1 INTRODUCTION

Immediate implant placement (IIP) presents as a highly reliable solution when a replacement of a hopeless tooth is needed, either for single-tooth treatments or full-arch rehabilitations.2-4, 1 Nevertheless, implant insertion should follow strict criteria to achieve functional satisfactory outcomes, especially at anterior fresh extraction sockets where a finer aesthetic demand is mandatory.5 The presence of a sufficient 3-dimensional bone volume, a fully intact buccal bone plate and a thick gingival biotype, have been presented as favorable indicators to a better prognosis at this treatment option.5 Borges and colleagues,6 in a recent study with a novel digital assessment protocol, have proven the influence of buccal bone plate thickness and the dimensional changes that occur after flapless maxillary IIP.

In order to compensate hard and soft tissue changes, some investigators stated different strategies to compensate the volume contraction that include the use of bone grafts such as autogenous bone7 and deproteinized bovine bone mineral (DBBM)8, 9 and also the use of a connective tissue graft (CTG).10 As an alternative to a CTG, xenogeneic collagen matrices have been also tested for ridge preservation after tooth extraction.11, 12 Moreover, a flapless approach that aims to minimize tooth extraction trauma, followed by IIP and immediate provisionalization, seems to achieve satisfactory results regarding interproximal bone levels, survival rates, and aesthetics after a 5-year follow-up.13 This procedure allows to maintain the peri-implant mucosa contours, improving aesthetics until the definitive crown placement.14 Recently, studies evaluating the use of customized healing abutments/screws have been performed aiming to assess possible advantages associated with this treatment modality.15-18 The utilization of a CAD/CAM technique to fabricate a perfectly adapted polymethyl methacrylate (PMMA) healing abutment aims to reproduce the precise contours of the cervical root area and maintain the soft tissue contours during osseointegration and the healing of the peri-implant mucosa. Also, they seem to provide a predictable outcome while reducing the number of surgeries, postoperative discomfort, morbidity related to open-flap technique, and the length of treatment.19

Thus, the aim of this study was to evaluate peri-implant tissues dimensional changes after using customized healing abutments compared with the use of xenogeneic collagen matrices as socket sealing options in flapless maxillary IIP.

2 MATERIAL AND METHODS 2.1 Study design

The present study was conducted as a prospective, controlled clinical trial with a parallel-group design and balanced randomization (ratio 1:1) to document the peri-implant tissues response in using a xenogeneic collagen matrix (group CM) or a customized healing abutment (group CA) as different treatment methods for socket closure in flapless maxillary immediate implants. The protocol was reviewed and approved by the Institute of Bioethics of the Catholic University of Portugal (ESR 06.2019) and the patients included were previously informed and agreed to participate in this investigation signing an informed consent considering the 1975 Declaration of Helsinki, revised in 2013. In addition, this investigation has been registered at U.S. National Library of Medicine (ClinicalTrials.gov) website under the reference number NCT04432519. Group designation was kept in opaque-sealed envelopes that were opened after implant insertion by an investigator (Danilo Fernandes), not involved in surgical procedures, randomly allocating participants to one of the two treatment groups. Twenty-eight patients in need of a single implant restoration in the maxillary arch following tooth extraction were included in this study. Patients were treated between June 2019 and June 2020. Study participants selection was adapted from Borges and colleagues.6 Patients' inclusion criteria were (1) ≥18 years of age; (2) patients who had a failing tooth and needed an implant placing therapy in the aesthetic zone (between 15 and 25); (3) the failing tooth has adjacent and opposing natural teeth; (4) sufficient mesial-distal and interocclusal space for placement of the implant and definitive restoration; (5) had an intact socket wall previously to the extraction; (6) had sufficient apical bone to place an immediate implant with minimum primary stability of 30 Ncm. Exclusion criteria were (1) individuals diagnosed with periodontal disease; (2) medical and general contraindications for the surgical procedure; (3) heavy smokers (>10 cigarettes/day); (4) an active infection at the implant site. A CONSORT 2010 check-list was performed in order to consider an appropriate guideline for the present randomized trial study.20

