| Part1:The Enamel Microstructures of Bovine Mandibular IncisorsObjective:The aim of this study was to investigate the detail enamel microstructures of bovine incisors including arrangements of prisms and interprisms, and their spatial relationshipMaterials and Methods:Nine freshly extracted bovine mandibular incisors were cut off roots with a low speed diamond saw (Isomet, Buchler, Lake Bluff). After the eight incisors were cut longitudinally into three fragments (mesial, middle, and distal thirds) at the labiolingual direction, each fragment was horizontally cut into three smaller fragments (incisal, middle, and cervical thirds) to obtain9fragments. Each fragment was further trisected longitudinally and horizontally to achieve77pieces before each piece was cut into two through the middle of the enamel parallel to enamel-dentin junction. All the sectioned surfaces were treated1mol/1HC1for10s to expose prism and interprisms, dehydrated in ascending concentrations of ethanol (25,50,75, and100%for20min), and then sputtered with platinum before they were analyzed by scanning electron microscopy (SEM, Zeiss Ultra55, Germany). Another bovine incisor was cut to prepare an enamel disk. The labial enamel surface was polished to3000-grit SiC paper, etched by10%citric acid for3s, air dried and observed with an atomic force microscopy (NanoScope IVa AFM, Veeco/DI, USA) using the tapping mode.Results:The SEM micrographs showed the parallel enamel prisms were located in all the outer enamel, the cervical region and the incisal ridge of the bovine incisors. Most labial inner enamel and the cingulum of lingual inner enamel were composed of the Hunter-Schreger Bands (HSBs) with the characteristics of decussating groups of prisms and decussating planes between interprisms and prisms. The interprisms were thicker in the inner enamel than in the outer enamel. The AFM micrographs revealed that the HAp crystals of bovine enamel were about600nm long and80nm wide.Conclusion:Bovine enamel is mainly composed of parallel prisms and HBSs with the characteristics of decussating groups of prisms and decussating planes between interprisms and prisms. The parallel enamel prisms are located in all the outer enamel, the cervical region and the incisal ridge, while HBSs are located in most labial inner enamel and the cingulum of lingual inner enamelPart2:Comparative Study on Enamel Microstructures of Bovine and Human IncisorsObjective:To comparatively investigate the enamel microstructures of bovine and human incisors.Materials and Methods:Seventeen human incisors (5maxillary central incisors,4each maxillary lateral and mandibular central/lateral incisor) freshly extracted for periodontal reasons without caries and defects and freshly extracted eight caries/defect-free bovine mandibular incisors were used in the study. All incisors were stored in1‰thymol solution at4℃and their roots were cut off1mm under cemento-enamel junction (CEJ) with a low speed diamond saw (Isomet, Buehler Ltd, Lake Bluff, USA). Sixteen Human incisors (4per specific incisor) and four bovine incisors were longitudinally cut into three fragments (mesial/middle/distal thirds) at the labiolingual direction before they were horizontally cut into three small fragments (occlusal/middle/cervical thirds). Each fragment of bovine incisors was further trisected in longitudinal or labiolingual directions. Human and bovine fragments were further trisected as in Part1. Subsequently, each fragment was bisected through the middle of the enamel parallel to enamel-dentin junction (EDJ). After the longitudinal section surfaces of each small piece were polished with a series of SiC abrasive paper (#500,#800, and#1,200; HERMES, Germany) under copious running water, they were submerged in1mol/1hydrochloric acid solution for10s to expose prisms and interprisms, and thoroughly water-sprayed. Subsequently, the specimens were dehydrated in a series of ethanol, dried in air, and sputtered with a platinum coat about5-6nm thickness. They were then observed with an SEM (Zeiss Ultra55, Germany) at4.5-6KV with a working distance of5-8.5mm in a secondary electron mode. The horizontal and tangential section enamel surfaces on each fragment were prepared and observed with the SEM as described above. The labial enamel surface of another human maxillary central incisor was prepared as the same as the bovine enamel surface in Part1and observed by AFM.Results:The SEM micrographs demonstrated that bovine and human incisor’s enamel was mainly composed of Hunter-Schreger Bands (HSBs) and parallel prisms (PP). HBS mainly located in most labial inner enamel and cingulum of lingual inner enamel while PP located in all the outer enamel, cervical region and incisal ridge. A transition zone was found between parazone and diazone within an HBS