Retention characteristics of individually milled bar systems with customized patrices: An in vitro comparison of electroplated and friction‐based retention concepts

PURPOSE: This in vitro study examined the initial and long-term retention behavior of individually milled bar (IMB) systems combined with customized patrices (CPs), contrasting electroplated patrices (EP), and friction pin patrices (FPP) concepts. Retention values were related to a previously reported laboratory reference threshold of 5 N. Given the exploratory nature of the design, the study aimed to describe material-dependent trends rather than to establish clinical sufficiency. MATERIALS AND METHODS: Seven IMB-CP combinations were fabricated-four with EP (gold, non-precious alloy, titanium, and zirconia) and three with FPP (non-precious alloy, titanium, and zirconia) (n = 5 per group). Each bar was mounted on two implants embedded in epoxy resin casts and subjected to 5000 insertion-removal cycles in artificial saliva (23°C) using a universal testing machine. Retention forces were continuously recorded, and surface alterations were assessed by profilometry, light microscopy, and environmental scanning electron microscopy. Material wear was determined gravimetrically. Data were analyzed after assessment of normality (Shapiro-Wilk); initial and final retention forces were compared within groups using paired t-tests or Wilcoxon signed-rank tests (α = 0.05). No inferential comparisons between materials or retention concepts were performed; differences between groups are reported descriptively. RESULTS: Initial retention ranged from 5.4 N (titanium-titanium FPP) to 21.7 N (non-precious EP), all exceeding the 5 N laboratory reference threshold. After cyclic loading, final retention ranged from 2.4 N (TF) to 18.5 N (NG). The change in retention (ΔF = F_final - F_initial) varied from -10.1 to +2.1 N across groups. Surface roughness decreased for most EP systems, whereas FPP systems showed greater wear and predictable retention loss. Material change ranged from 8 to 34 µg (IMB) and 36 to 180 µg (CP). CONCLUSIONS: Under the tested laboratory conditions, all IMB-CP systems showed initial retention forces above the 5 N reference threshold. After 5000 insertion-removal cycles, the titanium-titanium FPP combination exhibited the lowest retention and fell below this threshold, whereas the remaining systems maintained retention values above it. EP showed stable or slightly increased retention with minimal measured wear, whereas FPP showed greater, predictable wear-related retention loss. These exploratory observations demonstrate that material pairing plays an important role in retention behavior under in vitro conditions, whereas clinical performance, maintenance requirements, and long-term success should be evaluated in future clinical studies.