Pits and fissures: etch resistance in prismless enamel walls

The document attached has been archived with permission from the Australian Dental Association. An external link to the publisher’s copy is included.Background: In a previous study to examine the nature of etching on the walls of fissures, there was a consistent result of resistance to deep etching on parts of the walls and a zone of lesser etching on part of the walls as evidenced by the uptake of stain. The staining had been used to examine the nature of the etch pattern. The aims of this study were to define the nature of this etch resistant area. Methods: A sample of 55 teeth, both molars and premolars, were divided into three groups. In the first group the wetting of fissures by the etchant was examined; the second group tested for the effects of pellicle-cuticle-debris or air entrapment on the etching process. The final group looked at alternative mechanical treatments of the fissure prior to etching. Results: The specimens split along the fissures showed clearly that the etch resistant zone was not due to lack of contact with the etchant or the presence of a pellicle-cuticle-debris covering, but to the presence of a prismless enamel structure. This study showed that this zone inhibited tag development on the fissure walls. Conclusions: The mechanical removal of this prismless layer of enamel within the fissure system should result in an improved bonding of a fissure sealant through better tag development, in turn leading to a reduction in the failure rate of a sealant used to prevent caries.MF Burrow, JF Burrow and OF Makinso

Pits and fissures: remnant organic debris after acid-etching.

The purpose of this study was to compare the ability of liquid and gel etches to remove remaining debris in occlusal pits and fissures in vitro after cleansing using a conventional technique or air-water slurry method. A suitable stain differentiated between etched enamel, unetched enamel, and pellicle or debris. The results statistically indicate that etching does not remove much of the organic debris, and there was no difference between a liquid or gel etchant. Agitation of the etchant did not aid pellicle removal.link_to_subscribed_fulltex

Color change in light-cured resins exposed to daylight.

The clinical yellowing of anterior composite resin restorations with time is often the cause for their replacement. This work examined in vitro the effect of sunlight and water separately and together on color changes in the lighter shades of 16 resins. The natural radiation (ultraviolet and visible) was greater than would be expected in clinical use, and the color changes were generally only slight for most resins, as judged by standardized photographic recording and visual inspection of transparencies over time. The changes were greater when sunlight and water were combined. The light-cured surface was less affected than the distal surface. The hydrolysis action by water was particularly marked for one resin, which also showed a high release of camphoroquinone-type catalyst. Marked clinical discoloration may be as much or more affected by absorption of food colorants than by sunlight and water.link_to_subscribed_fulltex

Pits and fissures: Relative space contribution in fissures from sealants, prophylaxis pastes and organic remnants

Background: Previous studies by the authors have looked at the nature of the fissure system of human permanent molars and premolars, and has provided evidence for the presence of a prismless layer of enamel. It was noted during these studies that the fissure spaces were often occupied by material other than the fissure sealant. The aim of this study was to define these materials and to look at the percentage contribution of each to the sealed fissure space. Methods: A sample of teeth, both molars and premolars, were sealed with an unfilled fissure sealant after prophylaxis with a coloured prophylaxis paste. In one group, the crown of the tooth was removed by dissolution in hydrochloric acid following placement of the sealant. This revealed a negative image of the fissure system and its contents. The second group of teeth was sectioned following sealing, and the contents of the fissure space were analyzed. Results: The negative image of the fissure system displayed the fissure contents by colour and the sectioned teeth were able to be computer analyzed to establish the relative contribution of sealant, prophylaxis paste and organic material to the fissure space. Conclusions: Sealant contribution was in the range of 14-96 per cent, prophylaxis paste from 0-50 per cent and organic remnants 0-55 per cent. The presence of these last two components could contribute to sealant loss.link_to_subscribed_fulltex

Pits and fissures: morphology.

