The effect of bleaching, varying the shade or thickness of composite veneers on final colour: an in vitro study.

OBJECTIVE: To investigate whether bleaching prior to placement of a composite veneer had an effect on the final shade of the restoration and whether this was affected by the thickness or shade of the veneer. METHODS: Twenty bovine teeth were collected, sectioned and divided into two groups. One group was the non-bleached control, while the other was the bleached group. A colour reading was recorded using a spectrophotometer. The bleached group then underwent external bleaching with 38% hydrogen peroxide and a colour reading was recorded. Each of these two groups were further sub-divided into four subgroups, on which composite veneers were placed. These subgroups were: 0.5 m thick A1, 1 m thick A1, 0.5 mm thick A4 and 1 mm thick A4 composite veneers. Colour readings were recorded after veneer placement. Statistical significance was assessed using analysis of variance. RESULTS: There was a difference between the colour produced for the same veneer properties, between the bleached and non-bleached groups. For a thin (0.5mm) A4 veneer bleaching produced a statistically significant difference in the amount of colour change (DeltaE) compared to veneering alone. For A1, non-bleached group there is a significant difference in the DeltaE produced by altering the thickness of the veneer. CONCLUSION: Within the limitations of this study, we can conclude that bleaching prior to placement of a thin A4 dark veneer produces a significant difference in colour change. If no bleaching is performed, altering the thickness of an A1 veneer produces a significant colour difference DeltaE. However, if bleaching is carried out there is no significant difference.

Circadian distribution of in-hospital cardiopulmonary arrests on the general medical ward.

BACKGROUND: A circadian pattern has been convincingly demonstrated for the onset of many outpatient ischemic vascular events. A morning peak exists for the onset of acute myocardial infarction, sudden cardiac death, reversible myocardial ischemia, and ischemic stroke. Data regarding circadian patterns of disease in hospitalized patients, however, are lacking. We examined in-hospital cardiopulmonary arrest (CPA) occurring on the general medical ward to determine if a circadian distribution existed in time of onset. METHODS: All CPAs that occurred during a 9-month period and met entry criteria were included for study. The day was divided into 4-hour intervals and analyses were performed for evidence of periodicity in time of onset. The CPAs were then divided into those that were "expected" and those that were "unexpected," and further analyses of periodicity were performed. RESULTS: For the total study population (137 patients), a primary peak frequency of CPA occurred during the interval from 4 to 7:59 AM, and a secondary peak frequency occurred during the 8 to 11:59 PM interval. A minimum frequency occurred during the midnight to 3:59 AM interval. The onset of unexpected CPA peaked during the 4 to 7:59 AM interval, and expected CPA followed no circadian pattern. CONCLUSIONS: Our analysis of CPA occurring in patients hospitalized on the general medical ward demonstrated a circadian pattern of onset that favored the early-morning hours. This pattern is predominantly due to unexpected CPA. If further study confirms our observations, changes in the prophylaxis of in-hospital CPA and adjustments in staff responses to its occurrence may be indicated.