VLC—2型光固化粘结剂的研制

研制一种可取代ＶＬＣ－１型粘结剂的新型可见光固化粘结剂，按照有关试验标准和参考资料测定研制的新型粘结剂和ＶＬＣ－１型，ＤｕｒａｆｉｌｌＢｏｎｄ粘结剂的剪切粘结强度，压缩强度，径向拉伸强度，表面硬度和聚全程度。新型粘结剂的ＣＳ，ＤＴＳ，Ｈｖ，ＳＢＳ和ＤＰ分别为１９６．２ＭＰａ，４１．９ＭＰａ，２８６．８ＭＰａ，２８．４ＭＰａ和６３．１％，明显高于ＶＬＣ－１型粘结剂。     

先天性唇腭裂病儿TORCH感染的血清学研究

目的：为了探讨弓形虫（ＴＯ）,风疹病毒（ＲＶ）,巨细胞病毒（ＣＭＶ）和单纯疱疹病毒Ⅱ（ＨＳＶⅡ）感染与先天性唇腭裂发生的关系。方法：对１２０例２月龄至１０岁唇腭裂病儿和６２名正常儿童血清抗ＴＯ－ＩｇＭ,抗ＲＶ－ＩｇＭ,抗ＣＭＶ－ＩｇＭ和抗ＨＳＶⅡ－ＩｇＭ用ＥＬＩＳＡ法作检。结果：病儿阳性率分别为４．２％,３．３％,３３．３％和３．３％,正常儿分别为１．６％,３．２％,２１．０％和３．３％,两者统计学上无显著差异。２～３月龄组病儿抗ＣＭＶ－ＩｇＭ阳性率为４３．８％,显著高于正常儿的９．１％（Ｐ＜０．０５）。结论：唇腭裂的发生与ＴＯ,ＲＶ和ＨＳＶⅡ感染可能无明显关系,与先天性ＣＭＶ感染有一定关系。     

酸-盐体系预处理液的pH值对牙本质粘接强度的影响

目的探讨酸－盐体系预处理液（ａｃｉｄ－ｓａｌｔｐｒｅｔｒｅａｔｉｎｇｓｏｌｕｔｉｏｎｓｙｓｔｅｍ，ＡＰＳＳ）促进牙本质粘接的机理。方法以４－ＭＥＴＡ／ＭＭＡ－ＴＢＢ树脂为粘接体系，测试了酸处理后再用不同ｐＨ值ＡＰＳＳ处理牙本质的抗张粘接强度（ｔｅｎｓｉｌｅｂｏｎｄｉｎｇｓｔｒｅｎｇｔｈ，ＴＢＳ）。结果随着ＡＰＳＳ的ｐＨ值的降低，牙本质ＴＢＳ从１０．４１ＭＰａ逐渐升高至１５．７３ＭＰａ；金属盐溶液中是否含酸，对牙本质的ＴＢＳ有显著影响（Ｐ＜０．０５）。结论结果提示，ＡＰＳＳ中金属离子存在的形式与牙本质ＴＢＳ密切相关。     

硼酸铝晶须对不同树脂体系实验复合树脂力学性能的作用

目的：评价硼酸铝晶须对不同树脂体系实验复合树脂力学性能的作用。方法：采用四种基质树脂和两种稀释单体，按照有关实验方法测试各种实验复合树脂的表面硬度（Ｈｖ）、径向拉伸强度（ＤＴＳ）和压缩强度（ＣＳ）。结果：晶须组的机械性能优于对照组，表面硬度（Ｈｖ）对照组高于晶须组。结论：晶须对复合树脂的ＣＳ、ＤＴＳ有明显增强作用；ＰＵ基质树脂组的力学性能明显优于其它实验组（Ｐ＜０．０１）。     

抗S.mutans(血清型c)细胞表面蛋白P_1抗体对各型变链粘附的影响

目的：观察Ｓ．ｍｕｔａｎｓ遗传Ｉ型（血清ｃ型）Ｐ１抗体对遗传Ⅱ～Ｖ型（血清ａ～ｇ型）变链菌在唾液包被的羟磷灰石微珠（Ｓ－ＨＡ）表面粘附的影响。方法：用提纯的变链Ｓ．ｍｕｔａｎｓＭＴ６Ｒ的细胞表面蛋白Ｐ１加弗氏佐剂通过局部唾液腺和背部皮下注射免疫ＢＡＬＢ／ｃ鼠，得到含高效价Ｐ１抗体的鼠血清和唾液。结果：发现遗传Ｉ型变链菌的抗Ｐ１抗体可抑制除Ｓ．ｒａｔｕｓ（遗传Ⅱ型，血清ｂ型）以外的各型变链在Ｓ－ＨＡ表面的粘附（Ｐ＜０．０５）。结论：蛋白Ｐ１可作为各型变链菌间的共同抗原。     

