Quantitative observation on teeth during calcium deprivation in rats.

Adult female rats were subjected to severe calcium deprivation by feeding them a calcium-deficient diet containing oxalate (Group A). Furthermore, pregnant and lactating animals were subjected to the same diet (Group B). The mandibular teeth were collected for ash determination and for linear measurements. The ash content of the growing incisors was only slightly reduced in Group A, while the reduction in Group B was 27%. Linear measurements demonstrated that the outer dimensions of the incisors were not affected by the calcium-depriving regimen in either group, while the inner dimensions (pulp cavity) were considerably increased in Group B due to reduced thickness of the dentin mantle. The daily dentin apposition in Group A did not deviate much from the control values, while in Group B it was severely reduced. The thickness of incisor enamel was unaffected by the calcium-depriving regimen. The ash content of the molars was normal in Group A, but slightly reduced in Group B.     

Effect of extreme calcium deprivation on degree of mineralization of alveolar bone, dentin and enamel in rats

abstract – The effect of an extreme and prolonged calcium-depriving regimen on the degree of mineralization of alveolar bone, dentin and enamel in adult female rats has been studied by quantitative microradiography. This method is considered to be the method of choice for disclosing differences in V % hydroxyapatite (HA). Despite the calcium-depriving regimen causing a substantial loss of bone mineral from femur and tibia, as estimated by gravimetric methods, the mineral content of alveolar bone, expressed as V % HA, did not deviate significantly from the normal, indicating that no osteolytic processes had taken place. Neither did the degree of mineralization of the fully formed molar dentin deviate from the normal. However, dentin and enamel formed during the experimental period by the continuously growing incisors disclosed a degree of mineralization which was significantly lower than normal. It was further noticed that the mineral content of the lingual dentin of the incisors, from both experimental and control animals, was significantly lower than the labial dentin.     

Histologic and microradiographic observations on teeth during calcium deprivation in rats.

Adult female rats were subjected to severe calcium deprivation by feeding them a calcium-deficient diet containing oxalate (Group a). Furthermore, pregnant and lactating animals were subjected to the same diet (Group b). The mandibular teeth were examined by histologic, microradiographic and fluorescence microscopic techniques. The incisor enamel was found to be nearly unaffected by the experimental regimen; the dentin formed and mineralized during the experimental period was abnormal only in Group b. Characteristic features were reduced thickness, increased width of predentin and numerous globular defects. Both ameloblasts and odontoblasts were seemingly normal. No obvious differences could be observed between the molars from the controls and the test groups (a,b). "Cementolysis" seemed to be present to the same extent in all groups. In some of the animals of Group b some carious or erosional defects were observed in the molars. These may at least partially account for a small reduction in molar ash content observed in this group.     

Histologic and microradiographic observations on teeth during calcium deprivation in rats

ABSTRACT— Adult female rats were subjected to severe calcium deprivation by feeding them a calcium-deficient diet containing oxalate (Group a). Furthermore, pregnant and lactating animals were subjected to the same diet (Group b). The mandibular teeth were examined by histologic, microradiographic and fluorescence microscopic techniques. The incisor enamel was found to be nearly unaffected by the experimental regimen; the dentin formed and mineralized during the experimental period was abnormal only in Group b. Characteristic features were reduced thickness, increased width of predentin and numerous globular defects. Both ameloblasts and odontoblasts were seemingly normal. No obvious differences could be observed between the molars from the controls and the test groups (a, b). “Cementolysis” seemed to be present to the same extent in all groups. In some of the animals of Group b some carious or erosional defects were observed in the molars. These may at least partially account for a small reduction in molar ash content observed in this group.     

光学相干断层成像技术对牙本质成像及其厚度定量测量的研究

目的:研究光学相干断层成像(OCT)技术对牙本质的成像及量化测定能力。方法:磨除20颗下颌中切牙舌侧釉质,显微CT扫描并构建牙齿三维数字模型,标记每颗牙齿舌侧面牙本质最薄处为a点并测量该位点牙本质厚度,OCT扫描相同位点处,获取牙本质OCT影像,并测量对应牙本质厚度。测量结果采用Student’s t检验及相关回归分析。结果:同一位点牙本质厚度OCT测量值显著大于显微CT测量值(P=0.004),但两者间呈显著正相关联(R²=0.9877,P＜0.05)。结论:OCT可以用来对髓腔表面牙本质厚度进行无创定量测定。     

