Predictability of short dental implants for rehabilitation of the complete edentulous: A systematic review

Setyawan Bonifacius; Rasmi Rikmasari; Tatacipta Dirgantara; Cortino Sukotjo

doi:10.4103/JIOH.JIOH_295_21

REVIEW ARTICLE

Year : 2022 | Volume : 14 | Issue : 4 | Page : 331-341

Predictability of short dental implants for rehabilitation of the complete edentulous: A systematic review

Setyawan Bonifacius¹, Rasmi Rikmasari², Tatacipta Dirgantara³, Cortino Sukotjo⁴
¹ Biotechnology Doctoral Program, Graduate School, Universitas Padjadjaran, West Java, Indonesia; Department of Prosthodontic, Faculty of Dentistry, Universitas Padjadjaran, West Java, Indonesia
² Department of Prosthodontic, Faculty of Dentistry, Universitas Padjadjaran, West Java, Indonesia
³ Faculty of Mechanical and Aerospace Engineering, Institut Teknologi Bandung, West Java, Indonesia
⁴ College of Dentistry, University of Illinois at Chicago, Chicago, IL, USA

Date of Submission	26-Oct-2021
Date of Decision	25-Apr-2022
Date of Acceptance	28-Apr-2022
Date of Web Publication	29-Aug-2022

Correspondence Address:
Rasmi Rikmasari
Jalan Wartawan 2 No. 18, Bandung, 40264 West Java
Indonesia

Source of Support: None, Conflict of Interest: None

Check

DOI: 10.4103/JIOH.JIOH_295_21

Abstract

Aim: The use of short implants is emerging as a promising option in the implant-based rehabilitation of edentulous patients; yet their clinical performance is not fully documented. The purpose of this systematic review was to assess the clinical performance of the use of short implants on complete-arch implant-supported fixed dental prostheses and to compare their design with the in-vitro study. Materials and Methods: The PubMed database of the United States National Library of Medicine and EBSCOhost Research Databases were used as electronic databases, and a literature search was accomplished with a personal computer on articles published in English from January 2010 up to and including August 2020. Articles available online in electronic form before their publication in material form were considered eligible for inclusion in the present article. Results: The electronic search in both databases (PubMed and EBSCOhost) provided a total of 6779 titles and abstracts that were deemed potentially relevant to the influence of the short implant on a fixed complete denture. During the manual search of dental journals, 57 titles and abstracts were examined. In the second phase of study selection, the complete text of 1028 articles was retrieved and subjected to scrutiny. Throughout this procedure, 70 articles were obtained and the rest were excluded. Finally, the remaining 15 articles met the study inclusion criteria and were approved by all reviewers. Short implants offer benefits in terms of less invasive surgery, ease of handling, and reduced risk of damaging anatomical structures. Short implants can also be used in the rehabilitation of edentulous jaws. Avoiding or minimizing the length of the cantilever in dental implants is an important rule for the long-term success of implant treatment, including the rehabilitation of an edentulous jaw using an implant-supported fixed denture. The location of placement and the number of short implants are very influential in reducing the risk of excessive stress on the peri-implant bone. Conclusion: Short implants are potential alternatives to rehabilitating edentulous jaws, whether combined with standard size or longer implants or “All-on-short” as a whole. Further studies are still needed to obtain a guideline for the use of short implants to rehabilitate edentulous patients.

Keywords: Complete Short Implant Prostheses, Edentulous, Fixed Dental Prostheses, Short Implant

How to cite this article:
Bonifacius S, Rikmasari R, Dirgantara T, Sukotjo C. Predictability of short dental implants for rehabilitation of the complete edentulous: A systematic review. J Int Oral Health 2022;14:331-41

How to cite this URL:
Bonifacius S, Rikmasari R, Dirgantara T, Sukotjo C. Predictability of short dental implants for rehabilitation of the complete edentulous: A systematic review. J Int Oral Health [serial online] 2022 [cited 2023 Mar 23];14:331-41. Available from: https://www.jioh.org/text.asp?2022/14/4/331/355017

Introduction

Dental implants are one of the most dynamic topics in dentistry today. The manufacture of dentures especially complete dentures faces challenges when determining the bone volume of the patient. It is well known that patients with incomplete teeth have experienced sufficient alveolar bone resorption so that the remaining bone volume is insufficient for a standard size implant. Various techniques have been used to overcome this limitation, for example, sinus lifting procedures and bone grafts, but these methods will add a lot of costs, increase the overall treatment time, and in some cases the results are unpredictable and may even fail. Boyacigil et al.^[1] conducted a study on the incidence of perforation of the maxillary sinus membrane by performing the sinus lifting procedure using the crestal approach technique. From the results of this study, it can be concluded that the clinical and radiographical results show that crestal sinus lifting is a safe and predictable surgical procedure, but from these results there remains a membrane perforation, which in this study was 18.2%. However, the patients with membrane perforation need to be kept in close follow-up to control sinus infection and to maintain dental implant survival.^[1]

A systematic review conducted by Thoma et al.^[2] concluded that the outcomes of the survey analyses demonstrated predictably high implant survival rates for short implants and longer implants placed in augmented sinus and their respective reconstructions. Given the higher number of biological complications such as increased morbidity, costs, and surgical time of longer dental implants in the augmented sinus, shorter dental implants may represent the preferred treatment alternative.^[2]

