X-ray evaluation at 5–6 years of Straumann implants (part 2)

Long term preservation of crestal bone height around osseointegrated implants is often used as a measure of primary success [5, 12, 22]. Prospective long-term studies exhibited survival and success rates largely exceeding 95% after 5 and 10 years of follow-up for the Straumann R © implant system [3, 5, 18, 22, 45, 57]. A mean crestal bone loss ≤1.5 mm during the first year and ≤ 0.2 mm per year thereafter is proposed as one of the major success criteria. If we apply these strict success criteria then the CBL in 5 years should not exceed 2.3 mm [1.5 + (0.2 × 4)]. In the current study, 8.5% of the implants exhibited “supra-boundary bone”. In addition to 84.5% of the implants showing bone loss within the physiological range (0–3 mm), giving an overall successful pool of implants up to 93%. This represents a high success rate considering the private practice setting and the absence of exclusion criteria in the initial enrolment of the patients. Patients with implants exhibiting a bone loss of 2–3 mm (7.8%) would require careful monitoring, with closer hygiene recalls and increased education in regard to patient awareness for dental hygiene and maintenance. Bone loss greater than 3 mm was observed in 7% of the included implants. At the 5-6 year control, they were still well integrated in the jaw bone and the subjects did not manifest any symptoms that previously identified them as unsuccessful [7]. Moreover, the status and prognosis of such implants have to be carefully interpreted because other factors, mainly clinical parameters such as bleeding on probing and pocket depths, were not available, in contrary to previous studies [5, 12, 31, 38, 39, 45–47, 51]. Considering such arguments, and although these implants were put by the study group in the unsuccessful implants category, one could argue the contrary. This group deserves careful monitoring, with closer hygiene recalls, more follow-up radiographs, and extended patient awareness to dental hygiene. For the Straumann R © implants, the distance from the implant shoulder to the first bone–implant contact was called DIB (distance implant-bone) and was used in previous studies [16, 21]. These studies followed the changes in periimplant bone levels over time by taking measurement between two time points. A baseline and a postoperative radiograph were usually taken to identify initial and final bone levels, and therefore to calculate the difference: Δ DIB. In the present study, an original method was used to calculate the bone change: the interface of the smoothroughened surface (identified as the R interface) was considered as the baseline level. It was assumed to be the level up to which bone loss was considered as physiological, i.e. not affected by external factors. Bone loss occurring further from this point, in an apical implant direction, was thus identified as crestal bone loss (CBL). Bone localized coronally to this interface was defined as “supra-boundary bone”. When the bone level was stabilized at the interface, it was then considered that no bone change occurred (CBL and “supra-boundary bone” were equal to 0 mm). From that point, it was interesting to identify factors that might enhance bone loss or favor bone maintenance when single-staged Straumann R © implants with treated TPS/SLA surfaces were used. It could be argued that the mean CBL was even lower than the 1.2 mm obtained in this study, as this value was compensated with implants that had what was called “supra-boundary bone”. The present study did not quantify this “supra-boundary bone”, as was described in a recently published study [51]. A paralleling radiographical technique may sometimes be difficult to perform because of the implant inclination and patient anatomy. For example, in the case of an extremely resorbed mandible, the intra-oral placement of the film was impossible because of the interference of the mouth floor [33]. In the maxilla, where the palate is the most inclined, it was difficult to position the film without bending [34]. This explained the large number of un-interpretable radiographs in these two regions. When observing the comparative tables for the statistically significant results, namely surface texture, smoking status, anterior/posterior location and VBL, it is worth noticing