Tissue pressure in rat oral mucosa measured by micropuncture technique

Edema in Oral Mucosa after LPS or Cytokine Exposure

Lowering of interstitial fluid pressure (Pif) is an important factor that explains the rapid edema formation in acute inflammation in loose connective tissues. Lipopolysaccharide (LPS) and the pro-inflammatory cytokines interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) are pathogenetic in gingivitis. To test if these substances induce lowering of Pif in rat oral mucosa, we measured Pif with a micropuncture technique. IL-1β and TNF-α caused lowering of Pif, whereas LPS induced an immediate increase in Pif, followed by lowering after 40 min. Measurements of fluid volume distribution showed a significant change in interstitial fluid volume (Vi) 1.5 hr after LPS exposure as Vi changed from 0.41 ± 0.02 to 0.51 ± 0.03 mL/g wet weight ( p < 0.05), confirming edema. These findings show that LPS, IL-1β, and TNF-α induce lowering of Pif in the rat oral mucosa and contribute to edema formation in LPS-induced gingivitis.

Biomechanics of oral mucosa

The prevalence of prosthodontic treatment has been well recognized, and the need is continuously increasing with the ageing population. While the oral mucosa plays a critical role in the treatment outcome, the associated biomechanics is not yet fully understood. Using the literature available, this paper provides a critical review on four aspects of mucosal biomechanics, including static, dynamic, volumetric and interactive responses, which are interpreted by its elasticity, viscosity/permeability, apparent Poisson's ratio and friction coefficient, respectively. Both empirical studies and numerical models are analysed and compared to gain anatomical and physiological insights. Furthermore, the clinical applications of such biomechanical knowledge on the mucosa are explored to address some critical concerns, including stimuli for tissue remodelling (interstitial hydrostatic pressure), pressure–pain thresholds, tissue displaceability and residual bone resorption. Through this review, the state of the art in mucosal biomechanics and their clinical implications are discussed for future research interests, including clinical applications, computational modelling, design optimization and prosthetic fabrication.

Osmotic pressure of periimplant sulcular and gingival crevicular fluids: a split-mouth, randomized study of its measurement and clinical significance

OBJECTIVES

This study comparatively investigated periimplant sulcular fluid (PISF) and gingival crevicular fluid (GCF) by means of the osmotic pressure (OP) levels of PISF (PISFOP) and GCF (GCFOP). It was a preliminary research that aimed to quantify PISFOP and GCFOP as well as to evaluate their clinical significances around implants and teeth.

MATERIAL AND METHODS

Partially edentulous implant patients treated by the same clinicians and using the same implant system were randomized in a split-mouth trial design. Fifty-four implants and teeth from these patients were selected in the same mouth and jaw as matched pairs of samples, i.e. as symmetrical or corresponding implant and tooth. PISFOP/GCFOP measurement was performed by an osmometer following PISF/GCF sampling procedures. Clinical significance was evaluated by the correlations between PISFOP/GCFOP and some clinical examination parameters of periimplant/periodontal soft tissues. These parameters included Silness-Löe plaque index (PI), Löe-Silness gingival index (GI), bleeding on probing (BOP), probing pocket depth (PPD) and probing attachment level (PAL).

RESULTS

PISFOP was higher than GCFOP, and GI, BOP, PPD and PAL were higher in the implant group than in the tooth group (P<0.05). PISFOP positively correlated with the clinical parameters of implants (P<0.01 for PI, GI and BOP; P<0.05 for PPD and PAL), and GCFOP positively correlated with the clinical parameters of teeth (P<0.01 for PPD; P<0.05 for PI, GI, BOP and PAL).

CONCLUSIONS

The results reveal that PISFOP and GCFOP may be measured by osmometer, and their levels may be related with the clinical conditions of periimplant/periodontal soft tissues.

Fluid dynamics of gingiva in diabetic and systemically healthy periodontitis patients

OBJECTIVES

The influence of diabetes mellitus (DM) on the fluid dynamics of periodontium has not been reported in periodontal disease. The objectives of this study were (i) to investigate the alterations in the fluid dynamics of periodontium in diabetic periodontitis patients, and present the association of this phenomenon with the metabolic control of DM; (ii) to reveal any correlation between the fluid dynamics of periodontium and clinical signs of periodontal disease in DM and periodontitis.

