Introduction

After the extraction of a tooth remodeling of the soft and hard tissues occurs. Bone fills the defect in the alveoli and resorption occurs on the outer surface of the alveolar bone. Change in bone contour occurs both vertically and horizontally [1]. It is reported that around 87 percent of patients present with a buccal bone plate equal to or thinner than 1 millimeter [2]. Additionally, after the extraction majority of bone resorption takes place buccally from the extraction site [3, 4]. In part, this can be explained by the fact that the buccal bone plate contains bundle bone and blood flow is dependent on the periodontal ligament. Thus, the anatomy of the maxillary buccal bone plate in the esthetic zone indicates its susceptibility to significant resorption after the extraction of a tooth. Immediate dental implant placement is proven to be an effective method for maintaining the surrounding tissue stability, however incapable of stopping bone resorption entirely yet [5, 6]. This means that management of the surgical site requires that all factors must minimize the loss of hard tissues for a pleasing esthetic result and a successful dental implant retained restoration. This study aims to evaluate early bone volumetric changes of the buccal bone plate vertically and horizontally after the immediate dental implant placement. Two major surgical protocol factors that could impact the amount of bone remodulation are compared - full-thickness flap elevation and bone grafting.

Materials and Methods

This systematic review was carried out using the Preferred Reporting Item for Systematic Reviews and Meta-Analyses (PRISMA) statement. Before the beginning of the systematic review, the protocol was written and registered at PROSPERO (the University of York, Centre for Reviews and Dissemination). The unique ID of this publication is CRD42021291731.

Clinical question

The clinical question was prepared by following the Participant, Intervention, Comparison, Outcome (PICO) principle [5]. How does the grafting and flap elevation during the immediate implantation in the aesthetic zone of the maxilla influence early buccal bone plate resorption?

Inclusion and exclusion criteria

Inclusion criteria

• Prospective clinical trials.
• Human clinical studies in which immediate titanium dental implant placement was carried out.
• Participants must be healthy adults without any systemic diseases.
• Immediate implantation (dental implant placement in the fresh alveolar socket after the extraction of a tooth) must be performed in the aesthetic zone of the maxilla (second premolar to the second premolar). 
• Implant should be placed subcrestally (1 – 4 millimeters below the surface of the adjacent alveolar bone).
• Jumping space (space between the implant and the buccal wall)
• No buccal bone defects (dehiscence or fenestration) must be present after the extraction of the tooth.
• Buccal bone alterations must be measured using CBCT (cone beam computed tomography) before the intervention and at the follow-up.
• Follow-up period is between 6 to 12 months after the initial surgery.

Exclusion criteria

• Animal studies.
• Retrospective studies.
• Results from dental implantation performed in mandible.
• Buccal wall defects present or not evaluated after the extraction of a tooth.
• No information about the jumping space.

Search strategy and study selection

An electronic systematic literature search according to PRISMA guidelines [6] was conducted by two researchers (D.L and R.P.) individually in PubMed, Science Direct, and Cochrane library from September to November of 2021. The keywords used in the search were: (Immediate implantation), (Graft), (CBCT), (Radiograph), (Bone), (Loss), (Resorption). The publication search was conducted in two stages. The first stage consisted of screening the publications headlines and abstracts. Studies eligible for our inclusion criteria were included in the second stage of screening. Duplicate studies and studies that were not compliant with our inclusion criteria were excluded. The second stage consisted of analyzing the full-text publications. If they were compliant with the inclusion criteria, they were included in this systematic review. Researchers compared search results and resolved dissimilarities through discussion. When an agreement in a such way could not be achieved the consulting experienced researchers (G.J. and D.R.) were asked to help reach a consensus.

Risk of bias assessment

Two researchers (D.L. and R.P.) independently assessed the risk of bias using Cochrane's Risk of Bias 2 (RoB 2) tool [7]. If there were dissimilarities between the results – researchers discussed them to achieve a consensus. If an agreement could not be reached in such a manner, third consulting party (G.J. and D.R.) helped to resolve issues. The following domains were assessed: randomization process, deviations from the intended interventions, missing outcome data, measurement of the outcome, and selection of the reported result.

Results and Discussion

Study selection

A review of articles, abstracts, and full-text publications is depicted utilizing a PRISMA flow diagram (Figure 1). A total of 358 publications were identified in the initial search. After eliminating duplicates and articles with titles or abstracts that did not meet the inclusion criteria, 74 studies were included. Only one study was unavailable for full-text screening. After reading the available full-text articles 65 publications were excluded because they were not eligible for our inclusion criteria. The most common reason for article exlusion was that the results of buccal bone plate resorption were combined from surgeries performed in the aesthetic zone in both maxilla and mandible. 8 studies met the inclusion criteria and were included in this systematic review.

