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PubMed2006

The monocortical critical size bone defect as an alternative experimental model in testing bone substitute materials.

BACKGROUND: Reproducibility and comparability are prerequisites in testing bone substitute materials in an animal study. Various animal test models are used. The standard in testing bone substitute materials is the so-called critical size defect (CSD) model described by Schmitz and Hollinger. In most studies a bicortical (full thickness defect) CSD is used. OBJECTIVE: In this study, monocortical defects (10 x 10 mm) in calvarias of adult pigs were created and compared to examine the spontaneous physiologic healing process and the required criteria for a CSD. STUDY DESIGN: Regeneration of defects, either filled using autogenous bone (group 1) or unfilled (group 2), was evaluated by means of microradiography and light microscopy after 2, 4, 12, 26, and 52 weeks. RESULTS: No complete osseous regeneration was found microradiographically and light microscopically in the control group at week 52 (nonmineralized area: 30% +/- 1.7%; mineralized area: 55% +/- 1.7%; bone marrow area: 15% +/- 1.7%). Defects treated with autogenous bone showed a 100% osseous defect filling after 26 weeks. CONCLUSION: The monocortical CSD fulfills the requirements for a CSD and represents a procedure which can be handled simply for investigations focusing on bone regeneration and testing of bone substitute materials.

Animals↗
PubMed1998

In vitro testing of bioprostheses: influence of mechanical stresses and lipids on calcification.

BACKGROUND: Structural valve deterioration of bioprostheses is mainly caused by the progressive development of calcification. Mechanical stresses or lipid deposits in porcine aortic leaflets have been proposed as major factors contributing to the calcification process. METHODS: A new test protocol consisting of nondestructive holographic interferometry, which allows a quantitative deformation analysis of heart valves, and accelerated dynamic in vitro calcification was used. The rapid calcification fluid contained a final combined calcium and phosphorus concentration of 130 (mg/dL)2 in barbital buffer solution. The calcification of 32 bioprostheses donated by different manufacturers (SJM Bioimplant, Biocor standard, Biocor No-React, Carpentier-Edwards SAV, Bravo, pericardial prototype) was assessed after up to 25 x 10(6) cycles by microradiography and the areas of calcification were compared with the holographic interferograms. The distribution of lipid droplets of four porcine prostheses were visualized by Sudan III stain before the calcification process. RESULTS: Most of the tested bioprostheses had areas presenting with stress concentrations, and the dynamic in vitro testing resulted in leaflet calcification corresponding to the holographic irregularities. A strong correlation between calcification and stress distribution or lipid accumulation was found (r = 0.72; r = 0.81, respectively). After 19 x 10(6) cycles, the Carpentier-Edwards SAV and the pericardial valves had significantly less calcification than other prostheses tested (p = 0.003), but the variation among individual prostheses from the same manufacturer was even more pronounced. CONCLUSIONS: Mechanical stresses or lipid accumulation seems to play an important role in the calcification process of bioprostheses. Quality control of bioprosthetic valves using holographic interferometry has the potential to predict calcification before implantation.

Aortic Valve↗
PubMed2001

Eroded enamel lesion remineralization by saliva as a possible factor in the site-specificity of human dental erosion.

The composition and flow of saliva, which determine its functions, vary within intraoral sites and among individuals. Also, the susceptibility to tooth erosion reportedly varies among individuals and within the dental arches. A possible effect of saliva on early-eroded lesions may be a contributory factor. The aims here were firstly to determine the remineralization of eroded enamel lesions by saliva, and secondly to investigate any variation of this remineralization within the dental arches and among individuals. Early enamel erosion was produced on human premolars using orange juice. Control sections and two test slabs were cut from each tooth. The two slabs from the same lesion were bonded with composite resins to the palatal surface of upper right lateral incisor teeth and the lingual surface of the lower right lateral incisor teeth of volunteers, who then chewed a sugar-free gum four times daily. After 28-day intraoral exposure, mineral loss (DeltaZ) and lesion depth (ld) were quantified using microradiography and the data analysed by paired t-test (n=10, alpha=0.05). Mean DeltaZ was significantly lower in the group of slabs positioned palatally (P<0.001) and lingually (P<0.001) when compared with the control group, and in the lingually placed group when compared with the palatally positioned (P<0.01). A significantly lower ld was observed in the group of slabs positioned palatally (P<0.05) and lingually (P<0.001) when compared with the control group, and in the lingually positioned group when compared with the palatally placed (P<0.05). It was concluded that saliva can remineralize early enamel erosion, and that the degree of remineralization varies within intraoral sites and may be responsible for the differing susceptibility to erosion within the dental arches.

