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D01:10.31926/but.shk.2019.12.61.2.49
Hristov I. G.
Assistant of Department of Periodontology and Dental Implantology
Medical University - Varna, Bulgaria
IMPLANT DESIGN FACTORS THAT AFFECT PRIMARY STABILITY AND OSSEOINTEGRATION
Христов Ивайло Георгиев
ассистент кафедры Пародонтология и дентальная имплантология Медицинский университет - Варна, Болгария
ФАКТОРЫ КОНСТРУКЦИИ ИМПЛАНТАТА, ВЛИЯЮЩИЕ НА ПЕРВИЧНУЮ СТАБИЛЬНОСТЬ И ОСТЕОИНТЕГРАЦИЮ
DOI: 10.31618/ESSA.2782-1994.2022.3.77.249 Abstract. Osseointegration can be defined as a direct structural and functional link between bone and implant surface. Asymptomatic and rigid fixation of alloplastic material in bone is crucial for implant stability and long-term success of dental implant treatment. The connection between implant and surrounding tissue is extremely dynamic. This interaction is the basis for the formation of a new structure - implant-tissue interface. The process of osseointegration is a combination of biological mechanisms as a result of which bone is formed on the walls of the osteotomous lodge growing to the implant surface (remote osteogenesis) and direct osteogenesis of bone on the surface of the implant (contact osteogenesis). The process is complex and there are a number of factors that affect the formation and maintenance of bone in the peri-implant space. The aim of the present study is to review the literature data on the macroscopic implant factors that affect primary stability and osseointegration
Аннотация. Остеоинтеграцию можно определить как прямую структурно-функциональную связь между костью и поверхностью имплантата. Бессимптомная и жесткая фиксация аллопластического материала в кости имеет решающее значение для стабильности имплантата и долгосрочного успеха имплантации зубов. Связь между имплантатом и окружающей тканью чрезвычайно динамична. Это взаимодействие является основой для формирования новой структуры - интерфейса имплантат-ткань. Процесс остеоинтеграции представляет собой совокупность биологических механизмов, в результате которых происходит формирование кости на стенках остеотомической ложи, прирастающей к поверхности имплантата (дистанционный остеогенез), и непосредственного остеогенеза кости на поверхности имплантата (контактный остеогенез). Это сложный процесс, и существует ряд факторов, влияющих на формирование и сохранение кости в периимплантатном пространстве. Целью настоящего исследования является обзор литературных данных о макроскопических факторах имплантатов, влияющих на первичную стабильность и остеоинтеграцию.
Key words: dental implants, primary stability, osseointegration
Ключевые слова: дентальные имплантаты, первичная стабильность, остеоинтеграция.
Introduction: Treatment with intraosseous dental implants is a modern therapeutic method that achieves complete rehabilitation by fully restoring the patient's masticatory function and aesthetics. Long-term follow-up and accumulated research experience show that the treatment with dental implants is reliable and highly predictable. The success of implant use is associated with the process of osseointegration
The first evidence of osseointegration in intraosseous dental implants was in the 1960s, when Branemark reported a study of bone growth in direct contact with a titanium implant. Branemark defines osseointegration as direct contact between the vital bone and the implant surface without interposition of fibrous connective tissue. [5]
Traditionally, osseointegration has been studied in relation to the mechanical stability of dental implants in bone tissue [2]
Osteointegration is defined as a time-dependent treatment process that achieves clinically
asymptomatic rigid fixation of alloplastic material in bone preserved during functional stress. The histological appearance resembles functional ankylosis without the presence of fibrous or connective tissue between the bone and the implant surface. [61]
This process may be impaired due to insufficient primary stability of the implant, which leads to the appearance of micro movements and the formation of fibrous tissue [4] . A major factor influencing primary stability is bone-implant contact (BIC) [39, 45, 59].
According to Abuhusseini and Col. There are two main factors that influence the process of osseointegration: 1) the design of the implant, which is related to the achievement of primary stability, that is crucial for osseointegration; 2) implant surface.[1]
Material and methods: For the period 1900 -2021 in the available databases (PubMed, BioMedCentral, ScienceDirect, Scopus, Web of Science) a systematic analysis of the studies examining the osseointegration of dental implants was performed.