In the past, the use of short-length implants was related to lower success rates, with 10 mm considered as the minimum length for a correct occlusal load distribution throughout the implant body.^[3] However, further investigations demonstrated that the occlusal forces were concentrated on the cortical aspect of bone, independent of the implant length.^[4],[5],[6]

The results of previous studies indicated that implant length was not related to the overall survival rate of an implant restoration. The results of clinical and laboratory studies have shown that short implants have been tested to be able to survive in the long term and can be compared with long implants.^[7],[8],[9] Extra-short implants that are 6 mm long or shorter have a high success rate. Implants of this type have a high success rate, especially when displaced compared to without discipline.^[10] The research of Lombardo et al.^[11] proved that short and extra-short implants have a high success rate in the single restoration of maxillary premolar and molars.^[11]

In cases of patients with complete edentulous jaws, complete dentures are required. Problems that are often faced by a conventional complete denture include the lack of retention and support, which result in disruption of the stability of the denture. This will further affect the speech function, aesthetics, and even the effectiveness of the wearer’s masticatory function.^[12]

Various efforts were made to overcome the problems mentioned earlier, including the introduction of various impression techniques,^[13] arrangement of teeth in neutral zone,^[14] arrangement of teeth according to the principle of lingualized occlusion,^[15] the addition of various retention devices, and implant placement. Implants are especially helpful in cases in which the alveolar ridge is very thin or flat due to resorption. Edentulous patients, especially those who have not had teeth for a long time, usually have excessive resorption of the alveolar bone. This resorption can occur, both due to physiological and pathological factors.^[16] In such cases, conventional removable complete denture fabrication techniques often do not give satisfactory results, thus the use of implants is often unavoidable.

Implant-supported fixed complete dentures pose a challenge when compared with removable complete dentures. Severe alveolar bone resorption often occurs in patients who have lost all their teeth, so it is necessary to consider the best treatment options, even in some cases, implant placement without bone addition procedures and/or sinus lifting is contraindicated. The number of implants required for each jaw depends on the design of the fixed denture to be made, but, in general, the minimum number of implants for the maxillary and mandibular fixed complete dentures is 4.^[17],[18]

All-on-four as a concept of implant-supported fixed complete denture emerged as a solution in patients with severe alveolar bone resorption. This design consisted of two implants placed vertically in the left and right anterior regions of the jaw and two implants placed in the left and right posterior regions with an anterior tilt position. The four implants used are usually long, and this aims to provide adequate support for the superstructure above.^[19] The implant in the posterior region is tilted to avoid bone augmentation procedures and to avoid important anatomical structures (maxillary sinus and mandibular canal).^[20] The tilted implant also aims to reduce the length of the cantilever and to increase the anteroposterior stretch distance between the most anterior and posterior implants, which provides several prosthetic advantages.^[20] However, one of the drawbacks of All-on-four is it is very technique-sensitive and requires elaborate pre-surgical preparation such as CAD/CAM, surgical splint. In addition, in most cases, the cantilever arm at the distal end of the prosthesis cannot be eliminated, especially in the mandible.^[21]

There are gaps in the literature related mainly to the short implant number and distribution, since no consensus has been established regarding the use of a short implant to support fixed complete dentures. This systematic review aimed to summarize and update the use of short implants as well as number and location in the manufacture of fixed complete dentures, based on clinical and laboratories studies.

Materials and Methods

Search strategy for identification of studies electronic search

The PubMed database of the United States National Library of Medicine and EBSCOhost Research Database were used as electronic databases, and a literature search was accomplished with a personal computer on articles published in English from 2000 up to and including August 2020. Articles available online in electronic form before their publication in material form were considered eligible for inclusion in the present article.

The studies selected for the present analysis met the criteria established by the Population, Intervention, Comparison, Outcome (PICO) question: How is the clinical performance of the use of short implants on complete-arch implant-supported fixed dental prostheses and compared their design with in-vitro study? In this question, “population” referred to edentulous patients rehabilitated using short dental implants; “intervention” was the design of complete-arch fixed prostheses supported by multiple implants, and among these implants, there are one or more short implants per jaw both in combination with standard size implants or with all short implants (All-on-short); “comparison” was the in-vitro design of complete-arch fixed prostheses supported at least by one or more short implants per jaw; and the primary “outcome” evaluated was the predictability of short dental implants for rehabilitation of the complete edentulous.

The electronic search was carried out by applying the following terms and keywords: short implant, fixed complete prosthesis, complete edentulous AND short implant, complete edentulous AND full arch, complete short implant prostheses OR complete implant bridge, fixed complete prostheses AND short implant, edentulous jaws AND short implant, complete edentulous AND short implant AND, complete edentulous AND full arch AND, complete short implant prostheses AND biological complications, and complete short implant prostheses AND technical complications.

Manual search of journals

Journal article searches are also done manually via Google search by entering other keywords such as short implant finite element analysis (FEA), short implant fixed prostheses, and short implant finite element method. All selected articles were filtered by title and abstract. Articles that were not found in the full article were not included, even though the title and abstract might match the search topic criteria.