根管再湿润对纤维桩粘接强度及粘接耐久性的影响

目的 利用薄片推出实验检测脱水及再湿润过程中纤维桩与根管各区段的粘接强度及粘接耐久性,以期为临床桩核修复提供实验依据.方法 将36颗离体牙用随机数字表均分为过干燥组、再湿润组及对照组,分别进行纤维桩粘接,将牙根横向切割为1.0 mm厚的切片,每颗牙选取根颈部、根中部和根尖部各2个切片,即刻及水储存2个月后进行薄片推出实验,并对破坏试件进行扫描电镜观察.结果 过干燥组、再湿润组和对照组纤维桩即刻实验的粘接强度分别为(5.97±1.97)、(7.67±2.19)和(8.46±2.35)MPa;水储存2个月后粘接强度分别为(2.08±1.67)、(2.99±1.48)、(3.22±1.43)MPa.即刻实验和水储存2个月后,过干燥组与再湿润组、过干燥组与对照组间差异均有统计学意义(P＜0.05).根颈段牙本质比根管其他区段能提供更大的粘接强度(P＜0.05);水储存对纤维桩粘接强度有显著影响(P＜0.05).结论 根管过度吹干处理可影响纤维桩的粘接强度及粘接耐久性.水灌注可使过干燥管壁牙本质重新恢复湿润状态,恢复纤维桩正常的粘接强度及粘接耐久性.

Abstract：

Objective To analyze the push-out bond strength of fiber post and the durability of interface between dentin and composite resin during over drying and re-wetting of root canal. Methods Thirty-six extracted human maxillary central incisors were randomly divided into three groups: Group A for the process of over drying, Group B for re-wetting, Group C for control. All teeth were sliced into several thin discs with thickness of 1.0 mm for micro push-out test and scanning electron microscope (SEM)observation. Results Push-out shear strengths of fiber post immediately after bonding in group A, B and C were (5. 97 ± 1.97), (7.67 ± 2. 19) and (8. 46 ± 2. 35) MPa. Push-out strengths of fiber post two months after water storage were (2. 08 ± 1.67), (2. 99 ± 1.48) and (3. 22 ± 1.43) MPa. There was significantly difference in push-out strength between Group A and Group B(P ＜0. 05). Significantly difference in pushout strength was also found between Group A and Group C. In the condition of immediate testing, there was also significantly difference between push-out strength of cervical slice and middle slice, and between cervical slice and apical slice(P ＜0. 05). The water storage time has significant effect on the push-out bond strength of fiber posts (P ＜ 0. 05). Conclusions Inappropriate condensation air blowing operation can cause extracted teeth root canal dentin over dry. Dehydration can destroy the formation of general structure of interface between composite resin and dentin. The over dry dentin can be turned back to wetting stage by water pouring, which can help fiber-reinforced composite post regain its normal retention strength and original adhesive durability.     

Influence of bleaching agents and desensitizing varnishes on the water content of dentin

This in vitro study investigated the possible dehydration of dentin caused by bleaching agents. Furthermore, it tested whether protective dentin varnishes can maintain the physiological moisture of dentin during bleaching treatment. Fifty-five standardized dentin cylinders were prepared from freshly extracted bovine incisors under constant water irrigation. Prior to bleaching, the treatment specimens were conditioned at room temperature in a hygrophor for 14 days. The samples were divided into 11 groups. The Group A specimens, which were completely dehydrated, and Group B, which was stored for 2 weeks in a hygrophor, served as controls (A, B n=5). The other samples (n=10 each group) were coated with Vivasens [VS] (C), Bilfuorid [BF] (D) and Seal&Protect [SP] (E). Five specimens from each group (C-E) were subsequently treated with an experimental bleaching gel (Exp BG) (20% carbamide peroxide [CP], glycerine-based gel): Cb, Db, Eb. The remaining specimens were bleached with Exp BG (F) only, Vivastyle (G: 16% CP, glycerine-based gel) or Vivastyle Paint On (H: 6% CP-varnish) for 7 days (n=5 each group) with bleaching time for gels: 2 hours/day, paint on: 20 minutes/day. After the respective treatments, the overall water content of each specimen was determined using the analytical method of Karl-Fischer-titration. The water content of bovine dentin (Group B, mean%+/-SD) obtained in this study amounted to 15.24+/-0.4. All bleaching products significantly reduced the water content compared to the controls (exp BG: 13.32+/-0.47, Vivastyle 13.2+/-0.27, paint on 13.72+/-0.54; p<0.05). Also, application of SP before bleaching resulted in reduced water content (14.06+/-0.12; p=0.0005). However, bleaching with exp BG following use of VS (14.99+/-0.42) or SP (13.85+/-0.26) did not result in a reduction of water content in dentin. Pretreatment with BF did not protect dentin from water loss during bleaching (12.44+/-0.38; bi p=0.0009). All glycerine-based bleaching products used in this study had a significant dehydrating effect on dentin. The application of protective varnishes prior to bleaching treatment may reduce or even prevent dentin dehydration.     

