Journal of Dental Research

Two salivary 20-kDa proteins [the human lipocalin Von Ebner's gland protein (VEGh) and extra-parotid glycoprotein (EP-GP)] show several remarkable similarities and differences. The latter is identical to secretory actin-binding protein (SABP), gross cystic disease fluid protein-15 (GCDFP-15), prolactin-induced protein (PIP), and 17-kDA CD4-binding glycoprotein (gpl7). Much is known about the distribution, localization, biochemical characteristics, and molecular biology of these two proteins, yet there are only few clues about their functions.

The dental follicle, a loose connective tissue sac which surrounds the unerupted tooth, is required for eruption to occur. Injection of colony-stimulating factor-1 (CSF-1) will accelerate molar eruption in rats, as well as stimulate tooth eruption in osteopetrotic rats. Utilizing in situ hybridization and reverse- transcription polymerase chain-reaction techniques, we show here that CSF-1 mRNA is present in vivo in the dental follicle of the first mandibular molar of the rat. Analysis of the molars from day 0 through day 10 post-natally demonstrates that the maximal expression of CSF-1 mRNA is at day 3 post-natally. Immunostaining also reveals that the CSF-1 mRNA is translated, with immunostaining for the CSF-1 itself, being heavy in early post-natal days and absent by day 9 post-natally. In view of the fact that there is a maximal influx of mononuclear cells (monocytes) into the dental follicle at day 3 post-natally-an influx which increases the numbers of osteoclasts needed to form a tooth eruption pathway-it is probable that the maximal expression of CSF-1 mRNA by day 3 post-natally contributes to this monocyte influx. Thus, this study establishes a relationship among a molecule (CSF-1), cell (monocyte), and tissue (dental follicle) that appear to play a major role in tooth eruption.

We demonstrated for the first time that 9,10-dimethyl-l,2-benzanthracene (DMBA)-treated hamsters showed hypertriglyceridemia followed by cachexia. Hypertriglyceridemia is believed to be caused in part by the decreased lipoprotein lipase (LPL) activity, and by cytokines such as tumor necrosis factor (TNF)-a. In addition, TNF-a action is associated with the LPL activity. Therefore, we determined the content of triglyceride (TG), LPL, and TNF-a in the serum from DMBA-treated hamsters. Elevated TG concentration in the serum of tumor-bearing hamsters was more remarkable and preceded the increase in other lipids, whereas the activity of LPL, the key enzyme of TG metabolism in vivo, was drastically reduced. TNF-a, known as an endogenous inhibitor of LPL activity, was detected in both the sera and the extract of tumors from DMBA-treated hamsters, whereas it was not detectable in any control samples. Pre-incubation of control sera with exogenous recombinant human TNF-a resulted in a potent inhibition of endogenous LPL activity in a dose-dependent manner in vitro. Therefore, the presence of TNF-a might lead to the increase in plasma TG mediated by LPL in tumor-bearing hamsters.

This study concerns the complex interaction between active muscle forces and passive guiding structures during jaw-closing movements. It is generally accepted that the ligaments of the joint play a major role in condylar guidance during these movements. While these ligaments permit a wide range of motions, it was assumed that they are not primarily involved in force transmission in the joints. Therefore, it was hypothesized that muscle forces and movement constraints caused by the articular surfaces imply a necessary and sufficient condition to generate ordinary jaw-closing movements. This hypothesis was tested by biomechanical analysis. A dynamic six-degrees-of-freedom mathematical model of the human masticatory system has been developed for qualitative analysis of the contributions of the different masticatory muscles to jaw-closing movement. In simulated symmetrical jaw-closing movements, it was found that the normally observed movement, which includes a swing-slide condylar movement along the articular eminence, can be generated by various separate pairs of masticatory muscles, among which the different parts of the masseter as well as the medial pterygoid muscle appeared to be the most suitable to complete this action.