Adult↗
PubMed2003

A study investigating the formation of artificial sub-surface enamel caries-like lesions in deciduous and permanent teeth in the presence and absence of fluoride.

OBJECTIVES: Clinical and in situ studies have shown that caries formation and progression is faster in primary than in permanent teeth. Ambient levels of fluoride are also known to influence the processes of carious lesion formation. The aims were, firstly to investigate the incidence of artificial sub-surface caries lesion formation in the enamel of deciduous and permanent teeth in vitro. Secondly, to compare quantitatively the mineral content and distribution of these lesions and assess the possible influence of fluoride upon the lesion parameters. METHODS: Twenty primary molars and 20 permanent premolars were randomly assigned to one of four experimental groups. Samples in each experimental group were immersed in a 0.05M lactic acid gel (6% w/v hydroxyethyl cellulose, pH 4.5) either in the absence or presence of fluoride for 7 days. Subsequently, lesion parameters of mineral loss (vol x % microm) and lesion depth (microm) were assessed by transverse microradiography and image analysis. RESULTS: No significant differences existed between the lesion parameters of permanent and primary teeth (P=0.20). Irrespective of tooth type, lesion parameters were significantly reduced in samples demineralised in the presence of fluoride (P< or =0.002). CONCLUSIONS: Fluoride significantly reduces the severity of sub-surface caries lesions formed in vitro and in contrary to previous studies, there were no significant differences in lesions parameters between permanent and primary teeth.

Cariogenic Agents↗
PubMedDate not supplied

Effect of ascorbic acid deficiency on primary and reparative dentinogenesis in non-ascorbate-synthesizing ODS rats.

Ascorbic acid is essential to the biosynthesis of collagen, the major organic matrix component of dentine. The ODS rat is a mutant strain of Wistar rat characterized by hereditary lack of L-gulono-gamma-lactone oxidase and thus is unable to synthesize ascorbic acid. ODS rats were given an ascorbic acid-free diet to investigate how ascorbic acid deficiency affects dentine formation in vivo. Histomorphometric analysis on their growing molars and incisors showed a significant reduction in both size and mineral apposition rate of dentine, as revealed by contact microradiography and fluorescent time-marking, respectively. A similar reduction in bone formation was simultaneously demonstrated in the mandible, confirming the previously reported osteopathic effects of ascorbic acid deficiency. When pulp inflammation was induced in lower first molars by making unsealed pulp exposures, specimens from control animals showed continuous deposition of an osteodentine-like tissue in the radicular pulp chamber; this type of mineralized tissue formation was greatly reduced in ascorbic acid-deprived animals. These results indicate that ascorbic acid deficiency hampers dentine formation under both physiological and pathological conditions of the dentine/pulp complex. ODS rats could be useful in investigating in vivo effects of ascorbic acid deficiency on the formation of dentine and other dental mineralized tissues.

Animals↗
PubMed1998

A pilot study of mineralization distribution in the cortical bone of the human mandible.

Twenty-three specimens from immediately anteroinferior to the mental foramen were obtained from male and female, dentate and edentate, human mandibles. Planoparallel 80 microm thick sections were prepared from the mandibular specimens and computerized quantitative microradiography undertaken, which allowed the production of mineralization frequency distribution curves and mean mineralization. No differences in mean mineralization with age, sex, presence or absence of dentition were found, but mineralization distribution curves indicated differences between males and females. Within the age range and small sample size examined (40-90 years) there were no age-related differences. There was a lower level of mineralization distribution in the edentulous than the dentate mandible.