牙龈成纤维细胞和牙周韧带细胞前列腺素含量分析

作者对体外培养的人牙龈成纤维细胞（ＧＦ）和牙周韧带细胞（ＰＤＬＣ）采用免疫组化ＡＢＣ染色及显微分光光度法分析，测定ＧＦ和ＰＤＬＣ中前列腺素Ｅ２（ＰＧＥ２）、６－酮一前列腺素Ｆ１ａ．（６－Ｋ－ＰＧＦ１ａ）和血栓素Ｂ２（ＴＸＢ２）含量，以探讨其与牙周炎的关系，结果表明ＧＦ的ＰＧＥ２吸光度为０．２５±０．０３，６－Ｋ－ＰＧＦ１ａ的吸光度为０．２０±０．０３，与对照组相比均有非常显著性差异；ＰＤＬＣ的吸光度分别为ＰＧＥ２０．２１±０．０２、ＴＸＢ２０．１６±０．０３和６－Ｋ－ＰＧＦ１ａ０．１３±０．０２，与对照组相比均有非常显著性差异。表明ＧＦ和ＰＤＬＣ均可分泌一定量的ＰＧＥ２、ＴＸＢ２和６－Ｋ－ＰＧＦ１ａ，但分泌的量略有差异，提示ＧＦ和ＰＤＬＣ可通过分泌ＰＧ，影响牙龈炎症变化和牙周组织再生。     

聚乳酸和无活性脱钙骨基质载体对rhBMP-2异位诱导骨形成的比较性研究

目的：为了研究聚乳酸和无活性脱钙骨基质载体对ｒｈＢＭＰ－２异位诱导的骨形成。方法：将重组人骨形态发生蛋白－２（ｒｈＢＭＰ－２）与无活性脱钙骨基质（ＤＢＭ）和聚乳酸（ＰＬＡ）复合,植入小鼠股部外侧肌肉陷窝比较ＰＬＡ和ＤＢＭ载体对ｒｈＢＭＰ－２诱导骨形成的影响。通过组织学检查、碱性磷酸酶（ＡＬＰ）和钙含量测定以及骨钙素（ＢＧＰ）放疫测定,进行对比观察。结果：术后２１天,实验组均可见新生软骨细胞和软骨岛,ｒｈＢＭＰ－２／ＰＬＡ和ＤＢＭ／ｒｈＢＭＰ－２组还可见部分骨组织形成,见骨小梁、板层结构和红骨髓,ｒｈＢＭＰ－２／ＰＬＡ组ＰＬＡ部分吸收,ＤＢＭ／ｒｈＢＭＰ－２组ＤＢＭ无吸收迹象。各实验组与对照组对比,ＡＬＰ、ＢＧＰ水平和Ｃａ量均有显著性差异（Ｐ＜０．０５）,ｒｈＢＭＰ－２／ＰＬＡ与ＤＢＭ／ｒｈＢＭＰ－２组在ＡＬＰ和ＢＧＰ水平上相比无显著差异（Ｐ＞０．０５）,但前组比后组的Ｃａ量为高（Ｐ＜０．０５）,这二组与单独植入ｒｈＢＭＰ－２组相比,定量检测指标均有显著性差异（Ｐ＜０．０５）。结论：（１）ＰＬＡ和ＤＢＭ均为ＢＭＰ的良好载体;（２）ｒｈＢＭＰ－２／ＰＬＡ是一种新的有价值的骨修复材料     

