Prolonged antimicrobial effect of tissue conditioners containing silver-zeolite

OBJECTIVES

The purpose of this study was to elucidate the in vitro antimicrobial effect of tissue conditioners containing silver-zeolite on Candida albicans and nosocomial respiratory infection-causing bacteria, Staphylococcus aureus and Pseudomonas aeruginosa.

METHODS

Five commercially available tissue conditioners were selected: Visco-gel (VG), GC Soft-Liner (SL), Fitt (FT), SR-Ivoseal (IV) and Shofu Tissue Conditioner (TC). Samples, 10 x 10 x 2.5 mm in size, contained silver-zeolite (SZ sample) and no SZ (N sample). The antimicrobial effects of these two samples were evaluated as a percentage of viable cells (CFU) in a microbial suspension (100 microliter) in phosphate-buffered saline with or without immersion in artificial saliva for four weeks. The borderline of the antimicrobial effect was determined at 0.1% viable cells.

RESULTS

With the SZ samples, all tested microbes were killed under both conditions of no immersion and immersion in saliva. In non-immersed N samples, however, no cells of C. albicans (except with VG) and S. aureus survived, whereas the percentage of viable cells of P. aeruginosa was similar to that found in the control. However, with immersion in saliva, viable cells of C. albicans in some N samples (VG, SL and TC) increased compared with non-immersion samples by more than 0.1%.

CONCLUSION

Tissue conditioners containing SZ have been shown to have antimicrobial effects for four weeks on C. albicans and nosocomial respiratory infection-causing bacteria in saliva in vitro.

Clinical application of short hydroxylapatite-coated dental implants to the posterior mandible: a five-year survival study

STATEMENT OF PROBLEM

The surgical and restorative procedures at the posterior region of the maxilla and the mandible present a complex task in the treatment of partially edentulous patients.

PURPOSE

The purpose of this study was to investigate the applicability of short hydroxylapatite-coated dental implants to the posterior mandible of partially edentulous patients.

MATERIAL AND METHODS

Eight and 11 mm implants were evaluated as to their cumulative survival rate, clinical status (plaque index, gingival index, probing depth), and marginal bone loss over a 5-year period.

RESULTS AND CONCLUSIONS

The verified overall cumulative survival rate was 94% for implants and 91% for prostheses. These results suggest predictable success for the application of short implants to the posterior mandible.

Effect of friction coefficient on Akers clasp retention

STATEMENT OF PROBLEM

Retentive force control of clasp retainers is one of the most essential factors for the successful function of removable partial dentures. However, it is not yet known how the friction coefficients differ among restored abutments and clasp materials, and how the friction coefficients affect the retention of clasps.

PURPOSE

The purposes of this study were to clarify the friction coefficients among restored abutments and clasp materials and to estimate the effect of friction coefficients on the retention of clasps.

MATERIAL AND METHODS

The coefficients of static friction between three clasp materials (type IV gold, high Pd, and cobalt-chromium [Co-Cr] alloys) of two surface treatments (polished and sandblasted) and four abutment materials (human enamel, porcelain, type IV gold, and high Pd alloys) were evaluated under three conditions (dry, wet with water, and wet with saliva), and theoretically, the effect of the friction coefficients on clasp retention was estimated.

RESULTS

The friction coefficients under various conditions ranged from 0.08 (polished Co-Cr clasp on type IV abutment in dry condition) to 0.37 (sandblasted Co-Cr clasp on high Pd abutment in dry condition). The theoretical estimation clarified that the retentive force of the clasp was linear to the friction coefficient.

CONCLUSION

The retentive force increased linearly with increasing friction coefficient between abutment material and clasp material according to the newly developed formula. This study suggested that clasp designs should be changed depending on abutment materials.

