KNOW IMMEDIATE IMPLANT LOADING
This video describes the guidelines in order to perform an immediate implant loading case. Protocol on Implants
Introduction (KNOW IMMEDIATE IMPLANT LOADING)
Dental implants have been widely used to retain and support cross-arch fixed partial dentures (Adell et al. 1981; Albrektsson 1993; Albrektsson et al. 1986; Arvidson et al. 1992; Astrand et al. 1996; Branemark et al. 1969; Branemark et al. 1977). It has been advocated that after implant placement, surgical sites should be undisturbed for least for 3 to 6 months to allow uneventful wound healing, thereby enhancing osseointegration between the implant and bone (Adell et al. 1981). The rationale behind this approach is that implant micro-movement caused by functional force around the bone-implant interface during wound healing may induce fibrous tissue formation rather than bone contact, leading to clinical failure (Adell et al. 1981). In addition, coverage of an implant has also been thought to prevent infection and epithelial downgrowth (Branemark et al. 1977; Branemark et al. 1985). Akagawa et al. performed an animal study comparing two types of implants; one was submerged and the other was projecting into oral cavity approximately 9mm (Akagawa et al. 1986). Histological observation showed direct bone apposition to the submerged implants, while the non-submerged implants had connective tissue at the apical portion. The authors concluded that initial exposure/biomechanical stimuli often induced fibrous connective tissue interface between implants and bone. Hence the submerged implants was preferable for the initial rigid fixation. However, certain problems/concerns remain when this 2-stage surgical protocol was used. These include: avoid any prosthesis for a minimal of 2 weeks to promote uneventful healing; loose denture, pain, difficulty in chewing during transitional removable prosthesis wearing period (Schnitman et al. 1997), and the necessity of additional surgery to expose implant fixture. These concerns have commonly caused physiologically, psychologically, or sociologically challenges for patients who underwent implant treatment (Salama et al. 1995). Therefore, focus on loading implant soon after their placement has been attempted and has gained some acceptance among clinicians, but the results are not conclusive.
Animal studies have been conducted to test the feasibility of achieving osseointegration while loaded implant right away. Early studies have shown conflict results. Some reported that load implant immediately jeopardizes osseointegration (Akagawa et al. 1986; Schatzker et al. 1975; Uhthoff 1973) and promotes fibrous tissue encapsulation (Brunski et al. 1979). Others have observed direct bone to implant contact (BIC) when newly designed screw implant as well as coated implant surface were used (Sagara et al. 1993). However, the authors also found more crestal bone loss in the loaded one-stage implant group when compared to 2-stage unloaded control group. It was speculated that the early occlusal loading during healing may account for this observation since early loading may interfere with the ability of new bone being formed to uptake the necrotic bone at the implant/bone interface usually from surgical trauma (Albrektsson et al. 1981) Similar findings were also reported in non-human primates (Lum & Beirne 1986). Later animal data indicated that osseointegration could be accomplished in immediately loaded implants regardless type of surface coating (Lum & Beirnc 1986, Evans et al. 1996, Piattelli et al. 1997a, Corso et al. 1999, Romanos et al. 2001).
In fact, earlier results with immediate implant loading were often unpredictable (Rosenlicht 1993; Schnitman & Shulman 1980). Fibrous encapsulation around implants was a common finding due to variety reasons such as poor implant materials/designs, lack of understanding the mechanical aspect of implant loading and others. (Brunski et al. 1979; Cross et al. 1974; Hodosh et al. 1969; Linkow et al. 1973; Listgarten & Lai 1975; Piliero et al. 1973; Strock & Strock 1939). With the introduction of one-stage implants, improvement in implant designs (e.g., screw shape) and development of roughened implant surfaces (e.g., plasma coated implant, HA coated implants) and better force management/understanding (e.g., cross-arch stability) have all made this concept of immediate implant loading possible. Studies in the area of immediate loading have been proposed and shown encouraging results (Buser et al. 1988; Piattelli et al. 1993; Henry & Rosenberg 1994; Salama et al. 1995; Bijlani & Lozada 1996; Tarnow et al. 1997; Chiapasco et al. 1997; Piattelli et al. 1997a, 1997b, 1998; Randow et al. 1999; Scortecci 1999; Gatti et al. 2000; Ericsson et al. 2000b; Horiuchi et al. 2000; Jaffin et al. 2000; Malo et al. 2000; Ganeles et al. 2001; Colomina 2001; Cooper et al. 2001). However, achievement of predictable outcomes is dependent on certain principles. These principles were largely based on clinical experience rather than scientific-based data. Therefore, the objectives of this article are to 1) critically review and analyze currently available literature in the field of immediate implant loading, and 2) discuss, based on scientific evidence, factors that may influence this treatment modality.
