Comparative evaluation of peri-implant tissues in definitive and repeated abutment replacements: A randomized clinical trial.

BACKGROUND: Repeated abutment replacements may insults the soft tissue (mucosal) barrier mechanically, that might initiate other toxic irritants and bacteria into the mucosal-implant barrier that may affect the strength of the tissues around implants. The development of the "definitive abutment," might minimize the chances of peri-implant soft and hard tissue loss. Therefore, the study was designed to assess peri-implant tissue dimensions in dental implants with definitive abutment (Test group) and repeated abutment replacements (Control group).
MATERIALS AND METHODS: Twenty edentulous sites from systemically healthy participants were selected for the study. Parameters registered were bleeding on probing, Sulcus probing depth, peri-implant marginal bone loss (PMBL) and additionally, two parameters were measured both clinically and radiographically, which included distance of cement enamel junction to alveolar crest (CEJ-AC) and distance of CEJ to gingival margin (CEJ-GM). At the time of surgery, sites were allocated randomly to either test group or control group. All the measurements were recorded at baseline, 3 and 6 months.
RESULTS: The PMBL increased from baseline to 3 months in control (1.05 ± 0.28 mm) and test groups (0.65 ± 0.41 mm). When the clinical values of CEJ-AC and CEJ-GM were compared with their respective radiographic values, no substantial differences were noticed between both the groups. The soft-tissue margins in both the groups remained comparatively stable across all the time points.
CONCLUSION: The findings of this study point toward the use of implants with definitive abutment are more beneficial in achieving better maintenance in terms of marginal peri-implant tissue health. Copyright:

INTRODUCTION

One of the central objectives of prevailing concepts in implant dentistry is to achieve osseointegration and to perpetuate the long-term equilibrium of the hard and soft peri-implant tissues.[1] Although it should also be noted that two-piece implant supported by bone exhibits resorption at the time of healing, after adaptation of the abutment and during the prosthetic phase, i.e., until the delivery of the final prosthesis. Despite the fact that the probable understandings for initial crestal bone loss have been comprehensively reviewed, but it still requires further elucidation.[2] Reaction of bone to the load,[3] a microgap at implant abutment junction,[4] polished neck of implants[5] are listed as few factors that are responsible for early peri-implant bone resorption. Another essential criterion concerning initial crestal bone resorption is reaction of tissue to the abutment shift. Accepted conventions for the use of dental implants clinically, comprise of the healing abutments placement preceding to the custom-made or standard abutments at the loading time. The frequent reconnection and disconnection of provisional/healing abutments can definitively affect the mucosal barrier and promote the connective tissue attachment to migrate apically and remodeling of the alveolar bone.[67] The apical positioning of the reformed biologic width may be one of the basis for explain crestal bone loss. Thus, it was suggested to connect the definitive abutment at the surgical stage (one abutment-one time concept), and to leave it undisturbed, in order to avoid numerous replacements of prosthetic components of and/or abutments.[89] Also, given that repeated abutment dis/reconnections may jeopardize the advantages of platform switching, the use of a definitive abutment connected to implant body without removal during the restoration process should be an additional strategy for using platform-switching implant system. Vital criteria of defining implant success have characteristically included a threshold for marginal bone loss around implants and radiographic measurement is necessary to assess the peri-implant marginal bone loss. Radiographic imaging using conventional periapical radiography helps in assessing the success and survival of implants and is a valuable noninvasive diagnostic tool.[10] Various studies have suggested that periapical radiography are superior at identifying minor bone defects around implants than cone-beam computed tomography (CBCT).[11] The radiographic images, combined with clinical measurements, will definitely increase our ability to determine the treatment outcome.

Hence, this study has been designed to evaluate and compare the dimensional stability of peri-implant tissues in dental implants with definitive and repeated abutment replacements.

MATERIALS AND METHODS

This randomized controlled clinical trial comprised of healthy males/females within the age range of 21–70 years. Twenty sites requiring dental implant treatment and patients willing to sign a written informed consent form were eligible for this trial. Each patient demonstrated at least one missing teeth in the mandibular molar region. The dimensions of the implant were standardized to 4.2 mm × 11.5 mm. Implants achieving an initial torque of at least 35 Ncm while insertion as confirmed with a manual ratchet was considered in the trial. The design of the study was scrutinized and approved by the Institutional Ethics Committee of our institute and was performed between September 2018 and October 2019. It confirmed with the norms of the Helsinki Declaration of 1975, as revised in 2013. This clinical trial was enrolled at Clinical Trial Registry–India.

