J Korean Acad Prosthodont.  2008 Oct;46(5):479-489. 10.4047/jkap.2008.46.5.479.

Stress distribution in bone surrounding maxillary molar implants under different crown-to-fixture ratio: A 3D FEM analysis

• Park JC
• Shin SW
• Kwon KR

• KMID: 2000405
• DOI: http://doi.org/10.4047/jkap.2008.46.5.479

Abstract

STATEMENT OF THE PROBLEM: Under anatomical limitations on maxillary posterior region, a poor crown-to root ratio acting on dental implants can result in undesirable stress in surrounding bone, which in turn can cause bone defects and eventual failure of implants. PURPOSE: The purpose is to compare stress distribution due to different crown-root ratio and effect of splinting between natural teeth and implants in maxillary molar area under different loads. MATERIAL AND METHODS: Analysis of stress arising supporting bone of the natural teeth and the implant was made with 3-dimensional finite element method. The model simulated naturel teeth was made with 2nd premolar and 1st molar in the maxillary molar region (Model T). The model simulated implants placed on same positions with two parallel implants of Straumann Dental Implant cemented abutment (Model I). Each model was designed in different crown-root ratio (0.7:1, 1:1, 1.25:1) and set cement type gold crown to make it non-splinted or splinted. After that, 300 N force was loaded to each model in five ways (Load 1: middle of occlusal table, Load 2: middle of buccal cusp, Load 3: middle of lingual cusp, Load 4: horizontal load to buccal cusp of anterior abutment only, Load 5: horizontal load to middle of buccal cusp of each abutment), and stress distribution was analyzed. RESULTS AND CONCLUSION: On all occasions, stress was concentrated at the cervical region of the implant. Under load 1, 2 and 3, stress was not increased even when crown-root ratio increases, but under load 4 and 5, when crown-root ratio increases, stress also increased. There was difference in stress values between natural teeth and implants when crown-root ratio gradually increases; In case of natural teeth, splinting decreased stress under vertical and horizontal loads. In case of implants, splinting decreased stress under vertical loads 1,2 and 3, but increased maximal stress under loads 2 and 3. Under horizontal loads, splinting decreased stress, however the effect of splinting decreased under load 5 than load 4. Furthermore, the stress was increased, when crown-root ratio is 1.25:1. CLINICAL IMPLICATIONS: This limited finite element study suggests that the stress on supporting bone may be increased under non-axial loads and poor crown-root ratio. Under poor crown-root ratio, excessive stress was generated at the cervical region of the implant, and decreased splinting effect for stress distribution, which can be related to clinical failure.

Keyword

Stress distribution; Implant; Maxillary molar; Finite element analysis; Crown-fixture ratio

MeSH Terms

Bicuspid
Crowns
Dental Implants
Finite Element Analysis
Molar
Splints
Tooth
Dental Implants

Figure

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  Fig. 1. Natural teeth model to Crown/Root ratio: Model T1 is 0.7:1; Model T2 is 1:1; Model T3 is 1.25:1.

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  Fig. 2. Implant model to Crown/Fixture ratio: Model I1 is 0.7:1; Model I2 is 1:1; Model I3 is 1.25:1.

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  Fig. 3. Load conditions : buccal (left) and oblique occlusal view (right).

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  Fig. 4. Stress contour on Model T under Load condition 5: non-splinted and splinted situations (left to right); C/R ratio 0.7:1, 1:1, 1.25:1 (top to bottom).

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  Fig. 5. Stress contour on Model I under Load condition 5: non-splinted and splinted situations (left to right); C/R ratio 0.7:1, 1:1, 1.25:1 (top to bottom).

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  Fig. 6. Maximun von Mises stress under Load condition 1 (MPa); Tns: non-splinted tooth model, Ts: splinted tooth model, Ins: non-splinted implant model, Is: splinted implant model.

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  Fig. 7. Maximun von Mises stress under Load condition 2 (MPa); Tns: non-splinted tooth model, Ts: splinted tooth model, Ins: non-splinted implant model, Is: splinted implant model.

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  Fig. 8. Maximun von Mises stress under Load condition 3 (MPa); Tns: non-splinted tooth model, Ts: splinted tooth model, Ins: non-splinted implant model, Is: splinted implant model.

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  Fig. 9. Maximun von Mises stress under Load condition 4 (MPa); Tns: non-splinted tooth model, Ts: splinted tooth model, Ins: non-splinted implant model, Is: splinted implant model.

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  Fig. 10. Maximun von Mises stress under Load condition 5 (MPa); Tns: non-splinted tooth model, Ts: splinted tooth model, Ins: non-splinted implant model, Is: splinted implant model.

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