Abstracts

Introduction

In the past, short implants were commonly associated with lower survival rates due to the reduced bone-to-implant contact allied to the fact that short implants are mostly installed in the posterior zone, once the quality of the alveolar bone is relatively poor ^{( 1}1Romeo E, Bivio A, Mosca D, Scanferla M, Ghisolfi M, Storelli S. The use of short dental implants in clinical practice: literature review. Minerva Stomatol 2010;59:23-31. ^{, 2}2Lee JH, Frias V, Lee KW, Wright RF. Effect of implant size and shape on implant success rates: a literature review. J Prosthet Dent 2005;94:377-381. ^{, 3}3Weng D, Jacobson Z, Tarnow D, Hurzeler MB, Faehn O, Sanavi F, et al.. A prospective multicenter clinical trial of 3i machined-surface implants: results after 6 years of follow-up. Int J Oral Maxillofac Implants 2003;18:417-423. ⁾. Moreover, the posterior region commonly presents moderate to extensive resorption, which results in very outsized crowns and a high crown-to-implant ratio when short implants are placed ⁽⁴⁾4Telleman G, Raghoebar GM, Vissink A, den Hartog L, Huddleston Slater JJ, Meijer HJ. A systematic review of the prognosis of short (<10 mm) dental implants placed in the partially edentulous patient. J Clinic Periodontol 2011;38:667-676.. In this sense, it is reasonable to suppose that the long-term performance of such implants is reduced; however, recent literature has demonstrated no significant differences in the survival rate reported by short and standard implants ^{( 5}5Misch CE, Steignga J, Barboza E, Misch-Dietsh F, Cianciola LJ, Kazor C. Short dental implants in posterior partial edentulism: a multicenter retrospective 6-year case series study. J Periodontol 2006;77:1340-1347. ^{, 6}6Atieh MA, Zadeh H, Stanford CM, Cooper LF. Survival of short dental implants for treatment of posterior partial edentulism: a systematic review. Int J Oral Maxillofac Implants 2012;27:1323-1331. ⁾.

The development of modified implant designs and surfaces including different micro-topography and chemistry might probably have contributed for the increased survival rates of short implants ^{( 1}1Romeo E, Bivio A, Mosca D, Scanferla M, Ghisolfi M, Storelli S. The use of short dental implants in clinical practice: literature review. Minerva Stomatol 2010;59:23-31. ^{, 4}4Telleman G, Raghoebar GM, Vissink A, den Hartog L, Huddleston Slater JJ, Meijer HJ. A systematic review of the prognosis of short (<10 mm) dental implants placed in the partially edentulous patient. J Clinic Periodontol 2011;38:667-676. ⁾. Nevertheless, standard outcome criteria to assess the clinical performance of the short implants are still missing in literature, becoming difficult to draw conclusions. Considering that these criteria would be used during subsequent appointments after the insertion of short implants, it could configure as an important instrument for the decision-making process on the future clinical interventions. Furthermore, the related decision should be derived from the highest level of evidence such as a systematic review ⁽⁷⁾7Sterne JA, Egger M, Smith GD. Systematic reviews in health care: Investigating and dealing with publication and other biases in meta-analysis. BMJ2001;323:101-105.. Thus, this article summarizes, through a systematic review of the literature, the essential parameters required to assess the long-term clinical performance of short and extra-short dental implants, allowing standard comparisons in future studies.

Material and Methods

Search Strategy and Study Selection

An electronic search, without language restriction, was conducted to identify studies focused on the clinical performance of short and extra-short dental implants. For that purpose, PubMed/MEDLINE, EMBASE, LILACS, and Cochrane Library databases were searched between the period of January 2000 and March 2014. The search was limited to the following filters from the referred website: "Clinical Trial", "Randomized Clinical Trials", "Prospective Studies", and "Humans". The key words used in this search were "short dental implants", "short dental implants" [MeSH term] AND "treatment outcomes", "short dental implants" [MeSH term] AND "failures", "short dental implants" [MeSH term] AND "complication", "short dental implants" [MeSH term] AND "biologic complication", "short dental implants" [MeSH term] AND "alveolar bone loss", "short dental implants" [MeSH term] AND "bone loss", "short dental implants" [MeSH term] AND "success", "short dental implants" [MeSH term] AND "clinical success".

