The Effects of Disconnection and Reconnection of Definitive Abutments on Peri-Implant Bone Levels: A 1-year Split-Mouth Randomized Controlled Clinical Study
Phase: NA
Conditions: Bone Loss, Implant Complication, Gingival Recession
Sponsor: Loma Linda University

 
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The Effects of Disconnection and Reconnection of Definitive Abutments on 
Peri-implant Bone Levels Changes: A 1- Year Split-Mouth Randomized 
Controlled Clinical Study 
 
 
This study has been registered in ClinicalTrial.gov ID. NCT04043286  
 
 
Document Date: Sep 10th, 2024 
 
 

 
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Abstract 
Background: There is evidence suggesting non-removal of a definitive abutment on an 
implant from the day of surgery helps to preserve the peri-implant marginal bone levels. 
However, the limited literatures available still contains contradictory conclusions to this 
finding. 
Objective: The aim of this prospective study was to evaluate the effects of definitive 
abutment connection at the time of implant placement on peri-implant bone levels and soft 
tissue changes in posterior maxilla and mandible regions. 
Materials and Methods: A total of 38 implants were placed in 17 patients with at least 2 
missing posterior teeth in the maxilla or the mandible for this study. Each patient received 2 
or 4 implants. A definitive prefabricated abutment (test group) was randomly connected to 
one implant at implant placement (T0) and left undisturbed throughout the duration of the 
study. On the other implant, a healing abutment (control group) was connected and subjected 
to go through three disconnections and reconnections at 3 months (T3), 6 months (T6), and 
12 months (T12) after the implant placement. Throughout the study period (1 year), all 
implants remained unrestored. Marginal bone level changes (MBLC) were assessed using 
standardized periapical radiographs taken at T0 and T12. Peri-implant soft tissue parameters 
including the keratinized mucosa width and lingual mucosa thickness were also recorded and 
evaluated. 
Results: At the 1-year follow-up, the test group showed significantly less MBLC compared 
to the control group. The mean MBLC in the test group was 0.32 ± 0.47 mm, which was 
significantly lower than the 0.80 ± 0.92 mm observed in the control group (p=0.009). The 
test group also had a smaller reduction in keratinized mucosa width, with a mean reduction of 
0.42 ± 0.42 mm compared to 0.90 ± 0.77 mm in the control group (p=0.049). Lingual mucosa 
thickness changes were 0.38 ± 0.26 mm in the test group and 0.71 ± 0.59 mm in the control 

 
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group, but this difference did not reach statistical significance (p=0.053). However, a 
significant correlation was identified between changes in keratinized mucosa width and 
MBLC in the test group (p=0.02). 
Conclusion: The results of this study support the hypothesis that connecting a definitive 
abutment at the time of implant placement results in less MBLC compared to repeated 
abutment disconnections. Additionally, the test group demonstrated better preservation of 
peri-implant soft tissue compared to the control group. These findings suggest that the one-
abutment-one-time protocol may contribute to improved peri-implant tissue stability. 
 
Keywords: abutment disconnection-reconnection, one-abutment one-time, definitive 
abutment, one-time abutment, marginal bone loss 

 
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1. INTRODUCTION 
 
The peri-implant mucosal barrier consists of two key components: (i) a junctional epithelium 
approximately 2 mm, and (ii) a connective tissue compartment about 1–1.7 mm.1-3 During 
healing, it is hypothesized that the connective tissue adheres to the transmucosal implant 
components, forming a barrier that inhibits epithelial downgrowth and helps prevent peri-
implant bone resorption due to bacterial and mechanical insults.4-7 To preserve the marginal 
bone level around dental implants, it is important to improve the quality and stability of the 
connective tissue integration, in addition to utilizing a minimally invasive surgical 
technique.2 
Several factors may influence the connective tissue-implant interface, including the 
type of implant, initial soft tissue thickness,8 depth of implant placement,9-12 and the stability 
of the implant-abutment connection.10 Additional factors include the size of the microgap at 
the implant-abutment connection, the material and surface topography of the abutment,13-15 
abutment height,16 and the abutment emergence profile.17 The reaction of peri-implant soft 
tissue to repeated disturbance, such as disconnections and reconnections of the abutment, has 
also been shown to impact bone resorption.18-20 
Abrahamsson et al19 were the first to report, in an animal study, that repeated 
abutment disconnections and reconnections can compromise the mucosal barrier, resulting in 
approximately 0.7 mm of additional peri-implant bone loss and soft tissue recession. This 
finding led to the development of the "one-abutment-one-time" (OAOT) concept, which 
advocates placing a definitive abutment at the time of implant surgery to avoid disrupting 
connective tissue adaptation during restorative procedures. However, subsequent studies in 
both animals and humans have produced contradictory results regarding peri-implant bone 
changes.21-23 Human studies by Degidi et al reported a significant reduction in horizontal 
bone remodeling around subcrestally placed tapered implants when a definitive abutment 

