Peri-Implant Tissue Stability: A Series of Five Case Reports on an Innovative Implant Design

Abstract

Background/Aim: The stability of peri-implant tissues is crucial for the long-term success of dental implant treatments. A new cervical implant design has been developed to address the challenges associated with peri-implant tissue stability, featuring a concave cervical portion to increase tissue volume in this area. The present study aimed to clinically evaluate the effectiveness of the new cervical implant design in maintaining peri-implant tissue stability. Materials and Methods: Five clinical cases involving completely edentulous patients were selected, in which 25 implants were installed. The marginal bone level around each implant was assessed at three different time points—T0: immediately after the prosthesis installation, T1: 6 months post installation, and T2: at the last control visit, up to 38 months later. Measurements were taken to analyze changes in marginal bone levels (MBLs) and the keratinized mucosa (KM) over time. Furthermore, the keratinized mucosa (KM) around the implants was evaluated. Results: The mean and standard deviation values of the marginal bone levels at each time point were as follows—T0: 0.59 ± 0.55 mm; T1: 1.41 ± 0.59 mm; T2: 1.76 ± 0.69 mm. Statistical analysis showed significant differences across the time points (ANOVA p < 0.0001). The overall mean KM values were 3.85 mm for T1 and T2, showing the stability of the peri-implant soft tissues at ≥1-year controls. Conclusion: Within the limitations of the present study, the results showed that the Collo implants presented measured MBL values increasing within the time range analyzed in each case but within the normal values cited in the literature for these types of rehabilitation treatments. However, the measured KM values presented, in all cases, an average above the values referenced in the literature as a minimum for maintaining the health of the peri-implant tissues.

1. Introduction

The long-term maintenance of dental implants depends on sustained osseointegration and many other factors such as local and systemic risk factors, prosthetic rehabilitation, implant positioning, and correct biofilm control [1,2,3]. In addition, the stability of the mucosal tissue around the implant not only serves as a barrier separating the oral environment from the implant’s supporting bone structure but also plays a crucial role in protecting against microbial invasion and in the health of the peri-implant tissues [4]. The literature suggests that the absence or an inadequate quantity of the keratinized mucosa (KM) can negatively affect the patient’s oral hygiene control [4,5,6,7].

However, there is a growing amount of high-level evidence associating an inadequate KM quantity (<2 mm) with peri-implant mucositis. Lin et al. related that a minimum quantity of 2 mm of KM was essential to minimize the incidence of peri-implant mucositis and future marginal bone loss [4]. Thus, maintaining the health and integrity of the epithelial lining and connective tissues above the peri-implant bone crest is vital to ensure long-term implant health and stability [8].

In this sense, several approaches have been suggested to improve the quality and stabilization of the soft tissues around implants, such as modifications in the micro and macro design of the trans-mucosal implant abutment or the coronal area of the implant. This can promote the formation of woven bone in the healing chambers and facilitate further morphological changes in the bone toward a haversian-like structure, which, over time, significantly improves its mechanical properties. As a result, the adjacent bone experiences minimal loading, preventing stress concentrations that could surpass the minimum effective strain needed for bone modeling and remodeling [9,10,11,12,13]. Other authors have shown that concave or convergent abutment designs attempt to increase the thickness of the peri-implant tissues [14]. The concave emergence profile of the implant design plays a significant role in promoting soft tissue growth and stability, in comparison to traditional designs [15], providing more space for fibroblast proliferation, tissue fixation, and reduced bone resorption [12].

Figure 1 schematically shows the proposed innovative design of the Collo implant. New dental implant designs that focus on increasing soft tissue stability and promoting optimal healing processes around dental implants may enhance the long-term success of implant-supported rehabilitation. However, as far as we know, there have been no reports in the literature of well-designed clinical studies on the development of dental implants that consider their interaction with bone tissue and the peri-implant mucosa.

