A.M. Kielbassa

Resin Infiltration of Natural Caries Lesions

Infiltration of non-cavitated caries lesions with light-curing resins could lead to an arrest of lesion progression. The aim of this study was to evaluate the penetration of a conventional adhesive into natural enamel caries after pre-treatment with two different etching gels in vitro. Extracted human molars and premolars showing proximal white-spot lesions were cut across the lesions perpendicular to the surface. Corresponding lesion halves were etched for 120 sec with either 37% phosphoric acid gel (H3PO4) or 15% hydrochloric acid gel (HCl), and subsequently infiltrated with an adhesive. Specimens were observed by confocal microscopy. Mean penetration depths (SD) in the HCl group [58 (37) μm] were significantly increased compared with those of the H3PO4 group [18 (11) μm] (p < 0.001; Wilcoxon). It can be concluded that etching with 15% hydrochloric acid gel is more suitable than 37% phosphoric acid gel as a pre-treatment for caries lesions intended to be infiltrated.

Surface Layer Erosion of Natural Caries Lesions with Phosphoric and Hydrochloric Acid Gels in Preparation for Resin Infiltration

The infiltration of proximal enamel lesions with low-viscosity light curing resins could be a viable approach to stop lesion progression. However, penetration of sealant might be hampered by the comparatively highly mineralized surface layers of natural lesions. Therefore, the aim of this study was to compare the efficacy of three different etching gels in removing the surface layer in various etching times. Extracted human molars and premolars showing proximal white spot lesions were cut across the demineralized areas. Ninety-six lesions expected from visual examination to be confined to the outer enamel (C1) were selected. The cut surface and half of each lesion were varnished, thus serving as control. Subsequently, the lesions were etched with either phosphoric (37%) or hydrochloric (5 or 15%) acid gel for 30–120 s (n = 8/group). Specimens were examined using confocal microscopy and transversal microradiography. Surface layer reduction was significantly increased in lesions etched with 15% HCl gel for 90 and 120 s compared to those etched with H3PO4 gel for 30–120 s (p < 0.05). No significant differences regarding the depths of erosion in the lesions compared to sound enamel could be observed (p > 0.05). An effective reduction in the surface layer of natural enamel caries can be achieved by etching with 15% hydrochloric acid gel for 90–120 s.

Progression of Sealed Initial Bovine Enamel Lesions under Demineralizing Conditions in vitro

The use of sealants for the infiltration of proximal enamel lesions could be a promising alternative to the common strategies of remineralization and operative treatment. The aim of the present study was to compare the progression of sealed initial enamel lesions after exposure to a demineralizing solution in vitro. In each of 54 bovine enamel specimens three subsurface lesions were created. Two of the lesions were etched with phosphoric acid and sealed with either a fissure sealant or with various adhesives (1–5) for 15 s or 30 s, respectively, whereas one lesion remained as the untreated control. Subsequently, half of each specimen was covered with nail varnish (baseline) and the other half was reexposed to a demineralizing solution for 14 days (experimental). The specimens were cut perpendicularly to the surface, infiltrated with a low-viscosity fluorescent resin and observed with a confocal laser scanning microscope (CLSM). For lesions sealed with the fissure sealant and adhesives 1–3, the progression of lesion depth (0–31 µm) was significantly decreased (p < 0.01; paired t test) compared with the untreated control (57 µm). For the fissure sealant and adhesives 1 and 3 extended penetration times (30 s) resulted in significantly reduced lesion progression compared to 15 s. It can be concluded that filling of the pores in initial enamel lesions with the fissure sealant and adhesives 1–3 can inhibit further demineralization in vitro.

Profilometric and Microradiographic Studies on the Effects of Toothpaste and Acidic Gel Abrasivity on Sound and Demineralized Bovine Dental Enamel

The objective of this study was to assess the abrasive effects of toothpastes and acidic F gels on sound and demineralized enamel. Pairs of enamel specimens were cut from bovine incisors, embedded in epoxy resin and polished. An artificial subsurface lesion of 80–90 µm depth was created in one specimen from each pair. The samples were covered with adhesive tape, thereby exposing the enamel for abrasivity testing. All samples were divided into six groups of 15 and brushed with a slurry (1:3) of F gel or toothpaste and human saliva. Brushing with water (control) or with slurry was carried out (16,000 strokes) using a medium toothbrush (load 275 g) mounted in a brushing machine. Abrasion was evaluated using laser profilometry, and was about 50% less on sound than on demineralized enamel (p < 0.001). In the latter, brushing with water (0.09 ± 0.03 µm) or with fluoride-free gel (0.08 ± 0.03 µm) resulted in negligible wear. With a medium-abrasive paste (1.76 ± 0.85 µm) and an acidic F gel (2.48 ± 0.72 µm), brushing abrasion was significantly greater (p < 0.001) than with a low-abrasive paste (0.84 ± 0.38 µm). The greatest wear (16.6 ± 10.8 µm) was observed with high-abrasive paste (p < 0.001), and here transversal microradiography revealed a complete loss of the pseudointact surface after brushing. In vitro formed caries-like lesions can be abraded (by toothbrushing) more easily than sound enamel; hence, initial white spot lesions should preferably be brushed with oral hygiene products of low abrasivity.