Materials and Methods (KNOW IMMEDIATE IMPLANT LOADING)
A medline search was performed and the most valuable and relevant articles were selected. Studies involving 1-stage surgical placement were included only if the fixtures were immediately or early loaded (within 3 weeks) after placement. Case reports with few samples were only utilized if they presented unique information that was not demonstrated in major retrospective or prospective trials. Only the data from human studies was evaluated and presented. It is the intent of this article to include the most valuable information of each article as well as to critically assess their methodology. In the discussion, data was organized to address factors that had significant support on immediately implant loading. These include surgery, host, implant, and occlusal related factors. A summary from these reviews were then concluded.
High success rates from immediately loaded implants in humans were first documented in the middle 80’s, when the one stage implant protocol gained popularity. Babbush and collaborators reported a cumulative success rate of 88 % on 1739 immediately loaded TPS implants (Babbush et al. 1986). Subsequently, many authors have showed the possibility of loaded implant immediately (Buser et al. 1988; Piattelli et al. 1993; Henry & Rosenberg 1994; Salama et al. 1995; Bijlani & Lozada 1996; Tarnow et al. 1997; Chiapasco et al. 1997; Piattelli et al. 1997a, 1997b, 1998; Randow et al. 1999; Scortecci 1999; Gatti et al. 2000; Ericsson et al. 2000b; Horiuchi et al. 2000; Jaffin et al. 2000; Malo et al. 2000; Ganeles et al. 2001; Colomina 2001). Early implant loaded (within 3 weeks) had also shown to be highly predictable. A prospective multi-center study reported a resultant of 96.2% survival rate of 53 fixtures placed in 47 patients, 12 months after placement (Cooper et al. 2001). However, this article will only discuss the immediately loaded implant studies.
Henry & Rosenberg (1994) reported 2-year clinical results using a single stage surgical protocol in conjunction with controlled immediate loading. They suggested that clinical performance and prognosis of the procedure was comparable to the traditional two-stage method (e.g., allowing time for implant healing without any interference from occlusal contact). Schnitman et al 1997 observed 61 implants placed in 10 patients. Out of these 61 implants, 28 were placed and immediately loaded to support an interim fixed bridge. Eighty-five percent of success rate was reported in immediately loaded implants compared to 100% for submerged unloaded implants. However, it should be noted that 30% of immediately loaded implants were connected with natural teeth and that no more than 3 implants were used to support an interim fixed partial denture. In addition, the force distribution between test and control were also different. Therefore, results of this trial should be interpreted with caution. However, it illustrates that it is possible to achieve long-term success when implants were placed in function even in their earlier stage.
Tarnow et al. (1997) placed minimum of 10 implants with half of them being submerged to load free healing. Subsequently, more implants were loaded immediately in the last four patients. Totally, 69 implants were immediately loaded and 38 were submerged without loading. Almost 97% (104/107) were successfully integrated. One submerged implant failed due to infection that spread from adjacent extraction socket. Two immediately loaded implants were lost when the cemented provisional restoration was tapped off to verify healing. Interestingly, no difference was found between maxillary and mandibular implants.
Bijlani & Lozada (1996) in a retrospective study evaluated the success rate of immediately loaded implants placed in four patients after 3 to 6 years of clinical function. All implants placed and loaded immediately were successfully osseointegrated, according to the criteria described by Albrektsson (1986). It is important to note that patients in this study received complete removable prosthesis in maxilla and soft tissue-supported overdenture in mandible (Bijlani & Lozada 1996). This suggests that the occlusal scheme may be another key factor for a successful outcome with immediately loaded implants. This was later confirmed by Balshi & Wolfinger (1997), who found that 75% of failures in immediately loaded implants occurred in patients with bruxism. In this study, 130 implants were placed in ten patients, 40 being immediately loaded and 90 left submerged according to the second stage protocol. Results after 12-18 months showed a survival rate of 80% for immediately loaded implants, while unloaded implants had an average of 96% success rate.
