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The choice between cement and screw retention in implant prosthodontics may be a matter of personal preference or dictated by specific clinical situations. As set of clinical guidelines based on implant angulation and arch position and clinical considerations are presented to aid the clinician in determining the most appropriate method of retention for implant prostheses.
OBJECTIVES: This study aimed to evaluate the retention on two or four implants of eight resilient and nonresilient retentive anchors used in overdentures. METHOD AND MATERIALS: Eight groups of retentive anchors were used: Dyna and Shiner (magnets); Dalla Bona and O-Ring (balls); Ceka Revax and Zaag attachments (studs); the cast bar (Dolder type) system with plastic clips; and the milled bars system. These specimens with their respective overdentures were prepared on two similar acrylic resin models with four implants (3.75 x 13 mm). Ten tensile strength tests (Instron) were performed on each group at a speed of 3 mm per minute. The statistical analysis (one-way analysis of variance, Tukey's HSD test) was considered significant. RESULTS: The pull force values ranged between 0.400 and 3.800 daN (International System of Units). There was a significant difference in retention in favor of the milled bars in comparison with the Ceka Revax, Hader bars, Zaag attachments, O-Ring, and Dyna groups, and a marginally significant difference compared with the Dalla Bona group. There was a highly significant difference with the Shiner magnets. CONCLUSION: The milled bar system was the most retentive anchor, with the Dalla Bona, Ceka Revax, Hader Bar, Zaag attachment, and O-Ring groups being the second most retentive. The least retentive groups were the Shiner and Dyna magnets. Proper abutment placement in the mandible and the correct selection of the retentive anchor will improve overdenture retention.
PURPOSE: The purpose of this in vitro study was to evaluate the influence of cement type and application technique on seating discrepancies and retention forces of noble alloy castings cemented on titanium abutments. MATERIALS AND METHODS: Eugenol-free zinc oxide (Freegenol), zinc phosphate (Harvard), glass ionomer (KetacCem), polycarboxylate (Durelon), and self-adhesive resin (RelyX Unicem) cements were used. The inner surfaces of the castings were either completely coated or half-coated with cement. Abutments were used as delivered with a machined surface for the first part of the study. Groups of 8 castings were cemented in both ways. For the second part of the study, the abutments were air-abraded (aluminum oxide, 50 microm particle size), and groups of 8 completely coated castings were cemented with all cements. Marginal discrepancies were measured before and immediately after cementation. Tensile tests were conducted to measure the retention forces. Statistical analysis was performed with pair-wise comparison using the Wilcoxon rank sum test modified by Bonferroni-Holm. RESULTS: Change in seating discrepancies did not differ significantly among the different application techniques. The median retention forces for completely-coated castings were 177 N for eugenol-free zinc oxide, 346 N for zinc phosphate, 469 N for glass ionomer, 813 N for polycarboxylate, and 653 N for self-adhesive resin. With respect to retention force, 3 significantly different groups (P < .05) were identified: (1) zinc oxide, (2) zinc phosphate/glass ionomer, and (3) polycarboxylate/self-adhesive resin. No differences in retention between the 2 coating techniques were found for any cement. However, air abrading the abutments resulted in increased retention of the castings for some of the cements. CONCLUSIONS: Half-coating of the restorations with cements did not result in reduced retention values compared to the complete coating technique, but air abrasion resulted in increased retention with some cements.
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The maintenance requirements of a group of 58 patients, treated with the IMZ osseointegrated implant system and mandibular overdentures were investigated. Prostheses were retained by either bar and clip or separate stud attachments. The patients were followed up regularly for periods of between one and six years. The median number of maintenance procedures required per patient per year varied between 1-5. Detailed examination of the data revealed that a wide range of maintenance procedures was required, including replacement prostheses in 46% of cases. There were some differences related to the retentive elements used for the prostheses.
Parametric three-dimensional finite element studies were conducted on the Hader bar to determine mechanical properties with respect to bar length, stiffener height, and material properties. Three bar lengths (6, 12, and 18 mm) were analyzed with a 1-mm stiffener height. For the longest bar length (18 mm), two additional stiffener heights were evaluated (2 and 3 mm). In addition, three material types were studied for each of the design cases which represented a selection of alloys commonly used clinically. The model consisted of a representative Hader bar which was constructed of a bar of 1.8 mm diameter. The ends of the bar were fixed to a 2.5-mm diameter coping which was attached to a 1.8-mm diameter root form-type implant, rigidly fixed in a representative block of bone. The bone was modeled as fixed at its distal end to eliminate rigid body motion. A 200-Newton occlusal force was modeled as being transmitted through one, two, or three attachment clips, 5 mm in length, for the three respective bar lengths. The results of these analyses did not predict yielding (failure) for any of the cases studied. Span length and stiffener height were found to play a stronger role in the adequacy of the overall design as compared with changing material properties in the range of alloy stiffness tested. For the span length studies, factors of safety, with respect to static yield strength, ranged from 2.93 to 10.3 and fatigue factors of safety ranged from 1.41 to 3.36.(ABSTRACT TRUNCATED AT 250 WORDS)
To avoid stress between bone, implant and supra construction, the connection between implants must be passive. This is clinically difficult, if not impossible, to achieve with current procedures. Two techniques are presented in which pre-machined titanium abutment cylinders or discs are intra-orally luted to a cast supra structure. The objective is to create a stress-free implant frame-work connection. Possible advantages and disadvantages are discussed.
