Patrick R. Schmidlin

Influence of study design on the impact of bleaching agents on dental enamel microhardness: A review

OBJECTIVE Numerous studies investigated the impact of bleaching procedures on enamel microhardness. The outcomes of these studies reveal inconsistencies regarding the fact whether a microhardness reduction due to bleaching occurs or not. Aim of the present review was to summarize the existing literature of external bleaching therapies, which used microhardness tests for evaluation of possible effects on enamel and to weigh up different parameters of the study designs with respect to the outcome of these studies. METHODS The data from original scientific full papers listed in PubMed or ISI Web of Science (search term: enamel and (bleaching or peroxide) and (hardness or microhardness or Knoop or Vickers)) and received by additional hand-search meeting the inclusion criteria were included in the review. Influences of different parameters on the outcome of the bleaching treatments were analyzed with the Fishers-exact-test. RESULTS A total of 55 studies were identified with 166 hardness measurements conducted directly after bleaching and 69 measurements performed after a post-treatment episode. Directly after bleaching, 84 (51%) treatments showed microhardness reduction compared to baseline, whereas 82 (49%) did not yield microhardness reduction. After the post-treatment episode, 20 (29%) treatments showed hardness reduction and 49 (71%) did not. A significant higher number of bleaching treatments resulting in enamel microhardness reduction were observed, when artificial instead of human saliva was used for storage of the enamel samples in the intervals between the bleaching applications and when no fluoridation measures were applied during or after the bleaching phase. SIGNIFICANCE The review shows that in those studies, which simulated the intraoral conditions as closely as possible, the risk of enamel microhardness decrease due to bleaching treatments seems to be reduced. Nevertheless more in situ- and in vivo-studies are needed to verify this observation.

IN VIVO AND IN VITRO EVALUATION OF FLEXIBLE, COTTONWOOL-LIKE NANOCOMPOSITES AS BONE SUBSTITUTE MATERIAL FOR COMPLEX DEFECTS

The easy clinical handling and applicability of biomaterials has become a focus of materials research due to rapidly increasing time and cost pressures in the public health sector. The present study assesses the in vitro and in vivo performance of a flexible, mouldable, cottonwool-like nanocomposite based on poly(lactide-co-glycolide) and amorphous tricalcium phosphate nanoparticles (PLGA/TCP 60:40). Immersion in simulated body fluid showed exceptional in vitro bioactivity for TCP-containing fibres (mass gain: 18%, 2 days, HAp deposition). Bone regeneration was quantitatively investigated by creating four circular non-critical-size calvarial defects in New Zealand White rabbits. The defects were filled with the easy applicable cottonwool-like PLGA/TCP fibres or PLGA alone. Porous bovine-derived mineral (Bio-Oss) was used as a positive control and cavities left empty served as a negative control. The area fraction of newly formed bone (4 weeks implantation) was significantly increased for TCP-containing fibres compared to pure PLGA (histological and micro-computed tomographic analysis). A spongiosa-like structure of the newly formed bone tissue was observed for PLGA/TCP nanocomposites, whereas Bio-Oss-treated defects afforded a solid cortical bone.

Radiographic evaluation of different techniques for ridge preservation after tooth extraction: a randomized controlled clinical trial

OBJECTIVE To evaluate the radiographic changes of the alveolar ridge following application of different ridge preservation techniques 6 months after tooth extraction. MATERIALS AND METHODS Four treatment modalities were randomly assigned in 40 patients: β-tricalcium-phosphate-particles with polylactid coating (β-TCP), demineralized bovine bone mineral with 10% collagen covered with a collagen matrix (DBBM-C/CM), DBBM-C covered with an autogenous soft-tissue graft (DBBM-C/PG) and spontaneous healing (control). Cone-beam computed tomography scans were performed after treatment and 6 months later. RESULTS After 6 months, the vertical changes ranged between -0.6 mm (-10.2%) for control and a gain of 0.3 mm (5.6%) for DBBM-C/PG on the lingual side, and between -2.0 mm (-20.9%) for β-TCP and a gain of 1.2 mm (8.1%) for DBBM-C/PG on the buccal side. The most accentuated ridge width changes were recorded 1 mm below the crest: -3.3 mm (-43.3%, C), -6.1 mm (-77.5%, β-TCP), -1.2 mm (-17.4%, DBBM-C/CM) and -1.4 mm (-18.1%, DBBM-C/PG). At all three levels, DBBM-C with either CM or PG was not significantly differing (p > 0.05), while most other differences between the groups reached statistical significance (p < 0.05). CONCLUSIONS Application of DBBM-C, covered with CM or PG, resulted in less vertical and horizontal changes of the alveolar ridge as compared with controls 6 months after extraction.

Effect of different surface pre-treatments and luting materials on shear bond strength to PEEK.