Adult↗
PubMed1988

Dry mass and water content in the corneal epithelium and superficial stroma during healing of corneal alkali wounds.

The dry mass contents of the rabbit corneal epithelium and of the superficial stroma were determined during healing of a standardized corneal alkali wound. Quantitative microradiography was applied to freeze-sectioned corneal specimens. This method allows a morphological resolution of the order of 1 micron and quantitative dry mass determinations in volumes down to about 100 microns 3. For comparison, the epithelial morphology was studied using Toluidine Blue stained sections. Flat epithelial cells covered the wound surface during the first day, the dry mass content being equivalent to that of the normal wing cells. The dry mass content in the epithelium and, indirectly, the water content, followed the hydration state of the superficial stroma. A progressive thickening of the epithelium and a varying morphological picture were found during the first 2 months following initial damage. Normal thickness and cytoarchitecture were found after 6 months. Generally, the dry mass content of the epithelium was reduced compared with physiological values for 2 months. Later, the cells close to the stroma regained normal values. Cells in the middle zone and the superficial zone reached normal values after 6 months. The significance of the endothelial damage for the hydration state of the epithelium was discussed.

Animals↗
PubMed1998

A waveguide-based acoustic microscope.

A new instrument is presented which is capable of high resolution acoustic imaging at relatively low frequencies. This approach results in increased complexity of the signal processing required and reduced throughput of the instrument. However, these disadvantages are amply compensated by the ability to create velocity scan images of materials with either high attenuation or low material velocities. These measurements are not possible using traditional/acoustic microscopes. The initial performance of the new instrument is demonstrated using thin samples of shim materials to show that acceptable spatial resolution and highly accurate time delay measurements are possible. An application is then shown using the instrument to evaluate subchondral sclerosis in horse bones. It has been hypothesized that changes in the elastic modulus may be associated with fatigue-induced microdamage. The modulus change may further represent bone damage which precedes the development of microcracking. Thin samples are used to allow complementary microradiography to be performed on the bone slices. Because of the low material velocity, surface wave interference methods (so called V(z) curves) are not well suited for use in some bone samples. The thickness of the samples eliminates the potential for the samples to be evaluated using pulse-echo time delay measurements. The new instrument is thus unique in its ability to create velocity scans of these samples.

Animals↗
PubMed1994

A comparative study of osseointegration of titanium implants in corticocancellous block and corticocancellous chip grafts in canine ilium.

PURPOSE: This study was undertaken to compare the relative rates and extent of osseointegration of dental implants when placed simultaneously with either corticocancellous block or particulate corticocancellous bone grafts. MATERIALS AND METHODS: Using the canine ilium as a model site, the implants were placed so that each served as its own control. The implants were harvested at 1, 2, or 3 months for evaluation by light microscopy, microradiography, and histomorphometry. RESULTS: Both types of grafts were determined to be viable by microscopic evaluation of fluorescent labels. Qualitatively there appeared to be greater bone density in the corticocancellous block graft implant sites. At 3 months, the block graft implant sites had a level of osseointegration (59.6%) that approximated the control implant sites (65.2%), but was significantly greater than the particulate graft sites (39.2%). CONCLUSIONS: These results indicate that implants in corticocancellous block grafts develop osseointegration more rapidly than those in particulate bone grafts. The clinical implications of these findings are discussed.

Animals↗
PubMed1996

Histologic study of the effect of hyperbaric oxygen therapy on autogenous free bone grafts.

