Matrix metalloproteinase-8 level in the peri-implant sulcular fluid around dental implant abutments with different geometries and manufacturing strategies: A randomized controlled trial

doi:10.21203/rs.3.rs-2192748/v1

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Matrix metalloproteinase-8 level in the peri-implant sulcular fluid around dental implant abutments with different geometries and manufacturing strategies: A randomized controlled trial

https://doi.org/10.21203/rs.3.rs-2192748/v1

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Background. The purpose of this clinical trial was to assess soft tissue reaction around custom dental implant abutments by evaluation of Matrix Metalloproteinase-8 (MMP-8) level in peri-implant sulcular fluid (PISF) and clinical parameters.

Methods. Thirty participants with missing mandibular first molar were enrolled in this randomized controlled trial. Each participant underwent implant placement following the standard 2-stage surgical protocol. All participants were randomly allocated to one of the two groups; Control Group (n=15): Pre-machined stock titanium abutment, and Study Group (n=15): Custom titanium CAD-CAM abutment. Combined screw- and cement-retained zirconia crowns were used to restore implants. The PISF samples were collected at 1, 3, 6 and 12 months after placement of restorations. MMP-8 level was assessed by Enzyme-Linked ImmunoSorbent Assay. Peri-implant probing depth (PPD), simplified mucosal index (SMI) and modified plaque index (mPI) scores were assessed at all time-points. Crestal bone loss (CBL) was assessed by using bitewing radiographs made at baseline and 12-month time points. Two-way repeated-measures ANOVA and Friedman test were used to analyze data.

Results. There was a significant effect of the interaction of time and abutment type where the change in MMP-8 and PPD in CA was higher than in SA. SMI, mPI and CBL recorded no statistical differences between the two groups after one year (P > 0.05).

Conclusions. The change in the level of MMP-8 and in PPD after one year is significantly higher in custom abutments. However, this change was of low clinical impact.

Trial Registery: the trial was registered in the Pan African Clinical Trial Registry under identification number PACTR201809736563842 (25/ 09/ 2018)

Matrix Metalloproteinase-8

custom abutment

stock abutment

Peri-implant soft tissue

Peri-implantitis

Custom dental implant abutments have been developed to provide contours similar to natural teeth offering various advantages over stock abutments, including increased retention and resistance of the restorations, easier removal of excess cement, and increased support of the final restorations [1]. Moreover, the contour of the custom abutments help the effectiveness of oral hygiene practice, while stock abutments are more likely to have plaque retentive areas due to their circular shape and small size in comparison to custom abutments. Various factors are involved in the causation of peri-implant mucositis and peri-implantitis, but the main cause is the microorganisms that reside in dental plaque [2].

Despite the aforementioned disadvantages, commercial stock abutments are still used extensively, due to their low cost, ease of accessibility, and precision of fit at the implant-abutment interface (IAI). Various materials have been used to fabricate custom abutments such as zirconia, titanium, or hybrid abutments using pre-machined titanium inserts [3–5]. However, titanium is considered the gold standard for implant abutment materials, especially at the posterior region [6].

Fabrication of custom implant abutments has been performed by using either casting techniques or industrial-scale computer numerical control (CNC) milling machines at central laboratories supported by various implant manufacturers. In more than one study [7,8],casting techniques showed imperfect seal at IAI and the highest microleakage when compared to pre-machined stock implant abutments. For central production, dental casts or digital impressions are sent to a central laboratory, that may be located in another country, and abutments are then mailed back after manufacturing [1]. These abutments are manufactured by capable machines that offer different milling strategies compared to “dental” CNC milling machines [5].

Recently, specialized dental CAD and CAM software programs integrated implant modules with multiple libraries that enable the designing and milling of custom implant abutments in the dental laboratory [9]. The main advantages of the “in-house” fabrication of CAD-CAM custom abutments are time- and cost-effectiveness compared to central manufacturing, especially when mails are exposed to customs. However, there is a paucity of information regarding the accuracy and fit of such abutments and, accordingly, the amount of microleakage produced.