The results seem to be in contrast to the general opinion that a muscle with a forward-directed force component may not be suitable for generating jaw movements in which the condyle moves backward. The results can be explained, however, by biomechanical analysis which includes not only muscle and joint forces as used in standard textbooks of anatomy, but also the torques generated by these forces.

Our earlier studies have shown that some radiographic structural findings in the mandibular condyles are more common in orthodontically treated populations than in normal populations. To test the hypothesis that these findings are stable, we studied condylar findings in panoramic radiographs longitudinally in 39 subjects and in 39 sex- and age-matched controls. The subjects had condylar findings at the end of orthodontic treatment at about 15 years of age; no such findings were seen in the controls. The subjects and controls were re-examined radiographically about 12 years after the posttreatment radiographic examination.

We also tested the hypothesis that radiographic condylar findings are associated with temporomandibular disorders (TMD). No statistically significant differences were found between subjects and controls in terms of reported subjective TMD symptoms. Clinically, the subjects had temporomandibular joint (TMJ) crepitation significantly more frequently (27%) than controls (8%) (p < 0.05). Crepitation correlated with some reported symptoms and clinical signs, suggesting that osteoarthrosis might have been an important etiological factor for TMD in the present subjects.

At the follow-up examination, radiographic condylar findings were seen in 25 subjects and in four controls (p < 0.001). The condylar findings varied greatly between the time of orthodontic treatment and follow-up in the subjects. The findings had become more severe in 49% of the subjects, more often in females than in males (p < 0.05), whereas in 28% of the subjects the condylar findings had disappeared. Although the radiographic findings after orthodontic treatment fluctuated with age, in most adolescents with changes in their condyles, these findings remained constant or became more severe. It should be emphasized, however, that although there were certain associations between radiographic findings and TMD, the subjective symptoms and clinical signs seemed to cause the subjects no or only minor problems.

Bad breath (halitosis, oral malodor) is a common condition, usually the result of microbial putrefaction within the oral cavity. Often, people suffering from bad breath remain unaware of it, whereas others remain convinced that they suffer from foul oral malodor, although there is no evidence for such. The purpose of the present investigation was to determine whether objective self-measurement of oral malodors is possible. Each of 52 volunteers was asked to sample the odor from his/her mouth, tongue, and saliva. Results were compared with (i) self-assessments prior to (preconception) and following (post-measurement) self-measurements; (ii) odor judge scores; (iii) dental measurements (plaque index, gingival index, and probing depth); (iv) volatile sulphide levels; (v) salivary cadaverine levels; and (vi) intra-oral trypsin-like activity. Among the self-measurements, only saliva self-scores yielded significant correlations with objective parameters. Despite the partial objectivity of saliva self-estimates, subsequent post-measurement self-assessments failed to correlate with objective parameters. The results suggest that (i) preconceived notions confound the ability to score one's own oral malodors in an objective fashion; and (ii) partial objectivity can be obtained in the case of saliva self-measurement, presumably because the stimulus is removed from the body proper.

Sealants are highly effective in preventing dental caries in the pits and fissures of teeth when applied by trained operators in clinical trials and public health programs. The effectiveness of fissure sealants when applied in dental practices is still not known. The purpose of this longitudinal study was to evaluate the effectiveness of fissure sealants applied in dental practices in preventing dental caries on occlusal surfaces of first permanent molars. In 1990, on the Island of Montreal, 911 randomly selected children, from 6 to 9 years of age, were examined; out of those, 816 and 733 were re-examined in 1991 and 1992, respectively. Only the 733 children with complete examination records were included in this evaluation. Sealant applications were either personally paid for or were paid for by private dental insurers. All children were covered for diagnosis and restorative care by a publicly financed and universal insurance program. Dental treatment records were provided by Quebec's health insurance board. In the epidemiological examination, the occlusal surfaces of first permanent molars, which are the only surfaces included in this analysis, were classified into: sound, non-cavitated and cavitated status, restored, and sealed. Sealants were evaluated for full or partial coverage of the occlusal surface and presence of dental caries. During the first and second years, 11.6% and 17.5% of the students had new sealants. The number of new sealants placed during the two years was 507. Children with caries-free status and whose parents had high school education or higher were significantly more likely to receive sealants during the study. Of the sealants found in 1990, 73.5% were still fully sealed after two years. Compared with sound first permanent molars in 1990, fully sealed first permanent molars had 75% lower incidence of new restorations. This pragmatic evaluation of sealants shows that even when applied in dental practices under uncontrolled conditions, they were effective in preventing dental caries over a two-year period.

