Comparing of retention of cast crowns cemented with two kind of permanent cement with and without prier use of temporary cement

Introduction: This study evaluated the effects of eugenol –free temporary cement remnants on the retentive strength of casting crowns luted via zinc phosphate and resin cement (Maxcem) to the tooth structure. Material and methods: 40 extracted human molars ware randomly divided into 2 groups. each group was then divided into 2 subgroups and the teeth were paired so that the size of each tooth in each subgroup was the same as a tooth in the other subgroups. 40 standardized Ni-cr complete crowns were made on teeth prepared with a milling machine using conventional laboratory techniques. For each adhesive system, in one subgroups a provisional restoration was cemented using an eugenol –free temporary cement. Temporary crown was remained on the tooth structure for an hour and then extracted and cement remnant was removed by an excavator. Then the casing crowns were adhesively luted via zinc phosphate, adhesive resin(Maxcem) to prepared teeth. After 24h storage in distilled water, Retention was evaluated by measuring the tensile force required to dislodge the crowns from tooth preparations with a universal testing machine after thermo cycling (1500 cycles between 5c and 55c with 1- minute dwell times). The data were analyzed by means of paired T-test and wilcoxon test in SPSS software version 11.5 Results: The analysis showed the mean retentive strength for 2 subgroups with and without prior use of temporary cement in the maxcem group was 176 ± 55 and 274 ± 169 N, there was not a significant difference between the 2 subgroups. (p value = 0.174). And the mean retentive strength for 2 subgroups with and without prior use of temporary cement in the zincphosphate group was 257 ± 125 and 238 ± 135 N, there was not significan t difference between the 2 subgroups (p value = 0.782). Discussion: The use of an eugenol –free temporary cement does not alter the retentive strength of casting restorations lutted to prepared teeth using the tested adhesive system, when temporary cements are removed properly

Observing the Cross-Infection Control Among Dental Clinics and Laboratories

Introduction: Dentists and all related oral hygiene occupations are endanger of cross contamination because of close contacts with patients. Dental laboratories are one of those which have a direct contact with dentist and cross infection control plays an important role to prevent exposure to pathogens. According to the fact that many dental laboratories are not well informed about cross infection control; the aim of this study is to prepare a questionnaire for evaluating both dentists and dental laboratories knowledge about cross control infections. Materials & Methods: 250 dentist and 50 dental laboratories were randomly chosen and prepared questionnaire distributed. The collected data were analyzed by SPSS software and Chi-Square test. Results: There was no significant differences between general and post graduated dentist in using gloves, masks and protective eye glasses (p value > 0.05).the results showed no significant differences in uses of protective eye glasses between dentist who worked in clinics and private offices (p value = 0.384), but there was significant differences in using gloves (p value = 0.02).condensation silicones (90.5%) and alginates (90%) were the most impression materials and 88% of dentist rinsed the impressions always while 0.8% never did that. Conclusion: The cross control infection is no

Effects of Physical and Chemical Characteristics of Slags and Cements on Durability of Portland Cement-Slag Blended Systems

