Finite element analysis of the effect of superstructure materials and loading angle on stress distribution around the implant

A general process in implant design is to determine the reason of possible problems and to find the relevant solutions. The success of the implant depends on the control technique of implant biomechanical conditions. The goal of this study was to evaluate the influence of both abutment and framework materials on the stress of the bone around the implant by using three-dimensional finite element analysis.A three-dimensional model of a patient's premaxillary bone was fabricated using Cone Beam Computed Tomography [CBCT]. Then, three types of abutment from gold, nickel-chromium and zirconia and also three types of crown frame from silver-palladium, nickel-chromium and zirconia were designed. Finally, a 178 N force at angles of zero, 30 and 45 degrees was exerted on the implant axis and the maximum stress and strain in the trabecular, cortical bones and cement was calculated.With changes of the materials and mechanical properties of abutment and frame, little difference was observed in the level and distribution pattern of stress. The stress level was increased with the rise in the angle of pressure exertion. The highest stress concentration was related to the force at the angle of 45 degrees. The results of the cement analysis proved an inverse relationship between the rate of elastic modulus of the frame material and that of the maximum stress in the cement.The impact of the angle at which the force was applied was more significant in stress distribution than that of abutment and framework core materials

Effect of beverages on the hardness and tensile bond strength of temporary acrylic soft liners to acrylic resin denture base

Statement of Problem: Two potential problems commonly identified with a denture base incorporating a resilient liner are failure of the bond between acrylic resin and soft liner material, and loss of resiliency of the soft liner over time. Since patients may drink different beverages, it is important to evaluate their effects on physical properties of soft lining materials

Purpose: The objective of this in vitro study was to evaluate the effect of different beverages on the hardness of two temporary acrylic-based soft lining materials and their bond strength to the denture base resin

Materials and Method: For the hardness test; a total of 80 rectangular specimens [40mm×10mm×3mm] were fabricated from a heat-polymerized polymethylmethacrylate

Two commercially auto-polymerized acrylic resin-based resilient liners; Coe-Soft and Visco-gel were prepared according to the manufacturers' instructions and applied on the specimens. For the tensile test, 160 cylindrical specimens [30mm×10mm] were prepared

The liners were added between specimens with a thickness of 3 mm. The specimens of both soft liners were divided into 4 groups [n=10] and immersed in distilled water as the control group, Coca-Cola, 8% and 50% ethanol. All groups were stored in separate containers at 37oC for 12 days. All beverages were changed daily. The hardness was determined using a Shore A durometer and tensile bond strength was determined in a ZwickRoell testing machine at a cross-head speed of 5mm/min. The results were analyzed using two-way ANOVA

Results: There was no significant interaction between the soft liners and the drinks for both hardness [p= 0.748] and bond strength [p= 0.902]. There were statistically significant differences between all drinks for both hardness [p< 0.001] and bond strength [p< 0.05]

Conclusion: Within the limitations of this study, it seems that drinking Coca-Cola and alcoholic beverages would not be potentially causing any problems for the temporary acrylic soft liners

Comparison the marginal and internal fit of metal copings cast from wax patterns fabricated by CAD/CAM and conventional wax up techniques

Statement of Problem: Metal-ceramic crowns are most commonly used as the complete coverage restorations in clinical daily use. Disadvantages of conventional handmade wax-patterns introduce some alternative ways by means of CAD/CAM technologies

Purpose: This study compares the marginal and internal fit of copings cast from CAD/CAM and conventional fabricated wax-patterns

Materials and Method: Twenty-four standardized brass dies were prepared and randomly divided into 2 groups according to the wax-patterns fabrication method [CAD/CAM technique and conventional method] [n=12]. All the wax-patterns were fabricated in a standard fashion by means of contour, thickness and internal relief [M1- M12: representative of CAD/CAM group, C1-C12: representative of conventional group]

CAD/CAM milling machine [Cori TEC 340i; imes-icore GmbH, Eiterfeld, Germany] was used to fabricate the CAD/CAM group wax-patterns

The copings cast from 24 wax-patterns were cemented to the corresponding dies. For all the coping-die assemblies cross-sectional technique was used to evaluate the marginal and internal fit at 15 points. The Student's t- test was used for statistical analysis [alpah=0.05]