Patients were excluded from the study if they exhibited: General contraindications to implant surgery; had a history of irradiation in the neck and head area, within the past 6 months; Treated with amino-bisphosphonates; smokers or patients with poor oral hygiene; pregnant or lactating females; and any acute or chronic infection at the site designated for implant placement.

The sample size was determined using mean bone level changes as the primary outcome. It was calculated that a sample size of 10 sites in each group would qualify for a Type II error of β = 0.20 (80% power) and a Type I error level of 5% probability (α = 0.05). It was hence resolved to have 10 sites in each group.

Procedure

Appropriate sites in patients requiring dental implants were divided randomly into two groups -Control group (Multiple Disconnections and Reconnections of abutment) and Test group (Definitive abutment). All the selected patients were subjected to presurgical hygiene therapy, which comprised of detailed oral hygiene instructions, scaling and root planing. Prior to initiating the surgery, recording of clinical data was carried out by the same examiner in all the patients, which included Gingival Index[12] and Plaque Index,[13] for the evaluation of gingival health and oral hygiene.

After the administration of local anesthesia, mid-crestal incision was given in the edentulous area and full thickness mucoperiosteal flap was reflected. Implants (Adin One™, Adin Dental Implant Systems, Ltd., Afula, Israel) were placed with definitive abutment in the test group. In both the groups, implants were inserted till the alveolar crest (AC) level. Healing abutment was placed in the Control group implants (Adin Touareg™ S, Adin Dental Implant Systems, Ltd., Afula, Israel) at the time of surgery. The flaps were sutured without tension using 3-0 Mersilk sutures. Patients were placed on antibiotics and analgesics to control postsurgical discomfort and were called after 7 days for suture removal.

In control group patients, after removal of the standard healing abutments, the impressions were made on the implant platform directly with a customized tray using standard prosthetic components. Disconnection of abutments was done at three stages: At the try-ins of metal and bisque framework and at the time of final prosthesis delivery, then they were replaced by new abutments. Patients allocated to the test group were treated with the “one abutment” protocol. Impressions were recorded directly on the abutments using a standard tray. These abutments were kept as it is during all the procedures, until the fabrication of final prosthesis. Thus, no other healing or provisional abutment was needed. All the final prostheses were fabricated approximately 3–4 months after the initial implant placement [Figures 1-4].

Figure 1

Control group (a) Preoperative clinical picture; (b) Placement of implant with healing abutment; (c) Flap approximation with sutures; (d) Delivery of final prosthesis

Figure 4

Intraoral periapical radiographs of test group. (a) Baseline radiograph (immediately after implant placement); (b) 3 months after implant placement; (c) 6 months’ postloading radiograph

Intraoral Periapical radiographs of Control Group. (a) Baseline radiograph (immediately after implant placement); (b) 3 months after implant placement; (c) 6 months’ postloading radiograph

Test group (a) Preoperative clinical picture; (b) Placement of implant with definitive abutment; (c) Flap approximation with sutures; (d) Delivery of final prosthesis

Outcome measures

The clinical parameters such as bleeding on probing (BOP) and sulcus probing depth (SPD) were evaluated by a single examiner (PR) using a manual periodontal probe (PCP-UNC 15; Hu Friedy, Chicago, IL, USA) at 3 and 6 months.[14] Peri-implant marginal bone level (PMBL) was assessed by Radiovisiography (RVG) (Kodak Carestream RVG 5200 Sensor, Atlanta, GA, USA with CS imaging software version 7) at baseline, 3 months, and 6 months’ postloading. The outcome measures evaluated both clinically and radiographically included, Distance of cement enamel junction (CEJ)-AC at mesial and distal sites and distance between CEJ to gingival margin (CEJ-GM) [Figure 5].

Figure 5

Measurement of peri-implant marginal bone loss and cement enamel junction-alveolar crest on radiograph. CEJ – Cemento-enamel junction; AC – Alveolar crest; PMBL – Peri-implant marginal bone loss

Readings were repeated by the same examiner (PR) to perform intra-observer reproducibility analysis. Intra-class correlation coefficient was obtained for each periodontal parameter, which indicated excellent intra-observer reliability.

Statistical analysis

The parametric measurements were expressed in terms of mean, standard deviation, and median for each group. The comparison of means in parametric measurement between study groups was evaluated using Student's t-test. The comparison of the presence and absence of BOP parameter between study groups was performed using Pearson's Chi-square test. The correlation of parametric measurements between two-time points was performed using paired t-test. For more than two-time point's comparison, repeated measures analysis of variance was used. The paired comparison was carried out using Tukey's post hoc test. The data analyses were achieved using a statistical software (IBM SPSS Statistics for Windows, version 20.0. Armonk, NY, USA) and the statistical significance was tested at 5% level.

