Annual bone loss and success rates of dental implants based on radiographic measurements

Abstract

Objectives: Bone loss around dental implants is generally measured by monitoring changes in marginal bone level using radiographs. After the first year of implantation, an implant should have <0.2 mm annual loss of marginal bone level to satisfy the criteria of success. However, the process of measuring marginal bone level on radiographs has a precision of 0.2 mm (or more) owing to variations in exposure geometry, exposure time and observer perception. Therefore, the value of the annual loss may vary considerably, especially when short intervals are considered. This study investigates how the success rate of dental implants depends on the way annual bone loss is calculated.

Methods: Panoramic radiographs of 82 implant patients with an average follow-up of 10.4 years were analysed. Marginal bone levels near the implants were indicated by one observer. The annual loss of marginal bone level was determined according to four different calculation methods.

Results: The methods yielded success rates of 9%, 45%, 81% and 89%.

Conclusions: The success rate of dental implants measured on radiographs greatly depends on the details of the calculation method. Without rigorous standardization, annual bone loss and implant success rate are not well defined.

Keywords: criteria; marginal distance; noise; radiographs; success rate.

Figure 1

Marginal bone levels, top of implant neck and apex of implant body were indicated. The depicted points are obtained by averaging over four trials.

Figure 2

Two implants with body of 12-mm length and neck of 2.8 mm. Marginal bone levels are projected on the central axis of the implant body. The distance of the projected point to the top of the implant body is calculated in millimetres using the length of the implant body. Marginal distances from right to left: 1.1, 1.4, 2.4 and 3.2 mm.

Figure 3

Follow-up plots of marginal distance (mm) vs years after operation. Both distal and mesial sides are plotted. The plots running out of the scale correspond with two failing implants of the same patient. Negative marginal distances correspond with deeply placed implants (bone touching the implant neck).

Figure 4

Changes in marginal distance (mm) vs year after implantation. The first measurement of marginal distance is used as a baseline. Mesial and distal changes are calculated, but only the highest value is plotted. Method 1 pertains to the implants meeting the strictest criteria. Method 2 pertains to the implants meeting the relaxed criteria. The region of bone loss allowed by Methods 2 and 3 is shaded grey.

Figure 5

Changes in marginal distance (mm) vs year after implantation. Example of a successful implant according to Methods 3 and 4 but not according to Methods 1 and 2. Owing to one single radiograph, made 0.7 years after implantation, the marginal distance rises 3.5 mm and then falls 3.9 mm during the next year. The region of bone loss allowed by Methods 2 and 3 is shaded grey.