Controversias en Cirugía Oral y Maxilofacial: Parte I

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Immediate loading of dental implants
Carga inmediata en implantes dentales

 

C. Concejo Cútoli, N. Montesdeoca García

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Abstract: The protocol for conventional loading in one or two surgical stages has been evaluated over the last 30 years under all the possible clinical conditions. By comparison, immediate loading is a relatively new protocol that requires strict clinical evaluation. We conducted a search of the literature published concerning clinical trials on immediate loading according to the different therapeutic options that could be considered. Comparable results were found for both loading strategies in edentulous mandibles. For treatment involving an immediate prosthesis for totally edentulous mandibles, partial and single tooth restorations, patients have to be selected adequately and provisional prostheses have to be designed conservatively. In order to completely confirm the safety of the technique, double-blind, simple, randomized clinical trials have to be carried out with a sufficient number of patients and proper followups that compare precise clinical situations with a provisional prosthesis that has a specific occlusion pattern. Key words: Immediate loading; Dental implants.

Resumen: El protocolo de carga convencional en una o dos fases quirúrgicas ha sido evaluado durante los últimos 30 años bajo todas las condiciones clínicas posibles. En comparación, la carga inmediata es un protocolo relativamente nuevo que necesita de una estricta evaluación clínica. Realizamos una búsqueda bibliográfica sobre los ensayos clínicos publicados de carga inmediata en función de las diferentes opciones terapéuticas que se pueden plantear. Se hallaron resultados comparables para las dos estrategias de carga en mandíbulas edéntulas. Para el tratamiento con prótesis inmediata de maxilares totalmente edéntulos, restauraciones parciales e unitarias es todavía necesaria una selección adecuada de pacientes y un diseño conservador de la prótesis provisional. La necesidad de ensayos clínicos sencillos aleatorizados de doble ciego, con suficiente número de pacientes y adecuado seguimiento, que comparen una determinada situación clínica con un patrón oclusal de la prótesis provisional bien definido, son imprescindibles para acabar de confirmar la seguridad de la técnica. Palabras clave: Carga inmediata; Implantes dentales.

Recibido: 03.10.2005

Aceptado: 17.10.2005

 

 

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1 Cirujano Oral y Maxilofacial, Jefe de Servicio.
2 Médico Adjunto.
Servicio de Cirugía Oral y Maxilofacial. Clínica Universitaria.
Universidad de Navarra. Pamplona. España

Correspondencia:
Dr. Carlos Concejo Cútoli.
Departamento de Cirugía Oral y Maxilofacial.
Clínica Universitaria. Universidad de Navarra
Avda. Pío XII, 36, 31008 Pamplona, España
Email: cconcejo@unav.es

 

Introduction

Dental implants are now part of a routine and predictable technique, and they are today the therapeutic standard according to which teeth are replaced in adults. An osseointegrated oral implant is anchored directly into bone, however, if there is movement, a soft-tissue interface can encapsulate the implant leading to failure.¹

The classical protocol established by Brånemark is currently under debate. During the last 15 years various authors have confirmed the successful² integration of dental implants in a single surgical stage, thus eliminating the need for exposing the implant in a second surgical stage. This resulted in improved patient comfort, and mature soft tissue was obtained before making the prosthesis.

The improvement in implant surfaces led to conventional loading times being reduced and the success rate was comparable to that of the standard protocol. Implants with SLA surfaces (ITI Dental Implant System, Institut Straumann, Waldenburg, Switzerland) have been successfully loaded at six weeks.³

In 1979 Lederman,⁴ was the first to introduce the concept of immediate loading with titanium plasma-sprayed coatings, and he obtained a global survival rate of 91.2% after a follow-up of 81 months. But it was not until 1990 when Schnitman,⁵ published the first series of patients that it was suggested that implants could be loaded immediately in the mandibles of selected patients, and that the survival rate was comparable with that of the standard protocol.