Inclusion/exclusion criteria and selection of studies

In the first phase of study selection, the titles and abstracts of all identified publications were screened autonomously and in duplicate by all reviewers to evaluate their eligibility for selection in this systematic review based on predetermined inclusion and exclusion criteria. The following inclusion criteria were accepted by all reviewers, including all publications in the dental literature must be in English, the period of publications was between 2010 and 2020, articles can be in the form of research or case reports, the study and case report should be a complete implant-supported fixed denture involving one or more short implants, and case report articles can follow success in the short-, medium-, and long-term; or if something fails. The exclusion criteria in this review were implanted for a fixed partial denture, articles of a complete but removable denture, and articles of the fixed complete denture but all implants with a length of ≥10 mm.

Data collection and selection techniques

Titles and abstracts that could potentially be included in the inclusion were selected initially by all calibrated reviewers. All titles and abstracts selected by the reviewer were discussed together for the possibility of inclusion in the full-text reading inclusion. If the title and abstract did not provide sufficient information, the reviewer would read the article in full. If an article was found with questionable content by one reviewer, the reviewer could discuss it with other reviewers to decide whether the article could be included in inclusion or not.

Results

Study selection and classification

The electronic search in both databases (PubMed and EBSCOhost) provided a total of 6779 titles and abstracts that were deemed potentially relevant to the influence of the short implant on a fixed complete denture. During the manual search of dental journals, 58 titles and abstracts were examined. In the second phase of study selection, the complete text of 1029 articles was retrieved and subjected to scrutiny. Throughout this procedure, 71 articles were obtained and the rest were excluded. Finally, the remaining 15 articles met the study inclusion criteria and were approved by all reviewers [Figure 1].

Figure 1: Search flow diagram

Click here to view

From the results of a clinical group journal search of eight studies, two studies were conducted on the maxilla only, four studies on the mandible, and two studies on both the maxilla and mandibles. The minimum short implant diameter used was 3 mm^[22] and the widest was 5 mm,^[23] whereas the shortest size was 4 mm^[24] and the longest was 8.5 mm.^[25] The design of the implant placement configuration that used all short implants (All-on-short) in one jaw was 5 studies, and 32 studies were a mixture of long and short implants in one jaw [Table 1].

Table 1: Articles obtained that met the inclusion criteria (clinical group)

Click here to view

For the in-vitro group, a total of seven studies were obtained, of which six studies were using FEA and one was using photo elastic analysis. Two studies were conducted in the maxilla and five studies in the mandible with the smallest short implant diameter at 3.75 mm and the widest at 5 mm, while the minimum length was 4 mm and the maximum was 9 mm. All studies compared various implant placement configuration scenarios with the “All-on-four” implant configuration introduced by Maló et al.,^[25] except in the study of Pimentel et al.^[26] [Table 2].

Table 2: Articles obtained that met the inclusion criteria (in-vitro group)

Click here to view

Discussion

Minimally invasive implantology has gained popularity in recent years. This popularity could be related to improvements in the surface and design of the implants and to the development of minimally invasive surgical techniques that preserve, at most, the residual alveolar bone.^[22]

The use of short implants could be an alternative to bone augmentation surgery. Short (length #8 mm) implants have been shown to have high survival rates and have resulted in three times fewer intra-operative complications compared with long implants. Different meta-analysis studies have found similar implant and prosthesis survival rates for short dental implants and standard implants placed in a vertically augmented bone. Short dental implants may be the preferred treatment in atrophic alveolar bone, as they have been associated with lower biological complications and decreased morbidity, costs, and surgical times.^[22]

The use of conventional complete dentures for the treatment of edentulous patients is a therapeutic approach that has been used for a decade. Nevertheless, due to the alveolar ridge resorption, complications such as lack of stability and reduction of the masticatory function are often assigned to the lower complete denture. To improve oral function, chewing capacity, and comfort, mandibular full-arch restorations (either fixed or removable) supported by conventional implants in the interforaminal region have been introduced and claimed as a foreseeable modality, with high success rates (from 87% up to 100%).^[27]

Short implants offer benefits in terms of less invasive surgery, ease of handling, and reduced risk of damaging anatomical structures, thus supporting the concept of a “stress-minimizing surgery.” For this reason, it would be reasonable to hypothesize their use also in clinical conditions in which longer fixtures can be inserted.^[28]

This literature review aimed to determine the performance of short implants in the rehabilitation of edentulous jaws using fixed complete dentures, both in vitro and in vivo. All of the studies indicate that short implants could be used to rehabilitate edentulous jaws used fixed denture support implants, although further research was needed to determine the best design and clinical observations that could provide long-term success.^{[7],[23],[24],[25],[26],[29],[30],[31],[32],[33],[34],[35],[36]}

In vitro, various studies using short or extra-short implants aim to provide alternative treatments for patients who require implant-supported complete fixed dentures but insufficient bone size remains. For in-vitro studies obtained from the majority, the search was studied using FEA.^{[7],[26],[33],[34],[35],[36]} Only one journal used photo elastic analysis, namely, that conducted by Pimentel et al.^[26]

Pimentel et al.^[26] in their research that studied the distribution of stress in the area around the implant showed that short implants increase stress levels in the peri-implant area when used to support a fixed prosthesis in the atrophic mandible. In this study, they placed four implants in the interforaminal area, for each group. This study found similar stress behavior when a long implant (11 mm) with a 4 mm diameter was compared with short/wide implants. Wide (5 mm in diameter) short implants showed behavior similar to the long implants, whereas implants with 5 and 7 mm length × 4 mm diameter increase the stress level around analyzed implants.^[26] A short implant with a diameter of 5 mm has the same stress level in the peri-implant area as an 11 mm long implant with a 4 mm diameter.^[26]