Growth and differentiation of periodontal ligament-derived cells in serum-free defined culture

We have developed a serum-free medium for the growth and differentiation of periodontal ligament-derived cells (PLC). In addition, the expression of both fibroblast growth factor (FGF) and FGF receptor (FGFR) in the PLC was investigated by immunohistochemical examination, heparin affinity chromatography (HAC), and reverse transcription-polymerase chain reaction (RT-PCR) analysis. Optimal growth of the cells was achieved in Iscove's modified Dulbecco's medium supplemented with insulin, transferrin, 2-mercaptoethanol, 2-ethanolamine, sodium selenite, and oleic acid in type-I collagen-coated dishes. Both FGF-1 and FGF-2 stimulated cell growth and inhibited differentiation as measured by inhibition of alkaline phosphatase activity of the cells. An immunohistochemical analysis of FGF-1 and FGF-2 revealed that immunoreactive FGF-1 and FGF-2 were detected predominantly in the cytoplasm of growing cells. In addition, perinuclear FGF-1 staining and nuclear FGF-2 staining were observed in the same growing cells. In contrast, a faint diffuse staining of FGF-1 and FGF-2 was detected in cytoplasm of the confluent differentiated cells. The 2.15 M NaCl eluate from HAC of the cell extracts exhibited growth-promoting activities for the PLC, and it also stimulated the growth of human umbilical vein-derived endothelial cells and inhibited binding of [125I]-FGF to its receptors, indicating the cells produced FGFs or FGF-like growth factors. RT-PCR analysis revealed that the cells expressed FGFR-1 mRNA but not mRNAs for FGFR-2, FGFR-3 and FGFR-4 mRNA. These results suggest that the FGF-FGFR-1 system plays an important role in the growth and differentiation of periodontal ligament-derived cells.

Characterization of a cartilage-derived 66-kDa protein (RGD-CAP/beta ig-h3) that binds to collagen

A 66-kDa collagen fiber-associated protein (RGD-CAP) was isolated from a fiber-rich fraction of pig cartilage by ultrafiltration and collagen-affinity chromatography. Amino acid sequencing and cDNA cloning indicated that the RGD-CAP is identical or closely related to beta ig-h3 protein which is induced in human adenocarcinoma cells by transforming growth factor-beta (TGF-beta) (Skonier, J., Neubauer, M., Madisen, L., Bennett, K., Plowman, G.D., and Purchio, A.F. (1992) DNA Cell. Biol. 11, 511-522). The RGD-CAP, as well as beta ig-h3, has the RGD sequence in the C-terminal region. The native RGD-CAP bound to type I, II, and IV collagens even in the presence of 1 M NaCl. A recombinant preparation of RGD-CAP expressed in Escherichia coli cells also bound to collagen but not to gelatin. The RGD-CAP mRNA was expressed in chondrocytes throughout all stages, although the expression level was highest during the prehypertrophic stage. In addition, TGF-beta increased the RGD-CAP mRNA level in chondrocyte cultures. Since RGD-CAP transcripts were found in most tissues, this novel collagen-binding protein may play an important role in cell-collagen interactions in various tissues including developing cartilage.

Trabecular bone pattern of the mandible. Comparison of panoramic radiography with computed tomography

OBJECTIVES

To analyse the possible correlation between the trabecular bone pattern of the edentulous mandible visualized by panoramic radiography and the bone mineral density (BMD) measured by computed tomography (CT).

METHODS

Panoramic radiography and CT were performed on 28 patients with edentulous mandibles. The trabecular bone pattern of 47 regions on the panoramic radiographs was classified into one of five grades. BMD was measured within circular regions of interest on the axial CT images in the corresponding trabecular area. The gradings were correlated with the CT values using one-way analysis of variance.

RESULTS

There was a significant correlation between the grade of the trabecular bone pattern and the BMD (P < 0.0001).

CONCLUSION

The proposed classification for the trabecular bone pattern on panoramic radiographs might be a useful aid for the evaluation of the edentulous mandible prior to implant placement.

Observer agreement in the assessment of mandibular trabecular bone pattern from panoramic radiographs

OBJECTIVES

To study the observer agreement in the assessment of trabecular pattern of the mandible from panoramic radiographs.

METHODS

Seven observers were asked to classify the trabecular pattern of 100 edentulous regions of the mandible in 80 randomly selected panoramic radiographs into one of five grades with the aid of a written description and reference images. Intra- and interobserver agreement was calculated as overall agreement and Kappa index.

RESULTS

The intra-observer agreement varied between 65% and 79%. The Kappa index for intra-observer agreement was moderate for three observers and substantial for four. For all seven observers, it varied according to the grade of trabecular bone pattern, but the majority deviated from each other by only one grade.