Histology behind immediate loading

The period with the greatest risk for implants is between the second and fourth week after placement. During this period primary stability decreases temporarily. The mechanical stability of the implant achieved by means of screwing it to the bone begins to diminish because the osteoclasts begin the process of bone resorption. The formation of new bone, during which the osteoblasts make new bone contact, is not sufficiently advanced to provide the implant with strong secondary stability. Resonance frequency analysis studies have shown that implants with good initial stability maintained this three to four months after attachment.⁶ Implants with low stability values after the first or second month of immediate loading have a high risk of failing.⁷

A certain degree of micromovement is beneficial for stimulating the osteoblasts. Bone responds favorably to compressive loads and experimental studies found bone-titanium contact of 60 to 80% on implant surfaces that had been loaded immediately.⁸ However, preventing micromovement is critical for avoiding the formation of fibrous tissue around the implant, and this should not be above 50 to 100 µm. Movement ranges above 150 µm can jeopardize osseointegration. ⁹

Primary stability

The stability of the implant after insertion is the most important factor influencing successful osseointegration. Primary stability of the implants is initially determined by bone density, trabecular bone structure, surgical technique, by the number and design of the implants used, and their distribution in the dental arch. Later this is helped by a correct occlusal design to control the masticatory forces, an absence of extensions, and the firm union of all implants by the provisional prosthesis.

The density and trabecular structure is as important as the bone marrow cellularity that will house the implants.

Primary stability quantification

In order to evaluate immediate loading, a quantitative method is needed for measuring implant stability. An objective intraoperative assessment of implant stability is crucial for making decisions with regard to immediate loading. From a practical point of view there are various techniques that will give an idea of the clinical stability of the implant before loading, although to date none of these have been formally accepted as a reference.

Johansson y Strid,¹¹ developed the cutting torque measurements during the preparation of the low-power osteotomy (OsseoCar; Nobel Biocare, Göteborg, Sweden), which allowed measuring bone resistance on drilling. Bone density was expressed according to the energy required to cut each unit of bone volume. Thus, low-density bone would need at least 30 Ncm for placing an implant, medium density bone varies between 30 and 40 Ncm and high density is over 40 Ncm. For immediate loading implants, an insertion torque is recommended between 35 and 45 Ncm.

Resonance frequency analysis (Osstell; Integration Diagnostics, Götegorg, Sweden) is a non-invasive method developed by Dr. Neal Meredith¹² for making quantitative measurements of the stability of the implant by analyzing the bonetitanium interface. In this case an electric transducer sends a vibration wavelet over piezo-ceramic material screwed to the implant and a receptor picks up the frequency variations of the wave. It measures the resonance between 3.500 and 8.500 Hz. These values have been transferred to a more manageable index that varies between 0 and 100, the ISQ (Implant Stability Quotient). The experience of many authors 13 shows that values under 40 imply a high-risk situation for the implant, whereas values over 55 are considered favorable. The values that should be recommended for immediate loading have yet to be established. It has been postulated that values between 60 and 80 with antirotational stability could be adequate for this technique. Case 1 (Figs. 1-4).

Implant choice

The type of implant most suited for immediate loading has still to be developed, but in this sense, innovations in macrostructure (design) and microstructure (surface) have contributed to improving stability and prognosis under such stressful situations.

Randomized clinical trials (RCT) that compare two different types of rough surfaces under immediate loading have not been published. In fact, most surfaces that have been patented by different manufacturers have been authorized by the FDA for immediate loading in patients with edentulous lower jaws. In a recent meta-analysis by Esposito¹⁴ no difference was found between various types of implant surfaces. There is no solid evidence that demonstrates that a certain type of dental implant has a higher success rate in the long term.

The macrostructure of the implant itself is capable of improving primary stability following surgery. In D1 and D2 bone, force transmission along the implant axis is produced on the cortical bone. This bone is ten times more rigid than spongy bone, which explains why implant length and shape do not play a critical role in these densities. ¹⁵

In D4 bone the cortex is very thin or inexistent, the implant is surrounded by spongy bone that is very elastic and the forces are transmitted towards the apical portion of the implant that does not have sufficient resistance for supporting immediately loading implants. Finite-element analyses showed that in lowdensity bone, the distribution of forces was more relevant than existing bone volume.¹⁶

The use of anatomically designed implants, with a reduction of the cervico-apical diameter and with a wider platform, allows a strong consolidation on the cortical bone.

A decreasing, non-cutting thread in the apical part, helps to compact spongier bone.

