Application of survival analysis to carious lesion transitions in intervention trials

OBJECTIVE

To demonstrate the usefulness of a survival-time regression model for the analysis of data from two 3-year trials of the caries-preventive effect of sugar-substituted chewing gums and fluoride toothpaste, carried out among 892 Lithuanian children.

METHODS

A caries onset was defined as a transition from sound to carious and a caries recovery was defined as a transition from carious to sound. The time at risk for each type of transition was calculated. Using an exponential survival-time regression model, the hazard ratios for the covariates experimental group (control, sugar substitute, fluoride), age, gender, surface type and posteruptive surface age was estimated. This analysis was repeated using two alternative definitions of the caries transitions.

RESULTS

The analyses confirmed that caries rates are higher in occlusal surfaces, and that posteruptive surface age influences caries rates. Moreover, it also confirmed that fluoride affects the outcome of ongoing caries activity more than the initiation of caries.

CONCLUSIONS

Survival-time analysis of caries transitions allows for the extraction of much more information from caries trials than does the traditional DMF-based analysis, and traditional DMF incremental values may easily be derived from the models.

Tooth-surface progression and reversal changes in fluoridated and no-longer-fluoridated communities over a 3-year period

OBJECTIVE

To compare permanent tooth surface-specific progression/reversal changes between fluoridation-ended (F-E) and still-fluoridated (S-F) communities in British Columbia, Canada, over a 3-year period.

METHODS

D1D2MFS examinations were contrasted for 2,964 schoolchildren in 1993/94 (grades 2, 3, 8 and 9) and 1996/97 (grades 5, 6, 11 and 12). Generalized Estimating Equation (GEE) models explored the relation between progression/reversal changes and fluoridation status, age, gender, socioeconomic status, and dietary/fluoride histories.

RESULTS

Within a scenario of low levels of caries overall, few children had multiple surfaces progressing. At least one smooth surface progressed in 31.4% of subjects; at least one pit-and-fissure (PF) surface progressed in 43.1% of subjects. At least one smooth surface reverted in 89% of subjects who had reversible stages; at least one PF surface reverted in 23.8% of subjects who had reversible stages. GEE (smooth) indicated that odds ratios of progression were twice as large in the F-E site compared to the S-F site, and slightly increased in older participants and in participants exposed to more fluoride technologies. GEE (PF) also indicated that progression was slightly more common in the F-E site; more frequent snacking and lower parental educational attainment had modest associations with increased progression in PF surfaces. For the two types of surfaces, GEE models demonstrated that unerupted surfaces were less likely to progress than sound surfaces. No associations were found between reversals and independent variables.

CONCLUSION

Progressions were found to be weakly linked to socio-demographic factors; baseline surface statuses were better predictors of progression. Using the current definitions for disease transitions, F-E communities had more frequent progressions than a S-F community.

Reversal of primary root caries using dentifrices containing 5,000 and 1,100 ppm fluoride

This study compared the ability of two sodium fluoride dentifrices, one containing 5,000 ppm fluoride (Prevident 5000 Plus) and the other 1,100 ppm fluoride (Winterfresh Gel), to reverse primary root caries lesions (PRCLs). A total of 201 subjects with at least one PRCL each entered the study and were randomly allocated to use one of the dentifrices. After 6 months, 186 subjects were included in statistical analyses. At baseline and after 3 and 6 months, the lesions were clinically assessed and their electrical resistance measured using an electrical caries monitor. After 3 months, 39 (38.2%) of the 102 subjects in the 5,000 ppm F- group and 9 (10.7%) of 84 subjects using the 1,100 ppm F- dentifrice, had one or more PRCLs which had hardened (p = 0.005). Between baseline and 3 months, the log10 mean +/- SD resistance values of lesions for subjects in the 1,100 ppm F- group had decreased by 0.06+/-0.55, whereas those in the 5,000 ppm F- group had increased by 0.40+/-0.64 (p<0.001). After 6 months, 58 (56.9%) of the subjects in the 5,000 ppm F- group and 24 (28.6%) in the 1,100 ppm F- group had one or more PRCLs that had become hard (p = 0.002). Between baseline and 6 months, the log10 mean +/- SD resistance values of lesions for subjects in the 1,100 ppm F- group decreased by 0.004+/-0.70, whereas in the 5,000 ppm F- group, they increased by 0.56+/-0.76 (p<0.001). After 3 and 6 months, the distance from the apical border of the root caries lesions to the gingival margin increased significantly in the 5,000 ppm F- group when compared with the 1,100 ppm F- group. The plaque index in the 5,000 ppm F- group was also significantly reduced when compared with the 1,100 ppm F- group. The colour of the lesions remained unchanged. It was concluded that the dentifrice containing 5,000 ppm F- was significantly better at remineralising PRCLs than the one containing 1,100 ppm F-.