RESULTS

The study participants comprised of systemically healthy participants between age range of 21–70 years. Twenty sites were considered and were equally distributed among the study groups. All the participants returned for cl radiographic examination at defined intervals postsurgery. The study concluded with implant and prosthetic success rate of 100% at the 6-month follow-up examination for both the test and control groups.

Table 1 represents the comparison of BOP at different time points between two groups. At baseline, 1 out of 10 patients in both the groups showed the presence of BOP. At 6 months, all the patients showed the absence of BOP in both the groups.

Table 1

Comparison of bleeding on probing at different time points between two groups

Time point	Levels	Groups		P
		Control (n=10)	Test (n=10)
3 months	Present	1 (10)	1 (10)	0.9999 (NS)*
	Absent	9 (90)	9 (90)
6 months	Present	0	0	-
	Absent	10 (100)	10 (100)

P>0.05 was considered as not significant; *Obtained using Pearson’s Chi-square test; n – Number of participants; P – Probability of occurrence; NS – Nonsignificant

Mean SPD at 3 months in both the groups was statistically insignificant, whereas, at 6 months, mean SPD was significantly higher in Control group (2.10 ± 0.43 mm) as compared to test group (1.60 ± 0.32 mm) [Table 2].

Table 2

Comparison of sulcus probing depth parameter at different time points between two groups and also across time points for each group

Time point	Levels	Groups		P
		Control (n=10)	Test (n=10)
3 months	1.70±0.28 (1.63)	1.40±0.43 (1.38)	0.0838 (NS)†
6 months	2.10±0.43 (2.25)	1.60±0.32 (1.50)	0.0088 (S)†
P ‡	0.0011 (S)	0.0528 (NS)

P>0.05 not significant; P<0.05 Significant; †Obtained using Student’s t-test; ‡Obtained using paired t-test; n – Number of participants; P – Probability of occurrence; SD – Standard deviation; S – Significant; NS – Nonsignificant

The bone level alterations were registered from shoulder of implant to first bone-implant contact. As all the implants were positioned at level of crest the baseline measurement was zero. 1.05 ± 0.28 mm and 0.65 ± 0.41 mm of bone resorption was seen at 3 months in control group and test group, respectively. At 6 months, the bone loss increased to 1.2 ± 0.26 mm in control group and 0.7 ± 0.40 mm in test group Table 3.

Table 3

Comparison of radiographic measurement: Implant shoulder to first bone to implant contact at different time points between two groups and also across time points for each group (mm)

Time point	Groups (mean±SD)		P*
	Control (n=10)	Test (n=10)
Baseline	0.00±0.00	0.00±0.00	-
3 months	1.05±0.28	0.65±0.41	0.022 (S)
6 months	1.2±0.26	0.7±0.42	0.006 (S)
P ‡	0.081 (NS)	0.343 (NS)

P>0.05 not significant; P<0.05 Significant; *Using independent sample t-test; **Using paired t-test; n – Number of participants; P – Probability of occurrence; SD – Standard deviation; S – Significant; NS – Nonsignificant

On mesial side in at 6 months, in control group, the mean difference was statistically significantly greater in clinical (2.85 ± 0.71) as compared to RVG (2.10 ± 0.81). On distal side, for both clinical and RVG measurements, the mean difference were statistically significant at different point of times [Table 4].

Table 4

Comparisons of measurements of distance between cemento-enamel junction to alveolar bone crest between clinical and radiovisuography sites at different time points and also across time points for each site

