The aim of this study was to measure the early peri-implant bone level changes before the completion of an implant–abutment connection and to evaluate the influence of demographic, biologically relevant, anatomical, and implant-specific variables on these changes. A prospective cohort study design was used. STROBE guidelines were followed. The sample comprised 493 implants placed using a two-stage surgical procedure. Random allocation was used to determine the implant placement depth. Peri-apical radiographs taken at implant insertion and at the second surgery 2 months later were matched. Kappa statistics were used to compute intra- and inter-examiner reliability. The statistical analysis was performed at the implant level. Two-way analysis of variance (ANOVA) with the Bonferroni adjusted post hoc test was used to evaluate the influence of variables. One-way ANOVA with Tukey’s range test and unpaired Student t -tests were used to analyze significant variables. Early marginal bone remodelling was −0.86 mm. The timing of implant placement ( P = 0.00) and the depth of implant placement ( P ≤ 0.05) significantly influenced early bone remodelling. Relevant radiographic early bone loss was found, but implants initially positioned below the alveolar crest and inserted ≥3 months after tooth extraction showed statistically significant higher marginal bone loss during the healing phase.
Marginal bone loss around implants appears difficult to avoid, particularly after abutment connection, and minimal or no marginal bone loss following the implant–abutment connection is considered to be an indicator of the long-term success of implant restorations. Understanding the biological rationale for this bone remodelling and the specifics of these changes is of paramount importance in order to predict the stability and the location of the gingival margin. Marginal bone loss originates from a combination of mechanical and biological factors. Factors hypothesized to be associated with marginal bone loss include surgical trauma to the periosteum and bone, the size of the micro-gap between the implant and the abutment, bacterial colonization of the implant sulcus, biological width, and biomechanical factors related to loading. However, with a two-stage implant surgical procedure, marginal bone loss has also been detected during the period between stage I and stage II. Factors involved in this bone loss include surgical complications, a less-than-ideal initial fit between the implant and the surrounding bone, insufficient osseous tissue volume to adequately surround the implant, premature loading with resulting micro-movement of the implant prior to integration, harmful patient habits including tobacco product abuse, and healing impairment resulting from poor overall patient health.
The purpose of this study was to measure any changes in peri-implant marginal bone levels in the interval of time between implant placement and the completion of the implant–abutment connection 2 months later, and to identify variables associated with increased rates of early bone remodelling.
It was hypothesized that peri-implant bone loss would already be present before the implant–abutment connection. Furthermore, it was hypothesized that there would be at least one variable associated with increased rates of early implant bone loss that the clinician could modify to improve the outcome.
Materials and methods
Study setting and patient selection
This prospective cohort study was conducted at the Department of Oral and Maxillofacial Sciences of the study institution between February 2008 and February 2013. The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines for prospective cohort studies were followed. This clinical investigation was conducted in accordance with the ethical principles of the World Medical Association Declaration of Helsinki and was undertaken after informing the patient of the content, risks, and benefits of the study; written consent was obtained from each participant. The investigation was reviewed independently and approved by the local ethics committee.
The main inclusion criteria were that the subjects were systemically healthy, aged between 18 and 75 years, and in need of an implant-supported partial fixed dental prosthesis or a single crown. Furthermore, sufficient bone volume was required in the prospective implant region to receive implants with a diameter of at least 3.5 mm and a minimum length of 10 mm. The subjects had a stable occlusal relationship and no severe parafunctional habits, and the implant sites were free of infection and/or tooth remnants.
Exclusion criteria were the abuse of alcohol or drugs and a general health condition contraindicating a surgical procedure, e.g. infectious disease, heart disease or disease of the circulatory system, metabolic disease, bone metabolism disorders, disturbance of the hematopoietic system, haematological disorders, wound healing disturbances, disorders of the endocrine system, and pregnancy. Local contraindications were, for example, tumours and ulcers. In addition, reason to believe that the treatment might have a negative effect on the subject’s psychological situation was also considered an exclusion criterion.
The areas for implantation were evaluated on orthopanoramic and intraoral peri-apical radiographs. A computed tomography scan was required only in the case of diagnostic doubt. A two-piece pure titanium (grade 4) dental implant with a cylindrical outer contour was used. The chemically modified, sand-blasted/acid-etched titanium surface (SLA), which extended onto the implant shoulder, covered the entire length of the implant (Osseothread; Impladent, Formia, LT, Italy). This implant was characterized by a cone-Morse connection; the abutments had a smaller diameter than their respective implant platforms (platform switching).