The use of a metal housing-retained attachment for implant-supported overdentures: (1) facilitates easy removal and replacement of a matrix attachment during routine recall examinations, and (2) ensures correct alignment and retention to the implant-supported bar assembly. This article describes a laboratory technique for processing the bar assembly (without allowing acrylic resin to seep under it) with the master cast invested in the metal flask. The technique ensures a precise fit of retentive attachments at the delivery of the overdenture to the patient.
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This clinical report presents a means of retaining implant supported superstructures using lateral fixation screws (Novadent). 244 lateral fixation screws have been used for the retention of a variety of restorations including single teeth, short span and full arch bridgework as well as overdenture bars. Over a period of observation of 4 years, the authors have found the restorations to have effective retention, ease of retrievability, good aesthetics and occlusal contours.
This study sought to determine the influence of mechanical fatigue on four varieties of implant overdenture studtype attachments (Supra-Snap, O'Ring, TSIB, ZAAG). Measurements of the initial vertical retentive force and the weight of the implant abutment were recorded. The same procedure was performed after the equivalent of 2 months, 6 months, and 12 months of clinical wear. For the four attachments, weight variation of the abutment between 0 and 1,080 cycles demonstrated no significant difference. Results indicated the TSIB to be significantly most retentive; next most retentive was the O'Ring, followed respectively by Supra-Snap and ZAAG.
Changes in the retention force of six prefabricated spherical and cylindrical attachments were examined in vitro under continuous loading. The testing machine permitted insertion-separation cycles to be tested under reproducible conditions while a calibrated measuring device determined the insertion and retention forces. At the beginning, during the so-called run-in period, all anchoring elements showed a very unstable behaviour characterized by a varying marked increase and subsequent decrease in the retention force. During the ensuing functional period, the retention force followed a more stable course. In this phase, the frictional attachments having lamellae for activation proved more stable than did the spring-loaded retention attachments. Furthermore, in two of five cylindrical anchors by Gerber, the spring broke. This provides support to the concept that prefabricated attachments should be constructed as robust elements composed of as few individual parts as possible. This would help to ensure that service and repairs remain at a minimum. Frictional attachments with lamellae for activation are to be preferred for use in matrices and patrices over attachments having spring-loaded retention.
Extracoronal Resilient Attachment (ERA) implant-supported overdentures, Class I, Division 1 or Division 3 prostheses, provide an exceptionally stable and retentive prosthetic design for edentulous patients with osseointegrated implants. The ERA System uses either an individual female implant abutment or plastic female patterns that can be incorporated into a bar. The male portion of the attachment is a nylon piece of varying retentive quality. The attachment is resilient, stable, and can be easily serviced.
The development of more sophisticated implant techniques to produce satisfying results improves the precise planning of both the surgical phase of the implantation and the following prosthetic rehabilitation. Ball and bar attachments are the main retainer systems for implant-bearing overdentures to achieve a successful treatment in the partial or full edentulism. In this clinical report, a 23-year-old male patient, presented with a large traumatic defect in the anterior mandible, was treated with ITI implant and ITI Dolder bar combinations. The reason to prefer this kind of treatment depends on the highest retention capacity and cleaning facilities of the system.
Implant supported restorations can be attached to implants with screws or can be cemented to abutments which are secured to implants with screws. Screw retained implant restorations are the authors' preferred method of securing restorations to implants. This article will be written from this perspective and the advantages and disadvantages of each method of retention will be discussed under the following headings: Aesthetics, Retrievability, Retention, Implant placement, Passivity, Provisionals, Occlusion, Immediate loading, Impression procedures, Long term treatment planning.
This article describes a simple, quick, and economical technique that makes use of a light-polymerized resin system to facilitate the retention and removal of cement-retained implant prostheses.
The screw access channels of 15 degrees angled Esthetic Abutments (Brånemark System) were either (a) completely filled with a vinyl polysiloxane impression material (Memosil), (b) partially filled with Memosil or (c) had lower portion filled with Memosil and the remainder with composite resin. The force required to remove a temporarily cemented restoration was measured. The removal force was significantly reduced with the channel completely filled with Memosil compared to those partially filled with Memosil (p<0.01) or with composite resin placed over Memosil (p<0.01). The method selected to fill the screw access channel of an implant abutment can be a significant factor affecting retention of a cemented restoration.
In another article in this series the authors' preference for screw retained implant supported restorations was presented together with a literature review and rationale.(1) There remain situations when screw retention is not possible due to implant position, implant trajectory, aesthetics or function.