A Review of the Literature A systematic review of orthodontic retention systems: The verdict

International Orthodontics

Summary

Introduction

Retention during both the active and passive phases of treatment has given rise to numerous publications concerning its efficacy, the range of systems available and its variability over time. There are currently many different retention protocols regularly used by orthodontists; however, their efficacy and duration are still subject to debate. There is as yet no consensus as to which retention protocol is the most effective or for how long the retention device needs to be worn. The aim of this research was to perform a systematic review of the scientific literature in order to evaluate the efficacy of the different retention systems and clinical protocols among those most widely used, so as to make recommendations beneficial to both patient and practitioner.

Materials and methods

A search of the literature was performed in the following databases: PubMed (MEDLINE), ScienceDirect and Cochrane Library. The search was limited to publications in English and French during the period 2006–2016.

Results

Out of 1952 references initially identified, 17 articles corresponded to our inclusion criteria. The results show that: fixed retention is more effective than removable retainers for the maintenance of incisor alignment during the first six months of retention; there is no significant difference in efficacy between the different fixed retention systems; there is no significant difference in efficacy between the vacuum-formed systems and the Hawley retainer; part-time use of removable retainers (between 8–10 h/day) is sufficient; the most widely used retention protocol combines a vacuum-formed splint or Hawley retainer in the upper arch with mandibular fixed retention.

Conclusion

Despite the large number of studies devoted to orthodontic retention only a few articles corresponded to the methodological criteria of bio statistical analysis. Also, on account of the variations in experimental protocols, the levels of proof relating to the efficacy of different systems are very weak. Research into this topic should first seek to normalize methods of analysis and then perform randomized controlled long-term trials to shed light on this problem.

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Research and Education Abutment screw loosening in angulation-correcting implants: An in vitro study

The Journal of Prosthetic Dentistry

Abstract

Statement of problem

Techniques that allow angulation correction for screw-retained implant-supported restorations are now available. However, whether angulation correction built into the head of the implant affects abutment screw loosening is unclear.

Purpose

The purpose of this in vitro study was to assess abutment screw loosening in angulation-correcting implants and straight implants subjected to simulated nonaxial occlusal loading.

Material and methods

Seven external connection 12-degree angulation-correcting implants and 7 straight implants were embedded in an acrylic resin housing, and titanium abutments were secured with titanium screws tightened to 32 Ncm. Each specimen was secured in a tooth wear machine and subjected to 1 000 000 cycles of 50-N nonaxial load to simulate 1 year of clinical service. The mean abutment screw removal torque values were calculated, and the association between number of cycles and the abutment screw removal torque was analyzed using a linear mixed-effects model and statistical software (α=.05)

Results

The mean abutment screw torque loss was 59.8% for the angulation-correcting implant group and 68.7% for the straight implant group. A statistically significantly greater mean abutment screw removal torque was recorded in the angulation-correcting implant group compared with the straight implant group after 1 000 000 cycles (P=.019).

Conclusions

A significant loss of abutment screw torque was found in both implant groups with increased cycles of occlusal loading. The angulation-correcting implants resisted screw loosening significantly more than the straight implants because of the reduced angle of abutment screw loading.
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Systematic Review Effects of modifying implant screw access channels on the amount of extruded excess cement and retention of cement-retained implant-supported dental prostheses: A systematic review

The Journal of Prosthetic Dentistry

Abstract

Statement of problem

Cement-retained implant-supported prostheses eliminate screw loosening and enhance esthetics. However, retrievability and the possibility of removing extruded excess cement (EEC) have been problematic.

Purpose

The purpose of this systematic review was to analyze the effects of modifying the screw access channel (SAC) on the amount of EEC and the retention of cement-retained implant-supported prostheses.

Material and methods

PubMed, Web of Science, Scopus, and Google Scholar databases were searched with appropriate key words. Related titles and abstracts published up to June 2017 were screened and selected on the basis of defined inclusion criteria. Full texts of all studies were read and subjected to quality assessments. After the initial search, 1521 articles were included in the study. Of these, 11 studies were subjected to critical appraisal, and 10 of them were reliable enough in methodology to be systemically reviewed.

Results

All the studies were in vitro and described a total of 260 specimens. According to the interpreted results, closed SACs caused lower retention with a higher amount of EEC, whereas open SACs caused the reverse. Also, as the abutment height decreased, retention decreased.

Conclusions

Extending the crown’s margin into the SAC, leaving the SAC open, and using internal vents in the SAC space are possible methods of modifying the SAC to gain higher retentive values. Also, the use of internal vents in the SAC system and open or partially filled SAC space reduce the amount of EEC.
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