Visual acuity of dentists under simulated clinical conditions

Objectives

This study examined the near visual acuity of dentists in relation to age and magnification under simulated clinical conditions.

Materials and methods

Miniaturized visual tests were performed in posterior teeth of a dental phantom head in a simulated clinical setting (dental chair, operating lamp, dental mirror). The visual acuity of 40 dentists was measured under the following conditions: (1) natural visual acuity, distance of 300 mm; (2) natural visual acuity, free choice of distance; (3) Galilean loupes, magnification of ×2.5; (4) Keplerian loupes, ×4.3; (5) operating microscope, ×4, integrated light; (6) operating microscope, ×6.4, integrated light.

Results

The visual acuity varied widely between individuals and was significantly lower in the group ≥40 years of age (p?<?0.001). Significant differences were found between all tested conditions (p?<?0.01). Furthermore, a correlation between visual acuity and age was found for all conditions. The performance with the microscope was better than with loupes even with comparable magnification factors. Some dentists had a better visual acuity without optical aids than others with Galilean loupes.

Conclusions

Near visual acuity under simulated clinical conditions varies widely between individuals and decreases throughout life. Visual deficiencies can be compensated for with optical aids.

Clinical relevance

Newly developed miniaturized vision tests have allowed, in a clinically relevant way, to evaluate the influence of magnification and age on the near visual acuity of dentists.     

Vertical root fractures in curved roots under simulated clinical conditions

The purpose of this study was to determine the incidence of vertical root fractures in the mesial roots of extracted human mandibular molars that were endodontically prepared by hand or ultrasonic instrumentation and obturated with laterally condensed gutta-percha and sealer using finger and hand spreaders. One-hundred twenty mesiofacial canals were prepared by hand or ultrasonic instrumentation. After placing the teeth in a simulated alveolus, they were obturated by laterally condensing gutta-percha and sealer with B-finger or D11T hand spreaders. Teeth were obturated using forces in the range of 1 to 3 kg or 4.5 to 7.5 kg. Three teeth obturated with the D11T hand spreader using 7.0 to 7.3 kg of force demonstrated vertical root fractures. The results suggest that in vitro the range of forces reported as most commonly used by endodontists to laterally condense gutta-percha (1.0 to 3.0 kg) and those of a higher magnitude up to 4.9 kg are safe and will not result in vertical root fractures of mesial roots of mandibular molars.     

Effect of pepsin on erosive tissue loss and the efficacy of fluoridation measures in dentine in vitro

Objectives. In dentine, erosive lesion progression and efficacy of fluoridation measures for symptomatic therapy of dental erosion are both dependent on the presence of the organic matrix. In patients with eating disorders in combination with chronic vomiting, the demineralized organic matrix can be degraded by gastric enzymes. The aim of this study was to investigate the effect of pepsin on erosion progression and the efficacy of fluoride in dentine. Material and methods. Human dentine specimens were prepared and randomly divided into 4 groups of 20 specimens each. They were subjected to a cyclic de- and remineralization procedure for 9 days. For demineralization (6×2 min per day), an HCl solution (pH 1.6) was used in all groups. In two groups, pepsin (1.5 mg mL^?1) was added to the demineralization solution. Fluoridation was performed in two groups 6×1 min per day with a mouth rinse (Olaflur/SnF₂; 250 ppm F^?) after demineralization with both the HCl solution and the pepsin containing solution. Degradation of collagen was quantified by analyzing hydroxyproline and tissue loss was determined microradiographically. SEM images were taken in addition. Results. In the pepsin group, 1.72 (0.26) µg mL^?1 (mean (SD)) hydroxyproline per day was detected, and in the pepsin-fluoride group 1.95 (0.50) µg mL^?1. Tissue loss after 9 days in the control group was similar to that in the pepsin group (122.2 (53.4) µm and 122.2 (38.0) µm, n.s., respectively). Fluoridation reduced tissue loss after demineralization (98.8 (30.2) µm) but not after pepsin treatment (125.2 (34.2) µm; p≤0.05). Conclusion. Under the conditions used, pepsin had no influence on tissue loss, but altered the efficacy of fluoridation measures.     