Titles and abstracts of the searched papers were initially screened by two independent reviewers for possible inclusion. A further search was performed through the bibliographies of all relevant articles. Any discrepancies between the reviewers were discussed until a consensus was reached. Cohen's Kappa-coefficient was calculated as a measure of agreement between the two readers, revealing an excellent degree of accordance (K=0.83).

Inclusion Criteria

The first author created a search strategy in which all the titles and abstracts of the studies were examined and relevant studies selected. The selection criteria included:

In this review, a wide range of inclusion criteria to obtain general findings was included without differentiating implant type, surgical procedure technique, patient characteristics or prostheses type.

Exclusion Criteria

Animal studies, retrospective studies, case reports, reviews, non-clinical studies, explanation of technique or clinical trials with insufficient information regarding the long-term performance of short implants were not considered to avoid any risk of bias. Studies using short and standard implants to support the same prostheses were also excluded.

Data Extraction

Based on the inclusion and exclusion criteria, selected potential articles were obtained in full text. The data extracted included the following: study design, number of subjects at baseline, number of implants at baseline, implant length (mm), implant system, location, type of prosthesis, prosthesis' material, loading protocol, type of implant surface, type of implant-abutment connection, follow-up regularity, follow-up years after loading, drop-outs, number of implants in the follow-up, clinical performance assessment, training and calibration, biological parameters evaluated, biological complication, mechanical complication, esthetical complication, references to measure marginal bone loss, marginal bone loss measured, crown-to-implant ratio, implant failure, prosthetic failure, cumulative implant survival, and cumulative prosthesis survival. To fill in missing or inadequately reported data, we attempted to obtain information by contacting the authors by e-mail. Unfortunately, the contacted authors did not respond on either of the attempts for obtaining more details about the study. On the other hand, no missing information was stronger enough to exclude or jeopardize the analysis of the selected studies.

Method of Analysis

All extracted data of the selected articles were double-checked and pulled out in the Tables 1 and 2. A sensitivity analysis was conducted to check the robustness of the pooled results with regard to study by removing them one by one. After a preliminary evaluation, it was found substantial heterogeneity among the studies which could jeopardize a quantitative analysis. Thus, only the cumulative implant survival rate percentage (CSR% - confidence interval 95%) based on the failure time reported allows meta-analysis. Consequently, a more descriptive data analysis was chosen for the remaining parameters. Meta-analysis was performed considering the fixed and random effects models and statistical heterogeneity was assessed by means of I2 statistics. All the analyses were performed with Comprehensive Meta-Analysis Software (Version 3, BioStat, Englewood, NJ, USA).

Results

Study Characteristics

The search from the electronic databases identified a total of 1174 titles of short implants studies, out of which 804 were excluded after discussion. From the 370 titles selected, only 185 abstracts were electable to search for detailed analysis based on inclusion criteria. Among them, 44 articles were selected to full text analysis. Additional searching on their bibliographies provided 3 more studies, with a total of 47 articles in the full text evaluation. Finally, 34 articles were excluded based on the exclusion criteria. This resulted in a final number of 13 publications for the current review (Fig. 1).

Overall Characteristics of the Included Studies

The 13 studies that met the inclusion criteria are summarized in Table 1. Among these selected articles, three were randomized clinical trials (⁸8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121.,⁹9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324.,¹⁰10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697.), two were prospective cohort studies (¹¹11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53.,¹²12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943.), and the remaining eight were prospective studies (¹³13Deporter D, Pilliar RM, Todescan R, Watson P, Pharoah M. Managing the posterior mandible of partially edentulous patients with short, porous-surfaced dental implants: early data from a clinical trial. Int J Oral Maxillofac Implants 2001;16:653-658.,¹⁴14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282.,¹⁵15Corrente G, Abundo R, des Ambrois AB, Savio L, Perelli M. Short porous implants in the posterior maxilla: a 3-year report of a prospective study. Int J Periodontics Restorative Dent 2009;29:23-29.,¹⁶16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368.,¹⁷17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403.,¹⁸18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508.,¹⁹19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289.,²⁰20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013.). The patients were majority treated at university settings (5 studies) or in private dental clinics (3 studies), but one study ⁽¹⁷⁾17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. has a multicenter approach, combining results from patients treated in an academic environment and two private offices. Such information was not provided in the remaining four studies.