 
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was delivered at the time of surgery.24,25 Similar studies arrived at the same conclusions for 
implants placed at both immediate post-extraction sites20,26,27 and healed sites.28-33 Other 
studies, however, demonstrated that peri-implant bone levels did not change significantly.34-
39 Several reviews and meta-analyses also found a lack of consensus on this topic.18,40-42 Two 
meta-analysis concluded that multiple abutment disconnections significantly affect marginal 
bone level changes in partially edentulous patients.43,44 The evidence on this concept remains 
controversial due to the wide variation in methodologies employed by the studies and the 
inclusion of confounding factors that may influence the results.45-47 
Marginal bone changes are critical for the long-term assessment and maintenance of 
dental implants, as they form the basis for implant success criteria and help determine the 
progression of peri-implant pathology.45,46 The present study aimed to evaluate peri-implant 
bone level changes one year after implant placement with a definitive abutment, before 
functional loading. The null hypothesis was that there would be no significant difference in 
peri-implant bone levels between implants with definitive abutments delivered at the time of 
surgery using the one-abutment-one-time protocol, and those subjected to multiple abutment 
disconnections and reconnections. 
 
2. MATERIALS AND METHODS 
2.1 Sample size 
Power analysis was carried out to determine the sample size. A sample size of 38 implants 
was needed to achieve 80% power to detect a difference between the null proportion of 0.500 
at a significance level of 0.05. 
2.2 Patient selection 
This study was designed as a single-center, prospective, randomized modified split-mouth 

 
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clinical trial. It was conducted at the Loma Linda University School of Dentistry (LLUSD) 
Center for Implant Dentistry, California, United States. The study followed guidelines 
established by the Loma Linda University Institutional Review Board (IRB No.#5190024) 
and was approved prior to initiation. 
To be included in the study, patients had to meet the following criteria: (i) read, sign, 
and receive a copy of the informed consent form, including consent for photos; (ii) Male or 
female with at least 18 years of age with good oral hygiene and good general health; (iii) 
have a healed site with two or more missing teeth in the maxillary or mandibular posterior 
region (excluding third molars); (iv) have adequate bone width and height to accommodate at 
least a 4.3 mm diameter and 8 mm length implant at each site; (v) have at least 8 mm of 
interocclusal restorative space; and (vi) be willing to participate and attend the planned 1-
year follow-up visits before starting the implant restoration procedures. 
Patients were excluded if they had the following: (i) history of alcohol or drug 
dependency, or any medical, physical, or psychological factors that might affect the surgical 
or prosthodontic procedures and follow-up examinations; (ii) history of radiation therapy to 
the head and neck region; (iii) history or current habit of smoking; (iv) history or current 
habit of bruxism; (v) no opposing occluding dentition or prostheses; (vi) need for bone 
augmentation during implant placement; or (vii) implant insertion torque value <35 Ncm. 
Each patient received at least two implants in the posterior maxilla or mandible. At implant 
placement (T0), one implant was randomly selected to receive a definitive prefabricated 
abutment (test group), which was left undisturbed throughout the study. The other implant 
received a healing abutment (control group), which underwent three disconnections and 
reconnections at 3 months (T3), 6 months (T6), and 12 months (T12) after implant surgery. 
All implants were restored with individual screw-retained crowns after the 1-year study 
period. 

