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 Table of Contents  
Year : 2022  |  Volume : 14  |  Issue : 4  |  Page : 386-393

Preservation of biological width to avoid marginal bone loss and implant failure - A retrospective study

1 Studio Dentistico Zaniol, Via Lodovico Boschieri, 45/4, 31035 Crocetta del Montello, Treviso, Italy
2 Studio Dentistico Tedesco Giffoni Valle Piana Salerno, Treviso, Italy
3 University of Campania “Luigi Vanvitelli”, School of Medicine and Surgery, Naples, Italy

Date of Submission02-Jan-2022
Date of Decision21-Apr-2022
Date of Acceptance24-Jun-2022
Date of Web Publication29-Aug-2022

Correspondence Address:
Dr. Stefania Palumbo
University of Campania “Luigi Vanvitelli”, Vico Luigi de Crecchio, 4. 80138, Naples
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JIOH.JIOH_1_22

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Aim: To evaluate the medium-term survival and the progression of marginal bone loss by determining the statistical relationship between the explanatory variables for dental implants with internal hexagonal connection in native bone and with guided bone regeneration. Materials and Methods: The present retrospective study was carried out on a total of 218 implants (143 implants in native bone and 75 implants with guided bone regeneration) placed in 53 patients selected without restrictive inclusion criteria. Clinical and radiographic variables, including marginal bone loss, were recorded up to 46 months of follow-up. Mann-Whitney U test was used to compare annual bone loss and total marginal bone loss. The cumulative survival rate was calculated according to the lifetable method and illustrated with Kaplan–Meier survival curves. Univariate and multivariate analysis was performed to investigate the association between study variables and the time to implant failure. Additional factors influencing marginal bone loss were also evaluated. Results: The cumulative survival rates for implants placed in native bone and with guided bone regeneration at 46 months were 97.9% and 97.3%, respectively. In our cohort, the univariate analysis identified marginal bone loss, gingival thickness, and bleeding on probing as risk indicators of implant failure. Moreover, bone loss was correlated with gingival thickness and implant depth. Conclusion: No statistically significant differences in survival rates were reported between two types of implants. On the other hand, the correlation of marginal bone to implant insertion depth and gingival thickness, suggests that the biological width measurement should be respected.

Keywords: Biological Width, Dental Implant, Gingiva Thickness, Marginal Bone Loss

How to cite this article:
Zaniol T, Zaniol A, Tedesco A, Palumbo S. Preservation of biological width to avoid marginal bone loss and implant failure - A retrospective study. J Int Oral Health 2022;14:386-93

How to cite this URL:
Zaniol T, Zaniol A, Tedesco A, Palumbo S. Preservation of biological width to avoid marginal bone loss and implant failure - A retrospective study. J Int Oral Health [serial online] 2022 [cited 2023 Mar 24];14:386-93. Available from:

  Introduction Top

The use of osseointegrated implants as support for dental prostheses has become a mainstream and established therapy. Given its high predictability and survival rate, the dental implant-based rehabilitation technique can provide a wide variety of treatment options to patients.[1] Most osseointegrated implants have successful long-term clinical results due to stabilization of bone remodeling activity.[2] However, when the equilibrium condition between bone apposition and resorption is compromised, marginal bone loss (MBL) occurs. MBL around dental implants has always been considered one of the main indicators of peri-implant health status and the extent of its level is considered a determining factor in assessing the quality of implant survival or the failure,[3] since even in the mildest cases, it can cause soft tissue collapse and an increased risk of peri-implantitis.[4] Since the 1970s and 1980s, clinical and experimental observations (radiological and histological evaluations) have shown a steady decrease in peri-implant bone level over time, starting from the time implants were exposed in the oral cavity. A certain amount of peri-implant bone resorption was and is still considered physiological, so much so that Albrektsson himself includes peri-implant bone remodelling among his universally accepted success criteria for osseointegrated implants. According to these criteria, bone loss should not exceed 1.5 mm during the first year and 0.2 mm for each subsequent year.[5]

Changes in the rate of bone resorption in the peri-implant region are considered a multifactorial phenomenon.[6] Several factors, both surgical (insufficient crestal width and/or implant malpositioning,[7],[8] implant insertion manoeuvres,[9] soft tissue thickness[10],[11] and prosthetic (type of implant/abutment connection,[12],[13],[14] the presence of microgap,[15] macroscopic and microscopic characteristics of the implant and collar,[16] number of abutment disconnections,[17]abutment heigh,[18] early loading[19]) have been actively explored to explain the phenomenon of MBL.

