Background and objectives: Long-term studies of clinical outcomes of mini-implants (MDIs) in the first premolar/canine sites retaining a bilateral free-ending removable partial dentures (RPD) in Kennedy class I subjects have not been well documented. The aim was to assess clinical outcomes in a prospective 5-year cohort study comparing the mandible and maxilla. Material and Methods: Participants (n = 92) who received two MDIs each and a new RPD were reviewed after one, three and five years. A total of 71 participants (82 mini-implants in the mandible; 58 in the maxilla) completed the study. Marginal bone level change, success, survival rates, Modified Plaque (MPI) and Bleeding Indices (MBI) were assessed. Results: The five-year success rate was 93.3% and 93.4% (p > 0.05), in the mandible and the maxilla, respectively. Mean peri-implant bone loss (MBL) increased significantly over five years (p < 0.01) to 0.50 mm in the mandible and 0.52 mm in the maxilla. Age had a significant effect on the MBL (higher rates in younger participants), while jaw of insertion, gender, and antagonistic jaw status did not. MPI and MBI were not significantly correlated with MBL. Conclusions: The insertion of two MDIs in previous first premolar/canine sites for retention of a free-end saddle RPD can be a successful treatment modality in subjects with narrow alveolar ridges.

Clinical indications for the newly released Ti-Zr (Roxolid^®) alloy mini-implants (MDIs) aimed for overdenture (OD) retention in subjects with narrow alveolar ridges are not fully defined. The aim of this study was to analyze peri-implant and posterior edentulous area microstrains utilizing models of the mandible mimicking a “real” mouth situation with two (splinted with a bar or as single units) or four unsplinted Ti-Zr MDIs. The models were virtually designed from a cone beam computed tomography (CBCT) scan of a convenient patient and printed. The artificial mucosa was two millimeters thick. After MDI insertion, the strain gauges were bonded on the oral and vestibular peri-implant sites, and on distal edentulous areas under a denture. After attaching the ODs to MDIs, the ODs were loaded using a metal plate positioned on the first artificial molars (posterior loadings) bilaterally and unilaterally with 50, 100, and 150 N forces, respectively. During anterior loadings, the plate was positioned on the denture’s incisors and loaded with 50 and 100 N forces. Each loading was repeated 15 times. The means with standard deviations, and the significance of the differences (two- and three-factor MANOVA) were calculated. Variations in the MDI number, location, and splinting status elicited different microstrains. Higher loading forces elicited higher microstrains. Unilateral loadings elicited higher microstrains than bilateral and anterior loadings, especially on the loading side. Peri-implant microstrains were lower in the four-MDI single-unit model than in both two-MDI models (unsplinted and splinted). Posterior implants showed higher peri-implant microstrains than anterior in the four-MDI model. The splinting of the two-MDI did not have a significant effect on peri-implant microstrains but elicited lower microstrains in the posterior edentulous area. The strains did not exceed the bone reparatory mechanisms, although precaution and additional study should be addressed when two Ti-Zr MDIs support mandibular ODs.

The new Ti–Zr (Roxolid^®) mini-implants have not yet been fully researched. We analyzed peri-implant and posterior edentulous area microstrains during mandibular overdenture (OD) loading at different sites with different extents of forces when one-, two-, three-, or four- mini dental implants (MDIs) as single-units supported the respective ODs. The models were designed from cone beam computed tomography (CBCT) scans of an appropriate patient with narrow ridges. The mucosal thickness was 2 mm. Strain gauges were bonded on the vestibular and oral peri-implant sites, and in the distal edentulous area under the saddles. The loads were applied posteriorly bilaterally and unilaterally with 50, 100 and 150 N forces, and anteriorly with 50 and 100 N forces. Each loading was repeated 15 times. Statistical analysis included descriptive statistics, boxplots and the MANOVA. Higher forces induced higher peri-implant microstrains, as well as unilateral loadings, especially on the loaded side, in all models except the one-MDI model where anterior loads (100 N) elicited the highest peri-implant microstrain (1719.35 ± 76.0). The highest microstrains during unilateral posterior loading (right side) with 150 N force were registered from the right MDI in the two-MDI model (1836.64 ± 63.0). High microstrains were also recorded on the left side (1444.48 ± 54.6). By increasing the number of implants, peri-implant microstrains and those in the edentulous area decreased. In the three- and four-MDI models, higher microstrains were found in the posterior than in the anterior MDIs under posterior loadings. None of the recorded microstrains exceeded bone reparatory mechanisms, although precaution and additional research should be provided when only one or two MDIs support ODs.