Precise fit at the IAI does not only prevent screw loosening and other mechanical complications but also, from a biological point of view, minimizes microleakage. Inaccurate fit at IAI may create microgaps that can present a suitable environment for bacterial colonization, which might lead to peri-implant disease, and could affect implant osseointegration [10]. The type of implant connection is also considered an important factor determining microgap at the IAI [11].Moreover, conical internal connection recorded the least interfacial microgap, which made it less prone to microleakage [12,13]. However, the tolerance of the fabrication method of the abutments seems to be an important factor in determining the accuracy of fit at IAI, regardless of the connection type [14].

Inflammatory biomarkers are recently considered a confident method of early detection of periodontal and peri-implant diseases [15]. Among all inflammatory mediators, Matrix Metalloproteinase-8 (MMP-8) has a capacity for the destruction of collagen type I and III that can lead to the degradation of the extracellular matrix of the connective tissue, basement membrane, and alveolar bone, and eventually lead to signs of periodontal and peri-implant disease [16]. Since MMP-8 is involved in periodontal inflammation, the level of its active form in the gingival crevicular fluid (GCF) can be used as a diagnostic indicator during periodontal maintenance therapy [17]. Peri-implant sulcular fluid (PISF) has comparable characteristics to that of GCF, hence, the MMP-8 level can also be used to detect inflammation around dental implants [16,18].

Accordingly, MMP-8 level would detect the physiological or inflammatory reactions of the soft tissues as a sign of remodeling or disease respectively [19]. Soft tissues around dental implant abutments may respond differently due to imprecise fit at the implant-abutment connection resulting from the diverse tolerances of manufacturing methods [20].Moreover, soft tissue inflammatory reaction may arise from plaque retention caused by the erroneous contour of the abutment and the restoration.

Although it is inevitable to prevent the occurrence of microgap at the IAI and the plaque retained around the possible unintentionally overcontoured implant-supported restorations [21], their effect may be dissolved clinically within the physiological mechanisms and oral hygiene habits of the individuals. The purpose of this randomized clinical trial was to evaluate the MMP-8 level and clinical periodontal parameters in custom titanium CAD-CAM and pre-machined stock implant abutments with conical connection. The null hypothesis of this study was that no difference would be found in peri-implant soft tissue behavior around both types of abutments.

2.1. Study Design and Settings

This study was a parallel, participant-blind, randomized controlled clinical trial comparing 2 geometrical shapes of dental implant abutments (anatomical and cylindrical) fabricated by 2 methods concerning their biological effect on the peri-implant soft tissues. Ethical approval was provided by the committee of the institutional review board of faculty of dentistry, Alexandria University (IRB NO 00010556- IORG 0008839), and the trial was registered in the Pan African Clinical Trial Registry under identification number PACTR201809736563842 at 15/09/2018. This research was executed following CONSORT 2010 guidelines [22]. The sample size was estimated by using a power analysis statistical software (G*power) [23]. The power of the study was assigned as 80% (β=20%), at a significance of 95% (α=0.05). The effect size was drawn from 3-month results of ten patients who received stock (n=5) and custom (n=5) abutments and evaluated for MMP-8 level in the PISF. The Mean ± SD of MMP-8 in PISF around stock abutments was 14.51 ± 1.19, and were15.76 ± 0.23 around custom abutments. The sample size was estimated to be 14 participants in each group and was increased to 15 to make up for the cases lost to follow-up.

All participants were recruited from the clinics of the Faculty of Dentistry, Alexandria University. The study population included patients with missing first mandibular molars. Eligibility criteria are presented in table 1. Eligible participants (N=30) underwent 2-stage surgical implant placement protocol (Superline; Dentium, Co) according to Adell et al. [24]. The sutures were removed 2 weeks after surgery, and the surgical sites were assessed regarding signs and symptoms of inflammation. Participants with successful implant placement were randomly allocated to one of two groups: stock (SA) and custom (CA) abutment groups with a 1:1 allocation ratio.

2.2. Randomization

Random sequence generation was done by using statistical online software (random.org/sequences). Numbers 1-30 were written on the back of 30 envelopes, while the corresponding group for each number was written on a small paper that was wrapped in aluminum foil, and the wrapped papers were inserted in corresponding envelopes. The number of the envelope for each participant was assigned the same as the sequence of enrollment, for example, the envelope assigned for the first participant enrolled in the study was carrying number 1. The participants were recalled after the surgical implant placement, and the envelopes were handed to the operator to either perform the second stage surgery immediately if the assigned group was SA or to make a radiograph to aid in the fabrication of a custom healing abutment for CA group.