The relevant influence on the MBL has the establishment of biological width after the abutment connection. In 1991, Berglundh et al. proposed the concept of biological width around the implant as a ‘size concept’, defining it as the necessary distance of 3–4 mm from the top of the peri-implant mucosa to the first bone-to-implant contact to create a protective barrier against inflammatory infiltration.[20] Subsequently, several studies have suggested that a variable amount of MBL may occur to provide the necessary space for the establishment of biological width.[21]

To our knowledge, the impact of soft tissue thickness on bone remodelling is a highly relevant clinical factor that should not be neglected during clinical studies. As reported by Linkevicius et al.,[22] implants in sites with thick mucosal tissues showed statistically lower crest bone loss when compared to thinner tissues supporting the hypothesis that there is a biological need to create enough space to reestablish protective soft tissue.

Therefore, the objective of the present study was to report cumulative survival data for 218 dental implants placed between 2017 and 2021 with a mid-term follow-up of 46 months, comparing the progression of MBL between dental implants placed in native bone (NB) and guided bone regeneration (GBR). The null hypothesis was that there were no differences in MBL around implants placed in native bone or with GBR, but that MBL might be related to other variables such as gingival thickness and implant depth that tend to re-establish the required biological width.

  Materials and Methods Top

Study design and setting

This retrospective observational study was performed at the Zaniol dental center in Crocetta del Montello (Treviso, Italy).

Sampling criteria

Medical records were selected from those of patients with atrophic ridges who presented between the October 2017 and July 2021 seeking implant-supported rehabilitation because of partial or total maxillary edentulism. A total of 53 patients (25 men and 28 women) was selected determined by their dental records and beam computed tomography (CBCT) scans before surgery. Based on starting bone thickness, patients received either in native or regenerated bone implants. A total of 218 implants (143 implants in native bone and 75 implants with GBR) were grafted. Patients were followed after functional loading of the definitive prosthesis for a minimum of 46 months. The records also reported the patients’ subjective assessment of their postsurgical progress.

Inclusion criteria were an age between 20 and 80 years and the absence of systemic disease. All patients were eligible for regenerative treatment, presenting with none of the following: pregnancy; osteoporosis, neoplasia, or psychiatric disease; acute oral infection; acute maxillary sinusitis; coagulation disorders; history of chemotherapy or radiation therapy in the head or neck region; immunocompromised status; ongoing bisphosphonate therapy; and chronic alcohol or drug abuse. Smoking and diabetes were not considered exclusion factors in the study cohort.


All implants were placed under sterilized conditions according to manufacturer guidelines. Avior implants (Mech and Human S.r.l. Grisignano di Zocco,Vicenza, Italy) with internal hex connection and marginal collar were inserted; the connections have been checked for quality control of the Roundness Profile with precision greater than or equal to 0.000549 microns [Figure 1]. The implants were inserted freehand or using surgical templates planned using any standard 3D digital software (54 implants), in native bone or regenerated bone, obtained using equine derived biomaterial (cortical-cancellous granules) (OsteOxenon; Bioteck Arcugnano, Italy) [Figure 2].
Figure 1: Roundness profile. The roundness profile is a measurement of the marginal seal: the average of the maximum errors is 0,549 micron

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Figure 2: Single implant positioning. The panel of pictures shows implant positioning depending on the thickness of the crestal gingival. A) Implant positioning; B) Radiograph preparation; C) Radiograph depicting gingival thickness measurements

