The present study tried to evaluate the effects of nicotine alone and in combination with arginine to find out any alterations in mechanical properties of early dental implant osseointegration in dogs’ mandible. The present study showed that nicotine could negatively affect the mechanical properties of the dental implant. Arginine partially compensated for the negative effect of nicotine. Nicotine alone or in combination with arginine resulted in inferior mechanical properties compared to placebo during 4 weeks of post-implantation.
Nicotine is known to reduce the proliferation of red blood cells, macrophages, and fibroblasts. It also affects tissue perfusion and healing by increasing platelet adhesion and vasoconstriction. Sympathomimetic action of nicotine stimulates epinephrine and norepinephrine release, which consequently causes vasoconstriction and limited tissue perfusion. Contemplating these effects, nicotine is expected to debilitate potential bone healing at the bone and implant interface. At 8 weeks, nicotine consumer rats showed that the bone matrix-related gene expression was downregulated, and bone formation around implants was decreased [20].
Berley et al. [21] found that bone-to-implant contact is decreased in rats receiving nicotine compared to control. Soares et al. showed a decrease in bone formation around hydroxyapatite implants placed in the tibia and femur of rats receiving nicotine compared to rats receiving water or alcohol [22]. On the other hand, Pereira et al. demonstrated that nicotine increases bone-forming enzymes’ synthesis and enhances osteoblasts’ growth and differentiation [23].
Cesar-Neto et al. found no difference in rats’ bone healing receiving or not receiving nicotine [24]. Balatsoaka et al. demonstrated an increase in bone density from 2 to 4 weeks around implants in the rabbit receiving nicotine [25]. These contradictory results might be due to cell cultures used and other methodological differences between these studies.
In the present study, nicotine has resulted in reduced removal torque compared to the placebo. Arginine supplementation has increased torque over 4 weeks, and there was no significant difference in removal torque between the nicotine and arginine consumer groups compared to placebo.
The bone around dental implants continues an active remodeling even after 5 years of implantation. Studies that investigated bone healing around dental implants after few weeks to 20 years or more implant functioning show that masticatory loads stimulate continuous remodeling after primary healing of an implant [6, 26]. The active remodeling is known to affect the bone quality, that is, the bone-implant contact area and the quality of the bone, which is influenced by the amount and distribution of collagen and minerals in the bone around dental implants. Thus, continuous remodeling contributes to implant mechanical stability over the functional years of a dental implant [4, 26, 27]. Although 4 weeks might be a short period in the present study, there was an increase in ISQ and removal torque values in all of the groups.
There is a strong correlation between the degree of tissue mineralization, as an indicator of bone quality, and mechanical properties of the bone [3, 28]. Incompletely mineralized newly formed bone due to bone remodeling adjacent to the implant is anticipated to be mechanically inferior to pre-existing bony tissues away from the implant. Therefore, In the present study, we have used mechanical measurements to evaluate the implant stabilities. Although histometric analysis would have given us more information, dental implants’ biomechanical behavior is one of the most important prognostic factors and an essential indicator of osseointegration.
Collagen is the dominant constituent of bony tissues that control the viscoelastic properties [3, 29, 30]. Under the load, protein fibrils of collagen show time-dependent deformation.
During the bone mineralization process, minerals are gradually arranged along the collagen fibrils and eventually create the mineral-collagen complex’s mechanical integrity. Thus, bone remodeling by changing the bone tissue composition alters bone’s mechanical properties such as viscoelastic characteristics—further studies are required to investigate bone’s viscoelastic properties around dental implants.
Many attempts have been made to find superior dental materials and growth agents to promote bone quality and quantity around and at the implant-bone interface. One of several agents is amino acids, which have been suggested that can hasten bone healing by enhancing local blood supply, stimulating growth factor, and increasing collagen synthesis [31].
In vitro studies have shown that amino acids such as arginine promote osteoblastic growth and differentiation by stimulating insulin growth factor-1 secretion [32,33,34]. Others found that arginine, lysine, and glycine are associated with collagen synthesis [10, 35]. Goel et al. [36] found that 2 g/day l-arginine increased bone mineral density by 11.6% in osteoporotic women for 2 years.
In the present study, arginine was supplemented to nicotine consumer dogs to help in the osseointegration of dental implants. Arginine supplementation’s beneficial effect might be due to arginine’s potential therapeutic effect on bone healing by enhancing nitrous oxide production and collagen synthesis. Cell proliferation precedes the synthetic phase of osteogenic bone-derived osteoblasts [10].