2.2 Surgical protocol

All surgical procedures were conducted under appropriate local anesthesia 4% articaine with adrenaline 1:100000 (UbistesinTM, 3M-ESPE, St. Paul, MN). In both groups, flapless tooth extractions were performed after sectioning the tooth, followed by the use of periotomes and elevators to separate the two parts of the tooth, avoiding damage to the buccal and palatal bone plates. The socket was inspected to search for any fenestration or dehiscence of the bone walls, which would have led to the exclusion of the patient. All patients were treated with cylindrical shape implants (OsseoSpeed EV, Astra Tech Implant System, Dentsply Implants, Möhndal, Sweden) with a narrow diameter internal connection platform following the surgical sequence protocol provided by the manufacturer. The implant was placed in a correct 3-dimensional position, engaging the palatal and apical bone to achieve high primary stability (Figure 1(A), (C)).21 After implant insertion, a gap of at least 2 mm between the inner cortical buccal bone plate and the implant surface was filled with DBBM material (Symbios, Dentsply Implants, Möhndal, Sweden).

CM and CA groups socket closure methods. (A, B) IIP and a xenogeneic collagen matrix (CM); (B, C) IIP and a customized healing abutment (CA)

The two groups differ on distinct methods in order to seal the fresh sockets. Group CM (Figure 1(A), (B)) sockets were sealed with a resorbable collagen matrix (Mucograf Seal, Geistlish Biomaterials, Wolhusen, Switzerland) stabilized with single interrupted 6/0 polyamide sutures (SeralonTM, Serag-Wiessner, Nalia, Germany), whereas group CA (Figure 1(C), (D)) received a healing abutment customized with a PMMA material allowing to close the socket without sutures. All customized healing abutments were manufactured in a CAD/CAM software (CEREC in LAB MC XL, Sirona Dental Systems Gmbh, Bensheim, Germany) and milled by a specific milling machine (Sirona MCX5, Sirona Dental Systems Gmbh, Bensheim, Germany).

All surgical procedures were performed by one experienced surgeon (Tiago Borges). The patients had provisional resin bonded crowns to the adjacent teeth on the same day as the implant surgery, being removed after 16 weeks. Postoperative instructions were given to the patients, which included a soft diet, oral hygiene procedures, and chlorhexidine 0.12% rinsing twice per day during 2 weeks. Systemic antibiotics (amoxicillin 1 g twice per day for 7 days) and paracetamol 1000 mg, three times per day, for pain control, were prescribed. Sutures were removed 10 days after surgery. A screw-retained provisional crown was delivered after 4 months of healing and definitive restorations were inserted at the 6-month appointment, consisting in a screw-retained all-ceramic crown and a customized titanium abutment (Atlantis, Dentsply Implants, Möhndal, Sweden).

2.3 Clinical observation and data acquisition

Examination protocol and data collection were adapted from Borges and colleagues6 and consisted of four appointments: (1) T0 (flapless tooth extraction and implant insertion); (2) T1 (1-month follow-up after implant placement); (3) T2 (4-month follow-up after implant insertion); and (4) T3 (1-year postoperative follow-up). An intraoral optical scan (Cerec Omnicam, Sirona Dental Systems GmbH, Bensheim, Germany) of the upper arch and a cone-beam computer tomography (CBCT) evaluation (Ortophos XG 3D, Sirona Dental Systems GmbH, Bensheim, Germany) were performed before tooth extraction and implant placement (T0). At this point, two clinical parameters were assessed with a periodontal probe (PCB 12; Hu-Friedy, Chicago, IL) to the nearest millimeter: BID (distance between implant shoulder and the buccal bone plate) and KM (distance between the gingival groove and the mucogingival junction). Intraoral scans were completed postimplant placement at 1 month (T1), 4 months (T2), and 12 months (T3). In all follow-up appointments, hygiene instructions were given to the patients and periodontal care was executed when necessary. Biologic complications such as mucositis or periimplantitis were recorded based at the peri-implant disease clinical and radiographic diagnosis. Technical complications were registered as the prosthetic problems such as screw loosening, abutment fracture, ceramic chipping, or ceramic fracture.