Clinical indications for the Ti-Zr alloy (Roxolid^®) mini-implants (MDIs) in subjects with narrow ridges are still under review. The aim was to analyze peri-implant and posterior edentulous area strains dependent on the MDI number, splinting status, loading force, and loading position. Six models were digitally designed and printed. Two, three, or four Ti-Zr MDIs, splinted with a bar or unsplinted (single units), supported mandibular overdentures (ODs), loaded with 50–300 N forces unilaterally, bilaterally, and anteriorly. The artificial mucosa thickness was 2 mm. Strain gauges were bonded on the vestibular and oral peri-implant sides of each MDI, and on the posterior edentulous area under the ODs. Loadings were performed through the metal plate placed on ODs’ artificial teeth (15 times repeated). Arithmetic means with standard deviations and the significance of the differences (MANOVA, Sheffe post hoc) were calculated. Different MDI numbers, loading positions, forces, and splinting elicited different peri-implant microstrains. In the two-MDI models, 300 N force during unilateral loading elicited the highest microstrains (almost 3000 εμ on the loaded side), which can jeopardize bone reparation. On the opposite side, >2500 εμ was registered, which represents high strains. During bilateral loadings, microstrains hardly exceeded 2000 εμ, indicating that bilateral chewers or subjects having lower forces can benefit from the two Ti-Zr MDIs, irrespective of splinting. However, in subjects chewing unilaterally, and inducing higher forces (natural teeth antagonists), or bruxers, only two MDIs may not be sufficient to support the OD. By increasing implant numbers, peri-implant strains decrease in both splinted and single-unit MDI models, far beyond values that can interfere with bone reparation, indicating that splinting is not necessary. When the positions of the loading forces are closer to the implant, higher peri-implant strains are induced. Regarding the distal edentulous area, microstrains reached 2000 εμ only during unilateral loadings in the two-MDI models, and all other strains were lower, below 1500 εμ, confirming that implant-supported overdentures do not lead to edentulous ridge atrophy.

Background: The biomechanical behaviour of mandibular Ti-Zr mini-implant (MDI) retained overdentures is influenced by implant number, loading conditions, and mucosal thickness. This study assessed the effect of mucosal thickness and other factors on peri-implant and distal edentulous ridge microstrain values under functional loading. Methods: Eight stereolithographic mandibular models simulating D2 bone were fabricated with one, two, three, or four Ti–Zr MDIs and covered with artificial mucosa of 1.9 mm (thin) or 3.8 mm (thick). Standardized overdentures were loaded anteriorly, unilaterally, and bilaterally with forces ranging from 50 to 300 N. Strain gauges measured micro-deformation at vestibular and oral peri-implant sites and the distal edentulous ridge. Data were analyzed using MANOVA and between-subject tests, with effect sizes (η²) calculated. Results: Peri-implant microstrain decreased with increasing implant number, with single-implant overdentures reaching more than 2500 µε under anterior loading, as well as two-implant overdentures under unilateral loading; four-implant configurations remained <2000 µε. Mucosal thickness had no influence on peri-implant strains in two- and four-implant setups; however, thicker mucosa showed a very small attenuation effect in one-implant arrangements and medium effect in three-implant arrangements. Loading force and position were the dominant determinants of peri-implant strain. Distal ridge microstrain was significantly attenuated by thicker mucosa (η² ≈ 0.449). Conclusions: Implant number, loading force and position predominantly govern peri-implant strain distribution, while thicker mucosa effectively reduces distal ridge strain beneath the overdenture. Single- or two-implant mandibular overdentures are more vulnerable to high unilateral or anterior loads, emphasizing the importance of careful implant planning and occlusal management in clinical practice.