A multicenter retrospective study was conducted by Chiapasco et al. (1997) on 226 patients with a mean follow up period of 6.4 years (ranged from 2 to 13 years). Totally, 904 immediately loaded implants had been placed between the interforaminal area of the mandibular symphysis (4 implants per patient). Thirty-two patients did not complete the study for unknown reasons. The overall failure rate of immediately loading implants was very small (3.1%). Randow et al. (1999) further compared the oral rehabilitation of edentulous mandibles with fixed implant prostheses using either a 1-stage immediate loading or a 2-stage unloaded protocol. For the unloaded cases, dentures were not used for the first 10 days and a relined of original denture was placed in function after this period. Results showed no differences between the 2 groups examined after 18 months. The survival rate for both groups was 100%. Scortecci et al. (1999) placed 783 titanium implants (627 laterally inserted disk implants, with or without 156 axially inserted structure implants). Implants were evaluated using Periotest® and torque testing at 20 N-cm. They found 98% of immediately loaded implants were considered osseointegrated after 6 to 48 months. The authors attributed their high long-term success to the unique implant design, which allow better stress distribution to ensure long-term success.
Gatti et al. (2000) evaluated long-term results of immediately loaded implant-retained overdentures supported by 4 TPS screw implants. Overdentures were supported by 4 implants and bar clips were immediately placed. A cumulative survival rate of 96% was reported in 19 patients who were followed for 25 months. Chiapasco et al. (2001) compared the success rate of immediately loaded versus delayed loaded implants in 20 patients with implant-retained mandibular overdentures and demonstrated similar success rate, 97.5% for both groups. Another study utilizing Brånemark fixtures have also obtained a high successful rate (98.3%) in edentulous mandibles (Chow et al. 2001). Similar success rate was also achieved in a newly protocol for immediately loaded implant treatment (Branemark et al. 1999). In this study, 150 implants were placed in 50 patients. The proposed guidelines involve prefabricated components and surgical guides, elimination of the prosthetic impression procedure and placement of a permanent bridge on the day of implant placement. Results from these studies clearly suggest that implant immediate loading could achieve equal success rate as those found in delayed or unloaded implants.
Few studies have been focused on immediate loading implants for single tooth replacement (Chaushu et al. 2001; Cooper et al. 2001; Ericsson et al. 2000a; Gomes et al. 1998; Malo et al. 2000). Gomes et al. (1998) placed hydroxyapatite (HA) coated implant and loaded immediately with a provisional crown. Clinically, the implants showed no mobility and remained in function for the duration of the study. However, it should be noted that the restoration was removed from any centric and lateral occlusal contacts. Malo et al. (2000) investigated 94 Branemark implants that were immediately loaded. This retrospective study indicated a cumulative survival rate of 96% (6 months to 4 years). Ericsson et al. (2000) reported the failure of 2 out of 14 (14%) immediately loaded single implants versus no failure in single implant placed in 2-stage protocol (8 out of 8). Implants were loaded via temporary crowns within 24 hours. More recently, Chaushu et al. (2001) compared immediately loaded implants placed in fresh extraction sites to that of healed sites in 26 patients. The survival rates were 82% and 100% respectively. It implies that immediate loading of single-tooth implants placed in fresh extraction sites may carry a risk of failure in 1/5 of fixtures. On the contrary, Jo et al. (2001) demonstrated a 98.9% success rate for implants placed into fresh extraction sockets and immediately loaded. The authors attributed this favorable result to the system used, an expandable implant. It is understandable that the occlusal scheme favors the placement of single immediately loading for tooth replacement compared to fully edentulous situations, since adjacent natural teeth may protect implant prosthesis from occlusal trauma during early phases of healing. However, the hypothesis remains to be proven.