A total number of 1260 implants were placed in 687 patients with age range 18-80 years (Table 1). The follow-up period varied from 1 to 10 years while the dropout rate ranged from 0% to 14.3%. Most of studies specified the region where the implants were placed, being the majority installed in the posterior region (61.5%) of both dental arches (46%). Nine commercially available implant systems were described including Endopore implants (Innova, Toronto, Canada), machined implants (Nobel Biocare, Göteborg, Sweden), SLActive implants (Straumann, Waldenburg, Switzerland), Nobelspeedy Shorty implants (Nobel Biocare, Zurich, Switzerland), Nanotite XP Certain and Nanotite Certain Prevail implants (Biomet 3i dental implants, Palm Beach, USA), TiOblast and OsseoSpeed implants (Astra Tech AB, Mölndal, Sweden), and Superline implants (Dentium, Suwon, Korea).

In most of the selected studies, the prosthetic treatment considered was the single crowns (77%), followed by splinted fixed prostheses (46.2%) and removable implant-retained prostheses (7.7%) (Table 1). The materials applied in these prostheses were described in 9 studies and included metal-ceramic (89%) and gold-palladium-ceramic crowns (11%), besides provisional acrylic crowns (22%).

Cumulate Implant Survival Rate

All the 13 studies informed the cumulative implant survival rate, which allows the meta-analysis (Fig 2). From the total of 1260 implants placed in 687 patients, 49 were reported to be lost. Thirty implants were lost before loading (61.2% of all placed implants) and nineteen implants were lost in the follow-up period, after loading (38.8 % of all placed implants).

The cumulative implant survival rate derived from the data of each study ranged from 84% at 5 years ⁽¹⁶⁾16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. to 100% at 2 ⁽¹³⁾13Deporter D, Pilliar RM, Todescan R, Watson P, Pharoah M. Managing the posterior mandible of partially edentulous patients with short, porous-surfaced dental implants: early data from a clinical trial. Int J Oral Maxillofac Implants 2001;16:653-658. to 10 years ⁽¹⁸⁾18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508., being the mean overall failure rate of 3.9%. The effect size range from 0.052 (Z=19.8; p<0.001) to 0.042 (Z=12.83; p<0.001) at fixed and random model analysis, respectively. The highest relative fixed weight found was 20.45 from Maló et al. 2011 ⁽¹¹⁾11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. and the heterogeneity was significant (I2 = 54.3%; p=0.01).

Different reasons were pointed out for the early failure including smoking habits ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 12}12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, lack of primary stability ⁽¹²⁾12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943., possible overheating of the parent bone ⁽¹⁵⁾15Corrente G, Abundo R, des Ambrois AB, Savio L, Perelli M. Short porous implants in the posterior maxilla: a 3-year report of a prospective study. Int J Periodontics Restorative Dent 2009;29:23-29., high insertion torque (≥ 60 Ncm) applied during the implant's placement in dense bone of mandible site ⁽¹⁹⁾19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289., and problems in the osseointegration process ⁽¹¹⁾11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53.. Concerning the late failure, the main causes highlighted were fracture of an implant placed in a patient with bruxer habits ⁽¹⁴⁾14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282., peri-implantitis ^{( 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ⁾, poor oral hygiene ⁽¹⁷⁾17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403., smoking habits ^{( 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ⁾, occlusal overloading that leads to excessive marginal bone loss ⁽¹⁷⁾, and loss of osseointegration without specific reasons ^{( 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ^{, 20}20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013. ⁾.

Implant Surface

With respect to implant surface treatment, almost all articles reported the type of implant surfaces, standing out the porous sintered surface treated with spherical titanium particles ^{( 13}13Deporter D, Pilliar RM, Todescan R, Watson P, Pharoah M. Managing the posterior mandible of partially edentulous patients with short, porous-surfaced dental implants: early data from a clinical trial. Int J Oral Maxillofac Implants 2001;16:653-658. ^{, 15}15Corrente G, Abundo R, des Ambrois AB, Savio L, Perelli M. Short porous implants in the posterior maxilla: a 3-year report of a prospective study. Int J Periodontics Restorative Dent 2009;29:23-29. ^{, 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ⁾, SLActive surfaces (modified ⁽¹²⁾12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. or not ⁽²⁰⁾20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013.), anodically oxidised surfaces ^{( 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ⁾, dual etched surfaces (covered or not with nanoscale calcium phosphate crystal ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ⁾, moderately rough titanium-blasted surface ⁽¹⁸⁾18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508., and non-treated machined-surface ⁽¹⁴⁾14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282..

