Are short implants an acceptable alternative to sinus floor elevation in the posterior maxilla?

Dr. Johan Hartshorne gives a critical appraisal of a systematic review into the evidence for avoiding longer implants in situations where augmentation techniques may be required

This article aims to provide a critical appraisal of a systematic review:

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 11:154-169.

The article was accepted for publication on April 13, 2015, and was first published online on May 21, 2015.

The research originated from the Clinic for Fixed & Removable Prosthodontics and Dental Material Science Center at the University of Zurich, Switzerland.

Summary

The outcomes of this systematic review demonstrated high implant and reconstruction survival rates for short implants and sinus floor elevation (SFE) with simultaneous placement of longer implants. Both treatment options are safe and predictable for implant therapy in the posterior maxilla. Biological complications are frequent, but mainly associated with SFE. The increased biological complications, costs, and surgical time associated with SFE with longer implants, favor the use of shorter dental implants in the posterior maxilla.

Educational aims and objectives

This article aims to critically analyze a systematic review and its findings in relation to the use of short implants over longer implants and sinus lift procedures.

Expected outcomes

Implant Practice US subscribers can answer the CE questions to earn 2 hours of CE from reading this article. Correctly answering the questions will demonstrate the reader can:

• Recognize how this systematic review contributes to the evidence base on the use of short implants.
• Realize if short implants are comparable to longer implants with sinus floor elevation (SFE) in terms of morbidity and surgically related complications.
• Realize if short implants comparable to longer implants with SFE in terms of clinical and radiographic outcomes.
• Identify some key factor in clinical decision-making for increasing implant and prosthesis success rates, minimizing complications and morbidity, and improving patient acceptance with implant therapy.
• Realize some ways to avoid complications and disadvantages associated with SFEs.

 

Critical appraisal conclusion

The evidence suggests the use of short implants (5 mm to 8.5 mm long) as an alternative to SFE with longer implants (of 10 mm or more) for rehabilitation of the posterior maxilla. The outcomes indicate that there are less intraoperative complications when short implants are used.

There is limited evidence that less postoperative complications with short implants and prosthesis will occur after loading compared to longer implants with SFE. The evidence presented should be interpreted and applied with caution because studies are limited, not all the important outcomes were measured, and the duration of follow-up was less than 18 months.

Implications for clinical practice
Implant treatment options for rehabilitation of the posterior maxilla are dictated by the available alveolar bone height, type of bone, and interarch space.

The evidence suggests that both short implants or SFE with longer dental implants can be recommended for implant therapy in the posterior maxilla presenting with limited alveolar bone height, provided careful case selection and evidence-based clinical protocols are followed. Where short implants are indicated, the best way to compensate for reduced implant surface and to ensure best possible primary stability is to use a wider diameter (4 mm-6 mm) implant.

Until more evidence is available, it would be prudent for clinicians to:

• avoid placing short implants in single free-end case
• follow a two-stage implant surgery approach
• allow for longer periods of osseo-integration
• avoid immediate loading
• consider splinting of prosthesis

Clinical choice of the most appropriate implant therapy modality should be based on assessment of the residual alveolar bone height, width, and sinus morphology with a cone beam computed tomography (CBCT) scan, current scientific evidence, surgical skills and experience of the surgeon, and the patient’s preferences. Following a good surgical protocol and excellent oral hygiene maintenance program are fundamental elements in achieving a successful and predictable outcome.

Clinical question
Are short implants comparable to longer implants with SFE in terms

• of morbidity and surgically related complications?
• Clinical and radiographic outcomes?

Review methodology

Search strategy
An electronic MEDLINE^® (PubMed^®) search was performed for controlled clinical studies, published from January 1990 up to October 31, 2014, comparing short implants (8 mm or less) (Group A) to longer implants (greater than 8 mm) with lateral window sinus floor elevation (SFE) (Group B) for rehabilitating the posterior maxilla. The search was limited to the English, German, Italian, and French languages.

The search was complemented by an additional hand search of the selected papers and reviews published between 2011 and 2014. Reference list of all included publications were screened for relevant studies.

Inclusion criteria
Eligible studies were selected based on the following inclusion criteria:

• Human trials with a minimum amount of 20 patients
• Randomized controlled trials (RCT) or controlled clinical trials (CCT)
• Short implants with an intrabony length of 8 mm or less
• SFE in combination with longer implants with an intrabony length of greater than 8 mm
• Screw-type implants with a moderately rough surface
• Implants placed within the alveolar bone and the augmented sinus floor
• Patients needed to be examined clinically

Data extraction
Two authors independently screened the titles and abstracts derived from the search. Eligible articles were then obtained in full text. Disagreements regarding eligibility of studies and data extraction between authors were resolved by discussion and consensus. Cohen’s Kappa coefficient was calculated to measure agreement between the two readers.

The primary outcomes were survival rates of implants and reconstructions. Secondary outcomes included complication rates for implants and reconstructions, radiographic bone levels, as well as patient-related outcome measures, surgical time, costs, and the feasibility to perform the two procedures.