The majority of immediately implant loading studies reported similar success rate when compared to traditional 2-stage approach (Buser et al. 1988; Piattelli et al. 1993; Henry & Rosenberg 1994; Salama et al. 1995; Bijlani & Lozada 1996; Tarnow et al. 1997; Chiapasco et al. 1997; Randow et al. 1999; Scortecci 1999; Gatti et al. 2000; Horiuchi et al. 2000; Jaffin et al. 2000; Malo et al. 2000; Ganeles et al. 2001; Colomina 2001; Cooper et al. 2001). Nonetheless, these findings do not imply that submerged wound healing is no longer necessary. Future studies are needed to identify the appropriate indications that may suit for either approach. Data from the current available literature already suggest that several factors may influence the results of immediate implant loading. These could be divided into the following four categories: surgery, host, implant, and occlusion related factors. Surgical factors consist of primary implant stability and surgical technique. Host factors compose of quality and quantity of cortical and trabecular bone, wound healing, and modeling/remodeling activity. Implant factors include designs, surface textures, and dimensions of the implant. Occlusal factors involve quality and quantity of force and prosthetic design. These factors are further discussed in the following paragraphs.
Surgery Related Factors:
Primary implant stability (KNOW IMMEDIATE IMPLANT LOADING)
Of all factors involved, primary stability seems to be the most important determining factor on immediately implant loading. Functional loading placed on an immobile implant is an essential ingredient to achieve osseointegration (Roberts et al. 1984). If an implant is placed in the soft spongy bone with poor initial stability, it often results in the formation of connective tissue encapsulation, similar to the pseudoarthrosis observed in a unstabilized fracture site (Albrektsson & Sennerby 1991; Aspenberg et al. 1992; Brunski et al. 1979; Hansson et al. 1983; Roberts 1993; Schroeder et al. 1981; Spector 1988; Szmukler-Moncler et al. 1998). Micromovements of more than 100 mm are sufficient to jeopardize healing with direct bone-to-implant contact (Brunski 1993). Observation that was also reported by Szmukler-Moncler et al. (1998) who indicated that micromotions at the bone-implant interface beyond 150 mm resulted in fibrous encapsulation instead of osseointegration. It can be further speculated that these movements would be detrimental in cases with immediate implant loading.
Some authors hypothesized that immediately loaded implants must engage dense cortical bone both at apical and crestal aspect to ensure extra stability (Chiapasco et al. 1997; Schnitman et al. 1997). However, a retrospective study reported that bicortically anchored implant in the maxilla failed almost 4 times more than monocortically stabilized implants (Ivanoff et al. 2000). It is also important to note that the assessment of mono- versus bi-cortical stabilization in this study was performed on pantographs and most of the causes of failure were fractures (~80%). Prosthetic misfit and unfavorable occlusal/stress factors might have also influenced the outcomes and, therefore, the data should be interpreted with caution. Biomechanically, the concept of bicortical placement is certainly valuable since higher surface of the fixture is engaged into compact bone. Further prospective studies need to be conducted to evaluate this hypothesis.
In summary, when primary stability is achieved and properly prosthetic treatment plan is followed, immediate functional implant loading is a feasible concept. However, if the primary fixture stability cannot be achieved or is questionable, it is strongly recommended to follow a conventional treatment protocol including an adequate healing time before loading.
Surgical technique (KNOW IMMEDIATE IMPLANT LOADING)
Gentle surgical placement is also a key element for implant success regardless of the applied treatment protocol. Excessive surgical trauma and thermal injury may lead to osteonecrosis and result in fibrous encapsulation of the implant (Satomi et al. 1988). Heat generated during drilling without adequate cooling is associated with bone damage (Eriksson et al. 1982; Eriksson et al. 1984a; Eriksson & Albrektsson 1984; Eriksson et al. 1984b). It has been shown that a temperature over 47ºC for 1 min causes “heat necrosis” in the bone (Eriksson & Albrektsson 1983). Without irrigation, drill temperatures above 100ºC are reached within seconds during the osteotomy preparation, and consistent temperatures above 47ºC are measured several millimeters away from the implant osteotomy (Yacker & Klein 1996). In addition, it is critical for the success of endosseous root-form implants that adequate load is placed on the drill during preparation of osteotomies. It has been demonstrated that independently increasing either the speed or the load caused an increase in temperature in bone. Interestingly, increasing both the speed and the load together allowed for more efficient cutting with no significant increase in temperature (Brisman 1996). Other factors related to heat generated into bone include: amount of bone prepared (Eriksson et al. 1984a), drill sharpness and design (Eriksson et al. 1984b; Matthews & Hirsch 1972; Wiggins & Malkin 1976), depth of the osteotomy (Babbush & Shimura 1993; Haider et al. 1993) and variation in cortical thickness (Eriksson & Albrektsson 1984; Hobkirk & Rusiniak 1977). It is shown that implant surgery generates microfractures in the surrounding bone, specially when press-fitting is intended. These fractures heal according to the following cascade: angiogenesis, osteoprogenitor cell migration, woven bone scaffold formation, deposition of parallel-fibered or lamellar bone, secondary bone remodeling (Schenk & Hunziker 1994).
