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Recent advancements in dental technology has led clinicians to convert from traditional methods to digital workflows. The purpose of this study was to analyze the effect of various finish line designs and occlusal morphologies on the accuracy of digital impressions. Six maxillary molar crown preparations were designed by using a digital sculpting software program. The samples differed in finish line design and occlusal surface morphology. Three different finish line designs (shoulder, chamfer, and shoulder with internal round angle) and two different occlusal morphologies (sharp and rounded) were used, giving six groups. Using three different intraoral scanners, each group was scanned and compared with a reference scan obtained from an industrial scanner. The accuracy of each scan was studied, and the data were statistically analyzed. A total of 180 scans were acquired by utilizing three different intraoral scanners. The reference scan was compared with the scans from each group and overall differences (marginal, axial, and occlusal) were assessed. A crown preparation with a chamfer finish line showed the lowest marginal discrepancy of 13.2 ± 4.18 μm while preparation with a shoulder finish line reported the highest discrepancy of 34.8 ± 7.9 μm (P < 0.05). Also, the occlusal discrepancies of the samples with rounded and sharp occlusal morphologies were 12.55 ± 3.09 μm and 19.13 ± 2.3 μm, respectively (P < 0.05). It has been suggested that chamfer finish line design and rounded occlusal anatomy may produce more accurate digital impression for single crown restorations. [ABSTRACT FROM AUTHOR]

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Abstract The ability to minimize vibrations in milling by the selection of cutting edge geometry and appropriate cutting conditions is an important asset in the optimization of the cutting process. This paper presents a measurement method and a signal processing technique to characterize and quantify the magnitude of the vibrations in an end milling application. Developed methods are then used to investigate the effects of various cutting edge geometries on vibrations in end milling. The experiments are carried out with five cutting edge geometries that are frequently used in machining industry for a wide range of milling applications. The results show that a modest protection chamfer combined with a relatively high rake angle has, for the most of cutting conditions, a reducing effect on vibration magnitudes. Furthermore, dynamics of a highly positive versus a highly negative cutting geometry is explored in time domain and its dependency on cutting conditions is presented. The results give concrete indications about the most optimal cutting edge geometry and cutting conditions in terms of dynamic behavior of the tool. [ABSTRACT FROM AUTHOR]

Single PDC cutter tests at a high pressure cell were conducted and analyzed to gain an understanding of the effect of cutter geometry on its frictional response. First, sets of tests conducted with sharp non-chamfered cutters are analyzed. A decreasing trend between the friction angle and back rake angle is consistently observed. The reason can be attributed to a change in flow direction of the rock in front and near the cutting face. A linear relationship between the friction angle and cutter back rake angle is proposed. The coefficient of this relationship can be calculated using the rock internal friction angle and at least one drilling data for the given drilling fluid and contacting surfaces. Four sets of tests with cutters of different diameters (13 and 16 mm) and chamfer lengths (0.010 and 0.016 inch) were conducted. The test results are presented and analyzed using the abovementioned semi empirical model. The method is to associate a chamfered cutter's action to an equivalent non-chamfered cutter back rake angle. It is observed that applying the test data to this analysis produces results that make physical sense with the geometric shape of a chamfered cutter. Finally, contact stress data, for the range of back rake angles tested, confirm a strong increasing trend with back rake angle. The observations indicate that, for the conditions of these tests, that the frictional response of a cutter with developed wear flat is dominated by the wear flat friction itself. [ABSTRACT FROM AUTHOR]

To evaluate residual dentin thickness (RDT) after different tooth preparations, 90 sound maxillary anterior teeth were selected and divided into 3 groups according to tooth type (n = 30), namely, maxillary central incisors, maxillary lateral incisors, and maxillary canines. In each group, specimens were randomly divided and prepared for single-crown coverage with shoulder (SHO, n = 10, control), slight chamfer (CHA, n = 10), and knife-edge (KNE, n = 10) finish lines. After tooth preparation, specimens were sectioned and divided into 4 subgroups (buccal, distal, palatal, and mesial) according to measurement area. RDT values were compared by using one-way ANOVA and Tukey's post hoc test (P = 0.05). Significant differences were found between SHO and the other two groups (P < 0.05) but not between CHA and KNE (P > 0.05). SHO was significantly more aggressive than CHA and KNE, which were comparable. Interproximal areas became critical due to thin RDT, which could potentially compromise the structural and biological integrity of teeth. The choice of finish line should be guided by careful clinical evaluation. [ABSTRACT FROM AUTHOR]

Abstract: Background and aim: One of the major problems of all ceramic restorations is their probable fracture against the occlusal force. The aim of the present in vitro study is to compare the effect of two marginal designs (shoulder and chamfer) on the fracture resistance of all ceramic restorations, INCERAM. Materials and methods: On an extracted first maxillary premolar 50in. chamfer margin (0.7mm) was prepared. Ten impressions were taken using a polyvinylsiloxane. The impressions were poured with epoxy resin to fabricate dies. The same tooth was retrieved and 50in. chamfer was converted into 90in. shoulder (1mm). Ten impressions were taken and ten more epoxy resin dies were fabricated. Impressions of each epoxy resin die were taken using polyvinylsiloxane impression material and poured with die stone. Alumina cores with 0.5mm thickness fabricated on the stone dies in a dental laboratory. The alumina cores were then cemented on the epoxy resin dies and underwent a fracture test with a universal testing machine and samples were investigated from the point of view of the origin of the failure. Result: The mean value of fracture resistance for the chamfer samples were 610.18±58.79N and 502.72±105.83N for the shoulder samples. The Student''s t-test revealed a statistically significant difference between groups. Conclusion: The result of this study indicates a relationship between the marginal design of the alumina cores and their fracture resistance. A chamfer margin could improve the biomechanical performance of posterior single crown alumina restorations. This may be because of the strong unity in the chamfer margin. [Copyright &y& Elsevier]

