This retrospective clinical study was conducted to evaluate the clinical usefulness of a freely removable microlocking implant prosthesis (MLP) that was developed to overcome the problems with conventional implant prostheses. A total of 54 patients (male: 31, female: 23) and 100 implant prostheses were included. Patients were divided into three groups such as 6-12 months, 12-18 months, and 18-24 months according to the used period after implant prosthesis delivery, and the patients in each group were recalled for examinations of survival rate, marginal bone resorption, peri-implant soft tissue indices, and complications. The prosthetic complications were analysed by combining the recorded chart data during the periodic checks including the last call for this study. During a 2-year observation period, all the implants showed a 100% survival rate without clinical mobility and functional problems. There was no significant difference in marginal bone resorption, plaque index, and bleeding index over the observation period after implant prosthesis delivery. Probing depth of the 18-24 months group (
Recovery of missing teeth using a dental implant does not damage adjacent teeth and offers the patient aesthetic and functional advantages when compared to removable dentures. As the use of implants is gradually expanded due to these advantages, various types of implant systems have been developed, and the results of evaluating the clinical success of inserted implants have been reported continuously [
A screw-retained prosthesis facilitates removal, repairs, and hygiene maintenances of the implant prosthesis [
Recently, a novel implant prosthetic system (microlocking implant prosthetic system (MLP); EZ crown; Samwon DMP), which is a freely removable using zirconia ball and Ni-Ti spring, has been developed to compensate for the shortcomings of the existing implant prosthetic system [
The MLP investigated in this study consists of completely different components, which may lead to unreported prosthetic complications previously. So, long-term clinical observations are very important because these prosthetic changes can affect the implant success rate. Thus, the present study investigated the periodontal indices and complications in the cases using MLP through retrospective clinical examination and radiological analysis. The purpose of this study was to evaluate the clinical usefulness and complications of the new developed MLP.
For the retrospective evaluation of the MLP, in 54 patients (male: 31, female: 23) who visited Pusan National University Dental Hospital from 2016 to 2019, 100 implant prostheses were evaluated after at least 6 months after implant prosthesis delivery (Tables
Distribution of implant placement.
Location | Anterior | Premolars | Molars | Total ( |
---|---|---|---|---|
Maxilla | 1 | 17 | 10 | 28 |
Mandible | 2 | 18 | 52 | 72 |
Distribution of implants according to the implant length and diameter.
Length (mm) | Diameter (mm) | Total ( | ||||
---|---|---|---|---|---|---|
3.5 | 4.0 | 4.5 | 4.8 | 5.0 | ||
7.0 | 2 | 2 | ||||
8.0 | 2 | 11 | 4 | 17 | ||
8.5 | 3 | 1 | 4 | 8 | ||
10.0 | 1 | 23 | 12 | 1 | 16 | 53 |
11.5 | 3 | 3 | 7 | 13 | ||
12.0 | 1 | 4 | 1 | 6 | ||
13.0 | 1 | 1 | ||||
Total ( | 2 | 35 | 28 | 2 | 33 | 100 |
The MLP evaluated in this study consists of a fixture, abutment, and cap, and the cap consists of four subcomponents: body, ball, spring, and cap. The body has several grooved hexagonal receptacles that match the hexagonal structure of the abutment cylinder to prevent the rotation of the prosthesis. The main components of the balls are zirconium oxide (ZrO₂) and hafnium oxide (HfO₂), and balls are seated in the retention groove so that they are directly involved in the retention and prevent the rotation of the spring. The spring consists of nickel-titanium (Ni-Ti) shape memory alloy and is enveloping the outside of the zirconia balls. This structure maintains a constant stress value, and retentive components are restored even in large deformational distortion. So, the prosthesis can be attached and detached without deformation or loss of retention. The spring used in this study expands slightly when the cap is engaged with the abutment, and the cap can be easily positioned on the undercut of the retention groove and applies a constant external force to the ball after the prosthesis is combined with the implant (Figure
Detailed illustration of the abutment and cap making up the MLP: (a) body, (b) ball, (c) spring, (d) cap, and (e) retention groove of the abutment.
Before making the MLP impression, the abutment was tightened to 35 Ncm according to the manufacturer’s instruction (Figure
Prosthesis setting process of MLP: (a) properly selected abutments were connected to the fixtures; (b) caps were attached on the abutments; (c) fabricated zirconia crowns were cemented on the caps with resin cement.
After the final implant prosthesis delivery, the patients were divided into three groups: (1) 6-12 months, (2) 12-18 months, and (3) 18-24 months, according to the used observation periods. The following items were evaluated with references to clinical examination and radiographs from implant placement to the final visit. The cumulative implant survival rates were assessed according to the criteria presented by Cochran et al. [
References used to measure actual marginal bone loss: (a) marginal bone level (distance from the implant platform to the top of the marginal bone) and (b) distance of the implant.