When a proper surgical/prosthodontic technique is followed, the crestal bone loss around immediately loaded implants seems to be in the normal range when compared to a submerged protocol (Bränemark et al. 1999; Ericsson et al. 2000a; Ericsson et al. 2000b; Randow et al. 1999). Crestal bone loss was found to be 0.14 mm in immediately loaded implants versus 0.07 mm in delayed approach in a period between 6 to 18 months (Ericsson et al. 2000a). Cooper et al. (2001) reported a mean change in marginal bone level of 0.4 mm at 12 months in single early loaded implants. Chow et al. (2001) later showed a mean marginal bone loss as 0.6 mm in a prospective study up to 30 months of immediately loaded implants. It is important to note that operator experience in implant dentistry may also indirectly influence the outcome of the treatment. Previous studies have reported an implant failure rate that was almost twice that of more experienced clinicians for who had placed fewer than 50 implants (Lambert et al. 1997; Morris et al. 1997).
Bone quality & quantity (KNOW IMMEDIATE IMPLANT LOADING)
Histological data on immediately loaded implants have demonstrated not only a direct bone to implant contact, but also a favorable bone quality around the fixtures (Henry et al. 1997; Piattelli et al. 1998; Piattelli et al. 1997a; Piattelli et al. 1993; Romanos et al. 2001). Although favorable histological data has been documented, clinical determination of successful immediately loaded implant remains challenge. Clinically, host bone density play an important role in determining the predictability of the immediate implant loading success. An implant placed in compact dense bone is more likely to ensure initial stability and, hence, better able to sustain such immediate forces. Resonance frequency analysis indicated that implants are as stable at time of placement as when measured at 3-4 months post-surgery, when placed into dense bone (Friberg et al. 1999). These results support the concept of direct loading of implants when inserted in the mandibular interforaminal regions. Therefore, this homologous, dense bone type may present several advantages for immediate loading implant dentistry. The cortical lamellar bone may heal with little interim woven bone formation, ensuring good bone strength while healing next to an endosteal implant (Roberts 1993; Roberts et al. 1987). In addition, its fine porosity (≤ 10%) favorers better mechanical interlocking compared to soft cancellous, which reaches 80-95% porosity (Schenk & Hunziker 1994). In fact, studies have showed less dense bone may cause higher implant failure, even when a second stage protocol is followed (Branemark et al. 1985; DeAngelis 1970; Engquist et al. 1988; Jaffin & Berman 1991; Schnitman et al. 1988). Jaffin & Berman (1991) evaluated retrospectively the success rate of 1,054 implants placed in different bone densities. Of implants placed in type I-III bone, only 3% of fixtures were lost; of the 10% of the fixtures placed in type IV bone with a thin cortex and poor medullary strength due to low trabecular density, 35% failed. Therefore, due to its favorable mechanical properties, a majority of studies involving premature/early loading were conducted in anterior mandible, where a dense bone is usually found (Ganeles et al. 2001; Lefkove & Beals 1990; Piattelli et al. 1998; Roberts et al. 1984). A review of literature demonstrated that 72% of cases placed in this region are either in D1 or D2 quality bone (Misch 1999a).