Sedov et al.^[28] in a case report placed a short implant in the edentulous mandible in the area between the mandibular foramen. The implant configuration is similar to that of Pimentel et al. Four implants (4.1 region—4 × 7 mm, 3.2 region—4 × 7 mm, 4.3 region—4 × 7 mm with 29^o angulation, 3.4 region—3.5 × 7 mm with 29^o angulation) were placed through the guide using a special implant driver for precise height adjustment. Likewise, Passaretti et al.^[29] placed four short implants of 5 mm with a diameter of 4 mm. However, in both cases, there were no reports during the next control so it was not known how long it lasted in the mouth. However, studies conducted by Cannizzaro et al.,^[23] Wagner et al.,^[22] and Maló et al.^[25] showed that prosthetic rehabilitation of atrophic maxilla or mandible with prostheses supported short implants, which seem to be a viable and cost-effective treatment option in the short term.^{[22],[23],[25],[37]} The only scientific evidence that shows the success of short-term outcomes is shown in a retrospective clinical study by Anitua and Alkhraisat.^[30]

Calvo-Guirado et al.^[24] conducted a study on 10 patients and placed 6 implants in each of these patients’ mandibles with the following configuration: 2 implants in length 10 mm in diameter 4.1 mm and 4 implants in the posterior with a length of 4 mm in diameter 4.1 mm. The results of their study indicate that the survival rates 12 months after implant placement were 97.5% for short and 100% for conventional implants, respectively. The marginal bone loss was lower for short implants 3, 6, and 12 months after the surgery without a statistically significant difference.^[24] In this study, there was one short implant that failed/lost and was replaced with another implant 2 weeks later. This case study was one of the interesting facts which were able to provide an alternative solution in a situation in which the residual bone size was limited.^[24]

Cantilever problem

In their research, Calvo-Guirado et al.^[24] used six implants with a standard configuration of two long implants anteriorly and four short implants posteriorly, with a configuration of placing two short implants at each terminal end of the denture framework, thereby eliminating the cantilevered arm. The removal of the cantilevered arm produced different results. Misch^[38] said that the first rule in achieving the ideal implant position is to avoid a cantilever (no cantilever) in the prosthesis design. The cantilevered design of the restoration or prosthesis will increase the amount of force acting on the implant, the implant abutment screw, prosthetic screw or cement, and the implant–bone interface.^[39] The length of the cantilever is directly related to the amount of force added by the implant abutment. This is also supported by the results of the study by Alencar et al.,^[40] which aimed to compare the pressure on peri-implant bone produced by partial prostheses with mesial and distal cantilevered dentures, on fixed partial dentures cemented or screwed into implants, which showed that cantilevering on the distal side produced more pressure on the peri-implant bone from the primary implant rather than the cantilever at the mesial.^[40]

The study of three-dimensional FEA aimed to compare the stresses transmitted to short, tilted, and vertical implants used in different configurations with the surrounding peri-implant bone in the atrophic mandible, which was conducted by Doganay and Kilic^[34] and was similar to that of Calvo-Guirado et al.,^[24] despite differing implant sizes and placement configurations. In their in-vitro research using FEA, Doganay and Kilic^[34] placed short implants at both ends of the framework terminal, thereby eliminating the cantilever extension. These variations of the non-cantilevered design are compared to the configuration that is similar to the standard All-on-four design (although they did not mention “All-on-four” in their writing). The conclusion of their research showed that distally placed short implants contributed to the reduction of stress values of the implants and the surrounding bone. The combination of two short and four straight implants without cantilevers may be a beneficial design in the rehabilitation of posteriorly atrophic mandibles.^[34]

The results of the study by Doganay and Kilic^[34] were similar to the results of the FEA study conducted by Bhering et al.^[31] and Almeida et al.,^[33] which compared All-on-four with All-on-six in the maxilla. The All-on-six treatment concept showed the most favorable biomechanical behavior and can be considered a viable alternative for moderate atrophic maxilla rehabilitation. In this study, they added one short implant each at the very end of the posterior position, and this strategy gave better results than using the basic concept of All-on-four.^[33] The basic principle between the studies of Doganay, Bhering, and Almeida was the same, namely, removing the cantilever arm by adding a short implant at the end of the cantilever. Thus there will be no more cantilever extensions. Avoiding cantilever loading should effectively reduce the risk of excessive stress on peri-implant bone,^[41] especially the cantilever extension at the distal.^[40] The effect of cantilever length seems to be a dominant factor that can diminish stress even with the fewer number of implants.^[40]