Figure 1
Flow chart of the search strategy

Crown-to-Implant Ratio

The crown-to-implant ratio was measured in four of the thirteen studies as a possible deleterious influence for short implants survival (Table 2). In these four articles, the measurements of the crown-to-implant ratio were approached differently. Two studies ^{( 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ^{, 20}20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013. ⁾ assessed the anatomical crown-to-implant ratio, which considers the fulcrum established at the interface between the implant shoulder and the crown-abutment complex ⁽²¹⁾21Blanes RJ. To what extent does the crown-implant ratio affect the survival and complications of implant-supported reconstructions? A systematic review. Clin Oral Implants Res 2009;20:67-72.. The other two articles ^{( 12}12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾ described the use of the clinical crown-to-implant ratio, where the fulcrum is positioned at the most coronal bone-implant contact. Regardless the considered crown-to-implant ratio, the majority of the implants reported by these four studies presented crown-to-implant ratio between 1 and 2, with extreme situations of crown-to-implant ratio >2 (16.2%) stated in only one study ⁽¹⁴⁾14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282..

Marginal Bone Loss

Marginal bone loss was calculated in all the selected studies, with the mean values varied from 0 to 2 mm; however differences on the reference points used to measure this outcome and the placement of the implants in different levels of the crestal bone could be remarked. Most of the selected studies ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ^{, 20}20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013. ⁾ considered the distance between the implant platform/shoulder or implant-abutment junction and marginal bone remodeling or the first visible bone-to-implant contact as references to measure the marginal bone loss (Table 2). However, other references such as the position of the alveolar bone at the machined/porous surface junction of the implant root component and the border between the conical and the cylindrical parts of the implant head are also cited as references ^{( 13}13Deporter D, Pilliar RM, Todescan R, Watson P, Pharoah M. Managing the posterior mandible of partially edentulous patients with short, porous-surfaced dental implants: early data from a clinical trial. Int J Oral Maxillofac Implants 2001;16:653-658. ^{, 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ⁾. Besides the quantitative value of the marginal bone loss, some studies ^{( 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾ have also considered standard success criteria such as those proposed by Albrektsson and Zarb ⁽²²⁾22Albrektsson T, Zarb GA. Determinants of correct clinical reporting. Int J Prosthodont 1998;11:517-521. or Karoussis et al. ⁽²³⁾23Karoussis IK, Salvi GE, Heitz-Mayfield LJ, Bragger U, Hammerle CH, Lang NP. Long-term implant prognosis in patients with and without a history of chronic periodontitis: a 10-year prospective cohort study of the ITI Dental Implant System. Clin Oral Implants Res 2003;14:329-339., which defines as successful the implant with vertical bone loss no greater than 1.5 mm during the first year of loading and 0.2 mm per year during the following years.

Mechanical Complications

Six studies recorded biomechanical complications which includes screw loosening ^{( 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, porcelain fracture ^{( 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ⁾, occlusal overloading ⁽¹⁷⁾17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403., food accumulation in interdental spaces ⁽⁸⁾8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121., crown decementation or fracture ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 19}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ⁾, and implant or component fracture ⁽¹⁹⁾19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289.. In the remaining studies ^{( 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ^{, 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 12}12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. ^{, 13}13Deporter D, Pilliar RM, Todescan R, Watson P, Pharoah M. Managing the posterior mandible of partially edentulous patients with short, porous-surfaced dental implants: early data from a clinical trial. Int J Oral Maxillofac Implants 2001;16:653-658. ^{, 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ^{, 15}15Corrente G, Abundo R, des Ambrois AB, Savio L, Perelli M. Short porous implants in the posterior maxilla: a 3-year report of a prospective study. Int J Periodontics Restorative Dent 2009;29:23-29. ^{, 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ^{, 20}20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013. ⁾, no further information was given in respect to biomechanical assessment of the short implants.

