International Journal of Prosthodontics and Restorative Dentistry
Volume 13 | Issue 4 | Year 2023

To Splint or Not to Splint Tooth and Adjacent Dental Implants: An Overview of Reviews

Kimia Baghaei1, Amirhossein Fathi2, Sara Hashemi3, Kiumars Tavakolitafti4, Ramin Mosharraf5, Seyedeh Farimah Fatemi6

1,3,4,6Department of Dental Prosthodontics, Dental Students Research Committee, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran

2,5Department of Dental Prosthodontics, Dental Materials Research Center, Dental Research Institute, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran

Corresponding Author: Seyedeh Farimah Fatemi, Department of Dental Prosthodontics, Dental Students Research Committee, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran, e-mail:

Received: 03 October 2023; Accepted: 30 November 2023; Published on: 30 December 2023


Purpose: This study has done a nonbiased and comprehensive assessment of the survival rate of splinted and nonsplinted implant restoration from published meta-analyses and systematic reviews.

Materials and methods: All the included studies were assessed based on the risk of bias in systematic reviews (ROBIS) tool. Furthermore, the corrected covered area (CCA) was calculated using a citation matrix for meta-analyses. Studies with low overlap were only included in the final analysis. In the case of a high degree of overlap, the newest higher-quality study was chosen. The “Metaumbrella” package and R software were used to perform the statistical analysis.

Result: The original randomized controlled trials (RCTs) had an overall CCA of 5%, indicating slight overlap. For quantitative synthesis, three studies with meta-analyses were included, which were of high quality and showed low overlap. The quantitative analysis revealed that splinted restorations have a higher implant survival rate. The ratio of success in splinted implants to nonsplinted implants was 1.13 (p-value = 0.001).

Conclusion: Based on the findings of this umbrella review, splint restorations have a higher survival rate. This overview review suggests that splinting implants to adjacent tooth is an affordable and effective solution for treating partially edentulous patients.

How to cite this article: Baghaei K, Fathi A, Hashemi S, et al. To Splint or Not to Splint Tooth and Adjacent Dental Implants: An Overview of Reviews. Int J Prosthodont Restor Dent 2023;13(4):242–248.

Source of support: Nil

Conflict of interest: None

Keywords: Adjacent tooth, Dental implants, Nonsplinted restorations, Splinted restorations, Survival rate


Dental implants are a successful and comprehensive treatment option that can be beneficial for edentulous patients.1 Implants can help patients regain their chewing ability and have a higher quality of life.2 However, having a fixed prosthesis supported by implants is not always possible due to anatomical or financial concerns. Therefore, tooth-implant-supported prostheses are considered as a suitable replacement.3,4

The effects of splinting vs not splinting dental implants on implant survival, overdenture survival, and patient satisfaction have been investigated. One of the important elements in implant survival rate is force distribution, which is better in splinted restoration than in nonsplinted restoration.5,6 As a result, splinted restorations may be a better treatment option when implant length is less than optimal due to anatomical limitations. Moreover, they have a preventive effect against screw loosening.7 Issues regarding the use of splinted restorations include an increased incidence of caries, tooth intrusion, and mechanical fracture.8 On the other hand, nonsplinted restorations provide better emergence profiles, cervical contour, and oral hygiene, but the prosthodontic components are under more stress.2,9

Number of systematic reviews have been done, which can make it possible to reach an agreement on the current level of available clinical evidence. An overview of review is necessary to comprehend the evidence from published systematic reviews regarding splinted and nonsplinted restorations. The quality of the previous studies may vary, and their outcomes may be deemed invalid for several reasons like methodology or biases. Therefore, the purpose of this study was to do a nonbiased, comprehensive evaluation of the survival rate of splinted and nonsplinted restorations for treating partially edentulous patients. As a result, the findings might provide information that can enhance treatment plan guidelines.


The following items are addressed in this review using the preferred reporting items for overviews of reviews (PRIOR) guidelines (updated in 2022).10

Eligibility Criteria

In this overview of reviews, partially edentulous patients (population) having splinted restorations (intervention) were compared to patients with nonsplinted restorations (comparison) for implant survival rate (outcome). The search included studies until November 2023.

Systematic reviews with or without meta-analysis on survival rates of splinted and nonsplinted restorations in partially edentulous patients were only included. Systematic reviews which have clearly stated a research question, a systematic search of at least two databases, a systematic data synthesis, and that have been peer-reviewed were only included. All other studies were excluded. No language or publication date restrictions are applied. Studies that included patients with systemic diseases and heavy smokers were excluded.