Özdemir Doğan et al.^[7] in their study that aims to evaluate the effect of the forces on the implant and supporting alveolar ridge in “All-on-four” concept and alternative designs using FEA concluded that although the “All-on-four” concept is a feasible approach clinically, short implants had decreased the amount of force transmitted to the supporting bone.^[7] In Design 1, implants were placed according to the “All-on-four” concept; Design 2, two long (13 mm long, 4 mm diameter) and two short (7 mm long, 4 mm diameter) implants; Design 3, four long and two short implants; and Design 4, two long and four short implants were placed vertically.^[7] It is not stated whether in this variation of the study design, the cantilever extension can be eliminated or not. If it is assumed that a short implant is placed at both ends of the cantilever extension framework, it can be said that the basic principles of alternative design offered by Özdemir Doğan are the same as those of Calvo-Guirado et al.,^[24] Doganay and Kilic,^[34] and Bhering et al.^[31] Furthermore, it can be said that the design of a two-short implant placement configuration as in the study conducted by Calvo-Guirado et al.^[24] and Özdemir Doğan et al.^[7] is according to the recommendations of Group 1 ITI Consensus Report. Group 1 ITI Consensus Report said that based on the findings from the studies, the clinical recommendation is made to splint restorations involving adjacent short implants.^[42]

In contrast, a randomized controlled trial that aimed to compare the performance between short implants and standard long implants was also carried out by Guida et al.^[27] In their study, they placed implants 6 and 11 mm in length in each group of 15 patients. Guida et al.^[27] placed five implants in the region between the mandibular foramen and then a screw-retained full-arch prosthesis with distal cantilevers was positioned (baseline). Evaluation results after 3 years show that the 6 mm long implant provides comparable success with the 11 mm long implant, both clinically and radiographically.^[27] Based on a study conducted by Pimentel et al.,^[26] this study was similar, in that both of them place a short implant in the interforaminal region of the mandible, without removing the cantilevered arm. These results provide a new alternative to the use of short implants to rehabilitate toothless jaws, although deep control/observation is still needed for a longer period.

The results of the FEA study by Peixoto et al.^[32] provided surprising results. The results of their research indicate that rehabilitation of severely resorbed mandibles with four short implants placed distally at 45°, without lower transcortical involvement, was biomechanically more favorable, generating lower stress peaks, than the models with short implants on an All-on-four, or on an upright configuration, with or without lower transcortical involvement.^[32]

From the results of this study, it can be seen that the configuration of placement and location of short implants clinically (in vivo) do not always follow/are not based on the results of in vitro studies. Although, for example, theoretically, the presence of a cantilever arm is a disadvantage in implant-supported fixed dentures, this has been proven from various studies, but in reality, cantilevering is a difficult thing to avoid. This is probably because anatomical forms of in-vivo studies vary widely. For the mandibular region, the remaining bone area is often only in the anterior area, but in the posterior area, bone is often found to be heavily resorbed due to early loss of posterior teeth.^[43],[44] Furthermore in the literature review, Jeyapalan and Krishnan^[43] said that with increasing age, the most common cases of tooth loss include Kennedy Class 1 and 2 classifications.^[43] Thus, if these remaining anterior teeth are damaged and must be extracted, then the side of the bone in the anterior region is relatively higher than that in the posterior region, which has already been lost. Coupled with the absence of the mandibular canal in the anterior region, the only possible implant insertion site is in the anterior region of the mandible, thereby creating a distal posterior cantilever arm.^[45],[46] In contrast, studies that have attempted to remove the distal cantilever arm assume that in the mandibular region there is considered sufficient bone for the placement of a short implant in the area of the far end of the prosthesis. Likewise, for clinical studies, patients who morphologically still contained bone with sufficient volume for placement of short implants were selected.^{[23],[24],[34]}

This also happened in studies in the maxilla region. The presence of the maxillary sinus exacerbated by severe alveolar ridge resorption due to long-term loss of posterior teeth makes it impossible to place even a short implant in the region adjacent to the maxillary sinus, so it is often difficult to avoid the cantilever arm distal to the prosthesis. Thus, in-vitro studies in the maxillary region aimed at removing the cantilever arm by placing a short implant at the distal end of the prosthesis assumed that the bone in that region was thick enough for the placement of a short implant.^[31],[33] However, from the results of this systematic review, clinical studies in the maxilla only find one article reported by Anitua and Alkhraisat^[30] that implant placement design aimed at removing the cantilever arm. This is most likely due to the position of the maxillary first molars, which are closer to the maxillary sinus than the premolars and canines so that when the posterior teeth, especially the maxillary first molars, are often damaged earlier than other teeth and are eventually extracted, they will experience alveolar ridge resorption which results in increased alveolar ridge resorption.^[47],[48] Thus, for a clinical study, it will be difficult to find patients with bone height in the maxillary first molar region that is still sufficient for the placement of short implants.^{[47],[49],[50]}

From the article search results, there were several in-vitro research articles with designs that place a short implant at the distal end of the prosthesis intending to remove the cantilever arm, namely, Doganay and Kilic^[34] and Kucukkurt and Tukel^[35] in the mandible and Bhering et al.^[31] and Almeida et al.^[33] in the maxilla.^{[31],[33],[34],[35]} Özdemir Doğan et al.^[7] also placed short implants in the posterior area of the prosthesis design but it is not clear whether the cantilever arm remains or not.^[7] Meanwhile, the studies conducted by Peixoto et al.^[32] and Pimentel et al.^[26] did not eliminate the cantilever arm in their research design. From these in-vitro studies, the majority used short implants combined with standard implants,^{[7],[31],[33],[34],[35]} except for the research conducted by Peixoto et al.^[32] and Pimentel et al.,^[26] which in their research design used all short implants in one of their research designs.