Table 1. Eligibility criteria

Inclusion Criteria

Patients with missing mandibular first molar/s, with natural tooth antagonist and adjacent teeth.
Age range 25- 50 years.
Good oral hygiene with attitude for compliance to perform strict oral hygiene measures (Plaque index score = 0-1). ⁽³⁴⁾
Adequate bone quantity and quality for the placement of dental implants.

Exclusion Criteria

Systemic or local diseases that might contraindicate surgical implant placement or interfere with proper osseointegration.
Parafunctional habits or any sign and symptom of pathologic occlusion.
Smoking.
Pregnancy.

2.3. Prosthetic protocol

Healing abutments were used to shape the peri-implant mucosa. For the SA group, stock healing titanium abutments with a diameter of 6.5 mm were used, while in the CA group custom acrylic healing abutments were fabricated based on bitewing radiographs [25]. A two-week healing period was commenced before the definitive impression making, by using closed tray impression coping and Poly Vinyl Siloxane impression material. Soft tissue casts were made by using type IV dental stone and gingival mask material.

For the SA group, stock abutments (Dual abutment; Dentium, Co) were selected with a diameter of 6.5 mm and mucosal height of either 1.5 or 2.5 mm. The abutments were prepared to achieve adequate prosthetic space. On the other hand, custom abutments were designed by a dental CAD software program (exocad dental DB; exocad, GmbH) and were manufactured by using a dental milling machine (Arum 200X -Doowonid) and titanium grade 5 blank (Coreitec Ti Disc, imes‑icore GmbH), with the help of dental CAM software program (hyperdent dental, FollowMe; Co). All abutments underwent evaluation regarding surface roughness at flat areas and mucosal cuff of the abutments by using laser scanning confocal microscope (Laser Microscope VK X-100; Keyence, Corp). Moreover, microgaps at implant-abutment interface were evaluated by using optical microscope (SZ-11; Olympus; Corp). The abutments were torqued into dental implants, that were held tight by using pliers, at 30 N.Cm according to the manufacturer’s instructions. The assemblies were held by using a special device at an angle to allow access for the visibility of the microgaps (Fig. 1). The device consisted of a base, a protactor and a holder that is connected to the zero position of the protractor by using a long screw and three nuts. Trials were made to achieve measuring of microgaps at different angles, however, 45º was found to produce the widest microgaps without making the finish line of the abutments obscuring the microgaps. Once abutments succeed to pass both tests with Ra values below 0.5 µm and microgaps values below 10 µm, they were eligible to be used for patients [21,26,27].

To minimize the effect of differences in the level of finish lines in different abutments and the resulting variation in excess cement removal, combined cement- and screw-retained restorations were fabricated [28,29]. Complete contour zirconia restorations were fabricated with a screw hole for both groups. The restorations were cemented to their corresponding abutments intraorally, then the restoration-abutment assemblies were retrieved to clean the excess cement. The combined restorations were torqued by using a torque wrench at 30N/Cm according to the manufacturer’s instructions. Prosthetic steps are shown in Figure 2. All patients were instructed to perform oral hygiene measures, including tooth brushing and flossing to maintain plaque level at its lowest level as much as possible.

2.4. Patient recall and outcome analysis

The first follow up recall of the participants for the baseline data was scheduled 1 month after cementation to allow for a washout period [30], after which the patient was recalled after 3, 6, and 12 months. In each visit, participants underwent sampling of the PISF around both types of abutments (Fig. 3). For the sampling of PISF, the field was dried with an air syringe and was partially isolated. A periodontal filter paper (Periopaper; Oraflow, Inc.) was inserted in the peri-implant sulcus for 30 seconds then retrieved. If the filter paper was contaminated with blood, it was discarded. The filter papers were inserted in Eppendorf tubes and a 0.5 ml Phosphate-buffered saline was added to each tube. After 60 minutes, the filter papers were removed and the tubes with the total extract were stored at – 20 º C till analysis.