Search Strategy and Database

Four databases were searched: PubMed, Scopus, Web of Science, and Embase. Keywords extracted from medical subject headings (MESH) to related free keywords (Table 1) were used for database search. In addition, a manual search of compatible journals, such as Journal of Prosthodontics, International Journal of Prosthodontics, Journal of Prosthetic Dentistry, the International Journal of Periodontics and Restorative Dentistry, Journal of the American Dental Association, Journal of Dentistry, Journal of Prosthodontic Research, the Journal of Periodontal and Implant Science, the International Journal of Oral and Maxillofacial Implants, Clinical Oral Implants Research, the Journal of Advanced Prosthodontics, Clinical Implant Dentistry and Related Research, European Journal of Oral Implantology, Implant Dentistry, and Journal Oral Implantology, and related textbooks, was done.

Table 1: Search strategy of electronic databases
Database Keyword Result
PubMed (“Dental Implants”[Mesh] OR “Dental Implantation”[Mesh] OR “dental implant” OR “implant”) AND (“Splints”[Mesh] OR “splint”) 13
Embase (’tooth implant’/exp OR ’tooth implant’ OR ’single tooth implant’/exp OR ’single tooth implant’ OR ’implant’/exp OR ’implant’ OR ’dental implant’/exp OR ’dental implant’ OR ’tooth implantation’/exp OR ’tooth implantation’ OR ’dental implantation’/exp OR ’dental implantation’) AND (’splint’/exp OR ’splint’) AND (’meta analysis’/de OR ’systematic review’/de) 51
Scopus (TITLE-ABS-KEY (“Dental Implants”) OR TITLE-ABS-KEY (“Dental Implantation”) OR TITLE-ABS-KEY (“dental implant”) OR TITLE-ABS-KEY (“implant”)) AND (TITLE-ABS-KEY (“splint”) OR TITLE-ABS-KEY (“splints”)) AND (LIMIT-TO (DOCTYPE, “re”)) 96
Scopus Secondary (TITLE-ABS-KEY (“Dental Implants”) OR TITLE-ABS-KEY (“Dental Implantation”) OR TITLE-ABS-KEY (“dental implant”) OR TITLE-ABS-KEY (“implant”)) AND (TITLE-ABS-KEY (“splint”) OR TITLE-ABS-KEY (“splints”)) AND (LIMIT-TO (DOCTYPE, “re”)) 12
Web of Science (TS=(“Dental Implants” OR “Dental Implantation” OR “dental implant” OR “implant”)) AND TS=(“Splints” OR “splint”) 77

Data Extraction Process

After the search was done, all studies were listed in EndNote software (version 20). Studies were reviewed precisely, and duplicated studies were removed. Titles and abstracts were independently reviewed for selecting eligible studies by authors (KB and SH). Further, full text of studies was independently reviewed by authors (KTT and KB) based on inclusion criteria. Two authors (SH and KB) extracted data from the confirmed studies. Any disagreement between the authors was addressed by a third author (AF).

Joanna Briggs Institute (JBI) data extraction form was used for data extraction.11 Study characteristics were filled in the form (Table 2). For quantitative synthesis effect sizes, 95% confidence intervals (CIs) and the number of subjects in each arm were extracted.

Table 2: Characteristic of qualitative studies
Author Database Included studies Analysis method Number of implants Implant characteristic Implant region Search period Population Interventions Comparison Assessment method Outcomes assessed Risk of bias Main results
Al Amri et al.2 PM, ML, EB, SP, GS, Web of Knowledge, Two RR
Two PR
SR 2,315 implants:
1,658 S
657 NS
7–13 mm
Regular 1,677
Wide 512
A, P
1965 to May 2016 Patients undergoing implant treatment Splinted restoration Nonsplinted restorations CASP Crestal bone loss around implants in SR and NSR group L Crestal bone loss was the same for adjacent implants in both groups
Shah et al.16 PM, CR, SP, GS, Science Direct Four PP
13 RP
SR, MA 3,682 implants:
2,529 S
1,153 NS
LE: 6–13
D: 3.3–5
A, P
January 2010 to August 2020 Patients undergoing implant treatment Minimum two implant placed in either arch Splinted and nonsplinted implant restoration ROB Crestal marginal bone loss around (primary outcome)
Implant survival rate and prosthetic complications (secondary outcome)
M Splinted implants had lower bone loss and failure, especially in the posterior of maxilla, prosthetics complication was the same
de Souza Batista et al.18 PM, ML, CR, SP Seven PP
11 RP
SR, MA 4,215 implants:
2,768 S
1,447 NS
LE: 8–20
D: 3–6
MAX, MAN To November 2017 Patients treated with dental implants Patients with non-splinted restorations supported by implants Compared with patients with splinted restorations supported by implants ROB Overall marginal bone loss is the primary outcome to be extracted and analyzed in the meta-analysis.
The survival rate of the implant and prosthetic complications were secondary outcomes
L There was no difference in the marginal bone loss and prosthetic complications of splinted and nonsplinted implant restorations; this is especially true for restorations in the posterior region. Nevertheless, splinted restorations were linked with a lower risk of implant failure
Kadkhodazadeh et al.17 PM, SP, WOS Two CS
20 RP
15 RCT
11 MA
SR, MA 11,271 implants:
9,393 single crowns
1,376 S multiunit prostheses
52 NS multiunit prostheses
450 cantilever prostheses
A, P
To March 2022 Patient treated with dental implants Had titanium implant supporting single-unit Compared with multiunit fixed prostheses ROB 2 The success rate of titanium dental implants L Implants for single-unit or multiunit prostheses have good survival and success rates. However, caution should be exercised when using cantilever and nonsplinted multiunit prostheses
Afrashtehfar et al.19 ML, EB, 13 journals manual
Searches, Open gray database
(One PR)
SR, MA 106 implants:
20 NS
86 S
LE: 5–12
D: 4.1–5
MAX, MAN September 2019 Patient receiving short implant, and need sinus augmentation surgery Implants with splinted restorations Implant supports free standings or single crowns ROB Success and survival rate of implants, secondary crestal bone loss, biological complications L Short implants had the same result regardless of being splinted or not

