|Year : 2019 | Volume
| Issue : 8 | Page : 1033-1040
Maxillary and mandibular all-on-four implant designs: A review
R Durkan1, P Oyar2, G Deste1
1 Department of Prosthodontics, Faculty of Dentistry, Afyon Kocatepe University, Afyonkarahisar, Turkey
2 Department of Dental Prostheses Technology, Health Services Vocational High School, Hacettepe University, Ankara, Turkey
|Date of Acceptance||28-Feb-2019|
|Date of Web Publication||14-Aug-2019|
Prof. P Oyar
Department of Dental Prostheses Technology, Health Services Vocational High School, Hacettepe University, D Block, 3rd Floor, 06100 Sihhiye, Ankara
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objective: The objective of this review is to evaluate maxillary and mandibular all-on-four implant designs, their indications and contraindications, advantages and disadvantages. Methods: By using Pubmed, Cochrane Library, and Google Scholar, data from January 2003 to February 2018 were scanned electronically and manually as the title, abstract, and full text. The keywords specified were determined to be the all-on-four concept, full-arch implant prostheses, 4-implant full-arch, and tilted implants. The inclusion criteria consisted of the all-on-four implant design, its use in completely edentulous maxillary and mandibular cases, advantages and disadvantages of the technique, and changes observed in the maxilla and mandible in completely edentulous cases. Clinical trials and laboratory studies on the subject using the full text and English language were evaluated. Results: A total of 176 articles were found as a result of Google Scholar, Pubmed, and Cochrane Library. Thirty-seven articles were selected according to inclusion criteria; of these, 20 were related to the clinical trials. In addition, a total of 13 articles were found as a result of an additional hand search by screening the reference list of all included publications; of these, 11 was related to the clinical trials. Conclusions: It is necessary to carry out longer-term clinical and laboratory studies to determine long-term success criteria in all-on-four implant designs and to use new ceramic systems.
Keywords: All-on-four concept, mandible, maxilla, tilted implant
|How to cite this article:|
Durkan R, Oyar P, Deste G. Maxillary and mandibular all-on-four implant designs: A review. Niger J Clin Pract 2019;22:1033-40
| Introduction|| |
It is accepted that fixed prosthetic restorations with full-arch implants are better in terms of aesthetics, function, and phonation than removable prostheses.
The all-on-four implant design is an implant application technique that is applied in severely resorbed completely edentulous maxilla and mandible. Principles, specifications, and application procedures of all-on-four implant designs were first applied by Malo in 2003 to atrophic completely edentulous mandible and to maxilla in 2005.
The abutment of the all-on-four concept is defined as full-arch screw-retained fixed prostheses made on a total of four implants, being two implants placed orthogonally to the occlusal plane in the anterior region and two implants placed 15-45° distal in the posterior region, in completely edentulous maxillary and/or mandibular jaws. It includes immediate making and loading of temporary prostheses (in the postoperative 8--48 h) and permanent fixed prostheses after the 3-month period.,,,
The objective of the design is to make full-arch fixed restorations with fewer implants in cases when implants cannot be placed in the posterior region because of anatomic limitations. Furthermore, it is also important that it is a design that minimizes or completely eliminates the posterior cantilever application. Implants are placed in the premaxillary region in the maxilla and in the interforaminal region in the mandible. Although it is widely used in the mandible, this method could not be fully evaluated in the maxilla. Because of the lower quality and quantity of the maxillary bone compared with the mandibular bone and also maxillary bones being more trabecular and less dense than the mandibular bone, it is more disadvantageous compared with the mandibular interforaminal region.,
In maxillary all-on-four implants, posterior implants are placed angularly to the premaxillary region, the anterior wall region of the maxillary sinus. Long-angle implants (≥13 mm) provide high primary stability.,
Misch (2009) emphasized that the part between the mental foramina of the mandible is more stable to bending and stress forces and that strains occurring along the opening phase and protrusive motion in the jaw occur on the distal of the mental foramina. The researcher stated that mandibular motions in the distal of the mental foramen in fixed restorations negatively affect the prognosis of implants and that upon the placement of implants between the mental foramina in full-arch fixed restorations fixed to each other, less bending forces occur in the mandible. In accordance with this opinion, in the all-on-four treatment technique, implants are placed between the mental foramina.