Results: The overall mean [SD] for absolute marginal discrepancy [AMD] was 254.46 [25.10] um for CAD/CAM group and 88.08[10.67] um for conventional group [control]

The overall mean of internal gap total [IGT] was 110.77[5.92]um for CAD/CAM group and 76.90 [10.17] um for conventional group. The Student's t-test revealed significant differences between 2 groups. Marginal and internal gaps were found to be significantly higher at all measured areas in CAD/CAM group than conventional group [p< 0.001]

Conclusion: Within limitations of this study, conventional method of wax-pattern fabrication produced copings with significantly better marginal and internal fit than CAD/CAM [machine-milled] technique. All the factors for 2 groups were standardized except wax pattern fabrication technique, therefore, only the conventional group results in copings with clinically acceptable margins of less than 120um

[Comparison of candidal and bacterial adherence to denture base acrylic resins]

Futura Gen and GC Reline Hard denture chairside reline materials have recently been introduced to the dental market. Although yet to be scientifically proven, these products are claimed to have optimal characteristics. This study aimed to compare the adherence of Candida strains and bacteria to denture base acrylic resins. In this in-vitro experimental study, 24 discs were fabricated of Futura Gen, GC Reline Hard and Meliodent reline acrylic resins. Specimens were inoculated with three Candida strains and Streptococcus mutans at three time points and after staining, their optical absorbance [microbial adhesion and biofilm formation] was calculated using spectrophotometry. Two-way ANOVA and Tukey's HSD test were applied for statistical analysis. Absorbance [optical density]of C. albicans strains on Futura Gen, GC Reline and Meliodent hard reline acrylic resins was 0.022, 0.011 and 0.028 at one hour, 0.057, 0.022 and 0.062 at 24 hours and 0.101, 0.051 and 0.11 at one week, respectively. Absorbance of C. glabrata on the mentioned resins was 0.012, 0.008 and 0.016 at one hour, 0.039, 0.029 and 0.044 at 24 hours and 0.075, 0.068 and 0.081 at one week, respectively. Absorbance of C. dubliniensis on these resins was 0.026, 0.035 and 0.027 at one hour, 0.064, 0.066 and 0.067 at 24 hours and 0.11, 0.12 and 0.13 at one week, respectively. Absorbance of standard strain of S. mutans was 0.027, 0.014 and 0.035 at one hour, 0.064, 0.026 and 0.064 at 24 hours and 0.11, 0.05 and 0.11 at one week, respectively. Candidal and bacterial adhesion to denture base acrylic resins was not significantly different at the understudy time points [P>0.05]. Except for C. dubliniensis, the lowest absorbance belonged to Meliodent. However, absorbance increased over time. Optical absorbance of S. mutans was lower in Meliodent. Among yeast strains, the highest absorbance belonged to C. dubliniensis

effect of microwave disinfection on dimensional stability and flexural strength of acrylic resins

Several studies have evaluated the effect of microwave radiation on physical properties of acrylic resins. However, due to the recent introduction of heat-cure and cold-cure acrylic resins into the dental market and rapid popularity of cold-cure resins with less distortion in denture base, the present study sought to assess the effect of microwave disinfection on dimensional stability and flexural strength of two recently introduced heat-cure [Ivoclar] and cold-cure [FuturaGen] acrylic resins. In this laboratory study, acrylic models were fabricated of an edentulous maxillary model using Ivoclar and FuturaGen acrylic resins. Three reference points were marked on the model: two in the back and one in the front of the edentulous arch. These reference points were used for the measurement of dimensional stability in the anteroposterior and cross-arch dimensions. Ten specimens of each acrylic resin were not disinfected. Ten samples were subjected to two 3 min cycles of microwave disinfection with 600 watt power. Distances between the reference points were measured by a Profile Projector. To evaluate flexural strength, a metal mould measuring 64x10x3.3 mm was used for the fabrication of resin specimens. Similar to what was done for dimensional stability testing, 10 specimens of each acrylic resin were not disinfected and 10 other samples were subjected to 3-point bending test after disinfection. Data were compared and statistically analyzed using Mann-Whitney U test. The mean difference in anteroposterior and cross-arch dimensions revealed that two cycles of microwave disinfection of Ivoclar and FuturaGen acrylic resins did not have a significant effect on their dimensional stability [P>0.017]. The mean and standard deviation of the flexural strength of FuturaGen acrylic resin before and after disinfection was 76.86 +/- 16.80 and 70.18 +/- 8.48, respectively. These values for Ivoclar acrylic resin were 85.92 +/- 12.23 and 81.91 +/- 6.59, respectively. Two cycles of disinfection with microwave did not cause a significant effect on flexural strength of the two understudy acrylic resins [P>0.05]. Two cycles of microwave disinfection had no negative effect on dimensional stability or flexural strength of FuturaGen and Ivoclar acrylic resins

