One Millimetre Apart and Still Standing: A 10-Year Case Challenges the 3 mm Interimplant Rule
A case report with 10-year follow-up shows two adjacent implants placed just 1 mm apart maintained interproximal crestal bone 1.40 mm above the implant shoulder, challenging the longstanding 3 mm interimplant distance guideline.
Source Paper
The impact of a 1 mm interimplant distance on the interproximal crestal bone height: a case report with a 10-year follow-up and literature review
The 3 mm interimplant distance rule is one of those clinical commandments that everyone follows and almost nobody has stress-tested at the extremes. We know the number. We teach the number. We plan our surgeries around it with the solemnity of people who believe that 2.9 mm might unleash biological catastrophe. Morales Schwarz and colleagues, in “The impact of a 1 mm interimplant distance on the interproximal crestal bone height,” published in the International Journal of Implant Dentistry, have presented a case that sat at one-third of that sacred distance for a full decade and, against every reasonable expectation, kept its bone.
The clinical scenario was familiar enough: a 57-year-old patient with two hopeless maxillary premolars and 12 mm of mesio-distal space to work with. Standard-diameter implants with the recommended 3 mm interimplant distance (IID) would have required 13.5 mm. The mathematics did not cooperate, so the team placed two narrow Ø 3.5 mm titanium grade 23 implants (Top DM, Bioner) into the extraction sockets with immediate provisionalization, accepting a 1 mm IID.
The Data Anchor
The implants featured a 24-degree internal conical connection, 0.25 mm platform switching, and concave prosthetic abutments with a 0.3 mm mismatch. At the 10-year recall, periapical radiography and CBCT confirmed the interimplant distance at 1.02 mm (CBCT: 1.04 mm), with crestal bone maintained 1.40 mm coronal to the implant-abutment connection. Bone completely filled the 2.04 mm space between the concave abutments.
PES scores were 12/14 and 13/14; WES was a perfect 10/10 for both crowns. The interproximal papilla filled the embrasure entirely. All this in a patient smoking more than 10 cigarettes daily, which makes the bone stability rather more impressive than the numbers alone suggest.
The accompanying literature review searched PubMed for studies specifically examining a 1 mm IID; only two preclinical studies qualified from the search.
A rabbit tibial crest study (Hatley et al., 2001; n = 15, external hex implants) found superior vertical bone growth at 1 mm compared to 1.5 and 3 mm IIDs. A loaded dog mandible study (Novaes et al., 2006; n = 7 per group, conical connection with platform switching) found no difference in crestal bone resorption or vertical bone loss between 1, 2, and 3 mm groups. Both reported that the narrowest distance was, if anything, the most favourable for bone response.
Key Findings
- Interimplant crestal bone was maintained 1.40 mm above the implant shoulder at 10 years, with complete bony fill between the concave abutments, despite an IID of just 1 mm
- Only two preclinical studies in the entire literature have examined a 1 mm IID; both found no detrimental effect on interproximal bone compared to the recommended 3 mm
- The 3 mm guideline was derived from external hex implants without platform switching (Tarnow et al., 2000); its applicability to modern conical-connection, platform-switched systems remains unvalidated
- This is a single case report with competing interests disclosed (lead authors consult for the implant manufacturer), and the patient was lost to follow-up between years 3 and 9; soft tissue recession observed at year 9 reversed after improved hygiene
The authors speculate that the internal conical connection, platform switching, subcrestal placement, and concave abutment design collectively created conditions that prevented the inflammatory bone loss Tarnow described with older implant designs. It is a plausible hypothesis, but one case does not rewrite a guideline.
💡 The Clinical Bottom Line
The 3 mm interimplant distance rule should remain the planning standard until stronger evidence arrives; the authors themselves say as much. But this case, supported by the only two animal studies that have examined the question, suggests that modern implant designs with sealed conical connections and platform switching may tolerate considerably tighter spacing than we have been taught to permit. For the clinician staring at 12 mm of bone and doing the arithmetic, it is worth knowing that the literature’s entire evidence base against a 1 mm IID consists of precisely zero studies showing harm.
Dr Samuel Rosehill is a general dentist with a prosthodontic focus, practising at Ethical Dental in Coffs Harbour, NSW. He holds a BDSc (Hons) from the University of Queensland, an MBA, an MMktg, and an MClinDent in Fixed & Removable Prosthodontics (Distinction) from King’s College London.
Reference: Morales Schwarz D, Szmukler-Moncler S, Morales Melendez H, Beuer F. The impact of a 1 mm interimplant distance on the interproximal crestal bone height: a case report with a 10-year follow-up and literature review. International Journal of Implant Dentistry. 2025;11:8. DOI: 10.1186/s40729-025-00589-8
Clinical Relevance
The 3 mm interimplant distance guideline was established with external hex implants two decades ago. This 10-year case and supporting preclinical evidence suggest that modern conical-connection, platform-switched implants may tolerate significantly closer spacing without interproximal bone loss.
Disclosure: The author has no financial conflicts of interest related to the products or topics discussed in this review. This is an independent summary prepared for educational purposes.
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