PURPOSE: This study was undertaken to evaluate the effect of hyperbaric oxygen therapy on autogenous free bone grafts transplanted from iliac crest to the mandibles of rabbits. MATERIALS AND METHODS: A piece of corticocancellous bone harvested from iliac crest was grafted to a same-size bone defect in the mandibles of 16 Japanese white rabbits. In 8 rabbits, 20 and 10 sessions of hyperbaric oxygen (HBO) treatment were carried out twice per day (2.4 ATA 60 min.) before and after operation, respectively. The other 8 rabbits served as controls. The graft and surrounding bone were sampled at 1, 2, 4, or 8 weeks after transplantation, and the effects of HBO were evaluated by light micrography and contact microradiography. RESULTS: At 1 week after grafting, osteoid formation in the experimental group was much greater than in the control group. Union between the grafted and the host bone was observed in the experimental group at 2 weeks after grafting, but it was not observed in the control group until 4 weeks. Although it was difficult to differentiate grafted from host bone in the experimental group at 4 weeks, it was readily distinguishable in the control group. CONCLUSIONS: These results indicate that HBO accelerates the union of autogenous free bone grafts.

Animals↗
PubMed1997

Repair of craniofacial defects with hydroxyapatite cement.

PURPOSE: The objective of this study was to evaluate the course of healing of craniofacial bone defects when filled with hydroxyapatite cement and to determine whether adding various percentages by weight of demineralized bone powder to the cement will result in enhanced bone formation. MATERIALS AND METHODS: The model for the study was the canine calvarium. The implants were placed into cranial defects and harvested at 3 or 6 months for qualitative evaluation by light microscopy, microradiography, and quantitative histomorphometry. RESULTS: The implantation of hydroxyapatite cement resulted in characteristic replacement of the material with new bone ingrowth. The addition of demineralized bone powder to the hydroxyapatite cement appeared to improve the handling characteristics of the cement; however, improvement in the replacement of the material by bone was not observed. The implantation of only allogeneic demineralized bone showed limited new bone formation within the defect site. CONCLUSIONS: Hydroxyapatite cement formed an effective osseoconductive scaffold for bone replacement. The addition of demineralized bone powder to the cement to serve as a carrier of osseoinductive factors did not result in additional bone being formed.

Animals↗
PubMed2001

In vitro remineralisation of eroded enamel lesions by saliva.

OBJECTIVES: It is speculated that saliva, with its mineral content, may possess a reparative effect on an early erosion which is characterised by softened surface and slight subsurface demineralisation in addition to a crater. This study aimed to determine the possible remineralisation of early enamel erosion by saliva. METHODS: Eroded lesions were produced in bovine incisors by 1-h immersion in orange juice. Control sections and three experimental slabs were produced from each tooth. The three slabs were assigned randomly to one of three remineralising agents: clarified natural saliva (NS), artificial saliva (AS) and remineralising solution (RS). All solutions had a pH of 7.2, a fluoride concentration of 0.022 ppm, and were changed daily. NS was collected daily from the same individual at the same time of day. The specimens were exposed to their respective remineralising agents for 28 days. Using microradiography and image analysis, the mineral loss (Delta z) and lesion depth (ld) were quantified in sections cut from the control and experimental slabs. RESULTS: A significant (p<0.001) amount of mineral was gained following exposure to each remineralising agent. Significantly less Delta z and ld were observed for the experimental groups compared with the control group (p<0.001; paired t-test). This effect was greatest with RS and least with AS. Inter-group comparison (Duncan multiple tests) showed no significant difference in Delta z among the experimental groups, however ld was significantly higher for AS (p<0.001) compared with RS and NS, and no difference was observed between RS and NS. CONCLUSION: Saliva as well as remineralising solutions can remineralise early enamel erosion.

Animals↗
PubMed2003

The erosive potential of commercially available mouthrinses on enamel as measured by Quantitative Light-induced Fluorescence (QLF).

