 Astra Tech
BioManagement Complex
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 MicroThread
MicroThread™ is the minute thread design on the neck of the Astra Tech implants, introduced as early as 1991. Scientific articles present the ability of MicroThread to ensure positive biomechanical bone stimulation and to maintain marginal bone levels in the long term. Summarized on the following pages, you will find articles about the continuous follow-up of the MicroThread.
 Effect of microthread on the maintenance of marginal bone level: a 3-year prospective study
Purpose: Maintenance of the peri-implant marginal bone is not only seen as essential for functional support of the implant but today it is identified as the key to the maintenance of a healthy and esthetic peri-implant mucosa, which is central to treatment success. Previous studies have identified that bone initially undergoes resorption settling typical 1.5 mm below the implant shoulder at the first thread. It has been proposed that such bone loss can be prevented by the provision of retention elements at the top of the implant in the form a rough microtextured surface (RMS) and/or the provision of MicroThread™ (MT). Within the Astra Tech system implants have been presented with both RMS and a combination of RMS with MT. This might explain the variable data on marginal bone levels, but to date no direct comparison has been made. As such this study was established to compare two RMS implants, one with and one without MT, to determine the impact on the long-term marginal bone levels.
Materials and Methods: Seventeen patients requiring implant therapy for replacement of at least two missing adjacent teeth were enrolled in the study. Subjects had to complete a periodontal program and demonstrate good oral hygiene maintenance. Implants were selected to be RMS (Astra Tech, 4.0 mm 0, TiOblast") or RMS/MT (Astra Tech, 4.5 nun 0, ST) and both types were placed in a randomized order in all patients. A two-stage surgical protocol was utilized and prostheses were delivered 3 months after exposure.
Patients were reviewed every 3 months and an assessment was made of pain, implant stability, gin-gival inflammation and superstructure complications annually along with evaluation of intra-oral radio-graphs taken in a Rinn device and with a standard-ized technique. Images were digitized and a measure was made on the mesial and distal aspects from a fixed reference point at the base of the coronal bevel to the first point of bone contact. Any bone above the reference point was given a value of zero. Results were subject to statistical analysis using Wilcoxon's signedrank test at the p < 0.01 level.
Results: A total of 34 implants were inserted, of which 22 were in the maxilla and 12 were in the man-dible. All implants osseointegrated and all prostheses were successfully delivered without complications or symptoms up to the 3-year recall. The mean marginal bone loss measured 0.14 mm, 0.21 mm and 0.24 mm for RMS/MT implants at the 1-, 2- and 3-year recalls respectively. These values were consistently lower than for RMS-only implants where bone loss mea-sured 0.28 mm, 0.48 mm and 0.51 mm respectively. Differences were highly statistically significant at all time frames, (P = 0.001 - 0.002). In addition there was a notable trend to indicate the rate of bone loss was lower for those implants which benefited from a MicroThread'", particularly from baseline to the end of the first year, (P = 0.002). The amount of bone loss was significantly higher for both implants when comparing the first year to those subsequent.
Discussion and Conclusion: Many factors have been identified as possible contributors to marginal bone loss. These include the presence of a machined surface without retention elements, the establishment of a biologic width, the disruption of the soft tissue interface by utilizing healing abutments, implant geometry the presence or absence of periodontal disease. In the current study both implants presented with an identical RMS to the top of the implant and both utilized an internal 11° conical interface which should in theory dictate identical biologic width requirements. In addition the use of healing abutments and a two-stage approach was identical for both implant types ruling out these factors as confounding variables. While it is recognized that the implants varied in diameter by some 0.5 mm, this has been shown in a previous study not to have influenced bone loss. As such it is believed that this study allowed a true interpretation of the influence of the MicroThread on the Astra Tech ST implant, although it is accepted that patients will have had different periodontal susceptibilities.
Although, early biomechanical resistance to initial loading within the first year could not be verified, this study clearly showed that implants that benefited from MicroThread demonstrated a significantly lower marginal bone loss over a 3-year period compared to implants without MicroThread.
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