Congenital insensitivity to pain with anhidrosis [CIPA]: a case report

Congenital insensitivity to pain anhidrosis [CIPA] is a rare disorder characterized by episodes of fever and the inability to sense of pain despite the fact that all other sensory modalities remain intact or minimally impaired. The patient also may exhibit the signs of self-mutation, mental retardation and little or no perspiration. We present a 10 years old Iranian patient diagnosed with CIPA with the above-mentioned clinical characteristics. The prosthetic treatment and the subsequent six month follow-up are discussed. Follow-up of the patient revealed that, with the use of this prosthesis, the patient's oral function and esthetics were established and the mouth lesions improved. Therefore especial dental management of CIPA patients according to their mental status, age, oral and dental condition is essential for solving the specific problems each case may present and the full mouth teeth extraction should be considered as the last treatment

[Bond strength of a silicone soft liner containing clotrimazole to acrylic denture base]

Proper bond of the soft liner to acrylic denture base is one of the most important factors in the longevity of soft liner. Since the antifungal efficacy of clotrimazole in soft liners had been approved, it is necessary to determine its effect on the physical properties of soft liners. Determination of the tensile bond strength of the silicone soft liner [GC-Extrasoft] containing clotrimazole to the acrylic denture base, when the specimens are stored in distilled water and washed daily with wet cotton, was the goal of this in vitro study. Forty two pairs of acrylic base [3 cm length and surface area of 10 mm2] were prepared. The specimens were divided into 2 equal groups of control and case, each consisting of 21 specimens. Silicone soft liner was added between them with a thickness of 3 mm after treating the acrylic surface with isopropyl alcohol and application of adhesive layer. Clotrimazole 1% by weight was incorporated into soft liner in the case group. The control group consisted of S1, S30, S60 and the case group of Sc1, Sc30, Sc60 that were stored in distilled water and washed with wet cotton for 1, 30 and 60 days, respectively. Tensile bond strength was measured by universal testing machine at a cross heads speed of 10mm/min. Seven specimens of the groups were evaluated each time. Finally, the results were analyzed, using Two-Way ANOVA. The means and standard deviations of tensile bond strength in the control group after 1, 30 and 60 days were 0.52 +/- 0.19, 0.58 +/- 0.28, 0.60 +/- 0.25 and were 0.60 +/- 0.32, 0.50 +/- 0.18 and 0.55 +/- 0.42 in case group, respectively. There was no statistically significant difference in tensile bond strength between control and case groups [p>0.05]. no significant effect on tensile bond strength of the soft liner into the acrylic denture base was seen by adding clotrimazole to the silicone soft liner [Gc-Extra soft] after 1, 30 and 60 days of storage in distilled water and cleaning with wet cotton

Cytotoxicity of resin-based cleansers: an in vitro study

Cell culture has been used to study the cytotoxicity of denture base resins. Indeed, denture cleansers and their effects on the resin cytotoxicity need deep concern. The aim of the present in vitro study was to investigate the cytotoxic effect of a heat cured denture base resin treated with two denture cleansers on mouse L-929 fibroblasts. Under aseptic conditions, sample disks of a heat treated resin were prepared, following manufacturers' instruction and divided into 12 groups of ten as follows: I] soaking in 1% sodium hypochlorite, II] soaking in alkaline peroxide solution, and III] soaking in water bath for 1, 24, 72 hours and a week. Suspensions of the fibroblasts with acrylic disks were put in 24-well culture plates, and the culture media containing RPMI-1640 environment plus antibiotics and 10% fetal bovine serum were added. After incubation of the plates at considered time intervals, cytotoxicity of the resin was carried out by MTT assay. A significant difference was noticed for solutions in relation to the biocompatibility of the acrylic resin samples at determined time intervals. The cleansers' soaking samples showed higher cytotoxicity in comparison to those immersed in water at each time interval. The difference between cytotoxic effects of the samples immersed in water or cleansers were significant after 72 hours and one week. Overnight immersion in alkaline peroxide and 1% hypochlorite solutions increased the cytotoxicity of the heat cured acrylic resin, but water storage improved the biocompatibility of the material tested

