Short Implants: An Answer to a Challenging Dilemma?

Simultaneous placement of short implants (≤ 8 mm) versus standard length implants (≥ 10 mm) after sinus floor elevation in atrophic posterior maxillae: a systematic review and meta-analysis

Purpose

The objective of this meta-analysis was to compare the clinical outcomes of using short implants (≤ 8 mm) inserted with osteotome sinus floor elevation (OSFE) and standard implants (≥ 10 mm) inserted with sinus floor elevation (SFE) in atrophic posterior maxillae with insufficient residual bone height (RBH).

Methods

An electronic search was performed on PubMed, EMBASE, and the Cochrane Library from 1994 to July 2022, in combination with a manual search of references in relevant articles. Randomized controlled trials (RCTs) that compared the clinical results between short and standard implant placement with SFE were included. The primary outcomes were implant survival rate and marginal bone loss (MBL); the secondary outcome was complication rate.

Results

Three RCTs were included, totaling 138 short and 156 standard implants. The results of the meta-analysis showed no significant differences between the short and standard implant groups in survival rate (RR = 1.02, 95% CI   0.96–1.08, p = 0.570), MBL (MD = − 0.13, 95% CI   − 0.32 to 0.07, p = 0.190) and complication rate (intra-surgical complication: RR = 1.14, 95% CI   0.46–2.83, p = 0.770; post-operative complication: RR = 1.34, 95% CI   0.71–2.55, p = 0.370).

Conclusions

Using short implants (≤ 8 mm) combined with OSFE might be an alternative to standard implants (≥ 10 mm) with SFE when the RBH of the posterior maxilla is insufficient. Based on a short-term clinical observation, short implants with OSFE show good results in terms of survival rate, MBL, and complication incidence.

Graphical Abstract

Converting Bilateral Free-End Removable Partial Dentures to Implant-Assisted Removable Partial Dentures Using 6 mm Short Implants: Patient-Reported Outcomes of a Prospective Clinical Study

The study assessed oral health-related quality of life (OHRQoL) of patients who received two 6 mm short implants in mandibular molar sites, converting existing bilateral free-end removable partial dentures (RPDs) to implant-assisted RPDs (IARPDs). After a postsurgical healing period of 4 months, the participants received a non-retentive dome abutment for 8 weeks, and then a retentive ball abutment for another 8 weeks. Afterwards, the participants made their final choice on which abutment to keep. The final follow-up was 1 year after implant placement. OHRQoL was evaluated with the 49-items version of the Oral Health Impact Profile (OHIP-49) at the abutment exchanges and the final follow-up. Furthermore, numerical rating scales were used to analyze patient satisfaction after 1 year. Questionnaire data of 13 participants were evaluated. Overall, OHRQoL increased with both the dome (p = 0.02) and the ball abutments (p < 0.001), without a significant difference between the abutments (p = 0.953). The questionnaires revealed an improvement in terms of oral situation, quality of life, and masticatory capacity (all p < 0.01). Patients showed a significant preference for the ball abutments (p < 0.001). Converting RPDs to IARPDs resulted in significant improvement of OHRQoL. Patients seem to prefer retentive over non-retentive abutments, although no differences in terms of OHRQoL were observed.

A prospective, multicentre study of 6-mm short implants in posterior alveolar bone supporting splinted crowns: A 5-year follow-up study

AIM

To evaluate the clinical and radiographic outcomes of 6-mm short implants, placed in the posterior jaws and supporting splinted crowns, at 5 years after early loading.

MATERIALS AND METHODS

Forty-five patients with 95 implants (diameter: 4 mm; length: 6 mm) were enrolled at three centres. Two to three implants were placed in either the maxillary or the mandibular posterior region in each patient and restored with screw-retained splinted crowns at 6 weeks later. Clinical and radiographic outcomes were evaluated at implant placement, at loading, and at 6, 12, 24, 36, and 60 months after loading. Biological and mechanical complications were recorded. Marginal changes in bone level in relation to clinical parameters were evaluated using a generalized linear mixed model.