Results and discussion: The open publications on osseointegration of dental implants are 9 239, using the following keywords in English - osseointegration and dental implants
Macroscopic characteristics of intraosseous implants
The shape, length, diameter of the implant and the geometry of the thread are characteristics relevant to the implant macrodesign.[1] Implant shape
Dental implants are designed to achieve primary mechanical stability and to stimulate bone-implant interaction during osseointegration [20, 28]
Macroscopic design is related to the overall surface of the implant. The larger the contact means that , the more of the implant surface will come into contact with the surrounding biological environment. Macroscopic design also influences the way stress is transmitted under functional load. It is also crucial for the exact correspondence between the implant and the prepared osteotomy cavity, which is a guarantee for tight contact between the two surfaces [52, 54]
The implant configuration affects the initial stability and long-term biomechanical properties of the bone-implant interface, which determines the success or failure of treatment.
The screw- intraosseous osteointegratable implants are the most widely used today.
These implants are made of: Ti (titanium) class 4, which is resistant to corrosion and shows greater strength properties compared to other classes. Ti alloys, mainly Ti6Al4V alloy, are used due to their greater strength and tensile strength than pure Ti. [23]
Intraosal implants differ greatly in the shape of the implant ( conical versus cylindrical). Several characteristics in the design of intraosseous implants affect the primary stability and survival rate, among them are: shape (macro design), size (length and diameter), chemical composition of the surface and topographic characteristics of the implant surface.
A wide variety of systems with different types of shape designs (implant body), thread sizes (pitch and depth) are available on the world market [51]
The most widely used are screw implants with cylindrical and conical in the apical part (tapered) shapes [8] Comparing cylindrical threaded implants with conical threaded implants, Kim et al. [21] Buchter2006, and O, Sullivan [6, 40] found that the primary stability of conical implants is greater than that of cylindrical implants. A number of other authors in their studies have shown that tapered implants show greater primary stability compared to the cylindrical ones, they use MIT-Maximum Insertion Torque, ISQ-implant stability quotient and RFA - Resonance Frequency Analysis to assess this stability. [29, 49, 55] Gehrke et al., 2022 [11] studied the degree of osseointegration in implants of three different shapes (cylindrical tapered implants, conically beveled with healing chambers)) performed histological analysis in experimental animals by monitoring the following parameters: implant-bone contact rate, newly formed bone and osteoid matrix. The authors found
significantly higher levels of the studied values in tapered implants.
In different researches on the influence of implant shape, a number of authors have concluded that tapered implants have better primary stability than cylindrical ones. [43, 44, 57]
Conical implants have greater compression on bone walls than cylindrical [42].
Lozano-Carrascal investigates the influence of implant macrodesign on primary stability, taking into account the results of resonant frequency analysis and placement torque, beveled implants show higher primary stability [26].
Rokn made a similar conclusion, taking into account higher ISQ values for conical implants [42].
Implants with the presence of healing chambers have been developed and tested, which have shown excellent results in terms of improving quality and reducing the time for osseointegration. [12]
It should be noted that the cortical bone is not significantly affected by the shape of the implant . however, the behavior of the trabecular bone is strongly influenced by it. [14]
The design of the implant thread The design of the implant thread affects the implant surface, the distribution of the masticatory load and the primary stability. [18]
The thread pitch is defined as the distance between two adjacent turns and determines the number of these turns per unit length. the smaller the pitch means that there are t more notches along the length of the implant and the larger the contact area. [33]
The smaller thread pitch is associated with a more favorable masticatory pressure distribution. Thread pitch plays a more important role in increasing primary stability in lower density bone. [45]
The depth / height of the thread - the difference in diameter between the outermost and innermost part of the profile, the greater depth means greater contact surface. [34]
Higher threaded profile increases contact surface and allows for greater primary stability in lower density bone. [25, 45]
In 2002 Neugebauer [38] in study related to the influence of thread design on the primary stability, found that in bone with lower density, greater primary stability is applied when using implants with a higher thread height (0.3-0.5 mm), in a bone with a higher density greater primary stability is achieved when placing an implant with a lower thread height (0.1 mm) The shape of the threaded profile (v-shaped / triangular profile , square profile, variable height thread)
In 2004, Geng et al. [13] analyzed four thread configurations: v-thread, small-width thread, 0.24-mm-wide squarevforms thread and 0.36-mm-wide square thread forms, the authors proved that v-thread and large square thread designs (0.36 mm thread width) are most effective for stress distribution in addition to that a thread with a small width (0.1 mm width) should be avoided due to the high concentration of stress in the bone. In an animal study, square-threaded implants