抗S.mutans（血清型c）细胞表面蛋白P1抗体对各型变链粘附…

目的：观察Ｓ．ｍｕｔａｎｓ遗传Ⅰ型（血清ｃ型）Ｐ１抗体对遗传Ⅱ－Ⅴ型（血清ａ－ｇ型）变链菌在唾液包羟磷灰石微珠（Ｓ－ＨＡ）表面粘附的影响。方法：用提纯的变链Ｓ．ｍｕｔａｎｓＭＴ６Ｒ的细胞表面蛋白Ｐ１加弗氏佐剂通过局部唾液腺和背部皮下注射免疫ＢＡＬＢ／ｃ鼠，得到含高效价Ｐ１抗体的鼠血清和唾液。结果：发现遗传Ⅰ型变链菌的抗Ｐ１抗体可抑制除Ｓ．ｒａｔｔｕｓ遗传Ⅱ型，血清ｂ型）以外的各型变链在Ｓ－ＨＡ表面     

胰岛素样生长因子-Ⅰ和骨形态发生蛋白-2对人牙周膜细胞增殖的作用

目的：重组人胰岛素样生长因子－Ｉ（ｒｈＩＧＦ－Ｉ）、重组人骨形态发生蛋白－２（ｒｈＢＭＰ－２）分别或联合应用对人牙周膜（ＰＤＬ）细胞增殖的影响。方法：采用组织块法体外培养人ＰＤＬ细胞,ＭＴＴ法测定ＰＤＬ细胞在不同生长因子刺激下的增殖情况。结果：ｒｈＩＧＦ－Ｉ、ｒｈＢＭＰ－２都可促进人ＰＤＬ细胞的增殖,这种促增殖作用呈一定的浓度依赖性,ｒｈＩＧＦ－Ｉ与ｒｈＢＭＰ－２联合应用对人ＰＤＬ细胞的增殖有协同作用,且与单独应用相比相差显著。结论：ｒｈＩＧＦ－Ｉ、ｒｈＢＭＰ－２可望作为牙周再生的生物活性介质,ｒｈＩＧＦ－Ｉ与ｒｈＢＭＰ－２联合应用对ＰＤＬ细胞的促增殖作用更强。     

先天性唇腭裂病儿TORCH感染的血清学研究

目的：为了探讨弓形虫（ＴＯ），风疹病毒（ＲＶ），巨细胞病毒（ＣＭＶ）和单纯疱疹病毒Ⅱ（ＨＳＶⅡ）感染与先天性唇腭裂发生的关系。方法：对１２０例２月龄至１０岁唇腭裂病儿和６２名正常儿童血清抗ＴＯ－ＩｇＭ，抗ＲＶ－ＩｇＭ，抗ＣＭＶ－ＩｇＭ和抗ＨＳＶⅡ－ＩｇＭ用ＥＬＩＳＡ法作检。结果：病儿阳性率分别为４．２％，３．３％，３３．３％和３．３％，正常儿分别为１．６％，３．２％，２１．０％和３．３％，两者统计     

Compressive and diametral tensile strength of glass ionomer cements

The aim of this study was to compare, in different periods of time, the compressive and diametral tensile strength of a traditional high viscous glass ionomer cement: Fuji IX (GC Corporation), with two new Brazilian GIC's: Vitro-Molar (DFL) and Bioglass R (Biodinamica), all indicated for the Atraumatic Restorative Treatment (ART) technique. Fifteen disk specimens (6.0mm diameter x 3.0mm height) for the diametral tensile strength (DTS) test and fifteen cylindrical specimens (6.0mm diameter x 12.0mm height) for the compressive strength (CS) test were made of each GIC. Specimens were stored in deionized water at 37o C and 100% of humidity in a stove until testing. Five specimens of each GIC were submitted to CS and DTS test in each period, namely 1 hour, 24 hours and 7 days. The specimens were tested in a testing machine (Emic) at a crosshead speed of 1.0mm/min for CS and 0.5mm/min for the DTS test until failure occurred. The data were submitted to two-way ANOVA and Tukey tests (alpha=0.05). The mean CS values ranged from 42.03 to 155.47MPa and means DTS from 5.54 to 13.72 MPa, with test periods from 1h to 7 days. The CS and DTS tests showed no statistically significant difference between Fuji IX and Vitro Molar, except for CS test at 1-hour period. Bioglass R had lowest mean value for CS of the cements tested. In DTS test Bioglass R presented no statistically significant differences when compared with all others tested GICs at 1-hour period and Bioglass R presented no difference at 24-hour and 7-day periods when compared to Vitro-Molar. Further studies to investigate other physical properties such as fracture toughness and wear resistance, as well as chemical composition and biocompatibility, are now needed to better understand the properties of these new Brazilian GIC's.     

