Impact of implant support on mandibular free-end base removable partial denture: theoretical study

Mini-Implants Retaining Removable Partial Dentures in Subjects without Posterior Teeth: A 5-Year Prospective Study Comparing the Maxilla and the Mandible

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.

In vitro study of the effect of implant position and attachment type on stress distribution of implant-assisted removable partial dentures

Background/purpose

Implant assisted removable partial dentures (IARPDs) improved biomechanical behavior of removable partial dentures (RPDs), but information of the effect of attachment type and implant position is limited. This study aimed to investigate the effect of implant position and attachment type on the stress distribution of IARPDs.

Material and methods

Four implants, 10 mm in length and 4.1 mm in diameter, were bilaterally placed close to first premolar and second molar regions of a mandibular Kennedy class I model having artificial dentition from canine to canine, vertical to the occlusal plane. Five IARPDs were fabricated to accommodate locator and magnetic attachments. Strain gauges were placed on the model surface to measure the strain around implants during loading. Unilateral vertical loading was applied to the right first molar area with magnitude of 120 N and crosshead speed of 10 mm/min. Measurements were recorded under following conditions: premolar IARPDs with locator or magnetic attachments, molar IARPDs with locator or magnetic attachments. Two-way multiple analysis of variance was performed to compare the maximum principal strain (MPS) around the implants with a significance level of 0.05.

Results

Implant position had significant effect on the MPS of IARPD on loading and nonloading sides while attachment type only significant on nonloading side. Molar implants showed larger MPS than premolar implants with both locator and magnetic attachments during unilateral loading.

Conclusion

The stress distribution of the IARPD is significantly affected by implant position wherein anteriorly placed implants exhibit lower MPS than relatively posteriorly placed implants.

Effect of the Location of Dental Mini-Implants on Strain Distribution under Mandibular Kennedy Class I Implant-Retained Removable Partial Dentures

Purpose

To investigate the effect of minidental implant location on strain distributions transmitted to tooth abutments and dental minidental implants under mandibular distal extension removable partial denture.

Materials and Methods

A mandibular Kennedy Class I distal extension model missing teeth 35–37 and 45–47 was constructed. Six dental mini-implants were placed at positions A, B, and C, where position A was 6.5 mm distal to the abutment teeth with 5 mm between each position. Fourteen uniaxial strain gauges were bonded on the model at the region of dental mini-implant and abutment (first premolar). Four groups were designated according to the location of the mini-implants. A load of 150 N and 200 N was applied using an Instron testing machine. Loadings consisted of bilateral and unilateral loading. Comparisons of the mean microstrains among all strain gauges in all situations were analyzed.

Results

Variation in mini-implant locations induced local strains in different areas. Strains at the tooth abutment were significantly decreased in the group in which implants were placed mesially. Strains around the mini-implants showed different patterns when loaded with different loading conditions. The group in which implants were placed distally showed the lowest strains compared to other groups.

Conclusion

Mesially placed mini-implants showed the lowest strain around abutment teeth, while a distally-placed mini-implants presented the lowest strain around mini-implants themselves. Under favorable biting force, mini-implant is an option to assist mandibular distal extension removable partial denture. Mesially placed mini-implants are recommended when the abutment has periodontally compromised conditions and a distally placed mini-implant when periodontal conditions are stable.

New Rehabilitation Concept for Maxillary Edentulism: A Clinical Retrospective Study of Implant Crown Retained Removable Partial Dentures

There have been no studies of implant-crown-retained removable partial dentures (IC-RPD) for the treatment of maxillary edentulism. The purpose of this study was to perform clinical and radiographic evaluations of implants in IC-RPD compared to implant overdentures (IOD) in maxillary edentulous patients. Twenty IC-RPDs with 74 splinted implant crowns and 18 IODs with 71 implants retained with magnet attachments were observed in 38 patients. We statistically analyzed survival rates and marginal bone loss (MBL) of implants based on multiple variables including first year pathologic condition, location of placed implant, age, and sex in both treatments. Patient reported oral measurements (PROMs) regarding functional/esthetic improvement after IC-RPD or IOD treatments and prosthetic complications were also statistically analyzed. After a median observation period of 47.1 months (up to 147 months), we observed 97.3% implant survival rates for IC-RPD and 70.4% for IOD (p < 0.001). Among variables, first year pathologic condition (p < 0.001) and sex (p = 0.027) influenced implant survival rates. The MBL of implants for IC-RPD and IOD groups at the final check-up were 1.12 ± 1.19 mm and 3.31 ± 1.71 mm, respectively (p < 0.001). In both groups, patients with peri-implantitis (p < 0.001) and patients older than 65 years (p = 0.029) showed significantly higher implant MBL regardless of treatment modality. Functional and esthetic satisfaction were significantly improved (p < 0.001) after both treatments. The IOD group showed more frequent prosthetic complications compared to the IC-RPD group. Within the limitations of a retrospective study, we concluded that RPD with few splinted implant crowns is a feasible alternative treatment modality for maxillary edentulous patients with anatomical limitations.

Influence of rigidity of retainers on dynamic behavior of implant-supported removable partial dentures

Background

Implant-supported removable partial dentures (ISRPDs) are an effective treatment for partially edentulous patients. ISRPDs improve patients’ satisfaction and oral function to a greater extent than RPDs by improving denture stability and enhancing support. However, the effect of a type of direct retainer on displacement of the abutment teeth and dentures in ISRPDs remains unclear. Therefore, we made a resin mandibular model of unilateral mandibular distal-extension partial edentulism for mechanical simulation and compared the dynamic behavior of the abutment teeth and the denture base among different tooth-borne retainers with various rigidities for RPDs and ISRPDs.

Methods

A resin mandibular model for mechanical simulation that had unilateral mandibular distal-extension edentulism and was missing the first molar, second molar, first premolar, and second premolar, and a denture fabricated from the patient’s computed tomography images were used. Three types of direct retainers with different connecting rigidities were evaluated. The vertical displacement of the denture base and buccal and lingual sides and the mesial displacement of the abutment teeth were measured.

Results

Regardless of the rigidity of the direct retainers and loading positions, the displacement of the denture bases in the ISRPDs was significantly smaller than that in the RPDs (P < 0.001). There was no significant difference in vertical displacement of the denture bases among direct retainers with various connecting rigidities in the ISRPDs. Conversely, horizontal displacement of the abutment teeth in both the RPDs and ISRPDs tended to be larger with the cone crown telescope, which has high rigidity, than with the cast cingulum rest and wire clasp, which have much lower rigidities.

Conclusion

Our results suggested that cast cingulum rest and wire clasps as direct retainers are appropriate ISRPDs to minimize denture movement and suppress displacement of the remaining teeth in patients with unilateral mandibular distal-extension partial edentulism.