The long-term outcomes of dental implants are influenced by a variety of factors, all of which play critical roles in their stability, functionality, and esthetic appeal. This review focuses on several key characteristics of dental implants that impact their success overtime: dimensional, morphologic, material, osseointegrative, and connective/prosthetic characteristics. This article synthesizes current literature to analyze how these factors influence the long-term success of dental implants, emphasizing the need for a comprehensive approach in implant selection and placement.
Key points
- •
Short and narrow implants show similar outcomes to long and wide implants, except in areas with particularly soft bone type.
- •
The Long-term effect of implant macro-design remaims ulclear. Roughened implants generally show less marginal bone loss than machined, especially in the maxilla.
- •
Zirconia implants show promising integration and esthetic properties. However, concerns about surface treatment affecting long-term strength need further study.
- •
The connection between an implant and abutment plays a critical role in the stability and longevity of dental implants.
- •
Platform switching has been shown to significantly reduce crestal bone loss.
Introduction
The long-term outcomes of dental implants are influenced by numerous factors that interplay to ensure their stability, functionality, and esthetic appeal overtime. Central to this success are the specific characteristics of the implants themselves, which significantly impact several critical interfaces within the oral environment. The biologic interface, involving the implant’s integration with surrounding bone and soft tissues, is crucial for ensuring stability through successful osseointegration. Equally important is the biomechanical interface, which deals with how the implant interacts with restorative systems and the occlusal system, thus ensuring proper load distribution and mechanical stability during functions such as chewing. The esthetic interface also plays a significant role, as dental implants must restore the natural appearance of the oral cavity, addressing issues of tooth loss and maintaining the overall harmony and functionality of the mouth. Therefore, achieving long-term success with dental implants requires meticulous attention to these factors, ensuring that each element is optimized to support the implant’s performance and patient satisfaction.
The characteristics of dental implants can be categorized into several groups:
- •
Dimensional characteristics : Pertaining to the length and diameter of the implants.
- •
Morphologic characteristics : Concerning the design and shape of the implants.
- •
Material characteristics : Involving the strength, elasticity, and composition of the implants.
- •
Osseointegrative characteristics : Related to the surface structure and its ability to integrate with bone.
- •
Connective/prosthetic characteristics : Focu-sing on the connection between the implants and the prosthetic systems attached to them.
The article aims to review current literature on the various characteristics of dental implants and to analyze how these factors influence the long-term outcomes of dental implants.
Dimensional characteristics
Under the category of dimensional characteristics, considerations may be separated into those concerning the length of the implants and those concerning the diameter. Initially, it is important to discuss the expectations from the implants. Conceptually, implants are intended to replace the roots of missing teeth and support the crown portion, which refers to dental restoration. Historically, and following the principles of the ante law, it was expected that implants would match the length and diameter of natural dental roots. The assumption was that implants with greater length and diameter, offering a larger surface area, would provide better bony support both during the initial phase of osseointegration and in the Long-term.
However, it has become clear over the years that the behavior of implants supporting dental restorations is fundamentally different from that of natural teeth. Consequently, the parameters and principles used for tooth-based restorations may not apply to implant-based restorations.
The attachment of natural teeth to bone is mediated by periodontal tissue, whereas implants form an ankylosed connection directly to the bone. This difference may be significant when considering the dimensional requirements of implant systems. Additionally, Frost’s law indicates that bone density around ankylosed elements is greater and increases overtime in response to bone strain.
These principles challenge the initial hypothesis that larger and wider implants are inherently superior.
Implant Length
The criteria for determining the necessary length of an implant to support a dental restoration have evolved numerous times over the past 60 years. In 1990, vanSteenberghe and colleagues defined implants shorter than 10 mm in the lower jaw and 13 mm in the upper jaw were considered risky for success. In 2003, in a prospective multicenter clinical trial, Weng and colleagues showed that 60% of the failed implants were “short implant” (≤10 mm), with a cumulative success rate at 6 years of 89.0%, compared to 93.1% for longer implants. Similar results were also demonstrated by Geckili and colleagues who also stated that “Ten millimeters is the minimal length for predictable success, and any implant less than 10 mm is considered short.” ,
To address the issue of insufficient bone for supporting dental implants of the necessary length, various surgical techniques and specialized materials have been developed for bone regeneration. These include, among others, autogenous bone transfer, guided bone regeneration, distraction osteogenesis, and sinus lift and augmentation techniques.