Effect of food and oral simulating fluids on dentine bond and composite strength

The effect of up to 30 days' immersion in 75% ethanol solution and in an artificial saliva (Moi-Stir) on the dentine shear bond strength (SBS) of three adhesive/composite systems (Tenure/Marathon One, Scotchbond Multi-Purpose/Z100 and Optibond/Herculite XRV) was evaluated. Two control series were stored either in 100% humidity or in air. Diametral tensile specimens (DTS) of the composites studied were stored in 75% ethanol for up to 30 days. The fracture mode and morphology of the failure interface were examined by scanning electron microscopy (SEM). Data were analysed using ANOVA and the Tukey LSD test. The SBS for all systems stored in Moi-Stir (24.8 ± 3.0 MPa) and air (28.3 ± 3.0 MPa) was not influenced by length of storage. Microscopic (SEM) examination of the debonded air, and Moi-Stir stored specimens showed that failure had primarily occurred through the dentine. Significant decreases (30–50%) in the SBS of all systems occurred after immersion in 75% ethanol. There was no significant difference among brands. The DTS of the composites showed significant decreases as a function of ethanol exposure. Marathon One and Herculite XRV showed significantly lower DTS after 14 days' storage while Z100 showed no reduction in DTS until after 30 days. The decrease in both SBS and DTS after storage in ethanol was a function of the square root of time (P < 0.001) and followed Fick's laws of diffusion. Ethanol diffusivity was approximated as 1.8 × 10⁻⁶ cm² s⁻¹ for both SBS and DTS specimens, suggesting that alcohol attack in SBS specimens occurred primarily in the composite system. Microscopic examination found, at 7 days and longer storage times, numerous cracks through the composite, around the filler particles, or within the bonding agent, but not in the dentine.     

Modification of conventional glass-ionomer cements with N-vinylpyrrolidone containing polyacids, nano-hydroxy and fluoroapatite to improve mechanical properties

OBJECTIVE: The objective of this study was to enhance the mechanical strength of glass-ionomer cements, while preserving their unique clinical properties. METHODS: Copolymers incorporating several different segments including N-vinylpyrrolidone (NVP) in different molar ratios were synthesized. The synthesized polymers were copolymers of acrylic acid and NVP with side chains containing itaconic acid. In addition, nano-hydroxyapatite and fluoroapatite were synthesized using an ethanol-based sol-gel technique. The synthesized polymers were used in glass-ionomer cement formulations (Fuji II commercial GIC) and the synthesized nanoceramic particles (nano-hydroxy or fluoroapatite) were also incorporated into commercial glass-ionomer powder, respectively. The synthesized materials were characterized using FTIR and Raman spectroscopy and scanning electron microscopy. Compressive, diametral tensile and biaxial flexural strengths of the modified glass-ionomer cements were evaluated. RESULTS: After 24h setting, the NVP modified glass-ionomer cements exhibited higher compressive strength (163-167MPa), higher diametral tensile strength (DTS) (13-17MPa) and much higher biaxial flexural strength (23-26MPa) in comparison to Fuji II GIC (160MPa in CS, 12MPa in DTS and 15MPa in biaxial flexural strength). The nano-hydroxyapatite/fluoroapatite added cements also exhibited higher CS (177-179MPa), higher DTS (19-20MPa) and much higher biaxial flexural strength (28-30MPa) as compared to the control group. The highest values for CS, DTS and BFS were found for NVP-nanoceramic powder modified cements (184MPa for CS, 22MPa for DTS and 33MPa for BFS) which were statistically higher than control group. CONCLUSION: It was concluded that, both NVP modified and nano-HA/FA added glass-ionomer cements are promising restorative dental materials with improved mechanical properties.     

