Long-term behaviour of implant borne overdentures in the lower jaw retained by rigid conical crown attachments

Purpose: The aim of this retrospective study is to evaluate the long term implant survival at 5 years, periimplantary conditions and prosthetic maintenance requirements for implant supported mandibular removable dentures retained on only 2 Ankylos® implants placed interforaminally in the mandible and using only conical double crown attachments. Materials and methods: Using the database at the Faculty of Dentistry, University of Frankfurt a selection process was performed to choose patients receiving only 2 Ankylos® implants placed interforaminally in the mandible and using only conical double crown attachments. Implant survival, periimplant condition (periodontal bleeding, plaque index and probing depth), bone loss (from panoramic radiographs) and mobility (using Periotest®) were monitored annually following implant loading. In addition a detailed prosthetic maintenance list was created for each patient based on their yearly checkups and emergency appointments. 37 patients with edentulous mandibles (34 with complete dentures in the upper jaw and 3 with tissue-tooth borne coverdentures) received 2 interforaminal Ankylos® implants (67 in the canine region, 7 in 2nd incisor region). Results: Mean Periotest® values at 5 years (-1.97 ±2.24) were lower than at loading (-1.47 ±2.33). A drop was seen in the Periotest® readings after the first year of loading. The decrease in mean Periotest® values between PTV5 and PTV 1 were not statistically significant (Tukey-Kramer test: p>0.05) 14 patients (37.8%) displayed no resorption at all with an average of 0.801 mm mesially and 0.807mm distally after 5 years. The most increase in bone loss was seen after the first year of loading. There was a gradual increase in bone resorption after the first year of loading. The differences between both distal and mesial bone resorption level at five years and at one year after loading are not significant (Tukey-Kramer test: p0.05 respectively). Mean probing depth values were higher after 5 years (2.61 ±0.92 mm) in comparison to the values at loading (2.15 ±0.75 mm). The difference between average values at year 5 and year 1 was statistically significant (Tukey-Kramer test: p0,05). 14Patienten (37,8%) zeigten nach 5 Jahren überhaupt keinen relevanten Knochenabbau mit Durchschnittswerten von 0,801mm mesial und 0,807mm distal.Der größte Anstieg der Knochenabbauwerte war im ersten Jahr nach Eingliederung. Danach war der Anstieg gleichmäßig. Knochenabbauniveaus mesial und distal nach 5 Jahren bzw. einem Jahr nach Eingliederung unterschieden sich nicht signifikant (Tukey-Kramer Test: p>0,05). Plaque- und Blutungsindizes waren niedrig mit durchschnittlichen Werten von 0,97 ± 0,86 bzw. 0,59 ± 0,77 nach einer Belastungszeit von 5 Jahren. Plaquewerte waren ab dem 1. bis 5. Jahr nach Eingliederung signifikant erhöht, Blutungsindizes hingegen nicht (Tukey-Kramer Test: p0,05). Durchschnittliche Taschentiefenwerte nach 5 Jahren (2,61 ± 0,92 mm) waren höher als beim Einsetzen (2,15 ± 0,75 mm). Die Differenz dieser Werte bei 5 Jahren und 1 Jahr war signifikant (Tukey-Kramer Test: p