ARTÍCULO ESPECIAL

 

Immediate loading of implants in the maxilla

Carga inmediata con implantes en maxilar superior

 

 

F. Monje Gil¹, C. Moreno García²,H. Serrano Gil², O. Maestre², A.J. Morillo Sánchez³,
J. Mateo Arias³, L. Ruiz Laza³, P. Quiros Álvarez³, D. Manzano Solo de Zaldivar³

1 Jefe de Servicio
2 Médico Residente
3 Médico Adjunto
Servicio de Cirugía Oral y Maxilofacial.
Hospital Universitario Infanta Cristina, Badajoz, España.

Correspondence

 

 

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ABSTRACT

Immediate loading in the mandible has been introduced into clinical practice taking first place and, and because of the characteristics of the bone, this is carried out following a protocol. However, in the maxilla there is no scientific evidence for routinely carrying this out. This is because the maxilla, in general, has a lower bone mass density. Moreover, in the maxilla various densities may coexist (according to Misch’s classification) in the same individual. In addition, given the anatomic characteristics of the maxilla (lip and palate resorption), axial alignment can be carried out, but implant parallelism is difficult.^16,17
The aim of this paper is to analyze the scientific information that we have at our disposal in order to confirm whether immediate loading in the maxilla is possible. For this we will study various aspects of immediate loading in the maxilla:
• Overdentures
• Fixed complete prostheses
• Fixed partial prostheses
• Fixed single tooth prostheses
• Prosthetic requirements
• Contraindications

Key words: Inmediate loading; Dental implants.

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RESUMEN

La carga inmediata en la mandíbula se ha incorporado a la práctica clínica en primer lugar y, por las características del hueso, se realiza de forma protocolizada. Sin embargo, en el maxilar superior no hay evidencia científica para realizarlo de forma cotidiana. Las razones son debidas a que el maxilar superior, en general, alberga una masa ósea de menor densidad. Por otro lado, en el maxilar superior pueden coexistir diferentes densidades óseas (según la clasificación de Misch) en el mismo individuo. Además, por las características anatómicas del maxilar superior (reabsorción labiopalatina) el alineamiento axial es asumible pero, sin embargo, el paralelismo de los implantes es difícil.^16,17
El objetivo del presente trabajo es analizar la información científica de la que disponemos para confirmar si es posible la carga inmediata sobre el maxilar superior. Para ello estudiaremos varios aspectos de la carga inmediata en el maxilar superior:
• Sobredentaduras
• Prótesis fija completa
• Prótesis parcial fija
• Prótesis unitaria fija
• Requerimientos protésicos
• Contraindicaciones

Palabras clave: Carga inmediata; Implantes dentales.

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Introduction

In the year 1979, Lederman¹ published the first studies on the immediate loading of dental implants. Four bar-splinted chin implants were placed and an overdenture was placed the same day of the intervention. However, this treatment was not carried out following a protocol. In fact in 1985, Branemark² defined osseointegration as the direct, functional and structural connection between vital bone and the surface of the implant. The initial implantological protocols^3,4 contraindicated immediate loading during a period that varied between 3 and 6 months after placement. They affirmed that surgical trauma, together with the immediate loading of the implant, would led to scar tissue developing in the bone-implant interphase.² In fact, studies in the orthopedic literature have shown the role of macromotion in the differentiation of tissue around endosseous implants placed in metaphyseal bones. Here, macromotion led to fibrous tissue being interposed between the implant and bone.⁵ As a result, primary stability and postponing the load approximately three to six months has been considered for years "conditio sine qua non" for achieving osseointegration of dental implants.

Later experimental studies, such as those carried out by Sagara,⁶ Zubery,⁷ Piatelli,⁸ and Romanos⁹ invalidated this affirmation. Nkenke and cols.¹⁰ who used minipigs, analyzed after a 6 month follow-up, the results of the histomorphometric parameters assessed (bone-implant contact and peri-implant bone area) in immediate loading implants in the maxilla. These were similar to those obtained with implants that were loaded after a load-free period of over 5 months.