Influence of root width and dentin wall thickness evaluated by endoscopy upon the outcome of periapical surgery. A cohort study

Background An analysis was made of the correlation between root width, the thickness of the remaining dentinal wall as determined by endoscopy, and the outcome of periapical surgery.Material and Methods A retrospective cohort study was carried out involving patients subjected to periapical surgery between 2017 and 2019 at the University of Valencia (Valencia, Spain).One year after surgery, cone-beam computed tomography (CBCT) was used to evaluate healing against the preoperative volumes. The maximum root width was measured on the postoperative CBCT scan at the apical section of the treated root. This measurement was transferred to the intraoperative endoscopic image, where the minimum root width, peripheral dentin thickness, and minimum dentin thickness were recorded. Root measurements, and the position (maxillary or mandibular) and type of tooth (roots of incisors, canines, premolars or molars) were further correlated to periapical surgery outcome.Results A total of 51 patients, comprising 52 teeth and 62 roots, were included in the study. The mean measurements were: maximum root width (4.13±0.84 mm), minimum root width (2.46±0.72 mm), peripheral dentin thickness (0.77±0.2 mm) and minimum dentin thickness (0.4±0.2 mm). The success rate was 82.2%. Premolar roots showed a greater minimum dentin thickness (0.58±0.25 mm) (p<0.003) than incisor roots. No significant association was found between the different measurements and the healing rate at one year, though the roots that failed to heal showed smaller minimum dentin thickness values than the roots that healed correctly. The position and type of tooth did not influence healing outcome.Conclusions The root width and thickness of the remaining dentin wall did not significantly influence healing. However, the roots that failed to heal showed smaller minimum dentin thickness values than the roots that healed correctly. Key words:Endodontic surgery, endoscope, dentin walls.     

桩核冠受力时的应力分析

目的：用三维有限元法对桩核冠进行应力分析,研究不同材质的冠对分析结果的影响。方法：采用测量法建模,根据标准的桩核冠制作要求,应用美国I-DEAS有限元分析软件分别建立三套上中切牙的三维有限元模型．其中A组包括铸造金属桩核、制备后的牙体组织、牙周组织;B组包括金属烤瓷冠、铸造金属桩核、制备后的牙体组织、牙周组织;C组包括树脂冠、铸造金属桩核、制备后的牙体组织、牙周组织。在同等条件下以上中切牙的平均糟力分别给予加载,并对计算结果进行综合分析。结果：（1）从牙本质的应力大小来看,A组中牙本质最大应力值比B组中牙本质最大应力值增大了1倍以上（最大主应力、最小主应力和最大剪切应力A组分别是B组的236．35％、228．83％和218．05％）,而B组与C组的牙本质最大应力值相差极小;（2）从牙本质的应力分布位置来看,A组与B组的牙本质最大应力分布位置相差甚远（A组主要集中在牙颈部唇舌侧肩台部的牙本质上．B组主要集中于牙槽嵴顶附近及铸造桩核尾端相对应的唇舌侧的牙本质上）,而B组与C组的牙本质最大应力分布几乎在同一位置。结论：用三维有限元法对桩核冠进行应力分析时,不同材质的冠对分析结果无明显影响。     

Effects of posts on dentin stress distribution in pulpless teeth.

A finite element analysis was carried out to study the roles of posts in reducing dentin stress in pulpless teeth. Two-dimensional plane strain models of the midlabiolingual section of a human maxillary central incisor were first analyzed. The results showed that the gold alloy post reduced maximal dentin stress by as much as 30%. However, the integrity of the dentin was compromised and the effects of the post were likely to be exaggerated in such models. In an effort to correct for these problems, plane stress models with side plates and axisymmetric models were analyzed. Posts were found to reduce maximal dentin stress by only 3% to 8% when the teeth were subjected to masticatory and traumatic loadings in these latter models. Although posts reduced maximal dentin stress by as much as 20% when the teeth were loaded vertically, teeth such as incisors and canines normally are not subjected to vertical loadings. Thus the reinforcement effects of posts seem to be doubtful in these teeth.     