Evaporative water loss from human dentine in vitro

The rate of spontaneous evaporation of water from dentine was measured in extracted human teeth in vitro. Spontaneous water loss was the same with or without a smear layer. When air was blown on the dentine, the rate of evaporation increased significantly. After removal of the smear layer, the air blast-induced evaporative loss was twice as great as before its removal. Thus, with a smear layer present, evaporation is the major route by which fluid is lost from dentine rather than by filtration of dentinal fluid. After smear layer removal, fluid filtration sometimes may exceed the spontaneous rate of fluid evaporation.     

不同氟离子导入条件对牙本质小管的封闭作用

目的通过体外实验研究导人氟离子的不同条件对牙本质小管封闭的效果。方法制备牙本质模型45个,每组5个共9组,其中正常牙本质组仅用打磨处理,其余8组模型用6％柠檬酸酸蚀后,除1个脱矿组之外,7个再矿化组用NF-Ⅱ型护齿仪在不同的电流、时间利NaF浓度下进行氟离子导入处理。扫描电镜观察各组牙本质模型表面及纵断面的形貌,将观测结果进行统计分析;另外,对钙、磷元素含量进行能量色散X射线分析。结果脱矿组大部分牙本质小管开放,再矿化组牙本质小管内可见明显的矿化物沉积,各组的牙本质小管面积和相对面积有显著性差异（P〈0．05）;而能量色散X射线分析显示脱矿组与再矿化各组表面钙磷比无显著性差异（P〉0．05）。结论NF-Ⅱ型护齿仪的氟离子导入对于牙本质小管有一定封闭作用,在本实验条件下,牙本质再矿化的最佳电流为0．1mA或0．3mA,最佳时间为6min,最佳的NaF浓度为1％。     

Fatigue life of three core materials under simulated chewing conditions.

There has been an increase in the use of prefabricated post systems to restore endodontically treated teeth. Various restorative materials are being used as core buildups on these posts. The purpose of this study was to compare three core materials that are used with prefabricated stainless steel posts. Two types of prefabricated posts were placed in extracted teeth, followed by core buildups in amalgam, composite resin, or glass ionomer. The teeth were prepared for full cast crowns with the margins of the crown preparation extending 0.5 to 1.0 mm below the margins of the core buildup. Crowns were fabricated and cemented with zinc phosphate cement. A custom-designed chewing machine was used to cyclically load the teeth with vertical and horizontal forces for one million cycles or until failure occurred. Results indicated highly significant differences in the survival of the post-core-crown restorations depending on which core buildup material was used. Amalgam cores had the lowest failure rate, followed by composite resin cores. All teeth restored with crowns over glass-ionomer core buildup failed. The type of prefabricated post used had no effect on the survival of the post-core-crown restorations regardless of the core buildup used.     

In vitro cytotoxicity of different desensitizers under simulated pulpal flow conditions

PURPOSE: To evaluate the cytotoxicity of three desensitizers, one nonrinse, and one etch-and-rinse adhesive system applied on dentin specimens of different thickness. MATERIALS AND METHODS: The test materials (A: Admira Protect, B: Gluma Desensitizer, C: Seal&Protect, D: Clearfil Protect Bond, E: Optibond FL) and a positive control (35% H2O2) were applied on 1.0-, 1.5-, and 2.5-mm-thick bovine dentin specimens (each subgroup n = 5) in a dentin barrier test device. The experiments were performed with perfusion (2 ml/h) of the pulpal part of the chamber. The eluates were obtained before (baseline) and 15, 30, 45, 60, and 120 min after application of the adhesives and pipetted onto L-929 fibroblasts. Cytotoxicity of the materials was determined in relation to the baseline value using the MTT assay (succinic dehydrogenase activity). Statistical analysis was performed using ANOVA and Student's t-test. RESULTS: With regard to 1.0-mm dentin specimens, application of Clearfil Protect Bond (D) decreased enzyme activity significantly, while test materials A to C and E were not cytotoxic. However, cytotoxicity of D was limited to up to 15 min and decreased thereafter. Application of the test materials A to E on 1.5- and 2.5-mm dentin samples exhibited no significant cytotoxic effects within 120 min. Generally, ANOVA found significant interactions between the test materials and dentin thickness. However, only for Admira Protect was a significant increase of enzyme activity with increasing dentin thickness observed. CONCLUSION: Desensitizing agents might exhibit cytotoxic potential when applied on dentin less than 1.0 mm thick. The tested desensitizers and the adhesive systems caused similar effects, in which cytotoxicty might be influenced by the duration of perfusion and dentin thickness.     