Ground granulated blast furnace slag (GGBFS) which is a commonly used supplementary cementitious material (SCM) needs to be more investigated for improving durability of concrete elements and service life of concrete structures. This research focuses on the effect of the physical and chemical characteristics of GGBFS and portland cement on durability of portland cement-slag blended systems. The effect of cement replacement level is also investigated using control mixes (no slag) and four different levels of slag content. To this end, eight GGBFS and eight portland cements were selected based on their physical characteristics and chemical composition. Four series of experimental studies were conducted using different mixtures of the selected materials. First, the length changes of the portland cement-slag mortar bars in sodium sulfate solution were measured for 18 months of exposure. Second, compressive strength of the cement-slag mortar cubes stored in sulfate and saturated lime solutions were assessed for 18 months. Third, chloride binding capacity of cement-slag blended systems, in five chloride solutions with different chloride concentrations, was assessed. Fourth, the chloride resistivity of portland cement-slag mortar cylinders was determined using electrical resistivity measurements. Moreover, statistical analysis was performed to model the effect of the cement and slag characteristics on the length changes of the cement-slag mortar bars when exposed to a sulfate environment. ASTM C989 [1] cautions that sulfate resistance of portland cement-slag blends may be dependent on the Al2O3 content of the slag. While the standard comments on the effect of low alumina (11% Al2O3) and high alumina (18% Al2O3) slags on sulfate durability, there is no comment on the effect of the slags with Al2O3 content of 11-18%. In this study, sulfate resistance of portland cement-slag mixtures was compared at 30, 50 and 70% cement replacement levels for slags with variable Al2O3 and MgO contents and variable fineness in combination with moderate- and high-C3A cements. Addition of slag changed the failure mode of the mortar bars exposed to sodium sulfate solution compared to the plain cement mixes. Sulfate resistance generally decreased with increasing slag Al2O3 content, although decreasing MgO also increased deterioration, particularly at 30% replacement. Increase in Al2O3 correlated with increased formation of secondary ettringite in the surface of the mortar bars. A linear relationship was observed between the solid volume increase on exposure to sulfate solution predicted by GEMS and the MgO/Al2O3 ratio of slag at all cement replacement levels. There was also a linear relationship between the solid volume increase and the length of the induction period for the mortar bars exposed to sulfate solution. Increasing slag fineness appears to decrease the sulfate durability of cement-slag mixtures. Addition of calcium sulfate for improving sulfate durability of slag mixes with high alumina content was observed to be affected by the cement composition. Although, the strength of Type I and Type II cement mixes is close in the lime solution, samples made with Type I cement which has a higher tricalcium aluminate content were observed to be highly vulnerable to sulfate attack. Partial replacement of cement with slag decreased the strength at early ages due to slow reactivity of slag but increased it at later ages both in lime and sulfate solution. Increasing cement replacement level was observed to generally increase the compressive strength of the cement-slag mixtures. In general, low-alumina (8%) slag showed the lowest expansion and the highest strength among OPC-slag mixtures with lower slag content, while high-alumina (16%) slag was observed to have the highest expansion and the lowest compressive strength in sulfate solution. This is due to the formation of more ettringite in high-alumina slag mixtures. The length changes and compressive strength at 70% mixes was observed to improve for all slag mixtures regardless of the slag composition. However, the fineness of the slag seems to play an important role at high replacement levels that increases both the expansion and strength of the cement-slag mixtures at high replacement levels when exposed to sulfate solution. In general, the effect of slag chemical composition is most notable at lower replacement levels and all cement-slag mixes showed lower expansion and higher strength at 70% replacement level. Therefore, high percentage of cement replacement is a key solution for improving the performance of all slags, especially high alumina slags, while only low alumina slags should be used if lower replacement levels of cement are desired. In addition to sulfate durability, chloride binding capacity of cement-slag blended systems was investigated using isotherms obtained from equilibrium method. It is known that pore connectivity and chloride binding capacity of the concrete cover determine the concrete resistance to diffusion of chloride ions. Since only the free chloride in the pore solution participate in corrosion of the reinforcing steel, it is essential to understand the chloride binding phenomena in cement-slag systems. In chapter 4 of this document, the effect of cement and slag characteristics on the chloride binding capacity of the cement-slag mixtures is discussed. Higher amount of bound chloride was determined in the cement mix with high C3A content. Alkali content and the pH of the pore solution is the other factor that affects the binding of chlorides. Lower alkali content was observed to increase the binding capacity of the cement mix. Addition of limestone to cement appears to decrease chloride binding in the blended system. Replacing cement with slag increased the C-S-H and alumina content of the system which led to higher binding capacity. Addition of slags with higher alumina content formed more AFm phases before chloride exposure which further increased the binding chloride capacity of the cement-slag systems by converting to Kuzel’s and Friedel’s salts. The electrical resistivity of the cement-slag systems was also measured to investigate the effect of different cements and slags on chloride ingress into the cementitious system. The objective of this part of the study was to investigate the influence of w/b ratio, cement fineness and slag alumina content on surface resistivity, and consequently, chloride diffusivity of the cement-slag blended systems. Lower w/b ratio and higher cement fineness increased electrical resistivity and decreased chloride diffusivity into the cement mix. Slag mixes showed higher resistivity and lower chloride diffusivity compared to those of the plain cement systems. Higher alumina content decreased the resistivity and increased chloride diffusivity at later ages. The statistical analysis in chapter 5 of this study showed that cement C3A content, slag alumina content, cement fineness and slag fineness as well as cement replacement level are among the most significant parameters that affect the performance of cement-slag mixtures in sulfate environment. Most of the work in chapters 2 and 3 of this study was partially funded by Florida Department of Transportation and the Federal Highway Administration under contract number BDV25-977-28. The report for the mentioned project [2] and this dissertation share some content. Additionally, part of this document have been published previously in Vol. 229 of the Journal of Construction and Building Materials [3]. Permissions are included in Appendix A