In the present five cases, 25 implants installed in the maxilla and mandible in edentulous patients, which were monitored clinically and radiographically at times ranging from 0 to 38 months, were evaluated. For each implant, the marginal bone level (MBL) was measured immediately after the installation of the implant/prosthesis, six months later, and at the most recent evaluation of each patient. Thus, the main objective of this study was to evaluate the long-term effects of a novel dental implant design, specifically focused on improving the quality and stability of peri-implant soft tissues, on the health and success of dental implants in edentulous patients. This study aimed to clinically and radiographically evaluate an implant with an innovative design (Collo implant), which presents a concave cervical emergence profile, and its relationship with the marginal bone level (MBL) and its influence on the quantity of the keratinized mucosa (KM) at different times.

2. Materials and Methods

2.1. Case Selection and Description

The present retrospective case series study was performed in the Center for Studies and Research in Dental Implants (CEPID) of the Faculty of Dentistry (Universidade Federal de Santa Catarina) in compliance with the principles of the Declaration of Helsinki on medical protocol and ethics. Five patients, who met the inclusion criteria, were selected for the study (age range: 61.4 years old; three males, two females). Healthy patients requiring multiple-tooth extraction or who were edentulous with the vestibular bone intact or partially missing were chosen for a full-arch implant-supported resin prosthesis (FIRP).

The inclusion criteria were as follows: (1) age > 18 years old; (2) general good health (ASA I-II); (3) adequate oral hygiene (Full Mouth Plaque Score 20%, Full Mouth Bleeding Score 20%). Patients were excluded from the study if they met the following exclusion criteria: (1) experiencing pregnancy or lactating period; (2) having untreated periodontitis or osteometabolic disease; (3) having intravenous bisphosphonate therapy; (4) having had hemotherapy or radiation therapy history of the neck–head area; (5) engaging in heavy smoking (>10 cigarettes/per day).

Written informed consent was signed by all patients for both the clinical procedure and the present study. Pre-operative CBCTs were performed. The medication protocol included the following: amoxicillin (500 mg every 8 h for 7 days), ibuprofen (600 mg every 12 h for 5 days), and 0.12% chlorhexidine gluconate (every 12 h for 12 days).

2.2. Surgical Protocol

After local anesthesia using 4% articaine with 1:200,000 adrenalin, extractions were performed if necessary, preserving the buccal bone.

For the implant insertion (Collo implant, Implacil de Bortoli, São Paulo, Brazil), the protocol was followed according to the standard procedures with the use of under-preparation, employed to guarantee a final torque of over 32 N/cm before the final implant seating. A total of 25 implants were installed and evaluated. The implant dimensions were between 11.5 and 13 mm in length and 4.1 mm in diameter.

The implants were installed following the direction determined by the anatomy of the jaw. The two posterior implants were installed with a distal tilting between 10 to 15 relative to the occlusal plane, aiming for good implant anchorage, large inter-implant distance, and short cantilevers.

The hexagonal platform implants were positioned at bone level (Figure 2). Soft tissue was readapted and sutured back into position on each patient using nylon 5-0 sutures (Microsuture, São Paulo, Brazil). The abutments used for the immediate and delayed prostheses were multiunit abutments (Implacil de Bortoli, São Paulo, Brazil).

The specific choice of abutments was made with the objectives of allowing the prosthesis to have a passive fit, maintaining the prosthesis with an acceptable thickness, and having the prosthetic screw-access holes emerging on the occlusal or lingual aspects of the prosthesis.

2.3. Prosthetic Protocol

For immediate provisional prosthetic protocol, polymeric acrylic resin prostheses were manufactured and captured with titanium cylinders and inserted on the same day or a maximum of 7 days after surgery. The occlusion scheme adopted in the provisional rehabilitation privileged anterior occlusal contacts and canine guidance during lateral movements. The prostheses exhibited a minimum of 10 teeth.

For definitive prosthetic protocol, the final full-arch hybrid rehabilitation was assembled with polymeric acrylic resin implant-supported fixed prostheses with cobalt–chrome (CO-CR) sub-structure, acrylic resin prosthetic teeth, and pink acrylic resin gingiva (Figure 3).

The occlusion for the final prosthesis was adjusted to a mutually protected occlusion scheme respecting the patients’ centric relations.