Overtime, advancements in implant development, surface treatment, and surgical and reconstructive techniques have made short implants a viable alternative to longer implants in areas with limited bone availability.
In 2016, at the European Association of Dental Implantologists consensus meeting, short implants were defined as 8 mm or less, and ultrashort implants were defined as 6 mm or less. They recommended that the use of short or diameter-reduced implants in sites with reduced bone volume can be a reliable treatment option, given the risks associated with the use of standard-dimension implants in combination with augmentation procedures.
Numerous studies have explored the effectiveness, safety, and short-term and long-term success and survival rates of short and ultrashort implants in comparison to the “standard” length implants.
In a systematic review on the long-term effectiveness of extra-short (≤6 mm) dental implants, Ravida and colleagues included 19 studies of 704 patients receiving 1404 extra-short implants (904–6 mm, 290–5 mm, 210–4 mm), with a mean follow-up of 5 years. The mean survival rate was 94.1% (90% in the maxilla, 96% in the mandible), and the marginal bone changes ranged from a gain of 0.3 mm to a maximum bone loss of 0.53 mm.
In an umbrella review and meta-analysis of success outcomes of short implants placed in pristine bone compared to regular dental implants installed in augmented bone in the atrophic posterior mandible, Sáenz-Ravello and colleagues showed that short implants (4–8.5 mm) performed similarly to standard-length implants (over 8.5 mm) over a period of up to 8 years. It was also shown that short implants had a higher survival rate after 1 year compared to standard implants (SIs) placed in augmented bone, with fewer biologic complications. Additionally, the marginal bone loss (MBL) around short implants was lower at 3, 5, and 8 years compared to SIs. It was noted that patients favored short implants over SIs in augmented bone.
In a systematic review and meta-analysis, Cruz and colleagues compared short implants (4–8.5 mm) versus longer implants (10–15 mm) with maxillary sinus lift. The meta-analysis included 11 articles of 420 patients and 911 implants (437 short implants and 474 long implants) with a mean follow-up period of 9 to 36 months. The study showed no significant difference between the short and long implants in survival rate (short implants—2.05%, long implants—1.89%) and in MBL (short implants—0.86 mm, long implants—0.99 mm). Higher rates of biologic complications for the long implants with maxillary sinus augmentation were observed, whereas a higher prosthetic complication rate for short implants was noted.
One other concern regarding the use of short implants is the feasibility to use them for cases of immediate loading. In a meta-analysis, Wu and colleagues evaluated the failure risk of short dental implants (<10 mm) under immediate loading as compared to SIs. The meta-analysis included 17 studies, with a total of 2461 dental implants, including 756 short dental implants under immediate loading, 1289 standard dental implants under immediate loading, and 416 short dental implants under early or delayed loading. The mean follow-up periods ranged from 12 to 105 months. It was concluded that short implants did not have a significantly increased failure risk under immediate loading (4.92%) compared with SIs (3.36%; odds ratio [OR]: 1.38, 95% confidence interval: 0.67–2.84, P =.997, fixed model).
Finite element studies have demonstrated that crestal bone loss in the posterior maxillary area is correlated with stress distributions at the bone-implant interface. These stress distributions, in turn, depend on the type of loading, mechanical properties of the implant and bone, implant dimensions, bone quality and quantity, and the characteristics of the bone-implant interface. ,
Additionally, stress distributions at the bone-implant interface in the posterior maxilla are directly influenced by the height of the maxillary bone, bone quality, and implant diameter. Increasing the bone-to-implant-contact (BIC), either by increasing the implant length or width, has been shown to reduce stress distribution.