Since the mode of failure of resin composites bonded to ceramics has frequently been reported to be cohesive fracture of either ceramic or resin composite rather than separation at the adhesive interface, this study was designed to question the validity of shear bond strength tests. The reasons for such a failure mode are identified and an alternative tensile bond strength test evaluated. Three configurations (A, conventional; B, reversed; and C, all composite) of the cylinder-on-disc design were produced for shear bond strength testing. Two-dimensional finite element stress analysis (FEA) was carried out to determine qualitatively the stress distribution for the three configurations. A tensile bond strength test was designed and used to evaluate two ceramic repair systems, one using hydrofluoric acid (HF) and the other acidulated phosphate fluoride (APF). Results from the shear bond strength tests and FEA showed that this particular test has as its inherent feature the measurement of the strength of the base material rather than the strength of the adhesive interface. In the tensile test, failure invariably occurred in the adhesive layer, with HF and APF showing a similar ability to improve the bond of resin composite to ceramic. It is concluded that the tensile bond strength test is more appropriate for evaluating the adhesive capabilities of resin composites to ceramics.

The use of 2-hydroxyethyl methacrylate (HEMA)-based polymer as a biocompatible material has been well-established. HEMA-based resins containing cross-linking agents have several potential clinical applications. It is hypothesized that the incorporation of cross-linking agent will improve the mechanical properties of HEMA-based polymers while reducing water absorption and solubility. The purpose of the work reported here was to test this hypothesis and to determine the most effective cross-linking agent.

A relationship among flexural strength, modulus, water absorption and solubility, and concentration of cross-linking agent was demonstrated. Strength and modulus tend to increase as the cross-linking agent concentration is increased, up to about 50%, after which the values level out or begin to fall. Water absorption drops with increasing cross-linking agent over the whole range of concentrations. Solubility tends to show a small decrease initially (up to 40%), followed by a noticeable increase as cross-linking agent concentration is increased. The trends were similar for all cross-linking agents, although there were differences in the absolute values in all properties depending upon the type of cross-linking agent used.

Previous studies have shown a wide range of pulpal reactions to dentin bonding systems and a poor correlation between in vitro and in vivo toxicity of dentin bonding agents. Because dentin bonding agents are composed of multiple components which may diffuse through dentin, we hypothesized that these components may cause cytotoxicity through interactive (synergistic) effects. We investigated the cytotoxicities of four dentin bonding components-HEMA, Bis-GMA, TEGDMA, and UDMA-and interactive effects for three binary combinations of the dentin bonding components-HEMA and Bis-GMA, Bis-GMA and TEGDMA, and TEGDMA and UDMA. Cytotoxicities to Balb/c 3T3 mouse fibroblasts were measured by the MTT assay. Concentrations which caused 50% toxicity compared with controls (TC₅₀ values) were compared, and the interactive effects were determined by evaluation of the differences between observed and expected MTT activities of the cells. The ranks of toxicity of the dentin bonding components in terms of TC₅₀ values were as follows: Bis-GMA > UDMA > TEGDMA >>> HEMA (least toxic) after 24- and 72-hour exposures. As binary combinations, the three combinations of dentin bonding components interacted in three ways—synergism, additivism, and antagonism-which were influenced by the concentrations of both components. The longer period of exposure resulted in a significant increase in the cytotoxicity of the dentin bonding components and combinations. The findings indicate that both exposure time and the interactions between the dentin bonding components may be important parameters in determining the cytotoxicity of dentin bonding agents in vivo.