2.4. Radiographic Assessment and Marginal Bone Level (MBL) Measurements

Conventional periapical radiographs were obtained using the bisector technique with the aid of plastic film holders. The films were photographed in high resolution and adjusted in grayscale for further analysis.

Periapical radiograph images were transferred to software 2.1.4.7 (Image J^®, National Institutes of Health) and a single calibrated examiner performed the measurements. To calibrate the software, the measurement was performed using the known distance of the implant length (11.5 or 13 mm), Once the software was calibrated, for the MBL, measurements were obtained as the linear distance from the implant shoulder to the first bone-to-implant contact, measured both mesially and distally, for baseline and follow-up radiographs (Figure 4). The marginal bone level was determined as the difference between T0, T1, and T2.

2.5. Keratinized Mucosa (KM) Measurements

A millimeter probe was used to measure the width of the peri-implant KM, which was measured as the distance between the gingival margin and the muco-gingival junction. To improve the visibility of the border between the keratinized and non-keratinized mucosa, an iodine solution (Povidine, São Paulo, Brazil) was applied to the mucosa if necessary.

2.6. Statistical Analysis

To analyze the data collected regarding the marginal bone level and keratinized mucosa 3 times, the ANOVA test was used. For the analysis of the different parameters, the Student t-test was used. All analysis were performed in GraphPad Prism 5.01 software (GraphPad Software Inc., San Diego, CA, USA), considering p < 0.05 as statistically significant.

3. Case Description and Results

Table 1. Demographic patients’ distribution.

Case No.	Gender	Age	Arch	n of Implants
1	Female	54	Maxilla	6
2	Male	63	Mandible	4
3	Male	68	Maxilla	4
4	Female	69	Mandible	5
5	Male	53	Mandible	6

shows the overall demographic patients’ distribution.

Case 1: A 54-year-old female patient presented a fully edentulous upper jaw (maxilla) following the loss of her natural teeth due to advanced gum disease. Despite wearing traditional dentures, she expressed dissatisfaction with their fit and stability, which were impacting her ability to eat and speak comfortably. The treatment plan included six Collo implants placed strategically with an immediate loading prosthesis protocol. Figure 5 shows the clinical and radiograph images of the implants at the following evaluation times: immediately after the implant installations (T0) and 6 months (T1) and 12 months (T2) after the installation.

Table 2. Bone level and keratinized mucosa measurements in millimeters (mm).

Case No.	Tooth No.	Initial MBL (mm)	MBL 6 Months (mm)	MBL 12 Months (mm)	KM 6 Months (mm)	KM 12 Months (mm)
1	25	0.12	2.51	2.73	3	3
1	23	0	1.85	2.73	4	4
1	22	0.08	0.21	0.37	3	3
1	12	0.32	0.33	0.36	3	3
1	13	0	0.37	0.53	4	4
1	15	0.12	2.09	2.34	4	4
Mean		0.06	1.23	1.51	3.5	3.5

MBL = marginal bone level; KM = keratinized mucosa.

presents the bone level and keratinized mucosa measurement data of each time point.

Case 2: A 63-year-old male patient presented with a partial edentulous lower jaw (mandible) resulting from advanced gum disease leading to the loss of natural teeth. Unsatisfied with his traditional partial prostheses, aesthetically and functionally, he was considered a suitable candidate for implant-fixed prostheses due to the fact that no contraindications were found in his medical history. The treatment plan involved multiple extractions, alveolar bone regularization, and the immediate placement of four dental implants with immediate loading. Figure 6 shows the clinical and radiograph images of the implants at the following evaluation times: immediately after the implant loading (T0) and at six months (T1) and 38 months (T2) after the implant loading.

Table 3. Bone level and keratinized mucosa measurements in millimeters (mm).