Biological Complications

Biological complications in the tissue surrounding short implants were reported in ten of the thirteen studies. The most cited parameters assessed were the Plaque Index (regular ^{( 12}12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ^{, 20}20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013. ⁾ or modified ^{( 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, modified Sulcus Bleeding Index ^{( 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ^{, 12}12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, Gingival Index ^{( 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ^{, 20}20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013. ⁾, probing pocket depth ^{( 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ^{, 12}12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ^{, 20}20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013. ⁾, mobility of implants ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ⁾, presence of dental calculus ^{( 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ⁾, width of keratinized mucosa ⁽¹⁹⁾19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289., resonance frequency analysis ⁽¹⁹⁾, peri-implant pathology ^{( 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ⁾, soft tissue inflammation ⁽¹¹⁾11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53., fistula formation ^{( 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ⁾, and pain ^{( 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ⁾. Peri-implantitis ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ⁾ was the most prevalent complication observed in the soft tissue followed by excessive probing pocket depths (≥6 mm) ^{( 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, poor hygiene ⁽¹⁷⁾17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403., mild pain and swelling ^{( 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, transient paresthesia ^{( 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, and bleeding on probing ^{( 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ⁾. Regarding the conducted treatment, only two studies cited such information, reporting the subgengival cleaning, open flap cleaning, bone tissue regeneration and a strict maintenance program ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ⁾. In cases of implant loss as a consequence of biological failure, most of the studies described the replacement of the referred short implants after a period of healing, without any further complication ^{( 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾. As regards the clinical parameters, it was noticed a good oral hygiene, with stable condition of gingival tissue around implants with tendency to bleeding on probing but predominantly weak, and probing depth <5 mm in most of the cases ^{( 9}9 Telleman G, Meijer HJ, Vissink A,. Raghoebar GM Short implants with a nanometer-sized CaP surface provided with either a platform-switched or platform-matched abutment connection in the posterior region: a randomized clinical trial. Clin Oral Implants Res 2013;24:1316-1324. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ^{, 12}12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾

Figure 2
Forest plot of cumulative implant survival rate and subgroup analysis per study design.

Esthetical Complications

Only one study ⁽⁸⁾8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. assessed the esthetical appearance as a primary outcome measurement, describing the replacement of the single crown due to patient satisfaction. The remaining articles did not assessed or not reported any esthetical complication.

Discussion

The main purpose of the current systematic review was to investigate the essential parameters required to assess the long-term clinical performance of short and extra-short dental implants. By means of this literature review, a standard evaluation protocol is proposed (Fig. 3), being helpful to regiment further investigations. The included articles embraced a wide range of approaches including the study design, data reporting, terms and definitions, measurements, implants system, and follow-up period of time. Concerning the short implants definition, several differences could be noticed in literature. Therefore, the definition of endosseous dental implant that has a 'designed intrabony length' less or equal to 8 mm, proposed by Renouard et al. ⁽²⁴⁾24Renouard F, Nisand D. Impact of implant length and diameter on survival rates. Clin Oral Implants Res 2006;17:35-51. was chosen to guide the search of the articles.

From the thirteen articles selected, the cumulative implant survival rate was the most common parameter assessed, ranging from 84% at 5 years ⁽¹⁶⁾16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. to 100% at 2 ⁽¹³⁾13Deporter D, Pilliar RM, Todescan R, Watson P, Pharoah M. Managing the posterior mandible of partially edentulous patients with short, porous-surfaced dental implants: early data from a clinical trial. Int J Oral Maxillofac Implants 2001;16:653-658. to 10 years ⁽¹⁸⁾18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508.. Data meta-analysis revealed positive effect size varying from 0.052 (Z=19.8; p<0.001) to 0.042 (Z=12.83; p<0.001) at fixed and random analysis, which means that the provision of short implant in atrophic alveolar ridges appears to be a successful treatment option. Similar results were described in a former systematic review ⁽²⁵⁾25Chiapasco M, Zaniboni M. Clinical outcomes of GBR procedures to correct peri-implant dehiscences and fenestrations: a systematic review. Clin Oral Implants Res 2009;20:113-123., even though the survival rates have being assessed in regards to implants placed in bone augmentation sites or guided bone regeneration technique (varying from 79.5% to 100%). In addition, authors suggested that despite the favorable results of standard implants associated with bone grafts, the priority should be given to simpler approaches such as short implants ^{( 25}25Chiapasco M, Zaniboni M. Clinical outcomes of GBR procedures to correct peri-implant dehiscences and fenestrations: a systematic review. Clin Oral Implants Res 2009;20:113-123. ⁾. According to Annibali et al. ⁽²⁶⁾26Annibali S1, Cristalli MP, Dell'Aquila D, Bignozzi I, La Monaca G, Pilloni A. Short dental implants: a systematic review. J Dent Res 2012;91:25-32., short implants should not be compared to longer implants placed in the native jawbone. The most suitable comparison should be performed between short implants and advanced surgical techniques, necessary to place longer implants in resorbed posterior jaws ^{( 26}26Annibali S1, Cristalli MP, Dell'Aquila D, Bignozzi I, La Monaca G, Pilloni A. Short dental implants: a systematic review. J Dent Res 2012;91:25-32. ⁾. In this context, due to the lack of randomized clinical trials, it was impossible to demonstrate that such augmentation procedures are actually needed to allow the long-term survival of implants or if the use of short implants is indeed a better choice ^{( 25}25Chiapasco M, Zaniboni M. Clinical outcomes of GBR procedures to correct peri-implant dehiscences and fenestrations: a systematic review. Clin Oral Implants Res 2009;20:113-123. ⁾.