With regard to bone that is less dense, threaded implants have more bone-implant contact than cylinder implants. But if they are over screwed on placement there can be a problem with breaking the thread in the bed and initial stability is lost. But implants that have a double thread or notches provide greater stability.¹⁷

In this type of density we should aim to obtain the greatest surface contact. Placing the largest number of implants possible is recommended with the maximum length possible. Primary stability can be improved by increasing the diameter of the implant.¹⁸

Surgical technique

Various studies indicate that the survival of the implants is directly related with the experience of the surgeon.¹⁹ Of the best results published, the majority are achieved by teams with great experience.

The surgical technique that guarantees the primary stability of the implant is closely related with bone quality. In D1 bone, most problems are determined by thermal necrosis of the peri-implant bone. Cortical bone dissipates heat worse than spongy bone, and there is a greater risk of it overheating. ²⁰ Cutting systems are needed that are highly effective and that cause little trauma. The implants should not be placed with maximum pressure, but they should be placed in a torque that is sufficient to guarantee the anti-rotational stability of the implant. Implants with little primary stability in this type of bone have a particularly bad prognosis.

The best results are to be found in D2 and D3 bone. Pretapping the site is not necessary for threaded implants. The use of bicortical anchorage for improving primary stability in the nasal fossa floor and in the maxillary sinus is preferred.

Most failures in D4 bone are related to lack of stability. The response of trabecular bone to mechanical stress is particularly critical.

Patient selection

Most of the articles published on immediate loading have been carried out on selected patients. However, other authors suggest that the immediate loading patients are no different from those that have undergone conventional loading.²¹

There is a generic tendency to avoid these placements in patient groups with medical conditions that imply reduced bone quality, as primary stability may be jeopardized and presumably there could be problems with bone microperfusion.

Primary or secondary osteoporosis does not imply that immediate loading is totally contraindicated.

A sufficient amount of bone volume is needed to place an implant with a minimum length of 10 mm and a diameter of 3.75 mm, and it should be surrounded by at least 1 mm of bone in a bucco-lingual direction. Anatomical structures may limit the length of the device, and placing more implants is recommended in order to increase the osseointegration surface. However, implants with a shorter diameter have been loaded successfully in good quality bone. Using the longest possible implants on the best quality bone would justify the use of angulated implants for immediate loading. The use of grafts for increasing bone volume should be considered before placing immediately loading implants.

Traditionally patients with a high degree of masticatory parafunctions have also been excluded from these trials. Habits such as lingual pressure, clenching and bruxism can be adverse factors in immediate loading, but not for the immediate prosthesis. With a centric occlusal design, the strength of occlusal forces and the presence of parafunction does not appear to be a decisive factor in implant survival.²²

The presence of acute untreated infection of the bony bed is contraindicative for placing an implant, but not if this is limited to an adjacent area providing proper surgical curettage and antibiotic treatment is carried out.

With regard to radiotherapy, there are no studies published covering immediate loading.

Prosthesis design in immediate loading

From the point of view of organization, the co-ordination effort between the surgeon, prosthodontist and laboratory should not be underestimated when preparing a provisional prosthesis within the first 48 hours. For successful case resolution, teamwork has to be considered, and the choice of implants, their distribution, and position should be guided by a restoration plan.

Special interest should be given to the distribution of implants in the arches of edentulous patients, with an optimum distribution of forces and a reduction of the effects of the extensions and all contacts should be away from the axial axis of the implant. The provisional restoration is made in acrylic material and all implants have to be splinted whenever possible, and biomechanical stability improved. It is important for the prosthesis not to be removed for 3 months during the osseointegration process. If any implant shows signs of infection, this should be treated as conservatively as possible. Dismounting a provisional prosthesis before time could interfere with the osseointegration of the remaining implants.

We should distinguish generally between two occlusal situations, totally edentulous arches and partial or single gaps. The fixed provisional prosthesis in totally edentulous arches should have a proper distribution, but with limited central contact or maximum intercuspidation. Excursion contact should be eliminated from the restoration together with any contact in the molar region whenever possible.²³ The role played by postoperative dietary recommendations has yet to be defined, together with that played by the opposing dentition type.

In provisional partial or single restoration, protrusive lateral excursive and premature contact should be avoided. But certain clinical situations result in provisional prostheses being subject to excursion contact if there is no centric occlusion. Single implants that do not have occlusal loading forces can be subject to secondary lateral loads around the food bolus. The skill of the prosthodontist in distributing the load between the natural teeth and the prostheses over the implant is fundamental. There is controversy as to whether they should remain completely out of the occlusion area for two to three months^24,25 or if they can be restored in centric occlusion. Calandriello restored 50 molars with wide implants in centric occlusion without restricting the diet of the patients.²⁶

In our opinion, we prefer to leave single restorations in the anterior sector load-free whenever possible. Premolars can be adjusted in occlusion so that there is no contact during protrusive movements and during lateral excursions. Partial restorations on good quality bone can be rehabilitated with smooth contact in centric occlusion.