In a finite element analysis study, Demenko and colleagues evaluated the influence of available bone height and implant dimensions on load-carrying capacity of short dental implants placed in edentulous posterior maxilla with poor bone quality. They showed that maximum stresses in cortical and cancellous bone were reduced by 47% to 49% and 42% to 45% respectively when using wide short implants compared to narrow short implants. These findings indicate that wide short implants utilize available bone thickness more effectively than narrow implants (NIs), due to a more favorable distribution of stresses. They suggested that the optimal diameter for a 7.0 mm length implant in the posterior maxilla was 5.0 mm or greater, and that the stresses of these implants were lower than those for 4.1 x 10 mm implants in type III bone, and similar to those in type IV bone.
In conclusion : Short implants can be a viable option for vertical bone deficiency, with higher success rates in the mandible compared to the maxilla. For type III or IV soft bone, it is advisable to use short implants with a wide diameter.
Implant Diameter
To the best of our knowledge, there is no established consensus in the literature that provides clear criteria for differentiating implants based on their diameter. Several authors have proposed categorizing implants into 3 groups: NIs—less than 3.75 mm, SIs—3.75 to 5 mm, and wide implants (WIs)—greater than 5 mm. ,
The rationale for selecting an implant of a particular diameter involves several factors, including the volume and type of bone available at the implantation site, the distance between adjacent teeth, and the type of tooth or dentition to be replaced. Additionally, the implant diameter may be influenced by whether the implant is placed immediately into fresh sockets after extraction or into healed bone sites. Furthermore, if an initially planned implant diameter does not provide sufficient primary stability after placement, it can be replaced with a wider implant to enhance stability.
Implants must be placed at least 2 mm away from adjacent teeth and 3 mm from neighboring implants, which is crucial for implant diameter planning. Also, at least 1.5 mm of bone thickness is desired around the implant, which also affects the choice of implant diameter.
Increasing the diameter in a 3 mm implant by 1 mm increases the surface area by 35% over the same length. In addition, the removal torque forces of WI are higher than for NI. These factors positively impact the initial stability and long-term resistance of implants to occlusal forces, potentially favoring the use of the widest possible implants.
However, WI may not be the best option in certain areas, like molar extraction sites, where the bone could be compromised due to significant compression. Small and Tarnow also reported that placement of WI (>5 mm) can apply excessive pressure on the buccal bone, leading to bone resorption and gingival recession.
Additionally, WIs have been suggested to generate heat during the drilling process, which could potentially harm the bone.
NI may be indicated for areas with limited horizontal ridge width or mesiodistal prosthetic space. This may be due to space collapse in the anterior region, congenitally missing incisors and reduced interdental space following orthodontic therapy.
The use of NI may prevent the need for bone grafting and hence reduce postoperative discomfort and healing time. Nevertheless, NIs have reduced BIC, increased risk of implant fracture due to lowered mechanical properties, and an increased risk of implant overloading. It has been shown that a 3.3 mm diameter NI possesses 25% less fracture resistance compared to SI of similar design. Reducing the diameter not only decreases mechanical stability but also elevates the risk of implant fracture and potential overload.
In a retrospective cohort, Anitua and colleagues evaluated narrow-diameter implants (2.5–3 mm) as definitive implants in different clinical situations and showed survival rates of 98.9% and 98.0% for the implant and the subject-based analyses, respectively, with a mean follow-up period of 48 months. The mean MBL was 1.26 mm (SD 0.51).
In a subsequent retrospective study, Anitua and colleagues evaluated the long-term outcomes of 2 piece 2.5 mm narrow-diameter implants supporting fixed prostheses and showed survival rate of 97.3% for implants and 92.0% for prostheses at a mean follow-up period of 6.5 ± 3.2 years. The mean MBL was 0.70 ± 0.55 mm.
In a systematic review, Javed and colleagues evaluated the role of implant diameter on long-term survival of dental implants placed in posterior maxilla. Nineteen studies of 5225 implants installed in 2236 patients with a follow-up ranging between 5 and 15 years. The authors did not find significant differences between the various diameters and concluded that the role of implant diameter on long-term survival of dental implants placed in posterior maxilla is only secondary to other characteristics such as surgical protocol, primary stability, and presurgical and postsurgical oral hygiene maintenance visits.
Mangano and colleagues, Oliveira and colleagues, Manso and colleagues, and Krennmair and colleagues also reported on comparable long-term outcomes with different diameter implants.