The typical method of calculating survival in most studies is another point of concern because several studies apply a simple ratio between the number of implants removed and the total number of implants placed. This method is misleading since it does not take into account the effects of time ⁽²⁷⁾27Chrcanovic BR, Albrektsson T, Wennerberg A. Reasons for failures of oral implants. J Oral Rehabil 2014;41:443-476.. Moreover, important clinical aspects not considered on the implants evaluation should be assessed because they are closely related to failures, especially in short dental implants. Factors such as patient's habits (smoking, bruxism and clenching); presence of systemic diseases (alcoholism, diabetes and osteoporosis); features related to implant insertion (primary stability, insertion torque, bone density, position of the implant in respect to the bone ridge and loading protocol); characteristics of the implants (brand, surface treatment, length, diameter, shape and implant-abutment connection); particularities of the prosthesis (screwed or cemented, type of abutment, single or multiple, length of the cantilever, occlusion, material, crown length and antagonist occlusion); and biological parameters (periodontal tissue and hygiene condition assessment) should be always assessed in the clinical practice. Thus, the development of standard criteria encompassing all these parameters would be helpful to regiment further investigations and allows comparisons in future studies.

Recent literature has credit the increased survival rate of short implants to the surface structure because of the higher bone-to-implant contact ^{( 4}4Telleman G, Raghoebar GM, Vissink A, den Hartog L, Huddleston Slater JJ, Meijer HJ. A systematic review of the prognosis of short (<10 mm) dental implants placed in the partially edentulous patient. J Clinic Periodontol 2011;38:667-676. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ⁾. Therefore, it is crucial to describe, in a standard survey, the surface characteristics as well as the degree of roughness of the implant system applied. The majority of studies selected in this review, except one ⁽¹⁹⁾19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289., described the type of surface, being the moderate rough surfaces selected in most of the cases. The detailed description of the implant system increases the reproducibility of the study and allows the comparison of results. Thus, it is possible to find out what is the most successful surface to be used in short dental implants ⁽¹²⁾12Rossi F, Ricci E, Marchetti C, Lang NP, Botticelli D. Early loading of single crowns supported by 6-mm-long implants with a moderately rough surface: a prospective 2-year follow-up cohort study. Clin Oral Implants Res 2010;21:937-943..

Figure 3
Standard evaluation protocol

Another concern when implants with rough surface are installed is the acute infection in peri-implant area, which may be more common and difficult to treat in the presence of very rough or porous surfaces ⁽²⁸⁾28Esposito M, Ardebili Y, Worthington HV. Interventions for replacing missing teeth: different types of dental implants. Cochrane Database Syst Rev 2014;7:CD003815.. In spite of that, no attention was given, in these four studies ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ⁾ with cases of peri-implantitis and mucosities, to the possible connection between the implant surface and a higher risk of peri-implantititis. Future studies evaluating short implant performance should consider this important aspect.