Case No.	Tooth No.	Initial MBL (mm)	MBL 6 Months (mm)	MBL 38 Months (mm)	KM 6 Months (mm)	KM 38 Months (mm)
2	34	0	1.25	1.40	2	2
2	32	0	1.44	1.51	3	3
2	42	0	1.74	1.79	1	1
2	44	0	1.86	1.94	2	2
Mean		0	1.57	1.66	2.0	2.0

MBL = Marginal Bone Level; KM = Keratinized Mucosa.

presents the bone level and keratinized mucosa measurement data of each time point.

Case 3: A 68-year-old male patient presented with a fully edentulous upper jaw (maxilla) following tooth loss due to advanced gum disease. Despite using traditional total prostheses, he expressed dissatisfaction with their aesthetics and function while eating, making him a potential candidate for implant-fixed prostheses with no contraindications in his medical history. The treatment plan entailed the placement of four dental implants with a late-loading approach. Figure 7 shows the clinical and radiograph images of the implants at the following evaluation times: immediately after the implant loading (T0) and at six months (T1) and 24 months (T2) after the implant loading.

Table 4. Bone level and keratinized mucosa measurements in millimeters (mm).

Case No.	Tooth No.	Initial MBL (mm)	MBL 6 Months (mm)	MBL 24 Months (mm)	KM 6 Months (mm)	KM 24 Months (mm)
3	24	1.43	1.51	1.82	6	6
3	22	0.38	0.6	0.97	3	3
3	12	1.57	1.86	2.23	3	3
3	15	1.81	1.89	1.99	4	4
Mean		1.30	1.47	1.75	4.0	4.0

MBL = marginal bone level; KM = keratinized mucosa.

presents the bone level and keratinized mucosa measurement data of each time point.

Case 4: A 69-year-old female patient suffered from a partial edentulous lower jaw (mandible) due to advanced gum disease causing the loss of natural teeth. Despite utilizing traditional partial prostheses, she expressed dissatisfaction with their aesthetic and functional properties, leading to consideration for implant-fixed prostheses as there were no contraindications in her medical history. Treatment involved multiple extractions and the immediate placement of four dental implants with immediate loading. Figure 8 shows the clinical and radiograph images of the implants at the following evaluation times: immediately after the implant loading (T0) and at six months (T1) and 36 months (T2) after the implant loading.

Table 5. Bone level and keratinized mucosa measurements in millimeters (mm).

Case No.	Tooth No.	Initial MBL (mm)	MBL 6 Months (mm)	MBL 36 Months (mm)	KM 6 Months (mm)	KM 36 Months (mm)
4	35	0.54	1.22	1.35	4	4
4	31	0.58	1.01	1.07	4	4
4	33	0.84	1.45	1.6	5	5
4	43	0.57	1.18	1.67	4	4
4	45	0.47	1.98	2.17	4	4
Mean		0.60	1.37	1.57	4.2	4.2

MBL = marginal bone level; KM = keratinized mucosa.

presents the bone level and keratinized mucosa measurement data of each time point.

Case 5: A 53-year-old male patient had a partial edentulous lower jaw (mandible) due to advanced gum disease resulting in the loss of natural teeth. Dissatisfied with the functionality and aesthetics of traditional partial prostheses, he was deemed a suitable candidate for implant-fixed prostheses with no identified contraindications in his medical history. The treatment plan comprised multiple extractions and the immediate placement of four dental implants with immediate loading. Figure 9 shows the clinical and radiograph images of the implants at the following evaluation times: immediately after the implant loading (T0) and at six months (T1) and 12 months (T2) after the implant loading.

Table 6. Bone level and keratinized mucosa measurements in millimeters (mm).

Case No.	Tooth No.	Initial MBL (mm)	MBL 6 Months (mm)	MBL 12 Months (mm)	KM 6 Months (mm)	KM 12 Months (mm)
5	46	1.30	1.92	2.30	4	4
5	44	1.06	1.25	2.27	3	3
5	42	0.63	1.09	2.29	5	5
5	32	0.71	1.44	1.61	4	4
5	34	1.25	2.03	2.52	4	4
5	36	0.86	1.24	2.48	2	2
Mean		0.97	1.50	2.25	3.7	3.7

MBL = marginal bone level; KM = keratinized mucosa.

presents the bone level and keratinized mucosa measurement data of each time point.