Statement of Problem: One of the major problems of the all ceramic restorations is their probable fracture against the occlusal force. However, there is not enough information about fracture resistance of all the ceramic crowns in different finishing lines. Purpose: The aim of present in-vitro study was to compare the effect of two marginal designs (shoulder and chamfer) on the fracture resistance of all ceramic restorations, Inceram. Methods and Material: On an extracted caries-free first maxillary premolar a 50-degree chamfer margin (0.7 mm) was prepared. Ten impressions were taken using a polyvinylsiloxane. The impressions were poured with epoxy resin to fabricate the dies. The same tooth was retrieved and the 50-degree chamfer was converted into a 90-degree shoulder margin (1mm). Ten impressions were prepared and 10 more epoxy resin dies were fabricated. The impressions of each epoxy resin die were taken using polyvinylsiloxane impression material and poured with die stone. Alumina cores with a thicknes of 0.5mm were fabricated on the stone dies in a dental laboratory. The alumina cores were then cemented with panavia on the epoxy resin dies and underwent a fracture test with a universal testing machine. The samples were then investigated regarding the origin of the failue. The statistical analysis was done using T-test. Result: The mean value of the fracture resistance for the chamfer samples was 610.18±58.79 N and that of the shoulder samples was 502.72±105.83 N. The student's T-test revealed a statistically significant difference between the groups ( p <0.05). Conclusion: The results of this study indicate a relationship between the marginal design and fracture resistance. A chamfer margin could improve the biomechanical performance of the posterior single crown alumina restorations. This might be due to the strong unity in the chamfer margin. [ABSTRACT FROM AUTHOR]

The primary purposes of this investigation were to evaluate sophomore dental student performance in the production of a chamfer finish line using two diamond bur types–a round–ended bur and a torpedo–shaped bur–and to gain student feedback about their preferences for bur type. Fifty students took part in the study, each of whom prepared the buccal surfaces of two mandibular molar typodont teeth, producing chamfer finish lines. Students prepared both teeth in the same laboratory session and were randomly assigned to two groups that were required to prepare the first of the two molars with a specific bur type. The prepared chamfer finish lines were scored and the data analyzed using the Wilcoxon signed–rank test. Student performance was significantly better when the round–ended bur was used (p=0.005). Student feedback was collected with a survey that consisted of four questions and the opportunity to provide write–in comments. In response to the question "Overall, was one bur type better?" 58 percent of the students preferred the round–ended bur for creating a chamfer finish line. The most frequent write–in comment, made by twelve of the fifty students, criticized the torpedo–shaped bur for creating finish lines that were too shallow or too long. [ABSTRACT FROM AUTHOR]

Abstract: Intraoperative disruption of the medial collateral ligament during total knee arthroplasty is an uncommon complication that can be avoided by retractor placement as well as by careful cutting of the femur and tibia. This study evaluated the excursion of a small and large oscillating saw blade and compared the data against the widths of both the medial and lateral femoral condyle cuts. We discovered that the large saw blade had a statistically significantly larger excursion than the medial and lateral condyle width in women, as well as the lateral condyle width in men. The small saw blade excursion did not exceed any condyle width. We conclude that the smaller saw blade should be considered when making these cuts because the excursion of the large saw blade may exceed the width of cut needed and endanger important structures such as collateral ligaments. [Copyright &y& Elsevier]

Statement of Problem: Porcelain laminate veneer is one of the most important restorations in dentistry because of stable esthetic and low destructive technique. But the main reason of failure in this treatment is porcelain fracture. Therefore, tooth preparation has an important role in fracture resistance of porcelain laminate veneer.Purpose: The aim of this in-vitro study was to compare the effect of tree preparation designs, shoulder and chamfer and heavy chamfer, on fracture strength of porcelain laminate veneer. Materials and Method: This experimental and in-vitro study was performed on 30 upper central teeth without fracture, carries or any problem. The teeth were divided into three-10 teeth groups. Then, the preparation design was performed perfectly. In the palatal surfaces of the first group we used deep chamfer preparation design and the shoulder and the chamfer designs were performed for the second and third groups, respectively. Then the samples were put in instron machine with the angle of 30 degrees. The force rate which led to break in those samples wasdetermined. The data were analysed usig t-test. Result: Resistance against breakage in the deep chamfer, shoulder and chamfer groups were 283.40 ± 17, 231.50 ± 25.61 and 254 ± 21.71 Newton, repectvely. No significant difference was found among the groups . Conclusion: The higher fracture resistance was observed in deep Chamfer/palatal over lap technique, so we prefer to use this kind of preparation for palatal extension of Porcelain Laminate Veneers. [ABSTRACT FROM AUTHOR]