OBJECTIVES To assess the bonding potential of a universal composite resin cement and an adhesive/composite system to differently pre-treated PEEK surfaces. METHODS One hundred and fifty PEEK disks were embedded in epoxy resin, polished (P4000 grit) and treated as follows (n=30/group): (A) no treatment, (B) acid etching with sulfuric acid (98%) for 1 min, (C) sandblasting for 10s with 50 microm alumina, (D) sandblasting for 10s with 110 microm alumina and (E) silica coating using the Rocatec system (3M ESPE). Polished and sandblasted (50 microm alumina) cp titanium (grade 4) served as a control. Acrylic hollow cylinders were either luted with a universal composite resin cement (RelyX Unicem) or an unfilled resin (Heliobond) and a hybrid composite (Tetric) to the specimens. Bond strength was measured in a shear test and failure modes were assessed. Statistic analysis was performed with one-way ANOVA followed by a post hoc Scheffé test and unpaired t-tests. RESULTS With the universal composite resin cement, no bond could be established on any PEEK surfaces, except specimens etched with sulfuric acid (19.0+/-3.4MPa). Shear bond strength to titanium was significantly lower (8.7+/-2.8MPa, p<0.05). Applying the adhesive/composite system, shear bond strength values on pre-treated PEEK ranged from 11.5+/-3.2MPa (silica coating) to 18.2+/-5.4MPa (acid etched) with no statistically significant differences (p>0.05). No bond was obtained on the polished surface. SIGNIFICANCE Bonding to PEEK is possible when using a bonding system. No adherence can be achieved with the tested universal composite resin cement except on an etched surface. The results strongly encourage further research in PEEK application in dentistry.

Polyetheretherketone—A suitable material for fixed dental prostheses?

OBJECTIVES To study the surface properties of polyetheretherketone (PEEK) and its bond strength with two veneering resins after different conditioning methods as well as fracture load of PEEK three-unit fixed dental prostheses (FDPs). METHODS Two hundred and twenty five PEEK specimens were fabricated and divided into five groups: no treatment (A), etching with 98% sulfuric acid for 1 min (B), air-abrasion for 10 s with either 50 or 110 μm alumina (C and D, respectively), and silica coating using the Rocatec System (E). On 15 specimens of each conditioning method, contact angle and surface roughness were determined. The remaining 150 specimens of each conditioning method were divided into two groups for the veneering procedure with the composites Gradia (GC Europe) and Sinfony (3M ESPE). Shear bond strength (SBS) was measured and failure types were assessed. In addition, 15 FDPs were milled and the fracture load was tested. Data were analyzed using descriptive statistics, one-way ANOVA (Scheffé test), two sample Students t-test, and Weibull statistics (p < 0.05). RESULTS Silica-coated PEEK surfaces showed the highest wettability. The highest roughness and lowest contact angles were observed for 110 μm air-abraded and silica-coated PEEK surfaces. The highest SBS values were, however, achieved in the acid-etched group. PEEK three-unit FDPs showed a mean fracture load of 1383 N with a plastic deformation starting approximately at 1200 N. CONCLUSIONS Acid etching should be applied when PEEK is used as substructure material and composite veneering material is applied. In this combination, PEEK might be a suitable material for FDPs, especially in load-bearing areas.

Flexible, silver containing nanocomposites for the repair of bone defects: antimicrobial effect against E. coli infection and comparison to tetracycline containing scaffolds

Bone regeneration in infected tissue or areas with high bacteria concentrations such as the oral cavity requires combining disinfection with biomaterial properties. Classical antibiotics typically provide excellent short term protection against re-infection of a defect but are typically washed out of an operation site within days. The present work investigates the use of silver on amorphous tricalcium phosphate (TCP) nanoparticles for electrospun, highly porous poly(lactide-co-glyclolide) (PLGA) fibrous composites. In vitro bioactivity tests of the wool-like composite PLGA/Ag-TCP (80 : 20) containing 0.5 wt% silver showed rapid hydroxyapatite deposition on the nanocomposite within 2 days. Antibacterial tests using E. coli demonstrated a strongly prolonged antibacterial effect of the scaffolds containing finely dispersed silver on TCP if compared to current clinically used methods based on soaking the scaffolds with a tetracycline solution prior to implantation.

