Frictional wear of stud implant overdenture abutments after 2 years of in vitro simulated function.

Progressive wear of the components of an implant-supported overdenture can lead to loss of denture retention, which affects masticatory function and the patient's quality of life. The primary objective of this in vitro study was to investigate frictional wear in a type of commonly used abutment and thereby estimate the general clinical lifespan of a typical stud abutment and establish a protocol for replacement. Therefore, simulated overdenture insertions and removals equivalent to 2 years of overdenture use were performed to evaluate surface changes in the metal stud abutment component. A digital caliper, scanning electron micrographs taken at ×500 magnification, and profilometer data were used to determine the wear rate and surface roughness. A universal testing machine was used to measure retention load force with 4 clear male nylon inserts (5.0-lb retention) during 2160 insertion and removal cycles. The results showed that with a 6-month replacement program for clear male nylon inserts, the frictional wear on the titanium nitride coating of abutments placed at a 0° position resulted in a decrease of up to 50% in removal forces of the inserts after a simulated 2 years of wear. The combination of wear of the titanium nitride coating and the decrease in retention load values suggests that stud abutments should be replaced after 2 years of use for optimal retention.

Retention Load Values of Telescopic Crowns Made of Y-TZP and CoCr with Y-TZP Secondary Crowns: Impact of Different Taper Angles.

This study aimed to examine and compare the retention load values (RL) of different telescopic crown assemblies (Y-TZP and CoCr primary crowns with electroformed and Y-TZP secondary crowns each) with three different taper angles (0°, 1° and 2°). Thirty Y-TZP primary crowns with electroformed gold copings (Z/G group) and Y-TZP secondary crowns (Z/Z group) and 30 CoCr primary crowns with electroformed gold copings (C/G group) and Y-TZP secondary crowns (C/Z group), each with taper angles of 0°, 1° and 2°, were fabricated, respectively. With the exception of the electroformed gold copings, all specimens were Computer-Aided-Design/Computer-Aided-Manufacturing (CAD/CAM)-milled, then sintered and afterwards manually adapted. In order to stabilize the gold copings, they were fixed in a tertiary structure. The secondary crowns were constructed with a hook, which ensured self-alignment with an upper chain. Afterwards, 20 pull-off test cycles were performed in a universal testing machine under artificial saliva and after weighing the secondary crowns with a 5 kg object for 20 s. Data were analyzed by one-way and two-way Analysis of Variance (ANOVA). C/Z with 1° showed higher (p = 0.009) RL than 0° and 2° tapers. C/G at 1° also showed higher (p = 0.001) RL than at tapers of 0° and 2°. Z/G and C/G at 0° showed lower RL than Z/Z and C/Z (p < 0.001). Primary crowns had no impact on the 0° group. Z/G showed lower RL as compared to C/Z within the 1° group (p = 0.007) and Z/Z in the 2° group (p = 0.006). The primary crown material had no influence on RL. Electroformed copings showed lower RL. Further investigations for 1° as well as for the long-term performance after thermomechanical aging are necessary.

Suitability of Secondary PEEK Telescopic Crowns on Zirconia Primary Crowns: The Influence of Fabrication Method and Taper.

This study investigates the retention load (RL) between ZrO2 primary crowns and secondary polyetheretherketone (PEEK) crowns made by different fabrication methods with three different tapers. Standardized primary ZrO2 crowns were fabricated with three different tapers: 0°, 1°, and 2° (n = 10/group). Ten secondary crowns were fabricated (i) milled from breCam BioHPP blanks (PM); (ii) pressed from industrially fabricated PEEK pellets (PP) (BioHPP Pellet); or (iii) pressed from granular PEEK (PG) (BioHPP Granulat). One calibrated operator adjusted all crowns. In total, the RL of 90 secondary crowns were measured in pull-off tests at 50 mm/min, and each specimen was tested 20 times. Two- and one-way ANOVAs followed by a Scheffé's post-hoc test were used for data analysis (p < 0.05). Within crowns with a 0° taper, the PP group showed significantly higher retention load values compared with the other groups. Among the 1° taper, the PM group presented significantly lower retention loads than the PP group. However, the pressing type had no impact on the results. Within the 2° taper, the fabrication method had no influence on the RL. Within the PM group, the 2° taper showed significantly higher retention load compared with the 1° taper. The taper with 0° was in the same range value as the 1° and 2° tapers. No impact of the taper on the retention value was observed between the PP groups. Within the PG groups, the 0° taper presented significantly lower RL than the 1° taper, whereas the 2° taper showed no differences. The fabrication method of the secondary PEEK crowns and taper angles showed no consistent effect within all tested groups.