CONCLUSION

The relatively high rates of observer agreement indicate that panoramic radiography can be used for the clinical assessment of the trabecular pattern of the mandible.

Stimulation of platelet-activating factor synthesis by neurotransmitters in salivary glands

Platelet-activating factor (PAF), a phospholipid mediator exhibiting potent biological activities, has been shown to stimulate amylase release from the pancreas and salivary glands. The capacity of salivary glands for PAF biosynthesis in response to stimulation has also been demonstrated. To elucidate the role of PAF in salivary glands, we studied the regulation of platelet-activating factor synthesis by the autonomic nervous system in canine salivary glands. Acetylcholine and ionomycin stimulated PAF production in dispersed cells from parotid, submandibular, and sublingual glands of dogs. Norepinephrine and phenylephrine, but not isoproterenol, also stimulated PAF production in submandibular gland cells. Norepinephrine-induced PAF production was blocked by phentolamine but not by propranolol. Acetylcholine and norepinephrine increased both the PAF production and liberation of [14C]arachidonic acid from cells pre-labeled with [14C]arachidonic acid in the presence of Ca2+ in the medium. These stimulants increased [14C]arachidonic acid liberation without the accompanying production of PAF in Ca(2+)-deprived medium. No activators or inhibitors of protein kinase C produced or affected acetylcholine-induced PAF production. Lyso-PAF:acetyl-CoA acetyltransferase was activated in the cells treated with acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP. Deprivation of Ca2+ in the medium markedly reduced acetylcholine-induced activation of the transferase, but little affected norepinephrine-, isoproterenol-, and 8Br-cyclic AMP-induced activation. Dithiothreitol-insensitive cholinephosphotransferase activity was also increased by acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP, and the deprivation of Ca2+ in the medium further increased the activation of the enzyme activity by these agents. These results suggest that PAF synthesis in canine salivary glands is under the control of muscarinic cholinergic and alpha-adrenergic systems via Ca(2+)-dependent remodeling pathways, and that the independent activation of either phospholipase A2 or acetyltransferase is insufficient for PAF production in submandibular gland cells, i.e., the concurrent activation of these enzymes is required.

Correlation between mucosal inflammation and marginal bone loss around hydroxyapatite-coated implants: a 3-year cross-sectional study

In this study, a possible correlation between peri-implant mucosal inflammation and marginal bone loss in a group of patients who received two-stage hydroxyapatite-coated dental implants was evaluated 3 years after implantation. Thirty-two implants were evaluated as to their Plaque Index, Gingival Index, and crevicular fluid volume. Patients were divided into three groups: a control group with no inflammatory signs; a borderline group with moderate inflammation; and a gingivitis group with an established inflammatory process. Three dental radiographs per implant were analyzed at 2 months, 9 months, and 3 years after implantation by measuring bone height at the mesial and distal sides. Preliminary results indicated increased bone resorption in the gingivitis group compared with the control and borderline groups at both the mesial and distal surfaces (P < .05), suggesting correlation between mucosal inflammation and marginal resorption observed around these implants. Statistical analysis of correlation between the assessed mucosal parameters and bone loss indicated significance for Gingival Index and crevicular fluid volume (P < .05).

An in vitro study of high-strength resin posterior denture tooth wear

This in vitro study evaluated the wear resistance of a high-strength resin posterior denture tooth against eight opposing dental materials. The tooth specimen was cusp shaped and the opposing materials were formed as a 10 x 10 x 5 mm plate. All material combinations were tested using a machine designed to produce sliding contact 20 x 10(4) times at 60 cycles per minute and a 4-mm sliding distance per stroke in the buccolingual direction under a load of 1 kg. Wear analysis was measured as the total height loss of each material combination and the volume loss of each material. Wear against human enamel was evaluated as a control. The least loss was observed opposing a gold-silver-palladium-copper alloy, and the greatest loss was observed opposing porcelain. The volume loss of high-strength resin against gold-silver-palladium-copper alloy was as small as that against human enamel. High-strength resin wear was more significant against castable ceramics and porcelain. The volume losses of high-strength resin against high-strength resin, polycarbonate, or cobalt-chromium alloy were significantly larger than those against polyethersulfone, poly(methyl methacrylate), gold-silver-palladium-copper alloy, or human enamel. These findings suggest that the were resistance of high-strength resin is influenced considerably by opposing dental materials, and that the best combination was high-strength resin-gold-silver-palladium-copper alloy, and the poorest combination was high-strength resin-porcelain.