In vitro study of the effect of clotrimazole incorporation into silicone soft liner on fungal colonization

Candidal colonization on soft liners is important in the development of pathogenesis, such as denture stomatitis. It has heen reported that combining anti-fungal agents into soft liners might be used in treatment and prevention of denture stomatitis. The aim of this in-vitro study was to determine whether incorporating Clotrimazole [C] into the silicone soft liner [S], would inhibit the growth of C. albicans when the specimens are stored in distilled water and washed daily with wet cotton. Experimental specimen disks incorporated with Clotrimazole [Sc[1], Sc[30], Sc[60] and without Clotrimazole [S[1], S[30], S[60]] into the soft liner [no = 8] were fabricated aseptically against the polyester film to produce a smooth surface. The treated and control disks were stored in distilled water for 1, 30 and 60 days and washed daily with wet cotton. For fungal growth assessment, they were inoculated with C .albicans suspension. The disks were rinsed and sonicated in sterile water to remove surface organisms. The attached yeast was measured by inoculation of the yeast suspension on Sabouraud's agar. The data were compared using two-way ANOVA. The mean colony forming units [CPU] per mm[2] for the specimens without Clotrimazole after water storage and washing with wet cotton for 1, 30 and 60 days was 6.5X10[6], 5.8X10[6] and 6.1X10[6], respectively. CPU for specimens with Clotrimazole decreased significantly to 2.6X10[6] and 3.9X10[6] and 4.6X10[6] after 1, 30, and 60 days, respectively. In comparison to those of the control disks, Clotrimazole in treated disks was effective in inhibiting C.albicans growth significantly following storage in water for 2 months [P < 0.05]. The addition of Clotrimazole significantly reduced C.albicans growth to the surface of the silicone soft liner. The samples continued to inhibit the fungal growth when they were washed daily with wet cotton for 2 months

[Dimensional accuracy in multiple casting with three different elastomeric impression materials]

The ability to produce multiple accurate casts from a single impression has been evaluated in a few impression materials. The aim of this study was to evaluate the effect of multiple casting in specific time intervals with three different elastomeric impression materials, on the dimensional accuracy. A stainless steel model composed of two dies with precut molar and premolar teeth were used in this study. The bigger die had a notch to reproduce undercut in order to study the elastic recovery. Seven impressions were made from this model by each of the following impression materials: Correct plus, Panasil [addition-cured silicones] and Speedex [condensation-cured silicone] according to manufacturer's instructions. The 21 impressions were poured in 30, 90, 150 minutes and 24 hours after impression taking. The stone casts were measured in six dimensions by an optical traveling, high precision [0.001 millimeter] microscope. The mean dimensions were compared with each other and the stainless steel model. For statistical analysis, Two-way ANOVA and Post Hoc tests were used to determine the significance levels. There were significant changes in most of the dimensions between the metal model and the first cast, but these changes were within the acceptable limits, according to ANSI/ADA Specification No. 19 for impression materials. No significant difference was observed between almost all of the dimensions of the second, third and fourth casts when compared with the first cast of each impression material [P>0.05]. The only significant difference was detected between the fourth cast and the first cast of Speedex in one dimension. Based on these results, four casts from Correct plus and Panasil as well as three casts from Speedex could be considered as acceptable from clinical stand points

[Comparison of anxiety and depression in patients with temporomandibular disorders and healthy individuals]

