1. Introduction
The dental implants presents high success rates and a growing market. The two main types of dental implants are cylindrical or conical geometries and other possibility is hybrid (mix of two). The implant shape influences the osseo-integration (Simmons et al. Citation2001) but the conical shape implant presents a higher compression capacity. The market presents several sizes but the main problem of dental implants remains bone loss, not completed explained until now (Oh et al. Citation2002). A critical aspect in dental implants is the healing time to bone integration; this phenomenon is affected by several factors, as the morphology of surface, topology, surface roughness, composition, surface energy and design (Richards Citation2002; Suzuki et al. Citation2009). The design is not the only factor affecting the integration of implant, but in this preliminary study we intend to study its influence for two commercial geometries in bone strains after the healing process. The hypothesis is that the conical geometry improves the distribution of bone strains more than the cylindrical one.
2. Methods
2.1. Commercial models of dental
The market of dental implants presents different designs of screws in diameter and length. The CAD models were developed according two designs from commercial Osstem implants™. The dimensions and principal variables associated in each model are in .
Figure 1. Commercial implant variables, a) cylindrical geometry, b conical geometry.
According to the previous drawings, the values of the variables are defined in . The implant size was selected according to the bone size: 4.9 for cylindrical and 5.1 mm for conical as the maximum diameter and same length 11.5 mm.
Table 1. Dental implant variables.
The bone geometry was acquired from a 2D section from the mandible geometry and designed according to the thickness of cancellous and cortical bone presented in . The geometry was considered linear in length.
Figure 2. CAD model (conical) and finite element model (cylindrical) of the commercial dental implants.
2.2. Finite element model (FEM)
The numeric models were developed based on CAD model previously defined and presented in . The FEM models were developed with a total of 82500 tetraedic second order (parabolic) elements in each model.
The FE model consider a load of 114 N in vertical direction and 30 N in lateral direction (Linetskiy et al. Citation2017), replicating the load on the teeth. The model was fixed in the posterior region and a friction coefficient (f = 0.3) at the interface between implant and bone tissues was taken into account (dos Santos et al. Citation2017).
3. Results and discussion
The strain distribution in the cancellous bone presents different behaviour in the two dental implant geometries. The most critical strains are the minimum principal strains presented in . The cylindrical model presents less level of principal strains in the proximal region of the cancellous bone, near the interface. The conical shape presents high level of strains near the screw and the blue region presents values higher than 3000µε (maximum was 6500 µε). As observed in several cases, this value induces bone loss. Near the interface with screws the strains is higher in both cases explained by the screw geometry and the concentration of strains.
Figure 3. Minimum principal strains distribution in bone.
If we analyse the strain in the cancellous bone far from the screw crest to avoid the concentration of strains. The results are collected in a line presented in , and was observed a different phenomenon of strain distribution. The cylindrical implant reduces the strain in proximal region of the cancellous bone, the strains reduces 30% in one side (left side).
Figure 4. Principal strains along the control line.
The tip in both implants presents similar strain distribution, with lower strain values; this underlines that the proximal region is critical as observed in clinical situation with proximal bone loss. In the cortical bone, the conical implant presents more 30% of strains than the cylindrical one, but these values are justified with the screw geometry in the cortical bone. Relatively to the implant stability, both geometries are similar, presenting lower values of micro movements, lower than 10 µm in the interface, but the cylindrical geometry of implant presents lowest values 7 µm.
4. Conclusions
The results point out the importance of the dental implant geometry in the strain distribution in the implant-bone interface. The cylindrical and conical shape presented different strain distribution and the conical shape increase the strains in cancellous bone. On the contrary the cylindrical implant induces more strains in cortical. The geometry of implant can induce bone loss in proximal region of fixation and promote the implant loss.
Additional information
Funding
References
- dos Santos MBF, Meloto G, de O, Bacchi A, CorrerSobrinho L. 2017. Stress distribution in cylindrical and conical implants under rotational micromovement with different boundary conditions and bone properties: 3-D FEA. Comput Methods Biomech Biomed Engin. 20(8):893–900.
- Linetskiy I, Demenko V, Linetska L, Yefremov O. 2017. Impact of annual bone loss and different bone quality on dental implant success: a finite element study. Comput Biol Med. 91:318–325.
- Oh T-J, Yoon J, Misch CE, Wang H-L. 2002. The causes of early implant bone loss: myth or science? J Periodontol. 73(3):322–333.
- Richards RG. 2002. The effect of surface roughness on fibroblast adhesion in vitro. Injury. 27(Suppl 3):C38–C43.
- Simmons CA, Meguid SA, Pilliar RM. 2001. Differences in osseo integration rate due to implant surface geometry can be explained by local tissue strains. J Orthop Res. 19(2):187–194.
- Suzuki M, Guimaraes MVM, Marin C, Granato R, Gil JN, Coelho PG. 2009. Histomorphometric evaluation of alumina-blasted/acid-etched and thin ion beam-deposited bioceramic surfaces: an experimental study in dogs. J Oral Maxillofac Surg. 67(3):602–607.