The process was consistent across all five reported cases. Their medical backgrounds showed no reasons against having implant surgery, making them suitable candidates for implant-supported prostheses. After discussing treatment options with the patients, a comprehensive plan was proposed, which included placing Collo dental implants in each patient’s jaw without teeth to support a fixed prosthesis. Hexagonal platform implants would be positioned at the bone crest level. Each patient was educated about the importance of regular follow-up visits, maintaining oral hygiene, and making periodic adjustments to ensure the long-term success of the implant-supported prosthesis. A follow-up assessment was carried out after 6 months, which included radiographic assessments and comparisons with subsequent follow-ups.

The five treated patients with implant-fixed prostheses recovered without complications or side effects. The patients were monitored closely during follow-ups. The patients did not complain about any pain or swelling. The lack of early or late complications (e.g., wound dehiscence, abscess, or site infection) also demonstrated the presence of healthy peri-implant soft tissues at the constricted areas, protecting the first threads at the implants’ constriction. Minimal physiological MBL changes occurred over a one-year follow-up, keeping these minimal changes in cases with more than 1 year of controls, with soft tissue adherence to the smooth part of the most coronal portion of the implant head (Figure 10), indicating an absence of apical migration. The mentioned adherence seemed to configure an important adaptation of the biological width structures, which may have contributed to the biological attachment of the intraosseous portion of the implant.

The mean and standard deviation values of MBL measurements in the 25 implants analyzed were 0.59 ± 0.55 mm at T0, 1.41 ± 0.59 mm at T1, and 1.76 ± 0.69 mm at T2 (ANOVA p < 0.0001). Figure 11 shows a graph distribution of the data collected at each time point.

The analysis of several factors—such as the evaluation time, gender, and the arch of the implant placement—indicated no statistically significant differences in marginal bone loss (MBL) measurements. This finding underscores the stability of the peri-implant tissues over time, particularly in the coronal region of the implants (see

Table 7. Comparison of marginal bone level (MBL) values among different variables.

Variables:	T1 Mean (±SD)	p Value	T2 Mean (±SD)	p Value
Last control at 12 months (n = 12 implants) versus Last control ≥ 24 months (n = 13 implants)	1.36 (0.76) 1.46 (0.41)	0.9349	1.88 (0.92) 1.65 (0.39)	0.0866
Maxilla (n = 10 implants) versus Mandible (n = 15 implants)	1.32 (0.85) 1.47 (0.34)	1.0000	1.61 (0.96) 1.86 (0.45)	0.8028
Female (n = 11 implants) versus Male (n = 14 implants)	1.29 (0.77) 1.51 (0.40)	0.4273	1.54 (0.89) 1.94 (0.45)	0.2856

). All implants in this study were placed at the crestal bone level; however, the variations in the initial measurements (T0) can be attributed to the fact that some implants had been installed in post-extraction sockets, which resulted in irregular bone crests at the time of placement, as depicted in Figure 2.

The differences in marginal bone loss observed are primarily associated with physiological bone remodeling, a natural response following the placement of implants. In this study, we defined “programmed bone loss” as the biological process that involves initial bone resorption around the implant, which occurs as a result of the dynamic interaction between the concave design of the implant neck and the surrounding tissues. Over time, this remodeling process reaches a stable state, allowing the area to become filled with the keratinized gingiva, which contributes to the overall health and stability of the implant, along with the maintenance of the biological width. The guidelines for implant installation in this study corresponded with those established for conventional external hex implants.

4. Discussion

As per our understanding, this case series study marked the initial attempt to investigate the potential radiographic marginal bone level (MBL) exhibited by Collo implants positioned in the maxilla and mandible, specifically in pristine bone settings following functional loading. Notably, the crestal bone alterations observed from implant placement to the 12-month post-loading period comfortably met the success benchmarks outlined by Renvert et al. [16]. It is noteworthy that the primary occurrence of the MBL was noted at the 6-month follow-up compared to the 12-month evaluation, with the criterion set at a bone loss of less than 2 mm within the first year [16]. This was consistent with the scientific literature showing that most contour changes around implants occur in the initial phase after the placement of definitive reconstructions and remain stable thereafter [17,18]. The mean MBL values measured in our study at 6 months were within the parameters reported by other authors, who proposed an MBL value of 0.5 mm as a distinct and objective criterion of success after loading within a 6-month follow-up period [19].