 
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2.3 Surgical procedures 
At the time of implant surgery, patients were escorted to the operating room at the LLUSD 
Center for Implant Dentistry. They were instructed to rinse their mouths with 0.12% 
chlorhexidine gluconate solution for 3 minutes prior to surgery. After being seated, monitors 
were placed to record blood pressure, pulse rate, and oxygen saturation. The patient's 
circumoral area was sterilized with a Povidone-Iodine swab (Aplicare, Aplicare Inc., 
Branford, CT), and the area was then draped for a sterile protocol. Oxygen was provided to 
the patient through a nasal cannula at a minimum flow rate of 3 liters per minute. 
Following the administration of local anesthetic (2% lidocaine with 1:100,000 epinephrine 
[Dentsply, York, PA, USA]), a surgical stent was used to determine the position of implant 
placement. Pre-operative keratinized mucosa width was measured and recorded at the center 
of the future implant placement site with a 1.0 mm marked periodontal probe (Hu-Friedy, 
Chicago, IL, USA). Crestal and intrasulcular incisions were made using a #15 blade (Miltex, 
Japan), and a buccal periosteal flap was reflected, leaving the lingual mucosal tissue 
undisturbed. Lingual mucosal tissue thickness was measured with a 1.0 mm marked 
periodontal probe from the bone crest at the center of the future implant placement. If 
indicated, lingual periosteal flap reflection and alveoloplasty were performed with a carbide 
bur (H21L, Komet, Rock Hill, SC) to level the alveolar ridge prior to implant placement. 
Osteotomy was performed following the manufacturer’s recommendations, using the surgical 
stent as a guide. 
The implants used in this study were 4.3 or 5.0 mm in diameter and at least 8 mm in 
length. They featured a tapered design with TiUnite surface, symmetric threads, and an 
internal conical connection (NobelReplace Conical Connection, Nobel Biocare, Yorba Linda, 
CA, USA). A one-stage implant surgery protocol was followed, and the implants were placed 
1 mm subcrestally with a minimum insertion torque of 35 Ncm. The minimum distance 

 
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between the implant and the adjacent natural tooth was at least 1.5 mm, and between 
implants, at least 3 mm. 
In the test group, definitive abutment (On1™ Base, Nobel Biocare, Yorba Linda, CA, 
USA) was randomly assigned to one of the implants, and were torqued to 35 Ncm as 
recommended by the manufacturer. A healing cap (On1™ Healing Cap, Nobel Biocare, 
Yorba Linda, CA, USA) was placed over the definitive abutment. In the control group, 
conventional healing abutment (Healing Abutment CC, Nobel Biocare, Yorba Linda, CA, 
USA) were hand-tightened onto another implant. The flaps were approximated to allow for 
non-submerged healing using resorbable polyglactin sutures (5-0 Vicryl Plus Antibacterial 
suture; Johnson & Johnson, Somerville, NJ, USA). Bite registration (Regisil, Dentsply Sirona 
Inc., Charlotte, NC, USA) mounted on a Rinn holder was used to create the custom jig for 
standardized radiographs. Baseline periapical radiographs were taken at implant placement. 
Patients were advised to avoid functioning over the surgical sites for the first 3 weeks. 
A soft diet was recommended throughout the remaining healing period (16 weeks). 
2.4 Data collection and outcome variables 
All examinations and data collection were performed by three calibrated examiners (S.B, 
Y.C, Q.F). After implant placement, patients were recalled for follow-up appointments at 3 
months, 6 months, and 12 months. During these follow-up visits, the healing caps (test 
group) and the healing abutments (control group) were disconnected and reconnected with 
hand torque. Clinical parameters and radiographic evaluations were performed and recorded 
at T0, and T12. The following parameters were recorded at the final follow-up appointment. 
Implant success Rate 
The overall implant success rate was assessed according to the 2017 classification criteria set 
by the American Academy of Periodontology (AAP). These criteria included factors such as 
the absence of pain, infection, mobility, and radiographic bone loss beyond acceptable 