The cantilever in implant-supported dentures has long been a concern and is considered to be a contributor to implant failure. A systematic review conducted by Keshavarz Valian et al.^[51] showed that in terms of the cantilever length, it seems that using fewer cantilever lengths would reduce the stress.^[51] Research conducted by Alencar et al.^[40] aimed to compare stresses in the peri-implant bone produced by fixed partial prostheses with mesial and distal cantilevers, when cemented or screwed onto implants, and concluded that distal cantilevers produce more stresses in the peri-implant bone of the primary implant than mesial cantilevers. In a study conducted by Silva et al.,^[52] FEA was used to compare the distribution of stress on maxillary fixed dentures supported by four and six implants, and with posterior implants placed at an angle of 45°. They found that the presence of a cantilever significantly increased the levels of stress on the implant prosthesis unit.^[52] However, from the results of a systematic review conducted by the authors, not all strategies to remove the cantilever arm by placing a short implant at the distal end resulted in decreased stress on the bone around the implant. Research conducted by Kucukkurt and Tukel^[35] concluded that the use of extra-short implants in the posterior region, for the elimination of cantilever extension, was decided to be the last method of choice among all the techniques compared in this study. This was because of the high stresses on bones in most conditions, even though it balances the forces on the implants against the forces applied from the molar region. In this study, Kucukkurt and Tukel^[35] used an extra-short implant with a length of 4 mm and a diameter of 4.1 mm with a configuration of two axial interforaminal implants and two posterior extra-short implants.^[35]

Some of the studies conducted in vitro used two short implants added to the configuration of four standard or long implants with various placement configurations, so there were a total of six implants.^{[31],[33],[34]} Meanwhile, research by Pimentel et al.,^[26] Peixoto et al.,^[32] Özdemir Doğan et al.,^[7] and Kucukkurt and Tukel^[35] made a configuration by still using four implants, including a short implant in it.

Conclusion

After having systematically reviewed the scientific literature regarding the use of short implants for the prosthetic rehabilitation of totally edentulous patients, both in vitro or in vivo, we can conclude, taking into account the limitations of this study, the following:

Short implants are potential alternatives to rehabilitating edentulous jaws, whether combined with standard size or longer implants or “All-on-short” as a whole.

Clinically, short implants combined with standard or longer implants for rehabilitating edentulous jaws have a good long-term success rate.

The cantilever is very influential in the success of rehabilitating edentulous jaws using implant support.

The long-term success of using short implants as a whole (All-on-short) is influenced by the number of implants used, the location of implant placement, and the elimination of the cantilever arm.

Further studies are still needed to obtain a guideline for the use of short implants to rehabilitate edentulous patients.

Short implants are potential alternatives to rehabilitating edentulous jaws, whether combined with standard size or longer implants or “All-on-short” as a whole.

Acknowledgements

The authors express their gratitude to the Biotechnology Doctoral Study Program, Graduate School Universitas Padjadjaran, Bandung, Indonesia and the Center for Oral Biomaterials Studies, Faculty of Dentistry in Universitas Padjadjaran, Bandung, Indonesia.

Financial support and sponsorship

This project was funded by Riset Disertasi Doktor Unpad (RDDU) Grant from Universitas Padjadjaran, Bandung, Indonesia.

Conflict of interest

The authors reported no conflicts of interest related to this study.

Authors’ contribution

All authors contributed in data collection, data acquisition and analysis, data interpretation, manuscript writing.

Ethical policy and Institutional Review board statement

Not applicable.

Patient declaration of consent

Not applicable.

Data availability statement

Not applicable.