Psychological factors have been suggested to play a role in the maintenance and etiology of temporomandibular disorders [TMDs], but its exact cause is complicated and multifactorial. This study aimed to compare anxiety and depression between patients with TMD and matched healthy individuals. A total of 150 individuals including 75 TMD patients and 75 healthy volunteers were included in this case-control investigation. The participants were matched according to age, sex, occupation and socio-economic status. In order to collect demographic and general health information, all subjects were asked to fill-out questionnaires. Symptoms of anxiety were measured with the Spielberger State-Trait Anxiety Inventory [STAI] scale and symptoms of depression with the Beck Depression Inventory [BDI] scale. Data were analyzed using Chi-square, independent sample T-test and two-way ANOVA with SPSS software. The mean score for BDI was 15.2 in the case and 8.36 in the control groups, which showed a significant difference. BDI was not significantly different between males and females. State and Trait scores were significantly higher in the TMD patients as compared to the controls. A significant difference was not observed in Trait anxiety between the two sexes but men revealed significantly higher State anxiety scores than women. These findings indicate that depression and anxiety were more prevalent among TMD patients in comparison to the normal population. Therefore psychological consultation for both men and women with TMD should be considered in the treatment plan

[Flexural strength of polymethyl methacrylate reinforced with glass fiber or with metal wire]

One of the most widely used materials in prosthetic dentistry is polymethyl methacrylate. Despite it's popularity, the primary problem is it's poor flexural strength and low impact strength. The aim of this study was to compare the flexural strength of unreinfored heat-cured polymer [group 1] with wire-reinforced polymer [group 2] and with glass fiber-reinforced polymer [group 3]. In this invitro experimental study 24 uniform specimens of 65.0x10.0x3.5 mm were fabricated as the manufacturer's recommendation and were assigned to 3 groups of eight. In the first and second group the samples were reinforced by glass fibers and wire respectively. The samples speciemens of third group were made of heatcure resin and served as control group. All of them were loaded up to failure, using a three-point bending test, and then the flexural strength was calculated. Data were analysed by one way analysis of variance [ANOVA]. The results showed that wire and fiber-reinforced polymers have higher flexural strength than unreinforced polymer. The one-way ANOVA revealed significant difference between group 1 and other groups statistically [P<0.05] however, there was no significant differences between groups 2 and 3. Based on the achieved results, we can use wires or fibers in order to reinforce polymer, regarding that glass fibers can be used as reinforcement of denture acrylic resin in patients who care about esthetic

Evaluation of dimensional stability of Iralgin and Alginoplast alginates after disinfection by sodium hypochlorite [5.2%] with immersion and spraying methods

Infection control is an integral part of dentistry and dental impressions are considered an important issue in cross contamination. The aim of this study was to investigate the dimensional stability of two irreversible hydrocolloid materials, Alginoplast and Iralgin after disinfection with 5.2% sodium hypochlorite, used with immersion and spraying methods. In this experimental study, impressions were made of a master mandibular arch [Typodont] containing three stainless steel inserts on the occlucal surface of both mandibular first molars and in the lingual surface of the mandibular central incisors, which served as reference marks for making measurements. Two types of irreversible hydrocolloid [Iralgin and Alginoplast] were tested. 5.2% sodium hypochlorite was used in two methods of spraying and immersion to disinfect the samples. The control group was not disinfected. Casts were made of type III gypsum. Stone casts were measured with a Nikon profile projector.Kruskall-Wallis and Mann-Witney test were used for statistical analysis using p<0.05 as the limit of significance. Casts prepared from Alginoplast disinfected by spraying method, were 0.38% larger in anteroposterior and 0.06% smaller in cross arch dimensions, whereas those prepared from Alginoplast immersed in hypochlorite were 0.47% larger in anteroposterior and 0.11% smaller in cross arch dimensions. Casts made from Iralgin were smaller after both methods of disinfecting, [0.01% smaller in anteroposterior and 0.001% smaller in cross-arch dimensions after spraying and 0.04% smaller in anteroposterior and 0.03% smaller in cross-arch dimensions after immersing in sodium hypochlorite]. Alginoplast and Iralgin impressions can be immersed or sprayed for disinfection without compromising the accuracy needed for diagnostic and opposing casts, as well as removable partial denture construction

[Comparison of dimensional accuracy of two acrylic resins polymerized by injection molding]