The morphology of fissures occlusally was examined by splitting teeth along fissures; this split occurred from the base of the fissure and was checked by serial sectioning. The conclusion is that fissures tend to be an association of adjacent pits. Staining of teeth for fissure shape determination indicates a high presence of organic material in fissures and pits with stained pellicle between pits. The pellicle is often very evident on the lower inclines of cusps, in the region where retention is sought for sealants. In a second phase, an examination of a large number of extracted molars showed that the occlusal fissure extension buccally in lower molars and lingually in upper molars was nearly always interrupted by an enamel col between adjacent cusps. Grooves occlusally or axially adjacent to fissures are often surfaced with stained pellicle. This may be mistaken on visual examination without magnification as extensions of fissures.link_to_subscribed_fulltex

Pits and fissures: Etch resistance in prismless enamel walls

Background: In a previous study to examine the nature of etching on the walls of fissures, there was a consistent result of resistance to deep etching on parts of the walls and a zone of lesser etching on part of the walls as evidenced by the uptake of stain. The staining had been used to examine the nature of the etch pattern. The aims of this study were to define the nature of this etch resistant area. Methods: A sample of 55 teeth, both molars and premolars, were divided into three groups. In the first group the wetting of fissures by the etchant was examined; the second group tested for the effects of pellicle-cuticle-debris or air entrapment on the etching process. The final group looked at alternative mechanical treatments of the fissure prior to etching. Results: The specimens split along the fissures showed clearly that the etch resistant zone was not due to lack of contact with the etchant or the presence of a pellicle-cuticle-debris covering, but to the presence of a prismless enamel structure. This study showed that this zone inhibited tag development on the fissure walls. Conclusions: The mechanical removal of this prismless layer of enamel within the fissure system should result in an improved bonding of a fissure sealant through better tag development, in turn leading to a reduction in the failure rate of a sealant used to prevent caries.link_to_subscribed_fulltex

ONE-YEAR EVALUATION OF THREE SMOKING CESSATION INTERVENTIONS ADMINISTERED BY GENERAL PRACTITIONERS

Three smoking cessation interventions designed for use by general practitioners(GPs) within the routine consultation were evaluated in a field setting using 26 GPs throughout metropolitan Sydney. A total of 450 smoking patients were allocated to either Structured Behavioral Change with nicotine gum (Grouo SBCN). Structured Behavioral Change without nicotine gum (Group SBC), or GPadvice with nicotine gum (Group AN). Although significant differences in the percentage of abstainers were observed between Groups SBCN and SBC three weeks after treatment (39% vs. 26%), the point prevalence abstinence rate for patients at 12 months declined to 19, 18, and 12% for Groups SBCN, SBC, and AN, respectively. Continuous abstinence to the end of the 12-month period was 9% for Groups SBCN and SBC, and 6% for Group AN. Forty-eight percent of the 450 patients made an attempt to stop smoking, and 89% reduced their cigarette consumption at some point during the study. Examination of 132 selfselecting patients who fully participated in the three interventions and attended all scheduled visits, revealed significantly larger proportions of abstainers within Groups SBCN (34%) and SBC (33%) than in Group AN (15%) at the 12-month follow-up

Anthropogenic fragmentation may not alter pre-existing patterns of genetic diversity and differentiation in perennial shrubs

Many plant species have pollination and seed dispersal systems and evolutionary histories that have produced strong genetic structuring. These genetic patterns may be consistent with expectations following recent anthropogenic fragmentation, making it difficult to detect fragmentation effects if no prefragmentation genetic data are available. We used microsatellite markers to investigate whether severe habitat fragmentation may have affected the structure and diversity of populations of the endangered Australian bird-pollinated shrub Grevillea caleyi R.Br., by comparing current patterns of genetic structure and diversity with those of the closely related G. longifolia R.Br. that has a similar life history but has not experienced anthropogenic fragmentation. Grevillea caleyi and G. longifolia showed similar and substantial population subdivision at all spatial levels (global F\u27 ST = 0.615 and 0.454; S p = 0.039 and 0.066), marked isolation by distance and large heterozygous deficiencies. These characteristics suggest long-term effects of inbreeding in self-compatible species that have poor seed dispersal, limited connectivity via pollen flow and undergo population bottlenecks because of periodic fires. Highly structured allele size distributions, most notably in G. caleyi, imply historical processes of drift and mutation were important in isolated subpopulations. Genetic diversity did not vary with population size but was lower in more isolated populations for both species. Through this comparison, we reject the hypothesis that anthropogenic fragmentation has impacted substantially on the genetic composition or structure of G. caleyi populations. Our results suggest that highly self-compatible species with limited dispersal may be relatively resilient to the genetic changes predicted to follow habitat fragmentation