Posterior open occlusion management by registration of overlay removable partial denture: A clinical report

This clinical report describes prosthetic rehabilitation of posterior open bite relationship in a patient with several missing teeth and skeletal Class III malocclusion. Primary diagnostic esthetic evaluations were performed by mounting casts in centric relation and estimating lost vertical dimension of occlusion. Exclusive treatments were designated by applying overlay removable partial denture with external attachment systems for higher retentions

Use of Low Melting Point Metals and Alloys (Tm < 420 °C) as Phase Change Materials: A Review

Phase Change Materials (PCMs) are materials that release or absorb sufficient latent heat at a constant temperature or a relatively narrow temperature range during their solid/liquid transformation to be used for heating or cooling purposes. Although the use of PCMs has increased significantly in recent years, their major applications are limited to Latent Heat Storage (LHS) applications, especially in solar energy systems and buildings. PCMs can be classified according to their composition, working temperature and application. Metallic PCMs appear to be the best alternative to salts and organic materials due to their high conductivity, high latent heat storage capacity and wide-ranging phase change temperature, i.e., melting temperature and chemical compatibility with their containers. This paper reviews the latest achievements in the field of low-melting point metallic PCMs (LMPM-PCMs), i.e., those with melting temperatures of less than 420 degrees C, based on Zn, Ga, Bi, In and Sn. Pure LMPM-PCMs, alloy LMPM-PCMs and Miscibility Gap Alloy (MGA) LMPM-PCMs are considered. Criteria for the selection of PCMs and their containers are evaluated. The physical properties and chemical stability of metallic PCMs, as well as their applications, are listed, and new application potentials are presented or suggested. In particular, the novel application of metallic PCMs in casting design is demonstrated and suggested

Use of Low Melting Point Metals and Alloys (T_m < 420 °C) as Phase Change Materials: A Review

Phase Change Materials (PCMs) are materials that release or absorb sufficient latent heat at a constant temperature or a relatively narrow temperature range during their solid/liquid transformation to be used for heating or cooling purposes. Although the use of PCMs has increased significantly in recent years, their major applications are limited to Latent Heat Storage (LHS) applications, especially in solar energy systems and buildings. PCMs can be classified according to their composition, working temperature and application. Metallic PCMs appear to be the best alternative to salts and organic materials due to their high conductivity, high latent heat storage capacity and wide-ranging phase change temperature, i.e., melting temperature and chemical compatibility with their containers. This paper reviews the latest achievements in the field of low-melting point metallic PCMs (LMPM-PCMs), i.e., those with melting temperatures of less than 420 °C, based on Zn, Ga, Bi, In and Sn. Pure LMPM-PCMs, alloy LMPM-PCMs and Miscibility Gap Alloy (MGA) LMPM-PCMs are considered. Criteria for the selection of PCMs and their containers are evaluated. The physical properties and chemical stability of metallic PCMs, as well as their applications, are listed, and new application potentials are presented or suggested. In particular, the novel application of metallic PCMs in casting design is demonstrated and suggested