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The patients were assessed by radiographic evaluation at 2–3 months after implant placement. MBL measurement was performed on periapical radiographs with a custom centering device and the bone loss was calculated with ImageJ software [Figure 3]. Bone loss was presented as annual bone loss (ABL) and as total bone loss during the 4 years follow-up (MBL).
Figure 3: Multiple implants positioning. A) Internal hexagonal implant/abutment connection; B) Radiograph depicting gingival thickness measurements

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Study variables

The major outcome variable of this study was implant failure. Failure was defined as the removal of an implant for any reason. Additional variable of implant outcome, such as the marginal bone loss (MBL), bleeding at probing (BOP), smoke, gingival thickness, and gender were also recorded during follow-up.

Statistical analysis

Statistical analysis was performed with SPSS (IBM Corp, Version 23.0, Armonk, NY, USA) and Microsoft Excel (Microsoft Corp, Redmond; WA, USA). As mean MBL values did not follow a normal distribution (Kolmogorov- Smirnov test P < 0.05), the Mann-Whitney U test for nonparametric statistical analysis was used to compare annual bone loss (ABL) and total marginal bone loss (MBL) over 4 years of follow-up. For all other statistical analyses, a square root transformation was performed for all continuous and not normally distributed data.

To describe our survival data set, we calculated the cumulative survival rate (CSR) according to the life table method and illustrated the results with Kaplan-Meier survival curves. Hazard ratios (HR) were calculated to estimate the association between variables and failure time. HR was obtained by constructing the proportional hazard Cox regression in a univariate and multivariate analysis.

  Results Top

General statistics

The study cohort consisted of 25 men (47.2%) and 28 women (52.8%) with no significant differences with respect to age and follow-up time. A total of 218 implants (143 in native bone and 75 in regenerated bone) were placed with a mean of 4.11 ± 1.43 implants per patient. The maximum number of implants in one patient was 8 implants. The mean ABL and MBL around implants on native bone (NB) and with guided bone regeneration (GBR) was calculated. During 4-year follow-up, maximum bone loss is reached the first year after implantation for both NB and GBR implants [Figure 4]A. The mean MBL, considered as cumulative bone loss at the end of 4-year follow-up, was 1.20 ± 0.30 mm for NB implants and 1.11 ± 0.28 mm for GBR implants [Figure 4]B. Although both ABL and MBL were greater around NB implants than GBR implants no statistically significant differences were found between the two groups.
Figure 4: Mean ABL and MBL according to the type of osseintegration. A) Mean ABL for implants integrated into native bone (NB) or guided bone regeneration (GBR) during 4 years of follow-up. Maximum bone loss is reached the first year after implantation for both NB and GBR implants. B) Mean MBL for NB or GBR osseointegrated implants

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Survival analysis

During the study period, 5 implant failures were documented; 3 failures occurred for implants placed in native bone and 2 failures for implants placed with GBR for an overall success rate of 98% and 97,4%, respectively.

The estimation of the implant survival rate was based on Kaplan-Meier analysis and a group comparison was made using the log-rank test. According to the analysis of the life table [Table 1] for implants in native bone, the cumulative survival rate (CSR) at 6, 18 and 46 months was 99,3%, 98.6% and 97.9%, respectively. While for GBR implants the CSR at 6 and 18 months was 98.7% and 97.3%. The Kaplan-Meier survival curves are illustrated in [Figure 5].
Table 1: Life table analysis for NB or GBR osseointegrated implants

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Figure 5: Kaplan-Meier survival curves for NB and GBR osseointegrated implants

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Univariate and multivariate analysis for risk indicators associated with implant failure

