Biomechanical Evaluation of Orthodontic Miniscrews: How Insertion Angle and Number of Insertions Impact Pull-Out Strength

Wilda Kemala Maulani*  -  Universitas Padjadjaran, Indonesia
Elih Sayuti  -  Universitas Padjadjaran, Indonesia
Endah Mardiati  -  Universitas Padjadjaran, Indonesia

(*) Corresponding Author
DOI: 10.30659/odj.13.2.162-171

Background: This study aimed to analyze the effects of insertion angle and number of insertions on miniscrew pull-out strength in polyurethane bone blocks.

Method: In this experimental study, 30 miniscrews (Mico One; 2 mm diameter and 10 mm length) were inserted into Sawbones polyurethane blocks consisting of a 2 mm cortical layer (40 pcf) and an 18 mm trabecular layer (20 pcf). Samples were divided into six groups based on insertion angle (45°, 70°, and 90°) and number of insertions (single vs. repeated). Pull-out strength was measured using a Universal Testing Machine (UTM). Data were analyzed using two-way ANOVA followed by Tukey's HSD post hoc test, with significance set at p<0,05.

Result: In the single-insertion group, the insertion angle significantly affected pull-out strength (p<0,05). The 70° angle yielded the highest mean pull-out strength (339,98±20,76N), which was significantly higher than that of the 90° angle (299,93±20,45N; p<0,05). In the repeated-insertion group, the insertion angle did not significantly affect pull-out strength (p>0,05). Although the repeated-insertion group showed a lower mean pull-out strength (307,88±24,78  N) than the single-insertion group (318,34±25,21N), the difference was not significant (p>0,05).

Conclusion: Insertion angle significantly influences pull-out strength in single-insertion miniscrews, with 70° providing the highest strength. The number of insertions (single vs. repeated) does not significantly affect pull-out strength. These findings have implications for clinical anchorage strategies and experimental protocols using polyurethane bone analogs.

Keywords: Biomechanical phenomena, bone screw, materials testing, polyurethanes

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