Interface effects on mechanical properties of particle-reinforced composites.

OBJECTIVES: Effective bonding between the filler and matrix components typically improves the mechanical properties of polymer composites containing inorganic fillers. The aim of this study was to test the hypothesis that composite flexural modulus, flexure strength, and toughness are directly proportional to filler-matrix interfacial shear strength. METHODS: The resin matrix component of the experimental composite consisted of a 60:40 blend of BisGMA:TEGDMA. Two levels of photoinitiator components were used: 0.15, and 0.5%. Raman spectroscopy was used to determine degree of cure, and thermogravimetry (TGA) was used to quantify the degree of silane, rubber, or polymer attachment to silica and glass particles. Filler-matrix interfacial shear strengths were measured using a microbond test. Composites containing glass particles with various surface treatments were prepared and the modulus, flexure strength, and fracture toughness of these materials obtained using standard methods. Mechanical properties were measured on dry and soaked specimens. RESULTS: The interfacial strength was greatest for the 5% MPS treated silica, and it increased for polymers prepared with 0.5% initiator compared with 0.15% initiator concentrations. For the mechanical properties measured, the authors found that: (1) the flexural modulus was independent of the type of filler surface treatment, though flexural strength and toughness were highest for the silanated glass; (2) rubber at the interface, whether bonded to the filler and matrix or not, did not improve toughness; (3) less grafting of resin to silanated filler particles was observed when the initiator concentration decreased. SIGNIFICANCE: These findings suggest that increasing the strength of the bond between filler and matrix will not result in improvements in the mechanical properties of particulate-reinforced composites in contrast to fiber-reinforced composites. Also, contraction stresses in the 0.5 vs 0.15% initiator concentration composites may be responsible for increases in interfacial shear strengths, moduli, and flexural strengths.     

Influence of the use of Er:YAG laser for cavity preparation and surface treatment in microleakage of resin-modified glass ionomer restorations

This study quantitatively assessed the amount of microleakage on Class V cavities prepared by Er:YAG laser and high-speed handpiece, varying the surface treatment and restoring with a resin-modified glass ionomer cement. Fifty cavities were prepared using either an Er:YAG laser device or a carbide bur at high speed. The surface treatment was performed as follows: Er:YAG laser irradiation (G1); 40% polyacrylic acid (G2); laser + acid (G3); finishing with low speed + laser + acid (G4); conventional bur preparation + acid (G5-control). The samples were restored with Fuji II LC, thermocycled, isolated and immersed in a 50% AgNO3 solution. The restorations were serially sectioned and the extent of dye penetration was measured in milimeters using specific computer software. Data were analyzed by two-way ANOVA and Tukey test. The lowest degree of microleakage was observed for G5, which was statistically similar (p>0.05) to G4 but different (p<0.05) from all the other experiental groups. Lesser microleakage was observed at the occlusal margins than at the cervical margins (p<0.05). It may be concluded that the use of Er:YAG laser for cavity preparation and surface treatment negatively affected the marginal sealing of resin-modified glass ionomer restorations.     

Locally applied isosorbide decreases bone resorption in experimental periodontitis in rats

BACKGROUND: The role of nitric oxide (NO) on bone metabolism is controversial, since it can either stimulate bone formation or resorption. We investigated the effect of local administration of the NO donor isosorbide in an experimental periodontal disease model. METHODS: Wistar rats were subjected to a ligature placement around the cervix of the right second upper molar and were sacrificed after 11 days. Alveolar bone loss was measured in one quadrant as the sum of the distances between the cuspid tip and the alveolar bone along the axis of each molar root, which was subtracted from the contralateral side, used as unligated control. The semiquantitative histopathological scale of the periodontium was based on cell infiltration and alveolar bone and cementum integrity. Groups were treated with a gel containing 1% or 5% isosorbide applied to the vestibular side of the molar gingiva 1 hour before the placement of the ligature and then twice daily until sacrifice. Controls included one group subjected to periodontitis and no treatment (NT) and another that received the gel containing just the vehicle (V). RESULTS: The application of the vehicle gel produced an increase of the alveolar bone resorption, without altering the inflammatory changes, compared to the NT group. The 5% isosorbide produced a significant reduction of the alveolar bone resorption, compared to V and NT. This reduction was confirmed by histological analysis, showing less inflammatory cell infiltration and preservation of the cementum and the alveolar process. CONCLUSION: Local application of isosorbide reduces alveolar bone resorption in experimental periodontal disease in rats, suggesting a local anti-inflammatory effect of isosorbide.     

Fixed prosthetics with a connective tissue and alloplastic bone graft ridge augmentation: a case report

Augmentation of the partially edentulous ridge can significantly improve the final prosthodontic rehabilitation. For enhancing soft tissue contours in the anterior region, the subepithelial connective tissue graft is the treatment of choice. The combination of connective tissue grafts with alloplastic bone graft material can optimize the ridge augmentation and reduce post extraction defects. The aim of this clinical report is to describe the use of subepithelial connective tissue in conjunction with an alloplastic bone graft for augmentation of a maxillary anterior ridge prior to prosthetic rehabilitation.     