Effect of chelating agents on the molecular composition and extent of decalcification at cervical, middle and apical root dentin locations

Abstract— The aim of this study was to investigate the interaction of two chelating agents used in endodontic treatment with dentin from different root locations. Standardized cervical, middle and apical root dentin specimens were prepared and subjected to treatment with 15% neutral EDTA and RCPrep. Following rinsing with water, dentin surfaces were studied by reflected light optical microscopy and micro-MIR FTIR spectroscopy, while the wash-off extracts were analyzed by atomic absorption spectrometry (AAS) to determine the content of calcium and phosphorus. Neutral EDTA removed the smear layer and opened tubules while RCPrep did not. FTIR measurements showed higher decalcification of dentin surfaces after neutral EDTA treatment although its effect was reduced at apical regions. AAS measurements of calcium and phosphorus confirmed the higher dentin dissolution potential of EDTA at cervical and middle root dentin locations. The results of the present study implied different reaction modes for the two chelating agents tested which might affect the efficiency of the chemo-mechanical preparation when these agents are used.     

Effect of a CPP-ACP agent on the demineralization and remineralization of dentine in vitro

OBJECTIVES: The aim of this study was to determine in vitro the effect of a commercial paste based on CPP-ACP complex on the demineralization of sound human dentine and on remineralization potential of artificial caries-like lesions formed on dentine surfaces. METHODS: Forty dentine specimens were prepared with hard tissue microtome. The specimens were divided in four groups the A, B, C and D (n=10). The specimen surfaces were subjected to surface analysis by Fourier transformance micro multiple internal reflectance infrared spectroscopy (micro MIR-FTIR). Tooth mousse was applied on surface specimens of A group, while no agent were applied on the specimens of B group. Afterwards, groups A, B, C and D were immersed in demineralization solution for 7 days. Afterwards, the surfaces were subjected to micro MIR-FTIR analysis and the mineral to matrix ratio was used to assess the extent of dentin demineralization (DM). Tooth mousse was applied on specimens of group C, while no agent was applied on specimens of group D. The groups C and D immersed in artificial saliva for 7 days and were subjected to analysis by micro MIR-FTIR and the mineral to matrix ratio was used to assess the extent of dentin remineralization (RM). RESULTS: Group A showed significant lower %DM in comparison to group B. Group C resulted in a significant higher %RM compared to group D. CONCLUSIONS: The presence of agent CPP-ACP on dentine surfaces provoked lower demineralization and higher remineralization in comparison with the dentine surfaces without agent.     

Adhesion to Er:YAG laser-prepared dentin after long-term water storage and thermocycling

This in vitro study evaluated the microtensile bond strength of a resin composite to Er:YAG-prepared dentin after long-term storage and thermocycling. Eighty bovine incisors were selected and their roots removed. The crowns were ground to expose superficial dentin. The samples were randomly divided according to cavity preparation method (I-Er:YAG laser and II-carbide bur). Subsequently, an etch & rinse adhesive system was applied and the samples were restored with a resin composite. The samples were subdivided according to time of water storage (WS)/number of thermocycles (TC) performed: A) 24 hours WS/no TC; B) 7 days WS/500 TC; C) 1 month WS/2,000 TC; D) 6 months WS/12,000 TC. The teeth were sectioned in sticks with a cross-sectional area of 1.0-mm2, which were loaded in tension in a universal testing machine. The data were subjected to two-way ANOVA, Scheffé and Fisher's tests at a 5% level. In general, the bur-prepared group displayed higher microtensile bond strength values than the laser-treated group. Based on one-month water stbrage and 2,000 thermocycles, the performance of the tested adhesive system to Er:YAG-laser irradiated dentin was negatively affected (Group IC), while adhesion of the bur-prepared group decreased only within six months of water storage combined with 12,000 thermocycles (Group IID). It may be concluded that adhesion to the Er:YAG laser cavity preparation was more affected by the methods used for simulating degradation of the adhesive interface.     