Antibiotic therapy of 1 g of amoxicillin was prescribed 1 h before the intervention and twice a day for the following 5 days. Patients were treated with a local anaesthetic by infiltration with mepivacaine (20 mg/ml) associated with adrenaline 1:100,000. Pain control was managed using ibuprofen. The patients used the analgesic after surgery according to their individual needs. The flap design for the placement of the implants was an envelope full-thickness flap. A distance of at least 2 mm from neighbouring teeth was taken. Each implant had a minimum thickness of 2 mm of bone around it. In no case was a temporary removable prosthesis used, so as to avoid hampering the healing process. All patients were treated with a two-stage implant surgical procedure. Implants were exposed 2 months after insertion, and a healing abutment was screwed on. At the time of suture removal, a temporary acrylic resin restoration was put in place. The final restoration was delivered at the 6-month follow-up.
Assessment of marginal bone
The level of the marginal bone was recorded at the time of the second surgery (T1) by taking a standardized radiograph and matching this to the peri-apical radiograph taken at the time of implant insertion (T0) ( Figs. 1 and 2 ). These peri-apical radiographs were obtained using the long-cone parallel technique and the Rinn XCP film holding system (Rinn XCP; Dentsply Rinn, Elgin, IL, USA). Care was taken to ensure that the alignment of the X-ray film in the film holder was parallel to the long axis of the implants. Digital radiographs were stored using a digital intraoral imaging system (DenOptix QST Digital X-ray Phosphor Plate System; Gendex Dental Systems, Hatfield, PA, USA). The stored images were displayed on a monitor, and direct measurements were performed using the software VixWin PRO (Gendex). Linear measurements from the implant shoulder to the marginal bone level were obtained mesially and distally using the software programme. These measurements were assigned a positive value if the marginal bone level was coronal to the implant shoulder, a value of zero when the marginal bone level was located at the implant shoulder, or a negative value if the marginal bone level was located apical to the implant shoulder ( Fig. 3 ).
The predictor variables, i.e. the clinical exposure factors, correlated with changes in peri-implant bone level, were grouped into the categories outlined below.
Biologically relevant variables
The biologically relevant variables assessed included the following: (1) Gender (male or female). (2) Age: the study population was separated into two groups according to the age at the time of implant placement as ≤50 or >50 years. (3) Depth of implant placement: the study population was divided into three groups on the basis of the position of the implant shoulder compared to the alveolar crest level, determined clinically at the time of insertion: supra-crestal implants (with the mesial and/or distal implant shoulder placed above the crest of the alveolar bone), crestal implants (with the mesial and/or distal implant shoulder placed within 0.5 mm or less of the alveolar ridge level), or sub-crestal implants (with the mesial and/or distal implant shoulder placed at least 0.5 mm below the alveolar ridge level). Random allocation to the three groups was performed using Clinstat (Martin Bland, York, UK). (4) Timing of implant placement in relation to tooth extraction: this was classified into two categories: ‘early delayed’, defined as implant placement within weeks after tooth extraction, and ‘prolonged delayed’, defined as implant placement ≥3 months after tooth extraction. (5) Type of edentulism: absence of a single tooth (mono-edentulism) and absence of more than one tooth (partial edentulism).
The anatomical variables assessed were the arch (maxilla or mandible) and the implant location, either anterior (incisor and canine area) or posterior (premolar and molar area).
Implant-related variables included (1) implant length: short implants (10 mm) and long implants (12 mm, 14 mm); (2) implant diameter: narrow implants with diameters of 3.5 mm and 4.2 mm; wide implants with diameters of 4.8 mm, 5.5 mm, and 6.5 mm.
Minimization of potential sources of bias
In order to reduce potential sources of bias, the same operator performed all the surgeries and radiographic follow-ups (MC). Furthermore, two researchers, who were not involved in the clinical part of the investigation, evaluated the peri-apical radiographs independently (SC, AD). With regard to the placement depth variable, the allocation of implants to the three subgroups was determined using software. The computer-generated randomization maximized the statistical power, which permitted the creation of groups of the same size. Likewise the selection and allocation bias was minimized.