Considering that implant failure could be a multifactorial event, several defined variables were analyzed for statistical significance in a univariate and multivariate risk analysis. The variables considered were classified as implant-graft dependent variables and patient condition dependent variables. Implant dependent variables were MBL, gingival thickness, implant depth and bleeding on probing (BOP); while patient dependent variables have been considered the age, the gender, smoke and co-presence of other pathologies such as diabetes. As shown in [Table 2], the univariate analysis reported statistical significance for most of the implant-graft-dependent variables, suggesting that implant failure is primarily affected by events that occur at or after the time of graft. The highest risk is represented by marginal bone loss with HR = 50.71. Since no significance was reported for variables dependent on patient condition, a multivariate analysis was performed only for implant-dependent variables. The significance highlighted by the univariate analysis is lost in the multivariate analysis showing how implant failure is affected by the risk of single independent factors.
Table 2: Results of the univariate and multivariate Cox regression (based on the entire cohort of patients)

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Correlation of factors influencing MBL

Recently, soft tissue thickness and the depth at which the implant is placed have been investigated as possible factors influencing bone loss contributing to implant failure. Given the high risk of MBL shown in the univariate analysis in relation to implant failure, we investigated whether there was a possible correlation between these three variables. A negative correlation between MBL and gingival thickness is reported (Pearson’s r = -0.60), suggesting that greater bone loss is detected in the presence of thin soft tissue. In contrast, MBL and implant graft depth are positively correlated even if weakly (Pearson’s r= 0.24). [Figure 6] shows the cumulative effect of the predictors considered. Although the depth of the implant contributes little to the change in MBL, based on this result, we think that the deeper the implant is grafted, the greater the bone loss.
Figure 6: The scatter plot indicates the relationship between the MBL dependent variable and the independent predictors, gingival thickness, and implant depth. R2 indicates the percentage of the variance in the dependent variable that the independent variables explain collectively. R2=0.374

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The observed data lead to the hypothesis that when a dental abutment is grafted with a depth greater than the gingival thickness, nature “digs” the bone to restore a necessary space of 3-4 mm between peri-implant mucosa and the bone surface. This space is called the biological width and can be defined by the formula:

Gingival thickness + implant depth = 3-4 mm = biological width.

  Discussion Top

The MBL is influenced by numerous variables related to surgical manoeuvres, implant design, bone substrate, abutment connection, and patient health and habits. Soft tissue thickness and implant depth are important aspects in maintaining implant stability. The purpose of the present study is to evaluate the mid-term results of implants in native or regenerated bone (GBR) with a maximum follow-up of 4 years. We assessed the marginal bone loss of a series of implants with an internal hexagonal connection with a peripheral collar whose roundness profile tolerance is known during quality control and analyzed the complications associated with implant survival/success rates through a multivariate analysis of different factors. Our data did not report statistically significant differences in success and survival rates between implants with and without bone regeneration. Success rates for NB and GBR implants were 98% and 97.4%, respectively, while implant survival rates were 97.9% for NB and 97.3% for GBR at 46 months after loading. These results compare well with systematic reviews[23],[24] that report survival rates of implants placed at sites with regenerated bone ranging from 79% to 100%, with most studies indicating >90% at least 1 year after surgery demonstrating how implants grafted with regenerated bone remain stable over time as native bone.[25]

The low failure rate reported in our cohort of patients is likely due to marginal bone loss that was within physiologic range during all follow-up period. Although threshold levels for the diagnosis of peri-implantitis vary in the literature, the criterion suggested by Albrektsson et al.[5] (maximum 1.5 mm of bone loss in the first year after loading and 0.2 mm per year in subsequent years until the last follow-up) was selected as the acceptable MBL limit in this study. In detail, we report a maximum mean annual loss after the first year of grafting with values of 0.74 ± 0.49 mm and 0.70 ± 0.53 mm for implants in NB or with GBR, respectively. Bone loss decreases in subsequent years with values after 4 years at post-loading of 0.14 ± 0.09 mm for implants in native bone and 0.13 ± 0.09 mm for implants with regenerated bone, with no significant differences between the two groups.