DESIGN

Fifteen well-controlled diabetic chronic periodontitis patients (Group 1), 14 systemically healthy chronic periodontitis patients (Group 2), and 14 systemically and periodontally healthy individuals were included in the study. Gingival crevicular fluid volume (GCF-V) and gingival tissue osmotic pressure (GOP) were used as the parameters of periodontal fluid dynamics. GCF-V was measured by a Periotron device, while GOP was measured by a digital osmometer. Silness-Löe plaque index (PI), Löe-Silness gingival index (GI) and clinical attachment loss (AL) levels were recorded to determine the periodontal health status.

RESULTS

PI, GI and AL were higher in Groups 1 and 2 than in Group 3 (P<0.05), but similar between Groups 1 and 2 (P>0.05). Increased GCF-V and GOP were observed in Groups 1 and 2 compared with Group 3 (P<0.01), and the increase in Group 1 was greater than that in Group 2 (P<0.01). There were strong positive correlations between GCF-V and GOP in all three groups: between GI and GCF-V and GI and GOP in Groups 1 and 2; and between AL and GCF-V and AL and GOP in Groups 2 and 3.

CONCLUSION

The results suggest that (i) DM may have an additive influence on the fluid dynamics of periodontium in the presence of periodontal disease; (ii) this phenomenon may not be prevented by the metabolic control of DM; (iii) the clinical signs of periodontal disease may be affected by the fluid dynamics of periodontium in both DM and periodontitis.

Osmotic pressure and vasculature of gingiva in experimental diabetes mellitus

BACKGROUND

Alterations in tissue osmotic pressure (OP) and vasculature are considered to be the inevitable aspects of an inflammatory process that subsequently alter the fluid dynamics of the tissues involved. The aim of this study was to reveal a profile of OP and vascular changes in periodontally healthy gingival tissues and analyze the relationship between them in diabetes mellitus (DM) to evaluate the possible effects of DM on the fluid dynamics of the periodontium.

METHODS

Experimental DM was created by intraperitoneal streptozotocin injection in 10 periodontally healthy rats. These rats were used as the test group, and 10 systemically and periodontally healthy rats served as the control group. Gingival tissue samples obtained from the groups were used for the test procedures. OP was measured in the supernatants of these samples by a semimicrodigital osmometer. Vasculature was assessed as the alterations in vascularization (vessel number [VN]) and vasodilatation (vessel diameter [VD]) by histomorphometric means.

RESULTS

There was a gross increase in the OP level of the test group (172.7 +/- 59.7 mOsm/kg) compared to the control group (11.4 +/- 4.2 mOsm/kg; P <0.001). VN was found to be significantly larger in the test group (12.7 +/- 2.8) than in the control group (6.8 +/- 1.1; P <0.001). VD was found to be smaller in the test group (10.1 +/- 2.8 microm) than in the control group (15.5 +/- 2.4 microm), and this difference was statistically significant (P <0.001). A positive correlation between OP and VN (r = 0.77; P <0.001) and a negative correlation between OP and VD (r = 0.1; P >0.05) were observed in the test group.

CONCLUSION

Our results reveal that the fluid dynamics of periodontal soft tissues may be affected by the diabetic conditions in this diabetic model because of the increased OP and VN during the pathogenesis of the disease.

Osmotic pressure and vasculature of gingiva in periodontal disease: An experimental study in rats

Alterations in vascularisation, vasodilatation and tissue osmotic pressure (OP) are inevitable aspects of the inflammatory process that have an adverse effect on the fluid dynamics of the tissue involved. The aim of this study was to investigate tissue OP and its relationship with the vasculature in inflammed gingival tissues, in order to reveal the possible effects of vascular changes on OP in the fluid dynamics of periodontal soft tissues during periodontal disease. The parameters of fluid dynamics assessed in this study were OP, vascularisation and vasodilatation. Ligature-induced periodontitis was performed in 10 rats (test group), and gingival biopsies taken from the diseased teeth were utilised for the test procedures. These biopsies were compared with biopsies of the same teeth from 10 periodontally healthy rats (control group). OP was measured in mosmol/kg using a semi-micro digital osmometer. Vascularisation and vasodilatation were examined histopathologically; the number of vessels (VN) was quantified and the micrometric changes in vessel diameters (VD) were calculated as the alterations in the vasculature. OP, VN and VD were found to be higher in the test group (84.3+/-37.1 mosmol/kg, 13.2+/-3.2 and 19.5+/-1.3 microm, respectively) than the control group (11.6+/-3.8 mosmol/kg, 6.8+/-1.1 and 15.5+/-2.4 microm, respectively) (P<0.000). There was a strong, positive correlation between OP and VN (r=0.55, P<0.000) and a weak, negative correlation between OP and VD (r=0.1, P>0.05) in the test group. These results confirm that the OP of periodontal soft tissues does change during inflammatory conditions. The increase in OP during this process may be affected by increased vascularisation in the inflammed tissue.