RESULTS

During the 5 years of follow-up, the mean change in the marginal bone level (MBL) was 0.04 ± 0.14 mm. Four implants in four patients were lost before loading, one implant in one patient was lost at the 5-year follow-up, and two patients were lost to follow-up. The survival and success rates were 88.4% (38/43) at the patient level. The incidence rates of peri-implant mucositis and peri-implantitis were 29.4% and 7.0%, respectively. The rate of technical complications was 14.0%.

CONCLUSIONS

Over a 5-year period, 6-mm short implants supporting early loaded splinted crowns in maxillary or mandibular posterior regions showed stable MBLs and acceptable technical and biological complication rates.

Effect of Variable Implant Tip Distances on Stress Distribution around the Mental Foramen: A Finite Element Analysis

AIM: This study aimed to evaluate the effect of gap between traditional implant tip and mental nerve using finite element analysis. METHODS: Four finite element models (FEM) were prepared for dummy crowns that were supported by traditional implants that were placed vertically in laser scanned mandibular bone geometry. Where gap distance were designed to be 1.5, 2.0, 2.5, and 3.0 mm. Dummy crown, 50 μm cement layer, and implant complex models’ components were modeled in 3D on engineering computer-aided design (CAD)/CAD (computer-aided manufacturer) software formerly collected in Finite Element Analysis package. Each model was subjected to two loading cases as 150N compressive load at central fossa, and 50N Oblique (45º) load at central fossa of the dummy crown. RESULTS: Good agreement of the FEM was obtained when compared to similar studies. Under applied study loads, all resulting values of stresses and deformations of the four models were within physiological limits. The obtained data showed no effect on cortical bone, implant complex, cement layer, and dummy crown to changing of gap distance. In addition, the cancellous bone, especially around the mental canal, was considerably affected by the variation in that gap distance. CONCLUSION: Increasing the gap distance between the dental implant tips may reduce the stress and deformation around the mental canal. Minimum gap distance of order 2.5 mm is recommended to reduce stresses and deformations around canal to favorable limits, while more gap distance is also recommended with larger bone geometries.

Effect of crown-to-implant ratio and crown height space on marginal bone stress: a finite element analysis

BACKGROUND

Crown-to-implant ratio and crown height space, associated with the use of short implants, have been related with marginal bone loss. However, it is unclear which of the two entities would play the most important role on the bone remodelling process. Using a finite element analysis, the present work aims to help clarifying how those two factors contribute for the stress generation at the marginal bone level. A numerical model (reference model), with a crown-to-implant ratio of 4, was double validated and submitted to a numerical calculation. Then, it was modified in two different ways: (a) by decreasing the prosthetic height obtaining crown-to-implant ratios of 3, 2.5 and 2 and (b) by increasing the implants length obtaining a crown-to-implant ratio of 2.08. The new models were also submitted to numerical calculations.

RESULTS

The reference model showed a marginal bone stress of 96.9 MPa. The increase in the implants' length did not show statistically significant differences in the marginal bone stress (p-value = 0.2364). The decrease in the prosthetic height was accompanied with a statistically significant decrease in the marginal bone stresses (p-value = 2.2e- 16).

CONCLUSIONS

The results represent a paradigm change as the crown height space appears to be more responsible for marginal bone stress than the high crown-to-implant ratios or the implants' length. New prosthetic designs should be attempted to decrease the stress generated at the marginal bone level.

Failure Risk of Short Dental Implants Under Immediate Loading: A Meta-Analysis

PURPOSE

Currently, there is no clear clinical evidence that short implants are suitable for immediate loading. Therefore, this meta-analysis aims to evaluate whether immediate loading increases the failure risk of short dental implants.