As mentioned earlier, fine trabecular bone presents the most arduous endeavor to obtain rigid fixation, no matter which implant is used. For the reasons just mentioned before, this type of bone may be unsuitable for immediate loading implant techniques. Interestingly, few human reports have shown similar predictability regardless anatomic location (Salama et al. 1995, Tarnow et al. 1997, Horiuchi et al. 2000). Levine et al. (1998) placed 10 implants in maxilla (3 loaded immediately and 7 followed 2-stage protocol) and showed all implants osseointegrated after 2 years. Horiuchi et al. (2000) also reported no difference in the success rate between arches in immediately loading implants in 14 patients. In this case series, 44 implants were placed in maxilla and 96 in mandible, providing a successful rate of 95.5% and 97.9%, respectively. A multi-center prospective study involving single and partial fixed prosthesis in 93 patients with 142 implants also demonstrated no difference in success rate between maxilla and mandible (Buchs et al. 2001). In this trial, a temporary prosthesis was constructed from non-heat generating material and temporary cemented into place. Within the limited available information, it appears that primary stability, more than the arch (anatomical) location may be the fundamental requirement for immediate implant loading technique. On the other hand, there has been no unanimous protocol to be followed regarding bone density and number of implants, or type of prosthesis to be used in immediate loading cases. In addition, majority of implants placed in different jaw locations/type of bone will not require identical healing periods. For this reason, clinicians should utilize this protocol mainly in areas where dense bone is located and primary stability could be achieved. Studies on softer/cancellous bone have been scarce, therefore; further studies are needed to understand how immediately loaded predictability function in this type of anatomic location.
Wound healing (KNOW IMMEDIATE IMPLANT LOADING)
Metabolic diseases that directly affect bone metabolism such as osteoporosis/osteopenia or hyperparathyroidism may significantly influence on implant wound healing. Osteoporosis, a pathology process leading to an absolute decrease in bone mass, has risen rapidly in the population, and poses a major public health problem (Riggs & Melton 1986). Although animal research has commonly shown impairment of bone formation around implants in osteoporotic specimens (Hara et al. 1999; Lugero et al. 2000; Mori et al. 1997; Yamazaki et al. 1999), human trials have demonstrated that dental implant placement in patients diagnosed with osteoporosis may be successful over a period of many years if a extended healing period is advocated (Becker et al. 2000; Dao et al. 1993; Friberg et al. 2001; Fujimoto et al. 1996). So far, no attempt has been made in loading implant immediately in patients who are diagnosed with systemic diseases such as diabetes and hyperparathyroidism as well as smokers. Similar situation was also true for patients who have undergone radiation therapy. Therefore, it is strongly suggested to follow the standard 2-stage protocol or even utilize longer periods of healing in patients diagnosed with those disorders. The same standard guidelines are suggested to be used in smokers or patients under radiation therapy on oral cavity, until future research proves otherwise. Prior to surgery, a medical consultation and throughout explanation to patients of possible risks should be mandatory.
Under optimal conditions (atraumatic surgery), it has been demonstrated that only after 6 weeks of implant placement lamellar bone was present at or near the implant surface (Roberts et al. 1984). The surrounding bone heals according to the cascade mentioned earlier: angiogenesis, osteprogenitor cell migration, woven bone scaffold formation, deposition of parallel-fibered or lamellar bone and secondary bone remodeling (Schenk & Hunziker 1994). Although there is no quantitative data for the early healing process in humans, it is reasonable to assume that loading of implants immediately after their placement wound involve certain biological risks, since the initial healing process is still outgoing. Interestingly, histological animal data for implants immediately loaded has actually shown no adverse effects in either the osseointegration process or the bone morphology around the fixtures (Henry et al. 1997; Piattelli et al. 1998; Piattelli et al. 1997a; Piattelli et al. 1993; Romanos et al. 2001). In fact, same data have demonstrated that early load increased BIC and allowed a faster remodeling process when compared to unloaded controls (Piattelli et al. 1998; Piattelli et al. 1997a; Piattelli et al. 1993). This concept of mechanical stimulation of bone around implants was also evaluated and confirmed by Rubin and McLeod. In this animal study, data demonstrated that brief exposure to extremely low-amplitude mechanical strains could enhance the biologic fixation of cementless implants (Rubin & McLeod 1994). In conclusion, it can be speculated that immediate loading of dental implants may accelerate bone formation, but it is also imperative to state that primary stability is essential for this process to occur.
Implant Related Factors
Implant design/configuration (KNOW IMMEDIATE IMPLANT LOADING)
The implant configuration has long been considered as an essential requirement for implant success. As a general concept, the screw implant design develops higher mechanical retention as well as greater ability to transfer compressive forces (Lefkove & Beals 1990; Randow et al. 1999; Skalak 1985; Wolfe & Hobkirk 1989). The screw design not only minimizes micromotion of the implant but also improves the initial stability, the principal requirement for immediate loading success. Additionally, the thread increases surface area (Misch 1999c). Studies have shown absence of fibrous tissues at the interface of screw-shaped implants, even if they are loaded immediately after insertion (Skalak 1985; Wolfe & Hobkirk 1989). Hence, due to its mechanical retention properties, it is generally recommended to use threaded type implants for immediate loading cases. It is also important to note that favorable clinical outcome with cylinder-type implants have been documented when a delayed loading regimen was employed (Wheeler 1996). However, cylinder-type implant would appear contraindicated for immediate or early loading regimens due to lower of primary stability and less resistance to vertical movement and shear stress.