Based on the clinical performance of conventional crown-to-root, closely susceptible to harmful lateral occlusal forces ⁽²⁹⁾29Grossmann Y, Sadan A. The prosthodontic concept of crown-to-root ratio: a review of the literature. J Prosthet Dent 2005;93:559-562., it was believed that excessive crown-to-implant ratio could be detrimental to long-term implant survival, especially when short implants are considered ⁽³⁰⁾30Birdi H, Schulte J, Kovacs A, Weed M, Chuang SK. Crown-to-implant ratios of short-length implants. J Oral Implantol 2010;36:425-433.. It is because the higher the crown, the longer is the lever arm, and consequently the greater is the stress in marginal bone which could contribute to increase the risk for marginal bone loss ^{( 21}21Blanes RJ. To what extent does the crown-implant ratio affect the survival and complications of implant-supported reconstructions? A systematic review. Clin Oral Implants Res 2009;20:67-72. ^{, 30}30Birdi H, Schulte J, Kovacs A, Weed M, Chuang SK. Crown-to-implant ratios of short-length implants. J Oral Implantol 2010;36:425-433. ^{, 31}31Rangert BR, Sullivan RM, Jemt TM. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-370. ⁾. Contrary to this belief, the majority of the selected studies were not able to establish a strictly relation between the crown-to-implant ratio and marginal bone loss (Table 2). The only aspect, underlined in one of the studies ⁽²⁰⁾20Kim YK, Yun PY, Yi YJ, Bae JH, Kim SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013., was the higher pocket depth observed on implants with crown-to-implant ratios ≥1.5 (Table 2). Recently, several studies ^{( 21}21Blanes RJ. To what extent does the crown-implant ratio affect the survival and complications of implant-supported reconstructions? A systematic review. Clin Oral Implants Res 2009;20:67-72. ^{, 30}30Birdi H, Schulte J, Kovacs A, Weed M, Chuang SK. Crown-to-implant ratios of short-length implants. J Oral Implantol 2010;36:425-433. ^{, 32}32Anitua E, Alkhraist MH, Pinas L, Begona L, Orive G. Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: the effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis. Int J Oral Maxillofac Implants 2014;29:682-689. ⁾ have shown the absence of a significant association between crown-to-implant ratio and marginal bone loss, even in cases of high crown-to-implant ratio of 2.4 ⁽³²⁾32Anitua E, Alkhraist MH, Pinas L, Begona L, Orive G. Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: the effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis. Int J Oral Maxillofac Implants 2014;29:682-689.. Different reasons can be pointed out to explain such fact, including the treatment of the implant surface and the level in which the implant shoulder is placed at the crestal bone. Beyond that, different approaches applied to measure the crown-to-implant ratio make it difficult to compare the results.

Another important parameter related to the crown-to-implant ratio, not assessed in the selected articles, is the crown height space ⁽³²⁾32Anitua E, Alkhraist MH, Pinas L, Begona L, Orive G. Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: the effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis. Int J Oral Maxillofac Implants 2014;29:682-689.. This measurement represents the vertical distance between the occlusal plane and the alveolar bone level ^{( 32}32Anitua E, Alkhraist MH, Pinas L, Begona L, Orive G. Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: the effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis. Int J Oral Maxillofac Implants 2014;29:682-689. ^{, 33}33Nissan J, Ghelfan O, Gross O, Priel I, Gross M, Chaushu G. The effect of crown/implant ratio and crown height space on stress distribution in unsplinted implant supporting restorations. J Oral Maxillofac Surg 2011;69:1934-1939. ⁾. Previous studies revealed that the increased crown height space (higher than 15 mm) results in higher stress concentrations at the bone-implant interface and significantly marginal bone loss ^{( 32}32Anitua E, Alkhraist MH, Pinas L, Begona L, Orive G. Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: the effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis. Int J Oral Maxillofac Implants 2014;29:682-689. ^{, 33}33Nissan J, Ghelfan O, Gross O, Priel I, Gross M, Chaushu G. The effect of crown/implant ratio and crown height space on stress distribution in unsplinted implant supporting restorations. J Oral Maxillofac Surg 2011;69:1934-1939. ⁾. Thus, the crown height space is a more effective parameter to study the relationship between the crown-to-implant ratio and marginal bone loss and should be included in the assessment of long-term evaluation of short implant performance ^{( 32}32Anitua E, Alkhraist MH, Pinas L, Begona L, Orive G. Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: the effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis. Int J Oral Maxillofac Implants 2014;29:682-689. ⁾.

The second parameter assessed in all the selected articles as an important outcome to measure implant success was the mean marginal bone loss. In such parameter, a great range of values were noticed with mean marginal bone loss varying from 0 to 2 mm after 1 year follow-up. The possible reason for such differences might be the limits used as a reference to measure the marginal bone loss or the placement of the implants in different levels of the crestal bone. For instance, the highest marginal bone loss (2 mm) observed in two studies ^{( 15}15Corrente G, Abundo R, des Ambrois AB, Savio L, Perelli M. Short porous implants in the posterior maxilla: a 3-year report of a prospective study. Int J Periodontics Restorative Dent 2009;29:23-29. ^{, 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ⁾, might be a consequence of the implant system applied, because the system applied presents a rough surface and a smooth collar, being usually placed with the smooth collar submerged in the crestal bone. This characteristic might change the reference when the marginal bone loss is assessed, explaining the higher values encountered. Different assessment of the actual marginal bone loss by different studies should be avoided, because it jeopardizes the outcome interpretation.