Lowering of interstitial fluid pressure in rat submandibular gland: a novel mechanism in saliva secretion

The submandibular gland transports fluid at a high rate through the interstitial space during salivation, but the exact level of all forces governing transcapillary fluid transport has not been established. In this study, our aim was to measure the relation between interstitial fluid volume (Vi) and interstitial fluid pressure (Pif) in salivary glands during active secretion and after systemically induced passive changes in gland hydration. We tested whether interstitial fluid could be isolated by tissue centrifugation to enable measurement of interstitial fluid colloid osmotic pressure. During control conditions, Vi averaged 0.23 ml/g wet wt (SD 0.014), with a corresponding mean Pif measured with micropipettes of 3.0 mmHg (SD 1.3). After induction of secretion by pilocarpine, Pif dropped by 3.8 mmHg (SD 1.5) whereas Vi was unchanged. During dehydration and overhydration of up to 20% increase of Vi above control, a linear relation was found between volume and pressure, resulting in a compliance (ΔVi/ΔPif) of 0.012 ml·g wet wt−1·mmHg−1. Interstitial fluid was isolated, and interstitial fluid colloid osmotic pressure averaged 10.4 mmHg (SD 1.2), which is 64% of the corresponding level in plasma. We conclude that Pif drops during secretion and, thereby, increases the net transcapillary pressure gradient, a condition that favors fluid filtration and increases the amount of fluid available for secretion. The reduction in Pif is most likely induced by contraction of myoepithelial cells and suggests an active and new role for these cells in salivary secretion. The relatively low interstitial compliance of the organ will enhance the effect of the myoepithelial cells on Pif during reduced Vi.

Effect of the sensory neuropeptide antagonists h-CGRP((8-37)) and SR 140.33 on pulpal and gingival blood flow in ferrets

In a previous study, it was concluded that the neuropeptides calcitonin gene-related peptide (CGRP) and substance P are released during resting conditions in the (exposed) ferret dental pulp, contributing to a basal vasodilator tone in the pulpal vessels. In order to exclude the possibility that the method used elicited axon reflexes, which might be responsible for neuropeptide release, the present study was designed without pulp exposure. Non-invasive laser-Doppler flowmetry was used to measure the effects of intra-arterial infusions of the antagonists h-CGRP((8-37)) and SR 140.33 (neurokinin 1-receptor antagonist) on pulpal and gingival blood flow before, during and after electrical tooth stimulation. Infusions of h-CGRP((8-37)) reduced the basal blood flow in the pulp by 31.4+/-5.2% (p<0.001) and in the gingiva by 22.6+/-4.8% (p<0.05). A further significant decrease in basal blood flow was measured in both pulp and gingiva following SR 140.33 administration. The reduction in blood flow was 16.9+/-1.9% (p<0.005) in the pulp and 19. 3+/-5.6% (p<0.05) in the gingiva. The systemic arterial pressure remained unchanged both during and after the periods of infusion. Tooth stimulation before the antagonist infusion significantly increased the pulpal blood flow by 71.9+/-15.3% (p<0.005). Infusion of h-CGRP((8-37)) greatly reduced this electrically induced vasodilatation, indicating that CGRP is the principal factor responsible for the vasodilatation observed after tooth stimulation. This study confirms the previous finding that a resting vasodilator tone due to the release of CGRP and SP exists in the ferret dental pulp. It is concluded that spontaneous, basal release of the neuropeptides CGRP and substance P exists both in dental pulp and gingiva in the ferret.

Interstitial fluid pressure in normal and inflamed pulp

Tissue pressure is the hydrostatic pressure in the interstitial fluid which surrounds the pulpal cells. This pressure outside the vessels is normally considerably lower than the blood pressure inside the vessels. The dental pulp has a relatively low interstitial compliance due to its enclosure between rigid dentin walls. Accordingly, even a modest increase in pulpal fluid volume will raise the tissue pressure, which may compress blood vessels, leading to ischemia and necrosis. Inflammation may lead to an increase in both interstitial fluid volume and blood volume in the low-compliant pulp and thereby increase the tissue pressure. However, the increased tissue pressure may, in turn, initiate increased lymph flow and absorption of fluid into capillaries in nearby non-inflamed tissue. Both of these latter factors will transport fluid out of the affected area and subsequently out of the tooth and consequently lower the tissue pressure. Increased tissue pressure, whether caused by increased blood volume or increased capillary filtration, will promote outward flow of fluid through exposed dentin tubules and thereby help to protect the pulp against entry of harmful substances. It seems physiologically beneficial, therefore, for the pulp to have a high tissue pressure, which promptly increases when blood flow increases due to its low compliance.

