[Dimensional accuracy of three polyvinyl siloxane putty-wash impression techniques]

There is much controversy with regard to the effect of the impression technique on accuracy of cast restorations. The aim of this study was to evaluate the accuracy of 3 putty - wash impression techniques using polyvinyl siloxane material. Three putty-wash impression techniques were used for this experimental in vitro study. [1] two-step with 1mm relief [using prefabricated copings for wash space], [2] two-step technique with a polyethylene spacer and [3] one-step. For each-technique, 15 impressions were made of a maxillary edentulous model that contained 4 ITI analogue abutments [one with undercut]. The impressions were made by standard trays with same, space and poured with type IV dental stone. The stone die measurements were made on digital photographs by a computer software. The percentage of dimensional changes of intra abutment [diameter and height] and inter abutment were analyzed by ANOVA, Turkey HSD and t - student tests [a=0.05]. One way analysis of variance showed statistically significant differences among the 3 putty- wash impression techniques, for all measurements[P<0.05]. The dimensional changes of technique 1 were significantly less than another two techniques. There were significant differences between height and diameter of the dies with undercut in techniques 2 and 3 .The diameter of the die was increased in technique 1 and decreased in the other techniques. The height of the dies decreased and the intra abutment spaces increased in all impression techniques. The polyvinyl siloxane 2-step with 1 mm relief putty-wash impression technique was the most accurate for fabricating cast restoration

Average annual crestal bone loss of ITI implants following the first year of loading

Long term success of dental implants directly depends on marginal bone resorption. The aim of this study was to determine the annual average bone loss on the mesial and distal aspects of implants following the first year of implantation. This was a descriptive analytical study of patients treated with ITI [International Team of Implantology] implants at the Dental School of Isfahan University of Medical Sciences from 1998-2002 [1377-81]. A total of 15 patients with 41 implants were selected by convenience sampling method. The height of the alveolar bone was measured using panoramic radiography before and after loading with calipers to determine the average bone loss. Other information such as pocket depth, bleeding index, plaque index, gingival recession, was obtained by clinical examinations. The mean bone loss on the mesial and distal sides was analyzed by ANOVA at 0.05 level of significance. The average bone loss on the proximal sides of ITI implants obtained annually after the first year of loading was 0.084 +/- 0.035 mm with slight difference on the mesial [0.092 +/- 0.035] and distal [0.072 +/- 0.033] sides. There was negligible difference between male and female patients. The average survival rate for thirty three months was 95.1%. The average bone loss on the mesial and distal sides of ITI implants compared with other studies was satisfactory. Survival and success rates were acceptable

[Evaluation of silent period duration of masseter muscle before and after placement of an occlusal splint in persons with normal occlusion]

Silent period is defined as transient electromyographic activity following a stimulus of some kind during a sustained period of muscle contraction. The exact mechanism of this reflex and the factors that influence it are still unknown. One important unanswered question is the relationship between the length of muscle and duration of silent period. The aim of this study was to compare the silent period duration of masseter muscle before and after placement of an occlusal splint in the mouth. Twenty five persons with complete dentition [28 natural teeth with no prosthesis and class I occlusion, without signs and symptoms of muscle or TMJ dysfunction and without history of orthodontic treatment were chosen for this study. The mean age of subjects was 22.3 years. For each subject, a maxillary occlusal splint with 3mm thickness in premolar area was fabricated and adjusted. Silent duration was measured during maximum muscle activity using chin tap as stimulus. Silent period was evoked and measured 3 times and the mean of the measurements was used as individual SPD. The mean SPD taken without splint was 20.03 +/- 1 and 14.19 +/- 0.83 with splint. Pair Wise Comparison test with use of LSD test showed that the mean SPD with and without splint were significantly [P<0.05] different. The result of this study showed that placement of a splint shortens the SPD of masseter muscle, significantly. Therefore, it is suggested that SPD can be used as a Para clinical factor to evaluate the full mouth restorative treatments that probably change VD. It also shows that muscle and TMJ receptors have a more important role in SPD than periodontal receptors

investigation on metallic ion release from four dental casting alloys

Element release from dental casting alloys into the oral environment is of clinical concern and is considered to be a potential health problem to all patients. The aim of this study was to investigate the metallic ion release of four base metal alloys. Two Ni-Cr [Minalux and Supercast] and two Co-Cr alloys [Minalia and Wironit] were examined. Nine specimens of each type were prepared in 13×11×1.4 mm dimensions and each of the four alloys [3 specimens per group] were conditioned in artificial saliva at 37 c for one, three and seven days. The conditioning media were analyzed for element-release using Inductive Coupled Plasma Atomic Emission Spectrophotometer [ICPAES]. Collected data were statistically analyzed using ANOVA and Duncan multiple range test [P< 0.05]. The greatest amount of element release was seen after seven days [134.9 ppb Supercast, 159.2 ppb Minalux, 197.2 ppb Minalia, and 230.2 ppb Wironit]. There was a significant difference between the released elements from the alloys after the three conditioning times [p<0.001]. Element release from the studied alloys is proportional to the conditioning time. The Ni-Cr alloys tested in this investigation were more resistant to corrosion as compared to the Co-Cr alloys in artificial saliva. Supercast had the highest corrosion resistance

Comparative study of ceramometal tensile bonding strength in two base metal alloys

One of the greatest problems in metal -ceramic restorations is debonding of porcelain from dental alloys. Production of dental alloys by Iranian companies necessitates the evaluation of physical and handling properties of these products. In this study the bond strength between porcelain and two types of base metal alloys, Supercast [with beryllium] and Minalux [without beryllium] was investigated. In this experimental study 10 cylindric bars from each base metal alloy were prepared. The bars were degassed and porcelain was applied around them in a disc form [8 mm diameter and 2 mm thickness]. The bond strength of porcelain to metal bars was tested with the shear strength test by Instron. Data were analyzed with student t-test and P<0.05 was considered as the limit of significance. The mean failure load was 71.58 +/- 6.4 KgF for Supercast and 67.34 +/- 5.48 for Minalux alloy. The bond strength of Supercast and Minalux were 55.85 +/- 4.99 MPa and 52.54 +/- 4.27 MPa respectively. The difference was statistically significant [P<0.001]. This study showed that nickel-chromium-beryllium alloy [Supercast] produced significantly better ceramometal bonding than nickel chromium alloy without beryllium [Minalux]