An analysis of the corrosion process of the Nova-T IUD.

OBJECTIVE: To measure the copper from Nova-T IUDs that have been used for up to 9 years. To examine the composition and extent of surface deposits on these used IUDs. DESIGN: Nova-T IUDs were randomly collected at normal replacement or removal. The copper, silver and calcium content was quantified by X-ray fluorescence; surface topography and analysis was by scanning electron microscopy and X-ray dispersive analysis. RESULTS: Copper loss slowly increased at an exponential rate over the study period but the copper was stabilized by the silver core and did not show increased fragmentation with extended use. No corrosion of the silver core was detected. Calcium- and sulfur-containing surface deposits built up on the copper but did not modify the rate of copper release. CONCLUSIONS: The mean rate of copper loss was 0.25 mumol/day during the first 40 months of use, which is not significantly different from that of similar IUDs without a silver core. The silver core of the copper coil on the Nova-T IUD prevented its fragmentation. Surface deposits containing calcium and sulfur that built up on the IUD did not affect the rate of copper loss.

The multisleeved copper T model TCu220C: effect of long-term use on corrosion and dissolution of copper.

Corrosion and dissolution of copper were studied in 136 multisleeved TCu220C models used for up to 158 months. Surface alterations were examined at low magnification. Topography and depth of copper corrosion were evaluated microscopically in cross-sections of the TCu220C devices. Amounts of residual copper were determined by X-ray fluorescence spectrometry. Sleeve and wire corrosion differ in two respects: edge corrosion is typical for tubular copper and the corrosion process is more pronounced in the upper part of multisleeved devices. Despite considerable individual variation, maximum corrosion depth in relation to duration of IUD use is topographically similar for copper sleeves and copper wire. Calcareous deposits reduce both the dissolution and the corrosion of copper but not the contraceptive effectiveness of the TCu220C. Up to 125 months, the loss of copper from deposit-bearing devices amounts on average to 8 micrograms/day as against 23 micrograms/day for TCu220C models without visible coating.

Consequences of intrauterine contraception in diabetic women.

A study has been performed covering the clinical consequences of copper intrauterine device insertion in 103 insulin-dependent women and in 119 nondiabetic control subjects. Furthermore, the progress of corrosion has been measured in 15 intrauterine devices removed from diabetic women, and the results were compared with data obtained from nondiabetic women. The clinical data did not reveal any differences in the total continuation rates or in the removal rates because of accidental pregnancy or pelvic inflammation between the diabetic and the nondiabetic women after 3 and 12 months. Also, the maximal depth of corrosion as well as the distribution and the biochemical constitution of the corrosion products deposited on the copper wires were found identical in the two groups studied.

PIP: The clinical consequences of copper IUD insertion in 103 insulin-dependent women and in 119 nondiabetic control subjects were studied. The progress of corrosion was also measured in 15 IUDs removed from diabetic women, and the results were compared with data obtained from nondiabetic women. The clinical data did not reveal any differences in the total continuation rates or in the removal rates because of accidental pregnancy or pelvic inflammation between the diabetic and nondiabetic women after 3 and 12 months. The maximal depth of corrosion as well as the distribution and biochemical constitution of the corrosion products deposited on the copper wires were identical in the 2 groups studied.

Corrosion of filamentous intra-uterine copper. The MLCu250 and the MLCu375.

Although the effective life span of an IUD provided with filamentous copper is, calculated on the basis of the rate of dissolution of copper, several years, corrosion may lead to breakage of the wire after a shorter period of use. When copper wire with a diameter of 0.20 to 0.25 mm is used, the proportion of IUDs with broken wires increases with time after three years of use. It was not known whether this disadvantage could be reduced or eliminated by the use of a thicker wire. In this study the corrosion behaviour was observed in MLCu250 and MLCu375 devices, which have copper wire with a diameter of 0.30 and 0.40 mm, respectively. The earliest breakage was observed after 8 months of use for 0.30 mm wire and after 9 months of use for 0.40 mm wire. In IUDs with 0.30 mm wire the proportion with broken wires increased after 3 years of use. Since examples of the MLCu375 with 0.40 mm wire used for more than 3 years were few, it was impossible to make definite conclusions in this respect. In general, the corrosion behaviour in copper diameter range of 0.3 to 0.4 mm is the same as indicated in previous studies for diameter range of 0.2 to 0.25.