The three-dimensional bone interface of an osseointegrated implant. II: A morphometric evaluation after three months of loading

To clarify the three-dimensional bone structure around two plasma-sprayed hydroxyapatite-coated titanium implants loaded for 3 months in a monkey, computer graphic evaluation was performed after computer-assisted integration of 70 serial buccolingual sections at 75 microm intervals. Quantitative analysis of the bone contact ratio (BCR) was also conducted with programmed software. The graphics revealed the macroscopic bone structure. The BCR values varied in portions from the top to the bottom of the implant and in the buccolingual or mesiodistal directions. Because these two implants had more cortical bone at the top portion in the lingual direction, the BCR was greatest in the lingual direction. The BCR values at the bottom portion of the two implants were greater than those at the top portions along the horizontal plane, which suggested the effect of loading. The lowest BCR value was observed at the top portion of one implant at a site where moderate periimplant gingivitis was observed. The total surface BCR value for the implants was 69.3% and 64.5%. These results provide additional detailed information on the bone structure around the hydroxyapatite-coated implant after short-term loading.

The three-dimensional bone interface of an osseointegrated implant. I: A morphometric evaluation in initial healing

Direct bone-implant interface as an indicator of endosseous implant success appears to have been overinterpreted because 100% bone apposition is not necessarily obtained at the surface of the endosseous dental implant. The purpose of this study was to obtain quantitative information about the three-dimensional bone structure around three hydroxyapatite-coated titanium alloy dental implants. Implants were placed in the mandible in three monkeys, and the surface bone contact ratio in the buccal, lingual, mesial, and distal directions was computed. Computer graphics were generated by the integration of data for serial ground surfaces obtained at 75 microm intervals of the tissue block involved with the implant. The bone contact ratio of the whole surface of each of the three implants was 80.8%, 68.1%, and 68.8%, and the bone contact ratio for each direction and portion varied with the conditions of implant placement. The bone volume ratios around the implant at the 0 to 300 microm zone were also calculated, and total ratios ranged from 58% to 81%. These results may provide useful quantitative information about the bone structure around the hydroxyapatite-coated implants and contribute to the development of realistic finite element analysis models based on the biologic bone structure around the implants.

Isolation and characterization of teichoic acid-lake substance as an adhesin of Staphylococcus aureus to HeLa cells

A cell wall component that bound to HeLa cells (HeLa cell-binding CWC) was isolated from a clinical isolate of Staphylococcus aureus. The HeLa cell-binding CWC was resistant to heat (100 C, 1 hr) and proteases, did not stain with Coomassie Brilliant Blue R-250 on SDS-PAGE but stained as a broad band with antiserum against the strain on Western blots. These data suggest that the HeLa cell-binding CWC is not a protein, and may be teichoic acid. Purified teichoic acid bound to HeLa cells, whereas fractions without teichoic acid did not. In Western blots, HeLa cell-binding CWC appeared as a broad band of less than 35 kDa, similar to that of purified teichoic acid. These data suggest that the HeLa cell-binding CWC obtained in this study is teichoic acid. Teichoic acid inhibited S. aureus adherence to HeLa cells and bound to the cells time and dose dependently, in a saturable and reversible manner, and therefore appears to be an adhesin of S. aureus to HeLa cells.

Hardness and fracture toughness of four commercial visible light-cured composite resin veneering materials

Four commercial visible light (VL)-cured composite resin veneering materials with a dentine shade were examined for their Knoop hardness and fracture toughness. Composite specimens were classified into three groups. The first group was cured by VL only, the second group was cured by VL and post-cured by VL and the third group was cured by VL and post-cured by heat. It became evident that one composite containing four-functional urethane monomer had both hardness and fracture toughness greater than those of the other three composites containing two-functional urethane monomer. The filler content (vol%) in the composite tended to be linearly proportional to both hardness and fracture toughness. Post-curing by VL and heat were proven to effectively increase both hardness and fracture toughness of once light-cured composites. These results suggest that the clinical performance (e.g. wear resistance and colour stability) of VL-cured composite resin veneering materials might be improved with the aid of post-curing.

