Primary Stability and Implant Macrogeometry

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This has nothing to do with Pythagoras. Primary stability is one of the key factors for success in dental implantology. A recent article in the International Journal of Implant Dentistry examined in detail how the macrogeometric features of implants influence this initial stability.

But what is macrogeometry?

It is the macroscopic shapes that characterise the implant — something entirely different from the microscopic surface features of the same fixture.

According to the review by Heimes et al. (2023), implant macrogeometry includes:

1. Implant body shape (cylindrical vs conical)
2. Implant length
3. Implant diameter
4. Thread design

Body shape

The implant body shape varies widely, and the market is crowded with mixed forms. See the figure below.

Given this, the classic split into cylindrical and conical implants is not universally applicable, though it remains a useful first-order distinction.

Conical implants show superior primary stability compared with cylindrical ones, because they:

1. Distribute lateral forces better onto the cortical bone
2. Create greater, more progressive bone compression during insertion
3. Are especially suited to immediate loading protocols

This is not theory. Nascimento et al. (2024, Oral and Maxillofacial Surgery) measured deformation and torque during insertion in D2-density synthetic bone: conical implants require a higher insertion torque than cylindrical ones and — a detail few report — distribute stress better, while some machined cylindrical implants actually cracked the bone during seating. Hsueh et al. (2025, Journal of Dental Sciences) confirmed the gap with hard numbers: under matched conditions, a conical bone-level implant generated around 29 Ncm against the 8-9 Ncm of a standard cylinder. Body shape alone can triple primary stability. That is why, in protocols that engage the apex early, conicality is not a flourish — it is a prerequisite. The same logic runs through implant shape innovation.

Implant length

The relationship between length and primary stability is linear up to 12 mm. Beyond that, added length brings no meaningful improvement in initial stability.

Implant diameter

A larger diameter:

1. Increases the bone-implant contact area
2. Improves load distribution
3. Matters most in posterior regions with high occlusal loads
4. Is not the devil — no one has ever shown that large diameters cause more problems

The systematic review by Kreve et al. (2024, Oral and Maxillofacial Surgery) sets the record straight: among all macroscopic features, it is the balance between compressive and tensile stress that decides osseointegration, not a single number. Diameter counts because it enlarges the contact area, but it must be read together with the bone quality of the site, never in isolation.

Thread design

Threads with the following features favour primary stability:

1. Depth: 0.34-0.5 mm
2. Width: 0.18-0.3 mm
3. Pitch: above 0.8 mm
4. Profile: V-shaped and square threads reduce stress on the bone

Here the clinical evidence is sturdier than people assume. Barbosa et al. (2024, Brazilian Dental Journal) compared two thread configurations on the same patient in a split-mouth RCT: hybrid threads — perforating plus condensing — produced a markedly higher ISQ already at insertion (63 vs 41) and held it through 90 days. The trapezoidal profile, in Nascimento’s (2024) tests, demands more torque than the triangular one: a sign it bites the bone harder. The thread is not a cosmetic detail of the design. It is where the implant decides how much bone to compress.

A caveat on torque

The more aggressive the macrogeometry, the higher the torque it generates. And here honesty is due: high torque is not free. Dodo et al. (2025, Clinical Implant Dentistry and Related Research) showed that high-torque insertions damage the thread crests and release titanium particles right at the crestal cortical bone — a possible cofactor in marginal bone loss. This is not an argument against conical bodies or deep threads. It is an argument against the idea that more Ncm is always better. Macrogeometry exists to win stability without strangling the bone, not to win a tightening contest. Which is also why, before falling in love with a shape, it is worth remembering why smooth implants stopped convincing anyone: it is the geometry, not the smooth surface, that does the work — the same theme behind the conical vs flat connection debate.

Clinical recommendations

The authors suggest choosing implant macrogeometry according to:

1. Bone quality at the receiving site
   • Dense bone: cylindrical or standard conical implants
   • Poor-quality bone: conical implants with aggressive threads
2. Loading protocol
   • Immediate loading: prefer conical implants with double threads
3. Anatomical site
   • Aesthetic zone: conical implants for lower perforation risk
   • Posterior regions: consider larger diameters

Does a recent implant made in Italy, fitted with exactly these features, come to mind?

Conclusions

The choice of implant macrogeometry should not be random but based on a careful assessment of local and systemic patient factors. As the review highlights, there is no single “universal” optimal design: selection must be personalised for every clinical situation.

Frequently Asked Questions (FAQ)

Are conical implants always superior to cylindrical ones?

Conical implants show superior primary stability because they distribute lateral forces better, create progressive bone compression and suit immediate loading. But the choice is not absolute: cylindrical implants remain valid in good-quality bone, and the decision must consider the specific bone quality of the site.

What is the optimal implant length for stability?

The relationship between length and stability is linear up to 12 mm. Beyond that, added length brings no meaningful gain in initial stability, so standard 10-12 mm lengths are generally enough for most cases.

Does a larger implant diameter always guarantee better results?

A larger diameter increases the bone-implant contact area and improves load distribution, which matters in posterior regions with high occlusal loads. Still, there is no evidence that large diameters cause more problems: the choice must follow available anatomy and expected occlusal loads.

Which thread features favour primary stability?

Optimal threads have depth 0.34-0.5 mm, width 0.18-0.3 mm, pitch above 0.8 mm, and a V or square profile that reduces bone stress. Hybrid configurations — perforating plus condensing threads — push primary stability even higher.

Should I always pick conical implants with aggressive threads?

The choice must be personalised. In dense D1-D2 bone, standard conical implants work well. In poor-quality bone, more aggressive threads and a conical body are preferable. The bone quality of the receiving site should guide macrogeometry selection.

References

1. Heimes D, Becker P, Pabst A, Smeets R, Kraus A, Hartmann A, et al. How does dental implant macrogeometry affect primary implant stability? A narrative review. Int J Implant Dent. 2023;9(1):20. DOI: 10.1186/s40729-023-00485-z · PMID: 37405709
2. Kreve S, Ferreira I, da Costa Valente ML, Dos Reis AC. Relationship between dental implant macro-design and osseointegration: a systematic review. Oral Maxillofac Surg. 2024;28(1):1-14. DOI: 10.1007/s10006-022-01116-4 · PMID: 36171302
3. Nascimento LRXC, Torelly GM, Elias CN. Measurement of bone deformation and insertion torque during dental implant installation. Oral Maxillofac Surg. 2024;29(1):19. DOI: 10.1007/s10006-024-01294-3 · PMID: 39661169
4. Barbosa PP, Oliveira VXR, Goulart JV, Margonar R, Moura MB, Oliveira GJPL. Effect of different thread configurations on hydrophilic implant stability. A split-mouth RCT. Braz Dent J. 2024;35:e245632. DOI: 10.1590/0103-6440202405632 · PMID: 38537016
5. Hsueh PY, Yamaguchi Y, Yajima Y. Effect of insertion load on insertion torque value. J Dent Sci. 2025;20(3):1861-1868. DOI: 10.1016/j.jds.2025.03.029 · PMID: 40654426
6. Dodo C, Senna PM, Del Bel Cury AA, Meirelles L. Impact of high insertion torque on implant surface integrity. Clin Implant Dent Relat Res. 2025;27(2):e70030. DOI: 10.1111/cid.70030 · PMID: 40200410