Effect of platform switching on crestal bone stress distribution around 3i implants: a finite element analysis

Over the last few years, concept of platform switching has gained popularity for reducing degree of crestal bone resorption. Many researchers believe that, this theory can be used for improving stress distribution in implant-bone interface. The purpose of this three dimensional Finite Element Analysis [FEA] was to study and compare stress distribution in implant-bone interface and implant-abutment interface of 3i implants [Biomet 3i, USA] in mandibular molar area. For this FEA, computed tomography [CT] images of an adult human mandible was used to make the three-dimensional model of posterior edentulous mandible .The implant systems which used was the 3i system consisted of 3i fixtures: 4 and 5 mm in diameter and 11.5 mm in length, and 3i Certain abutment 4.1 and 5mm [Biomet 3i, USA]. This implant systems were assembled on the mandible model in 3 different designs: a platform-switched configuration; MODEL 4: 4-mm 3i fixture, 4.1-mm abutment; MODEL 5: 5-mm 3i fixture, 5-mm abutment; MODEL 6: 5-mm 3i fixture, 4.1-mm abutment, a platform-switched configuration. A linear static analysis was performed on the prepared 3D solid models with two different oblique load of 100 and 250 N in the lingobuccal direction with 15 degrees of inclination on the center of the abutment. Regardless of the implant system used, maximum Von Mises stresses in cortical bone around implants were lower in platform switched models compared to matching diameter implant-abutment. This effect was not related to the usage of larger implant diameters in these models. However, Von Mises stresses in implant-abutment interface were the lowest in models with larger implant diameter. The platform switching technique reduces the stress concentration in the area of crestal bone-implant interface and shifted it to the area of implant-abutment interface. In the present study, this stress reduction was not

[Evaluation of fixed splinting in periodontally compromised abutments; utilizing 3-D finite element method [FEA]]

Fixed splinting of abutment teeth can alter the stress distribution characteristics of removable partial denture [RPD]. However, periodontally compromised abutments may complicate free end RPD treatment plans. The purpose of this study was to determine the effects of fixed splinting of periodontally compromised abutments on load distribution in free end RPD. Three-dimensional finite element models were designed for mandibular first and second premolars including their PDL and surrounding bony structures. In the first model the teeth had no periodontal involvement; in the second model, the first premolar was healthy, the second premolar had periodontal involvement [C/R=1]; and, in the third model both teeth had periodontal involvement [C/R=1]. Likewise, before and after fixed splinting, situations were defined for each model. The Von misses stress in surrounding bone was analyzed after applying 50 N loads on the specimens. In all three models the maximum Von misses stress before splinting were found to be in the apical area of teeth and the minimum was detected near the mesial crest of first premolar and distal crest of second premolar. After splinting the teeth together, a stress reduction was observed in the interdental crest areas; while in model 1 and 2, increase in the stress was observed in apical areas. The greatest remedy was demonstrated in model 2 where a periodontally compromised tooth was splinted to a healthy one. Fixed splinting of periodontally compromised teeth can reduce the stress concentration in the interdental crest areas and it can improve the stress distribution in the surrounding bone

[Frequency of dental cements application by general practitioners and prosthodontists in Tehran, 2004]

Nowadays various types of dental cements are used in fixed prosthetic treatments with different indications. On the other hand, these indications may be changed over a lot every day and new materials are being produced. The aim of this study was to determine the practice of dentists [included general practitioners and prosthodontists] about applications and manipulations of dental cements in fixed prosthetic treatments. The study was designed as a cross-sectional, descriptive method. Samples were 362 general practitioners [GP] and 32 [academic and non-academic staff] specialists worked in Great Tehran in 2004. Sampling was done in a simple random method. The questionnaire consisted of 11 questions. After determining the validity of questionnaire, it's reliability was confirmed by means of a test-retest exam. Zinc phosphate was the most frequent cement in fixed partial denture restorations [FPDs] in non-vital teeth [54.4% of GPs and 51.3% of specialists]. In vital teeth, both in preparations near and distant to the pulp, polycarboxylate were used frequently by GPs [50.8% and 56.4%, respectively] and specialists [531% and 34.4%, respectively]. The most of dentists in both groups were using zinc oxide with eugenol in temporary restorations near the pulp [55.5% and 62.5%, respectively]. Zinc phosphate was frequently used for post and core cases [54.5% and 71.9%, respectively]. The choices of general practitioners were relatively similar to specialists

evaluation of compressive strength in three brands of zinc phosphate cement in two different powder/liquid ratios

This study was conducted to evaluate the compressive strength of 3 brands of Zinc Phosphate Cements determining the influences of eye estimated [rough measurement] of powder/liquid ratios on the compressive strengths of these cements. The three tested Zinc phosphate cements were Hoffmann's [Harvard Dental GmbH], DeTrey Zinc [Densply] and Ariadent [Asia Cherri Teb]. The specimens were divided into 6 groups, each one containing 10 samples. These samples were prepared according to ISO 9917 [2003] and stored in distilled water at the temperature of 37 °C for 24 hours. The compressive strengths of samples were measured with the Zwick testing machine. The ANOVA and Tukey statistical tests were used to identify the significant differences between these groups. There were significant differences between compressive strengths of cements prepared with manufacturer suggested mixing ratios and clinically used [eye estimated] ratios. The least compressive strength was recorded for Ariadent samples with clinical mixing ratio and the highest was recorded for Hoffmann's samples with manufacturer's suggested ratio. In clinically used ratios, Hoffmann's cement had the highest compressive strength. The differences between the strengths of manufacturer suggested mixing ratios and clinically used ones were the most in DeTrey Zinc cement