Microhardness of sub-restoration dentine in primary molars after carious tissue removal to soft and firm dentine

ObjectivesTo compare the microhardness of sub-restoration dentine after selective carious tissue removal and placing glass ionomer restorative cement.MethodsForty-three primary molars with carious lesions extended to the inner third of dentine in subjects aged 8–12 years were included. The teeth were randomly assigned to the following carious tissue removal conditions: Group 1 - removal to the soft dentine, Group 2 - removal to the firm dentine, and Group 3 - removal to the hard dentine. Following restoration with glass ionomer restorative cement for three to six months, 30 tooth samples underwent microhardness testing performed on sub-restoration dentine and sound dentine. The Wilcoxon signed-rank test was used to compare the microhardness values of sound dentine and sub-restoration dentine within the group. The Kruskal–Wallis test was used to analyse the microhardness of the sub-restoration dentine across the three groups.ResultsAll 30 teeth available for analysis were asymptomatic, with no signs of pulpitis. The average microhardness values of sub-restoration dentine and sound dentine ranged from 16 to 23 KHN and 20 to 27 KHN, respectively. In each group, the microhardness value of the sub-restoration dentine was significantly lower than that of the sound dentine (p < 0.01). There were no significant differences in the microhardness values of sub-restoration dentine relative to that sound dentine among three groups (p = 0.86).ConclusionThe microhardness values of sub-restoration dentine with selective carious tissue removal were comparable to those with complete carious tissue removal after glass ionomer restorative cement placement.     

牙本质基质颗粒大小及脱矿条件对其性能的影响

目的 观察牙本质基质制备粒度与脱矿程度对其性能的影响。方法 选取成年家兔的上颌门牙随机分为2组，A组：采用稀盐酸（HCL）溶液（浓度1 mol/L）脱矿45 min，干燥后制备成3种不同粒径（400μm以下、400-800μm、800-1200μm）的脱矿牙本质基质材料（Demineralized dentin matrix，DDM），进行扫描电镜及静态接触角检测；B组：采用3种不同浓度（1 mol/L、0.5 mol/L和0.25 mol/L）的HCL溶液脱矿45 min，干燥后制备成粒径400μm以下的牙本质基质材料，分别进行红外光谱检测及电子能谱仪钙元素测定。结果 扫描电镜显示粒径400μm以下的DDM材料呈片状，随机观察牙本质小管充分暴露。A组3种DDM材料的静态接触角由粒径从小到大分别为6.0°、67.0°和96.7°。B组红外光谱检测显示：随着HCL溶液浓度增大，DDM材料中以羟基磷灰石为代表的无机物含量随之降低（P<0.05），但胶原的含量受影响较小；钙元素测定显示：在一定范围内随着脱矿程度增加，样品钙含量呈现梯度式降低（P<0.05）。结论 粒径较小的DDM材料牙本质小管暴露更充分，且具有更优的亲水性，脱矿程度的增加会降低DDM材料中无机物的含量，但对胶原含量影响较小。     

Volumetric polymerization shrinkage of resin composites under simulated intraoral temperature and humidity conditions

This study measured the volumetric shrinkage of resin composites polymerized under temperature and humidity conditions simulating the oral cavity and compared them to those occurring under ambient room conditions. Small, semispherical specimens of a microhybrid (Z100), microfill (Filtek A110) and flowable microhybrid (4 Seasons Flow) resin composite were manually formed and light activated for 40 seconds using a halogen light-curing unit (Spectrum Curing Light). The volumetric polymerization shrinkage of 10 specimens of each brand of resin composite was measured using a drop shape analysis unit (Drop Shape Analysis System, model DSA10 Mk2) under each of two temperature/relative humidity conditions: room conditions (22 +/- 2 degrees C and 60 +/- 5%) and those simulating intraoral conditions (35 degrees C and 92 +/- 5%). Mean volumetric shrinkage values were calculated for each resin composite and the data were analyzed using two-way analysis of variance and t-test (a=0.05) to determine if significant differences existed between the amount of volumetric polymerization shrinkage that occurred under ambient room conditions and that which occurred under simulated intraoral conditions. Mean volumetric shrinkage values measured for the resin composites were: 2.26 +/- 0.04% (ambient) and 2.61 +/- 0.04% (intraoral) for Z100; 1.96 +/- 0.04% (ambient) and 2.28 +/- 0.04% (intraoral) for Filtek A110 and 4.53 +/- 0.06% (ambient) and 5.34 +/- 0.05% (intraoral) for 4 Seasons Flow. For each resin composite, statistical analysis indicated that the amount of volumetric shrinkage measured under simulated intraoral conditions was significantly greater than what was measured under ambient room conditions (p<0.0001).     

