A prospective multicenter clinical study on the efficiency of detachable ball- and spring-retained implant prosthesis

PURPOSE

This prospective clinical study was conducted to evaluate the clinical usefulness of the freely detachable zirconia ball- and spring-retained implant prosthesis (BSRP) through a comparative analysis of screw- and cement-retained implant prosthesis (SCRP).

MATERIALS AND METHODS

A multi-center, randomized, prospective clinical study evaluating the clinical usefulness of the detachable zirconia ball- and spring-retained implant prostheses was conducted. Sixty-four implant prostheses in 64 patients were examined. Periodic observational studies were conducted at 0, 3, 6, and 12 months after delivery of the implant prosthesis. Factors such as implant success rate, marginal bone resorption, periodontal pocket depth, plaque and bleeding index, and prosthetic complications were evaluated, respectively.

RESULTS

During the 1-year observation period, all implants survived without functional problems and clinical mobility, showing a 100% implant success rate. Marginal bone resorption was significantly higher in the SCRP group than in the BSRP group only at the time of implant prosthesis delivery (P = .043). In all observation periods, periodontal pocket depth was slightly higher in the BSRP group than in the SCRP group, but there was no significant difference (P > .05). The modified plaque index (mPI) scores of both groups were moderate. Higher ratio of a score 2 in modified sulcus bleeding index (mBI) was observed in the BSRP group in the 6- and 12-months observation.

CONCLUSION

Within the limitations of this study, the newly developed zirconia ball- and spring-retained implant prosthesis could be considered as an applicable and predictable treatment method along with the existing screw- and cement-retained prosthesis.

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.

The Strength of Ethical Matrixes as a Tool for Normative Analysis Related to Technological Choices: The Case of Geological Disposal for Radioactive Waste

The ethical matrix is a participatory tool designed to structure ethical reflection about the design, the introduction, the development or the use of technologies. Its collective implementation, in the context of participatory decision-making, has shown its potential usefulness. On the contrary, its implementation by a single researcher has not been thoroughly analyzed. The aim of this paper is precisely to assess the strength of ethical matrixes implemented by a single researcher as a tool for conceptual normative analysis related to technological choices. Therefore, the ethical matrix framework is applied to the management of high-level radioactive waste, more specifically to retrievable and non-retrievable geological disposal. The results of this analysis show that the usefulness of ethical matrixes is twofold and that they provide a valuable input for further decision-making. Indeed, by using ethical matrixes, implicit ethically relevant issues were revealed-namely issues of equity associated with health impacts and differences between close and remote future generations regarding ethical impacts. Moreover, the ethical matrix framework was helpful in synthesizing and comparing systematically the ethical impacts of the technologies under scrutiny, and hence in highlighting the potential ethical conflicts.

Reversible Experiments: Putting Geological Disposal to the Test

Conceiving of nuclear energy as a social experiment gives rise to the question of what to do when the experiment is no longer responsible or desirable. To be able to appropriately respond to such a situation, the nuclear energy technology in question should be reversible, i.e. it must be possible to stop its further development and implementation in society, and it must be possible to undo its undesirable consequences. This paper explores these two conditions by applying them to geological disposal of high-level radioactive waste (GD). Despite the fact that considerations of reversibility and retrievability have received increased attention in GD, the analysis in this paper concludes that GD cannot be considered reversible. Firstly, it would be difficult to stop its further development and implementation, since its historical development has led to a point where GD is significantly locked-in. Secondly, the strategy it employs for undoing undesirable consequences is less-than-ideal: it relies on containment of severely radiotoxic waste rather than attempting to eliminate this waste or its radioactivity. And while it may currently be technologically impossible to turn high-level waste into benign substances, GD's containment strategy makes it difficult to eliminate this waste's radioactivity when the possibility would arise. In all, GD should be critically reconsidered if the inclusion of reversibility considerations in radioactive waste management has indeed become as important as is sometimes claimed.

Retention of Implant Supported Metal Crowns Cemented with Different Luting Agents: A Comparative Invitro Study

INTRODUCTION

To overcome limitations of screw-retained prostheses, cement-retained prostheses have become the restoration of choice now a days. Selection of the cement hence becomes very critical to maintain retrievability of the prostheses.

AIM

The purpose of this study was to assess and compare the retention of base metal crowns cemented to implant abutments with five different luting cements.

MATERIALS AND METHODS

Ten implant analogs were secured in five epoxy resin casts perpendicular to the plane of cast in right first molar and left first molar region and implant abutments were screwed. Total of 100 metal copings were fabricated and cemented. The cements used were zinc phosphate, resin modified glass ionomer cement, resin cement, non-eugenol acrylic based temporary implant cement & non-eugenol temporary resin cement implant cement. Samples were subjected to a pull-out test using an Instron universal testing machine at a crosshead speed of 0.5mm/min. The load required to de-cement each coping was recorded and mean values for each group calculated and put to statistical analysis.

RESULTS

The results showed that resin cement has the highest retention value 581.075N followed by zinc phosphate luting cement 529.48N, resin modified glass ionomer cement 338.095 N, non-eugenol acrylic based temporary implant cement 249.045 N and non-eugenol temporary resin implant cement 140.49N.

CONCLUSION

Within the limitations of study, it was concluded that non-eugenol acrylic based temporary implant cement and non-eugenol temporary resin implant cement allow for easy retrievability of the prosthesis in case of any failure in future. These are suitable for cement retained implant restorations. The results provide a possible preliminary ranking of luting agents based on their ability to retain an implant-supported prosthesis and facilitate easy retrieval.

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.