The literature provides interesting cues into the relationship between the implant abutment / peri-implant tissues and on the influence that the vertical dimension and the shape of abutments can have with respect to the stability of the marginal bone. Galindo et al.[12] recently reported how the type of connection can lead to bone loss independent of other parameters. Their study shows that internal hexagonal-connection implants lead to greater bone loss when compared to internal conical-connection implants during 12 months of follow-up. This finding would suggest that implants with an internal hexagonal-connection may represent a higher risk of bone loss (more than 2 mm) after 18 months. Data collected in our study cohort show that internal hexagonal-connection implants, placed both on native bone and with guided bone regeneration, never reach pathological bone loss rates, remaining below 2 mm even after 46 months of follow-up.

We next tested the second part of our null hypothesis, aka that MBL may be related to other variables such as gingival thickness and implant depth. The literature provides interesting cues into the relationship between implant abutment height,[26] the mucosal height[27] and bone loss. Recently, it has been reported that the highest marginal bone resorption could be determined in implants with the strongest biological width violation, both due to both their peri-implant mucosa insufficient dimension (< 3 mm) and the absence of effective connective tissue attachment.[28] Based on this knowledge, we evaluated the dynamics of marginal bone resorption as a function of biological width violation. We hypothesized that if a dental implant is grafted to a depth greater than the available gingival thickness, bone loss will occur to restore a necessary space of 3-4 mm between the peri-implant mucosa and the bone surface. Therefore, a reduced gingival thickness may promote a faster MBL. Feng et al.[21] reported that crestal bone loss correlated positively with placement depth and had a negative correlation with mucosal thickness. This suggests that if the initial biologic width deviates only slightly from the final biologic width, bone loss will be less, in contrast if the initial biologic width is inadequate, greater bone loss may occur to ensure proper development of the biologic width. In line with these data, we revealed that the bone loss in our patients correlated with the thickness of the gingival and implant depth, suggesting that the biological width can be defined by the formula: Gingival thickness + Implant depth=3-4 mm= Biological width.

The health of periodontal tissues therefore depends on reduced bone loss. Poor implant placement and a limited gingival margin violate the biological width. During implant procedures the factors to be taken into account are: sufficient area of attached gingiva and the implant grafting depth. Although biological width violation can be corrected by surgically removing bone from the vicinity of the restoration margin or orthodontic tooth extrusion and then moving the margin away from the bone, it can be avoided from the outset by observing good surgical practices. Management of implant rehabilitation must consider whatever is necessary to keep the biological width intact, such as, for example, soft or deep tissue grafting procedures to increase keratinized tissue or peri-implant mucosal thickness. Moreover repeated maintenance visits, cooperation and motivation of the patient are important to improve the success of implantation procedures with pristine periodontal health.

Limitations of the present study include small cohort analyzed; more studies with appropriate controls and larger samples with longer follow-up should be conducted to confirm or reject these findings. This study also had the limitation of being record-dependent, which is an inherent issue in retrospective studies.

  Conclusion Top

In conclusion, implants associated with bone regeneration showed the same survival and success rates as those placed in native bone with no significant difference in bone resorption. On the other hand, MBL seems to be related to the depth of implant insertion in relation to the alveolar ridge and gingival thickness, which seems to have to respect the measure of biological width.



Financial support and sponsorship

This study was self-funded by the authors.

Conflict of interest

The authors declared that they had no potential conflicts of interest with respect to the investigation, authorship, and/or publication of this article.

Authors’ contributions

TZ contributed to study conception, study design, data collection, analysis, interpretation, supervision; AZ contributed to study execution, data collection, data interpretation; AT contributed to data collection, data interpretation; SP statistical analysis, manuscript writing, reviewing and editing.

Ethical policy and institutional review board statement

The present retrospective observational study was conducted in a single center the Zaniol dental center in Crocetta del Montello (Treviso, Italy). All the procedures have been performed as per the ethical guidelines laid down by Declaration of Helsinki (1975).

Patient declaration of consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Data availability statement

Some or all data sets generated during and/or analyzed during the current study are not publicly available but are available from the corresponding author on reasonable request.

  Abbreviations Top

ABL - annual bone loss

BOP - bleeding at probing

CSR - cumulative survival rate

GBR - guided bone regeneration

MBL - marginal bone loss

NB - native bone

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

  [Table 1], [Table 2]


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