Article

Feature Article
May 25, 2021 // 14 min read
The Use of Narrow Diameter Implants: Definition, Indications and Limitations
Bilal Al-Nawas
Eik Schiegnitz
DOI: 10.3290/iti.fi.45626
Abstract

Atrophy of the alveolar crest with reduced bone width and height is a challenging limitation for dental implant placement. In these cases, additional surgical procedures could be necessary to augment the insufficient bone volume. However, these augmentation procedures are cost- and time-intensive and could lead to morbidity and postoperative complications. In addition, in medically compromised patients augmentation procedures may carry a higher risk of complications. Therefore, the focus of clinical and scientific research is increasingly on alternative concepts such as narrow diameter implants (NDI). At the 6th ITI Consensus Conference, NDI were defined as implants with a diameter ≤ 3.5 mm. This general classification does not give full consideration to the different clinical indications for NDI. Therefore, NDI were divided into the following three categories:

  • Category 1: Implants with a diameter of < 2.5 mm (“mini-implants”)
  • Category 2: Implants with a diameter of 2.5 mm to 3.3 mm
  • Category 3: Implants with a diameter of 3.3 mm to 3.5 mm

Promising survival rates have been published for all 3 groups. However, long-term evaluation of clinical success rates is rare. NDI will not be replacing standard-diameter implants any time soon due to their challenging handling. New indications for NDI like the highly atrophic edentulous jaw or the small tooth gap are opening up. In addition, they offer dental implant treatment for medically compromised patients. Therefore, NDI are a promising extension of implant treatment options, but they will not turn complex implant cases into easy cases.

“History” of implant dimensions

Implant dimensions developed empirically and also had a certain evolution. At early stages of implant dentistry the idea was for a large implant that would support and transfer the high forces during the chewing procedure. Some groups tried the opposite concept, especially in the lower jaw, due to the narrow ridge, and worked with small needle implants made from tantalum (“Pruin’s Needle Implants) (Pruin 1974). Later one-piece mini-implants with the screw design evolved out of these concepts. With the wide availability and acceptance of two-piece implants, a certain diameter was technically necessary to allow the screw-connection between the implant and abutment (Schroeder et al. 1976; Branemark et al. 1969). Most of these implants were used in the edentulous lower jaw, and single tooth restorations were not in the focus of early implant dentistry (Branemark et al. 1977; Ledermann 1979). Based on this biological focus a certain implant diameter and “osseointegration surface” were deemed to be necessary, especially in the molar area with high chewing forces. More recently animal studies and also some clinical data have shown that, from a biological point of view, implants could be much smaller (shorter and thinner) than we thought in the early days of implant dentistry. This shifted both the research focus as well as manufacturers’ efforts into the development of diameter-reduced implants. With this paradigm change, the mechanical properties of the implant neck and the abutment connection have turned into the focus of interest.