Therapeutic versus prophylactic plus therapeutic administration of omega-3 fatty acid on endotoxin-induced periodontitis in rats

BACKGROUND: The aim of the present study was 1) to evaluate the possible effects of therapeutic usage of omega-3 fatty acid on the gingival tissue levels of prostaglandin E2 (PGE2), prostaglandin F2alpha (PGF2alpha), platelet activating factor (PAF), and leukotriene B4 (LTB4) in endotoxin-induced periodontitis in rats and 2) to investigate whether prophylactic usage provides any additional benefits to therapeutic doses of omega-3 fatty acid. METHODS: Experimental periodontitis was induced by repeated injection of Escherichia coli lipopolysaccharide (LPS). Thirty-six adult male Sprague-Dawley rats were divided into four study groups: 1) saline controls; 2) LPS; 3) therapeutic omega-3 fatty acid (TO3); and 4) prophylactic plus therapeutic omega-3 fatty acid (P + TO3) groups. In TO3 group, omega-3 fatty acid was given for 15 days following induction of experimental periodontitis. In P + TO3 group, omega-3 fatty acid was started 15 days before baseline, and then periodontitis was induced at baseline and omega-3 fatty acid was continued for 15 days after baseline. On day 15 after baseline, all rats were anesthetized and sacrificed. PGE2, PGF2alpha, and LTB4 levels in gingival tissue samples were analyzed by enzyme immunoassay and PAF levels were analyzed by radioimmonoassay. Data were evaluated statistically by using parametric tests. RESULTS: LPS injection resulted in significant amount of bone loss (P<0.05). Neither therapeutic nor prophylactic plus therapeutic administration of omega-3 fatty acid with the doses and duration of therapy used in the present study was effective in preventing endotoxin-induced alveolar bone loss. TO3 group exhibited significant decreases in the gingival tissue levels of PGE2, PGF2alpha, LTB4, and PAF compared to the LPS group (P<0.05). PGE2 and PGF2alpha levels in TO3 group were similar to those of the saline group (P>0.05), while LTB4 and PAF levels were statistically higher than the saline group (P<0.05). Prophylactic plus therapeutic usage of omega-3 fatty acid provided similar levels of all these mediators to those of the saline controls (P>0.05). CONCLUSIONS: Therapeutic omega-3 fatty acid significantly reduced the gingival tissue levels of PGE2, PGF2alpha, LTB4, and PAF in experimental periodontitis. Furthermore, prophylactic usage of omega-3 fatty acid provided additional beneficial effects to the therapeutic administration by decreasing the gingival tissue levels of these mediators to levels of healthy tissue. These findings should be verified by longitudinal clinical trials investigating clinical and biochemical periodontal parameters to better define the possible role of omega-3 fatty acids in periodontal treatment.     

Literature survey of apexification in connection with three cases

Endodontic treatment of three non-vital immature teeth is discussed. According Moorrees et al. root formation was in the stage two, six and four respectively. After access to the root canal, removing necrotic pulp and effective chemo-mechanical cleansing, Ca(OH)2 paste was used as a temporary filling material in each case. In two cases after closing the apical opening, permanent obturation was performed with half heated gutta-percha and lateral condensation to obtain a good seal. In one case permanent filling of the canal occurred with gutta-percha and AH26 as a sealer. In the first case two years, in the second case five years after obturation of the root canal with gutta-percha, periapical healing was evident in the control radiograph. In the third case using gutta-percha with AH26 as a sealer after two years new periapical lesion has developed. On the bases of literature data and our experiences in the case of non-vital immature teeth. Ca(OH)2 paste is the best temporary filling material to induce apexification process, and the half heated gutta-percha obturation is the most suitable permanent root filling material.     

Angioleiomyoma of the tongue

A case of angioleiomyoma of the tongue is detailed. The patient sought treatment for a painless, rubbery mass of 10 years duration. The tumor was unusual, appearing bilobed, with the dorsal aspect whitish in color and a blue ventral component. Occasional episodes of numbness were noted. Biopsy of the lesion demonstrated bundles of smooth muscle cells surrounding numerous vascular spaces. The patient was lost to follow-up; as a result, a complete surgical excision of the tumor was not performed.     

Non-contact removal of coadhering and non-coadhering bacterial pairs from pellicle surfaces by sonic brushing and de novo adhesion

Coadhesion between oral microbial pairs is an established factor in the spatiotemporal development and prevalence of mixed-species communities in early dental plaque in vivo. This study compares removal and de novo adhesion of pairs of coadhering and non-coadhering oral actinomyces and streptococci by sonic brushing on salivary pellicles in a non-contact mode as a function of the distance between the brush and the pellicle surface in vitro. First, actinomycetes were adhered to a pellicle surface, after which streptococci suspended in saliva were allowed to adhere. Removal was examined by non-contact, sonic brushing with a wetted brush on a either a wetted or a substratum immersed to a depth of 7 mm. After brushing, de novo adhesion of streptococci to brushed pellicles was studied. For coadhering and non-coadhering pairs, 34% and 9%, respectively, of the adhering bacteria were involved in aggregates comprising more than 10 organisms. Non-contact, sonic brushing removed up to 99% of the adhering bacteria, regardless of the state of immersion of the substratum. Bacterial removal decreased with increasing distance of up to 6 mm between brush and pellicle surface. For the non-coadhering pair, subsequent exposure of pellicles to a streptococcal suspension yielded about 6% of bacteria involved in large aggregates. Alternatively, de novo adhesion of the coadhering streptococcal strain to pellicles brushed on the wetted substratum yielded 31% of bacteria involved in large aggregates, but after brushing the immersed substratum only 12% of the adhering bacteria were found in large aggregates. It is concluded that non-contact sonic brushing, under immersion, removes high percentage of adhering bacterial pairs up to a distance of 6 mm between the brush and the pellicle surface. However, non-contact, sonic brushing with only a thin wet film on the substratum may leave footprints to which streptococci preferentially adhere.