With regard to patient choice, a risk-benefit assessment has to be made when considering immediate restoration. We give more value to functional restoration of a totally edentulous arch and to maintaining aesthetic appearances of a single or partial prostheses in the anterior sector, than to the rehabilitation of the posterior sections of both arches.

Discussion

Immediate loading of dental implants is a consequence of the technical evolution and the demands of patients that want to return to their usual routines as quickly as possible. Some patients do not tolerate removable prostheses, they may be uncomfortable during mastication or speech, or they simply do not want to wait three to six months for a fixed prosthesis to be placed.

There are only three Randomized Clinical Trials (RCT) that compare an immediate loading protocol with the conventional protocol. Two of them were carried out on mandibular overdentures in edentulous patients and the remaining RCT was carried out in partially edentulous patients.

In 2001 Chiapasco carried out a parallel study that included ten patients in each group. He compared 4 Brånemark System implants (Nobel Biocare, Göteborg, Sweden) located in the interforaminal areas of edentulous mandibles, and which were immediately loaded with bars supporting overdentures, with 4 that were loaded conventionally. One implant failed in each group and there was no difference between sexes, age and implant length. The patients were considered as a unit in the analysis and there were no significant differences between both groups.²⁷ In 2002, Romeo in a similar study with ITI implants (ITI Dental Implant System, Institut Straumann, Waldenburg, Switzerland) failed to find any differences between loading strategies a year after being brought into function.²⁸

In a split mouth study, Romanos included 12 patients in each group, and 3 Ankylos implants (Ankylos Dental Implant Systems, Friadent, Mannheim, Germany) that were distal to the mandibular canines and loaded on the same day with temporary restorations, were compared with 3 implants on the contralateral side that were loaded conventionally three months later. The patients were followed for a year and none of the implants failed. There was no difference that was statistically significant with regard to prostheses or implant failure between the different loading strategies.²⁹

In spite of the fact that no Randomized Clinical Trials (RCT) have been published that compare immediate and delayed loading of fixed prostheses over edentulous mandibles, there are prospective long-term multicentric studies with a large number of patients that allow conclusions to be made with undoubted scientific value.

In 1990 Schnitman compared implants that were loaded immediately in the mandible, with implants that were submerged in the same patient who was then used as a control source. He reported that the implants that were distal to the mental foramen were more susceptible to failure and he published the first recommendations for increasing long-term survival of immediately loading implants. Decreases in micromovements during the bone remodelation period could be achieved by using a provisional threaded prosthesis screwed with a perfect passive adjustment that splinted together all the implants.⁵

In 1999 Brånemark presented the Novum System (Brånemark Novum, Nobel Biocare, Göteborg, Sweden) for immediate loading.30 The system united three implants that were positioned in the anterior region of the mandible, with a diameter of 4 mm and a minimum length of 13 mm, with a titanium platform (infrastructure). On this a superstructure was screwed that had the fixed prosthesis. Later, Henry el al, in a multicentric study that included 51 patients, reported an accumulated survival rate of 91% for implants and 94% for prostheses after a follow-up of one year.³¹

In our opinion, immediate loading with pre-designed prosthetic systems (prefabricated titanium structures) before implant placement has not resolved the problem efficiently of passive prosthesis adjustment. The possibility of excessive micromovement is increased leading to the resulting biomechanical failure.

