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Purpose: To quantify the rate of maintenance interventions of mandibular prostheses: complete dentures and overdentures retained by two implants, with either internal hex or external hex connections. Materials and Methods: This study analyzed patients with edentulous mandibles treated with distinct treatment protocols: a control group received complete dentures; a second group received Locator-retained overdentures supported by two external hex connection implants; and a third group received overdentures supported by internal hex connection implants. All of the maintenance interventions associated with the prosthetic treatment after delivery were recorded (starting from 2000 until the final assessment in 2012). Moreover, patient satisfaction was assessed using a 0 to 10 visual analog scale. Results: The final sample was composed of 136 patients: 56 in the control group, 31 in the hex implant overdenture group, and 49 in the internal connection overdenture group followed over a period of 60 months (ranging from 3 to 144 months). Prosthetic adjustment was the most frequent intervention carried out, particularly within the control group (a mean rate of 1.1 ± 1.9 times/subject/year) in comparison with the internal connection (0.6 ± 0.8 times/subject/year) and hex implant overdenture groups (0.3 ± 0.2 times/subject/year). Relining was also frequently required, occurring on average every 4 years in the control group and every 7 years in the overdenture groups. Abutment loosening was more frequent in the hex implant overdenture group than in the internal connection overdenture group (8/31 versus 8/49), as well as abutment wear (5/31 versus 5/49). Gingival inflammation was significantly more common in the hex implant overdenture group (19/31 patients), as compared with the controls (16/56 subjects), and satisfaction was higher in patients in the two overdenture groups (mean Oral Satisfaction Scale [OSS] score of 8.1 ± 1.9 for external and 8.4 ± 1.6 for internal connections) than in the control group (5.3 ± 3.3). Conclusion: Locator-retained overdentures needed less than half the number of maintenance interventions when compared with the control group, and maintenance was required every 2 to 4 years. [ABSTRACT FROM AUTHOR]

Background: It is necessary to know the in vitro behavior of different attachment systems to be used clinically. The evolution of retention capacity over 10 years (14,600 insertion/de-insertion cycles) was determined in vitro , evaluating two overdenture attachment systems (Locator® and OT Equator®)., Material and Methods: The study used an implant replica compatible with the abutments of both systems. 10 Locator® and 10 OT Equator® attachments were screwed to the abutments. Nylon inserts were attached and tested, subjecting them to 14,600 insertion and de-insertion cycles (representing 10 years functional life) in axial direction. The universal test machine crosshead speed was 50 mm/min with a de-insertion range of 2 mm., Results: The initial retention of Locator® was 17.02 N and of Equator® 16.36 N. After 14,600 cycles, Locator® suffered a mean loss of retention of 50.89%, while Equator® lost 69.28%. Both systems showed retention increases up to the first 1,000 cycles, which decreased thereafter up to 14.600 cycles. Statistically significant differences between the systems were found after 7,500 cycles., Conclusions: Both systems presented acceptable retention capacities after 14,600 cycles. Significant differences in retention force between the systems evolved after 7,500 cycles (5 years in vitro use). These results should be treated with caution and should be verified clinically. Key words: Denture, mandibular prosthesis implantation, attachment, dental implant-abutment connection, denture retention., Competing Interests: Conflict of interest statement: The authors declare that the paper has been submitted without conflict of interest, and without funding.

Background: For implant-supported hybrid prostheses, high mastication forces and reduced acrylic resin thickness over a metal substructure often cause failures arising from tooth or resin fractures. To assay fracture resistance of artificial teeth and resin in implant-supported hybrid prostheses in relation to the titanium structure and retention design supporting teeth., Material and Methods: 40 specimens bearing incisors were divided into four groups according to the titanium structure supporting the teeth and the type of load force applied: Group I (Control; n=10): Application of static loading to ten incisors set over a metal structure with internal retention. Group II (Control; n=10): Application of static loading to ten incisors set over a metal structure with external retention. The remaining study specimens (n=20) were subjected to 120,000 masticatory and thermal cycles in a chewing simulator. Afterwards, static loading was applied until the point of fracture using an Instron machine. Group III (Study; n=10): Application of dynamic and static loading to ten incisors set over a metal structure with internal retention. Group IV (Study; n=10): Application of dynamic and static loading to ten incisors set over a metal structure with external retention. Data obtained for the four groups was analyzed and compared, determining the type of fracture (cohesive or adhesive) using a reflected light microscope., Results: Statistical analysis confirmed that there were significant differences in fracture resistance between the four groups. External retention was found to have more fracture resistance than the internal retention., Conclusions: Hybrid prostheses with titanium substructures and external retention obtained significantly better results than samples with internal retention., Key Words: Chewing simulator, thermocycler, fatigue, implant-supported hybrid prosthesis, acrylic teeth, fracture, metal structure design.