References

1.	Boyacigil DU, Er N, Karaca Ç, Koç O The incidence of sinus membrane perforation in crestal sinus lift technique. Clin Oral Implants Res 2018;29:435.
2.	Thoma DS, Zeltner M, Hüsler J, Hämmerle CH, Jung RE EAO Supplement Working Group 4—EAO CC 2015 short implants versus sinus lifting with longer implants to restore the posterior maxilla: A systematic review. Clin Oral Implants Res 2015;26(Suppl. 11):154-69.
3.	Block MS, Delgado A, Fontenot MG The effect of diameter and length of hydroxylapatite-coated dental implants on ultimate pullout force in dog alveolar bone. J Oral Maxillofac Surg 1990;48:174-8.
4.	Pierrisnard L, Renouard F, Renault P, Barquins M Influence of implant length and bicortical anchorage on implant stress distribution. Clin Implant Dent Relat Res 2003;5:254-62.
5.	Kitamura E, Stegaroiu R, Nomura S, Miyakawa O Influence of marginal bone resorption on stress around an implant—A three-dimensional finite element analysis. J Oral Rehabil 2005;32:279-86.
6.	Nunes M, Almeida RF, Felino AC, Malo P, de Araújo Nobre M The influence of crown-to-implant ratio on short implant marginal bone loss. Int J Oral Maxillofac Implants 2016;31:1156-63.
7.	Özdemir Doğan D, Polat NT, Polat S, Şeker E, Gül EB Evaluation of “All-on-four” concept and alternative designs with 3D finite element analysis method. Clin Implant Dent Relat Res 2014;16:501-10.
8.	Himmlová L, Dostálová T, Kácovský A, Konvicková S Influence of implant length and diameter on stress distribution: A finite element analysis. J Prosthet Dent 2004;91:20-5.
9.	Al-Hashedi AA, Taiyeb-Ali TB, Yunus N Outcomes of placing short implants in the posterior mandible: A preliminary randomized controlled trial. Aust Dent J 2016;61:208-18.
10.	Ravidà A, Barootchi S, Askar H, Suárez-López Del Amo F, Tavelli L, Wang HL Long-term effectiveness of extra-short (≤ 6 mm) dental implants: A systematic review. Int J Oral Maxillofac Implants 2019;34:68-84.
11.	Lombardo G, Pighi J, Marincola M, Corrocher G, Simancas-Pallares M, Nocini PF Cumulative success rate of short and ultrashort implants supporting single crowns in the posterior maxilla: A 3-year retrospective study. Int J Dent 2017;2017:8434281.
12.	Basker RM, Davenport JC, Thomason JM Stability of dentures. In: Prosthetic Treatment of the Edentulous Patient. 5th ed. West Sussex: John Wiley & Sons, Ltd, Publication; 2011. p. 55-67.
13.	Rao S, Chowdhary R, Mahoorkar S A systematic review of impression technique for conventional complete denture. J Indian Prosthodont Soc 2010;10:105-11.
14.	Beresin VE, Schiesser FJ The neutral zone in complete dentures. 1976. J Prosthet Dent 2006;95:93-100; discussion 100-1.
15.	Phoenix RD, Engelmeier RL Lingualized occlusion revisited. J Prosthet Dent 2010;104:342-6.
16.	Zmysłowska E, Ledzion S, Jedrzejewski K Factors affecting mandibular residual ridge resorption in edentulous patients: A preliminary report. Folia Morphol (Warsz) 2007;66:346-52.
17.	Resnik RR, Misch CE The edentulous mandible: Fixed versus removable prosthesis treatment planning. In: Misch’s Contemporary Implant Dentistry. 4th ed. Canada: Mosby Elsevier Inc.; 2021. p. 567-88.
18.	Mericske-Stern RD, Taylor TD, Belser U Management of the edentulous patient. Clin Oral Implants Res 2000;11(Suppl. 1):108-25.
19.	Maló P, Rangert B, Nobre M “All-on-four” immediate-function concept with Brånemark system implants for completely edentulous mandibles: A retrospective clinical study. Clin Implant Dent Relat Res 2003;5(Suppl. 1):2-9.
20.	Cavalli N, Barbaro B, Spasari D, Azzola F, Ciatti A, Francetti L Tilted implants for full-arch rehabilitations in completely edentulous maxilla: A retrospective study. Int J Dent 2012;2012:180379.
21.	Taruna M, Chittaranjan B, Sudheer N, Tella S, Abusaad M Prosthodontic perspective to All-on-4® concept for dental implants. J Clin Diagn Res 2014;8:16-9.
22.	Wagner F, Seemann R, Marincola M, Ewers R Fiber-reinforced resin fixed prostheses on 4 short implants in severely atrophic maxillas: 1-year results of a prospective cohort study. J Oral Maxillofac Surg 2018;76:1194-9.
23.	Cannizzaro G, Felice P, Ippolito DR, Velasco-Ortega E, Esposito M Immediate loading of fixed cross-arch prostheses supported by flapless-placed 5 mm or 11.5 mm long implants: 5-year results from a randomised controlled trial. Eur J Oral Implantol 2018;11:295-306.
24.	Calvo-Guirado JL, López Torres JA, Dard M, Javed F, Pérez-Albacete Martínez C, Maté Sánchez de Val JE Evaluation of extra-short 4-mm implants in mandibular edentulous patients with reduced bone height in comparison with standard implants: A 12-month results. Clin Oral Implants Res 2016;27:867-74.
25.	Maló P, de Araújo Nobre MA, Lopes AV, Rodrigues R Immediate loading short implants inserted on low bone quantity for the rehabilitation of the edentulous maxilla using an all-on-4 design. J Oral Rehabil 2015;42:615-23.
26.	Pimentel MJ, Silva WJ, Del Bel Cury AA Short implants to support mandibular complete dentures—Photoelastic analysis. Braz Oral Res 2017;31:e18.
27.	Guida L, Annunziata M, Esposito U, Sirignano M, Torrisi P, Cecchinato D 6-mm-short and 11-mm-long implants compared in the full-arch rehabilitation of the edentulous mandible: A 3-year multicenter randomized controlled trial. Clin Oral Implants Res 2020;31:64-73.