Micromovements of over 150 micras are considered excessive and harmful to osseointegration. But, on the other hand, micromovements of less than 50 micras are well-tolerated. Therefore, the critical threshold, depending on the morphology of the implant, would be between 50 and 150 micras.^11-15

Currently we refer to immediate loading as placing an implant-supported prosthesis, once the fixation has been inserted into the bone, in such as way that the implant receives a functional load in less than 48 hours as from the placement of the implants. In immediate restoration, also known as immediate non-functional loading, the prosthesis is placed in the same period of time but out of occlusion. In conventional loading there is a delay of 3 to 6 months before the implants are loaded. We would refer to early loading when the implants are loaded between 48 hours and 3 months after placement.5 Immediate loading has been of interest for some time because treatment times are shortened and provisionalization is avoided. The refinement of clinical protocols, the application of adequate biomechanical principles, the improvement in implant designs and the development of new surfaces, has given rise to the introduction of this modality.

Immediate loading in the mandible has been introduced into clinical practice taking first place and, and because of the characteristics of the bone, this is carried out following a protocol. However, in the maxilla there is no scientific evidence for routinely carrying this out. This is because the maxilla, in general, has a lower bone mass density. Moreover, in the maxilla various densities may coexist (according to Misch’s classification) in the same individual. In addition, given the anatomic characteristics of the maxilla (lip and palate resorption), axial alignment can be carried out, but implant parallelism is difficult.^16,17

The aim of this paper is to analyze the scientific information that we have at our disposal in order to confirm whether immediate loading in the maxilla is possible. For this we will study various aspects of immediate loading in the maxilla:

• Overdentures

• Fixed complete prostheses

• Fixed partial prostheses

• Fixed single tooth prostheses

• Prosthetic requirements

• Contraindications

 

Overdentures

We have not been able to find any articles on the immediate loading of implant-supported overdentures in the edentulous maxilla.¹⁸

 

Fixed complete prostheses

In 1997 Tarnow¹⁹ described an immediate loading protocol for the edentulous maxilla with the aim of obtaining stabilization of intra- and interarch implants. This same author and others^19-21 pointed out the clinical factors that have to be considered when carrying out immediate loading. Factors that can make immediate loading in the maxilla possible are considered to be the following:

• Primary implant stability.

• Adequate implant splinting.

• Provisional restorations that favor implant splinting and that reduce the control of the mechanical load applied on the implants.

• Movement prevention of provisional restorations during the healing period.

• Team work if in the immediate loading procedure various professionals collaborate (surgeon, prosthetist, prosthetics maker, periodontist, orthodontist and anesthetist).

It should not be forgotten that the objectives that should determine choosing immediate loading are the same as those for conventional loading: planning and complete design of the treatment strategy, evaluation of the aesthetic expectancies of the patient, evaluation of the quality, quantity and morphology of soft tissue and verification of bone pathology in the area of the adjacent teeth or of the teeth to be extracted, as well as the patient’s bone tissue.

From the surgical point of view, it is important to bear in mind certain considerations, such as:²²

• The choice, position and distribution of the implants should follow a complete restoration plan that takes into consideration not just the moment of loading.

• Surgical splints should be used to indicate the prosthetic plan and these should be stable and perfectly adapted to the alveolar area and palate. They should be rigid, and they should ensure adequate access and visibility. They should also be able to guide three dimensional implant placement.⁵⁴

• Attempting to minimize biomechanical risks.

• An adequate number of implants have to be positioned in order to facilitate splinting and the possible effects of micromotion.

Primary stability of the implants should be achieved. This may be possible by choosing patients that have adequate bone in terms of quantity and quality. An implant with a particular surface and adequate dimensions, and an adequate clinical technique should be used to maintain the contact between the implant and bone.²³ With regard to the surgical technique to be carried out, different modifications have been put forward:²⁴

• Reducing as much as possible the trauma to the osteotomy area, and if this is carried out it should only be carried out in areas with dense bone.

• Countersinking should be avoided.

• Bicortical stabilization should be attempted.

• Finer drills should be used than those stipulated for conventional loading in order to achieve greater primary stability.