Groups	Sides	Time point	Sites, mean±SD (median)		P*
			Clinical	RVG
Control	Mesial	Baseline	2.35±0.71 (2.50)a	1.90±0.88 (2.00)a	0.2234 (NS)
		3 months	2.40±0.70 (2.75)a	2.05±0.90 (2.50)a,b	0.3438 (NS)
		6 months	2.85±0.71 (3.00)b	2.10±0.81 (2.50)b	0.0411 (S)
		P ‡	<0.0001 (HS)	0.0410 (S)
	Distal	Baseline	2.14±0.85 (2.00)a	1.57±1.24 (1.00)a	0.3371 (NS)
		3 months	2.21±0.81 (2.00)a,b	1.93±1.02 (2.00)b	0.5723 (NS)
		6 months	2.64±0.63 (2.50)b	1.93±1.02 (2.00)b	0.1450 (NS)
		P ‡	0.0086 (S)	0.0465 (S)
Test	Mesial	Baseline	2.00±0.78 (2.00)	2.25±0.54 (2.25)a	0.4176 (NS)
		3 months	2.25±0.75 (2.00)	2.25±0.54 (2.25)a	0.9999 (NS)
		6 months	2.30±0.86 (2.00)	2.45±0.64 (2.25)b	0.6635 (NS)
		P ‡	0.0679 (NS)	0.0368 (S)
	Distal	Baseline	1.81±0.80 (1.75)	2.25±0.38 (2.00)	0.1918 (NS)
		3 months	2.13±0.58 (2.00)	2.31±0.53 (2.25)	0.5119 (NS)
		6 months	2.19±0.46 (2.00)	2.19±0.37 (2.00)	0.9999 (NS)
		P ‡	0.0605 (NS)	0.7362 (NS)

P>0.05 not significant; P<0.05 Significant; *Obtained using paired t-test; ‡Obtained using repeated measures ANOVA; n – Number of participants; P – Probability of occurrence; SD – Standard deviation; HS – Highly significant; S – Significant; NS – Nonsignificant; Means with different superscripts (a, b) shows statistical significance, RVG; Radiovisiography

In control group, on mesial side, the mean difference of measurements between Clinical and RVG site was statistically insignificant (P > 0.05) for all the time points. Same was the results obtained for test group. For both clinical and RVG types, the mean difference in soft tissue findings from CEJ to GM measurements was zero, hence P value was not evaluated [Table 5].

Table 5

Comparisons of soft-tissue findings from cemento-enamel junction to gingival margin measurements between clinical and radiovisuography sites at different time points and also across time points for each site

Groups	Sides	Time point	Sites, mean±SD (median)		P*
			Clinical	RVG
Control	Mesial	Baseline	0.35±0.47 (0.00)	0.05±0.16 (0.00)	0.0844 (NS)
		3 months	0.30±0.48 (0.00)	0.10±0.32 (0.00)	0.2900 (NS)
		6 months	0.30±0.48 (0.00)	0.20±0.35 (0.00)	0.6030 (NS)
		P ‡	0.3434 (NS)	0.3670 (NS)
	Distal	Baseline	0.00	0.00	-
		3 months	0.00	0.00	-
		6 months	0.00	0.00	-
Test	Mesial	Baseline	0.50±0.71 (0.00)	0.50±0.71 (0.00)	0.9999 (NS)
		3 months	0.50±0.71 (0.00)	0.60±0.81 (0.00)	0.7721 (NS)
		6 months	0.50±0.71 (0.00)	0.60±0.81 (0.00)	0.7721 (NS)
		P ‡	-	0.1679 (NS)
	Distal	Baseline	0.19±0.53 (0.00)	0.25±0.71 (0.00)	0.8446 (NS)
		3 months	0.19±0.53 (0.00)	0.25±0.71 (0.00)	0.8446 (NS)
		6 months	0.19±0.53 (0.00)	0.25±0.71 (0.00)	0.8446 (NS)

P>0.05 not significant; P<0.05 significant; *Obtained using paired t-test; ‡Obtained using repeated measures ANOVA; n – Number of participants; P – Probability of occurrence; SD – Standard deviation; NS – Nonsignificant; RVG–Radiovisuography

DISCUSSION

The measures in the outcome of dental implant therapeutics remain one of the most investigated and predictable criterion in modern dentistry. One of the major challenges in implant treatment is constant stability of peri-implant soft and hard tissues.[15]

BOP is an accurate and simple indicator of the peri-implant tissue health. BOP alone yields higher diagnostic accuracy to clinically assess health of soft tissues around implant sites compared with tooth sites.[16] The absence of BOP at 6 months’ follow-up in the present study confirmed that the peri-implant sites were healthy and stable. It has been reported by Lang and coworkers that sites devoid of BOP indicate the healthy state of tissues around implants and would remain stable for considerable period.[17]

PMBL is critical aspect in determining the success of implants and radiographic measurement is essential to assess marginal bone loss around implants. Bone level changes around implants were calculated on periapical radiographs and the mean value was considered. The results obtained are in agreement with the trial done by Molina et al.[1] where the authors reported similar values of mean bone loss in both the groups. Whereas few other studies reported lesser quantity of bone resorption in both test and control groups.[181920] The possible explanation for this is the effect of abutment reconnection/disconnection on crestal bone level changes depends on the number of times abutment was disconnected. An animal study revealed that five times abutment reconnection and disconnection, compromised the peri-implant mucosal seal which lead to an shift in the zone of connective tissue apically and increased marginal bone resorption.[21] While another study on dogs, demonstrated that abutment reconnection/disconnection, done two times did not influence the dimensional and qualitative characteristics of a trans-mucosal attachment.[6]