Comparative evaluation of hydroxyapatite and nano-bioglass in two forms of conventional micro- and nano-particles in repairing bone defects (an animal study)

Context: Many synthetic bone materials have been introduced for repairing bone defects. Aim: The aim of this study is to comparatively evaluate the efficacy of nano-hydroxyapatite (HA) and nano-bioglass bone materials with their traditional micro counterparts in repairing bone defects. Materials and Methods: In this prospective animal study, four healthy dogs were included. First to fourth premolars were extracted in each quadrant and five cavities in each quadrant were created using trephine. Sixteen cavities in each dog were filled by HA, nano-HA, bioglass, and nano-bioglass and four defects were left as the control group. All defects were covered by a nonrestorable membrane. Dogs were sacrificed after 15, 30, 45, and 60 days sequentially. All 20 samples were extracted by trephine #8 with a sufficient amount of surrounding bone. All specimens were investigated under an optical microscope and the percentage of total regenerated bone, lamellar, and woven bone were evaluated. Statistical Analysis Used: Data analysis was carried out by SPSS Software ver. 15 and Mann–Whitney U-test (α =0.05). Results: After 15 days, the bone formation percentage showed a significant difference between HA and nano-HA and between HA and bioglass (P < 0.001). The nano-HA group showed the highest rate of bone formation after 15 days. Nano-bioglass and bioglass and nano-HA and nano-bioglass groups represented a significant difference and nano-bioglass showed the highest rate of bone formation after 30 days (P = 0.01). After 45 days, the bone formation percentage showed a significant difference between nano-bioglass and bioglass and between nano-HA and nano-bioglass groups (P = 0.01). Conclusions: Nano-HA and nano-bioglass biomaterials showed promising results when compared to conventional micro-particles in the repair of bone defects

Internal and Marginal Fit Accuracy of Pre-sintered CAD/CAM Implant-Supported Frameworks Before and After Porcelain Layering

Purpose: Internal and marginal fit accuracy of an implant-supported fixed partial denture (I-FPD) along with passive fit are required for long-term clinical success. This study compared the fit accuracy of three-unit CAD/CAM-fabricated cement retained I-FPDs milled from pre-sintered cobalt-chromium (Co-Cr) and zirconia (Zr) and evaluated the effect of applying porcelain. Materials and Methods: Two implant analogs were positioned parallel at first premolar and first molar sites in an acrylic model. Their corresponding abutments were tightened with 25-Ncm torque force. Four groups were designed: two groups of I-FPD frameworks with pre-sintered Zr (ZrF) and soft millable Co-Cr alloy (SF) blocks, and two groups by applying porcelain to the Co-Cr (SP) and Zr (ZrP) frameworks (n =4 in each group). Absolute marginal gap (AMG), marginal gap (MG), and internal discrepancies were measured. Kolmogorov-Smirnov, Levene, one-way analysis of variance (ANOVA), and Scheffe tests were used for statistical analysis using SPSS software version 22 at a significance level of .05. Results: All measured criteria were significantly different from each other (all P values <.001). The rankings from the lowest gap to the highest gap for the main criteria were as follows: MG: SF < SP < ZrF < ZrP; AMG and internal discrepancies: SF < SP < ZrP < ZrF. Comparing molars and premolars, molars had smaller MGs, larger internal discrepancies, and smaller AMG in ZrP but larger AMG in SP. Conclusion: All three-unit CAD/CAM-fabricated cement-retained I-FPDs were in the clinically acceptable range of fit accuracy. The lowest and highest misfit values were observed in the SF and ZrF groups, respectively