A, anterior; CASP, critical appraisal skills program; CR, Cochrane; CS, case series; D, diameter; EB, Embase; GS, Google Scholar; L, low; LE, length; M, moderate; MA, meta-analysis; MAN, mandible; MAX, maxilla; ML, Medline; NS, nonsplinted; P: posterior, PM, PubMed; PPQS, prospective qualitative synthesis; PR, prospective; RCT, randomized clinical trials; ROB 2, revised Cochrane risk of bias tool for randomized trials assessment tool; ROB, Cochrane collaboration tool for assessing risk of bias in randomized trials; ROB, risk of bias; RR, retrospective; S, splinted; SP, Scopus; SR, systematic review; WOS, Web of Science

Assessment of Risk of Bias

The selected systematic reviews were assessed by two independent authors (SH and KB). Systematic reviews were appraised based on the risk of bias in systematic reviews (ROBIS) criteria.12 This tool has two main phases and one optional stage. In the first stage, the relevance of a study was evaluated (optional phase I), then the review process and risk of bias were evaluated in phases II and III. Four main domains that can cause bias in a review article (study eligibility, selection process of studies, data collection and assessment, and synthesis) were assessed by the ROBIS tool. Studies were then classified into three categories—high (3–4 negative), moderate (2 negative), and low (<2) based on the risk of bias.

Assessment of Overlap

To determine whether there was an overlap between studies, a citation matrix was created using all the included randomized controlled trials (RCTs) in included review studies. The corrected covered area (CCA) was calculated and measured quantitively at the review level.13 Overall overlap was divided into four stages based on overlap threshold as slight (0–5%), moderate (6–10%), high (11–15%), and very high (above 15%).

Data Synthesis

Risk ratios and mean differences of splinted and nonsplinted implants were extracted and converted into standardized mean differences. The “Metaumbrella” package and R software (R Foundation, Indianapolis, Indiana, United States) were used to perform the statistical analysis.14

For each study, one effect size was calculated, and the restricted maximum likelihood (REML) method was used as the between-study variance estimator. A directed test of excess statistical significance (TESS) was utilized for excess of significant bias. The Ioannidis criteria were used for evaluating the evidence. The Ioannidis criteria have five classes—class I (p < 10–6, number of cases is above 103, I² < 50%, 95% prediction interval excluding the null, publication bias p > 0.05, and p-value of the Ioannidis test > 0.05), class II (p < 10–6, number of cases are above 1,000, and class I criteria not met), class III (p < 10–3, number of cases are above 103, and class I and II not met), class IV (p-value of the meta-analysis < 0.05 and previous classes criteria not met), and class ns (p-value of the meta-analysis ≥ 0.05).15 Finally, the outcome was converted to the equivalent odds ratio to compare the success rate of splinted and nonsplinted implants.