Factors influencing the dissolution of copper in utero.

PIP: The wide variability of individual release rates of copper from IUDs suggests that other factors influence copper dissolution which may differ from person to person; these factors seem of 2 sorts: 1) physiological and 2) metal. Physiological factors suspected of affecting copper release, which are out of the hands of clinicians to alter, are: 1) composition of uterine secretions; 2) quantity of the secretions; and 3) calcification, or layering, of devices in situ. Metal factors, which the developer has some control over, include: 1) surface quality; 2) composition of copper; 3) the surface area; and 4) corrosion. To determine ideal metal conditions, comparative studies between copper devices need to be performed more rigorously; however, a few suggestions have come to light. Manufacturing defects in the metal, if kept free of foreign material, should not affect dissolution rate. The toxic elements of copper must be kept to 1-2 ppm; and it has been found that when alloyed with nontoxic metals, corrosion was influenced. When copper is alloyed with precious metals, the dissolution rate is reduced in proportion to the quantity of alloying element. Surface area is the most important factor affecting dissolution. A surface area of at least 200 mm sq. yields the best pregnancy rate (about 1/100 users). Definition of surface area is tricky: any copper wire lying against the plastic body is not calculated as surface area. 3 main factors influencing IUD performance are saturation of the solvent with copper; effective surface area; and performance of plastic carrier. IUD breakage increases after 3 years of use.^ieng

Copper in the uterus.

PIP: Copper-releasing IUDs seem to have a greater antifertility effect due to their continuous releasing of copper. This release results from an interaction between the copper and uterine secretions. Several agents in the uterine secretions, the amount of surface area of the copper, and the quantity of the solvent all influence the copper release rate. Microscopic photographs illustrate the progress of copper corrosion. The process of corrosion involves the replacement of copper atoms by other atoms from the uterine secretions on the corroded areas. Only a cross-sectional picture of the wire will indicate the amount of corrosion which has occurred. The corrosion occurs in variable locations, indicating that increasing the wire dimensions will not increase the lifetime of the devices. Studies with a copper IUD having a noncorrodable silver core--the Nova T--have shown this device to have significantly lower pregnancy rates than the Copper T 200 and a functional lifetime of up to 5 years.^ieng

Randomized comparison of clinical performance of two copper-releasing IUDs, Nova-T and Copper-T-200, in Denmark, Finland and Sweden.

A randomized study was conducted simultaneously in three countries to compare the clinical performance of two new IUDs, the Nova-T and Copper-T-200. Forty-four persons, midwives, general practitioners, residents and specialists in obstetrics and gynecology inserted 907 Nova-Ts and 936 Copper-Ts. The pregnancy rate of Nova-T (0.7 at one year) was significantly lower than that of Copper-T (2.2 at one year). No significant differences were observed in other termination rates. The continuation rates were 72.6 for Nova-T and 71.3 for Copper-T-200. The total experience was based on 18,035 woman months of use, with a lost to follow-up of less than 7 per cent for both IUDs.

Corrosion of copper in utero.

The influence of corrosion on the copper wire in the Copper T-200 intrauterine device (IUD) was studied in devices which had been in utero for 3 to 52 months. This was done mainly by examining cross-sections of the wires under a light microscope. Corrosion was normally localized to narrow areas and led to breakage and fragmentation of the copper wire. Neither deposits on the wire nor corrosion products prevented the dissolution of the copper. The progress of the corrosion over a given time was determined by comparing the depth of corrosion with the original dimension of the wire. The lifetime of the IUD was evaluated on the basis of the progress of corrosion, the calculated copper release, and the number of cases of wire breakage. It was found that the Copper T-200 could be left in place for up to 45 months.