Fatigue behavior of restorations used under the rest of removable partial denture

The question about resistance of resin composites under rest in removable partial denture [RPD] is still unanswered. It is important to find the strongest material that withstands the applied stresses when used under RPD components.To evaluate and compare the fatigue behavior of amalgam and composite restorations used under the rest of the removable partial denture. Forty-five permanent human upper premolars were prepared with standard class II DO cavities and divided into 3 groups of specimens [n=15 for each group]. Group I was filled with amalgam [Dispersalloy], group II and III were filled with resin composite [Flitek Z250 and Tetric ceram, respectively]. The teeth were stored in distilled water for 14 days before testing. After thermocycling, the [staircase] approach was used to determine the flexural fatigue limits [FFL]. The mean differences were evaluated using One-Way ANOVA and post hoc test. A strong significant differences of flexural fatigue strength have been found between amalgam and composite groups [P<0.001]. There was no significant difference between two groups of resin composite [P=0.1]. To achieve more flexural fatigue strength in the rest seats, the use of resin composite in comparison with amalgam is recommended

Comparison of the effect of two denture cleansers on tensile bond strength of a denture liner

Statement of Problem: One of the most clinical challenging issues in prosthodontics is debonding of soft liners from the denture base

Purpose: The aim of this study was to evaluate and compare tensile bond strength between soft liner and heat-cured acrylic resin when immersed in two different types of denture cleanser and distilled water, at different period of times

Materials and Method: In this experimental in vivo study, 238 heat-cured acrylic blocks were made. A soft liner was embedded between the acrylic blocks. Samples were divided into four groups: 17 samples were in the control group and were not soaked in any solution

The remaining samples were divided into 3 groups [Distilled water, Calgon and Fittydent]

Each group was then subdivided into two subcategories, regarding the immersion time variable; 15 and 45 minutes. All samples were placed in tension force and tensile bond strength was recorded with the testing machine. One- way ANOVA and Tucky HSD posthoc test were adopted to analyze the yielded data [alpah> 0.05]

Results: Specimens which were immersed in two denture cleansers [Fittydent and Calgon] and in distilled water showed significant difference [p= 0.001] in bonding strength when compared to the control group. The subjects immersed in denture cleanser solutions and distilled water did not reveal any significant difference [p= 0.90]. For all groups; most of the bonding failures [72%] were cohesive type

Conclusion: The effect of the denture cleansers and distilled water on the bond strength was not statistically different; however, the difference was significant between the immersed groups with the non-immersed group. Moreover, type of the denture cleanser did not show any effect on the tensile strength. The tensile strength increases with time of immersion

[Evaluation of the relationship between upper and lower occlusal plane with ala-tragus and retromolar pad]

Statement of Problem: Orientation of the occlusal plan in complete denture prostheses therapies plays an important role, leading to appropriate esthetics, stability and mastication

Purpose: The aim of the present study was to define the best soft tissue index, by which the location and inclination of the occlusal plane in complete dentures could be established

Materials and Method: This cross-sectional study consisted of 200 individuals [76 male, 124 female], with the mean age of 26.05 [SD+/-4.39]. In order to determine the relationship between maxillary occlusal plane and ala-tragus line, fox plane and J plane were used. The relationships between maxillary occlusal plane and ALT1 [ala-superior border of tragus], ALT2 [ala-mid-tragus] and ALT3 [ala-inferior border of tragus] were evaluated. In the lower jaw, the occlusal plane was evaluated with the line between the upper and middle parts [ret1] and that between the middle and lower part of retromolar pad [ret2]. Data were analyzed by Chi-square test

Results: Evaluation of the difference between the number and percentage using Chi-square test [p < 0.05] showed that there were significant differences between ALT1, ALT2, ALT3 [ALT3 < ALT2 ret2]

Conclusion: Superior one third of the tragus and the upper and middle one third of the retromolar pad are suggested as a reference points for determining the posterior part of the occlusal plane in comparison with the middle and lower one third of the tragus and middle and inferior one third of the retromolarpad

[ invitro study into the effect of two denture cleaners on surface roughness of acrylic dentures]