Implant surface coating (KNOW IMMEDIATE IMPLANT LOADING)
Rough implant surfaces render a significant increase of bone to implant contact (Buser et al. 1991; Trisi et al. 1999; Wennerberg et al. 1995). The shear strength of implants with a rough surface showed to be about five times as high as that of implants with a smooth surface (Li et al. 1999). In addition, greater forces are required to remove implants with a rougher surface compared to implants with a smoother surface (Wennerberg et al. 1995). Despite these advantages, animal and human studies involving immediate loading placement have tended to show no significant differences in implant success when surface coating types are analyzed (Corso et al. 1999; Evans et al. 1996; Piattelli et al. 1997b; Piattelli et al. 1993). Human histological data reported by Piatelli et al (1993, 1997b) showed that a mature, compact, cortical bone was formed around immediately loaded implant, with 60-90% BIC. Similar results was also documented in 2 immediately loaded osseotite implants retrieved after 4 months (Testori et al. 2001). Although the critical BIC to guarantee implant success has not been defined, these findings are in agreement with the amount of BIC reported in most studies where a 2-stage protocol was utilized. Table 1, 2 and 3 lists current human studies in field of the immediate loading.
The reason for clinical success regardless implant surface coating may be due to the type of bone utilized in majority of human trials. As mentioned before, most of studies have focused on to using the anterior mandible, where the densest bone is located. It seems to suggest that the initial mechanical interlocking between threads and dense bone may overcome the beneficial properties that each coating type provides. In fact, peak insertion torque and resonance frequency values demonstrated similar implant primary stability regardless surface type when placed in type 2 and 3 bone (O’Sullivan et al. 2000). The same parameters showed that thread design was more of a determinant than surface characteristics for primary stability into softer type IV bone (O’Sullivan et al. 2000). Future studies still should be conducted in regions with softer bone to evaluate if implant surfaces play a relevant impact in loading immediate implant success.
Implant length (KNOW IMMEDIATE IMPLANT LOADING)
The implant length may also influence the outcome of immediate implant loading. For every 3 mm increase in length, the surface area of cylinder-shaped implant increases an average of 20% to 30% (Misch 1999b). Study has reported 50% failure rate with immediately loading for implant length ≤ 10 mm (Schnitman et al. 1997). The majority of studies have suggested that implants should be ³ 10 mm long to ensure high success rate (Buser et al. 1988; Horiuchi et al. 2000; Lefkove & Beals 1990; Tarnow et al. 1997). Some authors even speculate that it is beneficial to use implant ³ 14mm in length and ≥ 4 mm in diameter for immediate loading (Chiapasco et al. 1997). Nonetheless, data from these studies is based mainly on clinical experience and limited human research. Therefore, the critical length and diameter of immediate loaded implants remains to be determined.
Occlusion Related Factors
Quality and quantity of force (KNOW IMMEDIATE IMPLANT LOADING)
Controlling functional forces is one of the ingredients for obtaining success of immediate implant loading. Sagara et al. (1993) found more crestal bone loss in the loaded one-stage implant group when compared to 2-stage unloaded control group (Sagara et al. 1993). It was suggested that the early occlusal loading during healing may account for this observation, since early loading may interfere with the ability of new bone being formed to replace the necrotic bone at the implant/bone interface resulted from surgical trauma (Albrektsson et al. 1981). Vertical forces applied during function are less detrimental to implant stability rather than oblique or horizontal forces. Therefore, bruxism/occlusal overload has been considered as possible contraindication for immediate implant loading due to higher implant failure rates (Balshi & Wolfinger 1997; Colomina 2001; Jaffin et al. 2000). However, Ganeles et al. (2001) reported only 1 failure due to bruxism out of 161 immediately loaded implants. Unfortunately, there is not enough scientific information to correlate parafunction habits to immediate loading failure. Colomina (2001) reported 97% of success rate in immediate loaded implant, however failed implants (2 out of 61) were attributed to occlusal pathology and oral muscular tension. They further speculate that occlusal load control is essential for maintaining success. Future studies in this area are certainly needed to understand the influence of occlusion related factors. Nevertheless, it is often suggested that patients with parafunctional habits (e.g. bruxism) should be excluded or at least well informed about potential risks involved when immediate loaded cases are being planned.