The inorganic components of cementum- and enamel-related dentin in the rat incisor

Recently, we have shown that, in rodent incisors, the crown- and root-analogue dentin (enamel- and cementum-related dentin) show differences in mineralization rates (Beertsen and Niehof, 1986) and composition of the organic matrices (Steinfort et al., 1989). It was the aim of the present study to determine whether these differences were accompanied by differences in the inorganic components. Rat incisors were analyzed by means of hardness measurements, microradiography, and the determination of Ca, Mg, and PO4 content. The outer circumpulpal dentin layer of the enamel-related dentin (ERD) was considerably harder and denser than the comparable layer of the cementum-related dentin (CRD). Concomitantly, a higher Ca and PO4 content was found for the ERD than for the CRD, while the reverse occurred with respect to Mg. From the apical end of the incisor toward the incisal edge, the Ca/PO4 ratio tended to decrease for both ERD and CRD, while the Mg/PO4 ratio increased. All differences appeared to be statistically significant. It is concluded that differences in the non-collagenous organic matrix were accompanied by differences in the inorganic components. More specifically, a relatively high content of highly phosphorylated phosphoproteins (ERD) was associated with a higher Ca and a lower Mg content.     

Restoring the vertical dimension of mandibular incisors with bonded ceramic restorations

Mandibular incisors are difficult to restore with conventional anterior crowns due to their small axial diameters. Crown preparation risks pulp exposure and results in a thin core of dentine. An experiment was designed to determine if increasing the thickness of ceramic to restore incisal edges affects the load at the point of restoration failure. Forty-eight mandibular incisors were randomly divided into four groups. The incisal edges of the teeth in three groups were reduced so that the coronal height was 7.5 mm (Group A), 6.5 mm (Group B), and 5.5 mm (Group C). Group D was designated as the experimental control. A fifth group (Group E), independent of the random sample, was introduced to the study for discussion purposes and was characterized by each of the incisors having an intact incisal edge of enamel. Groups A, B and C were prepared in a standard fashion for ceramic veneer restorations that were constructed to restore the vertical height of each tooth to 8.5 mm. Prior to cementation, the preparation surfaces were analysed and the relative surface areas of enamel and dentine were calculated. The ceramic restorations were cemented using a resin luting agent. The teeth were then thermocycled prior to loading at 135 degrees C until failure. The mean fracture load was 305 N (SD 134 N) for Group A, 403 N (SD 101 N) for Group B, 515 N (SD 296 N) for Group C, 587 N (SD 187 N) for Group D and 395 N (SD 129 N) for Group E. As determined by analysis of variance followed by a Sheffè multiple comparison test there was a significant difference (p < or = 0.01) between Group A and Group D. There were no significant correlations of load at failure with the percentage of exposed dentine, enamel surface area, total preparation surface area, and the incisal surface area. The patterns of failure of the fractured specimens were also analysed. There were significantly (p < or = 0.05) greater fractures of the ceramic restorations when they were bonded with the minimum incisal thickness of ceramic.     

Influence of a desensitizing agent on efficacy of a paint-on bleaching agent

PURPOSE: To evaluate the influence of a desensitizing agent (VivaSens) on efficacy of a paint-on bleaching agent (VivaStyle Paint On Plus). METHODS: Bleaching was performed for 7 days with VivaStyle Paint On Plus. The varnish was applied twice a day for 10 minutes each. 80 subjects were included in the study and randomly distributed in two groups (n = 40) according to exposed cervical dentin and perceived hypersensitivities. Group A used VivaStyle without VivaSens while Group B used VivaStyle Paint On Plus after a single application of VivaSens. Tooth color was assessed on facial surfaces of first upper incisors with Vita shade guide at baseline and 10 days after bleaching therapy. Sensitivity, with intensity graded from 0 (no sensitivity) to 10 (high sensitivity), was assessed chair-side using a blow of air at baseline, at the end of therapy (7 days) and 10 days after bleaching therapy. Statistical evaluation was performed with non parametric ANOVA. RESULTS: Thirteen subjects dropped out of the study; six due to gingival burning sensation (A: 3; B: 3) related to the bleaching regimen and seven due to lack of compliance. Directly after completion of bleaching therapy, tooth color had changed significantly compared to baseline in both treatment groups without difference among the groups. Color changes (Delta) according to Vita shade guide were as follows (mean +/- standard deviation): Group A: Delta 2.7 +/- 1.0, Group B: Delta 2.8 +/- 0.9. After bleaching (7 days) the intensity of tooth hypersensitivity (mean +/- standard deviation) was increased significantly compared to baseline in both groups (P < 0.05): Group A: 1.58 +/- 1.91 (baseline: 0.4 +/- 0.5); Group B: 1.3 +/- 1.8 (baseline: 0.5 +/- 0.7). The number of subjects reporting tooth hypersensitivity increased in Group A by 5 (n = 13) and in Group B by 1 (n = 10) subject. Although degree of hypersensitivities and number of subjects with hypersensitivities were lower in Group B, there was no significant difference between the groups.     