Effect of simulated pulpal pressure on all-in-one adhesive bond strengths to dentine

OBJECTIVES: To evaluate the durability of all-in-one adhesive systems bonded to dentine with and without simulated hydrostatic pulpal pressure (PP). METHODS: Flat dentine surfaces of extracted human molars were prepared. Two all-in-one adhesive systems, One-Up Bond F (OBF) (Tokuyama Corp., Tokyo, Japan), and Fluoro Bond Shake One (FBS) (Shofu Co., Kyoto, Japan) were applied to the dentine surfaces under either a PP of 0 or 15cm H(2)O. Then, resin composite build-ups were made. The specimens bonded under pressure were stored in 37 degrees C water for 24h, 1 and 3 months under 15cm H(2)O PP. Specimens not bonded under pressure were stored under zero PP. After storage, the specimens were sectioned into slabs that were trimmed to hourglass shapes and subjected to micro-tensile bond testing (muTBS). The data were analysed using two-way ANOVA and Holm-Sidak HSD multiple comparison tests (alpha=0.05). RESULTS: The muTBS of OBF fell significantly (p<0.05) when PP was applied during bonding and storage, regardless of storage time. In contrast, although the muTBS of OBF specimens bonded and stored without hydrostatic pressure storage fell significantly over the 3 months period, the decrease was less than half as much as specimens stored under PP. In FBS bonded specimens, although there was no significant difference between the muTBS with and without hydrostatic pulpal pressure at 24h, by 1 and 3 months of storage under PP, significant reductions were seen compared with the control group without PP. CONCLUSION: The muTBS of OBF bonded specimens was lowered more by simulated PP than by storage time; specimens bonded with FBS were not sensitive to storage time in the absence of PP, but showed lower bond strengths at 1 and 3 months in the presence of PP.     

Microradiography of human pulp tissue and decalcified coronal dentine

The X-ray absorption of decalcified, dehydrated sections of the coronal portion of human teeth (mainly young premolars) was evaluated in the light microscope. With the exception of the matrix at the dentine-enamel junction, the dentine exhibited a fairly uniform X-ray absorption. The predentine was separable into two layers with different X-ray absorptions; the peripheral layer was generally of the same radiopacity as the rest of the dentine, while the layer nearest the odontoblasts was more radiolucent. The matrix of secondary deposits of mineralized tissue showed a variable degree of radiopacity. The contents of the tubules were discernable in the pulpal part of the dentine. Neither intracellular nor intranuclear details could be demonstrated in the pulp tissue but cell nuclei, bundles of collagen, capillary walls and especially red blood cells were more radiopaque than intracytoplasmic- and intercellular substance.     

The effect of simulated intrapulpal pressure on bond strength to enamel and dentine

The purpose of this study was to evaluate the effect of simulated intrapulpal pressure on the shear bond strength (SBS) of a self-etching bonding system (Clearfil Liner Bond II) to both enamel and dentine surfaces. Forty-two caries-free human molar teeth were randomly assigned to two equal groups (n=21). One group of 21 teeth was connected to a special pulpal pressure machine, which is developed to simulate in vivo conditions. The buccal and lingual surfaces of the teeth were prepared with a diamond wheel to create flat dentine and enamel surfaces. A self-etching bonding system was then applied under pulpal pressure and 2.5 mm diameter composite cylinders were bonded to the prepared surfaces. The samples were then stored in distilled water at room temperature for 24 h under pulpal pressure before SBS was tested. The second restored group was used as a control and the teeth were not connected to the pulpal pressure apparatus during material application and test procedures. They were stored for 24 h in distilled water at room temperature before the SBS test. Fracture analysis of the enamel and dentinal surfaces was performed using a stereomicroscope. Shear bond strength values to dentine was significantly reduced with pulpal pressure (P < 0.001). However, in the enamel, SBS was increased (P < 0.001). In the control group, the SBS values to dentine and enamel did not show any significant difference (P > 0.05). Based on these results, it can be concluded that further analysis of enamel histology and bonding mechanisms are needed.     

