Available online 18 November 2023

Author links open overlay panel, , , , AbstractStatement of problem

The 2-implant mandibular overdenture (2IMO) is a popular treatment for patients with mandibular edentulism. However, information on the influence of implant positions on crestal strain is lacking.

Purpose

The purpose of this in vitro study was to evaluate the crestal strain around 2 implants to support mandibular overdentures when placed at different positions.

Material and methods

Edentulous mandibles were 3-dimensionally (3D) designed separately with 2 holes for implant placement at similar distances of 5, 10, 15, and 20 mm from the midline, resulting in 4 study conditions. The complete denture models were 3D designed and printed from digital imaging and communications in medicine (DICOM) images after scanning the patient’s denture. Two 4.3×12-mm dummy implants were placed in the preplanned holes. Two linear strain gauges were attached on the crest of the mesial and distal side of each implant (CH1, CH2, CH3, and CH4) and connected to a computer to record the electrical signals. Male LOCATOR attachments were attached, the mucosal layer simulated, and the denture picked up with pink female nylon caps. A unilateral and bilateral force of 100 N was maintained for 10 seconds for each model in a universal testing machine while recording the maximum strains in the DCS-100A KYOWA computer software program. Data were analyzed by using 1-way analysis of variance, the Tukey post hoc test, and the paired t test (α=.05).

Results

Under bilateral loading, the strain values indicated a trend with increasing distance between the implants with both right and left distal strain gauges (CH4 and CH1). The negative (-ve) values indicated the compressive force, and the positive (+ve) values indicated the tensile force being applied on the strain gauges. The strain values for CH4 ranged between −166.08 for the 5-mm and −251.58 for the 20-mm position; and for CH1 between −168.08 for the 5-mm and −297.83 for the 20-mm position. The remaining 2 mesial strain gauges for all 4 implant positions remained lower than for CH4 and CH1. Under unilateral-right loading, only the right-side distal strain gauge CH4 indicated the increasing trend in the strain values with −147.5 for the 5-mm, −157.17 for the 10-mm, −209.33 for the 15-mm, and −234.75 for the 20 mm position. The remaining 3 strain gauges CH3, CH2, and CH1 ranged between −28.33 and −107.17. For each position for both implants, significantly higher (P<.05) strain values were observed on the distal strain gauge channels CH4 and CH1 than on the mesial channels CH3 and CH2 under bilateral loading and on the right side under unilateral loading.

Conclusions

Peri-implant crestal strains in the 2IMO increased by increasing the distance of the implants from the midline. The stress values progressively increased from 5 to 10 mm to 15 to 20 mm from midline, represented as lateral incisor, canine, and premolar positions. The distal side of the implants exhibits higher strains than the mesial side of the implants.

Section snippetsMATERIAL AND METHODS

This in vitro study (Project ID: IMU R 216–2018) was approved by the IMU joint committee on research and ethics. Edentulous mandibular models were developed by processing the cone beam computer tomography (CBCT) Digital Imaging and Communications in Medicine (DICOM) images of a 59-year-old man using a software program (Mimics; Materialise) (Fig. 1A). Four different study models were prepared by virtual positioning of the implants at distances of 5, 10, 15, and 20 mm from the midline of the

RESULTS

The strain gauges attached on the mesial and distal side of the 2 implants placed at different distances from the midline (5, 10, 15, and 20 mm) indicated varying changes in the strain values under bilateral and unilateral loading (Figure 5, Figure 6). Negative (-ve) values indicated compressive force, and positive (+ve) values indicated tensile force being applied on the strain gauges. Higher -ve values indicated higher compressive forces on the strain gauges and should not be confused with

DISCUSSION

The research hypothesis that more posterior positioning of the implants would result in higher crestal strains in the 2IMOs was accepted, as the results indicated an increase in the strain values with an increase in the distance of the implants from the midline. From a biomechanical point of view, the closer the position of the implants to the area of applied force, the higher the strains in the crestal area. A similar trend was observed by Patil et al5 in an FEA study that used similar virtual

CONCLUSIONS

Based on the findings of this in vitro study, the following conclusions were drawn:

1.

Peri-implant crestal strains in the 2IMO increased by increasing the distance of the implants from the midline. The stress values increased progressively from 5 to 10 mm and 15 to 20 mm from the midline, represented as the lateral incisor, canine, and premolar positions.

2.

The distal side of the implants exhibited higher strains than the mesial side under bilateral loading at any implant position studied.

3.

The distal

CRediT authorship contribution statement

Pravinkumar Patil responsible for Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Visualization, Roles/Writing - original draft, Writing - review and editing. Seow Liang Lin responsible for Conceptualization, Data curation, Formal analysis, Funding acquisition, Project administration, Supervision, Validation, Visualization, Writing - review and editing. Rashmi Uddanwadikar responsible for Conceptualization, Data

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