effect of steam sterilization without preparation steps on the accuracy of friction-style MTLDs

Inadequate torque application during screw tightening in dental Implants is one of the responsible factors of screw loosening and fracture and others technical complications. Mechanical torque limiting Devices [MTLDs] are necessary tools to control a peak torque and achieving a target values. Accuracy of these devices, particularly in friction-style type is reported with high variability. Due to vague and controversial aspect of steam sterilization on the accuracy of these devices their preparation steps [dismantling of the components, lubrication, broken position of the handle] before sterilization, this study aimed to evaluate the effect of steam sterilization without preparation steps on the accuracy of friction-style MTLDs. Fifteen new friction-style MTLDs from three different manufacturers, five for each group, were purchased. All peak torque measurement, considering their target torque, were measured ten times consecutively before and after 100 cycles of steam sterilization using Tohnichi torque gauge. For steam sterilization procedure, 100 cycles of autoclave without preparation steps before each cycle were performed. Comparison of error values and range of difference between the measured torque value and the target torque values before/after sterilization were performed with a One- way Repeated- measures ANOVA to significant level of P<0.05, considering type of devices as a between subject comparison. For pair wise comparison Bonferroni post hoc test was used. After steam sterilization without preparation steps, difference between target torque and peak values increased in all of the 3 groups studied [P<0.05]. Peak torque values showed more than 10% difference from the target torque [suitable clinically accepted torque] in some measurements. Range of error was -1 to 4 Ncm in Dr Idhe group, -1 to 3 Ncm in AstraTech group and -3.5 to 1 Ncm in Biohorizon group. Within the limitation of this study maximum error values were 12% in Astra Tech MTLDs, 13.3% in Dr Idhe MTLDs and 11.7% in Biohorizon MTLDs. Greater variability was seen for Biohorizon and Dr Idhe groups than for Astra Tech group. Sterilization without preparation steps affects the accuracy of friction-style mechanical torque limiting devices. Combined effects of sterilization and aging needs to be determined

effects of abutment screw access channel filling material and its amount on resistance to dislodgement of cement retained implant-supported crowns

Factors affecting the retention of fixed prosthesis to natural abutments are well understood. In contrast, little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that varying screw access channel filling materials and methods has on the retention of casting cemented to implant abutment. A 15 degree preangeled abutment [Noble biocare Replace] was placed in implant analogue. Ten crowns were constructed that incorporated an attachment to allow removal. The screw access channels were either fully or partially filled with Gutta perka, Composit or silicone .Crowns were cemented to the abutment with TemoBond .The tensile force required to separate the cemented crowns from the abutment was measured using an Instron universal load testing machine. The mean peak removal force was significantly higher with partially filled access hole compared with fully filled. About the material filling the screw access hole, the mean peak removal force was highest with Composit and that was greater than Gutta perka and silicone respectively. The method and materials selected to fill the screw access channel of an implant abutment can be a significant factor affecting retention of a cemented restoration

Comparison of the accuracy of standard putty-wash impression technique with the re-putty-wash technique using super light material

Impression making is considered as an important step in the fixed prosthodontics.the different impression material and techniques have been supposed to be important in the dimensional changes of dies. Furthermore, the results of different studies in this regard are contradictory. The present study compared the results of two impression making techniques of putty-wash including two-step with space and double -wash using LIGHT and SUPER LIGHT viscosity. In this experimentalinvitro study on the laboratory model, 10 impressions were made using two-step putty-wash technique with space and 10 impressions were made using double-wash techniqueby means of LIGHT and SUPER LIGHT viscosity. The impressions were poured using Velmix gypsum after 30 minutes. The height and diameter of the dies without undercut and the distance between two dies were measured 6 times while the variables were measured 3 times in the gypsum models by a blind operator using profile projector with an accuracy of micron. The mean values were calculated and the dimensions of the gypsum laboratory models were statistically analyzed by t- test. The die height was decreased using both techniques of two-step with space and double-wash technique with LIGHT and SUPER LIGHT viscosity. The decrease was more pronounced in the double-wash technique by LIGHT and SUPER LIGHT viscosity. However, no significant differences were found between both techniques [P>0.05]. Die diameter without undercut was significantly decreased in the double-wash technique by LIGHT and SUPER LIGHT viscosity [P<0.0001] while it was increased in the two-step technique with spaces. Slight distances were observed between two dies in the two-step impression technique with space. However, the distance between dies were increased using double-wash technique by LIGHT and SUPER LIGHT viscosity with significant differences [P<0.0001]. The die diameter was decreased in the impression technique of double-wash using LIGHT and SUPER LIGHT viscosity while the distance between base teeth have been increased in this technique. Therefore, the technique is not accurate and needs more assessments

Recommended loading protocols for dental implants in edentulous and partially edentulous patients with fix removable prosthesis