Prosthetic design (KNOW IMMEDIATE IMPLANT LOADING)
Primary stability can be enhanced when cross arch implant splinting is performed. Therefore, this prosthetic approach is recommended in immediate implant loading (Ledermann 1979, 1983; Salama et al. 1995; Spiekermann et al. 1995; Tarnow et al. 1997; Randow et al 1999). Glantz et al. have demonstrated that most favorable loading conditions were achieved via rigid fixed devices (Glantz et al. 1984a,b). Tarnow et al. (1997) used a cast metal frame enforced provisional restoration to ensure optimal stability and a high success rate for immediately loading implants. The authors further suggested that the temporary prosthesis, once inserted, should not be peaked or removed during the healing period to avoid any unnecessary movement.
Several authors have also proposed of U-shaped curved bar with rigid connection of 2-4 interforaminal implants with the presumption that it reduces any movement or non-axial load on implants (Ledermann 1979; 1983; Salama et al. 1995; Spiekermann et al. 1995; Tarnow et al. 1997). Others have avoided using cantilevers in the fixed implant provisional restorations since they increase by 2-fold of load to the terminal fixture (Brunski 1993; Skalak 1985; Tarnow et al. 1997) with many others adopted this concept (Randow et al. 1999, Ericsson et al. 2000b, Colomina 2001). Randow et al demonstrated similar predictability when compared to the traditional 2-stage surgical protocol. In this study, a permanent fixed supraconstruction with bilateral cantilevers corresponding to 2 premolar units were fabricated. This study, however, is based only on 18-month observation period. A “coversion prosthesis” as provisional appliance, modifying from the preexisting prosthesis was also attempted (Colomina 2001). In the case of a misfit, the prosthesis was separated into two or more parts that were again rigidly connected with resin. All the prostheses had two distal extensions from 5 to 15 mm, according to clinical necessities. Ganeles et al. (2001) placed and restored 161 immediately loaded implants with different prosthesis designs (laboratory processed, screw-retained, laboratory processed cemented, office processed, screw-retained and office-processed cemented) and reported no differences among these designs. When reviewing the literature, it seems to suggest that cross-arch splinting as well as potential load and movement caused by prosthesis removal should be avoided in immediately loaded implant cases. Careful occlusal analysis, such as assessment of parafunctional habits and distribution of occlusal support by remaining teeth, is also essential when loading regimen for implant is considered.
Conclusion (KNOW IMMEDIATE IMPLANT LOADING)
The level of predictability and high success of current implant therapy has provided reasons for reassessing long adopted surgical and prosthetic guidelines. With the trend of shortening treatment time and reducing patient discomfort/inconvenience, immediate loading implants has re-emerged as an alternate approach. This treatment approach has been studied and shown promising and predictable results. However, it is important to note that a meticulous case selection is still needed to integrate this treatment into daily practice. Certain criteria and guidelines have to be followed to avoid any unnecessary failure. Regular maintenance may be another factor to ensure long-term success of immediate loaded implants. In addition, factors that may influence the outcome of this approach (e.g., surgery, host, implant and occlusion related factors) should be considered and analyzed prior to initiation of treatment. Further studies are definitely needed to explore other possible influential factors. Following are the conclusions drawn from current available information:
KNOW IMMEDIATE IMPLANT LOADING
- Immediate implant loading achieved a similar success rate as those reported in the delayed 2-stage approach
- Primary implant stability is a key factor to consider before attempting of immediate implant loading
- Surgery, host, implant and occlusion-related factors may influence the outcomes of immediate implant loading
- Studies are needed to understand the possibility of immediate implant loading in patients who are diabetes, osteoportics and smokers as well as other systemic compromised diseases
- Long term, prospective studies are still needed to evaluate other potential determining factors on this technique.
Critical review of immediate implant loading.
KNOW IMMEDIATE IMPLANT LOADING