Method of analysis and quality assessment
Two reviewers independently evaluated the methodological quality of all included studies using the Cochrane Collaboration’s tool for assessing risk of bias in randomized trials. Any disagreement was discussed until consensus was achieved. Survival rates with corresponding 95% confidence intervals (95% CI) were calculated with implants as unit.

Main results

Eight RCTs comparing short implants with longer implants with SFE met the eligibility criteria. The studies were well-conducted with respect to randomization, allocation, data collection, and reporting, thus resulting in a low risk for selection, attrition, and reporting bias.

All of the studies presented with a high risk of performance bias due to a lack of blinding of patients and surgeons. Four studies had a high risk of bias from blinding of outcome assessment (detection bias). Surgeons placed implants in specialized clinical settings.

A total of 406 implants were placed in 217 patients with a mean age of 54 years. One hundred and ninety seven implants were placed in the short implant group (Group A) and 209 implants in the longer implant group with SFE (Group B). The length of the short implants varied between 5 mm and 6 mm, with diameters of either 4 mm, 5 mm, or 6 mm. The length of longer implants ranged between 10 mm and 15 mm. Lateral window SFE in Group B was performed simultaneously with implant placement.

Based on the pooled analyses of longer follow-ups (five studies, 16-18 months), the survival rate of longer implants with SFE amounted to 99.5% (95% CI: 97.6-99.98%) and for shorter implants 99.0% (95% CI: 96.4-99.8%). For shorter follow-ups (three studies, 8 to 9 months), the survival rates of longer implants were 100% (95% CI: 97.1-100%) and for shorter implants 98.2% (95% CI: 93.9-99.7%). Complications were predominantly sinus floor membrane perforations. Patient reported outcomes — i.e., morbidity, surgical time, and costs — were generally in favor of shorter dental implants.

Conclusion

The analysis demonstrated predictably high implant and reconstruction survival rates for both groups. Given the higher number of biological complications, increased morbidity, costs, and surgical time of longer dental implants with SFE, shorter dental implants may represent the preferred treatment alternative.

The authors declared that no funding was provided for the elaboration of this study nor was there potential conflict of interest with respect to the authorship and/or publication of this review.

Commentary

Background and importance
Alveolar bone height will often fall short of the optimum 10 mm in the posterior maxilla due to alveolar bone loss and sinus pneumatization. Clinicians are consequently faced with the challenge of optimizing success and limiting complications when placing implants where there is reduced alveolar ridge height and poor bone quality (type IV) in the rehabilitation of the posterior maxilla.

In cases presenting with reduced alveolar bone height in the posterior maxilla, SFE procedures using either a lateral or crestal approach have traditionally been the treatment of choice to increase bone height to allow the placement of dental implants of optimal length (10 mm or more). SFE procedures, however, are associated with an increased risk of complications, higher patient morbidity, longer treatment time, and costs and require advanced skills.

In order to avoid the complications and disadvantages associated with SFEs, the use of shorter dental implants (less than 10 mm in length) has been advocated as an alternative treatment option. Simultaneously, implant texture and design have been improved to compensate for situations with compromised bone quality and quantity.

The survival rates, complications and patient-related outcomes of short implants in the posterior maxilla have never been compared to those of longer implants in combination with SFE for the same indications. The literature comparing the two treatment options in well-designed controlled clinical trials was scarce for many years, but more recent evidence suggests that both treatment options are reliable and predictably successful (Esposito, et al., 2012; Gulje, et al., 2014).

Are the results valid?
The individual studies presented with various methodological limitations that could potentially increase risk of bias and thus affect the validity of the evidence.

Inadequate blinding of participants and investigators, short follow-up time, small sample sizes, and a calculation of sample sizes based on secondary outcomes contributed toward a high risk for bias.

Heterogeneity or group imbalances such as using different study designs, assessment tools, differing implant diameters, splinting of reconstructions within and between groups may also potentially affect the estimate of the outcome. The authors did not report whether tests for heterogeneity were conducted.

Overall, the limited number of studies, variation in study design, heterogeneity, and limitations in research methodology among individual studies could potentially result in increased risk of bias that may affect the estimates of effect and thus affect the validity of the evidence.

What are the key findings?
The pooled survival rates for shorter implants were similar to that of longer implants with SFE.

Due to heterogeneity in observation periods, no meta-analysis was conducted for the eight studies combined. The meta-analysis of the pooled data for short-term (8 to 9 months) (three studies) and longer term (16-18 months) (five studies) showed high implant and reconstruction survival rates for both the short implant group as well as with longer implants with SFE.

The high survival rates should be interpreted with caution due to the relatively short follow-up observation period (maximum 18 months).

Although the survival results were consistent throughout individual studies, the confidence intervals were wide, indicating that the estimate of survival of implants was lacking precision. This could be ascribed to the limitations in the research methodology.