 
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thresholds. Success was determined by the implant's ability to meet these clinical and 
radiographic standards over the course of the follow-up period. 
Marginal bone loss (MBL) and marginal bone level changes (MBLC) 
Standardized digital periapical radiographs (VistaScan, Durr Dental AG, Bietigheim-
Bissingem, Germany) were taken at T0 and T12 using the long-cone paralleling technique 
and custom jig. The radiographs were exported as JPEG files and analyzed using ImageJ 
(ImageJ Imaging Software version 2.0, Bethesda, MD, USA). Mesial and distal MBL were 
assessed by measuring the distance between the implant platform and the first bone-to-
implant contact at T0 and T12. The measurements were calibrated using the known implant 
length and were performed twice for each implant. MBLC was calculated as the difference in 
MBL measurements between T0 and T12. All measurements were performed by blinded and 
calibrated one examiner (S.B). Intra-examiner reproducibility was evaluated using double 
assessments on 10 randomly selected radiographs performed 2 months apart, with the intra-
class correlation coefficient (ICC) indicating a strong correlation (ICC = 0.998). 
Keratinized mucosa width 
At implant surgery, after the connection of healing abutments in the control group and 
definitive abutments with healing caps in the test group, the flaps were approximated and 
sutured. The width of the keratinized mucosa was recorded from the mid-buccal aspect of the 
abutments using a 1.0 mm marked periodontal probe (PCP UNC-15, Hu-Friedy, Chicago, IL, 
USA). At the 1-year follow-up, measurements were taken at the same location before 
disconnection and reconnection of the healing abutments and healing caps. 
Thickness of lingual mucosa 
Lingual mucosa thickness was measured at implant surgery and at the 1-year follow-up 
appointment. The method used for evaluating lingual mucosa thickness was based on the 
technique described by Linkevicius et al.49 At implant surgery, after crestal and intrasulcular 

 
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incisions, the buccal flap was raised while the lingual mucosa was not elevated to ensure 
direct visibility. Lingual mucosa thickness at each implant site was measured from the bone 
crest using a 1.0 mm marked periodontal probe (PCP UNC-15, Hu-Friedy, Chicago, IL, 
USA). At the 1-year follow-up, lingual mucosa thickness was measured from the definitive 
abutment platform and implant platform after disconnection of the healing cap and healing 
abutment, respectively. 
Modified plaque index (mPLI) 
Presence or absence of plaque was assessed and recorded at six sites around each implant 
(mesiobuccal, mid-buccal, distobuccal, mesiolingual, mid-lingual, and distolingual). Plaque 
assessment was performed with a periodontal probe following the criteria established by 
Mombelli et al.48 Each site was assigned a score according to the following criteria: 
• 
Score 0: No detection of plaque 
• 
Score 1: Plaque only recognized by running a probe across the smooth marginal 
surface of the healing abutments or healing caps 
• 
Score 2: Plaque visible to the naked eye 
• 
Score 3: Abundance of soft matter 
Modified sulcus bleeding index (mSBI) 
The mSBI was evaluated and recorded at the same six sites as described for the mPLI 
assessment following the criteria established by Mombelli et al.48 Each site was assigned a 
score according to the following criteria: 
• 
Score 0: No bleeding observed when a periodontal probe is passed along the 
gingival margin 
• 
Score 1: Isolated bleeding spots are visible 
• 
Score 2: Blood forms a continuous red line along the gingival margin 

 
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• 
Score 3: Heavy or profuse bleeding is present 
Surgical and prosthetic complications 
Complications were recorded and included soft tissue issues, the incidence of peri-implantitis 
based on the 2017 classification criteria from the American Academy of Periodontology 
(AAP), and occurrences of prosthetic complications. 
2.5 Statistical Analysis 
Implant was considered the unit of analysis. MBLC at the mesial and distal aspect of the 
implant during 1-year follow-up was considered the primary outcome of this study. 
Descriptive statistics, including means and standard deviations, were calculated for mesial, 
distal, and overall MBLC, keratinized mucosa width changes, and lingual mucosa thickness 
changes across the test and control groups. The Shapiro-Wilk test was used to assess the 
normality of the data. When the assumption of normality was violated, non-parametric 
methods were utilized alongside traditional parametric tests. Specifically, paired samples t-
tests were used to compare MBLC and soft tissue changes between the two groups. 
Wilcoxon signed-rank tests were conducted where normality assumptions were not met. 
Correlation analyses were performed to explore relationships between all measured 
parameters, including MBLC, keratinized mucosa width changes, and lingual mucosa 
thickness changes. All statistical tests were two-tailed, with a significance level set at p≤0.05. 
Statistical analyses were conducted using R Statistics version 4.3.3 (The R Project for 
Statistical Computing, Vienna, Austria).  
 
 
 
 

 
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