In all-on-four implant designs, screw-retained prostheses are preferred. Mechanical and biological complication rates decrease because of the easy removal of screw-retained implant-assisted prostheses. They can be used in cases when the abutment length is short. The prosthesis can be removed for prosthetic hygiene. It can be easily removed when there is a problem with the abutment and/or implants. It can be removed at the dentist's control. Cementation problems are not observed. Moment forces are low. It is used when the interocular distance is insufficient. However, clinical procedures are difficult. They require precise work. Its cost is high. Screw spaces on the occlusal surface should be closed. Occlusion may be affected by the occlusal screw areas. The screw may loosen and break. There may be ceramic breaks in screw areas in the superstructure. Bacterial invasion may occur in screw areas. A temporary restoration is difficult to perform.
The European Association of Osseointegration recommends screw-retained substructures in implant-assisted prosthetic treatments.
It has been reported that bone resorption is low in all-on-four implant designs. Overloads to the bone--implant interface in implant-assisted prostheses are activated by surgical trauma and bacterial invasion. Inappropriate occlusion, improper prosthesis and/or implant designs, and surgical implant placement failures lead to the inadequate load transfer mechanism of the overloaded peri-implant bone under functional forces. Consequently, a high-concentration stress accumulation occurs at the bone--implant interface. Stress areas in the bone tissue stimulate biological bone resorption and jeopardize the effectiveness of the implant. Bone resorption in the neck of the implant (crater cratering) becomes unavoidable.
In permanent prostheses in the all-on-four technique, a premature contact should not exist. Occlusal contacts are those that deflect the jaws from normal occlusal closure, conflict with the normal, smooth, and compatible sliding motion of mandibular movements, and/or disrupt the position of the condyle, tooth, or prosthesis. There should be a balanced occlusion around the canines and the first premolars. The occlusal contact distal to the prosthesis should be reduced. Occlusal forces should be concentrated in the region between anterior and posterior implants, and freedom should be ensured in the centric. The last tooth on the cantilever should be extracted from occlusion. However, there are not enough studies on occlusion in all-on-four restorations in the current literature.,
In all-on-four prostheses, cantilever extensions are either absent or shortened. Thus, high prosthetic complications, abutment loosening, prosthetic fractures, or implant failures, which are the disadvantages of cantilever prostheses, are reduced.
The main objective of this study is to compile detailed information on mandibular and maxillary all-on-four implant designs and prosthetic restorations.
| Materials and Methods|| |
What is the all-on-four implant design, what are the advantages, disadvantages, indications, and contraindications of this technique?
A computerized literature search was performed by three investigators using Google Scholar. Various keywords were used: all-on-four concept, full-arch implant prostheses, 4-implant full-arch, and tilted implants, using the search string “OR” and additional hand search was performed by screening the lists of all articles selected, and full texts of potentially interesting studies were examined. The search was limited to the English language. The search included scientific articles published until February 2018.
The inclusion criteria consisted of the all-on-four implant design, its use in complete edentulous maxillary and mandibular cases, advantages and disadvantages of the technique, and changes observed in the maxilla and mandible in complete edentulous cases. Clinical trials and laboratory studies on the subject using the full text and English language were evaluated.
Studies not meeting all inclusion criteria were excluded from the review. Publications dealing with the following topics were also excluded: all-on-six implant design.