In 2002 Cooper published a series of 10 patients that were fitted with 5 immediately loading implants in extraction sockets between both mental foramina that were immediately loaded, and he reported a survival rate of 100%. The authors concluded that immediate loading in recent extraction sockets had a high success rate.³²

In 2003 Wolfinger created two treatment groups in a study using Brånemark implants that had a 3 to 5 year follow-up. The first group was loaded with 6 implants in the anterior portion as well as the posterior portion of the mandible. The second group was treated with 10 implants per mandible, 4 of which were loaded with a provisional acrylic prosthesis and the remaining 6 were submerged and uncovered in a second procedure. The survival of the immediately loading implants in the first branch of the study was 97%, while in the second it was 80%. This study showed the inefficiency of submerging prosthetic salvage implants instead of providing more stability to the provisional prosthesis by having an adequate number. ³³

In 2003 Malo presented a retrospective study in which 4 interforaminal Brånemark implants were placed in 44 patients. He demonstrated the efficiency behind using angulated abutments at 45 degrees by the mental foramen in order to obtain a more distal position of the superstructure without compromising the lower alveolar nerve. The accumulative survival rate after a follow-up of 1 to 3 years was 96.7% and prosthetic survival was 100%.³⁴

In 2004 Testori published the first prospective multicentric study with Osseotite implants (3i, Implant Innovations, West Palm Beach, FL, USA) for immediate mandibular loading in 62 patients with 5 interforaminal implants in order to support a provisional hybrid prosthesis with extensions in complete occlusion. He reported an accumulative survival rate of 99.4% two years later, with no significant changes in marginal bone.³⁵

The data obtained suggest that the survival rate of the implants that were immediately loaded in order to rehabilitate totally edentulous lower jaws with a fixed prosthesis (mean 95%) is comparable to that obtained through the conventional protocol. This has been attributed to good bone quality in the region that ensures sufficient primary stability.

In our service the immediate load approach using a fixed prosthesis for edentulous mandibles is carried out in a routine fashion. The number of implants placed varies between 4 and 6 according to the degree of bone resorption. We use 4 to 5 implants between both mental orifices of the lower jaw with resorption in the posterior sector. In cases with sufficient bone volume that is distal to where the inferior dental nerve appears, we use 6 implants around the lateral incisor, first premolar and first molar. We use threaded implants with a treated coating and a diameter of 3.75 to 4 mm that have the longest possible length without reaching the bicortical anchorage. We load all the implants that have rotational stability with a torque that has a minimum insertion of 30 Ncm. We do not carry out resonance frequency measurements as a matter of practice.

To date there is no RCT published on immediate loading of fixed prostheses for edentulous maxillas, but on a lower scale of scientific proof we have found prospective series of cases or cohorts that provide very valuable information on this procedure. The first series was published by Tarnow in 1997 and it included only 4 patients. The implant and prostheses survival rate was 100%.³⁶ Later different authors^37-39 published small series with implant survival rates that varied between 87.5 and 100%, and with prosthesis success rates between 96.5 and 100%. In 2005 Balshi reported a consecutive series of 55 patients that were followed for at least one year. Ten Brånemark implants were placed in each edentulous maxilla in order to support an acrylic fixed provisional prosthesis. The implant survival rate was 99% and the prosthetic success rate was 100%.⁴⁰

Our group uses this procedure in a predictable fashion in selected patients with adequate bone volume, without serious maxillo-mandibular discrepancies in the vertical and antero-posterior axis. Case 2 (Figs. 5-10) We use between 6 and 8 threaded implants with a rough surface that are distributed using the most equidistant points possible in the arch. They have a diameter of 4 or 3.75 mm and the longest length possible, and a minimum height of 10 mm. We use bicortical anchorage on the nasal floor and in the maxillary sinuses and drilling protocols for soft bone with the aim of increasing primary stability. Only implants with a rotational stability and an ISQ value greater than 55 are loaded. In partially edentulous patients, in addition to the RCT previously mentioned, there are trials published that permit extracting certain practical conclusions. Rocci et al. compared two groups of 22 patients that were loaded with implants treated with anodic oxidation in order to rehabilitate partially edentulous patients in the posterior part of the mandible, with mechanical implants. After being loaded for one year, the implants with rough surfaces had a survival rate of 95.5% as opposed to those with a machined surface that had a survival rate of 85.5%. In both groups osseointegration failure was related with lowdensity bone and smokers.⁴¹ Glauser y cols. reported a series of clinical cases with a 97.1% success rate in which the same surface (Brånemark System Mk IV TiUnite, Nobel Biocare AB, Gothenburg, Sweden) had been used for partial and single-tooth prostheses in bone that was predominantly soft.⁴²

