The Effect of Three-Dimensional Stabilization Thread Design on Biomechanical Fixation and Osseointegration in Type IV Bone

Abstract

Achieving the appropriate primary stability for immediate or early loading in areas with low-density bone, such as the posterior maxilla, is challenging. A three-dimensional (3D) stabilization implant design featuring a tapered body with continuous cutting flutes along the length of the external thread form, with a combination of curved and linear geometric surfaces on the thread's crest, has the capacity to enhance early biomechanical and osseointegration outcomes compared to implants with traditional buttressed thread profiles. Commercially available implants with a buttress thread design (TP), and an experimental implant that incorporated the 3D stabilization trimmed-thread design (TP 3DS) were used in this study. Six osteotomies were surgically created in the ilium of adult sheep (N = 14). Osteotomy sites were randomized to receive either the TP or TP 3DS implant to reduce site bias. Subjects were allowed to heal for either 3 or 12 weeks (N = 7 sheep/time point), after which samples were collected en bloc (including the implants and surrounding bone) and implants were either subjected to bench-top biomechanical testing (e.g., lateral loading), histological/histomorphometric analysis, or nanoindentation testing. Both implant designs yielded high insertion torque (ITV ≥ 30 N⋅cm) and implant stability quotient (ISQ ≥ 70) values, indicative of high primary stability. Qualitative histomorphological analysis revealed that the TP 3DS group exhibited a continuous bone-implant interface along the threaded region, in contrast to the TP group at the early, 3-week, healing time point. Furthermore, TP 3DS's cutting flutes along the entire length of the implant permitted the distribution of autologous bone chips within the healing chambers. Histological evaluation at 12 weeks revealed an increase in woven bone containing a greater presence of lacunae within the healing chambers in both groups, consistent with an intramembranous-like healing pattern and absence of bone dieback. The TP 3DS macrogeometry yielded a ~66% increase in average lateral load during pushout testing at baseline (T = 0 weeks, p = 0.036) and significantly higher bone-to-implant contact (BIC) values at 3 weeks post-implantation (p = 0.006), relative to the traditional TP implant. In a low-density (Type IV) bone model, the TP 3DS implant demonstrated improved performance compared to the conventional TP, as evidenced by an increase in baseline lateral loading capacity and increased BIC during the early stages of osseointegration. These findings indicate that the modified implant configuration of the TP 3DS facilitates more favorable biomechanical integration and may promote more rapid and stable bone anchorage under compromised bone quality conditions. Therefore, such improvements could have important clinical implications for the success and longevity of dental implants placed in regions with low bone density.

Keywords: implant stability quotient; insertion torque value; lateral loading; nanoindentation; osseointegration; primary stability.

Figure 1

(a) Representative pictographic overviews of the implant macrogeometries, with dashed red boxes highlighting the location of the cutting flutes; (b) representative thread profiles; scanning electron microscopy of the (c) TP and (d) TP 3DS implant surfaces. Authors’ own work, adapted with permission [26], copyright 2025 Elsevier Ltd.

Figure 2

Representative schematic of osteotomy and implant placement within the ovine ilium. TP implants are shown in yellow and TP 3DS implants in red. Image not to scale.

Figure 3

Representative histological section showing the (a) total implant perimeter (yellow spline) for measurement of BIC, and (b) total area of the implant threads (sections highlighted in yellow) for measurement of BAFO. Implant macrogeometry is shown in black and calcified tissue in red.

Figure 4

(a) Insertion torque value (ITV, Ncm) at T = 0 weeks, and (b) implant stability quotient (ISQ, measured on a unitless scale) at T = 0 weeks. p < 0.05 is statistically significant.

Figure 5

Lateral load (N) data compared between the TP and TP 3DS groups at the various time points of evaluation. Baseline corresponds to the T = 0-weeks. p < 0.05 is statistically significant.

Figure 6

Representative histological overviews of TP and TP 3DS implants at (a,b) 3 and (c,d) 12 weeks post-implantation. Implant macrogeometry is shown in black and calcified tissue in red.

Figure 7

Representative high-magnification histomicrographs of TP and TP 3DS implants at (a,b) 3 and (c,d) 12 weeks post-implantation. Implant macrogeometry is shown in black and calcified tissue in red. The white arrow represents microcracks in bone, cyan arrows depict bone chips present within the implant healing chambers, green arrows identify sites of bone remodeling, and blue arrows highlight sites of lamellar bone growth. Yellow arrows depict lacunae within the healing chambers.

Figure 8

(a) BIC and (b) BAFO at 3 and 12 weeks post-implantation. p < 0.05 is statistically significant.

Figure 9

(a) Young’s modulus and (b) hardness of newly formed bone within the healing chambers at 3 and 12 weeks in vivo. p < 0.05 is statistically significant.