In contrast, in a meta-analysis based on prospective clinical trials, Ortega-Oller and colleagues evaluated the influence of implant diameter on its survival. They included 16 studies with a total of 3291 implants placed in 1470 patients. Seven of the studies used NIs (<3.3 mm), and the remaining used SIs (>3.3 mm), with an average follow-up time of 3.26 and 4.04 years, respectively. The failure rates were 1.21% (NI) and 0.34% (SI), with NI having 3.92 times greater failure rates than SI. NIs that were loaded less than 3 months after installation had 4.42 times greater failure rates than NIs that were loaded greater than 3 months after installation. It was proposed that this phenomenon was due to the decreased BIC and the lower bone quality at the implantation sites, which required a longer healing period. The authors attributed the higher failure rates to the fact that NIs are often placed in compromised clinical scenarios or are subjected to higher risks of implant body fractures and prosthetic complications.
Another interesting finding was that NI placed in the mandible had 5 times greater failure rates that NI placed in the maxilla. This was explained both by the different bone types in the maxilla and mandible, but even more by the different types of restorations supported by the NI. While in the maxilla the majority of the NI supported single crowns, mainly in the lateral incisors area, in the mandible, these implants were often used as to support overdenture and were subjected to heavier occlusal forces.
In conclusion : As implant diameter increases, so does the BIC, theoretically enhancing initial stability. However, anatomic, technical, and rehabilitation constraints often prevent the use of wider implants. While some studies indicate similar success and survival rates between narrow and SIs, others report decreased success rates and increased MBL, particularly with implants in the mandible or those supporting prostheses.
Morphologic characteristics
The shape of dental implants is a pivotal factor that significantly influences their long-term success. The primary shapes used in dental implantology are cylindrical and tapered, which have been further divided into hybrid shapes, each offering unique benefits and considerations for various clinical scenarios:
- •
Apical cylindrical and crestal conical
- •
Cylindrical with apical taper
- •
Crestal cylindrical and apical conical
- •
Conical design with crestal back taper
In a narrative review on the effect of implant microgeometry on the primary stability, Heimes and colleagues discussed several implant design characteristics.
Tapered implants are mainly secured through lateral and vertical bone compression, whereas cylindrical implants rely on static friction along the implant axis for stability. The relatively easier installation of tapered implants, along with fewer drilling steps, potentially shorter healing times, and reduced surgical trauma, has increased their popularity among clinicians.
Other advantages of the tapered design include a better load distribution higher primary stability and improved osseointegration properties. Due to the superior primary stability, they are also better for immediate implantation cases. On the other hand, taper implants may necessitate a more invasive surgical protocol.
However, the clinical significance of implant shape on long-term success remains unclear. According to the 2018 Group 1 ITI consensus, both tapered and cylindrical implants showed comparable success rates and MBL after 3 years.
Most implant systems employ a thread design to enhance BIC, increase the implant surface area, and improve primary stability. Key features of these thread systems include thread depth, width, pitch, face angle, and helix angle. These features collectively enhance primary stability.
The most common thread designs in dental implants include standard V-shape, spiral, buttress, reverse buttress, and square shapes. Each thread design plays a role in transferring loads from the implant to the surrounding bone, impacting both the magnitude and direction of the forces applied to adjacent tissues. This load transfer influences the mechanical stimuli distribution at the implant-bone interface, which in turn affects the primary and secondary stability of the implants. Misch and colleagues found that reverse buttress and square threads primarily transfer axial forces as compressive forces to the neighboring bone. In contrast, buttress and V-shaped threads transfer forces as a mix of compressive and shear forces. Huang and colleagues showed that the buttress thread type offers superior primary stability compared to other thread shapes. Kreve and colleagues found that implants with larger depth V-shaped threads and smaller pitches (averaging 0.6–0.8 mm) exhibit higher BIC.
The thread depth measures the extent to which the coils extend from the main body of the implant. Greater thread depth increases surface area and improves load distribution. This can be beneficial in softer bone and under high occlusal forces, enhancing primary stability. However, deeper threads may reduce insertion accuracy and impede adequate vascular supply to the bone at the thread’s root. Therefore, it is advisable to pre-tap threads with significant depth to avoid excessive compressive stress on the surrounding bone, especially in dense bone areas.