Despite the fact that polymethyl methacrylate is the most popular material in denture base construction, one of its main defects is the polymerization shrinkage that frequently leads in time consuming clinical problems. Several ways have been suggested to solve this problem; among them is "injection molding method". The purpose of this study was the assessment of dimensional accuracy of the two acrylic resins cured by injection molding method. In this experimental study, the dimensional accuracy of two acrylic resins after curing by injection molding method [Unipress system] was assessed by profile projector measurement. Twenty master casts were made of a master dye simulating both maxillary and mandibular edentulous arch. They were divided in two groups, each group containing 10 casts used for making denture bases. Three reference points were determined, one in the central incisor region and the other two symmetrical points in the posterior region in molar area. Three measurements were made: 1. on the master cast, 2. on the denture base just after removing the denture base from the master cast, and 3. after immersion in water for one week. The measurements were analyzed using Friedman and Mann-Whitney tests. All the denture bases in both groups, revealed significant shrinkage after removing from casts [p<0.05]. After immersion in water, there was no significant dimensional change [p>0.05] in any of the groups. Statistical analysis revealed no significant difference between the two acrylic resins too. Since there was no significant difference between dimensional accuracy of the two acrylic resins, it could be conclude that using Bayer acrylic resin with Unipress injection molding system would lead in acceptable results concerning dimensional accuracy

[Study of microbial contamination of laboratory dental pumice in the city of Shiraz, Iran]

Cross contamination via dental laboratories is an important problem. Among dental and laboratory procedures, two of the most important topics are disinfection of impressions and disinfection of prostheses. Because pumice slurry is widely used in final stages of polishing and finishing of prostheses, it should not be contaminated and if so, it could be a serious potential source of cross-infection. Therefore, this study was done to determine the incidence and also the type of pathogenic oral and non-oral microorganisms in polishing pumice of dental laboratories in the city of Shiraz. This study was a descriptive-analytical investigation. In the same controlled and sterilized condition, the used pumice samples were collected from 12 dental laboratories. Immediately, they were transported to microbiology section of standard institute and cultured in specific and non specific media. For isolation of different types of oral and non oral microorganisms, 16 different tests were applied. A wide range of microorganisms were isolated from all samples of dental pumices. Dominant bacteria in our study in order of frequency were: Acinetobacter lowffi, Bacillus cereus, Staphylococcus aureus, pseudomonas aeroginosa, diphtheroids, citrobacter frundi, enterobacter aerogenes, morganella morganii, clebsiella pneumonia, staphylococcus saprophyticus, streptococcus viridanse. 85.70% of the bacteria detected were non-oral microorganisms and 14.30% were oral microorganisms. This study showed that dental pumices are heavily contaminated with oral and especially with non-oral microorganisms and there was a high risk of cross-infection between clinician, patient and technician. Therefore infection control in all steps of prosthesis construction is recommended

[ survey of the principles of partial denture construction by dental laboratories in Shiraz]

Background: As conventional prosthesises are still the most common prosthetic treatment for public, this study has been conducted to assess the communication between the dentist and dental laboratories and find the supervision of the dentists on lab works

Materials and Methods: In this descriptive, cross- sectional study, by referring to ten dental laboratories, seven basic steps of the construction of PDRs have been considered and all the necessary information was recorded in a questionnaire

Results: In %83 of the cases, RPDs were constructed on the study diagnostic casts and for %100 of the cases no border molding had been done. %83.7 of the retentive clasps were not actually retentive, but again in %83.7 of them there was some form of reciprocal component. In %96.7 of the cases, the clasp arms were fabricated on unprepared tooth surfaces. All major connectors were rigid and in %42.9 of the cases they had enough distances to gingival margins. In most cases, indirect retainers were absent or were made in wrong places. Only in 10 out of 35 distal extension cases, RPD design was considered and for the rest, no special design was observed. In only %5, guiding planes were made on prepared tooth surfaces and finally it appeared that the majority of RPDs were designed by dental technicians rather than by dentists

Conclusion: The results indicate that dentists frequently use techniques that require a minimum of appointment time. Therefore, a greater emphasis is required to be put on continuation of education for dentist, along with better and more detailed communication between the dentists and dental laboratories