In the articles studied (Table 1)^25-30 the rehabilitation of 113 upper arches was undertaken (959 implants) with a mean success rate of 98.24%.

There are variables that are important to keep in mind when discussing immediate loading in the maxilla.

General conditions

From the point of view of the general health of the patient, general conditions such as diabetes or smoking are debated. Some authors^31-33 consider diabetic patients as a contraindication for carrying out immediate loading. However, others^23,27 exclude from their protocols only those that do not have adequate control of their condition.

Smoking is considered a contraindication in immediate loading protocols.^34-37 However, other authors^38,39 only exclude those that are heavy smokers (more than 10 cigarettes a day).

Post-extraction sockets

What occurs to post-extraction sockets has been identified by means of histological examination of animal material. ^40-42 The first phase consists in clot formation with blood circulation cells. In the second phase, that is to say on day 4 or 5, granulation tissue covers the socket completely. As from day 15, the connective tissue will completely substitute the granulation tissue and, at around 6 weeks, calcification of the osteoid tissue is produced and the trabecular bone will completely cover the socket. In the last phase, complete epithelial closure will take place in the extraction site. Maximum osteoblastic activity, as well as the proliferation of cells and connective tissue elements takes place 4-6 weeks after extraction. From week 8, the osteogenic process starts slowing down.³⁶ Therefore, the best time for implant placement seems to be between week 4 and 8. This is also the best period for achieving adequate soft-tissue volume and the least loss of bone volume in cases of active infection.⁴³

Immediate-type placement of implants, following extraction, can prevent bone loss that occurs after tooth loss, avoiding on occasions more complex techniques for restoring the future implant bed. Thus, immediate implants permit shortening treatment time, which is currently one of the objectives. Approximately 5-7 millimeters of horizontal or buccolingual resorption of the maxilla, that represents around 50% of the starting point, occurs at 6-12 months after dental extraction. An apicoronal, or vertical resorption, of 2 to 4 mm accompanies the horizontal changes.^44,45 Apicoronal changes are more evident in multiple extraction sites.^45-47 These changes are slightly greater in the molar region than in the premolar region, and in the mandible when compared to the maxilla. A large variety of factors can influence the dimensional changes in bone after dental extraction. Systemic factors can be included, in relation to the patient’s previous state of health and smoking. With in the local factors, we can include the causes behind the extraction, the number and proximity of the extracted teeth and the condition of the alveolus before and after dental extraction.⁴³ Follow-ups of between 1 and 4 years have not shown any significant differences with regard to radiographic changes in bone levels, in either implant areas where immediate loading was carried out, or other areas where conventional loading was carried out.^48-52 The sockets with dehiscence defects may not have the potential for complete bone regeneration, and the risk of long term complications can increase if the implants are immediately loaded.⁵³

It has been demonstrated in various studies, that the survival rates of immediately loaded implants, after the extraction of teeth with root fractures, perforations or with a combination of endodontic and periodontic problems, is similar to that of implants placed in areas that have already healed.^54-58 As always, the implants placed in areas where the tooth has been affected by chronic periodontitis, have been associated with slightly higher failure rates.^59,60 When implant placement is delayed following dental extraction, soft tissue will heal and increase in volume, which will permit adapting flaps in the future, and this will help to achieve good aesthetic results. Therefore, the period between dental and implant extraction will have advantages with regard to the amount of soft tissue achieved, but this will carry the risk of bone loss due to resorption.⁴³

An important variable in immediate post extraction implants and in immediate loading, is the greater distance between the implant and the socket wall. In cases where this distance is 2 mm or less, osseointegration is adequate.⁴³ If the distance is greater than 2 mm, this space should be filled by means of some type of biomaterial, and loading should therefore be postponed. On the other hand, in postextraction cases, using an osteotomy 5 cm coronal to the apex of the tooth to be extracted, is considered of interest in order to achieve primary stability.

Bone quality

The anatomic variables, which affect implant prognosis in a more dramatic fashion, with regard to the edentulous maxilla, are the quantity and quality of bone that is available. According to Misch’s classification, the areas of type IV bone are the areas with a risk of implant loss.^18,61 These authors have had an implant success rate of 66% in areas with type IV bone, and 91% in the remaining areas (type I, II or III). Bergqvist²⁵ had a 71% success rate in the maxilla with type III and IV bone.

