Influence of abutment height and convergence angle on the retrievability of cement-retained implant prostheses with a lingual slot

PURPOSE: Cement-retained implant prostheses can lack proper retrievability during repair, and residual cement can cause peri-implantitis. The purpose of this in vitro study was to evaluate the influence of abutment height and convergence angle on the retrievability of cement-retained implant prostheses with lingual slots, known as retrievable cement-type slots (RCS). MATERIALS AND METHODS: We fabricated six types of titanium abutments (10 of each type) with two different heights (4 mm and 6 mm), three different convergence angles (8°, 10°, and 12°), a sloped shoulder margin (0.6 mm depth), a rectangular shape (6 mm × 6.5 mm) with rounded edges, and a rectangular ledge (2 mm × 1 mm) for the RCS. One monolithic zirconia crown was fabricated for each abutment using a dental computer-aided design/computer-aided manufacturing system. The abutments and crowns were permanently cemented together with dual-curing resin cement, followed by 24 hours in demineralized water at room temperature. Using a custom-made device with a slot driver and torque gauge, we recorded the torque (N·cm) required to remove the crowns. Statistical analysis was conducted using multiple regression analysis and Mann-Whitney U tests (α=.05). RESULTS: Removal torques significantly decreased as convergence angles increased. Multiple regression analysis showed no significant interaction between the abutment height and the convergence angle (Durbin-Watson ratio: 2.186). CONCLUSION: Within the limitations of this in vitro study, we suggest that the retrievability of cement-retained implant prostheses with RCS can be maintained by adjusting the abutment height and convergence angle, even when they are permanently cemented together.

Effect of internal gap on retentivity in implant fixed prosthesis with lingual slot / 대한치과보철학회지

PURPOSE: Recently, a method of forming a slot in the prosthesis lingual has been introduced to solve the occlusal and aesthetic disadvantages of screw-retained prosthesis in the manufacture of implant-fixed prosthesis and to ensure retrievability in cement retained prostheses. The purpose of this study is to investigate the effect of the internal gap on the removal of the prosthesis in the preparation of cement-retained implant prostheses with lingual slots. MATERIALS AND METHODS: Titanium abutment and internal gap of the zirconia prosthesis to be attached to the upper part were set to 30, 35, and 50 µm, respectively. Three for each type total 15 were produced for each type. The zirconia prosthesis formed a retrievable cement-type slot with a space of 1 mm at the location where the titanium abutment meets the shelf area. Autocatalytic resin cement was used for bonding of abutment and zirconia prosthesis, and the maximum removal stress value was measured in units of Ncm by using the customized equipment of the cemented specimen. The Kruskal-Wallis test was used to compare the three groups by statistical analysis (α = .05), modified by post hoc test the Mann-Whitney U-test and the Bonferroni correction method were used to compare the two methods (α = .017). RESULTS: There was no statistically significant difference in removal stress between the 30 µm group and the 35 µm group in the internal gap (P = .032), and there was a significant difference between the 30 µm group and the 50 µm group, between the 35 µm group and the 50 µm group (P < .017). CONCLUSION: Thus, the internal gap of computer-aided design affected the retention between the zirconia prosthesis and the titanium abutment.

Effects of crown retrieval on implants and the surrounding bone: a finite element analysis

PURPOSE: The aim of this study was to observe stress concentration in the implant, the surrounding bone, and other components under the pull-out force during the crown removal. MATERIALS AND METHODS: Two 3-dimensional models of implant-supported conventional metal ceramic crowns were digitally constructed. One model was designed as a vertically placed implant (3.7 mm × 10 mm) with a straight abutment, and the other model was designed as a 30-degree inclined implant (3.7 mm × 10 mm) with an angled abutment. A pull-out force of 40 N was applied to the crown. The stress values were calculated within the dental implant, the abutment, the abutment screw, and the surrounding bone. RESULTS: The highest stress concentration was observed at the coronal portion of the straight implant (9.29 MPa). The stress concentrations at the cortical bone were lower than at the implants, and maximum stress concentration in bone structure was 1.73 MPa. At the abutment screws, the stress concentration levels were similiar (3.09 MPa and 3.44 MPa), but the localizations were different. The stress at the angled abutment was higher than the stress at the straight abutment. CONCLUSION: The pull-out force, applied during a crown removal, did not show an evident effect in bone structure. The higher stress concentrations were mostly observed at the implant and the abutment collar. In addition, the abutment screw, which is the weakest part of an implant system, also showed stress concentrations. Implant angulation affected the stress concentration levels and localizations. CLINICAL IMPLICATIONS: These results will help clinicians understand the mechanical behavior of cement-retained implant-supported crowns during crown retrieval.