Effect of Titanium Tetrafluoride and Amine Fluoride Treatment Combined with Carbon Dioxide Laser Irradiation on Enamel and Dentin Erosion

OBJECTIVE This in vitro study aimed to analyze the influence of carbon dioxide (CO(2)) laser irradiation on the efficacy of titanium tetrafluoride (TiF(4)) and amine fluoride (AmF) in protecting enamel and dentin against erosion. METHODS Bovine enamel and dentin samples were pretreated with carbon dioxide (CO(2)) laser irradiation only (group I), TiF(4) only (1% F, group II), CO(2) laser irradiation before (group III) or through (group IV) TiF(4) application, AmF only (1% F, group V), or CO(2) laser irradiation before (group VI) or through (group VII) AmF application. Controls remained untreated. Ten samples of each group were then subjected to an erosive demineralization and remineralization cycling for 5 days. Enamel and dentin loss were measured profilometrically after pretreatment, 4 cycles (1 day), and 20 cycles (5 days) and statistically analyzed using analysis of variance and Scheffes post hoc tests. Scanning electron microscopy (SEM) analysis was performed in pretreated but not cycled samples (two samples each group). RESULTS After 20 cycles, there was significantly less enamel loss in groups V and IV and significantly less dentin loss in group V only. All other groups were not significantly different from the controls. Lased surfaces (group I) appeared unchanged in the SEM images, although SEM images of enamel but not of dentin showed that CO(2) laser irradiation affected the formation of fluoride precipitates. CONCLUSION AmF decreased enamel and dentin erosion, but CO(2) laser irradiation did not improve its efficacy. TiF(4) showed only a limited capacity to prevent erosion, but CO(2) laser irradiation significantly enhanced its ability to reduce enamel erosion.

Attritional wear and abrasive surface alterations of composite resin materials in vitro

OBJECTIVES A laboratory study was performed with 232 specimens and 72 human enamel, 24 gold, 24 ceramic and 12 composite antagonists in 22 groups to test attritional and abrasive wear behavior of composite materials compared to wear behavior of human enamel. METHODS Belleglass HP, Concept Inlay/Onlay, Targis and Targis Upgrade 99 composite resin for lab-made restorations was tested as well as Tetric Ceram and FHC Merz light as resins for direct restorations. Natural human enamel specimens served as control. All specimens were subjected to long-term thermo-mechanical loading in a computer-controlled masticator, chemical degradation and toothbrush/toothpaste abrasion. Wear of specimen in occlusal contact area (OCA), contact-free occlusal area and wear of natural enamel cusps as well as antagonists made of gold, ceramic and composite in identical form was measured after 120,000, 240,000, 640,000 and 1200,000 load cycles. A qualitative SEM analysis was performed to support quantitative data. RESULTS Belleglass HP and Targis Upgrade 99 restorative materials showed wear resistance comparable to human enamel when loaded with enamel cusps. Wear of Targis versus composite and gold antagonists was significantly higher (p<0.0001). Analysis of surface alterations showed hygroscopic expansion in all composite resins during the test. CONCLUSIONS As a consequence of this study, necessity to further improve physical properties of composites for long lasting restorations was obvious. Beside of attritional wear in OCA, attention must be given to stable filler-matrix interfaces and prevention of water sorption.

Relationship between Nanohardness and Mineral Content of Artificial Carious Enamel Lesions

The aim of this study was to compare cross-sectional nanohardness, measured using an ultra-microindentation system, with mineral content, from transversal microradiography, of artificial enamel caries lesions. Sections (85 ± 10 µm) from 16 bovine enamel samples with artificial caries were prepared. The mineral content and cross-sectional nanohardness at known depths from the surface were compared. Both methods showed lesion profiles with a surface layer. The determination of nanohardness seems limited to lesions with a mineral content >45 vol%. There was a moderate linear relationship between mineral content and the square root of nanohardness (R2 = 0.81). It was concluded that the conversion of cross-sectional hardness into mineral content remains questionable and cannot be recommended.

Adhesive performance of a caries infiltrant on sound and demineralised enamel

OBJECTIVE Resin infiltration is considered as a treatment option for initial caries lesions. As cavitated early lesions might require additional restorative intervention, a caries infiltrant might be also used for enamel conditioning prior to composite insertion. This study aimed to analyse the shear bond strength of a flowable composite to sound and demineralised enamel pretreated with a caries infiltrant, a conventional adhesive or a combination of both. METHODS Flattened bovine enamel specimens (n=120) were either demineralised (14 d, acidic buffer, pH 5) or remained untreated. Sound and demineralised specimens (each n=20) were then treated with: (1) 35% phosphoric acid, conventional adhesive, (2) 15% hydrochloric acid, caries infiltrant or (3) 15% hydrochloric acid, caries infiltrant, conventional adhesive. Shear bond strength of a flowable composite was tested after 24 h water storage (37°C) and statistically analysed (ANOVA, p≤0.05). The mode of failure was assessed microscopically at 25× magnification. RESULTS On demineralised enamel, the combination of caries infiltrant and conventional adhesive showed significantly higher shear bond strength values than the conventional adhesive alone, while both being not significantly different from group 2. No significant differences between the groups could be detected on sound specimens. A higher percentage of cohesive failures could be observed in demineralised samples of group 2 (40%) and 3 (65%), while all other specimens presented almost only adhesive failures. CONCLUSION The use of a caries infiltrant before application of a conventional adhesive did not impair bonding to sound and demineralised enamel and might be beneficial as a pretreatment in demineralised enamel.