Peri-implant probing depth (PPD) was assessed by a plastic graduated periodontal probe at 4 points around each implant restorations, as the buccal and lingual contours might erroneously measure the depth of the sulcus [31]. Simplified mucosal index (SMI) scores were used to describe the condition of the peri-implant mucosa around the restoration, while modified plaque index (mPI) scores were used to describe plaque accumulation around dental implants (Table 2) [32–34]. Two investigators were responsible for collecting PPD, SMI and mPI data and Interexaminer reliability was performed that revealed excellent reliability between examiners for all scores and PPD.

Table 2. Simplified mucosal index and modified plaque index scores

Simplified Mucosal Index (SMI)

0= Normal mucosa

1= Minimal inflammation with color change and minor edema.

2= Moderate inflammation with redness, edema, and glazing.

3= Severe inflammation with redness, edema, ulceration, and spontaneous bleeding without probing.

Modified Plaque Index (mPI)

0 = No detection of plaque.

1 = Plaque only recognized by running a probe across the smooth marginal surface of the implant.

2 = Plaque can be seen by the naked eye.

3 = Abundance of soft matter.

To measure crestal bone loss, two bitewing radiographs were made for each patient, one at the baseline and the other at 12-month time point. All radiographs were made using D-speed periapical film size 2 (D-Speed, Carestream health), mounted on an x-ray film holder (Flipray, Dentsply Sirona) to correctly orient the film and x-ray cone during making of bitewing radiographs. After exposure, the films underwent processing, and scanned with an X-ray scanner to digitalize the radiographs into Photographic Experts Group (JPEG) computer file format. All radiographs were compared for the crestal bone resorption using image analysis software (ImageJ, NIH, USA). To measure crestal bone loss, a line was drawn in the baseline radiograph starting from the implant shoulder to the first contact of bone to the implant, at both mesial and distal aspects, and was measured in mm. The same procedure was done for the radiograph at the 12-month follow-up visit of the same patient. The measurements of the baseline radiograph were subtracted from the measurements of the 12- month follow up radiograph, and the resultant value was the amount of crestal bone loss. All measurements were conducted by one examiner, and intraexaminer reliability was analyzed by repeating all measurements with a two-week interval. Intraclass correlation coefficient showed excellent reliability.

2.5. Biochemical Analysis of MMP-8

MMP-8 specific sandwich ELISA kit (Human specific MMP-8 Sandwich ELISA; Cloud Clone, Corp) was used to analyze the MMP-8 level in the PISF. In brief, the standard solution, provided in the ELISA kit, was diluted to form predetermined concentrations that were added to the first 8 wells of the precoated microplate. A hundred µl of diluted PISF samples were added to the microplate, followed by an incubation period to allow the binding of MMP-8 to the precoated antibodies. The biotin-labeled MMP-8 antibody solution was added to the microplate, followed by Horse Raddish-Streptavidin solution, Tetramethylebinzidine, and stop solution. Between each solution used, a wash buffer solution was used to remove the excess of the unreacted solutions. After adding the stop solution, the color of the wells turned yellow, and the optical density of each well was measured by using a microplate reader with a wavelength of 450 nm. The optical density of the standard wells with known concentrations was plotted using spreadsheet software and the standard curve was generated, from which the MMP-8 concentrations of PISF samples were drawn.

2.6. Statistical analysis

Means and standard deviation (SD) were calculated for all variables. Normality was investigated for all variables by using descriptive statistics, plots (boxplot, Q-Q plot, and histogram) and normality tests. Within group comparisons of each variable within each group separately were done using repeated measures ANOVA (RM-ANOVA) or Friedman tests depending on normality of the variables, followed by post-hoc pairwise comparisons by using Bonferroni adjusted significance level in case of significant results. Comparisons between the two study groups at each point of time were created by using independent samples t-test or Mann-Whitney U test according to normality of the variables with calculation of mean difference and 95% confidence interval (CI).

3.1. Characteristics of the sample

Forty-six individuals were evaluated for the eligibility criteria and only 30 participants (11 men and 19 women) with 30 prosthetic spaces were included. Thirteen participants were not included in the study, where ten individuals were excluded due to mismatching with eligibility criteria (n=10), while others refused to participate in the clinical trial (n=3) (Fig. 4). The age range was 27-50 years. Implants used in the study were either 5 mm (17 prosthetic spaces) or 4.5 mm (13 prosthetic spaces) in diameter, and with an average length of 12 mm. The recruitment of all participants started in October 2018 and ended in December 2019.