In all of the studies, except one, the differences between the two groups with respect to complication rates were statistically insignificant. More intraoperative biological complications were observed in the longer implant group, the most frequent complication being sinus floor membrane perforation. The data in this review suggests that the risk of complications increased by threefold with sinus floor elevation procedures.

There were no statistically significant differences in marginal bone level changes between short implants and longer implants with SFE.

Available data indicates less morbidity and greater patient acceptance associated with the use of shorter implants.

Comparison between the two groups is difficult because only four studies reported patient-related outcome data. To complicate matters further, different assessment tools were used. Qualitative analysis of descriptive statistics were further hampered due to small sample sizes, different study designs, and variations in intervention within same populations (i.e., number of implants placed).

The single study that assessed surgical time and costs (Thoma, et al., 2015) showed that surgical time increased by 50% when a SFE procedure was performed compared to just using a short dental implant. It can be inferred that increased surgical time may be associated with the increase in morbidity, complication rate, and negative patient-related outcomes.

Shorter implants accounted for only half the costs compared to longer implants with SFE. Although the availability of data was limited, patient-reported outcomes, morbidity, costs, and surgical time were all in favor of shorter dental implants.

Most of the studies included in the review did not report on all the secondary outcomes. Only three studies reported on changes in marginal bone levels, and four provided data on patient-related outcome measures. The four studies reporting on patient-related outcome lacked standardization in methods and criteria, thus ruling out an appropriate comparative analysis.

Important patient-related outcomes such as postoperative pain or discomfort, morbidity, the impact on quality of life, surgical time, and costs were largely not reported on.

Secondary outcomes were only reported on descriptively and not subjected to meta-analysis. No data was provided on initial alveolar bone height, alveolar ridge width, type of bone, systemic conditions, smoking habits, periodontal health, parafunctional habits, sinus morphology, and interarch relations. These variables may be critical to clinical decision-making.

The evidence reported in this review supports that of a previous systematic review — namely, that there is not enough evidence to show whether SFE techniques are more or less successful in reducing the implant and prosthetic failures when compared to simply using short implants up to 1 year after loading, and that there were fewer complications when short implants were used without SFE (Esposito, et al., 2014).

How are the results of this review applicable in clinical practice?

Increasing implant and prosthesis success rates, minimizing complications and morbidity, and improving patient acceptance and satisfaction with implant therapy are key factors in clinical decision-making.

For the patient, costs, limiting surgical interventions, and associated discomfort also play an important role when making choices between treatment options.

Considering that SFE requires more treatment time, greater costs, have more complications and more advanced surgical skills, the use of shorter dental implants may open dental implant therapy to a broader spectrum of clinicians, and subsequently, a broader patient population may benefit from this treatment option.

Clinicians may elect to use short implants in cases where SFE are contraindicated (such as chronic sinusitis, abnormal sinus morphology, or smoking), provided there is adequate alveolar bone volume (5 mm or more). Implant surface roughness and increasing the diameter of the implant for achievement of sufficient primary stability at time of implant placement may contribute to the long-term survival of the implant and prosthesis (Javea, Romanos, 2015).

Proper case selection is essential to achieve a predictable and successful outcome, irrespective of which choice of treatment is selected. CBCT is critical tool for proper case selection and treatment planning.

Important factors that must be considered include:

• patient-related factors (systemic conditions smoking habits, perio-dontal health, para-function)
• biological factors (residual alveolar bone height, alveolar bone width, bone quality, and sinus morphology)
• surgical considerations (one or two stages, skills of the surgeon)
• prosthetic considerations (splinted or not)

Clinical resolution

Today, both patients and practitioners demand simplified, minimally invasive, affordable, and predictable approaches to increase acceptance and success of implant therapy.

Restoring the edentulous maxilla with dental implants is challenging due to reduced residual alveolar bone and proximity of the maxillary sinus.

Short implants can be a successful minimally invasive treatment alternative to placing longer implants with SFE in cases where the alveolar bone height in the posterior maxilla is 5 mm or more. Using short implants in the posterior maxilla with reduced alveolar ridge height has several advantages for the patient, including less surgical intervention and intraoperative complications, reduced waiting periods for treatment completion, and reduced costs. It may also render implant treatment accessible to a larger pool of patients.

The evidence presented in this systematic review offers modest evidence for placement and restoration of short implants provided that clinicians understand the limitations, indications, and risk factors thereof.

However, the results from this review should be interpreted with caution due to the lack of good quality studies and longer follow-up.

SFE may still be the procedure of choice for surgeons who do not elect to use short implants or when short implants are contraindicated.

The use of short implants is promising, but there are still many unanswered questions that require more research.

First, we do not know what the long-term success rates of short implants are from a biological and prosthetic perspective. Second, what is the optimum bone-to-implant contact surface (implant geometry, length, and width) that will ensure the best primary and secondary stability, and a predictable and successful osseointegration?

Further controversies include whether short implants should be used single or two-stage, should longer time for healing and bone maturation be allowed before loading, and whether prostheses on short implants should be splinted.