Update on immediate implant loading: A review of the literature

HERRERA-BRIONES FJ, ROMERO-OLID MN, VALLECILLO-CAPILLA M. UPDATE ON IMMEDIATE IMPLANT LOADING: A REVIEW OF THE LITERATURE. MED ORAL 2004;974-81.

ABSTRACT

The treatment of totally or partially edentulous patients with osseointegrated implants is an increasing part of daily dental practice. The greater aesthetic and functional demands made by these patients have created a constant pressure to reduce the waiting time before implants are loaded. In some cases, however, a shortening of the waiting period may compromise the osseointegration of the fixtures.
The present review aims to inform the clinician about the continuing controversy on this issue. Data from the reviewed studies allow comparisons to be made between the different success rates obtained after immediate implant loading, offering a more objective basis for our advice to patients on this type of treatment.
According to our review, the type and quality of the bone and the surface of the implant are the factors that determine the selection of patients who can undergo the premature loading of implants.

Key words: Dental implants, immediate loading, single-stage technique.

INTRODUCTION

From the beginnings of implantology, attempts have been made to reduce to the minimum the time required before implants can be loaded and become functional, their main purpose.

The ideal time to load implants depends on the time needed for the osseointegration of the fixtures. This delay can be influenced by the type and surface of the implant, the quality of the bone, the use of bone grafts and other variables, such as the general health of the patient.

In 1977, Bränemark et al. (1) published the first long-term study of buccal implantation, considering the goal of implant placement to be the creation of a good support for the prosthesis. For these authors, a prime requirement for achieving osseointegration was to leave the implants load-free for three to six months, making implant treatment very lengthy. They described these long waiting periods as necessary to avoid the formation of fibrous tissue around the implant, which would prevent direct bone apposition and, therefore, osseointegration. However, 80% of their patients presented advanced reabsorption, 10% extreme reabsorption and the remaining 10% moderate reabsorption. There was not only a small amount of bone but it was also of poor quality, offering unfavourable conditions for the mechanical retention of fixations and providing little primary stability. These limitations accounted for the need to delay loading for such long periods.

In 1979, Lederman (2) pioneered immediate loading through the use of implants with titanium plasma-sprayed (TPS) surface and bicortical anchoring. The implants were placed and loaded on the same day. In an 81-day follow-up of 476 implants in 138 patients, the implant survival rate was 91.2%. Forty-two implants were extracted, 34 during the first year (81% of the failures).

Misch (3) established different osseointegration time periods according to the quality of the bone: four months for type D1 bone, four months of osseointegration plus two of progressive loading for type D2, and 10 and 12 months of osseointegration, respectively, for types D3 and D4.

Attempts continue to be made to shorten these time periods, through the production of new implant surfaces, the development of new techniques such as PRP and the implementation of recently gained knowledge.

OBJECTIVE

This review of the relevant literature aims to present and discuss the current state of knowledge on the immediate loading of implants in Oral Surgery.

DISCUSSION

The initial research on the immediate loading of implants was followed by several studies that reported variable success rates for the long-term outcome of the implants (Table 1). Besides Brånemark and Lederman (see above), other authors underlined the importance of evaluating the time period required before loading the implants.

In 1983, Schroeder et al. (4) placed 53 ITI® cylindrical implants (Institute Straumann AG, Waldenburg, Switzerland) with TPS surface. A 48-month follow-up study showed a success rate of 98.1%. At the same time, three patients underwent the immediate loading of four ITI® cylindrical implants, and no losses were recorded after a 17-month follow-up.

In 1985, Thomas & Cook (5) studied the effect of 12 variables, and observed that bone quality was the factor with greatest significant effect on the osseointegration of the implants; the best outcomes were observed on rough surfaces.

Babbush et al. (6) (1986) also used implants with TPS surface in the anterior region of the mandible, loading the implants after a period of 2-3 days and obtaining a success rate of 96.1%.

However, Schnitman et al. (7) (1990), using Bränemark® implants (Nobel Biocare AB, Goteborg, Sweden), obtained worse outcomes with immediate compared with delayed loading. They concluded, in agreement with Thomas & Cook, that the quality of the bone was more important than implant length in determining implant survival.

Lum et al. (8) (1991) compared outcomes between mechanised (uncoated) and hydroxylapatite (HA)-coated titanium implants. Direct apposition of bone on implant was observed in all uncoated implants subjected to delayed loading, but when these were loaded immediately, connective tissue fibres could be seen around the implant, more suggestive of a fibrointegration. In contrast, osseointegration was observed for all HA-coated implants, whether loaded immediately or after a delay.

This research was followed by several comparative studies on the performance of implants with different surfaces. Dietrich et al. (9) (1993) compared the immediate loading of TPS implants with the delayed loading of IMZ® implants (Friatec, Mannheim, Germany). After a 6-month follow-up, the success rates of the two surfaces were similar (92.5% for TPS and 99.3% for IMZ®), while after five years, TPS implants showed a success rate of 86.3% versus 94.6% for IMZ®.

Akagawa et al. (10) (1993) observed no clear differences in clinical outcomes between unloaded and early loaded implants with a zirconia surface.

Henry & Rosenberg (11) (1994) used Bränemark® implants with bicortical anchorage. After leaving a time period of 6-7 weeks before loading the implants, a success rate of 100% was obtained.

Salama et al. (12) (1994) found no difference in success rate between the randomly applied immediate and delayed loading of 3i® (3i, Palm Beach Gardens, Florida) or Bränemark® implants.

In a work of some interest, above all because of the large sample size, Chiapasco et al. (13) (1997) studied the immediate loading of a wide variety of implant types, and found no relationship between the loss of implants and the type of fixation placed.