The remineralization of EDTA-treated human dentine

The remineralization of whole human dentine treated with a neutral EDTA solution was investigated: the treatment periods were 15, 30 and 120 min. From the literature it is known that EDTA removes noncollagenous proteins (NCPs) from dentine powders. In order to extract more phosphoproteins from dentine lesions, in part of this work samples were also treated with 1 M NaCl or 4 M guanidine chloride solutions. All the dentine samples after the treatments mentioned were immersed subsequently in a remineralizing solution without fluoride for 2 weeks and microradiographed. To investigate the effects of fluoride, samples treated with EDTA for 120 min were also remineralized with 2 ppm fluoride in solution. The results presented show that: (1) Measurable remineralization did not occur when fluoride was free in the remineralizing solution. Because remineralization occurred neither at the lesion front nor in the nonmineral part of the surface-softened tissue, presumably the NCPs (inhibitors) of underlying dentine diffused into the tissue during the remineralization period. (2) 2 ppm fluoride caused remineralization at the lesion front. In this case we assume fluoride either acted as nucleating agent or overcame the NCP effects at the lesion front.

Caries inhibiting and remineralizing effect of xylitol in vitro

This study aimed to determine the effect of xylitol on the development and remineralization of caries in vitro, and to compare this effect with that of fluoride alone and in combination. Two experiments were devised. In experiment 1, bovine incisors were each sectioned into 4 portions which were randomly assigned to 4 demineralizing agents: A) acidic buffer (x), B) x + 0.5 ppm fluoride, C) x + 20% xylitol, and D) x + 20% xylitol + 0.5 ppm fluoride. Caries-like lesions were produced in specimens. In experiment 2, carious lesions were produced in teeth. Five lesion-bearing slabs were cut from each tooth. While one was reserved as control (UN), others were randomly assigned to 4 remineralizing agents: 1) artificial saliva (y), 2) y + 0.05 ppm fluoride, (3) y + 20% xylitol, and 4) y + 20% xylitol + 0.05 ppm fluoride. Mineral loss (delta Z) and lesion depth (ld) were quantified after 4-week remineralization. In experiment 1, numerical values of delta Z and ld observed can be ranked as A > C > B > D. These differences were significant only in B and D when compared with A for delta Z, but not between any group for ld. In experiment 2, the numerical values of delta Z and ld for control UN (unremineralized) and remineralized groups (1-4) ranked as UN > 3 > 4 > 1 > 2. Compared with UN, this difference was significant in all groups with ld, but not in any group with delta Z. We concluded that tolerable levels of xylitol alone may not show a significant caries inhibiting and remineralizing effect, but may act as a caries inhibitor additively with fluoride.

Onset, development and arrest of dental caries in Brazilian pre-school children

The aim of this study was to describe the onset, development and arrest of dental caries in Brazilian 1- to 5-year-old children with limited access to dental care. The sample represented 40% of all children in these age groups attending public nursery school in the Federal District of Brazil. A total of 1465 children who benefited from fluoridated water soon after birth were examined for caries. For all teeth and tooth surfaces, the examination recorded whether they were sound, showing active or arrested lesions (non-cavitated or cavitated), filled or indicated for extraction. The onset of dental caries was identified at an early age; 89% of children were free of caries at the age of 1 year, decreasing to 28% at the age of 5 years. Non-cavitated lesions (active and arrested) accounted for 71% (<2 years), 58% (3 years), 47% (4 years) and 40% (5 years) of the total number of surfaces showing caries experience. The corresponding values for cavities were 28%, 38%, 47% and 47%, respectively. Maxillary incisors and molars disclosed the highest caries experience in all ages. For children older than 1 year, both mean deft and defs scores not including non-cavitated lesions were significantly different from those for which non-cavitated lesions were taken into account (t-test, P < 0.0001). At the age of 5 years, defs scores were 5.5 and 8.8, respectively. This study documented that the onset and development of dental disease started at an early age in the population studied, leading to a considerable need for dental care.

The influence of a mineralizing mouthrinse on the mineral contents and on the pH of dental plaque

The main objective of this study was to evaluate the effects of a single use of a mineralizing mouthrinse on dental plaque pH and on its mineral contents: an additional objective was to examine the effects of an oral prophylaxis and scaling on the same response variables. A total of 22 volunteer dental students (14 female and 8 male) participated in the study. The mineralizing mouthrinse contained calcium, phosphate, strontium and fluoride ions. Following a 48-hour period without oral hygiene and 2 hours after breakfast, dental plaque was collected twice from each participant for the evaluation of the effects of the oral prophylaxis and scaling, and twice more for the evaluation of the effects of the mineralizing mouthrinse. The pH was measured in vitro with a microelectrode and the mineral contents were determined by atomic emission spectrometry. The results demonstrate that the average post-prophylaxis pH was higher than the average pre-prophylaxis pH, and that a variation of the average contents of some minerals in the dental plaque was also observed after prophylaxis compared to the contents prior to prophylaxis. Although there was a significant reduction in the Fe content after the rinse with the mineralizing solution, no significant variation on the average pH was detected.

Enamel remineralization on teeth adjacent to Class II glass ionomer restorations

PURPOSE

To examine the in vitro remineralization of incipient carious lesions on teeth adjacent interproximally to teeth with Class II glass ionomer cement restorations.