DESIGN: Longitudinal in vitro. METHODS: Previously extracted, caries free, human premolars were selected and prepared by gentle pumicing and coating in an acid-resistant nail-varnish save for an exposed enamel window on the buccal surface. Each was assigned to one of eight groups (six per group, 10 in positive control); positive control (citric acid, pH 2.7, F(-) 0 ppm), negative control (pH 7.0, F(-) 0 ppm) Listerine (pH 3.87, F(-) 0.021 ppm), Tesco Value (pH 6.05, F(-) 289.00 ppm), Tesco Total Care (pH 6.20, F(-) 313.84 ppm), Sainsbury's (pH 6.15, F(-) 365.75 ppm), Sensodyne (pH 6.12, F(-) 285.30 ppm) and Corsodyl (pH 5.65, F(-) 0 ppm). The titratable acid values (TAV) for each rinse were established using volume (ml) of 0.1 M NaOH to achieve pH 7. Fluoride values were obtained by ion selective electrode. The solutions were kept at 37 degrees C and gently agitated. Teeth were removed at hourly intervals for 15 h, air-dried and subjected to Quantitative Light-induced Fluorescence (QLF) examination by a blinded examiner and DeltaQ values recorded. At the conclusion of the study each of the positive control teeth and one from each other group were sectioned through the eroded lesion, ground and polished to 100 micrometers and subjected to transverse microradiography and DeltaZ recorded for validation. RESULTS: TAVs were: Listerine 2.45 L > Sainsbury's 0.35 ml >Tesco Total Care 0.14 ml > Tesco Value 0.08 ml > Corsodyl 0.10 ml >Sensodyne 0.9 ml. DeltaQ increased over time for the positive control, (0 h 0.2, 10 h 95.2, 15 h 152.3). Negative controls remained stable. The increase in DeltaQ for each rinse after 15 h was Listerine (9.3(+/-7.2)), Corsodyl (1.5(+/-1.2)), Tesco Value (1.8(+/-1.2)), Tesco Total Care (1.4(+/-1.1)), Sainsbury's (3.4(+/-2.2)), Sensodyne (0.9(+/-1.6)). TMR confirmed the presence/absence of erosive lesions. CONCLUSIONS: QLF effectively monitored erosion in the positive controls and lack of erosion in the NC. Only one mouthrinse (Listerine) caused any erosion compared to the negative control, but this was only significant after 14 h of continuous use.

Analysis of Variance↗
PubMedDate not supplied

In vitro dentine fluoride uptake from three fluoride-containing composites and their acid resistance.

OBJECTIVES: The purpose of this study was to determine the dentine fluoride uptake from three fluoride-containing composites (FluorEver, FluoroCore and Pertac-Hybrid) and to investigate their ability to affect the resistance of dentine to an artificial caries challenge. METHODS: Three dentine slabs were prepared from each tooth. The baseline, total and bound fluoride concentrations of each tooth were determined by three successive abrasion biopsies performed on each slab followed by adjusting to standardized depths of 10 microns. Next, dentine slabs ligated with the composites were suspended in synthetic saliva for 1 week. After removal of the composites, these specimens and controls were immersed in an artificial caries medium (pH 4.5) for 5 days. Each slab was sectioned and analysed by quantitative microradiography. RESULTS: The results indicate that dentine acquired significantly different amounts of fluoride from the three composites. The acid resistance of dentine in contact with the composites was also significantly different among the composites and followed the same order as for fluoride uptake. CONCLUSIONS: Dentine fluoride uptake and artificial caries inhibition were significantly greater with FluorEver followed by FluoroCore and Pertac-Hybrid.

Biopsy↗
PubMed1998

In situ de- and remineralisation of enamel in response to sucrose chewing gum with fluoride or non-fluoride dentifrices.

OBJECTIVES: Enhancement of the remineralisation of artificial enamel lesions has been observed in an intraoral model whether subjects chewed gum sweetened with a non-cariogenic sweetener such as sorbitol [1-3] or sucrose [4] after meals or snacks, and with use of a conventional (1500 ppm F) fluoride dentifrice. Since most of the clinical surveys which have shown the potential cariogenicity of sucrose chewing gum [5] were conducted before use of fluoridated dentifrices became widespread, the effect of fluoride dentifrice on de- and remineralisation of artificial lesions in enamel in response to chewing sucrose-sweetened gum has been examined with the aim of attempting to resolve this apparent discrepancy. METHODS: Subjects wore an intraoral device bearing an enamel lesion and chewed one piece of sucrose gum for 20 min after each of three meals and two snacks daily for two 3-week periods, during which they used a dentifrice containing either 0 or 1500 ppm F in a double-blind, cross-over design. Measurement of the mineral content of the lesions was determined by microradiography or polarised light microscopy. RESULTS: It was found that remineralisation tended to occur with 1500 ppm F dentifrice, but demineralisation with non-F dentifrice; the difference in enamel mineral content between the two periods was significant (P < 0.05). CONCLUSIONS: The results indicate that the potential cariogenicity of sucrose-containing chewing gum may indeed be negated by the use of a conventional fluoride dentifrice.