2.4 Intraobserver agreement

A protocol was elaborated to study the variables of interest in three distinct computer software. One examiner (Danilo Fernandes), blinded for the surgical procedure, was calibrated through an intraexaminer test (Dahlberg d-value), consisting in a double consecutive data collection of 10 randomly chosen patients included in this study. An intraclass coefficient of 0.93 was obtained.

2.5 Matching digital models

All digital models were exported from the intraoral optical scanner software (Cerec Omnicam, Sirona Dental Systems GmbH, Bensheim, Germany) in stereolithography (STL) format and were examined with a specially designed software (Geomagic Control X, Geomagic, Inc., Cary, NC). The T0 and T1, T0 and T2, and T0 and T3 STL files were superimposed and a strict alignment was made into a common coordinate system. The final alignment was carried out through the best fit alignment algorithm for a perfect match of digital models.6

2.6 Linear and volumetric measurements

The digital analysis protocol was performed as described by Borges and colleagues.6 After the superimposition of study models, a color map was created allowing to quantitatively analyze dimensional variations occurring in the surgical areas and surrounding tissues. Green color represents areas where no 3-dimensional changes were found, while variations between yellow and red represent volume increase and variations between light blue and dark blue represent volume decrease (Figure 2(A)). A region of interest (ROI) composed with 10 section planes, perpendicular to the coronal section of the tooth, was computed at the buccal and palatal aspect of the ridge (Figure 2(A), (B)). These sections were set at the most apical point of the gingival margin and ended 5 mm above it. Mesially and distally, a line passing through the interproximal area limited the ROI. The same ROI was used in each patient, at the different comparison follow-ups. The intersection of these sections with the superimposed models resulted in the linear changes to be obtained in each area. The mean buccal change (MBCT0–T1, MBCT0–T2, and MBCT0–T3) representing the buccal area and mean total change (MTCT0–T1, MTCT0–T2, and MTCT0–T3) representing the buccal and palatal aspects were calculated in millimeters (mm) to evaluate the variations that occurred in the peri-implant area.

Linear and volumetric digital assessment. (A) Linear ROI selection (red); (B) buccal and palatal sections; (C) volumetric ROI assessment (red); (D) initial total volume

Moreover, the superimposed STL files were exported to another computer program (Materialise Magics, Materialise, Leuven, Belgium) for volumetric assessment. A 3-dimensional volumetric ROI was manually selected with “cut or punch” function considering interproximal areas as mesial and distal limits (Figure 2(C)). All cuts were performed in the same areas in all digital models ensuring that all measurements were carried out in the same regions. The use of “Boolean” function was performed to create STL files related to volume reduction and volume increase occurred at different time points. Volumetric variation considering volume increase and volume reduction were represented as buccal volume variation (BVvT0–T1, BVvT0–T2, and BVvT0–T3) and total volume variation (TVvT0–T1, TVvT0–T2, and TVvT0–T3) in cubic millimeters (mm3) and relative percentages (%). The initial total volumes evaluated from each ROI at the buccal (BVt) and palatal (PVt) aspect were also computed for further comparison with volume variations at the different appointments (Figure 2(D)). These calculations allowed to create relative percentages of volume variations which is essential to directly compare different patients due to anatomical variances. All measurements were recorded to the nearest 0.01 mm.

2.7 Midfacial mucosa and papillae outcomes

Midfacial mucosa and papillae height variation at the 1-year follow-up were analyzed using a computer software (Materialise Magics, Materialise). After precisely overlapping the T0 and T3 STL files in a common coordinate system, a standardized line (red) was created connecting the marginal gingiva two most apical points of adjacent teeth, which served as a horizontal reference for the vertical measurements (Figure 3). Three measurements were computed in each STL file to calculate marginal gingiva mucosa and mesial and distal papilla height at T0 (Figure 3(A)) and T3 (Figure 3(B)). The mean differences of these measurements allowed to calculate variables representing MGHv (mm) related to the marginal gingiva height variation and MPHv (mm) and DPHv (mm), both associated to mesial and distal papilla height variation, respectively. PHv (mm) variable was established as the mean difference considering both papillae.