An investigation of preferable taper and thickness ratios for cast circumferential clasp arms using finite element analysis

This study used a two-dimensional finite element method to investigate the preferred design for a cast circumferential clasp. Finite element models of the clasp arm with the constant flexibility were constructed, the stress was calculated, and the effects of taper and cross-sectional shape on stress were evaluated. The clasp arm with the taper of 0.8 showed less stress than those with other tapers, and the thinner and wider arms showed less stress than those with other cross-sectional dimensions. These results suggest that the use of the preformed clasp-pattern with a taper of 0.8 is preferable for reducing fatigue and/or permanent deformation of the clasp arm.

The effects of a stress-absorbing system involved in the superstructure supported by hydroxyapatite-coated implants in monkeys

To evaluate the effects of a stress-absorbing superstructure on the interface of an integrated implant, the bone/hydroxyapatite-coated (HA-coated) implant interface was histologically and histomorphometrically analyzed using monkeys. A total of 12 HA-coated implants were placed in the edentulous mandible of three monkeys. Polyurethane elastomer was selected as the stress-absorbing material. A superstructure incorporating a stress-absorbing system was placed on six implants (stress-absorbed group) and a superstructure without such a system was set on the other six implants (non-stress-absorbed group). After 12 months, undecalcified ground sections were prepared and the bone/implant interface was analyzed. Clinically, all implants in both groups were immobile and mild inflammation around the peri-implant gingiva was seen. Histologically, direct bone contact was observed around all of the implants in both groups. However, histomorphometrically, the amount of bone around implants was greater in the stress-absorbed group. Bone was more highly apposed to the implant at the apical portion than at the axial portion. These different findings could be the result of stress-breaking against functional loading to the bony interface of these HA-coated implants.

Periodontal tissue regeneration on the surface of synthetic hydroxyapatite implanted into root surface

Several studies have demonstrated that periodontal ligament (PDL)-derived cells can form a new connective tissue attachment (NCTA) not only on denuded dentin but also on nondental inorganic materials. Although the cellular response to these materials may be different than that to denuded dentin, the process of NCTA formation on the surface of non-dental inorganic materials is still undetermined. In the present study, we compared the process of NCTA formation on the surface of an inorganic material with that on a denuded root surface by implanting a block of synthetic hydroxyapatite (HA) into a root cavity prepared on the first molar of a rat. We then observed tissue regeneration under conditions where the PDL-derived cells could populate the HA surface using an occlusive membrane. After fibrinous exudation at 3 days postoperatively, granulation tissue from the PDL filled the space between the HA block and the membrane at 1 week. Four weeks after the operation, although the granulation tissue increased in density at the interface to the HA block, no obvious deposition of cementum-like tissue was seen on the HA block. Six weeks after the operation, the deposition of cementum was observed on the surface of the HA block. The deposition of cementum became more extensive and insertion of collagen fibers into the cementum layer became more obvious 8 weeks postoperatively. Twelve weeks after the operation, the cementum covered almost the entire surface of the HA block. On the surface of the denuded dentin in control teeth, cementum deposition was seen at 4 weeks after the operation and increased in thickness from 6 weeks on.(ABSTRACT TRUNCATED AT 250 WORDS)

Finite element and Weibull analysis to estimate failure risk in resin-bonded retainers

Three-dimensional finite element analysis and Weibull analysis were used to evaluate the effect of the thickness and the rigidity of the retainers on the risk of failure of an anterior resin-bonded prosthesis. Retainer thickness ranged from 0.4 to 1.4 mm. The physical properties of metals similar to Ni-Cr and type IV gold alloys were used. A concentrated load (100 N) was applied to the incisal edge of the finite element analysis modeled pontic, and the data of other loads (150 to 500 N in 50-N increments) were calculated from the data of 100 N. Subsequent Weibull analysis revealed that failure probability diminished when there was an increase in metal thickness at loads of 300 to 350 N, particularly for the retainer made of a type IV gold alloy. The reduction in failure probability caused by increasing the thickness of the metal was greater when type IV gold alloy was used than when Ni-Cr alloy was used. This investigation suggests that the longevity of resin-bonded retainers can be prolonged by thickening the retainers, rather than using more rigid metals.