Gingiva biotype

In cases of aesthetic compromise, a thin gingiva biotype is less favorable than thick, should immediate loading be undertaken. In the latter case, plate resorption would facilitate things with regard to aesthetic problems.¹⁹

Implant characteristics

Implant characteristics that favor immediate loading are the following: threaded implants with a rough surface: Acidetching and sand-blasting are the methods chosen by most authors.²⁶ With regard to implant length, some authors describe the failures, due to the use of short implants, especially when placed in areas with limited bone. A minimum length of 10 mm for carrying out immediate loading has been suggested.^22,24,62 However, Jaffin and cols29 used an implant with a minimum length of 8 mm and they placed between 6 and 8 implants in each of the 34 atrophic maxillas that they reconstructed with a success rate of 92.2% after a follow-up of a year. In some publications^26,63,64 a wider implant is used, when primary stability by means of the initial implant is not obtained. New implant designs (modification of spirals or expansive models) have improved the immediate loading perspectives in both jaws, but they have not been scientifically compared with the designs of other implants in long-term human studies.⁶⁵

Torque

Calandriello and cols66 suggest, as an immediate loading requirement, a minimum insertion torque of 60 Ncm for single implants, 45 Ncm for implants supporting restorations or partial arches, and 32 Ncm for restorations of complete arches. Probably, the most frequent method for evaluating stability is the subjective opinion of the surgeon himself. ³⁵ Degidi and Piatelli,²⁶ carried out a study that consisted in a comparative analysis of implants subjected to immediate functional loading and immediate non-functional loading, versus a control group subjected to conventional loading. These authors maintain that a torque of more than 25 Ncm is needed together with an implant stability quotient (ISQ) of more than 60, measured by means of frequency resonance (Resonance frequency, Osstell^®) as inclusion criteria.

Primary implant stability is a fundamental requirement in immediate loading. Various methods for measuring this have been suggested (torque and ISQ), but comparing results is impossible, as is extracting conclusions as to which is the more suitable measuring method for evaluating this parameter. ^23,24

Number of implants

With regard to the immediate loading of implants supporting fixed prostheses in the edentulous maxilla, most authors are in agreement on the following: a greater number of implants are needed in the maxilla than in the mandible for supporting complete arches immediately.^5,10 The mean number of implants in the maxilla is 7.82 as opposed to 4.54 in the lower jaw.^25-30 For example, Bergkvist and cols.²⁵ placed between 5 and 7 implants with a 1-2 year follow-up and a success rate of 98%. Therefore, in immediate loading of the maxilla, experience tells us that when 6 to 8 implants with a rough surface are used, there will be adequate osseointegration under loading conditions. Nevertheless, the number of implants that should be used is determined by other factors: ¹⁸

• Extension of prosthetic plans.

• Quality of available bone, the lower the quality of the bone, the more implants should be used.

• Estimated function during the loading period.

• Financial conditioning factors.

The "All on four," method described by Maló65 for edentulous maxillas, is unusual in that only 4 implants are used onto which a fixed prosthesis is anchored. Both lateral implants are placed as far back as possible at an angle of 30 degrees with regard to the occlusal plane, while following the anterior wall of the maxillary sinus but without penetrating it. The objective is for the implant to emerge as far back as possible to permit immediate loading. In these cases the author defends the use of a cantilever.

Some authors²⁸ have placed implants with immediate loading using a transmucosal approach (flapless surgery). In a multicentric study with 27 patients in which virtual planning was used with the help of a CAT scan together with prefabricated surgical splints through which the implants were placed, a success rate of 100% was achieved.