Selection of studies
Three authors independently screened the titles derived from the searches based on the inclusion criteria. On the basis of the selection of articles were then obtained in full text. The final selection based on inclusion/exclusion criteria was made for the full-text articles. Three authors evaluated together the reference lists of all articles selected, and full texts of these studies were examined.
| Results|| |
All recent publications on the all-on-four implant design, advantages, disadvantages, indications, and contraindications of this technique were selected [Table 1], [Table 2], [Table 3], [Table 4],,,,,,,,,,,,,,,,,,,,, as this was the primary aim of this review. A total of 176 articles were found as a result of Google Scholar, Pubmed, and Cochrane Library. Thirty-nine articles were selected according to inclusion criteria. In addition, 13 studies were found by screening the reference list of all included publications. The search included peer-reviewed publications only in English language.
General characteristics of included studies
Thirty nine articles were selected according to inclusion criteria; of these, 20 were related to the clinical trials. A total of 13 articles were found as a result of an additional hand search by screening the reference list of all included publications. Thirteen articles were selected according to inclusion criteria; of these, 11 were related to the clinical trials.
| Discussion|| |
All-on-four implant designs were developed especially for the application in severely resorbed mandibular completely edentulous cases, but later, they were also applied in maxillary completely edentulous cases. In cases when resorption is severe in the mandibular posterior region, full-arch fixed prostheses can be made with four implants placed in the interforaminal region. In cases when sinus-dependent implant applications in the maxilla are limited, the application is performed so that it will not cross the mesial wall of sinuses. It has many advantages compared with conventional complete edentulism implant applications. In all-on-four implant designs, digital, diagnostic, CAD/CAM-assisted surgical procedures are used. Moreover, dental ceramics or metal-reinforced ceramics with the CAD/CAM system are used in making full-arch fixed prosthetic restoration.
Factors affecting the construction of maxillary and mandibular full-arch all-on-four implant-assisted fixed prosthesis are the triangle, square, or U-shape of the arch, the position of mental foramina in the mandible, the position and resorption degree of maxillary sinuses in the maxilla, the value of the anteroposterior (AP) distance, the cantilever length, parafunctional status, crown heights, the status and prosthetics type of the opposite arch, the activity of the chewing muscles, the number, type, shape of implants, the quality and quantity of the bone, and the patient's systemic status.,,,
Implant loading protocols for completely edentulous mandible and maxilla include different protocols such as conventional loading, early loading, and immediate loading for full-arch fixed prostheses.
Immediate loading is preferred for all-on-four implant-assisted fixed prostheses.,,, Following the implant application, temporary prosthetic restorations are made and start to function immediately. Thus, patients do not remain edentulous, and they use prostheses phonetically, aesthetically, and functionally.
Within 1 week following the placement of implants in the all-on-four mandibular implant design, a temporary prosthesis consisting of an acrylic resin base and teeth is made, and implants are loaded immediately and start to function. The permanent prosthesis is made as a metal--ceramic full-arch fixed prosthesis approximately 3 months later.,
Prosthetic materials used in all-on-four implant-assisted prostheses are an important factor affecting stress/strains observed in implants and peri-implant bone. In this regard, while some researchers suggest , a metal substructure due to its rigid structure, others suggest full-acrylic resin prostheses and state that this structure is used for a longer period.,
The tensile strength limit values of materials are 552--1034 MPa for Co--Cr, 860--965 MPa for Ti, and 900--1200 MPa for Zr. Stress is higher in prosthetic materials with high hardness and durability. However, because of the high elastic modulus values of such materials, breakage or mechanical complications against bending and deformations are lower.