The thread width determines how the implant is guided when inserted and largely depends on the thread’s shape. Utilizing a substantial thread width, especially in cases of non-cutting threads, such as square-shaped threads, often necessitates pre-cutting the bone cavity, facilitating easier implant placement and reducing insertion torque. Conversely, self-tapping implants tend to increase primary stability, particularly in softer bone or fresh extraction sockets. Multiple cutting threads can also enhance primary stability in low-density bone. Square threads are advantageous for immediate implant loading. An optimal thread width is between 0.18 and 0.3 mm, with a thread depth of 0.34 to 0.5 mm.
It remains uncertain whether threads located at the crest contribute to better load distribution and the preservation of crestal bone, or to its degradation. In a systematic review, Lovatto and colleagues found that these micro-threads protect both hard and soft tissue. However, in a prospective, randomized, clinically controlled, multicenter study, Rothamel D and colleagues found no significant differences between machined tissue-level implants and roughened neck bone-level implants in terms of peri-implant bone loss, peri-implantitis rate, implant survival rate, and the condition of hard and soft tissues.
Double-threaded and triple-threaded implants are designed for quicker installment and provide enhanced initial primary stability. Nevertheless, their higher lead angle may require increased torque during placement, potentially causing damage to bone tissue, especially in dense bone.
In a nonrandomized retrospective, double-blind study, Ormianer and colleagues evaluated the effect of the thread design on the long-term MBL. The study included 1361 implants with a mean follow-up of 107 months (minimum follow-up of 82 months) and concluded that implants with a larger pitch, deeper apical threads, and a narrower implant core demonstrated favorable long-term bone loss results.
Unfortunately, there is a significant lack of studies examining the impact of macro-design on the long-term outcomes of dental implants. Therefore, further research is essential to determine whether any particular design outperforms others.
In conclusion : Tapered implants provide superior primary stability and enhanced osseointegration. Buttress thread types offer excellent primary stability and are ideal for immediate loading. Implants with deeper V-shaped threads and smaller pitches achieve higher BIC. The necessity of micro-threads at the implant neck remains uncertain, and there is a notable lack of research on the long-term effects of implant macro-design.
Osseointegrative characteristics
It has been reported that implant morphology and surface characteristics influence primary stability and long-term survival of dental implants. Studies have shown that increased surface due to micro-roughness enhances bone-to-implant contact early after implant placement. Alterations in the surface roughness of implants influence the response of cells and tissue by increasing the surface area of the implant adjacent to bone and thereby improving cell attachment. Implant surfaces have been classified on different criteria, such as roughness, texture, and orientation of irregularities. Implant surface roughness has been directly associated with increased osteogenic response and degree of implant primary stability attained.