Alveolar bone loss induced by the orthodontic tooth movement under hypofunctional conditions in rats

PurposeTo examine the effect of occlusal hypofunctional conditions on orthodontic tooth movement and its relation to the structure and quality of alveolar bone using the rat model.Materials and methodsTwelve-week-old male Sprague-Dawley rats were divided into 4 groups of 8 animals each: normal occlusion (N) group, normal occlusion with tooth movement (M) group, occlusal hypofunction (H) group, and occlusal hypofunction with tooth movement (HM) group. In H and HM groups, the anterior bite plate and metal cap were attached to the maxillary and mandibular incisors using a light-curing composite resin to induce the occlusal hypofunctional condition. In M and HM groups, an orthodontic force was applied in a palatal direction to the buccal surface of the maxillary first molar (M1) using a nickel–titanium alloy wire. Micro-CT imaging and histomorphometric analysis using fluorescent bone labeling of the alveolar bone surrounding the M1s were performed in each group.ResultsTooth movement of M1 in HM group, was rather accelerated with enhanced tipping than in M group. Micro-CT analysis revealed significant decrease in bone volume fraction, bone mineral density and trabecular thickness of the interradicular bone in HM group among the experimental groups. The fluorescent labeling lines in the interradicular bone were decreased in number in H and M groups compared with N group. A few discontinuous irregular dotted lines-like labeling was observed in HM group.ConclusionThe occlusal hypofunctional condition accelerates orthodontic tooth movement of the respective teeth, while it results in severe bone loss in the surrounding alveolar bone.     

The effect of tissue molecules on bacterial invasion of dentine

Bacterial invasion of dentinal tubules is a critical step in the pathogenesis of dental caries and pulp and periapical disease. The purpose of this study was to determine the effect some molecules commonly found in saliva and dentinal tubule fluid may have on the bacterial invasion of dentine. The results showed that invasion of Streptococcus gordonii or Enterococcus faecalis cells was inhibited when the bacterial cells were in solution with mucin, immunoglobulin G (IgG) and serum, and this was related to bacterial cell aggregation, as a result of interaction with agglutinins, and/or inhibition of collagen binding. When dentine was soaked in growth media containing fibrinogen, IgG, albumin or serum prior to inoculation, bacterial invasion was inhibited. It is suggested that this may be due to reduced dentine permeability as a consequence of the deposition of the compounds within dentinal tubules.     

Efficacy of tin-containing solutions on erosive mineral loss in enamel and dentine in situ

The addition of tin to mouth rinses is, at least in vitro, a promising strategy for symptomatic therapy of dental erosion. The aim of this study was to evaluate the in situ efficacy of an experimental tin-containing fluoride solution on erosive tissue loss in human enamel and dentine. The study was a three-cell (7 days each) crossover design involving eight healthy participants. Samples were mounted on buccal shields of mandibular mouth appliances, which were worn for 24 h except during meals and drinks. Specimens were demineralised extraorally with 0.05 M citric acid (pH 2.3) for 6 × 5 min daily and were treated with test solutions intraorally once per day for 30 s after the first demineralisation. Three solutions were used: placebo (negative control), a commercially available tin- and fluoride-containing (SnF₂) mouth rinse (positive control, 409 ppm Sn²⁺, 250 ppm F⁻, pH 4.2) and an experimental solution (pH 4.5) containing 1,900 ppm Sn²⁺ (SnCl₂) and 1,000 ppm F⁻ (AmF/NaF). Tissue loss (micrometre) was determined profilometrically. In enamel, tissue loss was 54.8 ± 8.6 in the placebo, 24.5 ± 14.4 in the positive control and 9.7 ± 4.1 in the experimental solution group. The respective values for dentine were 48.5 ± 13.0 in the placebo, 32.8 ± 9.6 in the positive control and 26.2 ± 6.7 in the experimental solution group. The experimental solution was notably effective for enamel but was less effective for dentine. The positive control solution was less effective than the experimental solution; its effects for enamel and dentine were similar.