Effect of Implant Height Differences on Different Attachment Types and Peri-Implant Bone in Mandibular Two-Implant Overdentures: 3D Finite Element Study
Implant-supported overdentures with self-aligning attachment systems are preferred to improve the stability and retention of complete dentures. The positioning of the implant attachments is a very important aspect of two-implant overdentures in obtaining better stress distribution. Therefore, the objective of this study was to compare two different attachment systems in a two-implant overdenture by evaluating the stress distributions in peri-implant bone and stresses on the attachments with positioning at different height levels using the 3D FEA method. Six models with ball attachments and 6 models with locator attachments—totaling 12 models (including 2 controls)—with the left implant positioned unilaterally at different height levels were subjected to 3 loading conditions (anterior, right posterior, and left posterior). Data for Von Misses stresses were produced numerically, color coded, and compared among the models for attachments and peri-implant cortical bone. The configurations in which implants presented 3 mm height differences in the bone level showed the most successful results in the peri-implant bone. When stresses on the attachments were compared, greater stress values were obtained from the ball attachments. As a conclusion, the configurations with a considerable (3 mm) height difference between quadrants of the mandible in the anterior segment showed the most successful results in the peri-implant bone. On the contrary, peak stress values around the implant observed from the models with less (1 mm) bone height difference may require leveling of the bone during surgery. However, these findings should be corroborated with clinical studies.
Figure 1. Models were divided into six groups. (a) Ball attachments, implants with the same vertical height level. (b) Locator attachments, implants with the same vertical height level. Ball attachments, implants with the same vertical height level. (c) Ball attachments, left implant, and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (d) Locator attachments, left implant, and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (e) Ball attachments, left implant, and the alveolar bone on the left side is unilaterally 3 mm higher than right side. (f) Locator attachments, left implant, and the alveolar bone on the left side is unilaterally 3 mm higher than right side. Figure 2. SSM was modeled spherically with a 20 mm diameter to avoid localized contact.
Figure 3. Distribution of stresses in peri-implant bone (anterior load). (a) Ball attachments, implants with the same vertical height level. (b) Locator attachments, implants with the same vertical height level. Ball attachments, implants with the same vertical height level. (c) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (d) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (e) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. (f) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. Figure 4. Distribution of stresses in peri-implant bone (left posterior load). (a) Ball attachments, implants with the same vertical height level. (b) Locator attachments, implants with the same vertical height level. Ball attachments, implants with the same vertical height level. (c) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (d) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (e) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. (f) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. Figure 5. Distribution of stresses in peri-implant bone (right posterior load). (a) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (b) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (c) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. (d) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. Note that right posterior load considered as the same with left posterior load image of the implants with the same vertical height level.
Figure 6. Von Misses values of the attachments and peri-implant bone of both sides when anterior load applied (N/mm2). Figure 7. Von Misses values of the attachments and peri-implant bone of both sides when left posterior load applied (N/mm2). Figure 8. Von Misses values of the attachments and peri-implant bone of both sides when right posterior load applied (N/mm2).
Distribution of stresses on attachments (anterior load). (a) Ball attachments, implants with the same vertical height level. (b) Locator attachments, implants with the same vertical height level. Ball attachments, implants with the same vertical height level. (c) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (d) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (e) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. (f) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side.
Distribution of stresses on attachments (left posterior load). (a) Ball attachments, implants with the same vertical height level. (b) Locator attachments, implants with the same vertical height level. Ball attachments, implants with the same vertical height level. (c) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (d) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (e) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. (f) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side.
Distribution of stresses on attachments (right posterior load). (a) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (b) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 1 mm higher than right side. (c) Ball attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. (d) Locator attachments, left implant and the alveolar bone on the left side is unilaterally 3 mm higher than right side. Note that right posterior load considered as the same with left posterior load image of the implants with the same vertical height level.
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