Effects of different etching methods and bonding procedures on shear bond strength of orthodontic metal brackets applied to different CAD/CAM ceramic materials

Objective:To investigate the shear bond strength (SBS) of orthodontic metal brackets applied to different types of ceramic surfaces treated with different etching procedures and bonding agents.Materials and Methods:Monolithic CAD/CAM ceramic specimens (N = 120; n = 40 each group) of feldspathic ceramic Vita Mark II, resin nanoceramic Lava Ultimate, and hybrid ceramic Vita Enamic were fabricated (14 × 12 × 3 mm). Ceramic specimens were separated into four subgroups (n = 10) according to type of surface treatment and bonding onto the ceramic surface. Within each group, four subgroups were prepared by phosphoric acid, hydrofluoric acid, Transbond XT primer, and Clearfill Ceramic primer. Mandibular central incisor metal brackets were bonded with light-cure composite. The SBS data were analyzed using three-way analysis of variance (ANOVA) and Tukey HSD tests.Results:The highest SBS was found in the Vita Enamic group, which is a hybrid ceramic, etched with hydrofluoric acid and applied Transbond XT Adhesive primer (7.28 ± 2.49 MPa). The lowest SBS was found in the Lava Ultimate group, which is a resin nano-ceramic etched with hydrofluoric acid and applied Clearfill ceramic primer (2.20 ± 1.21 MPa).Conclusions:CAD/CAM material types and bonding procedures affected bond strength (P < .05), but the etching procedure did not (P > .05). The use of Transbond XT as a primer bonding agent resulted in higher SBS.     

Mechanical properties of bioactive amorphous calcium phosphate/methacrylate composites.

OBJECTIVES: The aim of this study was to determine whether amorphous calcium phosphate (ACP)-containing composites, which have the ability to release mineralizing levels of Ca and PO4 ions, have appropriate mechanical properties for use as base and lining materials. METHODS: Composites of pyrophosphate-stabilized ACP particulates (mass fraction of 40%) and photo-activated methacrylate resins (mass fraction of 60%) were tested for biaxial flexure strength (BFS), diametral tensile strength (DTS), and compressive strength (CS). Hydroxyapatite (HAP; mass fraction of 40%), and micro-sized glass (mass fraction of 50%) composites as well as a commercial visible light curable base/liner were also tested. The significance between mean values was determined by Student-Newman-Keuls multiple comparisons (p < 0.05). RESULTS: BFS of dry and wet (24 h at 37 degrees C in water) ACP composites (60.3 and 62.0 MPa, respectively) were significantly lower than those of the comparison materials (79.2-109.3 MPa). CS values were likewise lower (62.9 MPa dry and 67.6 MPa wet vs 80.6-196.8 MPa) except for the wet base/liner (58.5 MPa). DTS of the dry ACP composite (21.8 MPa) was comparable with that of the HAP (22.8 MPa) and glass (25.5 MPa) composites, but lower than that of the base/liner (36.2 MPa). DTS decreased significantly when the ACP composite was wet (17.8 MPa). SIGNIFICANCE: These results suggest that the remineralizing ACP polymeric composites, although mechanically weaker in some respects than other polymeric composites, have properties suitable for use as base and lining materials.     

Mechanical properties of calcium phosphate based dental filling and regeneration materials

The objective of this study was to compare the mechanical properties of calcium phosphate cements (CPC) for possible dental applications with varied liquid and powder compositions under the same testing condition. Cements studied in this experiment were divided into two groups of CPC not containing polymer and polymeric CPC (PCPC). Cement powder was formed by combining equimolar amounts of dicalcium phosphate anhydrous and tetracalcium phosphate, or acrylic resin polymer powder mixture. The CPC specimens for the compressive strength (CS) and diametral tensile strength (DTS) measurements were prepared by mixing powder and liquid for 30 s with a powder/liquid ratio of 3:1, and subsequently packing the paste into a brass mould. The specimens were kept at 37 degrees C and 100% relative humidity for 24 h before measurements were conducted on a Universal Testing Machine with a cross-head speed of 1 mm min-1. The CS of CPC was 0.14-10.29 MPa and that of PCPC was 0.26-117.58 MPa. The DTS of CPC was 0.10-4.56 MPa and that of PCPC was 0.07-22.54 MPa. The CS and DTS were very diverse depending on the composition of powder and liquid. Some compositions showed higher values than commercial liners. Thus compositions of 2% carboxymethyl cellulose + 35% citric acid in phosphate buffered saline (PBS), 20% gelatin in PBS, 2% sodium alginate in PBS, 20-40% aqueous acrylic-maleic copolymer solution, and some of the HPMC and PMVE-Ma solutions exhibited promising formulae for dentine regenerating materials. Acrylic resin-PCPC group showed generally higher CS and DTS values. Based on this study, further studies on the reaction with odontoblast and resultant dentine regeneration should be performed using promising compositions.     