Descriptive statistics, including mean values and standard deviations, were used. A database was created using Excel (Microsoft, Redmond, WA, USA), with appropriate checks to identify errors. Kappa statistics were used to compute inter-examiner and intra-examiner reliability for the marginal bone measurements. To determine intra-examiner reliability, two examiners (SC, AD) measured and then re-measured (2 months later) a set of 25 random implants. To determine inter-examiner reliability, each examiner measured the set of 25 random implants that had been measured previously by the other examiner. The intra-examiner kappa coefficients were 0.85 and 0.89. The inter-examiner kappa coefficient was 0.77.
The statistical analysis was performed at the implant level. Early marginal bone loss data were illustrated using box plots. Two-way analysis of variance (ANOVA) with the Bonferroni adjusted post hoc test was used to evaluate the influence of different variables on the marginal bone levels (gender, age, depth of placement, timing of placement, type of edentulism, arch, location, and implant diameter and length). If any of the interaction terms was significant by two-way ANOVA, one-way ANOVA with Tukey’s range test was used to analyze these significant variables with more than two clusters. Unpaired Student t -tests were used to analyze the significant variables with only two clusters. All analyses were performed using SPSS version 20.0 software (IBM Corp., Armonk, NY, USA). For each test, the significance level was set at P < 0.05.
The potentially eligible population consisted of patients referred to the Department of Oral and Maxillofacial Sciences of the study institution. Two hundred and thirty-eight patients were examined for eligibility; 124 were confirmed to be eligible, all of whom participated for the entire duration of the study. The subject pool comprised 75 females (60.5%) and 49 males (39.5%). The age of subjects at the time of implant placement ranged from 22 to 72 years, with a median of 55 years. A total of 493 implants were inserted. In no case was regenerative surgery required. No healing disturbance was recorded during the healing phase. Detailed information related to the implants inserted is given in Table 1 .
|Variables||Number of implants||%|
|Implant placement depth|
|Implant placement timing|
|Type of edentulism|
At the 2-month follow-up, a mean bone loss of 0.86 mm was observed from implant insertion. One hundred and seventy-five (35.5%) implant sites gained bone and 318 (64.5%) lost bone. Three (0.6%) implant sites lost more than 2 mm of bone. A bone loss of more than 3 mm occurred with two implants (0.4%). Regarding the biologically relevant variables, a higher early mean marginal bone loss was observed in female subjects, in subjects aged ≤50 years, in subjects with partial edentulism, and in implants placed sub-crestally and at ≥3 months after tooth extraction ( Fig. 4 and Table 2 ). Evaluating the anatomical and implant-related variables, a higher early marginal bone loss was recorded in the upper arch, in the posterior area, and in wide and long implants ( Fig. 4 and Table 2 ).
|Variables||Average change in mesiodistal peri-implant bone levels (AvBL)|
|Implant placement depth|
|Implant placement timing|
|Type of edentulism|
|Source||Dependent variable||Type III sum of squares||df||Mean square||F||Sig.|
|Corrected model||Sex||0.018 a||1||0.018||0.074||0.785|
|Implant placement depth||131.312 c||67||1.960||4.054||0.000|
|Implant placement timing||2.814 d||1||2.814||11.716||0.001|
|Type of edentulism||0.801 e||1||0.801||3.736||0.054|
|Implant location||0.627 g||1||0.627||4.533||0.034|
|Implant length||1.759 h||1||1.759||7.833||0.010|
|Implant diameter||2.967 i||1||2.967||13.255||0.011|
|Implant placement depth||833.948||1||833.948||1724.902||0.000|
|Implant placement timing||464.142||1||464.142||1932.570||0.000|
|Type of edentulism||510.637||1||510.637||2381.021||0.000|
|Implant placement depth||131.312||67||1.960||4.054||0.000 *|
|Implant placement timing||2.814||1||2.814||11.716||0.001 *|
|Type of edentulism||0.801||1||0.801||3.736||0.054|
|Implant placement depth||204.027||422||0.483|
|Implant placement timing||58.121||242||0.240|
|Type of edentulism||51.900||242||0.214|
|Implant placement depth||2368.000||490|
|Implant placement timing||622.000||244|
|Type of edentulism||745.000||244|
|Implant placement depth||335.339||489|
|Implant placement timing||60.934||243|
|Type of edentulism||52.701||243|