spots. The Ag/Ag, Ag/Co, and control Ag underwent two heat treatments-softening (ST) and hardening (AH). A group of as-cast specimens serving as controls was not given either heat treatment. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min. RESULTS: The fracture resistance of Co/Co was similar to that of the control Co, while the fracture resistance of Co/Ag was significantly lower than that of both like alloy pairings for all heat-treating conditions. The control Ag had greater fracture resistance after AH and lower fracture resistance after ST. The AH treatment increased the fracture resistance, and the ST treatment decreased the fracture resistance of both Ag/Ag and Co/Ag, although not significantly. The percentage of elongation appeared to positively correlate with the fracture resistance results. CONCLUSIONS: The results obtained in this study indicated that the age-hardening heat treatment increased the weld strength between the paired Au-Ag-Cu-Pd alloys and between the Au-Ag-Cu-Pd and Co-Cr alloys.     

Thermal cycling distortion of porcelain fused to metal fixed partial dentures

Statement of problem. The initial fit of porcelain fused to metal restorations deteriorates during the firing cycle of porcelain. Purpose. This study evaluated thermal cycling distortion of 3-unit porcelain fused to metal frameworks at different firing stages. Material and methods. A master model was designed to represent the 2 abutments of a 3-unit fixed partial denture replacing a missing mandibular molar. Standard techniques were used to fabricate 10 castings. Half of the copings were cast in a Ni-Cr alloy and the other half in a Pd-Cu alloy. Framework distortion was measured by means of inner fit changes, horizontal linear measurements of the framework length, and vertical fit changes of each retainer. Measurements were made (1) initially, (2) after degassing firing, and (3) after glaze firing. Differences between the firing cycles created distortion values of the retainers in 3 dimensions. Repeated measures ANOVA was used to analyze data statistically. Results. Measured differences between the 2 firing stages ranged from –47 to 81.7 μm. For both alloy groups, retainers showed increase in vertical gap that implied poorer vertical fit after porcelain application. Mean values of inner fit change recorded for porcelain application firing were higher in magnitude than the values of metal-conditioning firing. In addition, no statistically significant differences were found among alloy types. Conclusions. A 3-dimensional distortion was observed both in Pd-Cu and Ni-Cr frameworks during porcelain firing cycle. The distortion seen after porcelain application firing was significantly greater than that seen after metal-conditioning firing. This result can be attributed to these factors, contamination of porcelain to the inner surface of metal coping and reduction in resilience of metal. (J Prosthet Dent 1998;80:654-60.)