With regard to single-tooth implant, in a prospective series of 24 patients in 2001 Hui placed Brånemark implants immediately after single-tooth extractions in the anterior region of the maxilla with a 40 Ncm torque. He reported a 100% survival rate after one year leaving provisional restorations without occlusion.43 In 2004 Drago in a similar series of 93 patients with Osseotite single-tooth implants out of occlusion, reported a 97.4% survival rate.⁴⁴ Ericsson, in a trial on single-tooth restorations that had an anterior position to the molars, compared a group of 14 patients against a control group of 8. No failures were reported with fixtures having a length of at least 13 mm and a diameter of 3.75 mm.⁴⁵

Abboud in 2005 reported a successful series of 20 patients that were restored with single-tooth implants in the molar region of the mandible and the maxilla with slight occlusion and maximum intercuspidation.⁴⁶ Calandriello, in his study on the loading of mandibular molars with wide implants with a TiUnite surface, included 44 patients and 50 implants, that were rehabilitated with provisional crowns in centric occlusion. The follow-up was of only 6 months and no implants were lost.²⁶

In our protocol we normally use one implant per tooth to be replaced providing the prosthetic space, bone volume and biological distance between implants and the former, and adjacent teeth is sufficient. In the case of single teeth we use the longer implants, which anatomically permit achieving a more favorable crown-root relationship, that are greater if possible than 12 mm.

In the anterior region, soft tissue as well as the available bone should be ideal for applying this technique. Case 3 (Figs. 11-13) In cases of extraction followed by an immediate implant, and when bone and papillary architecture have been conserved, we prefer flap-free surgery. Soft-tissue collapse should be avoided and the structure of the papilla should be preserved by means of a provisional restoration. If the periosteum is not released from the alveolar bone, bone absorption is limited to the neck of the implant.

Clinical studies indicate clearly that osseointegration is possible following the placement of implants in a single surgical phase with immediate occlusal loading. The results published indicate that the survival of the implants with the protocol initially defined by Brånemark can be used as a standard for comparing immediate loading. Although there are no long term studies that effectively compare this method with conventional techniques, the only remaining question with regard to immediate loading, is whether this leads to a greater percentage of early implant loss. Logical reasoning leads us to believe that once integrated, the behavior of the implant is independent of the loading time. Once osseointegration has taken place, the behavior of the implants is the same as that of delayed loading implants, and later losses would be due to the progressive decrease in bone-implant contact after prosthodontic rehabilitation. We therefore consider that study follow-ups of over a year are unnecessary for establishing whether the technique is reliable or not.

From the point of view of methodology, the greatest problem is not patient following but study design. The possible risk on selection, if the procedure in the randomized concealment of allocation is not clearly defined, can tend towards the immediate loading of the implants in the more favorable cases, which would overestimate the effect of the treatment.

The risk-benefit relationship should be evaluated in each case individually. In one extreme there would be the totally edentulous patient that do not tolerate a removable prosthesis, and in the other there would be the patients with implants as from the second premolar in partial rehabilitations. The situation with the greatest biomechanical risk is without doubt placing a single implant at the back of the maxilla, as the number of implants placed cannot be easily increased and the length involved is short. When dental replacement is carried out immediately in areas that are not aesthetically important, the benefit obtained is minimum.¹⁸

Immediate restoration does not necessarily mean immediate loading to the greatest magnitude that the masticatory apparatus can develop. A conservative approach in the design of the prosthesis reduces the stress that the implant is subjected to, and the success rate increases. In partially edentulous patients, carrying out an immediate restoration does not necessarily imply occlusal loading during the first weeks of bone healing. In these cases the aesthetic appearance is more important than the function carried out by the provisional prosthesis.

Conclusions

The literature that exists up to now, together with the experience of the authors, shows that immediate loading is a reliable procedure, providing a selection is made previously of the patients to be treated. Without any doubt the advantages consist in removable prostheses being unnecessary, together with two-stage surgery. Soft tissue is preserved and there is greater comfort for the patient. The only argument against a theoretical increase in the failure of implants has not been demonstrated in the trials carried out to date. For the authors the greatest inconvenience of the procedure is due to the need for adequate surgical-prosthodontic coordination. Finally, we conclude that although there may be a greater risk of implant failure in immediate loading, this can be accepted by the patient and the surgeon. The advantages of the technique in totally edentulous cases, or in areas with high aesthetic requirements, far outweigh the inconveniences of the loss of an implant, because the patient has been able to enjoy the advantages of fixed dentition from the beginning. In these cases, the loss of an implant rarely compromises the success of the provisional prosthesis.

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