Effect of Mucin Alone and in Combination with Various Dentifrices on in vitro Remineralization

The aim of this in vitro study was to evaluate the effect of combining various fluoridated dentifrices with mucin on remineralization of bovine enamel. Enamel specimens were embedded in epoxy resin, partly covered with nail varnish, and demineralized in a lactic acid solution (pH 5.0, 14 days). Parts of the demineralized areas of the specimens were then covered with nail varnish. Half of the samples were exposed to a mucin-containing (2.7 g/l) remineralizing solution, the other half to a mucin-free remineralizing solution for 30 days. In each group, the specimens were divided into four subgroups, which were brushed twice a day with a toothpaste containing sodium, stannous/amine, or amine fluoride. The specimens of the fourth subgroup were not brushed, but stored in one of the two solutions. Mineral loss and lesion depth were evaluated from microradiographs. After the remineralization period, specimens that were brushed with one of the dentifrices and stored in the mucin-containing remineralizing solution reacquired more mineral than those brushed and stored in the mucin-free solution (p < 0.05; Bonferroni post hoc test). The results indicate that mucin in combination with various fluorides seems to affect enamel remineralization significantly. Thus, mucin could be considered as an additive to saliva substitutes or mouthwashes in patients with hyposalivation.

Influence of endodontic treatment, post insertion, and ceramic restoration on the fracture resistance of maxillary premolars

AIM To investigate the effects of endodontic treatment, post placement and ceramic restoration type on the fracture resistance of premolars. METHODOLOGY One hundred and twenty teeth maxillary premolars were allocated to four groups (A-D; n = 30). In group A, mesio-occlusal-distal-inlays with a buccal and palatal wall of 2 mm (MOD), in group B partial onlays with palatal cusp coverage and in group C total onlays with buccal and palatal cusp coverage were prepared. Group D served as untreated controls. Groups A-C were divided into three subgroups (n = 10): (i) teeth received solely the described preparations, (ii) teeth were root filled, (iii) teeth were root filled and quartz fibre posts were placed. Teeth were restored using Computer-assisted design/computer-assisted machining-ceramic-restorations and subjected to thermo-mechanical-loading; subsequently, the buccal cusp was loaded until fracture. RESULTS Group D revealed significantly higher fracture resistance [mean (standard deviation)] [738 (272) N] compared to all other groups (P < 0.05; post hoc test Dunnett). For groups A-C, fracture resistance was significantly affected by the restoration type (P = 0.043) and endodontic treatment/post placement (P = 0.039; 2-way anova). Group A [380 (146) N] showed significantly lower fracture resistance compared to group B [470 (158) N] (P = 0.048; post hoc test Tukey). Compared to non-endodontically treated teeth [487 (120) N], root filled teeth revealed significantly lower fracture resistance [389 (171) N] (P = 0.031). CONCLUSION The restoration of cavities with a remaining wall thickness of 2 mm using ceramic MOD-inlays is inferior with respect to the fracture resistance compared to partial onlay restorations. Root filled teeth without post placement show lower fracture resistance compared to non-endodontically treated teeth.

Effect of a Fluoridated Food Item on Enamel in situ

After the consumption of food items prepared with fluoridated salt elevated fluoride concentrations can be observed in saliva, whereby enamel mineralization is supposed to be positively affected. The aim of this double-blind (with respect to fluoride), placebo-controlled, randomized, cross-over study was to evaluate the effects of the consumption of either a fluoridated (effect) or a placebo food item on the mineral content of sound and pre-demineralized human enamel in situ. During both phases of the study 8 enamel specimens in each of 10 intraoral appliances were positioned, either recessed or flush with the acrylic surface. One of the flanges was brushed twice daily with fluoride-free toothpaste prior to the storage of the appliance in sucrose solution. The subjects were asked to refrain from other sources of fluorides except for the consumption of either a highly fluoride-containing (0.5 mg) or a placebo cookie (3 times daily) during the respective study phase. Mineral content and lesion depth were measured in the enamel specimens and fluoride concentrations in saliva and urine. Significantly increased urinary and salivary (immediately after food consumption) fluoride concentrations compared to baseline were observed during the effect phase. In the absence of fluorides more pronounced demineralization was observed, especially for the recessed specimens of both surface conditions. Brushing was shown to inhibit demineralization, particularly during the placebo phase. In conclusion, fluorides added to food items seem to be efficacious to inhibit enamel demineralization in plaque-covered enamel but might be less effective if oral hygiene is adequate.