MATERIALS AND METHODS

This meta-analysis was registered at PROSPERO (CRD 42020195890). PubMed, Embase, and Cochrane Library databases were searched to collect all clinical studies comparing the failure rates of short dental implants (<10 mm) and standard implants (≥10 mm) under the condition of immediate loading and studies comparing the failure rates of short dental implants under immediate loading versus early or delayed loading. All of the clinical studies with available relevant data were eligible for inclusion. The Cochrane Risk of Bias tool was adopted to evaluate the risk of bias for the randomized controlled trial (RCT), while Newcastle-Ottawa Quality Assessment Scale (NOS) was used for the observational studies (OS). The OR value of each included study and its 95% CI were pooled to estimate the failure risk of short dental implants under immediate loading. The heterogeneity among studies was evaluated through Cochran's Q test and I² .

RESULTS

Seventeen studies, 5 RCTs and 12 OS studies, with a total of 2461 dental implants were analyzed. Four of the RCT studies were of low risk of bias and one was of unclear risk, while all of the OS studies were of moderate or high quality. Compared with standard implants, short implants did not have an increased failure risk under immediate loading (OR: 1.38, 95% CI: 0.67-2.84, p = 0.997, fixed model). In addition, the OR value of implant failure for short implants under immediate loading compared to that for short implants under early or delayed loading was 1.22 (95% CI: 0.33-4.55, p = 0.104, random model), which was also not significantly different.

CONCLUSIONS

There is not enough evidence to show that short dental implants under immediate loading may have higher implant failure risk compared to standard implants under immediate loading and short implants under early or delayed loading. Therefore, an immediate loading protocol may not increase the failure risk of short dental implants.

Short implants without bone augmentation vs. long implants with bone augmentation: systematic review and meta-analysis

PURPOSE

Anatomical limits such as the location of the lower alveolar nerve, the maxillary sinus in atrophied jaws might extend implant surgery treatment. The purpose of this systematic literature review is to review the literature and determine whether short implants can be an effective alternative to standard-length implants after bone augmentation.

MATERIALS AND METHODS

A systematic search was performed on PRISMA wizard. Searched for clinical trials 2010-2020 in the Medline database. The keywords chosen are "short versus long implants, augmented bone, clinical trial", and their various variations.

RESULTS

Meta-analyses of the studies of implant loss after 1, 3 and 5 years showed a statistically insignificant difference between groups. The number of complications after 1 year was statistically significantly higher in the control group. Meta-analyses with follow-up periods of 3 and 5 years showed a statistically insignificant difference; Meta-analyses of studies of marginal bone loss after 1, 3 and 5 years showed a statistically insignificant difference between the groups.

CONCLUSIONS

Short dental implants may be a suitable alternative to standard length dental implants after bone augmentation. The risk of their complications is possibly lower because of the lack of need for bone augmentation.

Survival Rate of 1008 Short Dental Implants with 21 Months of Average Follow-Up: A Retrospective Study

This retrospective study evaluated the survival rate of short, sandblasted acid-etched surfaced implants with 6 and 8 mm lengths with at least 120 days of follow-up. Data concerning patient, implant and surgery characteristics were retrieved from clinical records. Sandblasted and acid-etched (SLA)-surfaced tissue-level 6 mm (TL6) or 8 mm (TL8) implants or bone-level tapered 8 mm (BLT8) implants were used. Absolute and relative frequency distributions were calculated for qualitative variables and mean values and standard deviations for quantitative variables. A Cox regression model was performed to verify whether type, length and/or width influence the implant survival. The cumulative implant survival rate was assessed by time-to-event analyses (Kaplan–Meier estimator). In all, 513 patients with a mean age of 58.00 ± 12.44 years received 1008 dental implants with a mean follow-up of 21.57 ± 10.77 months. Most implants (78.17%) presented a 4.1 mm diameter, and the most frequent indication was a partially edentulous arch (44.15%). The most frequent locations were the posterior mandible (53.97%) and the posterior maxilla (31.55%). No significant differences were found in survival rates between groups of type, length and width of implant with the cumulative rate being 97.7% ± 0.5%. Within the limitations of this study, the evaluated short implants are a predictable option with high survival rates during the follow-up without statistical differences between the appraised types, lengths and widths.