of bovine incisors, but not in human incisors. Interprisms appeared as thicker plate-like structures and decussated with prisms in bovine incisors, but were thin and round prisms in human incisors. Thicker PP in cingulum and thinner interprisms in whole enamel were main two characteristics of human maxillary central incisors. The AFM micrographs revealed that the HAp crystal of bovine enamel were larger in both length and width than the HAp crystals of human enamel.Conclusion:Bovine incisor’s enamel was characterized as thicker plate-like interprisms, a transition zone between parazone and diazone within an HBS, and prism/interprism decussating plane, but not in human incisors. Differences of enamel microstructure between bovine and human incisors should be taken into consideration when bovine teeth were substituted as human teeth for dental research.Part3:The Effects of Different Locations and Differently Sectioned Angulations on Bovine Enamel Bonding StrengthsObjective:The aim of the study was to investigate the effects of different locations and differently sectioned angulations on bovine enamel microtensile bond strengths (μTBS) of six self-etch adhesives.Materials and Methods:Thirty bovine mandibular incisors teeth were randomly assigned into five groups according to the cutting directions and locations:A: longitudinal section in an incisal-cervical direction through the middle of incisors; B:longitudinal section in an incisal-cervical direction through the middle of incisors with a45degree angle; C:Horizontal section in a mesial-distal direction at incisal, middle and cervical thirds; D:Horizontal sections with a45degree angle at incisal, middle and cervical thirds; E:Tangential section (labial enamel surfaces). The groups(C, D, E) were further divided into three subgroups at incisal, middle and cervical thirds. All the surfaces were polished serially with300-,800-,1200-grit silicon-carbide papers (MoPao260E, Shangdong, China) under running water. Six self-adhesives (Clearfil SE Bond, Clearfil S3BOND, Kuraray Co, Tokyo, Japan; IBOND, Heraeus Kulzer GmbH, Germany; G BOND, GC, Tokyo, Japan; Adper Easy One,3M ESPE AG, Germany; Xeno Ⅲ, Densply, Konstanz, Germany) were applied to the polished enamel surfaces strictly according the manufacturer’s instructions. Subsequently, the respective composite resins from the same manufacture (Clearfil Majesty; Kuraray Co; Venus, Heraeus Kulzer GmbH; Gradia Direct, GC Co; Filtek Z350,3M ESPE AG; Spectrum TPH3, Densply) were respectively placed on the adhesive-pretreated enamel surfaces in two2mm increments. After24h water storage at37℃, the specimens were prepared into1mm×1mm×8mm multiple beams using a slow-speed diamond saw (Isomet1000, Buehler Ltd, Lake Bluff, USA) perpendicularly through the resin-enamel interfaces. The microtensile bond strength test was performed with a Micro Tensile Tester (BISCO, IL, USA) at a crosshead speed of1mm/min until fracture. Sectioned enamel surfaces and fractured surfaces were observed by SEM. Data was analyzed by factorial design ANOVA (three factors:cutting directions, locations, adhesives), Univariate analysis of variance (Full Model, quadratic sum type IV) and post hoc Tukey’s HSD multiple comparisons at significance level of0.05.Results:There was an interaction of three affecting factors (such as section directions, locations and adhesives) on the enamel microtensile bond strengths (p<0.05). The longitudinal section with or without a45degree angle resulted in lowest enamel μTBS among the all groups (p<0.001). The μTBS of the adhesive Clearfil SE Bond was highest among the six adhesives (p<0.001). Horizontal section at cervical third of bovine incisors resulted in significantly higher enamel μTBS than horizontal sections at incisal and middle thirds (p<0.001), however, there was no significant different enamel μTBS between the latter two. Sections with a45degree angle did not make significant improvement of enamel μTBS in all groups. The SEM findings revealed that majority of the enamel prisms of longitudinal sections with or without a45degree angle paralleled to the adhesive interface, while those of the other sections were perpendicular to the adhesive interfaces. Most of the fractured failures were adhesive failure in the study.Conclusion:The orientation of enamel prisms could affect the microtensile bond strengths. Enamel prisms of longitudinal sections with/without a45degree angle paralleling to adhesive interfaces produced significantly weaker enamel bond strengths than enamel prisms of the other sections with/without a45degree angle perpendicular to the adhesive interfaces. Enamel sectioned with a45degree angle did not improve the enamel bond strengths of enamel sectioned without a45degree angle. |
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