A Study of Grey Literature in the Field of Nutrition, Health and Food Safety.

Aims: Grey literature covers all reports from public research institutes, which are not peerreviewed scientific papers. The aim of this article is to explore the amount and extent of grey literature in the field of nutrition, health and food safety, the retrievability and the view of several scientists on this matter. Study Design: An explorative descriptive, semi-quantitative study. Methodology: During a three week survey in June 2013, a questionnaire was sent to 97 scientists in the field of nutrition, health and food safety, of which 44 were returned. Most of the scientists were working in European governmental, academic or research institutes. Questions included an estimation of the quantity and retrievability of the grey literature at that institute, as well as questions about better ways to make grey literature more accessible. To compare the current needs for grey literature and its accessibility with future needs, a questionnaire was also designed and distributed via email and social media among students in the Netherlands; in total 134 replies were received of which 96 were included in the analysis. Outcomes of the research were compared with literature. Results: Scientists were aware of the existence of grey literature, but had mostly no idea about the amount and extent of it within their own institutes, which was an important drawback in this study. Also, the reported number by scientists did not match the number found on websites of the institutes, which may be due to language barriers, costs and the use of passwords. Although there are various repositories especially for the storage of grey literature, most scientists are not aware of them. The results also gave some insight in the perceived needs and problems with retrievability. Conclusion: This study should be considered as a first attempt to explore the grey literature in the field of nutrition, health and food safety. The main finding was that the quantity and impact of grey literature is not to be underestimated. Scientists indicated that they want to improve retrievability of the documentation since they are considered often very valuable to the scientific community and the general public. Increasing the awareness of the amount grey literature and ways to improve the accessibility are points of attention for further research.

Implant overdenture using a locator bar system by drill and tapping technique in a mandible edentulous patient: a case report

Various options have been introduced for the selection of implant overdenture attachments. Attachment wear due to the repeated insertion and removal of dentures has caused problems such as decreased retention and the requirement for suprastructure remanufacturing. In these cases, a Locator bar system was applied using the drill and tapping technique to achieve total retrievability. In a 55-year-old female patient who showed three degrees of mobility in most of her teeth due to severe alveolar bone loss, a complete denture in the maxilla and an implant supported type overdenture in the mandible were planned after extracting all the remaining teeth. Six implants were placed from canine region to the distal molar region, and the locator was connected to the milled bar using the drill and tapping technique. For a 61-year-old female edentulous patient who complained of poor retention with old denture, a complete denture in the maxilla and an implant-tissue supported type overdenture in the mandible were planned. Four implants were placed in front of mental foramen, and the Locator was also connected to the Hader bar using the drill and tapping technique. With this technique, female parts can be easily replaced, and retention can be continuously maintained.

Retrievable SCP (screw-cement prosthesis) implant-supported fixed partial dentures in a fully edentulous patient: a case report / 대한치과보철학회지

Implant prostheses were classified into screw-retained prosthesis and cement-retained prosthesis by their method of retaining, and there is screw and cement retained implant prosthesis (SCRP) which has been made reflecting the strengths of these two. The advantages of the SCRP technique are easy retrievability and passive fit of implant prostheses. However, the occlusal screw holes of implant prostheses can be thought as a disadvantage with respect to esthetics and occlusion. Inappropriately positioned implants also limited the use of the SCRP technique. The present study is reporting about the case where nine implants (US II, OSSTEM, Seoul, Korea) were placed in maxilla and eight in mandible respectively in fully edentulous patients. Then, the cement-retained prosthesis was applied for the part in which the screw hole positioned improperly, and screw-retained prosthesis for properly positioned implants so that the combined screw-cement prosthesis has been produced where the satisfying result has shown in both function and esthetics. Three-year follow-up has been done for the patient.