Assessment of midfacial mucosa and papillae height at T0 (A) and T3 (B) for height variation calculation

2.8 Radiographic assessment

Radiographic examination was performed with a volumetric dimension of 8 × 8 cm for 14 s with the XG 3-dimensional tomography acquisition protocol, with a voxel size of 0.1 mm in high-definition mode. The obtained CBCT images were imported in a digital imaging and communications in medicine (DICOM) format to a specific software for radiographic assessment (Materialise Mimics, Materialise) in order to calculate buccal bone thickness (BT). All measurements were obtained through coronal slice reconstructions, using an adjacent line to the sinus/nasal plate as a reference as described by Borges and colleagues.6 BT was measured 1 mm above the coronal bone margin using a central slice, as well at the mesial and distal slices, ranging 1 mm from the central slice. Mean BT values were obtained as the average values of the three slices.

2.9 Statistical analysis

The statistical analysis was performed using a computer software (SPSS, Statistical Package for the Social Sciences, version 21.0, IBM Corp., Armonk, NY) by an independent statistician who was not involved in the surgical procedure or study design.

Sample size and power calculation were computed taking into consideration a significance value of α = 0.05 (type I error) based on the MBC evolution as primary outcome, obtaining a sample size power of 80% for at least 13 patients per group. The sample size computation for the present investigation was performed post factum using the sample size calculator G*Power version 3.1.9.6 (Franz Faul, University of Kiel, Kiel, Germany) taking in consideration the changes that were assessed between the initial situation and 1-year postimplant insertion.

The established variables were presented as mean values, standard deviation, minimum, maximum, and 95% confidence interval. Variables related to participant's characterization such as age, gender, implant site (incisive/premolar), BT, BID, KM, BVt, and PVt were evaluated with chi-square test, t test, or Mann–Whitney test, to examine possible significant differences between the initial characteristics of the groups. Linear and volumetric variables at the different time points (T1, T2, and T3) were evaluated with t test and the Mann–Whitney test was conducted to disclose differences for continuous nonpaired variables. The implant was defined as the statistical unit.

Moreover, a two-way ANOVA analysis was computed to understand the buccal bone thickness effect on study volumetric variables. All hypothesis tests were considered at the 5% level of significance.

3 RESULTS 3.1 Patients and implants

Participants characteristics and distribution data are detailed in Table 1. A total of twenty-eight participants with a mean age of 54.00 ± 12.20 years were enrolled in this randomized clinical trial, with 14 individuals allocated to each experimental group. In CM group, 36% of the patients were males and 64% females, whereas CA group had 57% males and 43% females. All participants were healthy and nonsmokers. Nonbiological and technical complications were found in patients or implants within the 1-year follow-up, revealing a 100% success rate. Also, no significant differences were found between groups in patient's initial demographic variable.

TABLE 1. Patients demographic data and characterization Subject characterization Group N Min Max SD p-value Patients CM 14 CA 14 Gender (male/female) CM 5♂/9♀ (36/64%) 0.449a CA 8♂/6♀ (57/43%) Age CM 14 36 76 53.43 12.33 0.810b CA 14 37 85 54.57 12.51 Implant site incisive/premolar CM 4I/10 PM (40/60%) 0.252a CA 8I/6 PM (57/43%) BT (mm) CM 14 0.10 2.53 0.98 0.73 0.589b CA 14 0.10 1.95 1.11 0.48 BID (mm) CM 14 2 5 2.86 0.86 0.329c CA 14 2 5 3.21 0.97 KM (mm) CM 14 2 6 3.79 1.53 0.427c CA 14 3 6 4.07 0.73 BVt (mm3) CM 14 177.73 313.16 264.25 41.21 0.596b CA 14 136.54 457.03 278.42 89.85 PVt (mm3) CM 14 135.19 287.29 223.53 43.60 0.247b CA 14 142.16 377.61 252.13 79.19 Abbreviations: BID, buccal implant distance (mm); BT, buccal thickness (mm); BVt, buccal volume total (mm3); KM, keratinized mucosa (mm); Min, minimum; Max, maximum; PVt, palatal volume total (mm3); SD, standard deviation; mean. a Qui-square with Yates correction. b T-test. c Mann–Whitney test. 3.2 Digital assessment of linear and volumetric variations