To improve the clinical performances of dental implants, chemical and topographic surface modifications have been introduced. Implant surface modifications aim at accelerating the rate and improving the quality of osseointegration compared to a machined implant surface. The modification methods can be divided into subtractive and additive processes. Basically, the subtractive methods remove material from the implant surface, whereas the additive methods add material. Results revealed that the bone on the acid-etched surface is harder and stiffer than that on machined surfaces. After 4 weeks, the hardness of the acid-etched surface-associated bone reached the level of cortical bone, whereas the bone hardness around the machined surface was equivalent to that of the trabecular bone. The European Federation of Periodontology scrutinized the available scientific evidence in 2008 stated that there was scarce information, and that only short-term studies not exceeding 3 years follow-up were available at that time. Nevertheless, it was acknowledged that surface-modified implants lead to the preservation of marginal bone without any clinically significant superiority for any particular implant surface or design. Jimbo’s systematic review examined 71 articles reporting on bone loss after at least 5 years of follow-up. Clinical implant survival was attributed to the implant surface. Maxillary moderately rough implants were found to have significantly higher long-term survival rates than maxillary minimally rough implants but this difference was not observed in the mandible. MBL occurred around all the implants in the first year but stabilized thereafter, indicating the absence of progressive bone loss. A comparison of implant systems with different implant topography revealed that some implants were associated with statistically significantly greater mean MBL, mainly seen during the initial bone remodeling phase. Titanium oxide blasted (TiOblast) and sanblasted, large grit, acid ethced (SLA) surface implants yielded less MBL than machined surfaces or TiUnite surface implants. However, all implant systems demonstrated no further progressive bone loss from the end of year 1 to year 5, indicative of stable peri-implant bone levels, and low peri-implantitis incidence. A review by Albrektsson summarized 10 papers reporting on the 10 year clinical outcome with surface-modified implants treated by sandblasting, grit blasting, acid etching, or combined treatments revealed that the survival was above 95%. Furthermore, fewer than 5% were diagnosed with purulent infection or peri-implantitis. One should keep in mind that these excellent results were often realized in academic development centers with often very strict inclusion criteria regarding patient selection and with treatment protocols performed by highly qualified surgeons. Additionally, a drawback in all these analyses is the fact that implants do not only differ in surface topography but also in implant design, prosthetic connection, and loading protocol, let alone that the baseline for bone loss calculation is often non-standardized. Hence, it is difficult to conclude to what extent surface topography alone is responsible for the encountered bone loss.
In conclusion : Bone at roughened surfaces reaches cortical bone hardness faster than at machined surfaces. No particular implant surface treatment shows clinical superiority. Long-term, maxillary moderately rough implants have higher survival rates than minimally rough ones, a difference not seen in the mandible. Roughened implants show less MBL compared to machined.
Material characteristics
Implant materials can be classified based on the type of material used and the biologic response they elicit when implanted. In the present era, due to the extensive research work and advancements in the field of biomaterials available for dental implants, newer materials came into use such as Zirconia, Roxolid, and surface-modified titanium (Ti) implants.
Implant material with a modulus of elasticity comparable to bone (18 GPa) must be selected to ensure more uniform distribution of stress and to minimize the relative movement at implant bone interface.
An implant material should have high tensile and compressive strength to prevent fractures and improve functional stability.
An implant material should have high yield and fatigue strengths to prevent brittle fracture under cyclic loading.
Increase in hardness decreases the incidence of wear of implant material and increase in toughness prevents fracture of the implants.
Metals employed for fabrication of endosseous implants included Ti, Ti alloys, stainless steel, cobalt–chromium alloys, gold alloys, and tantalum.
Nevertheless, the low success rates of some metals (gold, stainless steel, cobalt–chromium) have made them obsolete and replaced by newer ones. Ti and its alloys have become the metals of choice for dental implants. However, prosthetic components of the implants are still made from gold alloys, stainless steel, and cobalt–chromium and nickel–chromium alloys. Ti has a good record of being used successfully as an implant material and this success with Ti implants is credited to its excellent biocompatibility due to the formation of stable oxide layer on its surface. The commercially pure Ti (cpTi) is classified into 4 grades that differ in their oxygen content. Grade 4 is having the most (0.4%) and grade 1 the least (0.18%) oxygen content. The mechanical differences that exist between the different grades of cpTi is primarily because of the contaminants that are present in minute quantities. Ti alloys exist in 3 forms: alpha, beta, and alpha-beta. These types originate when pure Ti is heated with aluminum (Al) and vandium (Va) in certain concentrations and cooled. The alloys most commonly used for dental implants are of the alpha-beta variety, which most commonly contains 6% Al and 4% Va (Ti 6 Al 4V).
Ceramics such as alumina, hydroxyapatite, beta-tricalcium phosphate, bioglass, carbon–silicon, and zirconia have been developed as implant materials. Ceramics were used for surgical implant devices because of their inert behavior and good strength and physical properties such as minimum thermal and electrical conductivity. Certain properties of ceramics like low ductility and brittleness have limited the use of ceramics. Ceramics such as alumina and zirconia proved to be beneficial implant material due to its superior esthetics and excellent biocompatibility, which led to it being a viable choice for patients with preference for metal-free treatment.
