Early peri-implant bone loss: a prospective cohort study

Abstract

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.

Procedures

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 ).

Fig. 1
A single implant, diameter 4.8 mm and length 14 mm, inserted 4 weeks after extraction of the fractured 1.4 (early delayed implant placement). The marginal bone level at the time of implant placement (T0) below the ridge (A), at the 2-month follow-up (T1) (B), and at the time of final prosthesis delivery (6-month follow-up) (C).

Fig. 2
Two implants, diameter 3.5 mm and length 14 mm, inserted in a healed site (prolonged delayed implant placement). The marginal bone level at the time of implant placement (T0) below the ridge (A), at the 2-month follow-up (T1) (B), and at the time of final prosthesis delivery (C).

Fig. 3
Direct measurements on a standardized, digital peri-apical radiograph at the time of implant placement (T0). To ensure measurements were calibrated, an object of known size was placed in the image on the same plane as the implant. To adjust the measurements for magnification error, the following equation was used to determine the corrected crestal bone levels: corrected crestal bone level = measured crestal bone level × (actual implant length, e.g. length of implant based on manufacturing standards/measured implant length).

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).

Anatomical variables

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

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.

Statistical analysis

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.

Results

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 .

Table 1
Implants and treatment characteristics ( N = 493).
Variables Number of implants %
Sex
Male 236 47.9%
Female 257 52.1%
Age, years
≤50 133 27.0%
>50 360 73.0%
Implant placement depth
Crestal 162 32.9%
Supra-crestal 154 31.2%
Sub-crestal 177 35.9%
Implant placement timing
Prolonged delayed 212 43.0%
Early delayed 281 57.0%
Type of edentulism
Mono-edentulism 150 30.4%
Partial edentulism 343 69.6%
Arch
Maxilla 203 41.2%
Mandible 290 58.8%
Implant location
Anterior 59 12.0%
Posterior 434 88.0%
Implant length
Short 172 34.9%
Long 321 65.1%
Implant diameter
Narrow 318 64.5%
Wide 175 35.5%

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 ).

Fig. 4
Box plots showing the median, quartile, and minimum and maximum values of peri-implant early marginal bone loss (mm) in relation to the individual predictor variables, i.e. the clinical exposure factors. Boxes contain 50% of all values; the horizontal lines inside the boxes indicate the medians and the vertical lines extend to 1.5 of the interquartile range. Circles depict outliers.

Table 2
The early (2-month follow-up) average change in mesiodistal peri-implant bone levels (AvBL; mm) ( N = 493).
Variables Average change in mesiodistal peri-implant bone levels (AvBL)
Mean Max. Min. SD
Sex
Male −0.20 −2.85 2.50 0.70
Female −0.41 −3.40 2.50 0.68
Age, years
≤50 −0.52 −3.25 1.55 0.58
>50 −0.40 −3.40 2.50 0.88
Implant placement depth
Crestal −0.31 −2.85 1.55 0.64
Supra-crestal −0.03 −0.45 0.55 0.30
Sub-crestal −0.55 −3.40 2.50 0.88
Implant placement timing
Prolonged delayed −0.50 −3.40 1.65 0.72
Early delayed −0.17 −2.65 2.50 0.64
Type of edentulism
Mono-edentulism −0.21 −2.65 1.55 0.61
Partial edentulism −0.35 −3.40 2.50 0.73
Arch
Maxilla −0.40 −3.40 2.50 0.87
Mandible −0.25 −2.65 0.85 0.53
Implant location
Anterior −0.17 −2.30 1.65 0.64
Posterior −0.33 −3.40 2.50 0.70
Implant length
Short −0.27 −3.25 2.50 0.67
Long −0.37 −3.40 2.50 0.71
Implant diameter
Narrow −0.38 −3.25 1.65 0.67
Wide −0.41 −3.40 2.50 0.71
SD, standard deviation.

However, only the implant placement depth ( Tables 3 and 4 ) and the timing of implant placement ( Table 5 ) had a statistically significant influence on early peri-implant marginal bone loss.

Table 3
Two-way analysis of variance (ANOVA) used to evaluate the influence of different variables on early marginal bone loss ( N = 493).
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
Age 0.639 b 1 0.639 2.793 0.096
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
Arch 0.025 f 1 0.025 0.100 0.752
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
Intercept Sex 467.428 1 467.428 1911.596 0.000
Age 522.409 1 522.409 2284.442 0.000
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
Arch 400.992 1 400.992 1602.245 0.000
Implant location 608.332 1 608.332 4396.688 0.000
Implant length 674.229 1 674.229 780.624 0.000
Implant diameter 999.211 1 999.211 850.513 0.000
Bone remodelling Sex 0.018 1 0.018 0.074 0.785
Age 0.639 1 0.639 2.793 0.096
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
Arch 0.025 1 0.025 0.100 0.752
Implant location 0.627 1 0.627 4.533 0.056
Implant length 1.759 1 1.759 7.833 0.059
Implant diameter 2.967 1 2.967 13.255 0.054
Error Sex 59.174 242 0.245
Age 55.341 242 0.229
Implant placement depth 204.027 422 0.483
Implant placement timing 58.121 242 0.240
Type of edentulism 51.900 242 0.214
Arch 60.565 242 0.250
Implant location 33.483 242 0.138
Implant length 209.017 491 0.864
Implant diameter 284.310 491 1.175
Total Sex 673.000 244
Age 715.000 244
Implant placement depth 2368.000 490
Implant placement timing 622.000 244
Type of edentulism 745.000 244
Arch 580.000 244
Implant location 853.000 244
Implant length 1022.000 493
Implant diameter 1491.000 493
Corrected total Sex 59.193 243
Age 55.980 243
Implant placement depth 335.339 489
Implant placement timing 60.934 243
Type of edentulism 52.701 243
Arch 60.590 243
Implant location 34.111 243
Implant length 214.066 492
Implant diameter 291.488 492
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Jan 17, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Early peri-implant bone loss: a prospective cohort study
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