On the other hand, at observation times ≥ 12 months, follow-up reports for the MBL described in the literature varied greatly. Krennmair et al. reported MBL values of 1.11 ± 0.4 mm (1 year), 1.26 ± 0.42 mm (2 years), and 1.40 ± 0.41 mm (3 years), representing a significant (p < 0.001) continuing time-dependent annual reduction [20]. Malò et al., evaluating full-arch prostheses with the All-on-Four method in the mandible, reported average marginal bone losses of 1.72 mm and 2.32 mm at 10 and 15 years, respectively [21]. However, none of the 25 implants analyzed in the present study had a value exceeding an MBL of 3 mm, which, according to Berglundh et al. [22], if we use the radiographic parameters recommended by the 2017 definition of peri-implant diseases, could be classified as diseased if accompanied by clinical parameters.

The main goal of showing these cases results was to assess the effectiveness of Collo dental implants under immediate and delayed loading procedures through propensity across various factors like the time of evaluation, gender, and the implant placement arch. These findings align with similar results presented by Hingsammer et al. [23], indicating that factors such as age, gender, insertion torque, implant surface area, location, position, bone quality, and insertion torque did not impact peri-implant bone loss in short-splinted dental implants after a year of loading.

The success outcomes observed in this study either supported or challenged the hypothesis linked to this innovative Nobel implant design. Berglundh and Lindhe [24] highlight the critical role of mucosal thickness in the formation of supracrestal tissue attachments around dental implants. Their findings indicate that insufficient mucosal thickness can lead to crestal bone resorption as the body strives to create adequate space for the connective tissue and junctional epithelium. This underlines the necessity for proper soft tissue management in implantology to ensure long-term success and stability around dental implants [24].

The structure of the connective tissue surrounding implants is crucial to prevent epithelial downward growth and provide mechanical protection to the osseointegrated part of the implant. Of the five cases presented in this study, in only one of them (Case #2), the KM value measured was 2 mm on average for times T1 and T2 while, in the other cases, the overall average obtained was 3.85 mm at both evaluation times (T1 and T2). These values were above the KM value of 2 mm described by other authors as the minimum quantity essential to minimize the incidence of peri-implant mucositis and future marginal bone loss [4,25].

These results were in line with the results seen in the clinical studies of Bianchini et al., where the stability of the peri-implant tissues was seen in the modification of the implant diameter [26,27,28]. The strategic management of tissue fixation not only helps address potential challenges but also plays a significant role in enhancing the overall success and durability of dental implant interventions.

A proper tissue depth, typically around 3 mm or more, is vital for accommodating the required biological width crucial for successful dental implant integration [29]. This depth design at the coronal region of the Collo implant model plays a key role in providing essential soft tissue support around the implant, ensuring stability and long-term oral health. Insufficient soft tissue coverage around implants can trigger issues like mucosal dehiscence, a higher risk of peri-implantitis, and compromised aesthetic outcomes [30]. Hence, meticulous care in tissue fixation, especially around concave or narrow implants, is paramount to preserve the implant’s structural integrity and longevity.

Although the present study provided valuable information, it is important to recognize its limitations, particularly those related to the small patient size and number of implants and the large standard deviations at each time point. These factors may have introduced uncertainty as to the generalizability of the results and the robustness of the presented conclusions.

5. Conclusions

Within the limitations of the present study, the results showed that the Collo implants presented measured MBL values increasing within the time range analyzed in each case but within the normal values cited in the literature for these types of rehabilitation treatments. However, the measured KM values presented, in all cases, an average above the values referenced in the literature as a minimum for maintaining the health of the peri-implant tissues. Future studies with larger sample sizes and prospective designs are recommended to validate these findings.