Full-arch all-on-four implant-assisted fixed dental prostheses are metal-reinforced ceramic restorations, metal-reinforced hybrid fixed prostheses, and zirconia-reinforced ceramic fixed prostheses., The increased rigidity associated with the metal frameworks in prostheses had an important role in the survival rates seen with this design, although the literature is not conclusive in this matter. Grunder  found that implant failures were found in patients with nonmetal-reinforced restorations. Others  who have used acrylic resin prostheses have reported high survival rates. Although the literature is conflicting on this point,,, several authors maintain that the use of acrylic resin (shock absorbing occlusal surface) results in reduced stresses transmitted to the bone--implant interface., Patients who were treated with bar-retained implant supported overdentures experienced difficulties in maintaining good oral hygiene and have high plaque indexes. Mechanical problems occurred to the bar-retained acrylic superstructures could be resolved more cheaply than those occurred to the ceramic superstructures.,,,,, With the development of restorations made with zirconia substructure ceramic systems using computer-aided design and computer-aided manufacturing (CAD/CAM) and performing zirconia core ceramic systems with these methods for the last 20 years, more rapid, aesthetic, and durable prostheses have been made. It has been emphasized that implant-assisted full-arch fixed prosthetic restorations made according to the all-on-four concept are biomechanically adequate. Studies continue to make longer-lasting and advantageous treatments with fewer implants. All-on-four protocol indications [Table 1],,,, contraindications [Table 2],,, advantages [Table 3],,,,,,,,,,,, and disadvantages [Table 4],,,,,,,, are given in the following section.
There are generally macroscopic and microscopic differences between edentulous maxillae and edentulous mandibles. There should be an adequate amount of the alveolar bone for implants in the anterior of the edentulous maxilla. The maxillary bone is significantly more trabecular, and thus it is determined to be less dense. Posterior maxilla bone resorption, the current bone quality, and quantity are insufficient. The maxillary sinus leads to difficulties in the implant presence.,,,, [Table 5],,,, and [Table 6],,, contain information on atrophic edentulous maxilla implants to be performed in the process of implementation and the disadvantages of the mentioned process.
|Table 5: Atrophic edentulous maxilla transactions to be made in the implementation of the implant|
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|Table 6: The drawbacks of the atrophic edentulous maxilla in the implementation process|
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There should be an adequate amount of bone for the placement of implants in the anterior alveolar crest for the edentulous mandible. Higher posterior mandible bone resorption, the current bone quality, and quantity are inadequate. When posterior mandibular bone resorption is excessive, bone quality and quantity are observed to be inadequate. In this case, when the implant is placed, the implant may damage the nerve of the mandible.,,,, [Table 7],,, and [Table 8] contain information on the atrophic edentulous mandible implant to be performed in the process of implementation and disadvantages of the mentioned process.
|Table 7: Atrophic edentulous mandibula transactions to be made in the implementation of the implant|
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|Table 8: The drawbacks of the atrophic edentulous mandibula in the implementation process|
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| Conclusions|| |
Although there are many articles on mandibular all-on-four implant restorations, short- and medium-term clinical trials are available but no long-term clinical trials covering 10 years and above have been encountered. More studies and information are found on maxillary all-on-four implant designs. Furthermore, not much data were found on the use of different ceramic systems in implant-assisted prosthetic restorations. Although the vertical placement is standard for anterior implants, the application of posterior implant angles at different angles suggests that there is no standard for this situation and that it can vary according to the characteristics of the case. Moreover, despite being the implant recommended to be used in terms of implant types, not many studies were encountered on the use of different implant systems. No standard length and diameter could be determined for implant lengths. More studies are needed to be conducted on all-on-four implant-assisted prosthetic restorations which have many advantages.
Because of the fact that an increase in comfort and aesthetic expectations of both the mandible and maxilla has been observed during prosthetic dental treatment in all-on-four protocols, it is possible to use them successfully. Nevertheless, it is necessary to increase long-term reliability limit as a result of conducting further clinical-based studies. It is required to apply all-on-four protocols, full-arch implant osseointegration in conventional restoration, biological and mechanical concepts and rules by taking them into account since the overall treatment plan in implantology, surgical stage, the precision of technique, the rules of the temporary prosthesis, appropriate prosthetic superstructures, cantilever length, usage of materials produced with developed technology, and adequate know-how are necessary. It is a well-known fact that the all-on-four protocol performed by considering all of the above-mentioned increases the success rate of complying with the rules of prosthetic restoration that are specific to the system.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]