Characteristics of the included studies

The included articles were all prospective clinical trials published from 2016 to 2021 (Table 1).

Table 1. Characteristics of the included studies. Location of clinical trials took place in Europe, Asia, North America and Africa. Total number of evaluated dental implants was 272, follow-up period ranged between 6 and 12 months, 7 studies measured buccal bone plate change horizontally and 3 studies calculated the vertical bone resorption.

The total number of implants is 272. There were 4 studies [8, 10, 11, 13] in which no graft was used, in 6 [9-12, 14, 15] studies autogenic, allogenic, or xenogenic bone substitute was used to fill the jumping space. In 7 [8-13, 15] trials flapless immediate implantation was evaluated and in 5 [9-11, 14, 15] publications the results of flap elevation were described. 7 papers [8, 10-15] measured early changes in the buccal bone plate thickness and only 3 publications [8, 9, 12] evaluated the vertical resorption of the buccal bone plate. If the article included a group of patients that were eligible for our analysis – we included only that group in our paper. For example, Fujita et al. article includes group of patients in which the soft tissue augmentation procedure was performed and Abd-Elrahman et al. evaluates effects of socket shield technique. Groups of patients from these interventions groups were excluded from this study.

Risk of bias assessment

The results of the risk of bias assessment for each study is presented visually bellow in Figure 2. High risk of bias was arising from the randomization process in two [9, 14] papers that we included in our study. This occurred due to a suspect that enrolling investigators had knowledge of the forthcoming allocations. It is worth noting that none of the trials included had any baseline imbalances that would suggest a problem with the randomization process. Some concerns arose when evaluating the bias in measurement of the outcome in three studies [8, 14, 15]. In these studies, outcome assessors were aware of the intervention received, therefore the assessment could have been influenced. Also, there were some concerns with Bittner et al. trial regarding the randomization process due to lack of information on allocation sequence concealment. All studies demonstrated low risk of bias due to deviations from intended intervention, missing outcome data and selection of the reported result domains. Overall, three studies [10-12] were considered as low risk of bias, another three publications demonstrated some concerns [8, 13, 15], and two trials [9, 14] were rated as high risk of bias.

Results of individual studies

The results from individual studies were grouped according to the interventions made during the surgery. Four groups were formed: flapless and no graft, flapless and graft, flap and no graft, and flap and graft. Results of the buccal bone plate horizontal and vertical dimensional change in all studies were measured in the midline of the implant. As mentioned before, the follow-up period was between six and twelve months. The area of interest for the horizontal resorption was chosen to be the 5 millimeters starting from the neck of the implant (0 mm) advancing apically to the 5^th millimeter. Two subgroups were formed for the assessment of the horizontal resorption taking place in the bucco-palatal direction according to the location of measurement (0 – 2 mm. and 3 – 5 mm.). Results are presented in Table 2. The amount of dimensional bone change in the table is presented as a mean and a standard deviation. Negative numbers indicate bone resorption, positive numerical results indicate the growth of bone after the follow-up period.

Table 2. Results of the buccal bone plate resorption occurring vertically (buccally from the implant) and horizontally. Horizontal resorption group contains results of horizontal buccal bone plate resorption at 0-2 mm. bellow the shoulder of the implant and 3-5 mm. bellow the shoulder of the implant.

N/A – no available data.

Heterogeneity assessment

In order to compare the results of bone resorption occurring at different intervals of implant height both horizontally and vertically throughout the examination of significant variability among studies must be assessed. In order to evaluate variability in effect estimates which is due to heterogeneity rather than sampling error Levene’s Test for Equality of Variance is applied [16].

Firstly, the pooled standard deviation s is calculated:

s₁ and s₂ are the standard deviations of the two samples with sample sizes n₁ and n₂. the standard error se of the difference between the two means is calculated as:

Lastly, the significance level (also known as the P-value) between the two results is calculated using the t-test [17]:

All of the subgroup calculation results are presented in the following tables and divided according to the measurement location (Table 3). In each table “Sample size 1” represents the number of surgery sites from the first result of a particular publication. “Mean 1” and “Sd 1” represents the result of bone resorption mean with standard deviation from the same first publication. “Sample size 2” refers to the number of surgery sites from the second publication. “Mean 2” and “Sd 2” represents the result of bone resorption mean with standard deviation from the second publication. If the t-test indicates that the p-value between the first and second subgroup results is less than 0,05 – two different subgroup results are statistically different. All of the results are compared in such a manner. The last column of the table indicates whether the two results are significantly different or not. 

A total of 56 calculations were performed. 19 (34 %) of all two-tailed t-tests confirmed that heterogeneity is indeed present.

Table 3. Intergroup results of heterogeneity assessment. All of the individual results are compared between the same group results. If the difference between the results inside of one group are statistically significant – “ *” symbol is written in the last column.

N/A – no available data.