Utilization of denture cleaning solutions and toothpastes are common methods of cleaning the denture surfaces, which can increase the surface roughness of acrylic dentures. The aim of this study was to evaluate the effect of two cleaning agents in the form of solution and paste on the surface roughness value of denture following tooth brush application. Thirty acrylic discs with 20 mm diameter and 2 mm thickness were made and uniformly polished. These disc were randomly divided into three groups, each comprising ten discs. The roughness value [Ra] was measured, using talysurf. 10. The discs in the first group were brushed using tooth paste and brush. The discs in the second group were first brushed using water and tooth brush, and then immersed in cleaning solution for 92 hours, tooth brushing abrasion test was performed with 200 gr weight applied. The surface roughness of each specimen after 10.000 strokes was determined. Data were analyzed with ANOVA and post hoc Tukey test [alpha = 0.05]. An increase in the surface roughness was observed for all groups. However, surface roughness in the first group, for which tooth paste had been used was significantly increased as compared to the other groups [p = 0.01]. But there was no significant difference between the other two groups [p > 0.05]. Denture cleaning materials in the form of solution produce less surface roughness as compared to the ones in the form of pastes

clinical outcome comparison of the conventional altered cast impression with a modification altered cast impression technique

In order to improve the retention and stability of the mandibular removable prosthesis with distal extension, it is usually required to make a secondary impression [the altered cast impression]. This study was designed to clinically evaluate the conventional method of altered cast technique with modified altered cast technique. This prospective experimental study was conducted with 15 patients. They were treated with two methods of conventional and modified altered cast techniques. Following an oral examination, a questionnaire was used to collect clinical information on the occurrence of ulceration on the ridge, denture border areas, buccal shelf and retromolar pad areas, as well as the sufficiency of denture base extension. Patients were followed up 24 hours and one week after using the partial dentures. In conventional altered cast impression technique, it is required to dissect the casts and form the impression boxing in order to make sure that the master cast is properly registering the distal extension ridge anatomical features. Separation of the edentulous portion from the master cast is eliminated in the modified altered cast impression technique. This makes it more efficient, convenient for patient and less time consuming procedure. The X[2] and fisher's exact tests were used to detect significant levels. The percent of ulceration on the ridge, denture border areas, and buccal shelf as well as the retromolar pad areas were lower in modified altered cast impression technique compared with the conventional altered cast impression method. The percentage of the denture base extension in the modified altered cast impression technique was better than the conventional altered cast impression method. The extension of denture base in distolingual areas of modified altered cast impression technique was the same as the conventional altered cast technique. The difference between the two procedures was not statistically significant. The modified alerted cast technique can result in saving time, increasing the patient's satisfaction and comfort, which makes it the recommendable procedure for making removable partial dentures with distal extensions

Retentive ability of four denture adhesive materials: an in vitro study

One of the most important structural factors that facilitate patient's acceptance of full denture, is adequate and appropriate retention. The objective of this study was to evaluate the retentive ability of four denture adhesives in vitro: Safe Saze-Gum Sealing-Denstet-Corega. This experimental study was conducted in vitro on the basis of measurement of adhesion and cohesion forces between acrylic disk and glass, with denture adhesive applied between them. At first the retentive ability of alcohol, water and artificial saliva was measured and recorded as control. Then the retention ability of different adhesives mixed once with water and next with artificial saliva was measured and compared. The procedure was repeated 7 times for each denture adhesive with 7 similar acrylic disks. Data were analyzed using. ANOVA and paired t test with p<0.05 as the limit of significance. Comparison of four powder denture adhesives showed that the highest retentive ability was observed in Denstet and the lowest in Safe-Saze. The retentive ability of Gum-Sealing was higher than Corega. Based on the results of this study, significant differences exist among the retention ability of different denture adhesives

Evaluation of the effects of sodium hypochlorite disinfection on alginate impression by immersion and spraying methods

Difficulties in sterilizing impressions by traditional methods have led to chemical disinfections as an alternative, and some studies have shown that some methods may adversely affect impressions. This study evaluated the effectiveness of 5.25% sodium hypochlorite spray and immersion disinfection methods on irreversible hydrocolloid impressions [Iralgin alginate]. In this study, twenty normal individuals were randomly selected. Impressions were made by a sterile tray from the maxillary arch and then were contaminated with the following organisms: staphylococcus aureus, streptococcus mutans, beta-hemolytic streptococcus type A, Pseudomonas aeruginosa, Escherichia coli and Candida albicans. Impressions were cut and divided into three sections anterioposteriorly and longitudinally. Then, sections were randomly placed in three groups as 1] control [without disinfection], 2] immersion and 3] spray. Then, the provided samples [pieces] of impression materials were cultured and microbial count of the three groups were compared. All of agar models from 20 alginate pieces in control group showed a positive microbial growth. Ten agar models form 20 alginate pieces which were disinfected by spraying method, showed also positive microbial growth and only 2 agar models out of 20 alginate pieces which were disinfected by immersion method showed a positive microbial growth. The mean number of organisms recovered form the surface of the impressions in control group was 3.52><10[8] CFU/ml while in spay and immersion groups it was 132217 CFU/ml and 1915 CFU/ml respectively. According to the results of this study, disinfection by immersion method with 5.25% sodium hypochlorite was more effective than the spray method