Tarnow et al. (14) (1997) evaluated the immediate loading of implants with provisional restorations, using TPS, ITI® type F, NLS® (Friatec, Mannheim, Germany), Ha-Ti® ( Matthys Dental, Bettlanch, Switzerland), Bränemark®, 3i® and Astra® (Astra Tech AB, Mölndal, Sweden) systems, among others. These authors concluded that immediate loading may be a viable treatment option.

In contrast, Balshi and Wolfinger (15) (1997) concluded that the premature loading of implants might have a negative impact on their survival. They found no relationship between the loss of implants and the amount of bone, localisation of implants or type of antagonist. However, they detected a relationship with the quality of the bone, and there were no losses of implants on type II bone, according to the classification of Lekholm & Zarb (16).
Other authors such as Piattelli et al. (17) (1997) studied the apposition of bone on the implant, and reported a favourable contact area (60-70% bone contact) after both immediate and delayed loading of implants.

In an experiment using dogs, Henry et al. (18) (1997) subjected mechanized implants to immediate loading and reported a good clinical and radiological evolution, with no losses.

Klokkevold et al. (19) (1997) reported better outcomes using Osseotite‚ (Implant Innovations, Palm Beach Gardens, Florida) implants (acid-etched with the last 3 mm mechanized) compared with using implants with mechanized surfaces.

In another comparison between implant surfaces, Buser et al. (20) (1998) placed implants in the mandibles of miniature pigs and found that a significantly greater degree of torque was required to remove implants with SLA surface compared with Osseotite‚ implants.

Cochran et al. (21) (1998) also compared SLA and TPS surfaces, obtaining greater bone formation in short rest periods with the SLA compared with the TPS surface.

Collaert & Bruyn (22) (1998) subjected 170 implants to immediate loading and 70 to delayed loading and reported that the latter had a greater success rate.

In a histomorphometric study of TPS implants subjected to immediate loading, Lederman et al. (23) (1998) demonstrated the direct apposition of bone on 70-80% of the surface of the implants.

Another histomorphometric study was performed by Buser et al. (24) (1999), who compared between implants with SLA, TPS and mechanised surfaces, testing the degree of osseointegration by the torque required to remove them. The torque values were higher for the SLA versus TPS surface at 4 weeks, although the difference did not reach statistical significance, whereas at 8 and 12 weeks the results were similar. However, all SLA and TPS torque values were much higher than those for the mechanised surface. The study confirmed that the roughness of the surface had a significant influence on the osseointegration. The greater osseointegration at 4 weeks with the SLA surface allows a reduction in the loading times.
In contrast, a study by Coallert & Bruyn, Nicolopoulus (25) (1999) reported no statistically significant differences between immediate and delayed loading, although the success tended to be greater after the latter.

Scortecci (26) (1999) studied the immediate loading of implants with bicortical anchorage. This clinical study demonstrated that bicortical anchorage and the placement of a rigid prosthesis allows the immediate loading of implants, with a predictable outcome.

In the same way, Zubery et al. (27) (1999) obtained success with immediate loading. They used pure titanium Modular Transitional Implants® (MTI; Dentatus AB, Hägersten, Sweden) to support provisional prostheses. They concluded that the success was mainly influenced by the quality of the bone density and the control over the loading applied during the first moments of the healing stage.

Randow et al. (28) (1999) utilised Bränemark® implants with bicortical anchorage and obtained the same success rates for immediate and delayed loading. They observed that the loss of bone at the level of the first turns of the thread of the implants was greater in those subjected to delayed versus immediate loading.

Horiuchi et al. (29) (2000) also studied the immediate loading of Bränemark® implants and suggested it was as predictable as delayed loading in the placement of overdentures, both in the maxilla and mandible.

Calvo et al. (30) (2000) found that the apposition of the bone on the implant surface was produced more quickly with treated implants than with mechanised ones. They observed that the number of implants placed, their length (>10 mm) and distribution, and the type of rigid connection are the critical factors to take into account in deciding on the immediately loading of implants. Biomechanically, implants that are to be immediately loaded should be stable and resistant to macromovements in order to ensure a good osseointegration.
In the same line, Gatti et al. (31) (2000) found no differences in success rates between the immediate and delayed loading of ITI® implants in the mandible.

In common with many of the authors cited in the present review, Jo et al. (32) (2001) concluded that the main factor influencing the success of immediate loading is the primary stability of the implants at the time of the loading.

Pi-Urgell & Vericat-Queralt (33) (2002) used the Novum® system (Nobel Biocare AB, Goteborg, Sweden) to place three mandibular fixations loaded after 0-10 days with a screwed fixed prosthesis and achieved a success rate of 92%.

Reviewing the scientific articles in the literature shows how the waiting periods for loading implants have changed and evolved according to the clinical case, the surgical approach, and, especially, according to the amount and quality of bone and the type of implant surface.

Future studies should determine more precisely the influence of these parameters, in order to have real knowledge of the exact period before loading according to the type of implant used and the type of bone in the jaw, also considering the early loading option as a viable alternative treatment.

CONCLUSIONS

* In the studies reviewed, the outcomes tend to be more favourable for implants that are loaded after a period of osseointegration, although the difference in success rates between the immediate and delayed loading of implants do not reach statistical significance.

* The only parameter that appears to influence the success of immediate loading is the quality of the bone, which it is recommended should be type II (Lekholm & Zarb (16), 1985). Neither the length, the localication nor the antagonist of the implant has any significant influence.

* If account is taken of the quality of the bone and of the surface, bicortical anchorage and primary stability of the implant, we can in some cases adopt the immediate loading approach in implantology.

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