Micropuncture measurements of interstitial fluid pressure in normal and inflamed gingiva in rats

Interstitial fluid pressure (IFP) in normal and inflamed gingiva of rats was measured by sharpened glass capillaries (diameter 2-4 microns) connected to a servocontrolled counterpressure system ad modum Wiederhielm. Gingival inflammation was induced by a steel ligature placed unilaterally around the first maxillary molar. After 8 weeks, the ligature was removed and measurements of IFP in normal and experimentally inflamed gingiva were made by puncture through the intact oral epithelium. Average IFP on the control side was 3.5 mm Hg in free, and 7.4 mm Hg in attached gingiva. Compared to the control side, IFP on the experimental inflamed side was elevated significantly (p less than 0.05) both in free and attached gingiva. In the ligated inflamed side IFP in free gingiva averaged 6.7 mm Hg, whereas in attached gingiva it showed a mean value of 10.4 mm Hg. Histological examinations showed a dense infiltrate of inflammatory cells in the connective tissue, while the contralateral control side showed normal features of epithelial and connective tissue. The present finding of increased IFP in the inflamed gingiva may in theory contribute to augmented crevicular fluid flow during inflammation.

Edema-preventing mechanisms in rat gingiva

The long-term effect of increased local venous pressure (Pv) on interstitial fluid pressure (Pi), colloid osmotic pressure (COPi), and fractional removal rate of 125I-labeled human serum albumin (kAlb) was studied in rat gingiva. Measurements were performed on experimental animals and sham-operated controls up to 4 days after ligation of jugular veins. On the day of ligation Pv in the facial veins rose from 2.5 +/- 0.3 (SD) to 15.8 +/- 2.8 mm Hg and stayed at about this level for 2 days before a decrease to 7.4 +/- 0.9 mm Hg on day 4. In free gingiva Pi rose from an average of 3.5 +/- 0.4 to a maximum of 6.3 +/- 0.7 mm Hg, whereas in attached gingiva the corresponding increase in Pi was from 6.0 +/- 0.7 to 11.1 +/- 2.1 mm Hg. One day after the ligation COPi in wick fluid from gingiva was reduced from the control level of 10.6 +/- 1.4 to 4.5 +/- 0.9 mm Hg. COP in plasma and COPi in subcutaneous tissue on the back were unaffected. The removal rate of 125I-labeled albumin (kAlb) from the gingiva showed a nearly threefold increase after venous ligation, from 0.073 +/- 0.01 to 0.211 +/- 0.06 h-1. It is concluded that in free and attached gingiva, both a rise in Pi and a decrease in COPi will counteract the increased filtration pressure and thus prevent edema formation during venous stasis. The fall in COPi is most likely due to increased lymph flow and not dilution, as venous stasis significantly increased kAlb without any visible increase in gingival volume.

Non-invasive intravital fluorescent microscopy of the hamster gingiva

Several attempts have been made to visualize the gingival microcirculation of small animals. Most of these attempts have required surgical procedures without control of the local tissue environment. In our current study of the hamster gingiva, a tissue bath was designed to allow microcirculatory observations of the periodontium of the superior incisors without the need for invasive surgical procedures and with controlled pH and temperature of the bathing solution. Dextrans (m.w. = 70,000 and m.w. = 150,000), bovine serum albumin (mw = 66,210) or a globulin fraction (mw = greater than 450,000 less than 825,000) were conjugated to fluorescein isothiocyanate and injected into the animal. Fluorescent images, produced by epi-illumination, were analyzed for the light intensity of the interstitium. There was a large and rapid increase in light intensity (leakage of the macromolecules) near the venules while capillaries of the gingival margin developed interstitial fluorescence at a slower rate and with a lower maximal effect. Molecular weight, shape or charge of the macromolecular or age of the animal did not affect the results. This new preparation could be used to study the contribution of the microcirculation to gingivitis, the role of gingivitis in the development of periodontal disease, or the effects of drugs and hormones on the microcirculation of the gingiva.