Adolescent↗
PubMedDate not supplied

The effect of a resin-modified glass ionomer restorative material on artificially demineralised dentine caries in vitro.

OBJECTIVES: Recurrent caries is one of the most common reasons for the replacement of restorations. One method of reducing the frequency of this problem may be by using fluoride-releasing restorative materials. The aim of this in vitro study was to evaluate the progression of artificial lesions around resin-modified glass ionomer (Vitremer) restorations placed in root surfaces. Class V cavities were prepared on the mesial and distal surfaces of 28 human premolar teeth. Artificial carious wall lesions were created in all cavities. The root of each tooth was then hemisected through the middle of the two cavities, before being restored with either the glass ionomer or amalgam, while the opposing cavities on the same root portion were varnished as negative controls. Forty-eight specimens were pH-cycled in remineralising and demineralising solutions for 20 h and 4 h, respectively, each day for 4 weeks, whilst in a smaller control group of eight specimens, the demineralising solution was replaced with deionised water. Mineral changes in the carious lesions were evaluated using contact microradiography. RESULTS: Results showed that varying degrees of subsurface demineralisation and remineralisation were evident, with a laminated appearance in lesions adjacent to the glass ionomer. There was higher remineralisation in the glass ionomer-filled cavities compared with the amalgam-filled cavities. In the water-cycled group, glass ionomer showed an increase in mineral content (p < 0.05), while no changes were observed in the amalgam-filled cavities. CONCLUSIONS: This model has shown that glass ionomer has a greater potential than amalgam for remineralisation of artificially created wall lesions within an acidic environment.

Bicuspid↗
PubMed1981

Normal and retrograde blood supply to the body of the mandible in the dog. I. A new method for selective multicolor arterial perfusion, combined with microangiography and histology.

An experimental study was performed to evaluate a method for selective, multicolor arterial perfusion. In seven adult beagle dogs the lingual, facial and mandibular arteries on one side were cannulated and perfused selectively with different colored perfusates (Microfil and Colorpaque). Identification of the perfusates was achieved using a clearing technique combined with microradiography and histology. With this method, the vascular territories of the body of the mandible and its adjacent tissue could then be identified separately.

Angiography↗
PubMed1981

Normal and retrograde blood supply to the body of the mandible in the dog. II. The role played by periosteo-medullary and symphyseal anastomoses.

An experimental study was carried out in 8 dogs to delineate the blood supply to the body of the mandible under normal conditions and when the central (medullary) circulation was blocked. A vascular blocking technique combined with selective arterial perfusion using different colored perfusates was used. The results were based on an evaluation of cleared specimens, microradiography and histology. Under normal conditions, the inferior alveolar artery was shown to be the sole source of perfusate to the entire mandibular body, marginal gingiva and the subperiosteal layer, without any contribution from facial artery branches. Several perfused symphyseal anastomoses were found. When the medullary circulation was blocked, retrograde perfusion was evident only in the medullary bone of the frontal region 30 min. after blocking. Marked periosteal and symphyseal vascularity and an increased medullary perfusion were seen 3 days later. 30 days after vascular blocking, perfusion was demonstrated throughout the entire bone including dental pulps. The facial artery was found to be the source of the retrograde perfusion through symphyseal and periosteo-medullary anastomoses in cases with blocked central (medullary) circulation.

Angiography↗