28.	Sedov Y, Mordanov O, Grigoriev S, Avanesov A, Khabiev K The placement of four short implants and full-arch early loading in the edentulous patient suffering from severe mandibular alveolar ridge atrophy. Case Rep Dent 2019;2019:1656243.
29.	Passaretti A, Petroni G, Miracolo G, Savoia V, Perpetuini A, Cicconetti A Metal free, full arch, fixed prosthesis for edentulous mandible rehabilitation on four implants. J Prosthodont Res 2018;62:264-7.
30.	Anitua E, Alkhraisat MH Fifteen-year follow-up of short dental implants in the completely edentulous jaw: Submerged versus nonsubmerged healing. Implant Dent 2019;28:551-5.
31.	Bhering CL, Mesquita MF, Kemmoku DT, Noritomi PY, Consani RL, Barão VA Comparison between All-on-four and All-on-six treatment concepts and framework material on stress distribution in atrophic maxilla: A prototyping guided 3D-FEA study. Mater Sci Eng C Mater Biol Appl 2016;69:715-25.
32.	Peixoto HE, Camati PR, Faot F, Sotto-Maior BS, Martinez EF, Peruzzo DC Rehabilitation of the atrophic mandible with short implants in different positions: A finite elements study. Mater Sci Eng C Mater Biol Appl 2017;80:122-8.
33.	Almeida EO, Rocha EP, Freitas Júnior AC, Anchieta RB, Poveda R, Gupta N, et al. Tilted and short implants supporting fixed prosthesis in an atrophic maxilla: A 3D-FEA biomechanical evaluation. Clin Implant Dent Relat Res 2015;17(Suppl. 1):e332-42.
34.	Doganay O, Kilic E Comparative finite element analysis of short implants with different treatment approaches in the atrophic mandible. Int J Oral Maxillofac Implants 2020;35:e69-76.
35.	Kucukkurt S, Tukel HC Comparison of four implant-supported fixed rehabilitation options of the edentulous mandible: A 3D finite element analysis. J Adv Oral Res 2020;11:57-64.
36.	Pauletto P, Ruales-Carrera E, Gonçalves TMSV, Philippi AG, Donos N, Mezzomo LA Fixed and removable full-arch restorations supported by short (≤ 8-mm) dental implants in the mandible: A systematic review and meta-analysis. Int J Oral Maxillofac Implants 2019;34:873-85.
37.	Grant BT, Pancko FX, Kraut RA Outcomes of placing short dental implants in the posterior mandible: A retrospective study of 124 cases. J Oral Maxillofac Surg 2009;67:713-7.
38.	Misch CE Treatment plans related to key implant positions and implant number. In: Contemporary Implant Dentistry. 3rd ed. St. Louis, MO: Mosby Elsevier; 2008. p. 147-59.
39.	Misch CE, Resnik RR Treatment plans related to key implant positions and implant number. In: Misch’s Contemporary Implant Dentistry. 4th ed. Canada: Elsevier Inc.; 2021. p. 467-78.
40.	Alencar SM, Nogueira LB, Leal de Moura W, Rubo JH, Saymo de Oliveira Silva T, Martins GA, et al. FEA of peri-implant stresses in fixed partial denture prostheses with cantilevers. J Prosthodont 2017;26:150-5.
41.	Sugiura T, Yamamoto K, Horita S, Murakami K, Kirita T Micromotion analysis of different implant configuration, bone density, and crestal cortical bone thickness in immediately loaded mandibular full-arch implant restorations: A nonlinear finite element study. Clin Implant Dent Relat Res 2018;20:43-9.
42.	Jung RE, Al-Nawas B, Araujo M, Avila-Ortiz G, Barter S, Brodala N, et al. Group 1 ITI Consensus Report: The influence of implant length and design and medications on clinical and patient-reported outcomes. Clin Oral Implants Res 2018;29(Suppl. 16):69-77.
43.	Jeyapalan V, Krishnan CS Partial edentulism and its correlation to age, gender, socio-economic status and incidence of various Kennedy’s classes—A literature review. J Clin Diagn Res 2015;9:ZE14-7.
44.	Marimuthu S, Pandurangan KK, Muralidoss H Prevalence of partial edentulism of Kennedy’ s class I classification based on different age groups and arch—A retrospective study. PalArch’s J Archaeol Egypt/Egyptol 2020;17:3382-90.
45.	Kqiku L, Sivic E, Weiglein A, Städtler P Position of the mental foramen: An anatomical study. Wien Med Wochenschr 2011;161:272-3.
46.	Zmyslowska-Polakowska E, Radwanski M, Ledzion S, Leski M, Zmyslowska A, Lukomska-Szymanska M Evaluation of size and location of a mental foramen in the Polish population using cone-beam computed tomography. Biomed Res Int 2019;2019:1659476.
47.	Pietrokovski J, Massler M Alveolar ridge resorption following tooth extraction. J Prosthet Dent 1967;17:21-7.
48.	Sharif RA, Chaturvedi S, Suleman G, Elmahdi AE, Elagib MFA Analysis of tooth extraction causes and patterns. Open Access Maced J Med Sci 2020;8:36-41.
49.	Dehghani M, Motallebi E, Navabazam A, Montazerlotfelahi H, Ezoddini F, Ghanea S The relation between maxillary sinus floor and posterior maxillary teeth roots using panoramic and cone beam computed tomography. J Dentomaxillofac Radiol Pathol Surg 2017;6:49-60.
50.	Iwanaga J, Wilson C, Lachkar S, Tomaszewski KA, Walocha JA, Tubbs RS Clinical anatomy of the maxillary sinus: Application to sinus floor augmentation. Anat Cell Biol 2019;52:17-24.
51.	Keshavarz Valian N, Talebi Ardakani MR, Aziz Ahari A, Baghani MT, Shidfar S Patterns of stress and strain in complete-arch prostheses supported by four or six implants: A literature review of finite element analyses. J Adv Periodontol Implant Dent 2019;10:77-84.
52.	Silva GC, Mendonça JA, Lopes LR, Landre J Stress patterns on implants in prostheses supported by four or six implants: A three-dimensional finite element analysis. Int J Oral Maxillofac Implants 2013;25:239-46.