The majority of biomechanical complications, reported in the selected studies, were minor issues including screw loosening ^{( 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾, food accumulation in interdental spaces ⁽⁸⁾8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121., and crown decementation or fracture ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 14}14Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275-282. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾. All these problems are easily solved by the replacement of the crown, when necessary ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ⁾. The only major issue reported was the occlusal overloading, that resulted in excessive bone resorption ⁽¹⁷⁾17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. and, consequently, the loss of osseointegration or implant fracture ⁽¹⁹⁾19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289.. It is important to notice that most of the failures occurred in posterior location, area with low density bone and high occlusal forces, which could predispose the implants to failure. Accordingly, it is crucial the closely monitoring of the patients by a regular maintenance program, not focusing only in the cleaning of the prosthesis, but attempting to the proper occlusal adjustment to avoid future complications.

Regarding the biological complications, the most prevalent issue reported was the peri-implantitis ^{( 8}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ^{, 11}11Malo P, Nobre M, Lopes A. Short implants in posterior jaws. A prospective 1-year study. Eur J Oral Implantol 2011;4:47-53. ^{, 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ⁾. However, only 13 (1%) of the 1260 implants suffered from inflammation in the peri-implant tissue. The mean reason for this low prevalence of biological complication might be prospective design of the studies besides the maintenance program applied by most of the studies, comprising a professional cleaning and hygiene instruction, with recall visits every 4 to 6 months ^{( 16}16Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: a 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363-368. ^{, 17}17De Santis D, Cucchi A, Longhi C, Vincenzo B. Short threaded implants with an oxidized surface to restore posterior teeth: 1- to 3-year results of a prospective study. Int J Oral Maxillofac Implants2011;26:393-403. ^{, 18}18Mertens C, Meyer-Baumer A, Kappel H, Hoffmann J, Steveling HG. Use of 8-mm and 9-mm implants in atrophic alveolar ridges: 10-year results. Int J Oral Maxillofac Implants 2012;27:1501-1508. ⁾. It emphasizes the importance of a restrict follow-up monitoring of the patient, assessing different parameters to prevent further and more serious complications, consequently increasing the long-term success of short implants.

In respect to the esthetical issues, only one study ⁽⁸⁾8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. reported an issue of unsatisfied patient. It was expected because most of the short implants are installed in posterior regions, where the esthetical requirements are usually low. Although few studies ^{( 8}8Cannizzaro G, Felice P, Leone M, Ferri V, Viola P, Esposito M. Immediate versus early loading of 6.5 mm-long flapless-placed single implants: a 4-year after loading report of a split-mouth randomised controlled trial. Eur J Oral Implantol 2012;5:111-121. ^{, 10}10 Telleman G, Raghoebar GM, Vissink A, Meijer HJ.Impact of platform switching on inter-proximal bone levels around short implants in the posterior region; 1-year results from a randomized clinical trial. J Clinic Periodontol 2012;39:688-697. ^{, 19}19Pieri F, Aldini NN, Fini M, Marchetti C, Corinaldesi G. Preliminary 2-year report on treatment outcomes for 6-mm-long implants in posterior atrophic mandibles. Int J Prosthodont 2012;25:279-289. ⁾ had reported data among patient satisfaction and preferences, it is important to evaluate these subjective parameters because they are closely related to the survival rate, especially regarding the long-term success of the prosthesis.

The present review is a primary vision of this vast field of research. Thereby, it is impossible to guarantee that all parameters used in the follow-up evaluation of short implants were included because it requires a much more extensive description of literature, not usual in a systematic review. Moreover, a specific evaluation regarding the risk of bias of each selected study was not applied in the present review mainly because only few randomized clinical trials were included and the principal focus of the study was the parameters used for the implant assessment, not the result itself. In spite of that, it is important summarize the most common aspects pointed out in recent literature to evaluate implant performance, since it could fundament the development of standardized protocols in the near future. By means of this literature review, a standard evaluation scheme is being proposed and detailed (Complementary file) to regiment further investigations and be helpful to comparison in future studies.

The findings from this systematic review highlight different parameters, besides the implant survival rate and marginal bone loss, which are important to be observed in the long-term monitoring of the patients with short implant. By means of this literature review, a standard scheme is proposed to be used in the follow-up appointments, encompassing:

Combined with a well-established maintenance program, this standard protocol configures as an important instrument for the decision-making process, regimenting further investigations and comparisons on future studies.

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