Effect of chelating agents on the molecular composition and extent of decalcification at cervical, middle and apical root dentin locations

The aim of this study was to investigate the interaction of two chelating agents used in endodontic treatment with dentin from different root locations. Standardized cervical, middle and apical root dentin specimens were prepared and subjected to treatment with 15% neutral EDTA and RCPrep. Following rinsing with water, dentin surfaces were studied by reflected light optical microscopy and micro-MIR FTIR spectroscopy, while the wash-off extracts were analyzed by atomic absorption spectrometry (AAS) to determine the content of calcium and phosphorus. Neutral EDTA removed the smear layer and opened tubules while RCPrep did not. FTIR measurements showed higher decalcification of dentin surfaces after neutral EDTA treatment although its effect was reduced at apical regions. AAS measurements of calcium and phosphorus confirmed the higher dentin dissolution potential of EDTA at cervical and middle root dentin locations. The results of the present study implied different reaction modes for the two chelating agents tested which might affect the efficiency of the chemo-mechanical preparation when these agents are used.     

Remaining dentinal thickness after simulated post space preparation and the fit of prefabricated posts to root canal preparation shapes

BackgroundPost space preparation can increase the risk of experiencing perforation and root fracture. The authors assessed remaining dentin thickness after post space preparation and the fit of different prefabricated posts to root canal preparation systems in a theoretical model.MethodsTen datasets per type of tooth from cone-beam computed tomography were analyzed to determine the minimum root diameter from 5 through 13 mm from the apical foramen. The preparation shapes of 10 root canal preparation systems were calculated and compared with the root dimensions to determine the remaining dentin thickness. Eight post brands were compared with root dimensions to determine the areas where there was less than 1 mm dentin thickness.ResultsThe average root canal preparation shape produced canal diameters of 0.57 mm at 5 mm from the canal terminus and 0.94 mm at 13 mm from the canal terminus. The mean post size tip diameter was 1.03 mm, which is larger than the dimensions of the average canal preparation. Post preparation would result in less than 1 mm of dentin thickness remaining in premolars, smaller roots of molars, and mandibular incisors. The area with less than 1 mm of dentin thickness was around the post tip.ConclusionsEndosequence Fiber Post (Brasseler USA), RelyX Fiber Post 3D (3M), and Rebilda (VOCO) were the better fitting posts with the root canal preparation shapes.Practical ImplicationsMany posts would result in less than 1 mm dentin thickness. Clinicians should use posts that fit their root canal preparations to minimize dentin removal.     

Influence of cement thickness and mechanical cycling on the push-out bond strength between posts and root dentin

The aim of this study was to assess the influence of mechanical cycling and cement thickness on the bond strength between fiber posts and root dentin. Forty bovine teeth were sectioned (16 mm) and randomly assigned to four groups (n = 10). Specimens in Groups 1 and 2 were cemented using a thinner cement layer, while specimens in Groups 3 and 4 were cemented using a thicker cement layer. Groups 2 and 4 were submitted to mechanical cycling. Four slices per specimen were produced and submitted to push-out testing. Bond strength values were not affected by mechanical cycling (P = 0.2893), although the thickness of the cement layer did affect bond strengths (P = 0.0059, thinner > thicker). Tukey's test showed that Group 1 (19.27 MPa) had a higher mean bond strength value than Group 3 (12.4 MPa) and Group 4 (13.6 MPa), while Group 2 (15.0 MPa) was statistically similar to all groups. These results indicate that a thicker cement layer negatively affected the push-out bond strength between a fiber post and root dentin, regardless of whether the specimens were subjected to mechanical cycling.     

伢典化学机械去龋法的粘结性能研究

目的：利用健康离体牛牙,评价伢典对健康牙本质与复合树脂间剪切粘结强度的影响。方法：选取新鲜拔除的牛切牙28颗,磨除唇面釉质,暴露牙本质,分为4组,即空白对照组,酸蚀组,伢典处理组,伢典处理＋酸蚀组。分为不做预处理组,37%磷酸酸蚀组,伢典处理牙本质表面3min组,伢典处理牙本质表面3min后再用37%磷酸酸蚀处理组。在牙本质表面粘结形成直径5mm,高3mm的光固化树脂圆柱体。37℃水浴24h后,以1mm/min的加载速度进行剪切粘结强度测试。结果：伢典处理后的健康牙本质的剪切粘结强度大于不做预处理的健康牙本质。伢典处理不影响酸蚀效果。结论：伢典对复合树脂与健康牙本质间的粘结强度没有显著影响。