Evaluation of retrievability using a new soft resin based root canal filling material / 대한치과보존학회지

The aim of this study was to evaluate the retrievability of Resilon as a root canal filling material. Twenty-seven human single-rooted extracted teeth were instrumented utilizing a crown down technique with Gates-Glidden burs and ProFile system. In group1 (n = 12) canals were obturated with gutta percha and AH-26 plus sealer using a continuous wave technique and backfilled. In group 2 (n = 15) Resilon was used as a filling material. Then teeth were sealed and kept in 37degrees C and 100% humidity for 7 days. For retreatment, the samples were re-accessed and filling material was removed using Gates-Glidden burs and ProFiles. Teeth were sectioned longitudinally to compare the general cleanliness and amount of debris (x 75) using SEM. Chi-square test was used (alpha = 0.05) to analyze the data. The total time required for removal of filling materials was expressed as mean +/- SD (min) and analyzed by the Student t-test (alpha = 0.05). Required time for retreatment was 3.25 +/- 0.32 minutes for gutta percha/AH 26 plus sealer and 3.05 +/- 0.34 minutes for Resilon. There was no statistically significant difference between the two experimental groups. There was no significant difference between the groups in the cleanliness of the root canal wall. This study showed that Resilon was effectively removed by Gates-Glidden burs and ProFiles.

A study on the complete retrieval system of the cementation type implant abutment / 대한치과보철학회지

PURPOSE: This study was performed to investigate the retrievability of the cemented crown from the cementation type implant abutment. MATERIAL AND METHOD: The cementation type implant abutments (NEOBIOTECH implant abutment regular, 3 degree taper, 10mm length, 4mm diameter, Ti grade III, machined surface, Hwasung, Kyunggi-do) and cemented crowns were divided into 3 groups, depending on their hole angles formed in the crowns for their retrievability. The abutments and crowns were luted with 4 kinds of cements and separation test using metal wedge was executed with Instron 4465 Universal Testing Machine and the maximum impact force of the modified crown ejector was measured. RESULTS AND CONCLUSION: 1. All of the cementation type implant abutments and cemented crowns were separated with relatively small force by metal wedge. 2. The retrieving force was minimum when the metal wedge was applied perpendicular to the axis of abutment. 3. The force for retrieving crowns from abutments was maximum in resin cement group, and reduced in orders of zinc phosphate cement, glass ionomer cement and zinc oxide eugenol cement. 4. The maximum force obtained by the crown ejector was higher than the retrieval force in ZOE and GI cement and lower than that in ZPC and resin cement. 5. If it has similar conditions clinically, the cemented crowns luted with 2 types of cements (ZOE, GI cement) can be safely retrieved from the cementation type implant abutments by the modified crown ejector.

The Use Of Protein Characteristics To Assess The Retrievability Of Ancient DNA From Acient Bones.

The ability to retrieve DNA from ancient specimens has been one of the greatest achievements of the past decade, and has opened a totally new field of research with applications in seemingly distant domains such as archeobotany, the molecular phylogeny of extinct genomes, human paleopathology and the genetics of ancient human populations. However, extraction of ancient DNA often has a very low rate of success, prompting researchers to develop screening methods for the selection of promising specimens. With this goal in mind, we studied the amino acid content of nine human bones of ancient origin. We demonstrate that a single HPLC chromatogram is indicative of integrity of ancient bone proteins. Among five specimens containing amplifiable DNA, four exhibited a protein content similar to that of contemporary bone. Three of the four specimens, from which we were unable to extract any amplifiable DNA, had an amino acid content strikingly different from that of contemporary bone. A non-parametric statistical test, Kendall's tau, was used to show that protein content and PCR products, are probably correlated (at a 95% confidence level).In addition, the D/L Asp and D/L Glu racemization ratios obtained are indicative of the presence of ancient organic compounds. We propose that protein analysis should be systematically performed in studies where there are many samples, in order to select the specimens that are most likely to contain retrievable ancient DNA.