Follow-up examination of patients with mini-implants for the stabilization of existing removable partial dentures

Introduction: The aim of this study was to evaluate the clinical performance of mini-implants (MI), which were used for the stabilization of double crown retained removable partial dentures (RPDs), after a middle-term period of service in a dental practice. Additionally, implant stability and patient satisfaction with the dentures were evaluated. Material and Methods: Patients who had received 10 to 13 mm long MI with diameters of 1.8, 2.1, and 2.4 mm and ball attachments for supplementary support of their existing double crown retained RPDs at least 3 years ago were included in this study. After patient chart and medical history analysis as well as the completion of an 8-item questionnaire on satisfaction with the RPD (Likert scale 1 to 5) by the participants, an experienced dentist independently examined the periodontal/peri-implant conditions; this involved measurement of implant stability by using the Periotest and the Osstell device. In addition to descriptive statistics, survival analyses based on the Kaplan-Meier and Cox regression analyses were used to estimate possible risk factors for implant loss. Results: Out of 70 reachable patients, 66 study jaws in 57 patients were examined. The duration between the time of implant placement and the follow-up examination ranged between 3 and 9 years for the examined 77 MI in 25 upper jaws and 113 MI in 41 lower jaws. The MI in 20 jaws with good bone quality (insertion torque ≥ 35 Ncm) were loaded immediately using matrices (housing with O-rings), while the other RPDs were initially soft-relined for 3–4 months. The 5-year-survival rates of the MI in the maxilla and mandible were 97.4 % (3 failures) and 86.9 % (13 failures, one fracture), while the tooth survival rates were 88 % and 88.9 %, respectively. The Cox regression analyses revealed no statistically significant effect of possible risk factors on implant failure (tooth status, smoking habits, diabetes mellitus, loading modus). In 18 of the study participants, a total of 40 MI were placed subsequent to implant or tooth loss. The aftercare of the RPDs comprised of 8 O-ring replacements and 26 denture base relinings. The complications included denture base (n = 17), secondary crown veneering (n = 11) and artificial denture teeth (n = 2) fractures. The mean Periotest values were 5.5 and 6.7 (P = 0.078), while the mean Osstell values were 38 and 33 (P 0.0001), in the maxilla and mandible, respectively. The majority of participants were very satisfied with their RPD (80 % in the maxilla, 70 % in the mandible) and nobody was dissatisfied. Discussion: The lower MI survival rate in the mandible compared with the maxilla comes as a surprise and is contrary to previous studies performed on edentulous jaws. The complications were manageable, despite implant losses and denture fractures. The stability values of MI were lower than those of standard-diameter implants. Conclusion: Strategic MI under double crown retained RPDs are a recommendable therapeutic option in the dental practice. Prospective randomized clinical studies are required to investigate this therapeutic alternative. Keywords: double crown, mini-implant, removable partial denture, satisfaction, stability, strategic, survival