3.2. Surface Roughness and Microgaps at implant-abutment interface

Mucosal cuff areas of the custom abutments recorded Ra of 0.48 ± 0.03 µm, and 0.46 ± 0.03 µm in the premachined abutments. At flat areas, mean Ra of the custom abutments was 0.196 ± 0.02 µm, and 0.184 ± 0.069 µm in the premachined abutments. No significant differences were found between both types of abutments (P=.12 for mucosal cuff areas and P=.789). On the other hand, The mean microgap of the stock abutments was 4.53 ± 1.1 µm and 5.02 ± 1.08 µm for the custom abutments. No statistical differences were found between the two groups (P= .33).

Table 3. Repeated measures ANOVA of within-group comparisons and pairwise comparisons between groups for MMP-8 level and PPD in both groups

Timepoint	Mean ± SD of MMP-8 (ng/µl)		Mean ± SD of PPD (mm)
Timepoint	CA (n=15)	SA (n=15)	CA (n=15)	SA (n=15)
1-month	15.36 ± 2.20 ^A	16.10 ± 1.68 ^A	3.33 ± 0.49^A	3.13 ± 0.44^A
3-month	15.54 ± 1.81 ^{A, B}	16.47 ± 2.91 ^A.B	3.50 ± 0.57^A,B	3.17 ± 0.41^A,B
6-month	17.76 ± 1.81 ^A,B	16.81 ± 2.98 ^A,B	3.50 ± 0.53 ^A,B	3.27 ± 0.53^A,B
12-month	19.73 ± 1.40 ^B	18.72 ± 2.10 ^B	3.67 ± 0.45^B	3.40 ± 0.47^B
Difference between 1-month and 12-month timepoints	4.37	2.62	0.34	0.27

3.3. MMP-8 level

Means of MMP-8 levels in the PISF of SA and CA are illustrated in table 3. Two-way repeated measures ANOVA was performed to compare the effect of time, abutment type and their interaction on MMP-8 level in the PISF. Sphericity wasn’t assumed (P= .012), therefore Greenhouse Geisser correction was used for within subjects effects and it was found that the effect of time on the level of MMP-8 is significant (P< .001) with partial eta squared = .226. Further pairwise comparisons were performed as shown in table 3. Between subjects effects revealed that abutment type has no significant effect on the level of MMP-8 (P=.154) with partial eta squared= 0.071, however, there was significant effect of the interaction of time*abutment type on MMP-8 level (P< 0.001) with partial eta squared = .994.

3.4. Secondary outcomes

The means and standard deviation of PPD are tabulated in table 3. Repeated measures ANOVA was used to investigate the effect of time and abutment type on PPD. Sphericity was assumed (P= .135) and it was found that the effect of time on PPD was significant (P< 0.001) for within-subject comparison with partial eta squared = .235. Further pairwise comparison revealed significant differences between time points within a group as shown in table 3. Meanwhile, the effect of abutment type on PPD was not found to be significant (P=.123) with partial eta squared = .083. However, the interaction of time and abutment type was found to be significant (P< .001) with partial eta squared= .984.

The means and standard deviation of SMI and mPI are tabulated in table 4. No statistically significant differences (P>.05) were found related to within-subject comparisons. Pairwise between subjects comparisons were found to be insignificant as regard to SMI and mPI. For crestal bone loss, no statistical differences (P= .716) were found between CA (0.27 (±0.14)) and SA (0.29 (±0.17)) after 12-month clinical service.