Identification of Reports

From the searched databases, a total of 249 papers were found. Duplicate studies were eliminated. Titles and abstracts were checked, and twelve full articles that met the criteria were taken into consideration for this umbrella review. On reviewing full texts, seven studies were excluded for not meeting inclusion criteria. Finally, five articles2,1619 were eligible for qualitative analysis. Only there articles1719 were eligible for quantitative analysis as two papers were ruled out due to high overlap (Fig. 1).2,16

Fig. 1: The preferred reporting items for systematic reviews and meta-analyses (PRISMA) flow diagram

Quality Assessment

All studies fulfilled the Risk of Bias 1.0 (ROB 1.0) tool appropriately. Included studies in qualitative synthesis had a low risk of bias regarding the Risk of Bias 2.0 (ROB 2.0) tool.2,1719 Only one study had a moderate risk of bias regarding synthesis and findings (Fig. 2).16

Fig. 2: Risk of bias domain

Overlap Assessment

Corrected covered area (CCA) calculations were performed and presented in Figures 3 and 4. Three meta-analyses showed high overlap,2,16,18 and the one18 that had the highest quality according to the ROBIS tool was considered for further analysis. Two other meta-analyses showed slight overlap.17,19 Moreover, the overall CCA of the original RCTs was 5%, indicating slight overlap.

Fig. 3: Critical appraisal and assessment (CAA) grid of meta-analysis evaluating splinting implants

Fig. 4: Overlap matrix for included studies

Study Selection Process

Since the study by de Souza Batista et al.,18 had a lower risk of bias compared to Shah et al.16 and was published after the study of Al Amri et al.,2 it was chosen for quantitative analysis. The study by Afrashtehfar et al.19 and Kadkhodazadeh et al.17 had a low risk of bias and showed slight overlap. Therefore, these two studies were also included in the quantitative analysis.

Characteristics of Selected Meta-analyses for Qualitative Analysis

Five studies were selected, which were published between 2016 and 2023. There was no common database among selected studies.2,1619 Number of implants varied between 106 and 11,271. While only one of the studies used Cochrane ROB 2 assessment,17 others used Cochrane ROB 1 (Table 2).2,16,18,19

Analyses of the Quantitative Outcomes

Performing the data analysis in three studies17,19 showed that splinted implants have a significantly higher success rate compared to nonsplinted implants, and the ratio of success in splinted implants to nonsplinted implants was 1.13 [p-value =0.001, 95% CI = (1.05–1.22), I2 = 0, publication bias =0.08]. Moreover, based on the Ioannidis criteria, the overall outcome was categorized as class IV.


This overview of review investigated available data regarding splinted and nonsplinted tooth-implant restorations. As the number of published articles regarding splinted restoration implants has grown since implant characteristics are different in each study, a comprehensive review was needed to determine the effectiveness of splinted restorations. In this overview of reviews, five reviews comprising 89 (36 RCTs and 53 non-RCTs) articles were included. The outcomes showed the restoration survival rate.

There are many factors related to implant such as length, shape, and surface characteristics needed for implant efficacy. Due to this, all included studies reported the need for long-term and detailed research in order to confirm their data. Only one study stated that using splinted restoration will decrease marginal bone loss.17 Other studies concluded that there is no difference in using splinted or nonsplinted regarding marginal bone loss.18,19 However, de Souza Batista et al.18 stated that although there is no difference in marginal bone loss, using splinted restoration will reduce implant failure. It is believed that utilizing a greater number of implants and abutments to support a fixed restoration reduces the risk of implant failure due to decreased implant mobility.20

Two systematic reviews investigated prostheses complications as well as implant failure.17,18 de Souza Batista et al.18 stated that there was no difference in prostheses complication regarding single and multiunit restoration. However, splinted restoration has lower implant failure. The connection makes the restorations more stable and reduces the transformed stress to crestal bone, which will make the survival rate higher.20 Also, it was determined that single and multiunit restoration had the similar effect on peri-implantitis and implant loss.

Clinically, splinting posterior maxillary implants could reduce retention loss due to biomechanical forces.18 Kadkhodazadeh et al.17 investigated short-term and long-term complications with the prostheses. Although there was no significant difference in short-term complications, cantilever prostheses had a lower success rate in the long-term period. The problem might be caused by uneven force distribution in cantilever prostheses.21

Only one study by Afrashtehfar et al.19 investigated the short and extra short implants. They stated that there is no difference in using splinted or nonsplinted restoration, but more clinical trials with larger sample size and durations are needed.

The result of this overview of review must be interpreted with caution, as there is a limited number of systematic reviews and meta-analyses included. Further analysis with more clinical and overview of reviews should be done to get a clear clinical picture for splinted and nonsplinted restorations.


Based on the evidence in this overview of review, splinted implant restorations to adjacent tooth have a higher survival rate than nonsplinted restorations. This overview review suggests that splinting implants to adjacent tooth is an affordable and effective solution for treating partially edentulous patients.


Kiumars Tavakolitafti


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