Linear and volumetric peri-implant tissue variations from baseline to 1-year follow-up are shown in Table 2. At T1, MBC of −0.36 ± 0.34 mm at CM group and −0.19 ± 0.29 mm at CA group was assessed, while MTC showed a linear variation of −0.62 ± 0.47 mm at CM group compared with −0.32 ± 0.50 mm at CA group (p = 0.167 and p = 0.152, respectively). Volumetric analysis revealed a change in BVv(%) of −9.75 ± 6.65% at CM group and −4.76 ± 5.29% at CA group (p = 0.043) at T1, and TVv(%) showed values of −8.90 ± 5.03% for CM group, whereas CA group reported a significantly less TVv(%) of −4.17 ± 4.52% (p = 0.021) (Figure 4). At T3, CM group revealed less tissue variation than CA group in all evaluated variables, yet no statistical significance was detected. A BVv(%) of −9.76 ± 7.24% at CM group and −10.45 ± 3.99% at CA group were exhibited at T3 (p = 0.616).

TABLE 2. Linear and volumetric peri-implant tissue variations from baseline to 1-year follow-up Variable Time Group N Min, max SD CI (95%) p-value Lower, upper MBC (mm) T0–T1 CM 14 −1.15, 0.20 −0.36 0.34 −0.58, −0.15 0.167 CA 14 −0.86, 0.19 −0.19 0.29 −0.35, −0.02 T0–T2 CM 14 −1.03, 0.13 −0.35 0.36 −0.57, −0.13 0.418 CA 14 −0.96, 0.06 −0.24 0.27 −0.41, −0.08 T0–T3 CM 14 −1.01, −0.04 −0.42 0.31 −0.60, −0.24 0.720 CA 14 −1.13, −0.10 −0.46 0.31 −0.65, −0.28 MTC (mm) T0–T1 CM 14 −1.62, 0.10 −0.62 0.47 −0.93, −0.30 0.152 CA 14 −1.60, 0.16 −0.32 0.50 −0.61, −0.03 T0–T2 CM 14 −1.37, −0.01 −0.50 0.44 −0.77, −0.23 0.880 CA 14 −1.66, −0.11 −0.47 0.43 −0.73, −0.21 T0–T3 CM 14 −1.44, −0.06 −0.56 0.45 −0.82, −0.30 0.346 CA 14 −1.51, −0.26 −0.71 0.37 −0.94, 0.49 BVv (mm3) T0–T1 CM 14 −5.32, 9.73 −25.20 17.44 −36.28, −14.12 0.049* CA 14 −4.55, 7.81 −12.98 14.53 −21.37, −4.60 T0–T2 CM 14 −7.07, 7.05 −23.47 20.90 −36.10, −10.84 0.425 CA 14 −56.86, 3.42 −17.52 16.14 −27.28, −7.77 T0–T3 CM 14 −69.26, 7.05 −25.79 19.75 −37.19, −14.38 0.553 CA 14 −50.78, −7.30 −29.80 14.32 −38.46, −21.15 BVv (%) T0–T1 CM 14 −19.16, 3.53 −9.75 6.65 −13.98, −5.53 0.043* CA 14 −18.40, 3.05 −4.76 5.29 −7.81, −1.70 T0–T2 CM 14 −25.68, 2.56 −8.98 7.56 −13.54, −4.41 0.336 CA 14 −22.47, 1.34 −6.39 5.65 −9.80, −2.97 T0–T3 CM 14 −25.38, 2.56 −9.76 7.24 −13.94, −5.58 0.616 CA 14 −19.18, −5.35 −10.45