Luongo et al.[22] and Koutouzis et al.[18] reported lesser bone loss in both the groups but the study period was shorter. The present study reported the 6-month postloading data around implant restored with conventional protocol versus implants placed with definitive abutments. Even though this observation period is considered to be brief, however, it has been accepted to be crucial in terms of the initial marginal bone resorption occurring prior to and after abutment connection.

Few studies assessed the precision of periapical radiographs in visualizing peri-implant bone, concluded that periapical radiographs are more suitable at identifying minor bone defects around implants than CBCT, since periapical radiography offers better contrast, resolution and detail on bone quality than CBCT.[1011] Moreover, with the use of CBCT, Degidi et al.[23] found no statistically significant difference among the study groups with respect to the measurement of vertical bone height measurement. RVG being the digital variant of the intraoral periapical radiographs was used in the present study so as to have the benefits of precise measurements of the tissues surrounding implants.

The results of our study is in accordance with the earlier trial signifying that the considerable amount of marginal bone loss occurs immediately after connection of abutment, and was revealed that only minimal alterations in the bone levels could be identified subsequently in the 6 months’ observation period.[24] In addition, bone loss of 1.5 mm is probable to occur after functional loading of implants.[25] The present investigation also demonstrated bone loss between adjacent teeth and implants by measuring the distance from CEJ and bone crest. Such minimal bone resorption has been attributed in cases where the mucoperiosteal flaps are raised to place dental implants and which deprives the deeper tissues of nutrition and blood supply.

The PMBL are distinctly and positively linked to the peri-implant mucosal levels. Peri-implant tissue recession was measured by considering CEJ of adjacent teeth as reference points. Comparable to the results of our study, Degidi et al. reported similar recession at 6 months’ follow-up among the two study groups, but considerably greater gingival recession was exhibited in the group at the 24 months examination with frequent abutment reconnections/disconnections.[23] The soft tissue starts disintegrating as a consequence of making impression at a deeper levels in tissues which could be among the causative factor for the recession experienced, especially in the control group, after the placement of the permanent restoration. Moreover, repeated abutment replacements results in a mechanical trauma to the soft-tissue barrier, leading to recession by re-establishing more apically.[26] However, in the present study, the marginal tissue recession was minimal at both the control and test sites. Although the test sites exhibited greater soft-tissue recession, the quantum was not statistically significant. An animal experiment stated a greater apical shift in the position of peri-implant soft tissue after five abutment disconnections/reconnections.[27] Such differences may be ascribed to the extent of mucoperiosteal flap elevations and injury to the soft tissues at the time of repeated abutment disconnections and reconnections.

Increased probing depth (PD) was reported to be an important key indicator suggestive of increased risk for the development of peri-implant soft-tissue infection that may guide to bone loss ultimately. According to the study of Adell et al.[28] and Buser et al.,[29] SPD up to 3 mm around implants was considered “healthy.” The range of SPD obtained in our study is in accordance with previously reported mean PD of 2.04 mm with the use of “one-abutment one-time” protocol at 5-year follow-up.[9]

This trial concentrated on the sequelae of abutment replacements on mandibular posterior region. The drawbacks of the current trial are the limited sample size and the use of two dimensional radiographs that can only identify the defects in the cranio-caudal and mesial-distal planes. Additional prospective clinical studies with a larger sample size, and advanced radiographic imaging techniques will be desirable to confirm the findings of the present study.

CONCLUSION

The use of implants with definitive abutment could be more beneficial in achieving better results in terms of reducing the marginal PMBL. This protocol has the advantages in maintaining the stability of peri-implant tissue over the protocol of repeated abutment changes, though while predicting the future orientation of the final prosthesis at the time of implant placement may be a challenging issue. The results of present clinical trial are the most current human study statistics identifying PMBL changes with definitive abutments and conventional two-piece implants that require abutment disconnections and reconnections for its prosthetic rehabilitation. Further investigations are needed to precisely examine the effect of abutment re/disconnection, also in esthetic implant restorations, where peri-implant mucosal outlining and remodeling entails a frequent replacement of temporary abutments.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.