 

Partial reconstructions

There is a study in which limited scientific evidence is put forward for the maxilla, which suggests that reasonable success rates in immediate loading are limited to the anterior region.²⁴ However, in table 2, the results are analyzed of the articles studied.^26,30,66,67 A total of 31 patients were rehabilitated and 87 implants were used. The global success rate was 93.47%. Partial prostheses were used in the anterior portion of the upper arch with a success rate of 93.55%. For the posterior part of the maxilla a success rate of 92.78% was achieved. Significant differences were not found. In the posterior part of the upper arch the success rate for machined and rough surfaces was 77.53 and 96.15% respectively, while no significant differences were detected in the anterior region. This indicates that when placing partial prostheses in areas with bad bone quality, the performance of textured surfaces is significantly higher than machined surfaces.

Cannizaro and Leone⁶⁸ compared immediate and conventional loading, obtaining a success rate of 100% in both cases. In a randomized study,³² immediate loading was compared with early loading and a success rate of 96.6% and 96.3% respectively was achieved with a follow-up of two years.

In complete and partial reconstruction, more than 80% of implant failures in immediate loading of the maxilla took place during the first six months, and 97.1% took place in the first year after placement.⁶⁹

 

Single tooth reconstruction

There are two studies^68,70 available comparing immediate with conventional loading. Ericsson and cols, after a twoyear follow-up, claimed to have a success rate of 81.2% versus 100% when comparing immediate loading with conventional loading. However, there are a series of prospective studies (Table 3)^30,67,71-78 that indicate a success rate of between 96.7 and 100% with a follow-up of 5 years. Even for premolar replacement, the success rate was 100%.^72,76 A total of 157 single teeth were reconstructed in the maxilla of 157 patients. The global success rate was 96.19%. Immediate restoration located in the aesthetic region (anterior region) had a success rate of 96.96%. Reconstruction in the posterior region of the maxilla had a success rate of 93.06%. In single tooth implants with reconstruction of the immediate loading type, no significant difference was found in the survival rates of the implants with a machined versus rough surface in either the anterior or posterior area of the upper arch.

For some authors⁷⁹ single tooth implants that are situated in the posterior region are more susceptible to overloading. It would appear that increasing the diameter of the implant could be an effective manner of increasing resistance. A stronger implant does not resolve the problem of overloading completely, but it does lessen the consequences in the weakest point of the system: the implant or the contacting bone surface.⁷⁹

Hui⁷⁷ proposes a minimum torque of 40-50 Ncm for single tooth reconstructions. Others avoid incisal contact.⁷⁵ Currently there are no studies that compare immediate functional and non-functional loading for single tooth reconstructions. ⁸⁰ Only one study demonstrates the aesthetic satisfaction of patients with immediate loading, single tooth implants.⁷³

 

Prosthetic requirements

The prosthetic concepts that should be kept in mind are simple and essential:¹⁹

• Immediate loading represents a clear advantage with regard to the quality of life for the patient.

• The biomechanical effects of provisional restorations should be controlled (occlusal contact, limitation of excursion movements together with any undesirable cantilever effects).

• Follow-ups with the same principles as conventional prostheses (passivity).

• Provisional restorations should be kept in place while soft tissues and bone are healing.

 

Contraindications

Immediate loading is contraindicated in those situations in which adequate primary stability cannot be obtained because of a lack of bone quality. Most authors consider bruxism as an exclusion criteria.^63-66 Furthermore, infection can be considered another contraindication. Another contraindication would be if the aesthetic needs of the patient require a classical procedure (two stage).⁶⁹

 

Conclusions

Carrying out immediate loading and fixed prostheses in the maxilla is not supported by sufficient data that enable viewing this treatment modality as something routine, although the data concerning the preliminary results that are at our disposal is encouraging. Immediate loading in the maxilla is possible, but there is no standard protocol with regard to the number of implants and placement times with regard to tooth extractions. Treatment involving immediate loading provides satisfaction to the patient although there is no scientific evidence with regard to the effective cost of this technique.

Although there are studies with follow-ups of several years, there is a shortage of data with regard to long-term follow-ups and the aesthetic results of immediate implants. New techniques (non-submerged implants and flapless procedures) require additional evaluation.

 

 

Correspondence:
Dr. Florencio Monje Gil
C/ Vasco Núñez 8, 3B
06001 Badajoz, España

Recibido: 03.01.07
Aceptado: 29.01.07

 

 

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