Computational Modelling of Dental Implants

Znano je, da optimalen naklon zobnega vsadka sovpada z naklonom korenine naravnega zoba, ki je bila nadomeščena z zobnim vsadkom. Pomanjkanje kostne mase (atrofija kosti) zlasti v zadnjih segmentih spodnje in zgornje čeljusti ter anatomske omejitve, kot so maksilarni sinusi, nosna votlina in mandibularni živec, pa običajno zahtevajo poševno vgradnjo zobnih vsadkov. Vsak takšen naklon zobnega vsadka povzroča nastanek večosnih obremenitev vsadka, kar povzroča resorpcijo marginalne kosti in tako sčasoma izgubo zobnega vsadka. V okviru te doktorske disertacije so bili z namenom določitve mehanskega odziva kostnega tkiva razviti različni natančni numerični modeli vseh sestavnih elementov konstrukcije implantatno nošene zobne prevleke, podprte z zobnim vsadkom, ki je lahko vstavljen v čeljustno kost na mesto spodnjega levega prvega kočnika pod različnimi koti. Začetna geometrija v simulacijah uporabljenih modelov zobnih vsadkov in opornikov zobnih prevlek je bila posneta po dejanskih tovrstnih izdelkih z imenom Ankylos Plus, proizvajalca Dentsply. Pri analizah je bila upoštevana tudi anizotropnost kostnega tkiva. Kostno tkivo je bilo modelirano z linearno elastičnim materialnim modelom, pri čemer so bile elastične lastnosti tkiva odvisne od kostne gostote, ki je izražena v enotah Hounsfielda. Rezultati parametričnih računalniških simulacij kažejo, da je način modeliranja kostnega tkiva z elastičnim, od kostne gostote odvisnim ortotropnim materialnim modelom najprimernejši, saj je v njem prek kostne gostote neposredno upoštevan vpliv stanja kostnega tkiva. Nadalje se je izkazalo, da je trdnost v simulacijah uporabljenega zobnega vsadka pri večjih vrednostih okluzijskih sil nezadostna, saj je v tem primeru presežena meja plastičnosti materiala vsadka. Najpomembnejša ugotovitev je, da obstaja pri uporabi obravnavanega zobnega vsadka resna nevarnost trajne poškodbe kostnega tkiva pod vplivom vseh treh, v tej nalogi modeliranih vrednosti okluzijskih sil. Tako lahko na osnovi računalniških simulacij sklepamo, da obstoječa geometrija obravnavanega zobnega vsadka pri večjih vrednostih okluzijskih sil ni primerna, zato je v takšnih primerih priporočljivo uporabiti večji dimenzijski razred zobnega vsadka ali celo vsadek z drugačno geometrijo.It is known that the optimal implant inclination corresponds with inclination of the natural tooth root, which was replaced by dental implant. Lack of bone availability (bone atrophy) especially in the posterior segments of the upper and lower jaw, along with the presence of anatomical landmarks such as the maxillary sinus, nasal cavity and the mandibular nerve, sometimes necessitate inclined insertion of implants. Implant inclination leads to multiaxial loading of dental implant, which causes marginal bone resorption and in time results in implant loosening. In the context of this doctoral thesis detailed computational models of all components of the replacement tooth, supported by dental implant, which can be inserted under different angles into the jaw bone in the place of the lower left first molar, were developed. The purpose was to determine the mechanical response of the bone tissue. The initial geometry of dental implant and abutment models, which were used in the simulations, was based on real implants with commercial name Ankylos Plus, manufactured by Dentsply. Bone tissue anisotropy was also taken into account in the simulations. The bone tissue was modelled as a linear elastic constitutive model with density-dependent elastic properties. The bone density was defined in Hounsfield units. The results of the parametric computational simulations show that the method of the bone tissue modelling with elastic, density-dependent orthotropic constitutive model is the most appropriate. The bone tissue state is taken into account through bone density directly in this constitutive model. Furthermore, it seems that the strength of the dental implant, which was used in computational simulations, is insufficient at higher occlusal forces, since the yield stress of dental implant was exceeded in these cases. The most important finding in using this dental implant is that there exists a serious risk of permanent bone tissue damage under the influence of all three occlusal force values, which were modelled in this doctoral thesis. Based on the computational simulations it can be concluded that the existing dental implant geometry is not suitable for higher occlusion forces. In such cases it is recommended to use larger dental implant, or dental implant with different geometry