A study was conducted to evaluate qualitative and quantitative differences in bacterial colonization on titanium, hydroxyapatite, and amalgam surfaces in vivo. Six healthy adult individuals participated in the study. Two pieces each of titanium, hydroxyapatite, and amalgam of similar size were placed in cobalt-chromium splints and kept intra-orally in each individual for 10 min, and 1, 3, 6, 24, and 72 hrs. After removal of the splints, the pieces were rinsed in PBS and transferred to transport medium. After being vortexed, the samples were inoculated on selective and non-selective media for analyses of various facultative and anaerobic bacteria. During the experiment, total viable count increased on all surfaces. The investigated bacterial groups constituted, on average, approximately 60 to 99% of the total viable count on all three types of surfaces in each of the experiments, except in the 10-minute samples, when they constituted around 20 to 30%. Various streptococcal species predominated and usually constituted > 50% of total viable count. Similar colonization patterns of Streptococcus spp., Actinomyces naeslundii, Neisseria spp., Hemophilus parainfluenzae, Fusobacterium spp., and black-pigmented Prevotella spp. were seen at all three types of surfaces. No significant differences among the materials regarding colonization of investigated bacteria were found during the study period. This study failed to show any qualitative and quantitative differences in bacterial colonization among these materials. Titanium, hydroxyapatite, and amalgam do not seem to have a marked influence on the early colonization pattern in vivo.

We studied the mechanism by which the antimicrobial compound sucrose monolaurate inhibits Streptococcus mutans NCTC 10449 by determining its effect on the rate of acid production from glucose and sucrose and the intracellular and extracellular levels of glycolytic intermediates. Sucrose monolaurate was more effective than either sodium laurate or sodium fluoride in inhibiting acid production at pH 7.0 from glucose. Inhibition of acid production was the same when either glucose or sucrose was the carbon source and in the presence or absence of oxygen. Quantitative analysis of various glycolytic intermediates revealed that the steps inhibited by sucrose monolaurate were the reactions catalyzed by phosphofructokinase and glyceraldehyde 3-phosphate dehydrogenase and/or phosphoglycerate kinase. Since the activities of these enzymes in cell-free extracts were not decreased by the addition of sucrose monolaurate, the inhibition of acid production could not be ascribed to direct effects on the enzymes. A decrease in the rate of acid production with corresponding elevations in the extracellular levels of glycolytic intermediates indicates that sucrose monolaurate inhibits S. mutans by altering the permeability of the cell membrane, which causes a loss of important metabolites.

The effect of fluoride derived from fluorhydroxyapatite (FHAp) minerals on bacterial glycolysis under aerobic and strictly anaerobic conditions was studied to validate the claims that this mineral could be used as a reservoir of fluoride in plaque. To isolate the direct effect of fluoride on bacterial glycolysis from that of an indirect pH-buffering effect of hydroxyl or phosphate ions which are also dissolved from the mineral, we equalized the pH-fall time course of reactions by manually adding KOH or HCl. This ensured that pH effects on glycolysis were minimized. Under controlled pH-fall and strictly anaerobic conditions, fluoride derived from the dissolution of FHAp containing more than 30,100 ppm fluoride (i.e., when the substitution of OH by F in the mineral was greater than 80%) had a direct inhibitory effect on lactic acid production in Streptococcus mutans. Under free pH-fall and strictly anaerobic conditions, increasing amounts of fluoride in FHAp (starting as low as 2000 ppm fluoride), appeared to have a pronounced indirect inhibitory effect on lactic acid production. This was probably mediated through a reducing pH buffer effect of the mineral. Even in the presence of high-fluoride FHAp, only 0.01 to 0.025 mmol/L fluoride was found in the reaction mixtures, a probable result of non-stoichiometric dissolution of FHAp. In spite of such low levels of fluoride, marked inhibitory effects on bacterial glycolysis were demonstrated. The results of this study suggest that high-fluoride FHAp may serve as a reservoir of fluoride for the inhibition of anaerobic acid production by S. mutans.