Histomorphometric analysis of human retrieved implants is the method available to analyze the bone-to-implant interface behavior over time [13]. The reproduction of a human’s mouth environment in animals is tremendously difficult. Therefore, this study can contribute to the knowledge of human bone response to a dental implant under loading conditions.
Many efforts have been made by researchers and manufacturers to produce implant surfaces attractive to living cells and, consequently, to improve the quantity and quality of osseointegration. It has been reported that micro-rough topography observed in a porous implant could favorably affect angiogenesis, as well as cellular migratory events, activity, and function [14], resulting in a faster and higher bone-implant contact and mechanical interlocking [6, 7].
In this study, three commercially pure, titanium screw-type implants were used. They formerly received a sandblasting treatment with aluminum oxide to promote macroporosities, and they were acid-etched to achieve microporosities. Rates of 80.3% of bone-to-implant contact and 77.3% of bone area within the limits of the implant threads were found. These findings are similar to the result reported by Hayakawa et al. [15] (76.60%) when a sandblasted and acid-etched implant was placed into the palatal bone as anchorage for orthodontic treatment.
Other investigators reported similar results with different surfaces and follow-up. Piattelli et al. [5] found 60 to 70% of bone-to-implant contact to titanium plasma spray implant. Brunel et al [16] reported 74% with hydroxyapatite coating in maxilla after 14 months of follow-up, and Degidi et al. [17] found 60% after 9 months of follow-up in porous anodized implant submitted to immediate loading.
Based on the trustworthiness of the macro- and microimplant systems, the implant-tooth splinting has been considered as an alternative in some clinical situations. Although some studies show satisfactory success in short and near future [18, 19], the previsibility of the implant/tooth system is still unclear.
The amount of tooth movement with healthy periodontal ligaments against that of an osseointegrated dental implant can be 5–20 times greater [20]. This disparity causes the implant side to receive a higher bending moment as a result of the bridge function as a cantilever construction and is only supported by the implant when the occlusal load acts on the tooth [21]. A series of potential problems such as tooth intrusion, osseointegration loss, screw loosening, and implant or prosthesis fracture can arise, with resulting complicated physiological and engineering aspects [18, 19, 22].
In the present case, three implants with 3.3 mm in diameter and with internal hexagon abutment connection were positioned at the 12, 13, and 14 teeth region and united to the second molar with reduced periodontal support, having the first molar suspended between them. As described by the literature, the occlusal load over the first and second molars resulted in a cantilever force that concentrated on the implant neck [23]. The association of overload, inadequate implant diameter to the case, and internal hexagon connection resulted in the abutment screw and the internal hexagon wall fracture.
The studies already showed the relation between the load and the collagen fiber orientation in bone near threaded dental [24, 25]. The spatial orientation of collagen fibers has a direct bearing on its mechanical properties [24]. Based on a number of studies, several authors also correlate strongly the collagen fiber orientation to the loading regimen [26, 27].
In 1958, Evans [28] described the relation between the bone stiffness and predominant direction of the collagen fibers in the bone matrix. When collagen fibers ran parallel to the loading vector, the bone was more resistant. McElhaney [29] found that the ultimate compressive strength and modulus of elasticity of the cortical bone increased with increasing strain rate. The energy absorption capacity had a maximum at an intermediate strain rate. It was suggested that low strain rate shear failures result from a distortion of the lamellar substructure and fracture along several weaker planes. High strain rate failures appeared to follow the cement lines, constituting the boundaries of the haversian and lamellar systems.
Traini et al. observed that the load can influence the collagen fiber orientation in bone near threaded dental implants in immediately loaded implants [24, 30]. They found that loading has a relevant influence in the distribution of the collagen fibers in the peri-implant bone. Transverse collagen fibers, related to compressive loads, were found in a higher and statistically significant quantity in loaded than in unloaded implants or in the alveolar bone. The bone tissue responded to an overloading (until the threshold of the implant fracture was reached) by modeling and remodeling its microstructure. The predominance of transverse collagen fiber orientation should be related to a high compression state [24, 30].
Regarding BIC and high load occlusion, Chang et al. [31] performed a systematic literature review and concluded that the greatest peri-implant bone remodeling activity is found around implants subjected to high loading forces, when the applied force exceeds the biological adaptable limit. The authors reported that there was a limitation in the research due to the absence of experimental studies in humans. But the authors suggest that a possible correlation between occlusal overload and implant failures is related to the degree tolerance of the alveolar bone which varies according to the individual, the location, and other anatomic and physiological parameters.
