###### Abstract  
Little is reported about the prosthetic afterecare of implant-supported mandibular overdentures regarding the number of implants placed. The purpose of this study was to evaluate the prosthetic afterecare among edentulous patients restored with two vs. four mandibular implant-retained overdentures (MISOD). Forty-six consecutive edentulous patients treated by a new MISOD were retrospectively studied. Twenty-five patients had two-ball attachment MISOD (Group A), and 21 had four-ball attachment MISOD (Group B). The total amount of afterecare visits was recorded, as well as the type of treatments required (pressure sore spots relief, attachment liner replacement due to loss of retention, and metal ball attachment replacement due to wear). The mean follow-up duration was 93 \(\pm\) 57 months (range 9-246 months). None of the implants was lost. There were significantly more visits for pressure sore spots relief in Group A vs. Group B (6.2 \(\pm\) 2 in group A and 4.09 \(\pm\) 1.54 in group B, \(p\)\(<\) 0.0001). Differences in the other two tested parameters (number of visits for liner replacement (2.3 \(\pm\) 1.84 in group A and 2.4 \(\pm\) 1.63 in group B) and attachment replacement (2.36 \(\pm\) 1.85 in group A vs. 2.48 \(\pm\) 1.63 in group B) yielded a non-significant outcome (\(p\) = 0.814 for liner replacement and \(p\) = 1.000 for attachment replacement). The use of four-ball attachments in MISOD was more beneficial than two-ball attachments with regards to the aftercare of pressure sore spots. The number of implants did not influence the mechanical wear. mandibular implant overdentures; number of implants; aftercare; sore spots 2021  
17 August 2021  
Accepted: 21 September 2021  
Subscribed: 26 September 2021
In 2009, the York Consensus Statement [4] observed that the two-implant MISOD is not the gold standard of implant therapy, but rather the minimum standard offered to dedentious patients considering masticatory performance, patient satisfaction, cost, clinical time, and patient choice [7]. The 2015 EAO consensus conference also acknowledged that the oral health-related quality of life outcomes would improve by two or four implants MISOD [8]. Situations where, for example, a severely compromised available oral mucosa remains in contact with the planned overdenture will dictate, among other considerations, the need for four implants rather than two [9; 10; 11]. [PERSON] et al. 's meta-analysis showed a preference in favor of four implants supporting MISOD over two implants with regards to long-term implant survival [12]. That statistical finding even exceeded four implants supporting the mandibular fixed restoration. Therefore, using four implants to support an overdenture is common practice. The choice of the number of implants is affected by the following criteria: retention, patient satisfaction, implant survival, bone and tissue preservation, initial and long-term cost, complications, and aftercare [10]. Post-insertion prosthetic maintenance requiring aftercare over time causes discomfort for the patients in addition to being costly. The two main categories of complications that may occur in implant therapy are biological and technical (mechanical). Biologic complications include implant failure, marginal bone loss, sore spots, and reduction in ridge volume. Technical complications collectively refer to mechanical damage to the implant and its components and superstructures, and they include implant fracture, wear or corrosion of the retention elements, fracture of the retentive elements or superstructure, abutment fracture, abutment screw loosening or fracture, attachment screw loosening or fracture, activation or changing of the clip, matrix activation (requiring change of rubber ring) or replacement (requiring change of ring housing), rebasing or relining of the overdenture, and repreparing overdenture due to fracture [13; 14].