Zirconia has received great interest as a dental material. Zirconia has a high flexural strength, favorable fracture strength, and a suitable Young’s modulus. Reportedly, the survival rates for zirconia implants cumulatively after 1 year of loading is estimated to be between 74% and 98%, and success rates after 6 to 12 months of function range between 79.6% and 91.6%. A meta-review evaluating the literature on clinical outcomes of zirconia implants estimated that MBL for zirconia ranged between 0.7 and 0.98 mm in the first year after loading. Many systematic reviews agreed that zirconia had a clinically acceptable MBL that was similar to Ti implants ; however, one study in particular slightly disfavored zirconia and reported higher bone loss.
Zirconia being a substrate with high hardness is difficult to roughen. Some of the modification techniques on zirconia implant surfaces discussed in literature are mechanical grinding, nanotechnology surface modifications using calcium phosphate nanolayers, bioactive ceramic coating with calcium phosphate, bisphosphonate or collagen, sandblasting, and acid etching. Recently, carbon dioxide lasers have also been proven to produce surface alterations on zirconia. Although surface modifications on zirconia appear to positively affect osseointegration comparable to that of Ti, conflicting data suggest that they tend to create small defects on the implant that induces areas of stress concentration, and therefore, any form of surface modifications such as grinding and sand blasting or even minor scratches/notches has the potential to reduce the strength of zirconia.
Ti zirconium (TiZi) alloys with 13% to 17% zirconium (TiZr1317) have better mechanical attributes, such as increased elongation and fatigue strength, than pure Ti. Growth of osteoblasts that are essential for osseointegration is not prevented by TiZi. Straumann developed TiZi implants (Roxolid), composed of 15% zirconium and 85% Ti, that have shown to be 50% stronger than pure Ti. Their fatigue strength was found to be up to 21% greater than that of comparable Ti implants. In a systematic review and meta-analysis, Altuna and colleagues evaluated 9 clinical studies using Ti–Zr implants, with a total of 922 implants NI (3.3 mm) placed in 607 patients with a follow-up period ranged from 3 to 36 months. The mean survival and success rates were 98.4% and 97.8% at 1 year after implant placement and 97.7% and 97.3% at 2 years. The mean MBL was 0.36 ± 0.06 at 1 year and 0.41 ± 0.09 after 2 years. The authors concluded that the comparable success rates and the improved material strength may make this alloy more favorable for NIs. Nevertheless, more long-term research is needed.
In conclusion : Materials for dental implants should match the modulus of elasticity of bone and possess high tensile, compressive, yield, and fatigue strengths, as well as high hardness and toughness. The most commonly used alloy for dental implant is grade 4 alpha-beta with 6% Al and 4% Va (Ti 6 Al 4V). Zirconia implants have demonstrated promising integration rates and MBL comparable to Ti implants, along with superior esthetic results. However, concerns about surface treatment and its impact on long-term implant strength remain, necessitating further research.
Connective/prosthetic characteristics
The implant–abutment connection must be sufficiently rigid to endure strong occlusal forces. The connection between an abutment and an implant can be simply classified as a butt joint or a friction-fit joint, based on the way these components are assembled. In terms of the role of the abutment screw, the butt joint is a “screw-retained only connection”, while the friction-fit joint is a “friction and screw-retained connection” (FSR connection). In a butt joint, 2 right-angled flat surfaces mate, leaving a small space between the mating parts. By contrast, a friction-fit joint leaves no space between the mating parts since the parts are forced together. The Brånemark implant, the first commercialized screw-shaped endosseous dental implant, had an external and hexagon-mediated butt joint connection. Similar types of implants have been manufactured and sold in the dental market worldwide. The friction-fit type can limit the movement of an abutment by friction generated at the interface, which may enhance the stability of the soft tissue seal and prevent marginal bone resorption. Formation or lack of formation of a soft tissue seal may depend on the material attached to it. One study evaluated the stability of the soft tissue seal using 4 materials: gold, dental porcelain, Ti, and Al oxide. No soft tissue seal could form using gold and dental porcelain, and marginal bone resorption occurred; however, with Ti and Al oxide, the soft tissue seal formed correctly, and no marginal bone was resorbed. Nowadays, the main materials used for abutments are Ti and zirconia. A recent systematic review concluded that zirconia abutments are more advantageous as they cause less discoloration of the soft tissue than Ti abutments. In addition, a previous meta-analytic study described that zirconia abutments showed less bacterial adhesion, less plaque retention, and less soft tissue inflammation than Ti. In terms of the soft tissue seal, however, there is abundant evidence that there are no significant differences between the 2 materials ; furthermore, zirconia has lower fracture strength than Ti. In general, the abutment of implant systems with FSR connections is secured by a 111 conical connection to the inside of the implant, which converts the masticatory force into strain, stimulating the alveolar bone. The occlusal load allows the abutment to slightly descend and press the implant inner wall. When the implant region in contact with the marginal bone is expanded, strain occurs in the alveolar bone in the area, stimulating the alveolar bone, activating osteoblasts, and increasing the quantity and quality of alveolar bone.