Table 4. Modified Plaque index (mPI) and Simplified mucosal index in the two study groups at different timepoints

Timepoint	Mean ± SD of MMP-8 (ng/µl)		Mean ± SD of PPD (mm)
Timepoint	CA (n=15)	SA (n=15)	CA (n=15)	SA (n=15)
1-month	15.36 ± 2.20 ^A	16.10 ± 1.68 ^A	3.33 ± 0.49^A	3.13 ± 0.44^A
3-month	15.54 ± 1.81 ^{A, B}	16.47 ± 2.91 ^A.B	3.50 ± 0.57^A,B	3.17 ± 0.41^A,B
6-month	17.76 ± 1.81 ^A,B	16.81 ± 2.98 ^A,B	3.50 ± 0.53 ^A,B	3.27 ± 0.53^A,B
12-month	19.73 ± 1.40 ^B	18.72 ± 2.10 ^B	3.67 ± 0.45^B	3.40 ± 0.47^B
Difference between 1-month and 12-month timepoints	4.37	2.62	0.34	0.27

Screw loosening took place in 2 cases (one in each group) after one month of clinical service (at the first evaluation). The screws were replaced, and torqued in place. Occlusal adjustments were remade to eliminate any possible off axis loading. A washout period of one month was commenced before sampling.

The main objective of this RCT was to assess the biological performance of the custom CAD-CAM titanium abutments regarding clinical and radiographic outcomes and biochemical analysis of the MMP-8 level. The results of this study did not support the null hypothesis, where there was significant effect of the interaction between time and abutment type between the stock and custom abutment groups. To the authors’ knowledge, custom abutments fabricated by using dental CAD-CAM were not assessed clinically or biologically in the literature before; hence, this study is considered to be the first report to evaluate this type of abutment.

Level of MMP-8 after one year was significantly higher than the level at 1-month timepoint in both groups. This finding was augmented with the significant difference in PPD in both types of abutments between 1- and 12-month tomepoints. The abutment type did not influence the level of peri-implant MMP-8 or PPD. However, the effect of interaction of abutment type and time was found to be significant on the level of peri-implant MMP-8 and PPD in between-subjects comparison. This result revealed the only difference between two groups, where the change in MMP-8 and PPD over time in CA group is significantly higher than that of SA group. However, the difference in either MMP-8 or PPD between 1-month and 12-month timepoints in both groups, although statistically significant, was of limited clinical impact.

A period of year is enough to elucidate Pri-implant diseases of the soft and hard tissues in presence of local factors [35,36]. In a study conducted by Xu et al [37], the MMP-8 level in implants with peri-implantitis was greater than healthy implants by 971%, while the difference in PPD was around 2.6 mm. In the current study, the difference after one year was only 4.37 ng/ml in CA and 2.26 ng/ml in SA for the MMP-8 level and 0.34 mm in CA and 0.27 mm in SA for PPD, which, in comparison to the results of the aforementioned study, indicates its clinical insignificance. Another study reveled a difference of 12 ng/ml between healthy implants and those with peri-implantitis [38]. This finding is augmented by the results of crestal bone loss, where no significant differences were found between both types of abutments.

Machining strategy used for stock abutments uses turning and lathe CNC to produce circular mucosal cuff area with low surface roughness. Moreover, industrial machining is subjected to quality assessment that can discover any fluctuation of surface roughness by using suitable magnification and special tools. On the contrary, custom abutments have anatomic shape and the manufacturing strategy is created by using dental CAM programs that uses ball end mills to refine the abutments. This might have had an influence on the surface roughness of the abutment in general, and the mucosal areas in particular.

Milling the custom abutments in this study was done by using ball-end burs and it resulted in surface roughness values that were within the limits recorded in the literature [26,27,39]. However, questions should be raised about the minor chipping and the wear of the milling tools, where it may result in elevated values of surface roughness. It is a noteworthy remark that two custom abutments in this study had a rough surface at the mucosal cuff area identified with the naked eyes, and it was verified to have surface roughness higher than 1 μm. On examination of the milling tools, it was found that one ball-end bur was minimally chipped. The chipped bur was replaced, and the two specimens were milled again.

Subtractive milling results in a range of inherent errors which are called machining tolerance or the degree of permissible errors [40]. Most of the dental milling machines have a tolerance of ± 5 µm; so that the pieces could be tighter or looser than the original design by no more than 5 µm. When dealing with implant abutments, this tolerance might result in microgaps at the implant-abutment interface (IAI). Nonetheless, milling using old or minutely chipped ball-end burs might result in increased surface roughness which may widen the microgap at the IAI and results in adverse biological effects.

