Effect of a new conditioning agent on dentin

The effect of varying the duration of application of the conditioner for light-cured Zionomer was studied. The conditioner is a solution of oxalic acid and aluminum nitrate in a weak mineral acid and has a pH of 2.06. Recently extracted non-carious human premolars were sectioned horizontally 300 microns below the amelodentinal junction and then lightly ground with a high-speed diamond bur under copious water-spray to produce a smear layer. Each was then sectioned vertically into three and all the specimens were either treated with the Zionomer Conditioner for 5, 10, 20 or 30 seconds, or with distilled water as a control. All the specimens were examined in a scanning electron microscope at x1000 and photomicrographs taken which were then assessed, independently, by the authors. The results revealed that application of Zionomer Conditioner for as little as 5 seconds was sufficient to remove most of the smear layer. There was complete removal of the surface smear layer in specimens treated for 10 seconds or more. Either a 20 second or a 30 second application removed the smear layer completely and could also widen the exposed tubule orifices.     

Dentin exposure in tooth preparations for porcelain veneers: a pilot study

STATEMENT OF PROBLEM: The various clinical techniques available for even reduction of a tooth surface to receive a porcelain veneer restoration do not produce a consistently even conservative reduction. In addition, it is not known which technique is most conservative of enamel. PURPOSE: The purpose of this pilot study was to assess the effectiveness of 3 clinical techniques, namely, dimple, depth groove, and freehand, in producing an intraenamel preparation. The relation between overpreparation beyond the commonly accepted depth of preparation of 0.5 mm and dentin exposure was also examined. MATERIAL AND METHODS: A single operator prepared 3 groups of 5 extracted maxillary central incisors to a depth of 0.5 mm using dimple, depth-groove, and freehand methods of tooth preparation. The prepared teeth were scanned using an x-ray microtomography scanner. The reconstructed images were studied using software that provided a volume-rendering routine so that, by choosing suitable x-ray linear attenuation coefficient thresholds, enamel (2.78 cm(-1) at 40 keV) and dentin (1.63 cm(-1) at 40 keV) surfaces could be viewed. The percentage area of enamel conserved was analyzed from these images. Coordinate metrology was used to produce color-coded images depicting the depth of preparation. The Kruskal-Wallis test was used to determine the statistical significance (alpha=.05) in the difference between the mean percentage area of enamel conserved in the 3 technique groups. The coordinate metrology and x-ray microtomography images were visually compared to study the correlation between overpreparation and dentin exposure. RESULTS: The Kruskal-Wallis test did not demonstrate significant difference (P=.07) between the 3 techniques in conserving enamel. However, the dimple technique showed a greater trend to retaining a larger mean percentage area of enamel (77.5% +/- 14.2) compared to depth-groove (50.1% +/- 17.5) and freehand (76.8% +/- 24.4) techniques. Preparation depth in the range of 0.4 to 0.6 mm was largely seen to be intraenamel, except in the cervical region. CONCLUSION: Within the limitations of this pilot study, the 3 different techniques tested did not differ significantly in conserving enamel.     

Nuclear cataract and myopic shift in refraction

PURPOSE: Nuclear cataract is thought to cause a myopic shift in refraction in older persons. The authors tested this hypothesis by assessing the correlation of nuclear opacity with spherical equivalent refraction (SER) in an older population. DESIGN: Population-based cross-sectional study. METHODS: Three thousand six hundred and fifty-four participants aged 49 years or older were examined in the Blue Mountains Eye Study [BMES] (1992 to 1994). Eye examinations included subjective refraction and lens photographs. Nuclear opacity was assessed against four standard slit-lamp lens photographs using the Wisconsin Cataract Grading System. Nuclear cataract was defined as opacity level 4 or higher. RESULTS: Participants without nuclear cataract had an annual mean hyperopic shift of 0.05 diopters (P < .0001). In persons with nuclear cataract, this hyperopic shift disappeared. A myopic refractive shift occurred only in persons with nuclear opacity levels of 4 or higher. CONCLUSION: This study documents the contribution of nuclear cataract to the mild myopic shift that neutralizes the age-related hyperopic shift occurring in older persons.