Albrektsson and colleagues found that the installation of 2 piece implants healing in a submerged modality resulted in a crestal bone loss of 1.5 to 2.0 mm after 1 year of loading. Clinicians, researchers, and implant companies have, thus, dedicated time to finding ways to control the crestal bone loss that occurs after abutment connection.
The platform switching (PLS) technique, a technique in which an abutment that is one size smaller than the implant platform is placed, shifts the perimeter of the implant-abutment junction (IAJ) inward toward the central axis of the implant. Lazzara and Porter have hypothesized that shifting the IAJ inward also shifts the inflammatory cell infiltrate inward and away from the crestal bone. Hürzeler and colleagues compared crestal bone loss around platform-switched and nonplatform-switched implants. They found that the mean crestal bone loss was 0.22 mm in platform-switched implants and 2.02 mm in nonplatform-switched implants. They also concluded that reduction of the abutment of 0.45 mm on each side is sufficient to avoid peri-implant bone loss. Another study by Cappiello and colleagues found that vertical bone loss for the platform-switched cases varied between 0.6 and 1.2 mm (mean: 0.95 ± 0.32 mm), while for the cases without PLS, the bone loss was between 1.3 and 2.1 mm (mean: 1.67 ± 0.37 mm). An average of 1 to 2 mm of bone loss occurs in nonplatform-switched implants, while minimal bone loss occurs in platform-switched implants. Thus, all preliminary evidences in literature suggest that the anticipated bone loss that occurs around 2 stage hexed implants may be reduced or eliminated when implants are restored with smaller diameter abutments.
In conclusion: The connection between an implant and abutment plays a critical role in the stability and longevity of dental implants, with different designs like the butt joint and friction-fit joint offering distinct advantages. The use of materials like Ti and zirconia for abutments also influences outcomes, particularly regarding soft tissue seal and bone resorption. Techniques such as PLS have been shown to significantly reduce crestal bone loss, further improving implant success.
Summary
In conclusion, the long-term success of dental implants is influenced by various implant-associated factors. Dimensional characteristics, including implant length and diameter, impact primary stability and affect the long-term outcomes of dental implants. Short implants have proven to be effective in cases of vertical bone deficiency, particularly in the mandible. For the maxilla, especially in bone type III and IV areas, wider implants have been offered in such cases. Morphologic characteristics, such as the shape and thread design of implants, significantly affect load distribution and BIC, with tapered implants and specific thread designs enhancing stability and osseointegration. Osseointegrative characteristics, including the surface roughness and treatment of implants, influence the speed and quality of osseointegration, with roughened surfaces typically yielding better results compared to machined surfaces. Material characteristics, such as the choice of metals and ceramics, impact the mechanical properties and biocompatibility of implants, with Ti and zirconia being prominent choices due to their favorable clinical performance. Finally, connective and prosthetic characteristics, such as the implant-abutment connection, are vital for maintaining the stability of the soft tissue seal and minimizing MBL. PLS techniques have demonstrated promise in reducing peri-implant bone loss. Overall, a comprehensive approach that considers all these factors is essential for optimizing the long-term success of dental implants.
Disclosure
The authors have nothing to declare.
References
Stay updated, free dental videos. Join our Telegram channel
VIDEdental - Online dental courses
