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

Prevalence of temporomandibular disorders in clinics and health centers in Tehran during Summer 2002

Temporomandibular disorders [TMD] are defined as a series of signs and symptoms related to masticatory apparatus disorders. The prevalence of TMD [signs or symptoms] is high. Prevalent diagnostic and simple treatment can prevent the occurrence of sequeles. Due to different statistics on prevalence of TMD in different societies, the aim of the present study was to investigate the prevalence of temporomandibular disorders in dental clinics of Tehran city [2002]. One thousands and five hundred and three subjects were collected from 20 clusters [clinics in Tehran]. The research methods were descriptive and analytical, three students with two supervising prosthodontists completed 2 questionnaires for signs and symptoms with ICC = 0.819 and kappa = 0.772 via observation and interview. For statistical analysis, t and chi - square tests were used. The most frequently reported symptoms were: joint sounds [18.6%], muscle tenderness [9.1%] and joint pain [7.7%]. The most frequently signs were: joint sounds [30.2%], deviation patterns in mouth opening [23.4%], muscle tenderness [17%], joint pain [6%] and limited mouth opening [1.94%]. The prevalence of symptoms and signs were 36.5% and 45.7%, with a significant relationship between them [P<0.001]. The prevalence of TMD was 58.7%. There were significant relationships between TMD and bruxism and TMD and history of trauma [P<0.001]. The prevalence of inflammatory disease of temporomandibular joint demonstrated significant difference between different age groups [P<0.001] and increased with age. The prevalence of TMD in clinical centers of Tehran was more than 50% of population. Due to the significant relationship between bruxism, trauma and prevalence of TMD, awareness of society for prevention and beginning the necessary treatments seems indispensible

[Comparison of cellular toxicity of Iranian and non-Iranian self cure acryl and their effects on production of mouse IL-6 by L929 gingival fibroblasts]

Despite the various methods used to initiate the polymerization of resin, the conversion of monomers to polymers is not complete and some unreacted monomers are left in the polymer that is leachable into saliva. Substance leached from resin can cause adverse reactions in the oral mucosa adjacent to the denture. The aim of this study was the comparison of cellular toxicity of Iranian and non Iranian self cure acryl on mouse L929 gingival fibroblasts. Three types of acryl including Trim acryl [poly vinyl Ethyl Methacrylate], Duralay acryl [poly methyl Methacrylate] and Acropars acryl [poly methyl methacrylate] were used. A total of 90 rings [30 for each type] with predetermined sizes were prepared. Suspension of fibroblasts with acrylic rings was put in 24-wells culture plates and a culture media containing RPMI-1640 environment plus antibiotics and 10% FBS were added. The plates were incubated in the Co2 incubator and after one hour, 24 hours and seven days they were checked for cytotoxicity by MTT test and secretion of IL-6 by ELISA technique. Two-way ANOVA, Kruskal-wallis and Mann-Whitney U tests were used for data analysis. Significant differences were found in the biocompatibility of experimental acryl, Trim and Duralay [p<0.05] Acropars and Duralay [p<0.01] and Acropars and Trim [p<0.001], among studied time intervals. No statistically significant difference was seen in the production of IL-6 among these acryl [p=0.120]. Least cytotoxicity was seen at interval of 24 hours with significant statistically difference between one hour and one week time intervals [p<0.001]. This study showed that the acryl having methyl methacrylate [Acropars and duralay] have greater toxic effects on fibroblasts; although the toxic effects of Acropars were more than Duralay. The least cytotoxicity was seen in Trim which has vinylethyl methacrylate. There was no difference among studied acryl on induction of IL-6

[Effect of different sprue designs on the internal porosity of cast titanium crowns]

Porosity is a frequently observed casting defect in titanium dental casting. This study measured the effects of different sprue design on the internal porosity of cast titanium crowns. Sixty complete veneer crowns were fabricated on a stainless steel die with a 150- degree sloping shoulder using customized wax patterns. All wax patterns were sprued with 3 different sprue design [Reservoir, Runner bar and Rousseau] and were invested with an alumina- magnesia investment. Castings were made with commercially pure titanium [CP Ti [grade II]] according to the manufacturer's instructions. The castings were carefully cleaned. Internal porosities were quantified with photographs and radiographs by computerized image analyses. Data were analyzed with an ANOVA with a confidence level of 95%. There were statistically significant differences in the values of porosity between 3 types of sprue design. The reservoir sprue design had the least internal porosity comparing to the other designs. Improvements in the porosity of titanium crowns was the result of the Reservoir sprue design with vent. Effects of Different sprue designs on internal porosity and their effects on casting accuracy and marginal adaptation of cast titanium crown and bridges must be evaluated to achieve better evidence and clinical relevance

effects of time elapse, desinfection solutions and preservation places on dimensions of Duralay acrylic pattern

There is a wide clinical application of Duralay acrylic resin pattern for direct post and core fabrication. As the effect of time elapse, desinfection solution and preservation places is not studied together, this study was designed to evaluate the interaction of these variables on dimensions [length, coronal and apical diameters] of duralay acrylic resin patterns. In this in vitro and quasi experimental study 36 duralay patterns fabricated in simulation method were used. Then patterns were categorized in one of the 3 groups of glutaraldehyde, sodium hypochloride and control. Each group of 12 patterns was divided in the two groups of preservation places [wet and dry]. Patterns were measured in time intervals of 0, 1, 3, 6, 9, 24 hours. The 3 dimensions of length and apical and coronal diameter were measured with digital micrometer with 10 microten accuracy. Statistical analysis demonstrated that coronal and apical diameters differ significantly by the effect of time elapse and disinfection solutions and preservation places [P<0.005]. Coronal diameter demonstrated significant difference as the effect of time elapse. [P<0.005] Significant differences were not noted between wet or dry preservation places. Glutaraldehyde caused contraction and sodium hypochloride caused expansion of duralay patterns. The mechanism of this different effect was not understood. It was observed that linear dimensional change of duralay acrylic patterns didn't follow a linear correlation formula for prediction of duralay changes and the best time for casting. Different effects of desinfection solution on casting and cementation stages must be evaluated to achieve better evidence and clinical relevance