showed greater implant-bone contact compared to v-shaped threadsed implants. [53]
A number of authors confirm that greater implant-bone contact is achieved with a thread with a square profile. [7, 45, 53]
In 2016, Sabeva E, Peev S conducted a study with 200 test specimens of implants placed in 20 3 -D printed simulation models of the lower jaw. They investigated 4 implant designs: cylindrical with a thread pitch of 0.8, cylindrical with a thread pitch of 1.2, conically beveled implants in the apical area, conically beveled in the coronal area and cylindrical in the apical area. 3 lengths - 8mm, 10mm, 12mm and 3 diameters 3.3mm 4.1mm, 4.8mm. The authors found that conical implants have higher primary stability than cylindrical ones with the same other parameters, implants with higher threaded profile demonstrate higher primary stability, increase in implant diameter and length increases the primary stability of intraosseous screw implants. [46]
Continuous research has shown that changes in the shape, length and diameter of implants can affect success [24]
Lenth and diameter
The length and diameter of the implant affect the stress distribution at the bone-implant interface, as well as the primary stability and success rate of treatment. [15]
The length of the implant varies between 6 and 20 millimeters. The most commonly used length is between 8 and 15 millimeters. [48]
Research in dental implantology shows that longer implants guarantee better success and survival, and shorter implants have a statistically lower success rate due to reduced stability, which can be explained by the lower contact surface area between the bones and the implant. [24, 32]
However, short implants are used in areas with reduced bone volume. [27, 32]
In atrophic alveolar bone (bone deficiency), there are anatomical limitations (maxillary sinus, nasal floor, nasopalatine canal, mandibular canal with vascular nerve bundle passing through it) that make it difficult to place a standard implant. [17, 41]
A review of the literature shows that the overall survival of short implants is over 95%. [10, 33]
The use of short dental implants also has its drawbacks. Dismatch between implant length and crown ratio. This has a negative effect on the biomechanical aspects of the chewing process and often leads to impaired or failed osseointegration. In addition, there have been several reports of mandibular fractures associated with the use of short dental implants in atrophic jaws. The use of a short dental implant in the frontal area, where the alveolar bone has undergone significant resorption, will lead to prosthetic restoration with elongated clinical crowns and aesthetically unacceptable appearance. The poorer quality of the bone in the distal parts of the upper jaw affects the primary stability compared to the dense one, the use of short implants is not recommended in these areas. [9]
The use of short dental implants has limited indications
In their research, some authors come to the conclusion that the length of the implant does not significantly affect the stability of the implant. [30, 35] Other authors conclude that the length of the implant has a positive effect on primary stability. [37, 56]
The diameter of the implant usually varies from 3 to 7 millimeters; implants with a smaller diameter are used in narrow bone spaces, mainly in the frontal area of the lower jaw. [32, 48]
In clinical practice, the choice of implant diameter depends on the quantity and quality of the bone in which it will be placed, looking for optimal stability. For example, wider implants allow interaction with more bone. [24]
Ivanoff et al. [19] from animal studies concluded that implants with a larger diameter are more stable in Implant Removal Torque (IRT) and that they may be more successful in clinical conditions because there are more -large contact area with the surrounding bone.
Increasing the diameter of the implant has a beneficial effect on primary stability, mainly in bone with lower density. [38]
Larger diameter implants are used in areas with low bone density - type 4, with insufficient bone height, as well as when replacing non-integrated implants. [3, 22]
The diameter of the implant is more important for the primary stability than its length. [36]
Some authors find a positive correlation between the diameter of cylindrical implants and their primary stability and do not find one between the diameter and the primary stability of tapered implants. [26]
Other authors do not find a link between implant diameter and implant stability. [16]
Merheb et al. investigate the stability of the implant by resonance-frequency analysis, without establishing a significant effect of diameter on the stability. [30, 31]
In recent decades, there has been a significant increase in research and development of new models of dental implants (micro- and macroscopic design). [47, 58]
With the accumulation of knowledge about the biological behavior of materials used for implantation in living tissues, at macrogeometric, microgeometric and even nanogeometric levels.This would accelerate the process of osseointegration of implants, which makes it possible to reduce the time required for rehabilitation treatment. [50, 60]
Osteointegration is a complex process that depends on a number of factors,other than the macro design of the implant. These factors include: implant material, bone quantity and quality, implant surface, surgical technique, implant loading conditions, and not lastly the patient's health condition. Each of these factors must be carefully analyzed and evaluated by the implantologist before implant treatment.
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