New connective tissue attachment formation on various biomaterials implanted in roots

To determine whether connective tissue attachment can occur on implant materials by repopulating periodontal ligament (PDL)-derived cells and whether the new connective tissue attachments formation is influenced by the type of implant materials, periodontal tissue regeneration on four materials implanted into root cavities of cat canines was observed under conditions where PDL-derived cells could populate the surface of the materials. New connective tissue attachment occurred on bioactive materials such as bioglass and hydroxyapatite, while little or no cementum deposition was seen on bioinert materials such as titanium alloy and partially stabilized zirconium. Results showed that PDL-derived cells can form new connective tissue attachments on implant materials and that the formation of new connective tissue attachment is influenced by bioactivity of the materials.

New periodontal ligament formation on a synthetic hydroxyapatite surface

The aim of this study was to investigate whether a new connective tissue attachment can occur on a surface of hydroxyapatite (HA) when periodontal ligament (PDL)-derived cells with the ability to form new connective tissue attachment are allowed to populate the surface of HA. Six maxillary canines from 3 cats were used for this experiment. Under anesthesia, fenestration of the buccal alveolar bone was performed over the canine root and a cavity was prepared on the root surface. A synthetic HA block was inlaid and cemented into the root cavity. A Teflon membrane was then placed to cover the access opening of the alveolar bone to guide PDL-derived cell proliferation into the surface of the HA block. Finally, the gingival tissue flap was replaced and sutured. Six months after the operation, histologic evaluation was done by serial sections. In 4 of the 6 canines, PDL-derived cells successfully populated the HA surfaces and a layer of cementum-like tissue was formed on the HA blocks. A PDL-like connective tissue layer was seen between the cementum-like layer covering the exposed HA surface and the newly formed alveolar bone sealing the bone fenestration. Collagen fibers in the PDL-like tissue inserted their ends into the newly formed bone and the cementum-like tissue. The present findings demonstrated that PDL-derived cells can form a new connective tissue attachment on HA.

Interface histology of unloaded and early loaded partially stabilized zirconia endosseous implant in initial bone healing

Clinical and histologic evaluations of partially stabilized zirconia endosseous implants under unloaded and early loaded conditions in four beagle dogs were performed to examine the possibility of osseointegration of a newly developed one-stage zirconia implant during initial bone healing. No clear difference in clinical features was observed. Direct bone apposition to the implant was generally seen in both implants. However, loss of crestal bone height was quite evident around the loaded implants. These findings suggest that the initial unloaded condition is preferable to achieve osseointegration of one-stage zirconia implants.

Changes of subgingival microflora around single-crystal sapphire endosseous implants after experimental ligature-induced plaque accumulation in monkeys

A study was performed to evaluate the change of subgingival microflora with plaque accumulation around the single-crystal sapphire implant. Four implants were inserted into mandibular and maxillary edentulous regions, and the super-structure was inserted 1 month after implant insertion in each of nine monkeys. Plaque control was maintained for 3 months after insertion to establish the baseline. Plaque was allowed to accumulate on one side by placement of ligatures around the implants and natural teeth with no plaque control. On the other side plaque control was continued for 9 months. Both the implants and natural teeth on the ligature side showed significant increases in proportions of motile rods and spirochetes. No significant difference of microflora was detected between the implants and natural teeth. These findings indicate that plaque control is necessary to maintain the normal microflora around the implant.

The effects of early occlusal loading on one-stage titanium alloy implants in beagle dogs: a pilot study

The initial stages of bone healing with titanium alloy implants were compared clinically and histologically in three groups of beagle dogs: unloaded one-stage (group 1), loaded one-stage (group 2), and unloaded two-stage (group 3). No implant mobility was reported in any of the three groups. For the most part direct bone contact was achieved, but there was a significant difference in the histologic results of the interface among the animals in all three groups. Significant crestal bone loss was evident in group 2, which showed poor bone apposition to the bottom of the threads in the upper portion of the implant. New bone growth to these same areas of the threads was seen in the animals in groups 1 and 3, with the ratio of direct bone contact significantly higher for those in group 3. These differences could be attributed to the effect of early occlusal loading on the implant during initial bone healing.