MATERIALS AND METHODS

Artificial carious lesions were created at the contact area of 30 teeth. Ten teeth had Class II glass ionomer cement/resin composite restorations placed, 10 teeth had Class II glass ionomer silver cermet restorations placed and 10 teeth had Class II amalgam restorations placed. Sections 100 microns thick were obtained longitudinally through the caries sites and polarized photomicrographs were taken in imbibition media of water and Thoulet's (R.I. 1.41 and 1.47) solutions, representing 5%, 10% and 25% pore volume respectively. Varnish was placed on the section, leaving only the external section site exposed, then sections were situated back into the original tooth. The restored teeth were abutted to the carious tooth so that the restorations came into contact with the adjacent restoration. The specimens were placed into closed environments of artificial saliva for 14 days, then were photographed again under polarized light and areas of the carious lesions were quantitated.

RESULTS

An ANOVA indicated significant variance in adjacent tooth remineralization, when comparing the experimental groups, in imbibition media of water (P < 0.05), Thoulet's 1.41 solution (P < 0.008) and Thoulet's 1.47 solution (P < 0.006). Duncan's multiple range test demonstrated the glass ionomer cement/resin composite group to have significantly greater decrease in pore volume (P < 0.05) than the amalgam control group in water imbibition media and Thoulet's 1.47 media. There was no statistically significant difference between the glass ionomer cement/resin composite and glass ionomer silver cermet groups in these two imbibition media. The glass ionomer cement/resin composite group demonstrated significantly more (P < 0.05) decrease in pore volume than both the glass ionomer silver cermet group and amalgam control group in Thoulet's 1.47 imbibition media.

Laser fluorescence quantification of remineralisation in situ of incipient enamel lesions: influence of fluoride supplements

The aims of this study were to test the laser fluorescence method for quantification of remineralisation in situ of enamel with incipient lesions and to evaluate the enhancement of remineralisation by fluoride (F) supplements when a F dentifrice was used on a regular basis by healthy young subjects. Enamel samples were cut from extracted premolar teeth with the natural surface kept intact, and subjected to a pH-cycling system to produce subsurface demineralisation in vitro. The enamel blocks were then inserted into composite holders bonded to the buccal surfaces of both upper first molars of 12 panelists. Each panelist participated in 3 separate experiments in a randomised order; each lasted for 5 weeks with washout intervals of 2 weeks between experiments; experiment 1: F dentifrice (0.145% F as NaF) only; experiment 2: F dentrifice + F lozenges (0.25 mg F x 6/day); experiment 3: F dentifrice + F chewing-gum (0.25 mg F x 6/day). Fluorescence radiance was measured before, during, and after in vitro demineralisation, and once a week during the in situ experimental periods. The enamel samples were then sectioned and analysed with transverse microradiography (TMR). Anova and Pearson correlation coefficient were used for the statistical analysis. At the end of the 5-week in situ periods, fluorescence radiance had been regained to a level of 80-100% of the value before in vitro demineralisation, indicating remineralisation of the enamel samples. There were no differences in the fluorescence radiance gain between the 3 different F exposures. However, there was a statistically significant time trend (p < 0.001), and a highly significant linear dependence (p < 0.001) between the final measurements obtained with the laser fluorescence method (LAF) and the data obtained from TMR, r = 0.76. It was concluded that: (1) with the sensitive LAF method it was possible to register the small changes in the enamel week by week during in situ remineralisation: (2) when F dentrifice was used regularly, F supplements such as F lozenges or F chewing-gum did not significantly enhance the in situ remineralisation of incipient enamel lesions in healthy, young adults with normal salivary flow.

Quantitative assessment of the efficacy of amorphous calcium phosphate/methacrylate composites in remineralizing caries-like lesions artificially produced in bovine enamel

Recent studies show that methacrylate-based composites with amorphous calcium phosphate (ACP) as a filler can release supersaturating levels of calcium and phosphate ions in proportions favorable for apatite formation. These findings suggest that such composites could be effectively used as coatings for remineralizing teeth damaged by tooth decay. To examine this hypothesis, we tested composites in vitro for their efficacy to remineralize artificially formed caries-like lesions in extracted bovine incisors. Single 120-microns-thick sagittal tooth sections were placed in holders that exposed only the carious enamel surface. The exposed surfaces were coated with a 1-mm- to 1.5-mm-thick layer of the composite containing, by mass, 40% apatite, silica, or P2O7(-4)-stabilized ACP and 60% photoactivated resin comprised of Bis-GMA, TEGDMA, HEMA, and ZrM. The photocured composite-coated sections were immersed either in a remineralizing solution for 4 weeks at 37 degrees C (static model) or cyclically immersed in demineralizing (0.5 h) and remineralizing solutions (11.5 h) for 2 weeks (dynamic model). Quantitative digital image analysis of matched 102 microns x 220 microns areas from contact microradiographs taken of the sections before and after immersion showed that lesions coated with ACP-filled composites fractionally recovered 71% +/- 33% of their lost mineral compared with 14% +/- 13% for apatite controls in the static model and 38% +/- 16% compared with -6% +/- 24% in the dynamic model. The results suggest that sealants based on ACP-filled methacrylate composites have the potential to remineralize carious enamel lesions.