MMP-8 level in the PISF is dependent on many factors, including systemic diseases, age, and sex [41]. These confounding factors directly affect the MMP-8 serum level, while the main soft tissue reaction resulting in the secretion of MMP-8 in the PISF is dependent mainly on local mechanisms rather than systemic factors [15]. Hence, the control of local conditions, such as oral hygiene measures and the controlled surgical and prosthetic procedures was precisely done to ensure that the difference in the level of MMP-8 in the PISF of the two groups was only a result of the change of the two types of abutments

No differences were found between CA and SA groups regarding the level of MMP-8 in the PISF around implant restoration and clinical parameters. These results can be explained by the control of surface roughness of mucosal cuff area and the control of local factors that that might promote plaque accumulation and bacterial colonization. Based on these results, the effect of manufacturing method and abutment geometry did not have influence on the soft tissue reaction around dental implant abutments. However, the results showed increasing values of MMP-8 over time in PISF around dental implants of both groups. This could be due to the significant increase in the depth of the periimplant sulcus at the 12-month time point.

The finish lines of all abutments were at the level of the mucosal margin. However, it was difficult to maintain this level in the case of the circular stock abutments, where the finish line ran equally on all surfaces. This would have resulted in difficulty in cement removal at subgingival areas, resulting in possible fluctuation in soft tissue reaction. Hence, it was found that making a combined cement- and screw-retained restoration was a solution to eliminate the remaining excess cement [29]. The combined restoration was a cement-retained zirconia restoration with a screw hole in the crown so that, when cemented intraorally, it can be retrieved to facilitate excess cement removal [28]. The different levels of the finish lines also resulted in subgingival zirconia margins in some proximal areas. However, zirconia and titanium materials are believed to have similar soft tissue reaction at 1-year follow-up period [19].

Biochemical analysis of this study was limited to one inflammatory biomarker. Other inflammatory biomarkers might have presented evidence that could have supported the results. Additionally, the study was limited to missing first mandibular molar, which, as much as it can produce standardized control of local factors, was limited to one anatomic configuration of the abutments and restoration.

The main concern over the use of custom abutments fabricated by dental CAD-CAM is the fluctuation in the quality of milling as regard to surface roughness at the mucosal cuff area. The findings of this study recommend checking milling burs, reviewing milling strategy and milling results to improve the quality of the custom abutments.

1- The change in PPD and MMP-8 level in the peri-implant sulcular fluid around custom dental implant abutment showed increase over time that is significantly higher than stock abutments. However, this difference was of low clinical impact.

2- No differences were found between stock and custom abutments as regard to simplified mucosal index (SMI), modified plaque index (mPI) and crestal bone loss (P>.05).

3- Fluctuation of the quality was noted in custom abutments fabricated by dental CAD-CAM, hence, magnification should be used to evaluate this type of abutments along with regular check for the milling burs and milling strategy.

CAD-CAM: computer-aided design- computer-aided manufacturing; MMP-8: matrix metalloproteinase-8; PPD: peri-implant probing depth; SMI: simplified mucosal index; mPI: modified plaque index; IAI: implant-abutment interface; CNC: computer numerical control; PISF: peri-implant sulcular fluid; GCF: gingival crevicular fluid.

Ethical approval and consent to participate

All clinical and laboratory procedures reported in this study was approved by the committee of the institutional review board of faculty of dentistry, Alexandria University (IRB NO 00010556- IORG 0008839). Written informed consents were obtained from all participants involved in this study. All methods were carried out in accordance with relevant guidelines and regulations.

Consent for publication

Not applicable

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Funding

Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).

Competing interests

The authors declare that they have no competing interests.

Acknowlegements

The authors would like to thank Dr. Alaaeldin Elraggal and Dr. Norhan Hussein for their help in the statistical part of the study.

Author contributions

All authors contributed to conceptualization and design. IMAR: Conceptualization, Methodology, Investigation, Data curation, Writing Original draft preparation and Visualization. IAH: Conceptaulization, Methodology, Validtion, review and editing, Supervision. SHAK: Conceptaulization, Methodology, Validtion, review and editing, Supervision. ASEH and RAF: Conceptualization, Methodology, Investigation, review and editing, Supervision.

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No competing interests reported.

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Matrix metalloproteinase-8 level in the peri-implant sulcular fluid around dental implant abutments with different geometries and manufacturing strategies: A randomized controlled trial

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