Patients levels of knowledge and expectations for treatment with dental implants have increased tremendously in recent years. Also treatment with dental implants has proven to be a predictable modality for replacing missing or failing teeth with various types of fixed or removable dental prosthesis. It was traditionally thought that the healing period of 3 to 6 months is necessary. Recent studies show high level of survival rates with immediate and early loading. The object of this study was to evaluate current evidence for evaluating recommended loading protocols for dental implants. A comprehensive systematic review of the literature was conducted by using Pubmed and Science Direct by the end of September 2010. The selection of publications reporting on human clinical studies was based on predetermined inclusion criteria. One hundred thirty eight out of 971 papers were approved for inclusion criteria. 39 were discussing early loading. 40 were discussing immediate loading and 57 were discussing conventional loading and 7 were discussing fresh socket implant placements. Existing literature supports loading of micro roughened implants in edentulous and partially edentulous maxilla and mandible between six and eight weeks subsequent to implant placement with fix or removable prosthesis. It is also possible to load dental implants in mandible in less than one week after placement with fix and removable prosthesis. But current evidence does not support loading edentulous and partially edentulous maxilla in less than eight weeks and recommends conventional loading [after three months]. Special conditions such as lack of primary stability, alveolar ridge augmentation, sinus floor elevation, presence of parafunction, compromised host status and dental complication should be considered as risk factors for immediate and early loading. In these situations conventional loading is recommended. Loading between two and six weeks is not recommended

Comparison of porcelain fractures in the metal-ceramic implant-supported and tooth-supported crowns in patients referred to Specialist Ward of fixes prosthodontics departments: shahid Beheshti University of Medical Sciences, Dental School: 2001- 2010

Metal-ceramic crowns have been considered an acceptable treatment plan for the rehabilitation of edentulous patients in implant dentistry. Furthermore, porcelain fractures associated with an implant-supported metal-ceramic crown occur more than tooth-supported restorations; then, assessment of the associated factors in this regard needs more studies. The present study evaluated porcelain fractures in the implant-supported crowns compared to the tooth-supported metal-ceramic crowns in the patients referred to the Specialist Ward of Fixed Prosthodontics, Shahid Beheshti University of Medical Sciences, Dental School during 2001-2010. In this retrospective descriptive study, 42 patients [24 males, 18 females] having received implant or tooth-supported metal-ceramic crowns were underwent follow-up examinations by two operators. There were 185 tooth-supported and 158 implant-supported units in total. Porcelain fractures were assessed regarding California Dental Association criteria [severe, small, no fracture]. The presence of parafunctional habits, opposing dentition, treatment location, type of prostheses, implant system, type of occlusion, number of prostheses units and the applied cements were determined in the prostheses. The results were reported by descriptive statistics and the data statistically compared by Chi-square and Exact Fisher tests as well as odd's ratio calculation. Porcelain fracture occurred in 5.4% tooth-supported [1.6% severe and 3.8% small ratings] and 10.2% implant-supported [5.1% severe and 5.1% small ratings] crowns without significant differences. Porcelain fractures had approximately 2 times higher odds [odd's ratio=2.1] in patients with bruxism habits, with higher rates in mandibular regions than maxillary, in posterior regions than anteriorly located prostheses and in multiple-unit prostheses than single units. However, overbite, overjet, opposing type and angle classification showed no significant effect on the porcelain fractures. Implant-supported crowns showed 2 times more porcelain fractures than tooth-supported prostheses and the frequency of post-treatment complications was statistically higher in implant- compared to tooth-supported metal-ceramics. However, the difference of two systems was not statistically significant regarding porcelain fractures

effect of flowable composite and resin cement on shear bond strength of porcelain veneer to enamel

There are insufficient data on the shear bond strength of Porcelain Veneers to enamel by using flowable composite as a luting Cement. This study was conducted in order to compare the shear bond strength of two different systems by using bovine enamel. Thirty freshly extracted anterior mandibular intact bovine teeth were randomly divided into two groups. Feldespatic Porcelain discs were attached to the enamel by Panavia F2 resin Cement and Filtek Flow flowable composite according to the manufacture's instruction. The bonded specimens were immersed in 37°C water for 30 days and then thermocycled at 5°C and 55°C for 500 cycles. Samples were subjected to shear bond strength test. The modes of failure were determined under stereo microscope. Group differences were statistically analyzed by using the student-t test. The mean bonding strength in Panavia F2 group was 24.26 [ +/- 8.2] mega paschal [Mpa], and 17.25 [ +/- 8.1] Mpa, in Filtek Flow group. The statistical analysis showed significant difference between the two groups [P<0.005]. Mode of failure in the first group was mainly cohesive and adhesive in the second one. This study revealed that the shear bond strength of dual cure Panavia F2 resin cement is considerably higher than that of light cure Filtek Flow flowable composite