Fluoridated light-activated bonding resin adhesion to enamel and dentin: primary vs. permanent

PURPOSE: This study compared fluoridated bonding resin adhesion to primary enamel (Group 1), primary dentin (Group 2), permanent enamel (Group 3), and permanent dentin (Group 4). METHODS: The buccal surfaces of 24 primary molars and 24 premolars were used. The bonding system and resin composite used in this study were Imperva Fluorobond and Lite-Fil IIA (Shofu Inc., Kyoto, Japan). Effects of tooth surface conditioning by FB primer were observed using SEM (N = 2/group). Shear bond strengths (SBS) were tested, and the test surfaces of enamel, dentin, and resin specimens were observed using SEM (N = 10/group). Data was statistically analyzed using one-way ANOVA with subsequent post hoc Duncan's new multiple range test at P < 0.05. RESULTS: Effects of tooth surface conditioning by FB primer were appropriate to dentin but low to enamel. Means and standard deviations of the SBS for each group were: Group 1 (16.34, 5.53 MPa), Group 2 (15.06, 7.02 MPa), Group 3 (14.39, 6.52 MPa) and Group 4 (15.45, 5.35 MPa). There was no significant difference of SBS among Groups 1, 2, 3, and 4. CONCLUSION: Imperva Fluorobond system gave the same level of bond strength to primary enamel, primary dentin, permanent enamel, and permanent dentin.     

Role of bonding agents in the repair of composite resin restorations

Six commonly used composite resin materials and recommended bonding systems were tested to assess shear bond strength at the interface between aged and new composites with and without bonding. Test specimens were aged in water for 60 d before new composite was placed. Shear bond strength was assessed after 22 ± 2 h (Test 1) and after additional ageing by thermocycling (5-55°C/5,000 cycles) (Test 2). After an additional 180 d in water, the aged specimens were randomly divided into three groups to blind the test with respect to the aged composite. New composites were placed on aged specimens (two groups with and one without bonding agent) and thermocycled (Test 3). After 24 h (Test 1), the mean shear bond strength of the test specimens was 21-26 MPa when bonding agents were used, as opposed to 10-15 MPa without bonding agents. After thermocycling (Test 2), the mean shear bond strength was 16-23 MPa with a bonding agent and 17 MPa without a bonding agent. After 180 d in water and subsequent thermocycling (Test 3), the mean shear bond strength was 9-13 MPa with bonding agent and 2-3 MPa when no bonding agent was used. The results of this study therefore indicate that the use of bonding agents significantly improves the quality of composite repair.     

Diametral tensile and compressive strengths of several types of core materials.

PURPOSE: Compressive and diametral tensile strengths (DTSs) of core materials are thought to be important, because cores usually replace a large bulk of tooth structure and should provide sufficient strength to resist intraoral tensile and compressive forces. This study was undertaken to compare the mechanical properties of materials used for direct core foundations. MATERIAL AND METHODS: The differences between the compressive and DTSs of six core materials, including Duralloy (high-copper amalgam), Grandio (visible light-cured nanohybrid resin composite), Admira (organically modified ceramic), Filtek P60 (packable composite resin), Rebilda DC (dual-cure adhesive core material), and Argion Molar (silver-reinforced glass ionomer cement), were tested. A total of 120 specimens, half for the compressive strength (CS) test (6 mm in height, 4 mm in diameter) and the other half for the DTS test (6 mm in diameter, 3 mm in thickness), were prepared. The specimens were stored at room temperature in distilled water for 7 days. The Lloyd testing machine was used to load the specimens at a crosshead speed 0.5 cm/min, and the strength values were determined in MPa. RESULTS: The compressive and DTS test values (in MPa), respectively, of the materials were: Admira (361, 44); Filtek P60 (331, 55); Grandio (294, 53); Rebilda DC (279, 42); Duralloy (184, 40); and Argion Molar (107, 9). Kruskal-Wallis test was computed, and multiple comparisons test discerned many differences among materials (p < 0.05). CONCLUSION: Packable composite resin (Filtek P60), visible light cured nanohybrid resin composite (Grandio), and organically-modified ceramic (Admira) had higher compressive and DTS values than the other materials.