The probing depth was measured in parallel with implant length at four points around the implant (mesial, distal, buccal, and lingual) using a periodontal probe (Merrit-B; Hu-Friedy) at the final recall check, and the mean and standard deviation were calculated [
For the statistical analysis, one-way analysis of variance (ANOVA) with post hoc Tukey’s test was performed to compare the marginal bone resorption between groups. In the results of probing depth, the Kruskal-Wallis (KW) test with the post hoc Mann-Whitney
Two-year cumulative survival rates of 100 implants with MLP were evaluated in 54 patients. All the implants showed no clinical mobility and functional problems, yielding a cumulative survival rate of 100% (Table
Cumulative survival rate of implants.
Implants | Failed implants | CSR (%) | |
---|---|---|---|
6-12 months | 41 | — | 100 |
12-18 months | 40 | — | 100 |
18-24 months | 19 | — | 100 |
CSR = cumulative survival rate of implants.
The mean and standard deviations of implant marginal bone resorption are shown in Table
The average value of marginal bone resorption.
Observation period | |||
---|---|---|---|
Marginal bone resorption (mm) | 6-12 months | 0.452 | |
12-18 months | |||
18-24 months |
SD = standard deviation.
The mean and standard deviations of probing depth are shown in Table
The average value of probing depth.
Observation period | |||
---|---|---|---|
Probing depth (mm) | 6-12 months | 0.035 | |
12-18 months | |||
18-24 months |
In all groups, the score of 0 was most frequently observed for both mPI and mBI, but there was no statistically significant difference among the three groups (
Modified plaque index (mPI) and modified sulcus bleeding index (mBI).
Score | Occurrence rate (%) | ||||
---|---|---|---|---|---|
6-12 months | 12-18 months | 18-24 months | |||
mPI | 0 | 83.3 | 85.7 | 100.0 | 0.78 |
1 | 13.9 | 14.3 | — | ||
2 | 2.7 | — | — | ||
3 | — | — | — | ||
mBI | 0 | 72.2 | 81 | 100.0 | 0.60 |
1 | 16.7 | 14.3 | — | ||
2 | 11.1 | 4.8 | — | ||
3 | — | — | — |
mPI = modified plaque index; score 0: no detection of plaque; score 1: plaque only recognized by running a probe across the smooth marginal surface of the implant; score 2: plaque can be seen by the naked eye; score 3: abundance of soft matter. mBI = modified sulcus bleeding index; score 0: no bleeding when a periodontal probe is passed along the gingival margin adjacent to the implant; score 1: isolated bleeding spots visible; score 2: blood forms a confluent red line on the margin; score 3: heavy or profuse bleeding.
The total incidence of complications was most frequently observed at 12-18 months after implant prosthesis delivery. As the main complication, abutment loosening (1%) in the 6-12 months group, abutment loosening (2%) and food impaction (2%) in the 12-18 months group, and abutment loosening (1%) and implant prosthesis fracture (1%) in the 18-24 months group were most frequently observed (Table
The detected clinical prosthetic complications according to the observation period.
Complications | Groups according to the observation period | Total ( | ||
---|---|---|---|---|
6-12 months | 12-18 months | 18-24 months | ||
Abutment loosening | 1 | 2 | 1 | 4 |
Implant prosthesis fracture | — | 1 | 1 | 2 |
Food impaction | — | 2 | — | 2 |
Total ( | 1 | 5 | 2 | 8 |
The screw-retained type of implant-supported FDPs, which are widely used in clinical practice, may cause screw loosening, screw fracture, or fracture of implant abutment [
Although it has short duration of observation, the two-year retrospective clinical study conducted to evaluate the clinical stability showed the cumulative implant survival rate of 100%. Based on these results, it seems that the change in the retained structure of the implant prosthesis does not significantly affect the implant survival rate within the initial 2 years. For marginal bone resorption, the previous study reported a screw-retained prosthesis (
The main complications of the screw-retained prosthesis were screw loosening, abutment loosening, ceramic fracture, loss of composite resin in the screw access hole, and abutment fracture [
In this clinical study, no fracture or deformation of MLP components was observed and the structural stability was confirmed. However, this study is a retrospective study based on a chart review that recorded the clinical evaluation and radiographic evaluation. So, the factors that can be evaluated in the present study were limited. In addition, since the MLP system was a recently developed system, the amount of collected data was smaller and the follow-up period was shorter compared to the conventional types (e.g., screw retention and cement retention). Long-term clinical observations for more subjects should be conducted to verify these clinical findings of the present study. Moreover, other complications not found in this study can be identified through further studies, and it may help to find the correlation with the pathology of soft and hard tissues around the implants [
The present study attempted to confirm the clinical usefulness of the MLP through a 2-year follow-up of the clinical progress of the implant prosthesis. All implants had no clinical and functional problems, but abutment loosening was observed in four of the 100 implant prostheses, and further research should be conducted to get to the bottom of the problem. Within the limits of the present study, the implant prostheses with MLP are considered to be an applicable and predictable treatment method. However, more samples and long-term clinical studies should be conducted to establish reliable evidence.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that there is no conflict of interest, either directly or indirectly, regarding the publication of this paper.
This research was supported by a grant from the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number HI18C0594000020).